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The hot flow behavior, spheroidization, dynamic recrystallization (DRX) and fusing of lamellar ɑ phase for hot isostatic pressed Ti–6Al–4V titanium alloy was investigated at 950°C-900°C–850 °C with the total deformation amount of 70% during multi-pass deformation. The results show that all the flow stress value presented a peak value, followed by different flow softening extent. The flow stress is very susceptible to deformation parameters such as strain, strain rate and deformation temperature, and also the peak value decreased as the increase of temperature and the decrease of strain rate. The main softening mechanisms for different deformation pass are the DRX of β phase for one-pass deformation, spheroidization of lamellar α phase for two-pass deformation and DRX of α phase for three-pass deformation, respectively. The lamellar α spheroidization deformed in two-pass at 900 °C increased with decreased strain rate or the increased strain, and the maximum spheroidization fraction of lamellar α phase was 43% at 0.01s−1. The spheroidized mechanism of lamellar α phase is major give rise to the combined action of kinking deformation and element diffusion. Nevertheless, in the three-pass deformation process, the spheroidization degree did not significantly increase as increased strain, which principal give rise to the fusion of the same orientation of lamellar α phase. The fusion mechanism is the result of the joint action of the orientation of lamellar α phase and dislocation slip. And, the fraction of DRX of α phase is obviously higher than that of spheroidization in three-pass deformation, which is the main softening mechanisms.

An approach was proposed to optimize dissimilar friction stir lap welding of aluminum and titanium alloys. The basic concept of the new technique included (i) the plunging of the welding tool solely into the aluminum part (i.e., no direct contact with the titanium side) and (ii) the welding at a relatively high-heat input condition. It was shown that sound welds could be readily produced using an ordinary cost-effective tool, with no tool abrasion and no dispersion of harmful titanium fragments within the aluminum side. Moreover, the intermetallic layer was found to be as narrow as ~0.1 µm, thus giving rise to excellent bond strength between aluminum and titanium. On the other hand, several important shortcomings were also revealed. First of all, the high-heat input condition provided significant microstructural changes in the aluminum part, thereby resulting in essential material softening. Furthermore, the new approach was not feasible in the case of highly alloyed aluminum alloys due to the relatively low rate of self-diffusion in these materials. An essential issue was also a comparatively narrow processing window.

Metal injection molding (MIM) is an advanced manufacturing technology that enables the mass production of high-performance and complex materials, such as the Ti-6Al-4V alloy. The determination of the size change and deformation of the Ti-6Al-4V alloy after the sintering process is challenging and critical for quality control. The numerical simulation could be a fast and cost-effective way to predict size change and deformation, given the large degrees of freedom for the sintering process. Herein, a finite element method based on the thermal-elastic-viscoplastic macroscopic model is developed to predict the shrinkage, deformation, relative density, and crack of injection-molded Ti-6Al-4V after sintering, using the Simufact software. Excellent agreements between experimental measurements and numerical simulations of the size and deformation are demonstrated (within a 3% error), confirming the accuracy of the numerical model. This approach can serve as a guideline for the mold design and sintering optimization of the MIM process.

Ligas de titânio possuem uma combinação única de propriedades que as fazem ser empregadas, principalmente, na indústria aeronáutica. Alguns componentes do motor aeronáutico, como as pás, dentre outros, são submetidos ao processo de retificação ao final da sua cadeia produtiva, por exigirem uma elevada qualidade superficial. Contudo, as ligas de titânio são materiais de difícil usinabilidade e assim, a correta seleção dos parâmetros operacionais é fundamental. Tendo em vista que a dressagem é uma operação indispensável à retificação, a qual define a sua finalidade e a integridade superficial das peças retificadas, a correta seleção dos parâmetros de dressagem é igualmente importante. Todavia, são poucos os trabalhos disponíveis na literatura que buscam avaliar os efeitos da dressagem sobre a retificabilidade de ligas de titânio. Nesse sentido, o presente trabalho tem por finalidade avaliar os efeitos que diferentes condições de dressagem de um rebolo de carbeto de silício (SiC) podem exercer sobre a retificabilidade da liga Ti-6Al-4V, em comparação com os efeitos proporcionados por diferentes condições de penetração de trabalho. Para isso como parâmetros de entrada foram empregados dois tipos de dressadores (fliesen e ponta única de diamante), dois graus de recobrimento (Ud = 3 e Ud = 12), duas profundidade de dressagem (ad = 20 µm e ad = 40 µm), os quais foram utilizados na dressagem de um rebolo de SiC (#46), e três penetrações de trabalho (ae = 10 µm, ae = 20 µm e ae = 30 µm) utilizadas ao longo dos ensaios de retificação plana tangencial em amostras de Ti-6Al-4V. Os resultados mostraram que a mudança no condicionamento do rebolo de uma condição grosseira (dressador fliesen, Ud = 3 e ad = 40 µm) para uma condição suave (dressador ponta única, Ud = 12 e ad = 20 µm) proporcionou reduções de 54,62 %, 41,34 % e 49,25 % nas rugosidades Ra, Rt e Rz, respectivamente; melhorou a textura das superfícies retificadas; assegurou uma pequena variação na microdureza (4,75 %) em relação a referência, diminuindo inclusive a extensão dessa variação para 120 µm abaixo da interface de retificação; eliminou evidências de danos microestruturais; permitiu uma redução no consumo de energia em até 24,33 %; gerou uma queda de 96,85 % nos macroefeitos, bem como a redução nos microefeitos gerados na superfície de corte do rebolo e, em termos de relação G, a mudança no grau de recobrimento de Ud = 3 para Ud = 12 ocasionou um aumento de até 65,33 %. Ainda de acordo com a análise de variância, a penetração de trabalho, quando analisada isoladamente, não exerceu v influência sobre os resultados diferentemente de quando analisada em conjunto com o grau de recobrimento do rebolo que, assim como os demais parâmetros de dressagem, exerceu influência expressiva sobre os resultados. Constatou-se que a combinado entre a condição de dressagem do rebolo com dressador de ponta única com Ud = 12 e ad = 20 µm foi capaz de melhorar a retificabilidade da liga Ti-6Al-4V, independentemente da penetração de trabalho. Titanium alloys have a unique combination of properties that make them used mainly in the aeronautical industry. Some aeronautical engine components, such as blades, among others, are subjected to the grinding process at the end of their production chain, due to the need for high surface quality. However, titanium alloys are materials of difficult machinability and thus, the correct selection of operational parameters is essential. By considering that dressing is an essential operation for grinding, which defines its purpose and the surface integrity of the ground parts, the correct selection of dressing parameters is equally important. Nevertheless, there are few studies available in the literature that seek to evaluate the effects of dressing on titanium alloys grinding. In this sense, the present work aims to evaluate the effects that different dressing conditions of silicon carbide (SiC) grinding wheel play on the Ti-6Al-4V alloy grindability, in comparison with the effects provided by different radial depths of cut. Therefore, as input parameters two types of dressers were used (fliesen and single diamond tip), two overlap ratio (Ud = 3 and Ud = 12), two dressing infeed (ad = 20 µm and ad = 40 µm ), which were used in the dressing of a SiC grinding wheel (#46), and three radial depth of cut (ae = 10 µm, ae = 20 µm, and ae = 30 µm) used throughout the peripheral surface grinding tests on of Ti-6Al-4V alloy samples. As a results, the change in grinding wheel conditioning from a coarse condition (fliesen dresser, Ud = 3 and ad = 40 µm) to a smooth condition (single point dresser, Ud = 12 and ad = 20 µm) provided a reduction of 54.62%, 41.34% and 49.25% in roughness Ra, Rt, and Rz, respectively as well as improved the texture of ground surfaces and ensured a short deviation in microhardness (4.75%) concerning the reference, even reducing the extent of this variation to 120 µm below the grinding interface; this change also eliminated evidence of microstructural damage, allowed a reduction in energy consumption by up to 24.33%; generated a 96.85% drop in macro effects, as well as a reduction in micro effects generated on the grinding wheel's cutting surface and, in terms of the G ratio, the change in the degree of coating from Ud = 3 to Ud = 12, caused an increase up to 65.33%. Also according to the analysis of variance, when radial depth of cut is examined in isolation from other independent variables it did not influence the results, unlike when it was analyzed in combination with the degree of overlap ratio that, similar to the other dressing parameters, it has a significant influence about the results. Therefore, the dressing condition of the SiC vii grinding wheel capable of improving of Ti-6Al-4V alloy grindability is the use of a single-point dresser, combined with Ud = 12 and ad = 20 µm, regardless of radial depth of cut. Tese (Doutorado) 2024-06-24

Additive manufacturing (AM) using wire as an input material is currently in full swing, with very strong growth prospects thanks to the possibility of creating large parts, with high deposition rates, but also a low investment cost compared to the powder bed fusion machines. A versatile 3D printing device using a Direct Energy Deposition Wire-Laser (DED-W Laser) with Precitec Coaxprinter station to melt a metallic filler wire is developed to build titanium parts by optimizing the process parameters. The geometrical and metallurgical of produced parts are analyzed. In the literature, several authors agree to define wire feed speed, travel speed, and laser beam power as first-order process parameters governing laser-wire deposition. This study shows the relative importance of these parameters taking separately as well as the importance of their sequencing at the start of the process. Titanium deposit are obtained with powers never explored in bibliography (up to 5 kW), and wire feed speed up to 5 m.min-1 with a complete process repeatability.

In additive manufacturing, technologies based on the fusion of a metallic wire using an electric arc represent an interesting alternative to current manufacturing processes, particularly for large metal parts, thanks to higher deposition rates and lower process costs than powder or wire-laser technologies. A versatile 3D printing device using a DED-W Arc (Direct Energy Deposition by wire-arc) station to melt a metallic filler wire is developed to build titanium parts by optimizing the process parameters and control the geometrical, metallurgical and the mechanical properties of produced parts. In this study, the impact of two different CMT synergic lines on the energetic and geometric behavior of Ti-6Al-4V single deposits is highlighted. These are related to first order parameters: wire feed speed (WFS) and travel speed (TS). The results show difference on energy, geometric of deposits and different deposition regime between these two law with identical process parameters. The second part of this study focuses on the transition from single deposits to walls and blocks. By first choosing the best set of process parameters to make the construction of thin walls (composed of stacked layers), and then the research the optimal horizontal step of deposition (overlapping) for thicker constructions, results obtained made it possible to validate transition from single deposits (1D) to thick walls (3D) without any weld pool collapse or lack of fusion.

The thermal creep forming and thermo-hydrogen processing of titanium alloys have been used in industry production. The combination of these methods is a potential way to improve the plasticity of titanium alloys and the formability of complex components. The effect of hydrogen addition on high temperature creep behavior of Ti-6Al-4V alloy was investigated by creep tests and microstructural observations. The results show that β/α phase ratio increases with hydrogen content while α′ and αʺ martensites continuously precipitate in β phase. The α/β or α/α phase boundaries become wider. Hydrogen can promote creep rate through softening effect during primary and steady creep stage. However, the embrittlement happens in the tertiary creep stage. The hydrogenated alloy is more sensitive to initial stress and creep temperature. The creep strain of hydrogenated alloy with 0.2 wt%H is similar to that of as-received one. Meanwhile, the creep strain of hydrogenated alloy with 0.4 wt%H significantly decreases. Besides, the smaller initial stress is beneficial to obtain the larger creep strain.

3D printing (or more formally called additive manufacturing) has the potential to revolutionize the way objects are manufactured, ranging from critical applications such as aerospace components to medical devices, making the materials stronger, lighter and more durable than those manufactured via conventional methods. While the mechanical properties of Ti-6Al-4V parts manufactured with two major 3D printing techniques: selective laser melting (SLM) and electron beam melting (EBM), have been reported, it is unknown if the corrosion resistance of the 3D-printed parts is comparable to that of the alloy made with isothermal forging (ISF). The aim of this study was to identify the corrosion resistance and mechanisms of Ti-6Al-4V alloy manufactured by SLM, EBM and ISF via electrochemical corrosion tests in 3.5% NaCl solution, focusing on the effect of microstructures. It was observed that the equiaxed α + β microstructure in the ISF-manufactured Ti-6Al-4V alloy had a superior corrosion resistance to the acicular martensitic α′ + β and lamellar α + β microstructures of the 3D-printed samples via SLM and EBM, respectively. This was mainly due to the fact that (1) a higher amount of β phase was present in the ISF-manufactured sample, and (2) the fraction of phase interfaces was lower in the equiaxed α + β microstructure than in the acicular α′ + β and lamellar α + β microstructures, leading to fewer microgalvanic cells. The lower corrosion resistance of SLM-manufactured sample was also related to the higher strain energy and lower electrochemical potential induced by the presence of martensitic twins, resulting in faster anodic dissolution and higher corrosion rate.

Lanthanum oxide powder was added to improve the microstructure and properties of a Ti-6Al-4V alloy part during cold metal transfer (CMT) based on wire arc additive manufacturing (WAAM). The macrostructure, microstructure and properties of the part were studied by using an optical microscope (OM), scanning electron microscope (SEM), electron backscatter(ed) diffraction (EBSD), microhardness evaluation and a tensile test. The results showed that the β grain size and martensite (α) size were reduced by adding lanthanum oxide powder. The texture intensity of the part also decreased due to the change in microstructure. Accordingly, the microhardness and tensile properties of the part obtained by adding lanthanum oxide were improved. In addition, based on the interdependence theory model, adding La2O3 particles in the molten pool as heterogeneous nucleation points could reduce the distance of XSD, so fine equiaxed β grains can be formed in the deposition layer.

Hip replacement is one of the most effective surgical procedures in medicine. Despite the fact that the clinical results of arthroplasty are usually excellent, some implants loosen with time and require revision. To help resolve this problem, research has focused on providing conditions that have a positive biological effect on bone building elements, resulting in a fast, seamless proliferation and differentiation of mesenchymal stem cells (MSC) into osteoblasts. That is why developing an in vitro model for studying MSC functions at the implant–tissue contact zone is essential. The aim of this study was to investigate the proliferation and differentiation capacity of human bone-marrow derived MSC in contact with medical implant-grade Ti-6Al-4V alloy and β-tricalcium phosphate (β-TCP). Human MSC were isolated from bone marrow aspirates obtained from the femoral canal during hip replacement surgeries and seeded on Ti-6Al-4V alloy squared specimens and β-TCP granules. The results indicate that MSC were able to effectively adhere to both biomaterial surfaces and, at the same time, retain their proliferative and osteogenic/adipogenic differentiation potential. We suggest that both Ti-6Al-4V alloy and β-TCP surfaces provide suitable conditions for the proliferation and differentiation of bone marrow MSC and can be used as in vitro models to explore MSC functions at the bone–implant interface.

Recently, the production of well-defined patterned surfaces with random or regular micro and nano-features has brought new opportunities for research and development in the field of tissue engineering and regenerative medicine. Among advanced micro and nano processing technologies, laser surface texturing (LST) stands out due to its simplicity, flexibility, precision, reproducibility and relatively low cost. This work studies the development of patterned surfaces controlled by of LST into biomedical grade V titanium, Ti–6Al–4V–alloy. We present different cross-hatched micropatterns followed by the characterisation of surface morphology and topography. Structural integrity of the produced patterns is evaluated by friction tests against bone, mimicking the insertion of an implant. Wettability is studied as it is crucial for protein adsorption and cell adhesion. The results show that the surface topography obtained using different patterning plans influences the wetting behaviour and the coefficient of friction against bone.

The mechanical properties of Ti-6Al-4V alloy are affected by its microstructures. However, the effects of these microstructures on the high cycle fatigue behavior of Ti-6Al-4V alloy with a mixed structure (α + β phases) remain unknown. In this study, three alloy specimens were prepared using different hot-deformation methods, and their microstructures were investigated by optical microscopy and scanning electron microscopy. Fatigue tests were then performed to determine their high cycle fatigue and fatigue crack propagation behavior. All specimens showed a bimodal structure, but the morphology of each phase (e.g., diameter, shape, and volume fraction) showed notable differences. Among the samples prepared, the forged sample (FS) showed the lowest fatigue strength in all cycles. The fatigue strength of the homogeneously rolled sample (HS) was slightly higher than that of the rolled sample (RS) below 106 cycles but lower above 106 cycles. Compared with those of RS and HS, the secondary α (αs) grain width of FS was twofold larger. The interconnected primary α (αp) phase clusters in HS appeared to promote microcrack propagation.

Grain reduction in a widely used Ti-6Al-4V alloy increases its endurance limit at room temperature. In this work, the behavior of the ultrafine-grained alloy under cyclic load at the temperature of 625 K is considered. Research was conducted to examine the fatigue life in a low-cycle area of the ultrafine-grained Ti-6Al-4V alloy produced by equal-channel angular pressing. Tensile and fatigue testing of the Ti-6Al-4V samples with coarse-grained (CG) and ultrafine-grained (UFG) structures were carried out at 293 and 625 K. The alloy demonstrated an enhanced strength and fatigue life at both temperatures. The representative features of the microstructural evolution and the fracture features in the UFG and CG alloys after fatigue tests are described in detail. The prospects for the use of the UFG Ti-6Al-4V alloy for engineering applications, such as in the production of critical gas-turbine engine parts, is discussed.

This work thoroughly investigated the microstructure of laser powder bed fusion (LPBF) Ti64 alloy induced by electropulsing (ECP) with different current densities. The results show that as the electric current density increases, the small-sized (10 μm) α′ martensites decrease, resulting in a typical grading microstructure treated by the ECP treatment. The thermodynamic barrier was found to decrease as the electric current passed, recrystallization occurred, and the percentage of small-sized α′ martensites increased. At the same time, the unique electrothermal coupling effect of ECP treatment acted on the needle-like α′ martensites, causing an energy concentration on the tip to break the adjacent α′ martensite and the percentage of large-sized α′ martensites to decrease. When the current density of ECP treatment was 48.37 A/mm2, the grading phenomenon of acicular α′ martensites was the most obvious and its size distribution changed significantly, which simultaneously improved the strength and elongation of LPBF-Ti64 alloy. Thus, the typical grading phenomenon of the α′ martensites plays a decisive role in improving the mechanical properties of the LPBF-Ti64 samples induced by the ECP treatment. The present results provide new information on the ECP processing additive manufacturing metallic materials.

Journal of Metals, Materials and Minerals, 31, 2, 137-146

The high specific strength, good corrosion resistance, and great biocompatibility make titanium and its alloys the ideal materials for biomedical metallic implants. Ti-6Al-4V alloy is the most employed in practical biomedical applications because of the excellent combination of strength, fracture toughness, and corrosion resistance. However, recent studies have demonstrated some limits in biocompatibility due to the presence of toxic Al and V. Consequently, scientific literature has reported novel biomedical β-Ti alloys containing biocompatible β-stabilizers (such as Mo, Ta, and Zr) studying the possibility to obtain similar performances to the Ti-6Al-4V alloys. The aim of this review is to highlight the corrosion resistance of the passive layers on biomedical Ti-6Al-4V and β-type Ti alloys in the human body environment by reviewing relevant literature research contributions. The discussion is focused on all those factors that influence the performance of the passive layer at the surface of the alloy subjected to electrochemical corrosion, among which the alloy composition, the method selected to grow the oxide coating, and the physicochemical conditions of the body fluid are the most significant.

In the present work, the microstructure and mechanical properties of Ti-6Al-4V alloy during multidirectional isothermal forging (MDIF) were systematically investigated. The evolution of the microstructure and texture of Ti-6Al-4V alloy during MDIF was studied using TEM and electron backscattered diffraction (EBSD). The experiment results showed that the grain size decreased with the increase in cumulative strain, especially in the easy deformation zone. After four deformation cycles, a homogeneous equiaxed grained microstructure with an average grain size of 0.14 μm was achieved. The texture changes of the alloy were studied in detail. After one cycle of MDIF, the texture was mainly composed of (0002) [01 10], and the Euler angles were (8°, 30°, 30°). The density of texture decreased with the increase in loading cycle, but the dispersion of texture increased. After four cycles of MDIF, the non-basal texture (1010) texture was observed, and the Euler angles were (82°, 33°, 0°). The highest achieved mechanical properties for Ti-6Al-4V alloy in the MDIF condition were a yield strength 900 MPa, ultimate tensile strength of 921 MPa, and an elongation of 12.1% at room temperature. The increase in MDIF cycles improved the hardness of the alloy. The significant improvement in mechanical properties was attributed to the ultrafine-grained microstructure.

The application of titanium alloy micro-gears in microelectromechanical systems has been severely restricted, as the graphite mold is prone to abrasion or even to crack at high temperatures, mainly due to the forming load. We aimed to manufacture Ti-6Al-4V alloy micro-gears through hot extrusion under an electric field and to clarify the influence of holding time on the extrusion force. The results suggest that the formed gears had a complete filling and clear tooth profile. Moreover, the contact resistance and current density caused a gradient temperature distribution inside the billet, resulting in a carburized layer and inhomogeneous β grains. The extrusion force increased with an increased holding time, which can be ascribed to the increase in the thickness of the carburized layer and the β grain size. Among these two factors, β grain size played a leading role in the extrusion force. Continuous dynamic recrystallization dominated the deformation in a single β phase, and the misorientation of the transformed α laths from β grains followed the Burgers orientation relationship. This study may pave the way for the extrusion forming of other titanium alloy micro-components.

It is a significant issue to deeply understand the nature relationships between damage degradation and deforming parameters, and then identify the changes of initial ductile fracture time with processing parameters and further adjusting the forming processes for obtaining the fracture-free components. For Ti-6Al-4V alloy, the strain-stress data in the temperature range of 1023–1323 K and strain rate range of 0.01–10 s−1 were obtained by compression tests. The finite element model with stress-strain data was constructed to simulate the ductile damage cumulating processes under different conditions and obtained the maximum damage values. Subsequently, the ductile fracture criterion (DFC) of Ti-6Al-4V alloy was established and the effects of temperature and strain rate on DFC were discussed. The results show that the variation range of DFC under different deformation conditions is 0.07–0.15. Subsequently, the deformation conditions with higher fracture risk were identified as 1200∼1275 K & 1∼10 s−1 and verified with the experiment observations.

Additive manufacturing has emerged in recent years as one of the most in-demand technology for manufacturing of prototypes and components with complex geometries. Its application in biomedicine shows a big productive potential concerning customized implants with optimized geometries, reducing risks of rejection and achieving better ergonomic results. However, Ti-6Al-4V ELI pieces produced by Direct Metal Laser Sintering (DMLS) need a post heat treatment in order to reach optimum mechanical properties as well as to release internal stresses resulted from the manufacturing process. This study aims at analyzing the change of microstructure in DMLS samples by effect of heat treatments and its influence in the corrosion behavior and in the anodizing process. The surfaces were analyzed by 3D confocal profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. DMLS samples showed different microstructures after heat treatments in the range from 650 to 1050 °C. The main difference in the microstructures is the nucleation and growth of β phase, which could have a detrimental effect on its corrosion behavior. The corrosion behavior was studied by cyclic potentiodynamic polarization in phosphate buffered saline solution at 37 °C. After anodizing, an oxide film was grown on the material surface, composed of a barrier and a nanoporous layer doped with F ions. The passive current density was reduced by approximately two orders of magnitude for all conditions, despite morphological differences on the layers. This is not only an improvement of the corrosion resistance but also a decrease in the ion release into bloodstream., The authors would like to acknowledge the National Council for Scientific and Technological Development (CNPq) program Ciências Sem Fronteiras (202887/2015-4) and Coordination for the Improvement of Higher Level Personnel (CAPES) for the financial support. Part of this work has been funded by the project MAT2013-48224-C2-1-R from the Spanish Ministry of Economics and Competitiveness.

Ti6Al4V alloy is the most widely used titanium alloy due to its attractive properties such as heat resistance, strength, plasticity, toughness, formability, weld-ability, corrosion resistance and biocompatibility. However, the main problem with titanium and its alloys is that they have poor tribological performance. Boriding seems to be the effective way to improve the tribological performance of titanium alloys. Titanium borides have an attractive combination of low density, high hardness, excellent wear, and corrosion resistance. In this study, Ti6Al4V alloy was borided in a solid media at 1100°C for 20 h. The microhardness profile was studied by a Vickers indenter. The hardness value of surface increases from 330 HV to 2789 HV. Wear experiments were performed in Ringer's solution that simulates human body environment. It was observed that boriding process improved tribological performance of Ti6Al4V alloy under all test conditions. © 2018 Polish Academy of Sciences Institute of Physics. All rights reserved.

While machining thin-walled workpieces, the chatter and corresponding damage to the machined surface can be avoided if that is predicted well in advance. Currently, investigations of machining vibrations mainly rely on experiments, which are costly and difficult to perform and FEM simulation methods that are many times computationally cumbersome. This work presents a mathematical model to obtain time domain forced vibration deflection response of a thin rectangular cantilever plate for any time and space varying external loads. The model is adapted for a milling process to obtain machining vibration response of a thin impeller blade by simplifying its geometry as a thin rectangular cantilever plate. The developed model was verified by checking the natural frequencies and mode shapes obtained by the model with the Finite Element simulation results for a thin cantilever plate. Peripheral milling experiments were performed to machine a thin rectangular cantilever plate of Ti-6Al-4V alloy on a vertical 3-axis CNC milling machine. Milling forces and workpiece acceleration were acquired during machining. Workpiece material properties and moving machining forces obtained by Linear Edge Force Model are input to the model. The model was validated by comparing vibratory deflection of thin cantilever plate obtained by the model and by the acquired experimental data. In general, the developed model can be used to obtain time-domain forced vibration response of thin rectangular cantilever plate workpieces.

Made available in DSpace on 2018-12-11T16:51:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-04-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The plasma immersion ion implantation treatment (PIII) acts to increase mechanical resistance with solid solution formation, new phases and defects inclusion, besides chemical and residual stress profile modification. Ti-6Al-4V alloy presents poor tribological properties and high affinity with interstitial elements, such as nitrogen and oxygen, this makes it more reactive at high temperatures. This paper aims to study Ti-6Al-4V alloy fatigue behavior subjected to nitrogen addition by plasma immersion ion implantation. It was investigated the frequency parameter influence on fatigue resistance. Ti-6Al-4V alloy was PIII treated with voltage equal to 9.5 kV, frequencies varying between 1000 and 1500 Hz and submitted to axial fatigue tests. Axial fatigue tests were performed, at room temperature and R = 0.1. Ti-6Al-4V alloy fatigue results were supported by Weibull statistics analysis. Ti-6Al-4V alloy microstructural analysis showed equiaxed α + β grains. Weibull analysis at untreated condition presented m values greater than 1, indicating reliability and uniformity. For a lifetime of 107 cycles, fatigue resistance was equal to 829 MPa for untreated condition, 644, 767 and 417 MPa, for f = 1000, 1200 and 1500 Hz, respectively. The nitrogen-based compounds were detected only at the condition where f = 1200 Hz. Thus, the combination of PIII treatment parameters, when f = 1200 Hz, hindered crack nucleation and increasing fatigue resistance of treated Ti-6Al-4V alloy when compared with the other two treatment conditions. Faculdade de Engenharia de Guaratinguetá – UNESP Escola de Engenharia de Lorena – USP Instituto de Física “Gleb Wataghin” – UNICAMP Faculty of Engineering Science – Universität Bayreuth Universidad Nacional de Ingenieria – UNI Faculdade de Engenharia de Guaratinguetá – UNESP FAPESP: 2015/00331-2 CNPq: 303832/2014-2

A novel hot stamping process for Ti6Al4V alloy using cold forming tools and a hot blank was presented in this paper. The formability of the material was studied through uniaxial tensile tests at temperatures ranging from 600 to 900°C and strain rates ranging from 0.1 to 5 s−1. An elongation ranging from 30% to 60% could be achieved at temperatures ranging from 750 to 900°C respectively. The main microstructure evolution mechanisms varied with the deformation temperature, including recovery, phase transformation and recrystallization. The hardness of the material after deformation first decreased with the temperature due to recovery, and subsequently increased mainly due to the phase transformation. During the hot stamping tests, qualified parts could be formed successfully at heating temperatures ranging from 750 to 850°C. The forming failed at lower temperatures due to the limited ductility of the material. At temperatures higher than 900 °C, extensive phase transformation of α to β occurred during the heating. During the transfer and forming, the temperature dropped significantly which led to the formation of transformed β, reduction of the formability and subsequent failure. The post-form hardness distribution demonstrated the same tendency as that after uniaxial tensile tests.

Gradient structure metals have good comprehensive properties of strength and toughness and are expected to improve the dynamic mechanical properties of materials. However, there are few studies on the dynamic mechanical properties of gradient structured materials, especially titanium alloys. Therefore, in this study, ultrasonic surface rolling is used to prepare a gradient structure layer on the surface of Ti-6Al-4V, and the quasi-static and dynamic compressive properties of coarse-grained Ti-6Al-4V (CG Ti64) and gradient-structured Ti-6Al-4V (GS Ti64) are investigated. The results show that a GS with a thickness of 293 µm is formed. The quasi-static compressive strength of GS Ti64 is higher than that of CG Ti64. Both CG Ti64 and GS Ti64 exhibit weak strain hardening effects and strain rate insensitivity during dynamic compression, and the compressive strength is not significantly improved. The lateral expansion of CG Ti64 is more obvious, while the lateral side of GS Ti64 is relatively straight, indicating that uniform deformation occurs in GS Ti64. The α phase in the GS produces dislocation cells and local deformation bands, and the lamellar structure is transformed into ultrafine crystals after dynamic compression. Both of them produce an adiabatic shear band under 2700 s−1, a large crack forms in CG Ti64, while GS Ti64 forms a small crack, indicating that GS Ti64 has better resistance to damage. The synergistic deformation of GS and CG promotes Ti-6Al-4V to obtain good dynamic mechanical properties.

Defect-free joint of Ti–6Al–4V alloy was successfully friction stir welded below β-transus temperature and then tensile tests were performed. Microstructure, macrostructure, tensile properties and fracture position are mainly discussed in order to investigate how surface indentation and plate thickness influence the tensile property. Weld zone (WZ) attained below β-transus temperature that owns better tensile strength limit than base metal (BM). During the tensile test, the elongation is decided by whether BM yields. Compared with friction stir welding joint using 2.5 mm thick plate, it is very difficult for joint using 2 mm thick plates to get bigger elongation due to surface indentation. Due to the higher tensile property of the WZ, the joint without surface indentation fractures at BM, reaching the 58.46 % elongation of BM.

International audience; This work focuses on a series of microstructural predictions regarding the dynamic recrystallization (DRX) behavior, change in grain size and dislocation density. Additionally, this study includes the prediction of the room-temperature-strength and the processing map characterization of Ti-6Al-4V alloy after forging in the (aþb) region. The experimental tests of the forgings reveal that the mechanism of microstructural conversion depends on the testing conditions. That is, superplastic behavior is exhibited at lower strain rates and higher temperatures. With an increasing strain rate and decreasing temperature , DRX occurs in a continuous manner. A set of constitutive equations that model the microstructural evolution, processing map characteristics and room temperature strengths is established by optimization of experimental data, followed by implementation into the DEFORM-3D software package. There is satisfactory agreement between the experimental and simulated results. Thus, a series of constitutive models (established in this work) is found to enable the reliable prediction of properties of Ti-6Al-4V alloy after forging in the (aþb) region.

Titanium alloys are increasingly used for structural applications in transportation engineering (aerospace, automotive, railway, marine industry) because of their interesting properties (high mechanical properties to weight ratios, excellent corrosion resistance). In the present research work, the very high cycle fatigue behaviour of Ti–6Al–4V alloy of both bimodal and basketweave microstructures were investigated and compared. Fatigue tests at a very high number of cycles with R = −1 were carried out on titanium alloy - grade 5 specimens, cut from a forged flange used on a commercial aircraft. The experimental tests showed that this alloy has an always decreasing S-N curve, even for a number of cycles greater than 10 9 . It is the typical behavior of some alloys used in the aircraft industry, such as aluminum, titanium, nickel and high-strength steels. Moreover the very high cycle fatigue tests demonstrated that the Ti–6Al–4V alloy with bimodal microstructure has fatigue strength higher than the Ti–6Al–4V alloy with basketweave microstructure. The effect of microstructure on fatigue mechanism focused on internal crack initiation has been discussed through SEM observation of sub-cracks underneath the fracture surface. The temperature evolution during the tests was detected by means of IR cameras to study the temperature effect on the material response.

Made available in DSpace on 2020-12-11T19:25:49Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-06-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) In this work, alternating current (AC) voltage (V-AC) is applied to Ti-6Al-4V alloy in aqueous oxalic acid dihydrate solution to grow passive oxide films. The oxide layers are formed with V-AC values in the range of 10-80 V. The resulting surface oxide layers have estimated thicknesses in the 100-500 nm range and are expected to have a two-layer structure consisting of a porous outer layer and a compact inner layer. The AC anodization process is demonstrated to have a slight effect on the surface roughness. Porous regions are observed on the films formed at lower and high AC voltages (i.e., V-AC 10-30 and 80 V). The corrosion behavior in Ringer's solution over 48 h of exposure is studied with electrochemical impedance spectroscopy. The AC anodized samples have higher impedance values than the untreated alloy by more than an order of magnitude. The oxides formed at V-AC = 40 - 70 V exhibit optimal resistance to corrosion as demonstrated by the overall impedance values, the polarization resistance values, and the capacitive behavior. Univ Sao Paulo, Inst Quim Sao Carlos, BR-13566590 Sao Carlos, SP, Brazil Univ Sao Paulo, Escola Engn Sao Carlos, BR-13566590 Sao Carlos, SP, Brazil Univ Estadual Paulista Julio Mesquita, Fac Engn Ilha Solteira, BR-15385000 Ilha Solteira, SP, Brazil Metrohm Autolab BV, Kanaalweg 29-G, NL-3526 KM Utrecht, Netherlands Univ Estadual Paulista Julio Mesquita, Fac Engn Ilha Solteira, BR-15385000 Ilha Solteira, SP, Brazil CAPES: 001

Titanium alloys are widely used in many fields because of their excellent comprehensive properties. However, its poor friction and wear properties limit its many potential applications. In general, the surface roughness of important parts manufactured by titanium alloy should meet certain requirements. As a low-cost and high-efficiency processing method, barrel finishing has been used for the surface finishing of titanium alloys. The main material removal mechanism of barrel finishing is micro-cutting/grinding, which is similar to the material wear mechanism under some conditions. In addition, titanium alloys are subjected to a low force in common surface finishing processes. Cryogenic treatment is a method that can improve the comprehensive properties of titanium alloys. Therefore, the friction and wear behavior of cryogenically treated Ti-6Al-4V titanium alloy (CT Ti alloy) and non-cryogenically treated Ti-6Al-4V titanium alloy (NT Ti alloy) at a low load and scratch speed was studied comparatively in this paper. The results show that the CT Ti alloy exhibits a lower friction coefficient and wear rate under both dry and wet wear conditions. Under wet conditions, the stabilized friction coefficient is lower than that under dry conditions. The stabilized friction coefficient of CT Ti alloy is 0.18 after reaching a stable wear stage under wet conditions. Under dry wear conditions, the NT Ti alloy mainly showed typical abrasive wear, heavy adhesion wear and oxidation wear characters. The wear mechanisms of CT Ti alloy are mainly abrasive wear, slight adhesion wear and oxidation wear. Under wet wear conditions, the wear mechanism of NT Ti alloy is abrasive wear and slight adhesion wear. After cryogenic treatment, the mechanism for CT Ti alloy is slight abrasive wear.

Due to their high specific surface area and advanced properties, TiO2 nanotubes (TiO2 NTs) have a great significance for production and storage of energy. In this paper, TiO2 NTs were synthesized from anodization of Ti-6Al-4V alloy at 60 V for 3 h in fluoride ethylene glycol electrolyte by varying the water content and further annealing treatment. The morphological, structural, optical and electrochemical performances of TiO2 NTs were investigated by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), UV-Visible spectroscopy and electrochemical characterization techniques. By varying the water content in the solution, a honeycomb and porous structure was obtained at low water content and the presence of (α + β) phase in Ti-6Al-4V alloy caused not uniform etching. With an additional increase in water content, a nanotubular structure is formed in the (α + β) phases with different morphological parameters. The anatase TiO2 NTs synthesized with 20 wt% H2O shows an improvement in absorption band that extends into the visible region due the presence of vanadium oxide in the structure and the effective band gap energy (Eg) value of 2.25 eV. The TiO2 NTs electrode also shows a good cycling performance, delivering a reversible capacity of 82 mAh.g−1 (34 μAh.cm−2.μm−1) at 1C rate over 50 cycles.

The present study investigated the sensitivity of material constitutive models on thermomechanical responses in laser powder bed fusion additive manufacturing of Ti-6Al-4V. Uniform scan strategies with scan lengths of 0.5, 1, and 2 mm were applied so that wide ranges of thermal histories could be generated. The Johnson-Cook (JC) and Mechanical Threshold Stress (MTS) material plasticity models were chosen to capture the influence of strain, strain rate, and temperature. The JC model is a phenomenological model which is known for its easy implementation and excellent agreement with material testing results. On the other hand, the MTS model is a more complex physics-based internal state variable plasticity model that is expected to provide more accurate estimation, particularly for cases involving changes in strain rate and temperature. Numerical results revealed that both JC and MTS models provided a similar stress evolution, however, the plastic strain evolution was more realistic using the MTS model. Moreover, it was found that the maximum strain and the strain rate in the LPBF process are high compared to typical quasi-static testing, i.e., ~ 2% and ~ 4 s−1, respectively. Accordingly, the material models should be calibrated with data obtained under similar deformation conditions. The choice of scan length also strongly affects in-plane stress anisotropy. Ultimately, we show both qualitatively and quantitatively the dependency of mechanical behavior prediction in LPBF on the choice of material models.

The formation of the coarse columnar crystal structure of Ti-6Al-4V alloy in the process of additive manufacturing greatly reduces the mechanical performance of the additive manufactured parts, which hinders the applications of additive manufacturing techniques in the engineering fields. In order to refine the microstructure of the materials using the high intensity ultrasonic via the acoustic cavitation and acoustic flow effect in the process of metal solidification, an ultrasonic vibration technique was developed to a synchronous couple in the process of Laser and Wire Additive Manufacturing (LWAM) in this work. It is found that the introduction of high-intensity ultrasound effectively interrupts the epitaxial growth tendency of prior-β crystal and weakens the texture strength of prior-β crystal. The microstructure of Ti-6Al-4V alloy converts to fine columnar crystals from typical coarse columnar crystals. The simulation results confirm that the acoustic cavitation effect applied to the molten pool created by the high-intensity ultrasound is the key factor that affects the crystal characteristics.

Selective laser melting (SLM) is extensively used for fabricating metallic biomedical products. After 3D printing, it is almost always advisable to apply a heat treatment to release the internal tensions or optimize the mechanical properties of the printed parts. The aim of this paper is to investigate the effects of heat treatment of SLM printed Ti-6Al-4V (Ti64) circular specimens on the areal surface texture parameters and cell attachment. Areal surface texture parameters, including the arithmetic mean height (Sa), root-mean-square height (Sq), skewness (Ssk), and kurtosis (Sku) were characterized. In addition, wavelet-based multi-resolution analysis was applied to investigate the characteristic length scales of untreated and heat-treated Ti64 specimens. In this study, the vertical distance between the highest and lowest position of cell attachment for each sampling area was defined as DH. Results showed that an increase in the periodic characteristic length scale was primarily due to the formation of large-scale aggregations of Ti64 metal powder particles on the heat-treated surface. In addition, MG-63 cells preferred lying in concave hollows, in heat-treated specimens, values of DH statistically significantly decreased from 31.6 ± 4.2 to 8.8 ± 2.8 μm, while Sku decreased from 3.3 ± 1.4 to 2.6 ± 0.6, indicating a strong influence of Sku on cell attachment.

Ti-6Al-4V alloy exhibits a good combination of excellent properties, such as high specific strength, high fatigue strength, good ductility and weldability. However, Ti-6Al-4V alloy shows low stiffness and poor wear resistance. To further increase the strength properties and improve the stiffness and wear resistance, TiB reinforced Ti-6Al-4V alloy matrix (TiB/Ti-6Al-4V) composites were fabricated by a spark plasma sintering (SPS) process. The TiB/Ti-6Al-4V alloy composites with 4.2 vol.% TiB, which were fabricated at a sintering temperature of 900 °C and for a holding time of 30 min, had the highest tensile strength of 1174 MPa. The Young’s modulus and Vickers microhardness of the composites increased with increasing TiB volume fraction, and the composite with 16.7 vol.% TiB exhibited values of 159 GPa and 517 HV, respectively. The tensile strength of the composite with 4.2 vol.% TiB at 400 °C was higher than that of the mild annealed Ti-6Al-4V alloy. The fatigue limits (over 107 cycles) at room temperature and 600 °C of the composites with 4.2 vol.% TiB were 350 MPa and 200 MPa, respectively. The creep strains at room temperature of the composites with 1.4 and 4.2 vol.% TiB did not increase with increasing creep time.

This study presents a low-cost and environmentally friendly medium for the pack boriding (boronizing) of a Ti6Al4V alloy. Titanium and its alloys are known to be highly reactive and to have extreme oxygen affinity. Therefore, boriding is performed under vacuum or in protective atmospheric conditions. This work evaluated the pack boriding heat treatments of a Ti6Al4V alloy under atmospheric conditions via the various boriding media used by previous researchers. In addition, a new pack boriding medium was developed by adding aluminum. Consequently, this study demonstrated that it is possible to obtain an undamaged titanium surface by applying solid-state boriding under atmospheric conditions. C1 [Kaplan, Yavuz; Ulukoy, Arzum] Pamukkale Univ, Fac Technol, Dept Mfg Engn, TR-20020 Denizli, Turkey. [Can, Ahmet Cetin] Pamukkale Univ, Dept Mech Engn, Fac Engn, Denizli, Turkey.

Titanium alloys are used as an aerospace material due to their inherent properties such as high strength to weight ratio, corrosion, and fracture resistance. However, the low conductivity and reactivity towards plastic deformation causes these materials to be difficult to cut category. The prediction of various parameters like chip formation and actual cutting forces are important factors for better machinability which involves lot of resources. To overcome such issues, this work proposes three-dimensional FE approach to simulate the machinability behavior of Ti-6Al-4V especially on conventional turning. The impact of cutting speed and feed rate on the cutting force, thrust force, feed force and surface roughness were analyzed experimentally for various conditions. The predicted machining forces showed strong correlation with the experimental results and the effective von mises stress were examined.

Joint prosthesis failure is mainly related to aseptic loosening and prosthetic joint infections, both of which are associated with high morbidity and substantial costs for patients and health systems. The development of a biomaterial that is capable of stimulating bone growth while minimizing bacterial adhesion would reduce the incidence of prosthetic failure. We report antibacterial and osteostimulatory effects in a novel fluorine-phosphorus (F-P)-doped TiO2 oxide film grown on Ti-6Al-4V alloy with a nanostructure of bottle-shaped nanotubes (bNT) using five bacterial species (Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia) and MCT3T3-E1 osteoblastic cells. The interaction between the bacteria and bNT Ti-6Al-4V was complex, as the adhesion of four bacterial species decreased (two staphylococcus species, E. coli, and S. maltophilia), and the viability of staphylococci and S. maltophilia also decreased because of the aluminum (Al) released by bNT Ti-6Al-4V. This released Al can be recruited by the bacteria through siderophores and was retained only by the Gram-negative bacteria tested. P. aeruginosa showed higher adhesion on bNT Ti-6Al-4V than on chemically polished (CP) samples of Ti-6Al-4V alloy and an ability to mobilize Al from bNT Ti-6Al-4V. The cell adhesion and proliferation of MCT3T3-E1 osteoblastic cells significantly increased at 48 and 168 h, as did the matrix mineralization of these cells and the gene expression levels of three of the most important markers related to bone differentiation. According to our results, the bNT Ti-6Al-4V alloy could have clinical application, preventing infection and stimulating bone growth and thus preventing the two main causes of joint prosthesis failure.IMPORTANCE This work evaluates F-P-doped bNT Ti-6Al-4V from microbiological and cellular approaches. The bacterial results highlight that the antibacterial ability of bNT Ti-6Al-4V is the result of a combination of antiadhesive and bactericidal effects exerted by Al released from the alloy. The cell results highlight that F-P bNT Ti-6Al-4V alloy increases osseointegration due to modification of the chemical composition of the alloy resulting from P incorporation and not due to the nanostructure, as reported previously. A key finding was the detection of Al release from inside the bNT Ti-6Al-4V nanostructures, a result of the nanostructure growth during the anodizing process that is in part responsible for its bactericidal effect., This work was funded by a grant from the Spanish Ministry of Economics and Competitiveness (MAT2013-48224-C2-2-R and MAT2013-48224-C2-1-R). J.-J.A.-C. is funded by an FPI grant from the same institution (BES-2014-069007). We acknowledge Oliver Shaw for his help with the English language and Isabelle Schalk for providing the P. aeruginosa ATCC 15692 ΔpchA and ΔpvdF ΔpchA mutants.

The present study aims to reveal the mechanism of element vaporization of Ti-6Al-4V alloy during selective laser melting (SLM). The equations of Redlich&ndash, Kister and the thermodynamics principles were employed to calculate the vaporization thermodynamics, which contributes to the obtaining the vaporization kinetic based on the Chapman-Enskog theory and the diffusion model. According to the achieved vaporization model, the elements with the most prominent tendency and flux to vaporize were distinguished. Moreover, the effect of the process parameters on the vaporization of Al and Ti is experimentally investigated using inductively coupled plasma optical emission spectrometer (ICP) technology. The analyzed results of the chemical composition of the powders and builds show a great agreement with the kinetic results calculated by the vaporization model. Notably, the element vaporization can be curbed by regulating the laser energy input.

The research explores the use of femtosecond laser to clean the surface of Ti-6Al-4V alloy. The laser ablation threshold was determined from either depths or diameters of laser-induced craters. Both methods are expected to give the same results; however, it was found that ablation threshold can be determined more reliably from the diameters than from the depths. This can be understood from the study of the surface morphology. As the laser fluence increased, the ablated surface became increasingly rougher, making it difficult to measure the depths accurately. In contrast, diameters of laser-induced craters could be measured with much better certainty and thus enabled the ablation threshold to be determined more accurately. The ablation threshold was found to be 0.142 ± 0.010 J/cm2 for 100 laser pulses at 130 fs pulse duration and 790 nm wavelength and it tends to decrease with increase in number of laser pulses. The single-pulse ablation threshold was determined to be 0.272 ± 0.021 J/cm2. ASTAR (Agency for Sci., Tech. and Research, S’pore) Accepted version

The low-temperature superplastic tensile behavior and the deformation mechanisms of Ti-6Al-4V alloy are investigated in this paper. Through the experiments carried out, elongation to failure (δ) is calculated and a set of values are derived that subsequently includes the strain rate sensitivity exponent (m), deformation activation energy (Q) at low-temperature superplastic deformation, and the variation of δ, m and Q at different strain rates and temperatures. Microstructures are observed before and after superplastic deformation. The deformation mechanism maps incorporating the density of dislocations inside grains at temperatures of 973 and 1123 K are drawn respectively. By applying the elevated temperature deformation mechanism maps based on Burgers vector compensated grain size and modulus compensated stress, the dislocation quantities and low-temperature superplastic deformation mechanisms of Ti-6Al-4V alloy at different temperatures within appropriate processing regime are elucidated.

Fatigue cracks in titanium alloys are often found to initiate at faceted alpha grains. In the very high cycle fatigue regime, crack initiation tends to shift from the surface towards the interior of the material, and more initiation facets can be found on the fracture surface. In this study, fatigue tests were performed on drawn and heat-treated Ti-6Al-4V wires. Only a few samples fractured due to interior initiation. The facets at the initiation sites of these samples were not flat, but had markings on the nano-scale, and were highly inclined. A possible explanation for these aspects is the crystallographic texture of the wire, and a reflection is made on the suggested mechanisms of facet formation. peerreview_statement: The publishing and review policy for this title is described in its Aims & Scope. aims_and_scope_url: http://www.tandfonline.com/action/journalInformation?show=aimsScope&journalCode=ymst20 ispartof: Materials Science and Technology vol:32 issue:16 pages:1639-1645 status: published

In this paper a numerical investigation of replacement implant for partial hip arthroplasty is presented. The long-term stability of hip implants depends, among other things, on the loads acting across the joint. Forces occurring in vivo can be much greater than the recommended test values, because a typical gait cycle generates forces up to 6–7 times the body weight in the hip joint. A finite element analysis (FEA) was performed using 3-dimensional models to examine the mechanical behaviour of the femoral component at forces ranging from 2.5 to 6.3 kN. This implant design was chosen for numerical analysis because stress concentration in femoral component lead to implant fracture. Results show that the force magnitudes acting on the implant are of interest, and that they can cause implant stress field changes and implant stability problems, which can lead to implant failure.

In this paper, Taguchi method was employed to optimize the surfactant and graphite powder concentration in dielectric fluid for the machining of Ti-6Al-4V using Electrical Discharge Machining (EDM). The process parameters such as discharge current, surfactant concentration and powder concentration were changed to explore their effects on Material Removal Rate (MRR), Surface Roughness (SR), Tool wear rate (TWR) and Recast Layer Thickness (RLT). Detailed analysis of structural features of machined surface was carried out using Scanning Electron Microscope (SEM) to observe the influence of surfactant and graphite powder on the machining process. It was observed from the experimental results that the graphite powder and surfactant added dielectric fluid significantly improved the MRR, reduces the SR, TWR and RLT at various conditions. Analysis of Variance (ANOVA) and F-test of experimental data values related to the important process parameters of EDM revealed that discharge current and surfactant concentration has more percentage of contribution on the MRR and TWR whereas the SR, and RLT were found to be affected greatly by the discharge current and graphite powder concentration.

This paper presents the experimental investigation of machinability parameters in high-speed micro-end milling of Ti alloy (grade-2) with uncoated tungsten carbide micro-end mills to understand the cutting mechanism and surface roughness formation. Micro-milling experiments are carried out by using a Taguchi method. The lower the better-quality characteristic in signal-to-noise ratio, analysis of variance and regression analysis are considered to analyze the effect of machining parameters on cutting forces and surface roughness. Model validation is performed by comparing analytical predicted results of cutting forces with experimental and Taguchi approach that are in good agreement. The investigation showed that micro-milling at high spindle speeds, low depth of cut, and low feed rate ensures the high quality of surface roughness and lower cutting forces.

Ультразвуковая и электронно-пучковая обработка технического титана ВТ1-0 и его сплава ВТ6 (Ti–6Al–4V) создают в поверхностном слое неравновесную зеренно-субзеренную иерархическую субструктуру, которая обусловливает многоуровневую фрагментацию материала и проявляет эффект демпфирования. Высокотемпературная ОЦК-структура поверхностного слоя при охлаждении в градиентном поле температур (при электронно-пучковой обработке) и при разрушении ультразвуком β-фазы в исходном сплаве испытывает неравновесный фазовый переход в плотноупакованную ГПУ-структуру α-фазы. Избыточный удельный объем β-фазы иерархически распределяется в α-фазе распространением неравновесных мартенситных фаз α′, α″ и в виде локального образования ω-фазы по границам зерен α-фазы. Удельный объем неравновесных фаз превышает удельный объем α-фазы. Это позволяет исключить образование микропор и обусловливает фрагментацию материала на микрои наномасштабных структурных уровнях при неравновесном фазовом переходе β → α. Полосы мартенситной α′-фазы вызывают фрагментацию α-фазы на микромасштабном уровне. Полосы мартенситной α″-фазы распространяются в пределах неравновесных полос α′-фазы, имеют толщину ~1.5 нм и фрагментируют материал в пространстве наномасштабных уровней. Этот процесс контролируется электронной подсистемой, которая создает наномасштабные мезоскопические структурные состояния для образования мартенситных неравновесных фаз. Обратимость упругопластической деформации при образовании неравновесных мартенситных фаз на наномасштабном структурном уровне лежит в основе эффекта демпфирования поверхностного слоя, подвергнутого ультразвуковой или электронно-пучковой обработке. Получено экспериментальное подтверждение образования наномасштабных мезоскопических структурных состояний, обусловливающих новый механизм обратимой деформации, при нарушении трансляционной инвариантности решетки в деформируемом твердом теле., Ultrasonic and electron beam treatment of commercial titanium VT1-0 and its alloy VT6 (Ti–6Al–4V) produces a nonequilibrium grain-subgrain hierarchical substructure in the surface layer, which causes a multiscale fragmentation of the material and reveals a damping effect. When cooled in the gradient temperature field (during electron beam treatment) and when the β phase of the initial alloy is destroyed by ultrasound, the high-temperature bcc structure of the surface layer undergoes a nonequilibrium phase transition into an hcp α-phase structure. The excess specific volume of the β phase is hierarchically distributed in the α phase through the growth of nonequilibrium α′ and α″ martensite, and in the form of local ω-phase precipitation along the grain boundaries of the α phase. The specific volume of the nonequilibrium phases exceeds the specific volume of the α phase. This eliminates the formation of micropores and causes material fragmentation at the microand nanoscale structural levels during the nonequilibrium β → α phase transition. The growing α′ laths cause the fragmentation of the α phase at the microscale level. The α″ laths grow within the nonequilibrium α′ laths; they have a thickness of ∼1.5 nm and fragment the material at the nanoscale level. This process is controlled by the electronic subsystem that creates nanoscale mesoscopic structural states for the formation of nonequilibrium martensite phases. The reversible elastoplastic deformation of the nonequilibrium martensite phases at the nanoscale level governs the damping effect of the surface layer subjected to ultrasonic or electron beam treatment. The generation of nanoscale mesoscopic structural states and related with them the new mechanism of reversible deformation in the conditions of broken translational invariance of the lattice in a deformable solid has been confirmed experimentally.

A cold-rolled Ti-6Al-4V sheet was subjected to three different heat treatments prior to processing by high pressure torsion (HPT). Quantitative measurements revealed that the volume fractions were 70% equiaxed α phase and 30% lamellar (α + β) (Ti64-1), 47% equiaxed α phase and 53% lamellar (α + β) (Ti64-2) and 25% equiaxed α phase and 75% lamellar (α + β) (Ti64-3) and the grain sizes of the α phase were 7.0 ± 2 μm, 9.0 ± 1.5 μm and 9.5 ± 1.5 μm, respectively. The processing by HPT was performed at room temperature with a pressure of 6.0 GPa and a rotation speed of 1 rpm. Processing of the three heat treatment batches was conducted through a total number of revolutions, N, of 1/4, 1, 5, 10 and 20. The results show that the microhardness increases with increasing numbers of turns in HPT processing and for all three conditions stable microhardness values are reached after about 20 turns. The grain sizes after 20 turns of HPT were 115 ± 30 nm in Ti64-1, 85 ± 25 nm in Ti64-2 and 75 ± 15 nm in Ti64-3 so that the grain size decreases as the volume fraction of α phase decreases and the lamellar (α + β) increases.

Textured functional surfaces are finding applications in the fields of bioengineering, surface energy, hydrodynamics, lubrication, and optics. Electrical discharge machining (EDM), which is normally used to generate smoother surface finish on various automotive components and toolings, can also generate surfaces of rough finish, a desirable characteristic for texturing purposes. There is a lack of modeling efforts to predict the surface textures obtained under various EDM operating conditions. The aim of the current work is to capture the physics of the electrical discharge texturing (EDT) on a surface assuming random generation of multiple sparks with respect to (i) space, (ii) time, and (iii) energy. A uniform heat disk assumption is taken for each individual spark. The three-dimensional (3D) texture generated is utilized to evaluate a 3D roughness parameter namely arithmetic mean height, Sa. Surface textures obtained from the model are validated against experimentally obtained ones by comparison of distribution of Ra values taken along parallel sections along the surface. It was found that the distribution of simulated Ra values agrees with that of experimental Ra values.

Titanium alloys are widely used in aeronautics that demands a good combination of high strength, good corrosion resistance and low mass. The mechanical properties lead to challenges in machining operations, such as high process temperature as well as rapidly increasing tool wear. In this work, three carbide end mills have been used in machining of titanium alloy Ti-6Al-4V. The first tool is coated with TiAl; the second and the third are coated with multi-layers or with a single layer of TiAlN. The cutting force and the tool life have been experimentally investigated and put into relationship with the process parameters under dry cutting condition. The quality of the machined surfaces has been evaluated by measuring the roughness of the machined surfaces. Finally, the correlation among cutting force variation, tool wear propagation and surface roughness has been analyzed and discussed. These three tools demonstrate to be able to maintain their hardness and other mechanical properties at the high cutting temperatures that they encountered.