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During the thermal-mechanical processing of titanium alloys, the formation of macrozones is unavoidable within complex components, which significantly degrades their performance. This study systematically investigates the effects of rolling-induced macrozones on the static globularization of the microstructure during annealing. Furthermore, a comprehensive elucidation is provided on the influence of macrozones with different crystallographic orientations on the room temperature mechanical properties of the Ti-Al-Mo-Zr-Nb-V alloy through an analysis of slip activation and transmission. The findings indicate that within the macrozones, static globularization of the microstructure, primarily governed by the boundary splitting mechanism, is hindered due to the similar orientation of the α phase; In the unidirectionally rolled and annealed sheet featuring [0001]//TD macrozones (Type I), distinct deformation mechanisms emerge under rolling direction (RD) and (transverse direction) TD loading, resulting in significantly anisotropic mechanical properties; Conversely, in the cross-rolled and annealed sheet, macrozones characterized by average Euler angles of (155°, 80°, 30°) (Type II) and (175°, 120°, 0°) (Type III) are consistently adjacent to each another, facilitating crack nucleation at the interfaces of macrozones and propagation along the length. The room temperature plasticity of this sheet exhibits nonuniformity, with a wider distribution of macrozones correlating with poorer plasticity. This study will contribute to the advancement of knowledge in this field and aid in the development of improved strategies for controlling macrozones and optimizing performance in titanium alloys. [Display omitted] • The responses of globularization behavior and tensile properties to the macrozones are thoroughly discussed. • Crystallographic calculations and quantitative statistics are used to reveal the impact of macrozone on deformation mechanism. • FIB-EBSD and TEM technologies play crucial roles in analyzing the stability of mechanical properties and failure mechanism. • A deeper understanding of the issue of macrozone in newly developed marine engineering titanium alloy is achieved. [ABSTRACT FROM AUTHOR]

Abstract Nanotwinned nanocrystalline CoCrFeNi high-entropy alloy films were prepared by magnetron sputtering. A disordered face-centered cubic structure was identified, with a uniform distribution of chemical elements. Both <1 1 0> out-of-plane and <1 1 1> in-plane textures were also observed in the nanotwinned film with a thickness of 2.98 µm. The fatigue resistance of the films was analyzed by nanoindentation technique with up to 103 cycles under various impact energies, complemented by post-test atomic force microscopy investigation of indentation craters. Unlike coarse-grained samples, the nanotwinned films exhibited excellent fatigue resistance, characterized by history-independent and near-stable fatigue responses. Under the influence of the textures developed in the films, the nanotwin planes were oriented toward the loading direction under each fatigue cycle. As such, extremely stable correlated necklace dislocations structure formed and moved back and forth along the twin boundaries during cyclic loading, which preserved the slip systems as well as the coherency and stability of twin boundaries. [ABSTRACT FROM AUTHOR]

Abstract The effect of impurity level and inclusions on the mechanical properties, especially the ductility and toughness, of two low-temperature-aged U-5.5Nb alloys were extensively investigated. Two U-5.5Nb alloys with different impurity levels, i.e., total C+N contents of 330 and 840 mass ppm, are discussed here. The methods used in the present study were scanning electron microscopy with energy-dispersive X-ray spectroscopy, optical microscopy, time-of-flight secondary ion mass spectrometry, tensile and impact mechanical property tests, and nanoindentation measurement. According to the results, both the low- and high-impurity-level samples contain two types of inclusions, namely, U(N,C) and Nb 2 C inclusions. The inclusion volume fraction, average inclusion radius, inclusion spacing, and number of inclusion particles per unit area all increase with increasing impurity level. In addition, the ductility, i.e., elongation, reduction in area, and impact toughness decrease with increasing impurity level. However, the impurity level has little effect on the yield strength. The inclusions have a detrimental effect on the ductility and toughness of the alloys because the inclusions are the preferential sites for void nucleation. Based on the experimental observations, an illustration of the failure mechanisms for the tensile and impact fracture behaviors for the low-temperature-aged U-5.5Nb alloy is presented. [ABSTRACT FROM AUTHOR]

Abstract In this study, the microstructure, martensitic transformation, stabilization of the stress-induced martensite and shape memory effect of (Cu 78 Al 12 Fe 4 Mn 6) 100- x Zr x (x = 1 and 2) and (Cu 78 Al 12 Fe 4 Mn 6) 100- y Nb y (y = 1 and 2) alloys were investigated. All alloys exhibit bcc phase separation, resulting in a microstructure consisted of dominant L2 1 -Cu 2 AlMn parent, fine bcc β(Fe,Al,Zr) or β(Fe,Al,Nb) phase and a small quantity of 2H martensite. All the studied alloys show the reversible martensitic transformation, and the forwards martensitic transformation temperatures are below room temperature. Although the alloys have main L2 1 parent before deformation, during deformation and after unloading, the stress-induced 2H martensite can be stabilized due to the resistance of a large amount of β(Fe,Al,Zr) or β(Fe,Al,Nb) particles. Furthermore, the stabilization degree of the stress-induced martensite happens more obviously while further increasing the amounts of particles. The stabilized martensite can be recovered through heating, thus the alloys possess good shape memory properties. The largest shape memory effects are 4.1%, 4.4%, 4.4% and 4.0% respectively for x = 1, 2, and y = 1, 2 alloys. [ABSTRACT FROM AUTHOR]

Abstract The effect of the addition of Zr, Ni, and Mn and the elevated temperature thermal exposure on the mechanical performance (tensile and hardness properties) of Al-Si-Cu-Mg cast alloy were investigated for this research study. The evolution of the strengthening precipitates during the prolonged thermal exposure were also investigated using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) in order to correlate the variation in the mechanical properties to the nature of the strengthening precipitates. Varying the thermal exposure technique from static into dynamic had little effect on the tensile and hardness data obtained at room temperature. This permitted using the static exposure (stabilization) technique to simulate the behavior of the material under dynamic thermal exposure conditions as in the case of the automotive engine components. Coarsening of the strengthening precipitates following prolonged exposure at 250 °C had a deleterious effect on the tensile properties and hardness values. Noticeable reduction in the strength values, particularly the yield strength, and a remarkable increase in the ductility values were observed. The coarsening kinetics of the precipitates decayed with time, due to the continuously increased distance between the precipitates with increase in the exposure time, causing the observed deterioration in the mechanical performance after exposure at 250 °C up to the first 100 h. However, further thermal exposure up to 200 h did not result in further reduction in the strength and hardness values. [ABSTRACT FROM AUTHOR]

Abstract High pressure solution treatment was applied to prepare Al7Si1.7Cu solid solution which shows fast and considerable age-hardening response. The extraordinarily high peak hardness of the alloy (~ 170 HV) is attributed to the combined strengthening effect of the homogeneously distributed nanoscale Si and θ’’/θ’ precipitates. [ABSTRACT FROM AUTHOR]

Abstract Annealing often causes softening in conventional large-grained materials. However, annealing has been found to cause hardening in many nanocrystalline metals and alloys. This abnormal hardening by annealing has been explained by such factors as solute segregation at grain boundaries, grain boundary relaxation, grain boundary pinning by second phase particles, etc. In the present work, a homogenous single-phase nanocrystalline Ni(Fe) alloy prepared by electrodeposition was investigated. This alloy is with approx. 1 at% Fe and composed of a solid solution of Fe in Ni without any precipitated phase. The goal is to shed light on which mechanism dominates annealing hardening. Microhardness of the alloy was found to increase slightly just before the grains started to grow during annealing. In addition, long time annealing at the hardening temperature resulted in the decrease of hardness due to grain growth. Both lattice parameter and atom probe tomography studies suggest that the annealing hardening is caused by the segregation of solute and impurity atoms on grain boundaries in the nanocrystalline Ni(Fe) alloy. [ABSTRACT FROM AUTHOR]

Abstract In the present study, the effect of secondary phase particles and deformation localization on tensile behaviors of Mg-Zn-Ca alloy were investigated using micro-digital image correlation method. To isolate the effect of the secondary phase particles on tensile behavior, the fractions of the secondary phase particles were adjusted by controlling the annealing temperature. Thermodynamic calculations were performed to identify the fractions of the secondary phase particles. The finite element method was conducted to confirm the localized deformation around the secondary phase particles considering 3-dimensional microstructure. The results suggest that the total fraction of the secondary phase particles affected the localized deformation around the particles and micro-crack propagation process during a tensile test. [ABSTRACT FROM AUTHOR]

Abstract Grain refinement of non-equiatomic Cr-rich CoCrFeMnNi high-entropy alloys with an fcc structure was studied focusing on the precipitation of a Cr-rich σ phase along grain boundaries and shear bands. We found for the first time that the σ phase can be precipitated at the grain boundaries and the shear bands in the alloys at a significantly fast precipitation rate. The σ phase effectively suppressed the grain growth of the fcc matrix during recrystallization of the alloy after conventional cold rolling, resulting in a fine-grained microstructure with a mean diameter of approximately 1 µm. The alloys with this fine microstructure containing the σ phase exhibit high strength over a wide temperature range due to grain boundary strengthening and precipitation strengthening caused by the σ phase. Moreover, the alloys exhibit large ductility not only at room and high temperatures, but also at low temperatures. Deformation-induced twinning plays an important role in this ductility. [ABSTRACT FROM AUTHOR]

Abstract Here, Mg-0.4 wt%Sn based alloys containing different Y contents, Mg-0.4Sn- x Y (x = 0, 0.7 and 2.0 wt%) alloys, were extruded into the sheets to systemically investigate the role of Y element on the microstructure, texture and mechanical properties of extruded Mg-0.4Sn alloy. We found that, with the Y addition, the average grain size gradually was reduced and the typical basal texture was transformed into the splitting one tilted to the extrusion direction. Moreover, the evidence of low number density and rough grain boundary cracks after tension indicated the strengthening in grain boundary cohesion with the Y addition. Besides more basal slips, the activation of prismatic slip and high intergranular strain propagation capacity were observed, which efficiently accommodated the sheet strain at room temperature. Those mentioned key factors contributed to the high room-temperature ductility of Mg-0.4Sn-0.7Y sheet. However, the formation and coarsening of Sn 3 Y 5 and MgSnY phases were increasingly severe with increasing the Y addition to 2.0%. Those coarse secondary phases served as crack sources during tension deteriorating the ductility of Mg-0.4Sn-2.0Y sheet at room temperature. Therefore, we concluded that Y micro-alloying provided a new insight to achieve a superior room-temperature ductility of Mg-0.4Sn sheet. [ABSTRACT FROM AUTHOR]

Abstract In this work, the microstructure of Al-Mg-Si-Cu alloy was tailored by controlling the aging process and its effect on the fracture mechanism was systematically explored by in-situ tensile test and microstructural observations. It was found that the aging process influences the mechanical performance and leads to the alteration of the tensile fracture mode of the aged alloy. Microscopy observations revealed that the Al 2 Cu precipitates distribute heterogeneously in the peak-aged alloy. The density of the Al 2 Cu precipitates in the intergranular fracture regions is much higher than that in the transgranular regions. The effect of Al 2 Cu precipitates on the fracture mode was systematically discussed and a hybrid fracture mechanism was proposed. [ABSTRACT FROM AUTHOR]

Abstract The effect of electric pulsing treatment (EPT) on the solid-solutioned Al-Mg-Si alloy was investigated in this paper. It was interestingly found that EPT promoted the precipitation of the stable Al 5 FeSi phase. Besides, the precipitates pinned the dislocations effectively, thus the dislocations would be remained after the aging process. Moreover, the most interesting phenomenon was that the deformation bands induced by the remained tangled dislocation made the precipitates Mg 2 Si from rod-like to globular. Consequently, the superior strength (47.2% higher than T6 temper) alloy nearly without loss of ductility was obtained. [ABSTRACT FROM AUTHOR]

Abstract The rotary-bending fatigue tests of a high Nb-containing beta-gamma TiAl alloy based on microstructure control have been conducted at 800 °C. A fine nearly lamellar microstructure with the lamellar colony of 80 µm and slight content of B2 phase of 2% is obtained by an improved two-step heat treatment. The rotary-bending fatigue results perform the scattered S-N data, flat S-N fitting curve and an excellent fatigue limit reached at 355 MPa. SEM results exhibit an obvious transition between stable crack growth and fast fracture surface. Massive cracks initiate at lamellar interface, colony boundary and B2 phase on the specimen surface, which coalesce and propagate from the margin to the center of specimen. TEM analysis indicates that dislocation glide and mechanical twinning are the mainly deformation mechanism. The interlamellar and translamellar fracture result from dislocation pile-up and the inclined slip band or mechanical twinning, respectively. [ABSTRACT FROM AUTHOR]

Abstract Effects of Sn addition (0–1.5 mass%) on dynamic recrystallization (DRX) of Mg-5Zn-1Mn alloy during high strain rate (ε ̇ =9.1 s−1) deformation are investigated by hot compression testing. With a higher Sn addition, the strain corresponding to the maximum softening rate and the critical strain corresponding to the onset of DRX decrease at first and then increase, while the DRX fraction is just the reverse. The Mg-5Zn-1Mn-0.9Sn alloy shows the biggest DRX extent. Continuous DRX with twin nucleation is the dominant DRX mechanism for all the alloys. The high density dislocations inside twins gradually evolve into the cellular structures and sub-grains by dynamic recovery, and sub-grains turn into the DRX nuclei. The Sn addition can adjust the nucleation rate and the nucleus growth rate of DRX by regulating the inclination for twinning, adjusting stacking fault energy (SFE) and changing the amount of precipitates. Solute Sn atoms not only promote DRX nucleation by increasing twin density but also stimulate the DRX nucleus growth by reducing SFE. With the higher amount of MgZn 2 and Mg 2 Sn dislocation-induced precipitates, the negative effect on DRX derived from the precipitates becomes effective, including hindering the formation of cellular structures and preventing the rotation and the growth of sub-grains by the pinning effect. [ABSTRACT FROM AUTHOR]

In this study, we designed and fabricated high-performance Ti-Fe-N-B alloys by sintering a blend of Ti powder, Fe powder and BN nanopowder using spark plasma sintering. During sintering, TiB nanowires nucleated from the surfaces of Ti powder particles on which the BN nanoparticles were dispersed, and then grew into the nearby Ti matrix forming a three-dimensional (3D) network-woven architecture throughout the Ti matrix. The TiB nanowires were about 10–30 µm in length and 50–200 nm in diameter after sintering. Their existence suppressed the formation of the continuous α-Ti phase along the β-Ti grain boundaries and refined the microstructure of the Ti matrix. A large quantity of α-Ti nanoplates precipitated along the planes (110) β-Ti in the Ti-Fe-N-B alloys. The as-sintered Ti-4.5Fe-0.14N-0.11B alloy achieved a high tensile strength of 1176 MPa with a significant tensile elongation of 10.4%, which satisfied the requirements for the tensile properties of mill-annealed Ti6Al4V in the solution-treated and aged (STA) condition. The TiB nanowires, α-Ti nanoplates, Fe solute atoms, and N solute atoms in the matrix all contributed to the high tensile strength. [ABSTRACT FROM AUTHOR]

This study explores and compares two new alloys, namely 50In-50Bi and 17Sn-26In-57Bi (wt%), with melting peak temperatures of 95 and 82 °C, which are substantially lower than the melting points of lead-free solders commonly used for low-temperature applications. The microstructures and intermetallic compounds (IMCs) of the new alloys, which were reflowed on Cu substrates, were studied. Notable Bi 3 In 5 and BiIn 2 compounds were formed in the reflowed 50In-50Bi alloy. The IMCs detected at the interfaces of 50In-50Bi and 17Sn-26In-57Bi were Cu 11 (In, Bi) 9 and Cu 6 (In, Sn) 5 , respectively. Shear tests were systematically performed on organic solderability preservative (OSP) Cu substrates with 300-μm openings. Investigation of the fracture surfaces of both alloys indicated that the 17Sn-26In-57Bi/OSP Cu system had the higher shear strength and the more ductile joints. [ABSTRACT FROM AUTHOR]

Al-rich TiAl alloy system has recently become a focus of interest due to its higher oxidation resistance, 20% lower density and higher (200 °C more) operating temperature application possibility over conventional Ti-rich TiAl alloys. Tension-compression asymmetry of such type of high temperature material is an integral part of modern engineering problems. Rate dependent asymmetric phenomena of such alloys is specially important at high homologous temperature because of the appearance of one or more long period superstructures. However, micromechanical modeling endeavor of Al-rich family has not been attempted so far. In this work, we have presented two internal variable based phenomenological crystal viscoplasticity modeling approach for predicting rate dependent tension-compression asymmetry of single crystal like lamellar Ti-61.8at%Al binary alloy at hot compression state (1050 °C) by employing finite strain and finite rotation framework. Our material parameters were based on calibrating three different sets of compressive stain rate controlled plasticity data in two lamellar directions. Based on the set of identified material parameters we have predicted qualitatively the evolution of tension compression asymmetry of this alloy. It is found that tension-compression-asymmetry evolution is anisotropic and highly pronounced throughout the deformation process influenced by the lamellar morphology and long period superstructures. Slip system level operative stresses show that the slip domination and activity, more specifically, major contributing systems are different in tension and compression. [ABSTRACT FROM AUTHOR]

Cold forming processes present advantages to produce components with tight tolerances to the final (net) shape, eliminating significant production costs. These processes requires forming parts in a soft condition, with high ductility and formability. Jethete M152 alloy is a cold formable 13-Cr% martensitic stainless steel used in the aerospace industry. However, the inherent high strength of this material presents challenges in terms of the high loads and contact and friction stresses developed during cold forming processes. The main purpose of this work was to explore the impact of different types of annealing treatments (subcritical, full and isothermal treatments) on the softening and work hardening behaviour of this alloy. Microstructural and mechanical testing analysis were conducted. The results indicate that only subcritical annealing treatments ( T < A r1 ) were successful by reducing the strength and hardness levels. However no significant effect on both work hardening behaviour and uniform elongation was found. Due to the high hardenability of this alloy, those softening treatments which require the austenization of the material were translated into the formation of freshly (as-quenched) martensite, resulting into an increase of strength, loss in ductility properties and a significant change in the work hardening behaviour. Despite of the large differences in strength properties and work hardening behaviour across all the softening treatments analysed, no significant microstructural differences were found. These results indicate that such differences are associated mainly to both dislocation density and the substructure developed during tempering/annealing at high temperatures. [ABSTRACT FROM AUTHOR]

The effects of annealing temperature on the microstructure, mechanical properties and superelasticity of Ti-19Zr-10Nb-1Fe alloys were investigated. The as-rolled alloy was annealed at temperatures between 823 K and 1173 K. The alloy annealed at 823 K consisted of major β and partial α phases. Equiaxed β grains with nanoscale ω precipitates were observed in the alloys annealed above 873 K. The α/β transus temperature and recrystallization temperature of Ti-19Zr-10Nb-1Fe alloy were both determined to be between 823 K and 873 K. The alloy annealed at 823 K exhibits a higher ultimate tensile strengthen and a lower fracture strain than other alloys, due to the residual work hardening, and the coarse and non-uniformly distributed α precipitates. Ti-19Zr-10Nb-1Fe alloys annealed at 873 K and 973 K exhibited superelasticity in tension due to the stress induced martensitic transformation. However, no obvious superelasticity can be observed during the tensile deformation of the alloys annealed at 823 K or 1173 K, implying the suppression of stress-induced martensite transformation by high-density dislocations or increased β grain size, respectively. The alloy annealed at 873 K exhibited a good combination of large elongation of ~24.8%, low Young's modulus of ~58 GPa, high ultimate tensile stress of ~703 MPa and the maximum superelasticity of ~3.7%. [ABSTRACT FROM AUTHOR]

The microstructure and texture development of a cast Mg-Gd-Y-Zr alloy during hot deformation and subsequent annealing were investigated by optical microscopy (OM) and electron backscattered diffraction (EBSD) technology. Initial microstructures with partially and fully developed new fine grains (NFGs), separately attended by continuous or interrupted hot forging, were various mixed grain structures composed of NFGs in necklace and retained coarse grains. It is shown that, during annealing, the development of grain size can be divided into three stages: i.e. an incubation of grain growth, a rapid coarsening and a normal grain growth. After a long time annealing of over 10 4 ks at 693 K, the average grain size for samples continuous compressed to ε=1.2 and those interrupted compressed to ε=1.6 were close. Moreover, orientations of such strain-induced fine grains were relatively randomly distributed, leading to a weakened basal texture, while the basal plane of retained coarse grains were perpendicular to the forging direction. Such texture even became weaker during subsequent annealing. The results show that the development of necklace NFGs during hot deformation can be effective for homogeneous grain refinement under subsequent annealing. [ABSTRACT FROM AUTHOR]

Cyclic tensile loading tests and transmission electron microscopy investigation are conducted on a Ti-24Nb-4Zr-8Sn (wt%) alloy. Under tensile strain less than 3.3%, most of the deformation strain recovers after unloading but significant energy dissipation occurs during the loading-unloading cycle. Reversible migration of twin boundaries between α″ martensite variants, in virtue of dislocation movement on the twin boundaries, has been revealed by time resolved high-resolution transmission electron microscopy. This twin boundary migration contributes to the energy dissipation effect and consequently the damping property of the titanium alloy. [ABSTRACT FROM AUTHOR]

In the present work, effects of creep ageing (CA) on the mechanical properties and micro precipitates of Al-Li-S4 alloy was investigated. Compared with single stress-free ageing (SFA), experimental results show that CA has significantly improved the mechanical properties of Al-Li-S4 alloy, including hardness, strength and elongation. Meanwhile, the peak-ageing time was also prolonged under CA treatment. When specimens were continuously placed under an exterior stress of 240 MPa after CA treatment at 153 °C for 25 h, more T 1 (Al 2 CuLi) nano-precipitates developed and further contributed improvement in mechanical properties. It is mainly attributed to the exterior stress that promoted to form T 1 nano-precipitates. Moreover, CA enabled to restrict both the coarsening of precipitates at grain boundaries and the formation of precipitation free zone. In addition, fractographic examination of SFA-treated and CA-treated Al-Li-S4 tensile specimens were carried out, respectively. Through controlling the formation process of fine T 1 nano-precipitates during CA treatment, it can facilitate the development of novel microstructures in Al-Li-S4 alloys with certain promising mechanical properties. [ABSTRACT FROM AUTHOR]

High-entropy alloys have gained high interest of both academia and industry in recent years due to their excellent properties and large variety of possible alloy systems. However, so far prediction of phase constitution and stability is based on empirical rules that can only be applied to selected alloy systems. In the current study, we introduce a methodology that enables high-throughput theoretical and experimental alloy screening and design. As a basis for thorough thermodynamic calculations, a new database was compiled for the Co–Cr–Fe–Mn–Ni system and used for Calphad and Scheil simulations. For bulk sample production, laser metal deposition (LMD) of an elemental powder blend was applied to build up the equiatomic CoCrFeMnNi Cantor alloy as a first demonstrator. This production approach allows high flexibility in varying the chemical composition and, thus, renders itself suitable for high-throughput alloy production. The microstructure, texture, and mechanical properties of the material processed were characterized using optical microscopy, EBSD, EDX, XRD, hardness and compression testing. The LMD-produced alloy revealed full density, strongly reduced segregation compared to conventionally cast material, pronounced texture, and excellent mechanical properties. Phase constitution and elemental distribution were correctly predicted by simulations. The applicability of the introduced methodology to high-entropy alloys and extension to compositionally complex alloys is discussed. [ABSTRACT FROM AUTHOR]

The warm deformation behavior of precipitation hardening alloys depends on the changes in precipitate morphology. In this research, the kinetics of dynamic precipitation of AA2024 were investigated and compared to static precipitation at temperatures of 200 °C, 230 °C, and 260 °C. Results show that deformation increased the precipitation kinetics rate than that of the static precipitation. Also, the rate of increase in electrical conductivity and hardness of dynamic aging was more than static aging. The dynamic precipitation process considerably increased flow stress value during hot deformation in the supersaturated specimens. The most effective strain-precipitation-hardening was found in the temperature range of 200–230 °C. This effect was dependent on the strain rate while the diffusion mechanism controlled the precipitation process. [ABSTRACT FROM AUTHOR]

In this work, we are investigating the scaling effects on an austenitic stainless steel with changing grain size using microcompression testing. It is our aim to evaluate at what sample-to-grain size ratio the mechanical properties such as yield stress deviate from the macroscopically determined data. It was found that decreased yield stresses with decreasing specimen size (weakening) occur during the microcompression. The weakening was observed when the diameter-to-grain size ratio ( D / d ) dropped below a critical value. The effect of the grain size on the critical value, above which the bulk property can be obtained, was systematically investigated utilizing a wide range of D / d values (0.5–30) for specimens with a grain size ranging from 0.3 to 2 μm. It was found that the critical D / d value decreases with increasing grain size. A simple analytical model was developed, which is applicable to both micropillar and tensile tests. Comparison of the model equations with experimental data showed that the reduction in yield stress with sample size can be associated with the weaker near-surface zone, which has a reduced strength compared to the specimen interior zone. Furthermore, this study suggests that the size of the near-surface zone may be related to the dislocation structures in near-surface grains, and therefore the overall behavior is governed by the grain size and stacking fault energy. [ABSTRACT FROM AUTHOR]

Abstract: Effects of Cr content on microstructures and hot hardness of AlCoCr x FeMo0.5Ni high-entropy alloys (x =0–2.0) were investigated. The cast microstructure of AlCoCr x FeMo0.5Ni consists of B2 and σ phases, both being multi-element solid solutions. Increasing Cr content increases the volume fraction of σ phase and causes the matrix phase of the dendrite to change from B2 phase to σ phase. The alloy hardness increases from Hv 601 at x =0 to Hv 867 at x =2.0 as a result of increasing amount of hard σ phase. A phase diagram for the AlCoCr x FeMo0.5Ni alloy system is constructed based on SEM, HTXRD and DTA analyses, providing useful information for understanding and designing high-entropy alloys. All the AlCoCr x FeMo0.5Ni alloys possess higher hot-hardness level than that of Ni-based superalloys, In 718 and In 718 H, from room temperature to 1273K. Cr-1.5 and Cr-2.0 alloys exhibit a transition temperature higher than that of Co-based alloy T-800 by about 200K and have respective hardness values, Hv 374 and Hv 450 at 1273K, being much higher than those, around Hv 127, of In 718 and In 718 H. The mechanism of larger strengthening and softening resistance is related with B2 and σ phases, both having multi-principal-element effect. The AlCoCr x FeMo0.5Ni alloy system has a potential in high-temperature applications. [Copyright &y& Elsevier]

Abstract: Different shot peening conditions were applied to an austenitic stainless steel AISI 304L in order to transform austenite to martensite α′ at different depths. Magnetic Barkhausen noise measurements performed on this steel reveal a correlation between the strength of the signal and the depth of the treatment. The combined effect of the volume fraction of martensite and the residual stress in martensite determined using X-ray diffraction analysis were found to be responsible for the evolution of the Barkhausen noise response. Using tensile plastic deformation, the residual stress in martensite was changed, giving rise to a strong increase of the Barkhausen noise activity. This variation was correlated to a modification of the sign and amplitude of the residual stress in the martensite phase. Directional measurements of the Barkhausen noise revealed the anisotropy of the residual stresses induced by the tensile plastic deformation. It is concluded that the Barkhausen noise activity recording could lead to the determination of the residual stresses in martensite induced by shot peening processes. [ABSTRACT FROM AUTHOR]

Abstract: The electron back scattering diffraction (EBSD) technique has been applied in investigating the crystallographic mechanism of crack propagation in Al–Zn–Mg–Cu alloy. It is revealed that intergranular and transgranular crack propagation behaviours both exist and the relationship between crack propagation and orientations of adjacent grains complies with the crystal plastic deformation mechanism. When the interfacial angle between fracture surfaces of two adjacent grains is small, the crack propagates through grain boundaries with deflection of a certain angle; while small interfacial angles cannot form between slip planes in two adjacent grains, intergranular propagation occurs. [ABSTRACT FROM AUTHOR]

Abstract: Fe–C–V and Fe–C–V–Si alloys of various C, V and Si compositions were investigated in this work. It was found that the phases present in both of these alloy systems were alloyed ferrite, alloyed cementite, and VC x carbides. Depending on the alloy composition the solidified microstructural constituents were granular pearlite-like, lamellar pearlite, or mixtures of alloyed ferrite+granular pearlite-like or granular pearlite-like+lamellar pearlite. In addition, it is shown that in Fe–C–V alloys the C/V ratio influences (a) the type of matrix, (b) the fraction of vanadium carbides, f v and (c) the eutectic cell count, N F. In Fe–C–V alloys, a relationship between the alloy content corresponding to the eutectic line was experimentally determined and can be described by where Ce and Ve are the carbon and vanadium composition of the eutectic. Moreover, in the Fe–C–V alloys (depending on the alloy chemistry), the primary VC x carbides crystallize with non-faceted or non-faceted/faceted interfaces, while the eutectic morphology is non-faceted/non-faceted with regular fiber-like structures, or it possesses a dual morphology (non-faceted/non-faceted with regular fiber-like structures+non-faceted/faceted with complex regular structures). In the Fe–C–V–Si system, the primary VC x carbides solidify with a non-faceted/faceted interface, while the eutectic is non-faceted/faceted with complex regular structures. In particular, spiral eutectic growth is observed when Si is present in the Fe–C–V alloys. In general, it is found that as the matrix constituent shifts from predominantly ferrite to lamellar pearlite, the hardness, yield and tensile strengths exhibit substantial increases at expenses of ductility. Moreover, Si additions lead to alloy strengthening by solid solution hardening of the ferrite phase and/or through a reduction in the eutectic fiber spacings with a decrease in the alloy ductility. [Copyright &y& Elsevier]

Abstract: The correlation between compression conditions at temperatures in the range of 573–773K with the strain rate range of 0.002–2s−1 and grain size after solution heat treatment of 7075 alloy was investigated, as contrasted with 6061 alloy. The grain coarsening occurred under specific Zener-Hollomon (Z) parameters of 5×1010–1012 s−1 for 7075 alloy, 108–2×1012 s−1 for 6061 alloy, respectively. These phenomena could be explained by crystalline orientation analysis and stored deformation strain evaluation. The site of subgrains with less than 15° misorientation and stored strain after compression increased, but the site of recrystallized grains after solution heat treatment increased with Z parameter. Small Z parameter condition could get low stored strain with fine grain which is stable during SHT. Effect of Cr and Zr on the grain structure of 7075 alloy was also investigated. Cr or Zr addition could inhibit the grain coarsening. The role of Zr addition was confirmed to pinning effect of Al3Zr dispersoids to subgrain boundaries. [Copyright &y& Elsevier]

Abstract: In the present paper, we present the microstructure and mechanical properties of cryorolled and annealed Cu–5wt.% Zn and Cu–5wt.% Al alloys. Ultrafine grained microstructures with very fine annealing twins are obtained after cryrolling and annealing at 250°C for 15min. The study of Young''s modulus (E) variation with temperature revealed that E is lower (about ∼15%) in the as-rolled condition and it increases to the isotropic value after recrystallisation. This variation is attributed to the crystallographic texture that develops during rolling and recrystallisation. The Cu–Al alloy exhibited much higher strength (600MPa) with similar strain to fracture (0.26) in comparison to Cu–Zn alloy (355MPa). The higher strength of Cu–Al alloy is explained in terms of the higher contribution to solid solution strengthening of Al. [Copyright &y& Elsevier]

The aim of this study is to analyze the martensitic transformation in a shape memory alloy during a superelastic loading, focusing on internal strains, stresses and phases fractions. The behavior of the austenite phase is studied by X-ray diffraction stress analysis during in situ tensile test at room temperature. Both single-crystal and polycrystal samples have been investigated. The results are discussed with the aim to correlate the microstructural variations with the local stress state evolution in the austenitic phase while variants of martensite form and develop during a superelastic loading. [Copyright &y& Elsevier]

The medical market is a continuing success story for the application of shape memory alloy products. Increasing life expectancy and advances in surgical procedures mean that the medical market will remain an area of great opportunity for commercial applications.This paper will consider just why the shape memory effect holds so many opportunities for medical devices and will review a selection of current applications. Interventional radiology in particular has benefited from the unique properties of superelastic nitinol and this will be reviewed in detail.As well as considering the benefits of shape memory alloys in medical devices this paper will also consider the factors that impinge on the associated risk analysis of using nitinol in medical applications. [Copyright &y& Elsevier]

The stress-assisted two-way memory effect has been studied for successive cycles in a Ti–Ni–Cu alloy for two different thermo-mechanical treatments: recovery annealed (TT425) and fully recrystallized. Simultaneous tensile strain and electrical resistance measurements have been performed as a function of temperature and for different applied stresses. The thermoelectric power (TEP) in the stressed martensitic state has also been measured. For the treatment TT425 corresponding to 30% cold drawing followed by 425 °C annealing, a stable reversible strain &epsiv;m-β of 4.5% at maximum is found. A relatively low plastic strain &epsiv;p occurs for stresses above 125 MPa, which increases with the number of thermal cycles. For the recrystallized treatment, the maximum amplitude of the reversible strain is almost the same but a quite large plastic strain occurs even at 50 MPa and strongly increases with the number of cycles, reaching 12% for 20 cycles at 200 MPa. It is shown that the electrical resistivity change, associated with the reverse transformation, increases linearly with the reversible strain &epsiv;m-β. This effect is related to the electrical resistivity anisotropy of the martensite, with the slope being slightly different for the two treatments. In addition, the resistivity is relatively insensitive to the plastic strain. The TEP and the resistivity are sensitive to the orientation of the martensite, but the TEP also strongly depends on the plastic strain. [Copyright &y& Elsevier]

Ti–6Al–4V–TiB composites have been in situ deposited from powder feedstocks consisting of a blend of pre-alloyed Ti–6Al–4V and elemental boron using the Laser Engineered Net-Shaping (LENS™) process. The microstructure of the as-deposited composites has been characterized in detail using scanning (SEM) and transmission electron microscopy (TEM). A homogeneous refined dispersion of TiB precipitates is formed within the Ti–6Al–4V α/β matrix. The scale of the microstructure is substantially refined as compared with composites produced using other recently developed powder processing techniques. In addition to the refined dispersion of the reinforcing phase, the influence of the TiB precipitation on the solid-state β→β+α transformation that takes place in the matrix has been examined using SEM and TEM. Finally, heat-treatments carried out post-LENS™ deposition, suggest that LENS™ fabricated composites are thermodynamically stable, exhibiting limited TiB coarsening. [Copyright &y& Elsevier]

A CoNi-based γʹ phase strengthened superalloy was designed with alloy elements Al, W, Cr, Ti, and Ta added. The size and volume fraction of the γʹ phase can be tailored by the post-heat-treatment, which will then affect mechanical behavior of this alloy. The aged alloy was compressively tested at a wide temperature range, from room temperature to 1000 °C. Detailed microstructural analysis of the tested alloy was carried out using transmission electron microscopy. At 600 °C, the primary deformation mechanism is pairs of a/2 <110> type dislocations and stacking faults shearing in the alloy. The deformation mechanism changed to dislocation pile-ups and climbing in the γ phase when deformed at 800 °C. Further increasing the deformation temperature to 1000 °C, both nanotwins and dislocations were formed and their interactions will be the main strengthening mechanism of the alloy. The deformation mechanism transition and correlated mechanical behavior of this alloy was further discussed based on the defect analysis. [ABSTRACT FROM AUTHOR]

Aluminium alloys are susceptible to stress corrosion cracking (SCC) in specific conditions, which can be associated with hydrogen embrittlement (HE). Interrupted SCC tests are often performed to evaluate the susceptibility of the samples to a specific environment under mechanical loading. Those tests consist in a pre-corrosion step, which can lead to hydrogen-precharging, followed by a tensile test in air. The present study, performed on a 7046 aluminium alloy, confirmed literature data showing that tensile tests in laboratory air on as-polished samples at sufficiently low strain rates led to a significant hydrogen ingress. Depending on the sample microstructure, various hydrogen - dislocations and dislocations - microstructure interactions could be effective leading to a change in the tensile behaviour of the samples. Such a phenomenon could lead to misinterpret the interrupted SCC tests performed on hydrogen-precharged samples. In the present study, a corrected SCC susceptibility factor was defined to better analyse the interrupted SCC tests. • A critical 10−4 s−1 strain rate was found for embrittlement by H from moist air. • For T4 sample, H trapping at GBs led to brittle intergranular fracture mode. • For aged samples, hardening precipitates limited the dislocation motion. • For aged samples, hardening precipitates acted as strong H trapping sites. • H from moist air could lead to misinterpret SCC tests for H-precharged samples. [ABSTRACT FROM AUTHOR]

The high temperature deformation behavior of a Mg-5wt.%Y (Mg–5Y) binary alloy has been investigated using uniaxial compression test in the temperature range of 523 K–723 K and strain rate of 0.001 s-1 - 10 s-1. The true stress-strain curves depict that flow stress significantly decreases with the increase in temperature and decrease in the strain rate and vice-versa. An Arrhenius based hyperbolic sine equation was used to model the flow stress of the alloy at high temperature. Processing maps were developed for true strains of 0.25 and 0.45, which represent the strain near the peak stress and steady-state region, respectively. The safe region is found to be in the strain rate range of 0.001 s-1 – 0.1 s-1 and temperature range of 623 K–723 K, while the unstable region is found to be in strain rate range of 1 s-1 – 10 s-1 at a temperature range of 523 K–723 K. In the safe region, characterization of deformed microstructures using electron backscatter diffraction (EBSD) shows that the prominent deformation mechanism is continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) with manifestation of twin induced DRX and particle stimulated nucleation (PSN). The unstable region, however, consists of cracks, voids and deformation twins with little evidence of DRX. [ABSTRACT FROM AUTHOR]