Search

Preheating is the first step for thermal-mechanical processing of the materials. Several preheating schedules were designed based on industrial manufacturing to explore their effect on the microstructure and mechanical properties of AA2099 Al-Li alloy during the following hot rolling. The results show that the mechanical properties of as-rolled sheets are quite sensitive to preheating. Various types of secondary phases, including δ’, T1 and T2 phases, were precipitated during the heating process. The difference among precipitates is the main reason to induce the variation of mechanical properties for as-rolled sheets. A rapid heating rate gave rise to the precipitation of δ’ phase, which largely promoted yield stress and ultimate tensile strength in as-rolled sheets. T1 phase was more favorable in the preheating with a holding period at 150–250 °C, which caused a moderated strain hardening behavior. Precipitates formed during preheating induced different slip behaviors in the following deformation. The coexistence of T1 and δ’ phase could restrict planar slip, which inhibited the formation of the shear band. The difference in the activity of non-octahedral slips and planar slips determined the strain hardening effect, which should be the reason for the variation of mechanical properties of as-rolled sheets.

Microstructure characteristics and mechanical behavior of AA2099 Al–Li alloy with no pre-existing Li-containing precipitates (AA2099-1 sample), pre-existing δ′ precipitates (AA2099-2 sample), pre-existing T1 phase (AA2099-3 sample) and pre-existing T2 phase (AA2099-4 sample) are systematically investigated via isothermal uniaxial compression at 250 °C in the present study. Experimental results demonstrate that at the onset of plastic deformation, dynamic precipitation of small-sized T1 phase occurs rapidly within AA2099-1 sample, while it will be hindered within AA2099-2 sample. The increasing plastic strain benefits to dynamic precipitation of small-sized T1 phase in AA2099-2 sample. Consequently, AA2099-1 and AA2099-2 samples possess similar and intermediate mechanical behaviors. In terms of AA2099-3 sample, the existence of large-sized T1 phase results in the maximum yielding stress. However, some regions within these large-sized T1 precipitates are suspected to be sheared by cross-slip, leading to the destruction of crystallographic structure and the formation of Al matrix intervals. This aspect is responsible for the gradual degradation in true stress-strain curve after peak stress. As for AA2099-4 sample, dynamic precipitation rarely happens during plastic deformation and the interaction between dislocation and the pre-existing T2 phase belongs to Orowan looping, resulting in the minimal mechanical response. Besides, AA2099-1 sample possesses the average minimum deviation angle (MDA) of ~ 16.5° between the loading direction and the crystal direction, whereas AA2099-4 sample owns the average MDA of ~ 7.5°. The difference in MDA is mainly attributed to δ′ phase and T1 phase, which will separately accelerate and postpone the rotation of orientation towards the crystal direction.

In this study, typical microstructural characteristics of a metastable β Ti alloy (Ti–5Al–5Mo–5V–3Cr–1Fe) forged in a dual-phase region (strain of 54% at 820 °C) were investigated in detail by the combined use of X-ray diffraction, energy dispersive spectroscopy, electron channeling contrast imaging and electron backscatter diffraction techniques. Results show that the microstructure of the forged alloy is composed of bulk α grains, α plates and β matrix. The bulk α grains correspond to retained primary α phase (αp, average grain size ~ 2.4 μm), while the α plates are secondary α phase (αs, width ~ 70 nm) precipitated from the β matrix during air cooling. During forging, the β matrix experiences dynamic recovery with many subgrains and significant orientation gradients formed. Analyses of the orientation relationship between the α and β phases show that the Burgers orientation relationship is not maintained between some αp and β phases, which should be related to thermal deformation-induced changes of their orientations. In contrast, all of the αs plates are found to maintain well the Burgers orientation relationship with the β phase.

The true stress–strain curves of an as-extruded state AA2099 were determined by uniaxial compression tests under various hot deformation regimes. Constitutive analysis of the curves allowed calculation of the hot deformation activation energy (QHW). The microstructure of the as-compressed specimens were also characterized by electron back scatter diffraction (EBSD). EBSD data analyses showed that the major restoration mechanism corresponding to common industrial extrusion regimes was dynamic recovery. The precipitates in three states (T83, as-homogenized, and as-extruded) were characterized by X-ray diffraction (XRD) phase analyses and transmission electron microscopy. The results revealed that the QHW was closely relevant to the precipitates strengthening. The finite element method simulation results and the microstructure of the extruded products confirmed that AA2099 in as-extruded state possessed good workability.

The cold rolling texture of AA2099 sheets was strongly influenced by the prior heat treatment. Two typical heat treatments, including solid solution (T4) and underaging (T6) were utilized to control slip behavior by different precipitates during cold rolling. A much weaker texture with an orientation scatter towards higher $$\varPhi$$ angles was found in the as-rolled T6 specimen (T6R). Slip behavior was analyzed using geometry necessary boundaries distribution. Results show that the T6R specimen experienced a strong co-planar slip compared to the as-rolled T4 specimen. Prosperity of co-planar slips and limitation of co-direction slips were main reasons for the weakening of Copper texture component in the T6R specimen. The distinguish slip behavior was caused by existence of $${{\updelta ^{\prime}}}$$ phase with GP-I zones fillings in the T6 specimen. This phase could be easily sheared by dislocations and then promoted co-planar slips in further deformation.

Zirconia slurry aimed to apply in digital light process (DLP) printing technology were made of the 3 mol% yttrium oxide (Y2O3) stabilized micro-nano zirconium dioxide (3YSZ) powders. An overall mechanical strength can be obtained via a precise control of two-step sintering process. The results show that Y2O3 in 3YSZ would diffuses into the ceramic lattice, further stabilizing the metastable tetragonal zirconia (t-ZrO2) toughening phase in sub-micro sized grains with nearly 100% crystal phase transition ratio. The Vickers hardness of sintered ceramic parts reaches 12.94 ± 0.186 GPa. The fracture toughness (KIC) of sintered ceramics is 5.63 ± 0.015 MPa·m1/2. The propagation law of Vickers crack reveals the mechanism of strengthening and toughening of fine grains on matrix fracture toughness. Due to the uniform crystals also can make the corrosion better to construct a three-phase boundary sensitive process, the response of the T-ZrO2-SnO2 to 30 ppm NH3 is 15.7 mV which is 2 times more than the commercial ZrO2. A relative short response and recovery times of 6 s and 33 s can achieve with a good reproducibility of continuous response and recovery transients.

Diamond like carbon (DLC) film exhibits typical properties such as high hardness and low coefficient of friction, often used to improve fiction and wear performance. In the application of surface modification of medical implants, it is of great interests to investigate the failure mechanism of DLC in water environment, in order to avoid the early-stage delamination of DLC film in vivo and promote the application of DLC in implanted medical devices. In this work, four kinds of DLC films were prepared by electron cyclotron resonance plasma enhanced chemical vapor deposition, plasma immersion ion deposition and filtered cathode vacuum arc methods. The wear and failure behavior of DLC films in air and water environment were investigated by ball-on-disc tribological experiments. The results show the friction coefficient of DLC film with high hydrophilic is sensitive to the water environment. Both the interface corrosion and mechanical property affect the adhesion failure of DLC film in water. Hydrogenated DLC film is vulnerable to water environment because the hydrogenous interface is susceptible to corrosion, however, the low hardness and low modulus can reduce the contact stress, which is help to achieve a longer service life of hydrogenated DLC film in water. Hydrogen free DLC film is less sensitive to water environment compared with the hydrogenated one.

Glasses with the composition 50SiO2 · 20TiO2 · 15BaO · 7.5SrO · 7.5CaO doped with the varied content of CeO2 were prepared by conventional melt quenching technique. The effect of CeO2 on the structure of glasses was investigated by X-ray photoelectron spectroscopy and Raman spectroscopy. The density, thermal stability, dielectric properties and acid resistance of glasses were studied by Archimedes method, differential thermal scanning analysis and X-ray diffraction, dielectric measuring as well as the powder method. The results showed that the coordination of Ti, which existed in glasses as [TiO4], did not change. An increase in the content of non-bridging oxygen atoms and a corresponding decrease in the content of bridging oxygens correlated. The depolymerization of the glass network was attributed to an increase in the number of Si–O–Ti bonds and the change of the Qn distribution. With an increase in the CeO2 content, the thermal stability and acid resistance of glass first increased and then decreased, and the dielectric constant and dielectric loss of glass decreased first and then increased.

A sandwich structure of Mg alloy bulk consisted of two types of texture was fabricated by pre-twinning deformation. Its mechanical response and work hardening behavior during uniaxial compression were deeply analyzed to investigate the competition mechanism between basal slip and detwinning. Results showed that pre-twinning layer was a soft region. It undertook more than half of the strain by one third of the volume fraction of the bulk at the beginning of deformation. Slip behavior was significantly enhanced by detwinning and it took a more important role to coordinate local strain. Texture bonding promoted slip behavior in the grains exhibited “hard” orientations. Activation of detwinning behavior in pre-twinning region was mainly depended on basal slip behavior of their parents.

Corrosion behaviour of the low dielectric glass fibres in hydrochloric acid with different time and concentrations was studied. Leaching of cations, surface morphologies and structure of the low dielectric glass fibres before and after corrosion were investigated by ICP, SEM and FTIR, respectively. Both the change of weight and tensile strength of the low dielectric glass fibres in hydrochloric acid was discussed. The results showed that the decrease of weight and tensile strength of the low dielectric glass fibres with the increasing time was attributed to the leaching of the metal cations from the fibres surface which can disrupt the continuity of glass network. The equilibrium was eventually reached which was attributed to the formation of intermediate product, silica acid gel adhered to the fibres surface and complex of iron. The loss of weight and tensile strength had a maximum value after 8 h in 2 M hydrochloric acid and cracks were only generated on the surface after immersed in 2 M hydrochloric acid for 24 h. It suggested that the corrosion was significantly affected by the concentration of hydrochloric acid. The corrosion mechanism was not only attributed to ions exchange, but the hydrolysis of aluminoborate complex species.

The friction stir processed pure Ti was annealed at 550 °C with various annealing times. Dry sliding wear tests on friction stir processed and as-annealed pure Ti were performed at room temperature. Friction coefficient and wear rate of the alloys were measured. The results showed that the friction stir processed pure Ti with high hardness revealed lower wear resistance than as-annealed samples. The stored energy of the samples before and after annealing treatment were calculated. The relationship between work hardening and wear resistance of pure Ti was discussed. The run-in period increased as the stored energy in the pure Ti decreased. The fine-grained pure Ti with 400 kJ/m3 low angle grain boundaries stored energy exhibited the lowest wear rate. The wear mechanism of fine-grained pure Ti changed from fatigue wear and abrasive wear to adhesive wear after annealing treatment. Keywords: Titanium alloy, Friction stir processing, Annealing, Stored energy, Wear resistance

The microstructure and texture characteristics of commercial pure Ti after friction stir processing (FSP) with a slow rotation speed were studied. The shoulder friction zone (SFZ) which did not exist in the FSPed pure Ti with normal rotation speed (> 250 rpm) was observed in the sample treated with a slow rotation speed of 180 rpm. The texture of SFZ in the pure Ti was affected by shear stress from the shoulder of stir tool and the c-axes of the grains in this zone were nearly parallel to the processing direction. While crystallographic texture in the normal stir zone (SZ) were nearly perpendicular to the processing direction. The maximum depth of SFZ in the sample with 180 rpm was 1.2 mm, which decreased with the increased rotation speed until it disappeared. The grains in the SZ of specimen following FSP at a slow rotation speed were fine and homogeneous. The microhardness increased from 150.2 HV to 191.6 HV after FSP at 180 rpm. The microhardness trends were related to grain sizes, work hardening and texture evolution. The slow rotation speed processed alloy boosted the yield strength by 71.7% after the FSP.

Silicon and tungsten co-doped diamond-like carbon (Si-W-DLC) films with W gradually increased from the top surface to the internal layer were deposited via reactive megnetron sputtering. The mechanical and high-temperature tribological properties of the films were investigated by nanoindentation tester and reciprocating sliding tribometer, respectively. The structures, surface bonding states of the wear tracks were examined by Raman and X-ray photoelectron spectroscopy (XPS), respectively. The results reveal that the gradual W incorporation increases the hardness and elastic modulus from 19.8 ± 0.5 GPa and 183.3 ± 2.8 GPa GPa for the Si-DLC film to 21.6 ± 0.6 GPa and 192.6 ± 3.0 GPa for the Si-W-DLC film, respectively. The Si-W-DLC film maintains a coefficient of friction (COF) below 0.1 and a wear rate of 6.4 × 10−7 mm3/N•m at 500 °C, while the Si-DLC film is worn out. The graphitization of the Si-W-DLC film confirmed by the increment of the ID/IG ratio from 2.26 at room temperature to 3.44 at 500 °C is beneficial to reduce the coefficient of friction (COF). WO3, WO2, WC and silicon oxides are detected on the wear track tested at 500 °C. It is proposed that the synergistic effect of film graphitization, WO3, WO2, WC and silicon oxides formed on the wear track and the improved mechanical properties attributed to the gradual W distribution are responsible for the well high-temperature tribological properties.

A typical metastable β Ti alloy (Ti–5Al–5Mo–5V–3Cr–1Fe alloy) was β-solution treated (890 °C for 10 min) and then cooled at different rates (in water (WC), air (AC) and furnace (FC)). To clarify specific effects of β-cooling rates, multiple characterization techniques were jointly utilized to reveal their microstructural and orientation characteristics in detail, with hardnesses also measured and correlated with specific microstructures. Results show that both the WC and the AC specimens are mainly comprised of recrystallized β grains with no α phase, while the FC specimen consists of coarse equiaxed β grains, intragranular acicular α phase (width ∼48 nm) and grain boundary α phase. The Burgers orientation relationship is strictly obeyed during β→α transformation in the FC specimen. When adjacent β grains share a common 110 > axis, the boundary α phase maintains such orientation relationship with both of them. Compared to the as-received specimen (428 ± 9 HV), the WC (309 ± 5 HV) and the AC specimens (297±3HV) are softened, which can be attributed to the coarsened β grains as well as the disappearance of α phase and deformed structures. For the FC specimen, dense fine α precipitates appear inside β grains during slow cooling, leading to increased hardness (444 ± 9 HV).

Glasses with the composition 50SiO2-20TiO2-15BaO-7.5SrO-7.5CaO doped varied content of La2O3 have been prepared by the conventional melt quench technique. The effect of La2O3 on structure of the glasses was investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectra and Raman spectra. The density, thermal stability and dielectric properties of glass were measured and compared by the Archimedes method, differential thermal scanning analysis (DSC) and impedance spectroscopy, respectively. The results showed that the coordination of the titanium remained invariable with the addition of La2O3, while the number of Si-O-Ti bonds increased and the distribution of Qn changed. And the depolymerization of the glass network was observed. The thermal stability and resistance to crystallization increased significantly for glass containing 4 mol% of La2O3 resulting from the strong strength of La O bond and the La3+ clustering. However, the resistance to crystallization for glasses was decreased with further increasing La2O3. The dielectric constant of glass decreased first and then increased with the increase of La2O3 content, while the dielectric loss was almost constant.

A medium-strained (13% cold-drawing) 316L austenitic stainless steel rod was subjected to annealing between 750 and 1100 °C. Electron backscatter diffraction and electron channeling contrast imaging techniques were jointly employed to investigate the development of microstructures and grain boundary character distribution during the annealing treatments. Results show that annealing at temperatures below 900 °C does not evidently change microstructures of the as-drawn specimen. Full recrystallization is observed after the temperature reaches 1000 °C and the deformation microstructures are replaced by fine and uniform recrystallized grains. A large number of annealing twins (with Σ3 misorientation) are produced by the recrystallization, leading to markedly increased fractions of special boundaries (fSB). The maximum fSB is found to be 67.3% in the present study. In addition, for the recrystallized grains, rapid growth is noticed at relatively high temperatures due to easy migration of grain boundaries.

The structure and optical properties of CeO2/TiO2-doped boroalumnosilicate glass with the composition 54SiO2-10B2O3-13Al2O3-14Na2O-3ZnO-2Li2O-4CaF2 before and after gamma irradiation at varied dose were investigated by spectroscopy analysis. The results indicated that doping CeO2 and/or TiO2 can significantly improve structural stability against irradiation and that solely doping CeO2 or appropriate co-doping of CeO2/TiO2 achieves a perfect stabilization on optical property. A model based on self-repairing that irradiation may recover the structural defect via microstructure reconfiguration amid network depolymerization is employed to explain gamma irradiation-induced structural stability and stabilization of optical properties in presence of CeO2/TiO2.

An annealed Inconel 718 alloy was surface-treated by pulsed laser at three different powers (100, 50 and 25 W). Microstructural changes induced by the laser treatments were characterized by use of electron backscatter diffraction and electron channeling contrast imaging techniques. Results show that both annealing twins and strengthening precipitates profusely existing in the as-received specimen are dissolved at elevated temperatures during the laser irradiation. Meanwhile, in the melting zone (MZ), densities of low angle boundaries (LABs) are greatly increased with a large number of Laves phases preferentially distributed along such LABs. For different specimens, widths and depths of their MZs are found to be gradually reduced with decreasing the laser powers. Orientation analyses reveal that the columnar grains in the MZ of the 100 W specimen could inherit orientations existing in the matrix while lower laser powers promote the formation of more nuclei with scattered orientations to grow to be granular grains in the MZ. Hardness tests reveal that the MZs of all laser-treated specimens are softer than the matrix probably due to both precipitate dissolution and grain coarsening.

In this paper, electron backscatter diffraction and various other characterization and analysis techniques including X-ray diffraction, electron channeling contrast imaging and energy-dispersive spectrometry were jointly employed to investigate microstructural and textural changes of a hot-rolled Ti–6Al–4V (TC4) sheet after annealing at 800 °C for 5 h. In addition, the hardness variation induced by the annealing treatment is rationalized based on revealed microstructural and textural characteristics. Results show that the TC4 sheet presents a typical dual-phase (α + β) microstructure, with α-Ti as the major phase and short-rod-shaped β-Ti (minority) uniformly distributed throughout the α matrix. Most of α grains correspond to the un-recrystallized structures with a typical rolling texture (c//TD and //ND) and dense low angle boundaries (LABs). After the annealing, the stored energy in the as-received specimen is significantly reduced, along with greatly decreased LABs density. Also, the annealing allows recrystallization and grain growth to occur, leading to weakening of the initial texture. Furthermore, the water quenching immediately after the annealing triggers martensitic transformation, which makes the high-temperature β phases be transformed into submicron α plates. The hardness of the annealed specimen is 320.5 HV, lower than that (367.0 HV) of the as-received specimen, which could be attributed to reduced LABs, grain growth and weakened texture. Nevertheless, the hardening effect from the fine martensitic plates could help to suppress a drastic hardness drop.

Amorphous Si–C-based (a-SiC) thin films as protective coating have been attracting more and more attentions. But there are contradictory reports in the literature about the effect of sputtering power on the structural and mechanical properties of a-SiC films. Here, the influence of sputtering power on structural and mechanical properties of a-SiC thin films deposited by pulsed magnetron sputtering have been investigated. The results show that as-prepared films have a columnar structure and cauliflower-like pattern at lower sputtering power (100 W). Increasing the sputtering power from 100 W to 180 W, the columnar feature disappears and the thin films become denser. Meanwhile, the density of Si–C bond increases and the sp3/sp2 radio decreases. The hardness (H) and elastic modulus (E) of the a-SiC thin films increase when the sputtering power increases from 100 to 120 W and then their almost keep constant when the sputtering power increases from 120 to 140 W. Further increases in sputtering power, the H and E increase again. The maximum H and E are about 20.2 GPa and 223.1 GPa at 180 W, respectively. Reason for excellent mechanical property is proposed in combination with the theory analysis and experiment results.

The formation possibility of high-entropy alloy (CrNbSiTiZr)C was first studied by analyzing thermodynamics parameters through first-principles calculation. Then, the (CrNbSiTiZr)C film was successfully deposited by reactive radio frequency magnetron sputtering. Theoretical analysis results show that the mixing enthalpy and entropy values of (CrNbSiTiZr)C were 18.45 kJ/mol and 0.805 R, respectively, indicating that (CrNbSiTiZr)C is thermodynamically stable above the temperature of 2758 K. Experimental results show that the concentration of each metal element in the film is near an equimolar ratio and a mixture of Cr3C2, NbC, SiC, TiC, ZrC, and oxide formed in the (CrNbSiTiZr)C film. Moreover, the as-prepared film possesses a single B1 structure with a (111) preferred orientation and exhibits high nanohardness, elastic modulus, and fracture toughness. The friction coefficients and wear rate of the (CrNbSiTiZr)C film is as low as 0.3 and 4.2 × 10−6 mm3/N·m, respectively. The film also shows a superior corrosion resistance in a 3.5 wt% NaCl solution, a positive Ecorr and a low icorr value of −189 mV and 0.0026 μA/cm2, respectively. The film is proposed for industrial applications given its excellent mechanical, tribology, and corrosion performance and based on the theoretical analysis and experiment results.

Silicon containing diamond-like carbon films is of value for engineering applications operating at the temperature above 200 °C. This work presents a Si-gradually doped diamond-like carbon film with increasing the Si content from outer layer to inner layer deposited by plasma-assisted reactive magnetron sputtering process. The microstructure, chemical bonding state and temperature-dependence tribological properties upto 500 °C of the film are investigated by using focused ion beam/transmission electron microscope (FIB/TEM), X-ray photoelectron spectroscopy (XPS) techniques and ball-on-disk tribometer, respectively. The results show that the as-deposited Si-gradually doped DLC film exhibit amorphous structure. The wear track tested at 500 °C are composed of carbon, SiO2 and silicon oxide. High-temperature tribological tests show that the friction coefficient values are 0.05 ± 0.01, 0.02 ± 0.004 and 0.09 ± 0.04, while the wear rates are 1.17 × 10−7 mm3/N·m, 1.65 × 10−7 mm3/N·m and 1.4 × 10−6 mm3/N·m at 300 °C, 400 °C and 500 °C, respectively. It is proposed that the improved high-temperature tribological properties of the Si-gradually doped DLC film benefit from its special composition structure that the inner layer with high Si content provides the required mechanical properties and the outer layer with low Si content reduces the friction coefficient as well as the wear rate.

AA2099 Al-Cu-Li alloys were rolled by both asymmetrical and conventional rolling to a total thickness reduction of 80% at room temperature. Microstructure and texture evolution through thickness of rolling sheets were comprehensively investigated. Results show that large shear stress in ASR sample gave rise to a distortion of grain structure and a remarkable work hardening at region close to fast rolled surface. Shear banding behavior was largely promoted by ASR and various types of shear bands with higher density were observed. The shear bands triggered a kink of grain structure during rolling process. The kink behavior was related to the tilt angle and width of shear bands. The shear bands exhibited large tilt angle and width gave rise to a more significant kink of the grain structure nearby. Recrystallization during subsequent annealing was also promoted by ASR. Shear bands became favorable nucleation sites for rolled material. Growth advantage of some nuclei inside shear bands had a stronger influence on the recrystallized texture in AA2099 rolled sheets.

To improve the wear resistance of medical titanium alloy, Ta coatings were prepared by magnetron sputtering method on Ti6Al4V substrates. Phase structure and surface morphology of Ta coatings were characterized by X-ray diffraction and atomic force microscope, respectively. The properties of Ta coatings, including adhesion, nano-hardness, and wear resistance, were tested using nano-scratch, nano-indentation and tribometer, respectively. The results show that both stable body-centered cubic (α-Ta) phase and metastable tetragonal phase (β-Ta) coexist in a multi-layer structure, and it shows a non-columnar feature. Interestingly, only a pure phase with columnar crystals is found in monolayer Ta coating. A body-centered cubic (α-Ta) phase is found in a monolayer prepared under the pulse power bias voltage with low deposition temperature. A pure metastable tetragonal phase (β-Ta) is prepared under the direct current bias voltage, which has the best adhesion and wear resistance compared with other Ta coatings.

Hot compression deformation tests of AZ80 and AZ80-2 wt.% Sn magnesium alloys were performed on Gleeble-1500 at deformation temperature of 350 °C and strain rate of 0.1 s−1 to analyze the effect of Sn on the microstructure evolution. The results indicated that the addition of Sn promoted dynamic recrystallization and decreased flow stress during hot compression. Dynamic dissolution of discontinuous precipitation Mg17Al12 phases was promoted and dynamic precipitation of Mg17Al12 phases was suppressed in AZ80-2 wt.% Sn alloy. The quantity of Mg17Al12 phases of thermally compressed AZ80-2 wt.% Sn alloy was less than that of AZ80 alloy. Texture intensity increased in AZ80-2 wt.% Sn alloy during hot compression due to Mg17Al12 phases effectively induced particle-stimulated nucleation in recrystallization.

The aim of this work is to find how substrate bias affect the microstructure, mechanical, and tribological properties of the a-C/H films deposited on Ti6Al4V by magnetron sputtering. In order to attain this purpose, the structure of the deposited a-C/H film was investigated by scanning electron microscopy. Chemical bonding was examined by Raman spectroscopy techniques. Mechanical and tribological properties were evaluated using nanoindentation, scratch, internal stress, and ball-on-disk friction testing. The results showed that the sp2 content in a-C/H films increased as the bias voltage increased from − 400 to − 1200 V, indicating the graphitization of the films. The hardness (H) decreased from 29 to 18 GPa and the adhesion strength ranged from 13.1 to 25.3 N with increasing bias substrate. The average friction coefficient decreased at a bias voltage of − 300 V and increased when the bias voltage increased to − 1200 V. The best tribological performance was reached at − 600 V bias voltage. Reasons for the changing of structures, mechanical and tribological properties of a-C/H films were proposed.

The tribocorrosion behaviour of biomaterial Ti-25Nb-3Mo-3Zr-2Sn alloy in Ringer's solution was evaluated by micro-abrasion experiments, electrochemical tests and scanning electron microscope (SEM) observations. Potentiodynamic polarization results suggested that the effect of particle concentration on the electrochemistry characteristic is greater than the applied load. When the particle concentration and applied load were 0.05g·cm-3 and 0.25N, respectively, the Ecorr reached the maximum as -0.381V. The micro-abrasion-corrosion results showed that the wear rates of the Ti-25Nb-3Mo-3Zr-2Sn alloy increased with increasing particle concentration and decreased as applied load increased. The wear rates acquired under various conditions regarding to the main wear mechanism of two-body grooving wear with less three-body rolling wear; three-body abrasive wear modes are more efficient at material loss than two-body wear. The variation in material loss indicated that the contribution of corrosion is lower than the contribution of micro-abrasion. The wear regime, wastage and micro-abrasion-corrosion synergy maps associated with the particle concentration and applied load were established to evaluate the tribocorrosion behaviour of the Ti-25Nb-3Mo-3Zr-2Sn alloy as a potential surgical implant material.

Fluorine doped diamond-like carbon (F-DLC) coatings were deposited on Ti-6Al-4V alloy using a hollow cathode plasma immersion ion implantation deposition system. The aim of this work is to investigate the influence of F content on the surface morphology, structure, mechanical and tribological properties (under air and stroke-physiological saline solution) of the F-DLC coatings. The results reveal that the ratio of H/fE instead of H/E can be well predicting the anti-wear results when the F-DLC coatings have enough adhesion strength, where H is hardness, E is Young's modulus and f is friction coefficient. The F-DLC coatings with high F content exhibit excellent tribological property under air. The low F content F-DLC coatings present super-low friction coefficient and wear rate in stroke-physiological saline solution. Reasons for the tribological property are proposed in combination with the films' morphology and mechanical property.

Cylindrical specimens of as-extruded AA2099 Al-Li alloy are uniaxially compressed at temperatures ranging from 360 °C to 520 °C and strain rates ranging from 0.001 s−1 to 10 s−1. Processing map of these specimens was established. Electron backscatter diffraction (EBSD) measurements were performed for specimens deformed under various conditions to probe their microstructures and restoration mechanisms. Stored energies in various specimens are calculated based on statistics of low angle boundaries via EBSD data. The remarkable decrement of stored energy and misorientation characteristics reveal that dynamic recrystallization (DRX) happens at 480–520 °C and 0.001–0.1 s−1. Obvious DRX nucleation further suggests that this process should be classified to discontinuous dynamic recrystallization (DDRX). Stored energies in various specimens strongly affect the extents of dynamic recovery and dynamic recrystallization. By systemically considering the processing map and restoration behaviours of the specimens, the dynamic recrystallization regimes and the central high- η regimes are determined to correspond to preferable thermo-mechanical processing parameters for the as-extruded AA2099 Al-Li alloy.

The tribocorrosion behavior of the Ti-30Zr alloy as dental implant in Hank’s solution was evaluated. The results demonstrated that the wear volumes of the alloy increased as the applied load increase with/without electrochemical corrosion. The wear volumes acquired with corrosion exceeded the wear volumes without corrosion, whereas the difference between these two increased as the load increased. The material loss induced by the corrosion increased and the corrosion potential decreased as the loads increased, due to the interaction between wear and corrosion. The potentiodynamic polarization curves were acquired during wear. The corrosion potential (Ecorr) of −0.493 V was acquired at 1.0 N, while the Ecorr of −0.786 V was acquired at 5.0 N, indicating that the potential moved negatively as the applied loads increased, due to mechanical wear. Through observations of the 3-dimension surface and the SEM images of the worn surfaces, the visible scratches/grooves were observed along the sliding direction, indicating a predominant abrasive mechanism.

Solid solution treated AA 2099 alloy was rolled by a total reduction of 80% at both room and cryogenic temperature. Results show that nanocrystalline grain structure with a size around 20–100 nm was only observed in the cryogenic temperature rolled sample at high rolling strain. The formation of those nanograins related to shear banding behavior. Shear banding behavior was greatly promoted by cryogenic temperature rolling, which had a strong influence on mechanical homogeneity of rolled samples. The width of these high-density shear bands is around 0.2–8 µm. Shear strain partitioning between slip and shear banding was depended on slip behavior in deformed grains. Strain concentration inside shear bands may give rise to an obvious temperature increase, which caused significant grain refinement in or near the shear bands. The growth of nano-grains is retarded due to limited heat and pinning effect of nanosized precipitation.