Effect of Hot Isostatic Pressing Conditions and Cooling Rate on Microstructure and Properties of Ti-6Al-4V Alloy from Atomized Powder

The effects of temperature and pressure on density, microstructure and mechanical properties of powder compacts during hot isostatic pressing（HIPping） were investigated. Optimized HIPping parameters of temperature range from 900 to 940℃, pressure over 100 MPa and holding time of 3 h, were obtained. Tensile properties after different heat treatments show that both the geometry of samples and cooling rate have a significant influence on mechanical properties. Finite element method was used to predict the temperature field distribution during HIPped sample cooling, and the experimental results are in agreement with simulation prediction. The interaction of HIPping parameters was analyzed based on the response surface methodology（RSM） in this study.

Flow behavior and processing map for hot deformation of ATI425 titanium alloy

Flow behavior and processing map play important roles in the hot deformation process of titanium alloys. In this research, compression Gleeble tests have been carried out to investigate the stress-strain relationship at temperatures ranging from 700 to 1000 ℃ and strain rates ranging from 0.001 to 1 s-1 for ATI 425 titanium alloy. Arrhenius type constitutive equation was obtained to describe the compressive flow behavior with modification of additional deformation dead zone, friction model, temperature model and strain rate. The introduction of novel calculation method for α value in Arrhenius equation gives more accurate fitting than traditional one. Processing maps were drawn based on the distribution of dissipator co-content, and optimized deformation temperature and strain rate range obtained. It is proven to be accurate and effective through the experimental results. The microstructure analysis shows that more dynamic recrystallization can be achieved in the area with larger ηvalue on the processing map.

Fabrication of textured Ti2AlC lamellar composites with improved mechanical properties

Textured Ti2AlC lamellar composites have been successfully fabricated by a new method in the present work.The composites exhibit high compressive strength of ca 2 GPa,fracture toughness of 8.5 MPa m1/2(//c-axis),flexural strength of 735 MPa(//c-axis)and high hardness of 7.9 GPa(//c-axis).The strengthening mechanisms were discussed.The sintering and densification process was investigated and crystal orientation and microstructure were studied by electron backscattered diffraction techniques.The synthesis temperature is reduced to 1200?C by using high surface-to-volume ratio Ti2AlC nano flakes.The Lotgering orientation factor of Ti2 AlC and Ti3 AlC2{00 l}planes in the textured top surface reaches 0.74 and 0.49,respectively.This new route may shed light on resolving the difficulties encountered in large scale fabrication of textured MAX phases.

Optimization of annealing treatment and comprehensive properties of Cu-containing Ti6Al4V-xCu alloys

The Ti6Al4V-Cu alloy was reported to show good antibacterial properties, which was promising to reduce the hazard of the bacterial infection problem. For the purpose of preparing Ti6Al4V-Cu alloy with satisfied comprehensive properties, it’s important to study the heat treatment and the appropriate Cu content of the alloy. In this study, high Cu content Ti6Al4V-x Cu(x = 4.5, 6, 7.5 wt%) alloys were prepared, and firstly the annealing heat treatments were optimized in the α+β+Ti2Cu triple phase region to obtain satisfied tensile mechanical properties. Then the effect of Cu content on the tribological property, corrosion resistance, antibacterial activity and cytotoxicity of the Ti6Al4 V-x Cu alloys were systematically studied to obtain the appropriate Cu content. The results showed that the optimal annealing temperatures for Ti6Al4 V-x Cu(x = 4.5, 6, 7.5 wt%) alloys were 720, 740 and 760℃, respectively, which was resulted from the proper volume fractions of α,β and Ti2Cu phases in the microstructure. The additions of 4.5 wt% and 6 wt% Cu into the medical Ti6Al4 V alloy could enhance the wear resistance and corrosion resistance of the alloy, but the addition of 7.5 wt% Cu showed an opposite effect. With the increase of the Cu content, the antibacterial property was enhanced due to the increased volume fraction of Ti2Cu phase in the microstructure, but when the Cu content was increased to 7.5 wt%, cytotoxicity was presented. A medium Cu content of 6 wt%, with annealing temperature of 740℃ make the alloy possesses the best comprehensive properties of tensile properties, wear resistance, corrosion resistance, antibacterial property and biocompatibility, which is promising for future medical applications.

Effects of heating rate on the alloy element partitioning and mechanical properties in equiaxedα+βTi-6Al-4V alloy

The effects of heating rate on the alloy element partitioning and mechanical properties during the phase transformation ofα→βin Ti-6Al-4 V alloy under solution treatment have been investigated by the experiments and phase field simulations,which reveal the evolutions of microstructure and compositions at the non-equilibrium state and well verify the experimental results.The specific results indicate that the compositions measured through electron probe micro-analysis(EPMA)under a lower heating rate are close to the equilibrium ones corresponding to the solution temperature.Heating up to the target solution temperature,as the heating rate increases,the Al content decreases and V increases in the primaryα(α_(p))grain with a larger size,the volume fraction ofα_(p)increases and the composition gradient betweenα_(p)andβphases gets steeper.The interrelated relationship among the diffusion,compositions,solution temperature and free energy of the system has been discussed in detail.Moreover,increasing the heating rate(~20.0 K/min)may help to improve the mechanical properties of the alloy by mainly adjusting theα_(p)/β;volume fractions,α_(p)particle size and secondaryα(α_(p))size during the process of heating up to the solution temperature.These results may shed some light on the optimization of the knowledge-based heat treatment route.

Inhibition effect on microbiologically influenced corrosion of Ti-6Al-4V-5Cu alloy against marine bacterium Pseudomonas aeruginosa

With rapid development of marine infrastructures,materials with better biocorrosion resistance and antibiofouling performance will be highly demanded.Ti6Al4V alloy is susceptible to the above.The inhibition to the microbiologically influenced corrosion of Ti6Al4V-5Cu alloy against Pseudomonas aeruginosa was investigated using antibacterial test,electrochemical techniques,surface analysis,and weight loss test conducted for 2.5 months.At a sputtering depth of 0 nm,the passive film of Ti6Al4V-5Cu alloy was mainly composed of ideal oxide TiO_(2).With increasing sputtering thickness to 6 nm,Ti_(2)O_(3)and TiO were detected with a relative fraction of 14.6%and 14.8%,respectively,in the oxide layer of Ti6Al4V-5Cu alloy.In contrast,the outermost layer of Ti6AlV alloy was predominantly composed of TiO_(2)but Ti_(2)O_(3)(22.8%),Al_(2)O_(3)and V_(2)O_(5) were also detected.With increasing sputtering depth to 6 nm,fitting revealed the presence of Ti_(2)O_(3)and TiO with relative fractions of 25.3%and 35.8%,respectively.Yet,a spot of TiO(8%)was also observed at 12 nm in the oxide layer of Ti6Al4V alloy.Although the addition of Cu into Ti6Al4V alloy generated the self-healing property of passive film in the presence of P.aeruginosa,it also reduced resistance to corrosion in general condition.

Influence of Hot-Rolling Deformation on Microstructure,Crystalline Orientation,and Texture Evolution of the Ti6Al4V-5Cu Alloy

The influence of hot-deformation on the microstructure,crystalline orientation,and texture evolution of Ti6Al4V-5Cu,an antibacterial(α+β)titanium alloy,was investigated.The alloy was deformed using a hot rolling process in 15%,58%,and 73%thickness reduction ratios.It was found that the basal<α→>and pyramidal<c→+α→>type slip planes could be activated in theαphase,which dominated the deformation behavior of Ti6Al4V-5Cu alloy.Under various deformation conditions,the alloy revealed different microstructure features.On the 15%hot rolled alloy,the deformation was performed by the breakdown of priorβgrain boundaries(GBβ),which was attributed to the formation of coarseαgrains,rotated nearly 45°with respect to the transversal and rolling directions.The presence of different sub-structure geometries made the interior grain size distribution heterogeneous.On the 58%hot rolled alloy,Ti2Cu intermetallic compound was found at theα/βinterface.High-resolution transmission electron microscopy investigation showed the occurrence of grain rotation in different crystallographic directions.At room temperature,the percentage elongation(El)of the alloy reached 23.15%on the 58%hot rolled sample.On the 73%deformed alloy,refined and randomly oriented characteristics of grains were obtained due to higher thickness reduction,which resulted from the segregation of very fine granules.The influence of grain rotation during a hot rolling process revealed that theα/βtexture fiber separation angle to maintain the Burger orientation relationship of{0001}α//{110}βplanes decreased with increase of the thickness reduction ratio when Ti6Al4V-5Cu alloy was deformed by a hot rolling mechanism.Activation of tensile{1012}<1011>and compressive{1122}<1123>twins on the deformation of the alloy was also studied.

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