| Titanium alloy with a low density,high specific strength,corrosion resistance,good hot workability and biocompatibility,is the ideal structural materials for the aerospace engineering,marine,chemical,biomedical,energy,automobile and other fields.The so-called thermohydrogen processing is a technique in which hydrogen is used as a temporary alloying element in titanium alloys by controlling the microstructure and phase structure to improve.There are several reasons which made thermohydrogen processing most applicable to titanium alloys:First,Titanium alloys are widely applied.However,their plasticity is low at room temperature and they are easy to crack during their cold deformation,which restrict their applications.Their deformation is normally performed at temperatures as high as 800??950?.Second,Titanium and titanium alloys readily absorb and evolve hydrogen due to high solubility and diffusion mobility of hydrogen at moderate temperatures.Third,Hydrogen effect on the mechanical properties results in markedly enhanced ductility and lowered flow stress of the alloys therefore they become workable at much lower temperatures.Generally,thermohydrogen processing mainly is Melt hydrogenation and solid state hydrogenation.Usually,the thermohydrogen treatment is always solid state hydrogenation processing,which has already been applied extensively in processing of titanium alloys.In this paper,based on the above hydrogen processing technology of titanium alloy,Ti-6A1-4V titanium alloy as an example,hydrogen sintering were studied by powder metallurgy method for the influence of microstructure evolution and mechanical properties of Ti-6A1-4V titanium alloy.Using hydrogenated titanium(TiH2),metallic titanium,and Al-V master alloy powders as raw materials,Ti-6A1-4V titanium alloy was fabricated via pressing-sintering from different hydrogen content of blended powder which hydrogen mass fraction is controlled in 0?0.9%.Green Ti-6Al-4V compacts pressed at 300-500MPa via single-track pressure forming,sintering temperature is 1250 ?.First,the effects of hydrogen sintering of density and microstructure evolution Ti-6A1-4V titanium alloy were investigated in sintering of 2h,2.5h and 3h.Studies have shown that hydrogen sintering can lead to the higher sintered density of alloy,relative density of highest reaches 1069.9MPa,the relative density of alloy by non-hydrogen sinterin only reaches 983.1MPa.and can improve diffusion of titanium and alloy atoms at hydrogen sintering process.Secondly,the effects of hydrogen sintering of microstructure evolution of Ti-6A1-4V titanium alloy were investigated after dehydrogenation at different temperature.Studies have shown that,after dehydrogenation at temperature above 1000 ?,microstructure evolution of titanium alloy appear to have little influence on hydrogen sintering alloy.After dehydrogenation at temperature 900 ? and 850 ?,microstructure of titanium alloy were refined by hydrogen sintering and the structures get more fine with the hydrogen content increase,formed Widmanstatten structure.After dehydrogenation at temperature 750 ?,microstructure of alloy were significant refined by hydrogen sintering and the structures get more fine with the hydrogen content increase,the basket weave structure formed by a phase and ? phase.The microstructures were also refined because the growth of a phase restrained by the increase of ? phase.In this paper,the effects of dehydrogenation on process microstructure evolution and phase content of sintering of Ti-6A1-4V titanium alloy were investigated by Electron Back-Scatter Diffraction(EBSD).Studies have shown that,the fraction of ? phase increased,a phase decreased,resulted in the formation of a',a" martensite and hydride with the increase of hydrogen content in the non-dehydrogenation hydrogen sintering of alloy.After dehydrogenation at temperature above 1000? phase content of titanium alloy appear to have little influence on hydrogen sintering of alloy.After dehydrogenation at temperature 750?,the fraction of ? phase increased,a phase decreased,a' and a" martensite appear to have little influence with the increase of hydrogen content.Lastly,tensile tests were carried out through INSTRON 1346 materials tester to study the influence of room temperature mechanical property of hydrogen sintering Ti-6Al-4V titanium alloy.Studies have shown that,hydrogen sintering can improve tensile strength of alloy,tensile strength of highest reaches 1069.9MPa,the tensile strength of alloy by non-hydrogen sinterin only reaches 983.1 MPa.But elongation of alloy decline with the increase of hydrogen content.Fracture morphology analysis of Ti-6A1-4V shows that porosity of alloy increase with the increase of hydrogen content. |
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