Preparation And Research Of High Performance Powder Metallurgy Titanium Alloy

Titanium and titanium alloys can be used in many fields such as aerospace,petrochemical and biomedical because of the excellent performance.Due to the high cost,titanium alloys are only used in a few high-end fields.Powder metallurgy is an effective way to reduce the cost of titanium alloys.It avoids the complicated melting process and does not require billet forging.However,powder metallurgy titanium alloys are difficult to control the oxygen content and achieve full densities.So powder metallurgy titanium alloys have unsatisfactory performance and are unable to meet many applications of high requirements for strength,plasticity and fatigue properties.Although a series of enhancement techniques have been proposed,such as hot isostatic pressing,they also result in a large increase in costs.The increase in costs is contrary to reducing the costs of titanium products.In order to solve the problem of densification and purity of powder metallurgy titanium alloys the processes were improved in this paper.In this paper,ultrafine low oxygen Ti6A14V alloy powder,high dense sintered Ti6A14V alloy,high fatigue performance Ti6A14V alloy,high strength sub-stable β titanium alloy TB15 and the Ti-HCFeCr composite were prepared by powder metallurgy.TiH2 and AlV alloy were milled by high-energy ball milling and ultrafine Ti6A14V alloy powder could be achieved after vacuum dehydrogenation and diffusion at 700℃ for 4 h.The weak bonding effect generated by the escaping H atoms during dehydrogenation was the key to obtain the alloy.After adding 1.5%TiCl2 to the ultrafine titanium alloy powder,the of the titanium alloy powder was realized at 650℃ for 30 min.The gaseous product TiClxOy was formed,which sublimated and escaped during the chloro-deoxidation process.The oxygen content of the titanium alloy powder reduced from 2500 ppm to 970 ppm.So the ultrafine low-oxygen Ti6A14V powder with an average particle size of 9.6 μm and an oxygen content less than 1000 ppm was obtained.The greatest advantage of the chlorodeoxidation technology is that there is no impurity left.The mechanism of microstructure and mechanical properties during the vacuum sintering densification of ultrafine low-oxygen Ti6A14V powder was investigated.The forging properties were also discussed.Using ultrafine lowoxygen Ti6A14V titanium alloy powder as raw material,a high densification of 99.2%was obtained after sintering at 1150μ for 120 min.The microstructure was obtained with a fine short rod α phase with an average grain size of 25 μm.The alloys exhibited excellent properties with the ultimate tensile strength of 950 MPa,yield strength of 890 MPa and elongation of 13.2%.The densified sintering of ultrafine titanium alloy powder achieved at 1150℃ was the result of the combined effect of volume diffusion and grain boundary diffusion.Due to the fine sintered microstructure of PM Ti6A14V alloy,the alloy exhibited excellent plasticity after high-temperature forging at 1050～1200℃.The ultimate tensile strength of Ti6A14V alloy after forging at 1050℃ was 1025 MPa,yield strength was 980 MPa,and elongation was 15.5%.By controlling the final forging temperature of PM Ti6A14V alloy,fine bimodal structure and good fatigue properties can be obtained.The Ti6A14V sintered billet was first forged at 1050℃ and the final forging temperature was 980℃.The fine bimodal structure was obtained with primary a phase size of 9.0μm.At this time,the titanium alloy had the ultimate tensile strength of 1176 MPa,yield strength of 1100 MPa,elongation of 18.2%,and fatigue strength of 750 MPa.The fatigue performance was much better than conventional casting and forging titanium alloys.The TEM observation showed that a large number of dislocation tangles were formed in the fine primary α phase and at the interface,the dislocation tangles slowed down the crack initiation rate.The observation of crack extension by in-situ observation revealed that the crack propagations were hindered by fine primary α phase.The bimodal structure PM Ti6A14V alloy obtained by this process had a crack extension threshold of 11 MPa m1/2,which was higher than that of the conventional casting and forging process Ti6A14V alloy.The ultra-high strength TB15 alloy was prepared by powder metallurgy,and the evolution of the microstructures was investigated.The sintered TB15 alloy was sintered at 1150℃ to the density of 98.3%by ultrafine low-oxygen alloy powder as the raw material.And the equiaxed β grain size was 32 μm after sintering.A large amount of needle-like α precipitated in the equiaxed β grain and enhanced the mechanical properties.The ultimate tensile strength was 1124 MPa and the elongation was 5.2%after sintered at 1150℃.After high temperature forging at 1050℃,solid solution at 850℃/30 min,and aging at 500℃/6 h,the strength of PM TB15 alloy with good strong plasticity matching.The ultimate tensile strength was 1416 MPa,and elongation was 5.0%.The PM Ti-HCFeCr alloy was prepared by adding high-carbon ferrochrome to titanium.After adding 1～11%HCFeCr,the microstructure of Ti-HCFeCr consisted of fine lath a and TiC particles.The strengthening elements Fe and Cr increased the proportion of β phase and promoted the refinement of a laths.And C generated TiC in situ with an average size of 20 μm.The TiC particles inhibited the grain growth.The strength of Ti-HCFeCr was impacted by various strengthening mechanisms.When 9%HCFeCr was added,the ultimate tensile strength was 1228 MPa,yield strength was 1140 MPa,elongation 3.1%and hardness was 42.5 HRC,and has good wear resistance.