Basic Research On Preparation Of High-Temperature Titanium Alloys By Titanium Hydride Powder Metallurgy

High-temperature titanium alloys have high specific strength and good high-temperature oxidation resistance.They are widely used in aircraft engines.The common preparation method is the smelting method.This method is prone to non-uniform microstructure,which causes segregation and affects alloy properties.The powder metallurgy method can reduce the segregation of the composition and can be near net shape.In this paper,high temperature titanium alloy was prepared by powder metallurgy with titanium hydride as the main raw material through the processes of cold isostatic pressure and vacuum sintering.The design of high-temperature titanium alloy composition,the mechanism of dehydrogenation and deoxidation of titanium hydride,and the effect of titanium hydride on the properties and phase transition temperature of the alloy were studied theoretically,providing a theoretical basis for subsequent experiments.The effects of titanium hydride content,sintering temperature,?-phase stabilizing elements W and Nb on the phase composition,chemical composition,microstructure and mechanical properties of high-temperature titanium alloys were experimentally studied.The main conclusions were as follows:?1?The alloy composition was designed to be Ti-6.5Al-2.7Sn-4Zr-0.4Mo-0.4Si through calculation formulas of aluminum equivalent and molybdenum equivalent.The initial phase transition temperature of the alloy was determined to be 891?by differential thermal analysis.The phase transition temperature was 1273?;the constitutive equation of the alloy was calculated using the Arrhenius formula:^???28?.594?10¹⁴[sinh?.00036??].407exp?-340247/RT?.?2?When the sintering temperature was 1150?and the sintering time was 4h,with the increase of the content of titanium hydride,the metallic luster of the alloy appearance increased significantly,and the oxygen content in the alloy decreased,which indicated that titanium hydride can reduce the content of oxygen while promoting the sintering.The removal effect of hydrogen in titanium hydride was good,there was only a small amount of hydrogen in the alloy,and it had little effect on the phase composition of the alloy;With the increase of the content of titanium hydride,the microstructure changed from an equiaxed structure to a net structure,the porosity of the alloy decreased,the highest relative density was95.45%,the mechanical properties increased,the highest tensile strength at room temperature was 460.1MPa,and the highest hardness was 298.4HV.?3?When titanium source was only titanium hydride and sintering time was 4 hours,with the increase of sintering temperature,the grains gradually grew up,the relative density further increased to 95.84%,and the mechanical properties increased first and then decreased.When the sintering temperature was 1150?,the highest bending strength at room temperature was 556.2MPa.Compared with the theoretical phase diagram of the alloy,the Ti₃Al and Sn₃Zr₅ did not appear in the alloy obtained by the experiment.?4?When titanium source was only titanium hydride and sintering time was 4 hours,and the sintering temperature was 1150?,0.5%W could slightly improve the mechanical properties;1%W could increase the bending strength by 52.4MPa,increase the hardness by31.4HV and reduce the tensile strength by 122.5 MPa;W had a large effect on the high-temperature compressive strength of the alloy.When W content was 0.5%,the flow stress of the alloy could be increased,and the maximum flow stress was 505 MPa at 750?.When W content was 1%,it was favorable for the high temperature strength of the alloy at the strain rate(0.1s^-1)and the deformation temperature?750?⁸00??,but it was unfavorable for the high temperature strength of the alloy when the strain rate and deformation temperature were increased,so when W addition is 0.5%,the alloy with good properties at room temperature and high temperature can be obtained.?5?When titanium source was only titanium hydride and sintering time was 4 hours,and the sintering temperature was 1150?,with the increase of Nb,ZrSi and Mo₅Si₃ phases would be precipitated in the alloy,and the microstructure would be refined gradually.The addition of Nb would reduce the mechanical properties of the alloy at room temperature;Nb had a certain effect on the high-temperature performance of the alloy.When the addition of Nb was 1%,the high-temperature strength of the alloy could be increased slightly,and the maximum flow stress was 490.1MPa at 750?;When the addition of Nb was 2%,the high-temperature strength of the alloy would be reduced.Compared with the two?-phase stable elements,W had more influence on the high temperature properties of the alloy.