Study On The Superplastic Behavior Of Hydrogenated Ti-55 High Temperature Alloy

Ti-55 high temperature alloy are widely used in aviation and aerospace industry due to its high specific strength,good corrosion resistance and high temperature properties.However,the high forming temperature and low forming rate raise the requirements of mold manufacturing and forming equipments,and cause long production cycle and high cost.Based on the reversible alloying of hydrogen,hydrogen-enduced phase transformations and hydrogen-enhanced plasticity,thermohydrogen process can lower forming temperature and improve hot workability of titanium alloys.The effect of hydrogenation on superplasticity of Ti-55 alloy was investigated by studying the relationship of microstructure and mechanical properties.This study provides theoretical and experimental basis for the thermohydrogen process of Ti-55 alloy.The microstructure of hydrogenated and unhydrogenated Ti-55 alloy in room temperature was observed by OM,SEM,TEM and XRD.The evolution of metallography,phase fraction and substructure was studied.? and ? hydride was found and their generation mechanism was analyzed.The phase transformation behavior was studied by DSC and TGA,and the temperature of ???+??? and hydride decomposition was decreased.The effect of hydrogen content,forming temperature and strain rate on superplasticity of hydrogenated and unhydrogenated Ti-55 alloy was investigated by superplastic tensile tests.The results showed that,the superplasticity increases to maximum and then decreases with the increase of hydrogen content.Ti-55 alloy with 0.1%H has the best superplasticity and performs high elongation,low peak stress and high strain rate sensitivity index.And its best superplastic forming temperature is 825?,125? lower than as-received Ti-55 alloy.SEM was employed to scan the tensile fracture,and found that Ti-55 alloy with 0.1%H has more ductile fracture behavior.The microstructure of deformed Ti-55 alloy was observed by OM and SEM to study the mechanism of hydrogen-enhanced plasticity.The results showed that,the increasing of ? phase fraction benefits superplasticity in low hydrogen content,and the integrating and growing of ? grains reduce superplasticity in high hydrogen content.