The Behavior Analysis For Stress-Induced Martensitic Transformation Of Titanium Alloy Under Compression Loading

Titanium alloy is a lightweight and high-strength alloy with excellent performances,such as heat resistance,corrosion resistance,elasticity and good forming,and it has been widely used in energy fields,and now,it also has become the indispensable material in modern industries.However,Parts made by titanium alloy material in service are often subjected to varying degrees of compression loading that lead to fatigue damage,and the fatigue damage which is a great threat for mechanical devices in engineering project,can causes disastrous accidents.Therefore,it is great significant to investigate fatigue theory and application of titanium alloy.In this dissertation,three types of alloy,Ti-10V-2Fe-3Al,Ti-10V-Fe-3Al,and Ti-10V-2Cr-3Al were investigated and results are illustrated as follows:(1)Through the finite element simulation of the microstructure level and the unidirectional compression test of titanium alloy,the fatigue behaviors of titanium alloy was investigated in consideration of the volume fraction,grain size,and various microstrtucture components of the needle-like ?-phase produced by the stress-induced martensitic transformation.It was found that the ?-phase titanium alloy has larger shape change than that of ?-phase one with low hardness.The stress concentration and stress transfer were appeared in the junction between crystal faces,in which cracks was more easy appeared.Meanwhile,with enhancing of volume fraction,the yield strength of alloy material was increased;the yield strength was also increased with the size of crystalline grain under the same volume fraction,which can strength the properties of alloy.(2)Based on stress-induced martensitic transformation,the microcosmic effect mechanism of cyclic loading on mechanical properties of three kinds of alloys,Ti-10V-2Fe-3A1,Ti-10V-Fe-3Al,and Ti-10V-2Cr-3Al,were studied.At the same time,by comparing and analyzing two different size of titanium alloy materials,the relationships and differences between size and cyclic loading were explored.Results show that the yield stress of conventional size titanium alloy is improved with increasing the compression times and the compressed columnar alloy material had a uniform drum shape,moreover,the angle between the sliding surface normal and the Y axis of the compression deformation titanium alloy column is about 45 degrees.While the yield stress of micro-size titanium alloy is declined with the increasing the compression times and the compressed alloy material had an uneven drum shape,the angle is turned into 54 degrees.