Tailoring Microstructure And Mechanical Properties Of Tini Alloy By Using Electroplastic Deformation

An excellent metal biomaterial needs low elastic modulus,high strength and high plasticity.However,increasing strength always leads to the decrease of plasticity,and decreasing elastic modulus is often accompanied with the decrease of strength.So,it is very important to solve the two contradictory relationships for metal biomaterials science.In this paper,we chose TiNi alloy as research object processed by electricity plastic rolling deformation to achieve low elastic modulus,high strength and high plasticity.Then we systematically studied the effects of rolling parameters and pulse parameters on microstructure and mechanical properties of TiNi alloy.The NiTi alloy with ultra-low elastic modulus,high strength and high plasticity was prepared successfully by electro plastic deformation.The strength and elastic modulus are about 1745 MPa and 29.4 GPa respectively,and keep high failure elongation?12.7%?.The excellent comprehensive properties are mainly from high density dislocation,refined grain and the increasing of low elastic modulus martensite?B19'?.The effects of rolling parameters such as deformation and strain rate on microstructure and mechanical properties of TiNi alloy were researched.It could be found that the increasing of strain rate(1.19-1.99 s^-1)would increase strength and elastic modulus obviously;increasing deformation?0-82%?would increase strength,decrease elastic modulus gradually,and maintain high failure elongation rate relatively.That was because large deformation and high strain rate were beneficial to improve dislocation density,refined grain and increase martensite phase with low elastic modulus.The effects of pulse parameters such as frequency and voltage and pulse width on microstructure and mechanical properties of TiNi alloy were researched.The researches showed that the increasing of frequency?500-600 Hz?,voltage?24-25 V?or pulse width?80-120?s?would increase strength and elastic modulus obviously,which was not conducive to achieve the excellent comprehensive mechanical properties.Microstructures showed that high energy pulse could make grain grow,increase dislocation density,decrease B19'phase content.This article is of great significance to solving the inversion of the strength and plasticity of materials,and contradictory relationship between strength and elastic modulus of metal biomaterials,and could provides a new ideas for the development of high performance metal biomaterials.