NiTi40合金微观组织结构的电子显微学分析

采用扫描电子显微分析(SEM)、电子背散射衍射分析(EBSD)、透射电子显微分析(TEM)、高分辨电子显微分析(HRTEM)、高角度环形暗场-扫描透射(HAADF-STEM)等技术手段,对NiTi40(60%Ni+40%Ti,质量分数)合金淬火态样品的微观组织结构进行分析。结果表明:NiTi40合金在950℃、150 min固溶水冷和1050℃、150 min固溶水冷的硬度值相近,为60~61 HRC,但微观组织结构有显著的区别。经950℃固溶水冷后,合金中的粗大第二相主要为NiTi2和Ni3Ti相,还有少量和NiTi2相互伴生的TiC相;经1050℃固溶水冷后,合金中的Ni3Ti相接近完全回溶的,粗大第二相主要为相互伴生的NiTi2及Ti C相。随着固溶温度的升高,合金的晶粒尺寸明显增大,合金晶界处的小晶粒在1050℃固溶时基本消失。经950℃固溶处理,晶内析出相主要为10~20 nm的Ni4Ti3相;经1050℃固溶处理,晶内析出相主要为几十至几百纳米的Ni4Ti3相。

Electron microscopic analysis of microstructure of NiTi40 alloy

The microstructure of the quenched samples NiTi40(60%Ni+40%Ti,mass fraction)alloys was analyzed by means of scanning electron microscopy(SEM),electron backscatter diffraction(EBSD),transmission electron microscopy(TEM),high-resolution transmission electron microscopy(HRTEM)and high angle annular dark field-scanning transmission electron microscopy(HAADF-STEM).The results show that the hardness values of NiTi40alloys after solution treatment at 950℃and 1050℃for 150 min are equivalent,about 60-61 HRC,but the microstructure is significantly different.After solution treatment at 950℃,the alloy is mainly comprised of NiTi matrix,NiTi2 and Ni3Ti precipitates,Ni Ti2 and TiC mutually co-existed.After solution treatment at 1050℃,Ni3Ti phase is completely dissolved into the matrix,and the second phase is mainly NiTi2 and TiC phase associated with each other.When the solution temperature increases,the grain size of the alloy increases significantly,and the small grains at the grain boundary of the alloy disappear substantially after solution treatment at 1050℃.After solution treatment at 950℃,the precipitation in the crystal is mainly 10-20 nm Ni4Ti3 phase,while intracrystalline precipitates are mainly dozens to hundreds of nanometer Ni4Ti3 phase after solution treatment at 1050℃.