脉冲电子束诱发金属材料表层相变的取向相关性变体选择现象及其机理研究

Recent years, high current pulsed electron beam (HCPEB) is developing rapidly as a promising technique for surface modifications of metallic materials. The main feature of this technique lies in the interaction of pulsed electron beams with materials in microseconds, which causes fast heating and cooling, melting and solidification, deformations and phase transformations. Thereby, special surface modification effects can be achieved. Previous investigations revealed that HCPEB treatments can trigger autenitic/martensitic phase transformations in some alloys during both heating and cooling stages. The orientions of the austenite grains and matensite variants are closely related to crystalographic orientations of their own and neighbour grains,phase components and stress states before the phase transformation, namely, the orientation dependent variant slection, which will determine the final texture and residual stress states in the surface layers of the treated materials. To reveal the mechanisms of the above mentioned phenomenon, several typical Fe based and Ti based alloys will be treated by HCPEB and the treated materials will be carefully investigated from both surface and cross section views by using EBSD and TEM techniques. Based on the orientation relationships of martensite variants and between martensite and austenite grains, it is possible to reconstruct the parent autenite grains formed at high temperatures and obtain their grain orientations and texture states. Furthermore, by combining XRD residual stress analyses,temperature field and stress field simulations and comparing the characteristics of phase transformations in Fe and Ti based alloys, the mechanisms of the orientation dependent variants slection associated with the phase transforamtions in surface lalyers of metallic materials induced by pulsed electron beams will be revealed.

强流脉冲电子束是近年来发展迅速的新型金属材料表面改性技术，其特点是利用微秒级脉冲电子束与材料相互作用引发快速熔凝、形变及相变等过程，来实现特殊的表层改性效果。前期研究表明，某些合金表层在脉冲电子束加热和冷却阶段将出现奥氏体/马氏体相互转变，在此过程中奥氏体或马氏体变体的取向选择与转变前自身和周边晶粒取向、相组成及所处应力状态密切相关，即取向相关性变体选择现象，并将决定处理后表层的织构及残余应力。针对这一现象，本项目将选择几种典型的铁基与钛基合金材料进行脉冲电子束处理。采用EBSD和TEM手段从表面和截面对处理样品进行表征，确定相变层内各相间取向关系，并重构出高温母相奥氏体来获取其晶粒取向及织构信息；采用XRD技术测量脉冲电子束处理后表层残余应力状态，结合温度场与应力场模拟计算，并对比铁基和钛基合金中相变的异同性，从本质上揭示脉冲电子束诱发金属材料表层相变的取向相关性变体选择现象的内在机制。

强流脉冲电子束是近年来发展迅速的新型金属材料表面改性技术，其特点是利用微秒级脉冲电子束与材料相互作用引发快速熔凝、形变及相变等过程，来实现特殊的表层改性效果。研究表明，某些合金表层在脉冲电子束加热和冷却阶段将出现奥氏体/马氏体相互转变，在此过程中奥氏体或马氏体变体的取向选择与转变前自身和周边晶粒取向、相组成及所处应力状态密切相关，即取向相关性变体选择现象，并将决定处理后表层的织构及残余应力。针对这一现象，本项目研究了Cr12MoV模具钢，双相不锈钢及钛基合金材料在脉冲电子束处理条件下的表面相变及取向关系。采用EBSD和TEM手段从表面和截面对处理样品进行表征，确定了相变层内各相间取向关系，并通过软件重构出了高温母相奥氏体来获取其晶粒取向及织构信息；采用XRD技术测量脉冲电子束处理后表层残余应力状态，结合温度场与应力场模拟计算，并对比铁基和钛基合金中相变的异同性，揭示出了脉冲电子束诱发金属材料表层相变的取向相关性变体选择现象的内在机制，阐明了其与表面应力状态及合金成分的关系。此外，在项目的支持下还开展了几种轻金属材料的脉冲电子束表面改性研究，对相变、表面形变及再结晶等过程进行了深入表征和分析。