Formation Mechanism of Non-Equilibrium Phases during Bulk Mechanical Alloying by Accumulative Roll Bonding Process

采用累积叠轧焊（ARB）方法对大体积板材进行了机械合金化（MA）试验。ARB的MA使得在良好控制的工艺条件（例如温度和应变速率）下制造加工到各种应变水平的大体积样品成为可能，这使我们能够观察微观结构和相变作为应变的函数。在纳米尺度上分析了样品的结构和成分，并对Cu+Zr和Fe+Al多层叠层进行了ARB变形。Cu-Zr系是一个著名的非晶形成体系，而Fe-Al系一直被认为不能形成非晶相。对于Zr+Cu多层膜，在6次以上的ARB循环中，不仅确认了微观结构的混合，而且还确认了原子级的微结构，从而获得过饱和固溶体。在Cu和Zr的界面处形成了非晶相。这是一个令人惊讶的结果，因为严重的塑性变形（ARB）在本研究中在环境温度下进行。纳米片层结构的纳米束EDS分析澄清了一定水平的原子混合物是非晶形成所必需的。在ARB样品的热处理过程中，固态非晶化进行，形成非晶和纳米晶体的大体积复合物。在Fe-Al系中，ARB也进行原子混合，得到过饱和固溶体。而Fe-Al系中几乎没有非晶相。结果表明，非晶相是通过金属间化合物形成的，只有在有限的界面区域才有少量的非晶相存在.本研究表明了ARB工艺在机械合金化中的应用潜力，指出了剧烈塑性变形的重要性以及界面对机械合金化反应的重要性.

Mechanical alloying (MA) of bulky sheet materials was tried by means of accumulative roll bonding (ARB). The MA by ARB made it possible to fabricate the bulky samples processed to various strain levels under well-controlled process conditions, such as temperature and strain rate, which enabled us to observe the microstructure and phase transition as a function of strain. The structure and composition of the obtained specimens were analyzed in nano-meter scale.The multilayered stacks of Cu+Zr and Fe+Al were deformed by the ARB process. Cu-Zr is a well-known amorphous formation system, while it has been thought that no amorphous phase can be obtained in Fe-Al system. In case of Zr+Cu multilayer, not only microstructural mixture but also atomistic level of micture were confirmed above 6 cycles ARB, so that supersaturated solid solution was obtained. It was also found that amorphous phase formed at interface regions between Cu and Zr. It was a surprising result since the severe plastic deformation (ARB) was conducted at ambient temperature in the present study. Nano-beam EDS analysis for the nano-lamellar structures clarified that a certain level of atomistic mixture is necessary for amorphous formation. During a heat treatment of the ARB sample, solid state amorphization proceeded to form the bulky composites of amorphous and nanocrystals. Atomistic mixture by ARB also proceeded in Fe-Al system, and supersaturated solid solution was obtained as well. However, amorphous phase was hardely observed in Fe-Al system. Only in the limited interface regiuons, small amount of amorphous was found. It was also clarified that the amorphous phase was formed via intermetallic compound.The present study indicated the potential of bulk mechanical alloying by the use of the ARB process and pointed out the importance of severe plastic deformation as well as the importance of interfaces for mechanical alloying reactions.