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

采用累积辊焊的方法对大块板材进行了机械合金化试验。通过ARB的MA可以在良好控制的工艺条件下（如温度和应变速率）制备出各种应变水平的大块样品，这使我们能够观察到微观结构和相变作为应变的函数。在纳米尺度上分析了所得样品的结构和组成。采用ARB工艺制备了Cu+Zr和Fe+Al多层叠层。Cu-Zr是众所周知的非晶形成体系，而一直认为Fe-Al体系中不可能得到非晶相。对于Zr+Cu多层材料，在6次循环ARB以上，不仅微观结构混合物得到了证实，而且混合物的原子水平也得到了证实，得到了过饱和固溶体。在Cu和Zr的界面区形成了非晶相。这是一个令人惊讶的结果，因为本研究是在室温下进行的剧烈塑性变形（ARB）。纳米层状结构的能谱分析表明，一定程度的原子混合是形成非晶结构的必要条件。在ARB样品的热处理过程中，固态非晶化继续形成非晶和纳米晶的大块复合材料。在Fe-Al体系中也进行了原子混合，得到了过饱和固溶体。而在Fe-Al体系中几乎没有观察到非晶相。仅在有限的界面区域，存在少量的非晶态。澄清了非晶相是通过金属间化合物形成的。本研究指出了利用ARB工艺进行大块机械合金化的潜力，并指出了剧烈塑性变形和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.