Development of Non-Equilibrium PM Process to Precision Forming of Hard Materials using Pseud-Superplasticity

本文以Ti/Si系合金和W合金为研究对象，对非平衡-平衡相变等伪超塑性变形行为进行了系统的研究。结果，观察到与常规超塑性非常相似的大变形。此外，它被证实，在高应变速率下的低温和低应力变形发生的相变。变形行为能够通过控制显微组织以及通过初始相组成来控制。基于这些基本发现，使用了立命馆大学的同步加速器辐射研究设备，并使用同步加速器设备的LIGA工艺对微小尺寸零件进行了精密成形。在初始状态下具有非平衡的Ti-20mass%SiC粉末的情况下，非晶相的结晶使得能够实现大量的低温变形。这一现象可能是由于在通过加热由非晶相形成的材料中存在纳米尺寸的晶粒。此外，从低温超塑性的角度研究了机械球磨的W（钨）粉末。结果表明，纳米晶粒控制的钨粉压坯在压缩试验中表现出优异的变形性能，从而证明了纳米晶粒组织控制是实现低温低应力成形的有效工艺。

Systematical researches have been carried out using Ti/Si system alloy and W alloy, focusing especially to a pseudo-superplastic deformation behavior such as non-equilibrium to equilibrium phase transition. As a result, a large deformation very similar to conventional superplasticity was observed. In addition, it was confirmed that a low temperature and a low stress deformation under a high strain rate took place by the phase transition. The deformation behavior was able to be controlled by controlling the microstructure as well as by an initial phase constitution. The synchrotron radiation research facility of Ritsumeikan University was used based on these basic findings, and a precision forming of micro-size parts was applied with the LIGA process of the synchrotron facility. In case of a Ti-20mass%SiC powder with a non-equilibrium at the initial state, crystallization of an amorphous phase enabled a large amount of low temperature deformation. This phenomenon is presumably due to the existence of the nano size grains in the material formed from the amorphous phase by heating. Moreover, mechanically milled W (tungsten) powders were investigated from the point of view of low temperature superplasticity. As a result, nano grain controlled W powder compacts showed outstanding deformation properties by compression test, thus the nano grain microstructure controlling is proved to be an effective process for the low temperature and the low stress forming.