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

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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.