Kinematical Study on the Densification Process During Pressure Sintering of Alloy Powder Utilizin Superplasticity.

研究了超塑性性能在合金粉末压力烧结中的应用。作为基础研究，基于理论方程和致密化机理图，阐明了粉末组织对523 K真空热压zn -22%铝合金粉末致密化行为的影响。即，在有限的相对密度和施加压力范围内，由鳍状微双预制结构组成的粉末是通过超塑性变形致密化的，而由层状结构组成的粉末是根据功率低蠕变致密化的。作为上述基础知识的首次应用，研究了预先球磨和真空热压相结合的热处理对等离子体旋转电极工艺（PREP）制备的SCr420钢粉末致密化过程的影响。结果表明：热处理后粉末的致密化是通过粉末的超塑性变形进行的，致密体由细晶铁素体和球化渗碳体组成；作为本研究的第二个应用，我们对PREP生产的TiNi形状记忆合金粉末的致密化进行了检测。在这种情况下，由于粉末的晶粒细化程度很高，因此预先对粉末进行球磨可以加速973至1173 K温度下的致密化过程。晶粒细化后，形状恢复强度显著提高。

An application of superplastic behavior for the pressure sintering of the alloy powder was investigated in the present study.As a fundamental study, the effects of the microstructure of the powder on the densification behavior during vacuum hot pressing (VHP) of Zn-22%Al alloy powder at 523 K was clarified based on the theoretical equation and densification mechanism map. Namely, the powder consists of fin microduprex structure was dencified by superplastic deformation in the limited range of relative density and applied pressure, while the powder consists of lamellar structure was densified according to the power low creep behavior.As the first application of the fundamental knowledge mentioned above, the effects of thermomechanical treatment which performed by combination of priorball milling and vacuum hot pressing on the densification process of SCr420 steel powder produced by plasma rotating electrode process (PREP) was examined. The results showed that the densification of the thermomechanically treated powder progressed by superplastic deformation of the powder during VHP, and the compact was composed of fine grained ferrite and spheroidized cementite particles.As the second application in the present study, we performed the examination of the densification of TiNi shape memory alloy powder produced by PREP. In this case, the densification process at temperatures from 973 to 1173 K was accelerated by prior ball milling of the powder due to considerable grain refinement. Such a grain refinement became the noticeable increase in the shape recovery strength.