High-Temperature Deformation and Diffusional Relaxation of Particle-Dispersion Hardened Alloys

本研究的主要目的是了解扩散松弛对弥散硬化合金高温变形的影响。对Cu-SiO_2、Cu-GeO_2和Cu-Fe合金单晶和双晶进行了高温拉伸试验，得到了不同的应力应变曲线。此外，沿晶脆性断裂对晶界的性质非常敏感。为了定量地讨论这些实验结果，有必要获得关于分散颗粒在变形过程中的形状变化的信息。还必须表征非取向相关的晶界能。作为理论研究，将力学、热力学和动力学相结合，对分散颗粒周围的扩散松弛进行了分析，成功地得到了松弛过程的速率方程。用细观力学方法定量分析了在一定条件下弥散颗粒和析出相的稳定形态，并与高温变形试验进行了对比，揭示了弥散颗粒对稳定位错结构发展的影响。高温变形和循环变形在位错结构上的异同非常明显。诚然，这一研究项目的圆满完成，从某种意义上说，它大大提高了我们的认识。然而，更重要的是，这一项目导致了各种新的研究领域的发现，这些领域对于理解弥散硬化合金的高温变形是必不可少的。

The main purpose of this research is to understand the role of diffusional relaxation on high-temperature deformation of dispersion-hardened alloys. High-temperature tensile tests were conducted using Cu-SiO_2, Cu-GeO_2 and Cu-Fe alloy single crystals and bicrystals and various stress-strain curves were obtained. In addition, intergranular brittle fracture was found to be very sensitive to the nature of grain boundaries. To quantitatively discuss these experimental results, it was necessary to obtain information on the shape change of dispersed particles that occurs during the deformation. Misorientation-dependent grain-boundary energy must also be characterized. Therefore, basic data on these quantities were also obtained.As theoretical studies, diffusional relaxation around dispersed particles was analyzed by combining mechanics, thermodynamics and kinetics and the rate equations for the relaxation process could be obtained sucessfully. Furthermore, stable shape of dispersed particles and precipitates under a given set of conditions was quantitatively analyzed using micromechanics.In comparison with the high-temperature deformation tests, low-cycle fatigue of Cu-Fe alloy single crystals were performed to reveal the effect of dispersed particles on the development of stable dislocation structure. The similarities and differences in the dislocation structure between high-temperature deformation and cyclic deformation were found very clearly.It is true that this research project has been successfully completed in a sense that it has greatly improved our understanding. What is more important, however, is that this project resulted in the discovery of various new research areas that are essential to understand the high-temperature deformation of dispersion-hardened alloys.