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

本研究的主要目的是了解扩散弛豫在弥散硬化合金高温变形中的作用。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，晶间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，有必要获得变形过程中分散颗粒形状变化的信息。取向偏差相关的晶界能也必须被表征。因此，也获得了这些数量的基本数据。在理论研究方面，结合力学、热力学和动力学分析了分散粒子周围的扩散弛豫过程，成功地得到了弛豫过程的速率方程。此外，用微观力学方法定量分析了在一定条件下分散颗粒和沉淀的稳定形状。通过对Cu-Fe合金单晶的低周疲劳试验与高温变形试验进行对比，揭示了分散颗粒对Cu-Fe合金单晶位错组织发展的影响。发现了高温变形与循环变形在位错结构上的异同。从某种意义上说，这个研究项目的成功完成确实大大提高了我们的认识。然而，更重要的是，这个项目导致了各种新的研究领域的发现，这些研究领域对于理解弥散硬化合金的高温变形至关重要。

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.