Nanostructure control

本研究的目的是建立各种纳米结构控制方法，明确金属及合金、金属间化合物和陶瓷等各种材料的超塑性机理。得到的主要结果如下：(1)开发了双相不锈钢和高碳钢超塑性外观的新型热处理工艺。通过对双相不锈钢热轧板进行重冷轧和对高碳钢进行（γ + θ）温度淬火等简单处理，可获得晶粒尺寸为0.5 ~ 1.0μm的微双相组织。(2)研究了晶界液相对颗粒分散铝合金超塑性的影响。7475铝合金在低于固相温度下获得了较大的伸长率。7475合金在试验条件下与峰值伸长率相对应的液相厚度估计为10 ~ 60nm。(3)发现单片金属间化合物的超塑性变形机制依赖于有序的晶体结构。晶界滑动对fcc衍生物的细晶超塑性起重要作用，而动态再结晶和/或动态恢复对bcc衍生物的粗晶超塑性起重要作用。(4)研究了Mg、Ca、Sr和Ba添加量对Y-TZP和Ce-TZP晶粒细化的影响。结果表明，钙是晶粒细化最有效的元素。在Y-TZP中加入少量CuO可有效降低烧结温度、晶粒尺寸和超塑性变形所需的应力。

The purpose of the present research project is to establish various methods of nanostructure control and to make clear the mechanism of superplasticity in various materials such as metals and alloys, intermetallics and ceramics. The main results obtained are as follows.(1) New types of heat treatments for appearance of superplasticity in duplex stainless steel and high carbon steel were developed. Microduplex structure with a grain size of 0.5〜1.0μm can be obtained by simple treatments such as heavy cold-rolling of as-received hot-rolled plates in duplex stainless steel and the quenching from (γ + θ) temperature in high carbon steel.(2) Effect of liquid phase at grain boundaries on superplasticity was investigated in particle-dispersed aluminum alloys. A large elongation was obtained at temperatures just below the solidus one for a 7475 Al alloy. The thickness of liquid phase in the test condition corresponding to the peak elongation was estimated to be 10〜60nm for the 7475 alloy.(3) Mechanism of superplastic deformation in monolithic intermetallics was found to depend on ordered crystal structure. Grain boundary sliding plays an important role in fcc-derivative intermetallics exhibiting fine-grained superplasticity, while dynamic recrystallization and/or dynamic recovery is responsible for coarse-grained superplasticity in bcc-derivative intermetallics.(4) The effect of Mg, Ca, Sr and Ba additions on the grain size refinement of Y-TZP and Ce-TZP was studied. It was found that Ca is the most effective element for the grain refinement. The addition of small amount of CuO in Y-TZP was found to be effective in reducing the sintering temperature, grain size and the stress rcquired for superplastic deformation.