Effects of the liquid phase on the high-temperature tensile ductility: from embrittlement to superplasticity

摘要

Inclusions of liquid phase are generally considered to cause liquid-metal embrittlement. On the other hand, there have been some reports implying the enhancement of tensile elongation by liquid inclusions. In this paper, the possibility of elongation enhancement by liquid and its underlying mechanism were investigated in a model binary system of Al-Bi and a composite of(Al-Mg)-Si3N4. Clear evidence of elongation enhancement was observed in the Al-Bi alloy. Liquid inclusions of Bi were found to assist stress accommodation processes and to delay cavitation failure. In the (Al-Mg)-Si3N4 composite, a close correlation was found between the incipient melting temperature and an optimum temperature for high-strain-rate superplasticity. The liquid phase was observed along grain boundaries and interfaces of the composite, suggesting a similar stress accommodation process to that of the Al-Bi alloy. The interface microstructure was also studied by high-resolution transmission electron microscopy to understand the detailed mechanism of high-strain-rate superplasticity. [References: 49]