Grain boundary sliding in Ni 3Al(Ta,B) bicrystals

Abstract

Grain boundary sliding refers to displacements produced when individual crystals slide over each other at or in a region directly adjacent to their common interface. Grain boundary sliding has been found to have both beneficial and detrimental roles in deformation and fracture processes that occur in polycrystalline materials. For example, extensive grain boundary sliding makes superplastic forming possible where strains in excess of 1000% may be achieved. In contrast, the occurrence of grain boundary sliding may be detrimental in high temperature components by contributing strongly to the overall creep strain. It has also been shown that stress redistribution resulting from grain boundary sliding can significantly enhance the damage mechanisms that facilitate high temperature fracture. Thus it is important to develop an understanding of grain boundary sliding in materials considered for service at elevated temperatures. Polycrystalline nickel aluminide (Ni[sub 3]Al) is a promising matrix material for use at elevated temperatures as a result of its anomalous positive temperature dependence of strength, good oxidation resistance, low density compared to superalloys, and good ductility with the addition of a small amount of boron. However, Ni[sub 3]Al alloys exhibit a transition from ductile to brittle behavior at elevated temperatures. This decrease in ductility ismore » shown in this paper.« less