CORRELATION OF MICROSTRUCTURE AND FRACTURE-TOUGHNESS OF A RAPID SOLIDIFICATION POWDER-METALLURGY AL-FE-V-SI ALLOY

Abstract

The principal metallurgical factor leading to embrittlement of a rapid solidification-powder metallurgy (RS-PM) Al-Fe-V-Si alloy after high temperature exposure at 480-degrees-C was identified. Although the RS-PM Al-Fe-V-Si alloy showed excellent high temperature stability compared to an ingot metallurgy 2219 aluminium alloy, the Al-Fe-V-Si alloy exhibited a decreasing fracture toughness together with yield strength and ductility after high temperature exposure. In situ scanning electron microscopy observations of crack-opening processes showed that brittle cleavage-like fracture occurred at the coarse Al13Fe4 particles that were formed during exposure at 480-degrees-C. This led to the reduction in fracture toughness of the Al-Fe-V-Si alloy. Fracture toughness tests were interpreted using a simplified ductile fracture initiation model based on the assumption that crack extension initiates at a certain critical strain over a microstructurally significant critical distance. This model correlated microstructural factors with fracture toughness and confirmed that the presence of coarse Al13Fe4 particles was responsible for the embrittlement phenomenon in the Al-Fe-V-Si alloy after high temperature exposure.