Microstructure and mechanical behavior of in situ Ni-Ni3Si composite

Composite materials allow one to associate fragile and ductile phases in order to obtain a good combination of properties. In situ composites obtained through eutectic transformation may present a combination of phases under a condition of equilibrium. Samples of the eutectic Ni-Ni3Si alloy were arc-melted and characterized in the as cast and directionally solidified (DS) conditions. The as cast microstructure was refined and uniform, while the DS microstructure was aligned in the direction of heat extraction and presented a plane solid/liquid interface. The alloy displayed an interesting combination of relatively high strength and tensile ductility at room temperature (3.7% total strain; UTS=810MPa), and a modulus of elasticity E=264MPa. High temperature tests showed that the yield strength decreased almost linearly as the temperature rose. No brittle to ductile transition temperature was found.