Microstructural characterization and wear behavior of in situ TiC/7075 composites synthesized by displacement reactions and spray forming

A novel in situ reaction technique is developed to prepare TiC/7075 composites. This technique provides a new approach overcoming the problems of loss and agglomeration of reinforcement particles when they are in situ formed in a molten metal first and then injected into the spray cone of molten droplets during the spray forming process. Experimental results have shown that the presence of strip or rectangular-like Al₃Ti, which is detrimental not only to the fracture toughness, but also to the stability of the microstructure, can be avoided completely from the final product by using a proper Ti:C molar ratio in the Ti-C-Al performs. The mechanisms of formation or absence of Al₃Ti phase in the TiC/7075 composites are explained based on thermodynamics of the system. The modification of the microstructure of the spray-formed 7075 alloy can be understood in the light of atomic diffusion. The wear results showed that the wear rates of the spray-formed 7075 alloy and its composites increased with applied loads. At higher applied loads, the 7075 alloy exhibited superior wear resistance than that of the composites. This is attributed to increased microcracking tendency of the composites than the matrix alloy.