DIFFUSION-BASED MICROALLOYING VIA REACTION SINTERING

As a possible means of reducing the costs associated with the producti on of metal matrix composites, the use of inexpensive, naturally occur ring minerals as a reinforcing agent is one alternative currently bein g considered. In such efforts, the occurrence of extensive chemical re action between the minerals and matrix alloy has been noted. In an eff ort to utilize the reaction products from such reactions, a novel tech nique known as core/shell processing was developed. Core/shell and bul k alloy samples were prepared through powder metallurgy techniques (bl ending, cold isostatic pressing, and sintering) followed by hot swagin g and finally machining as required. Sintered samples were examined by means of mercury densitometry, optical/scanning electron microscopy, electron microprobe analysis, and mechanical testing (tensile and impa ct). Microprobe analysis of sintered core/shell samples indicated the occurrence of extensive chemical reactions between the alloy and miner al particles in the shell region, resulting in a rejection of calcium from the mineral into the surrounding matrix followed by eventual migr ation into the intergranular regions of the core. Mechanical testing r evealed core/shell processed samples had significantly improved impact properties while maintaining tensile properties similar to bulk alloy samples.