Diffusion-based microalloying via reaction sintering

As a possible means of reducing the costs associated with the production of metal matrix composites, the use of inexpensive, naturally occurring minerals as a reinforcing agent is one alternative currently being considered. In such efforts, the occurrence of extensive chemical reaction between the minerals and matrix alloy has been noted. In an effort to utilize the reaction products from such reactions, a novel technique known as core/shell processing was developed. Core/shell and bulk alloy samples were prepared through powder metallurgy techniques (blending, cold isostatic pressing, and sintering) followed by hot swaging 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 impact). Microprobe analysis of sintered core/shell samples indicated the occurrence of extensive chemical reactions between the alloy and mineral particles in the shell region, resulting in a rejection of calcium from the mineral into the surrounding matrix followed by eventual migration into the intergranular regions of the core. Mechanical testing revealed core/shell processed samples had significantly improved impact properties while maintaining tensile properties similar to bulk alloy samples.