The effect of ceramic reinforcement on residual stresses during spray atomization and Co-deposition of metal matrix composites

摘要

Metal matrix composites (MMCs) are attractive candidate materials for high-performance structural applications that require unusual combinations of physical and mechanical properties [1,2). Among the various types of MMCs available, those that are reinforced with discontinuous fibers or particles are of interest because they can be formed utilizing conventional fabrication processes, such as forging, extrusion, and pressing, rendering them attractive for cost-critical applications. Discontinuously reinforced MMCs have been successfully fabricated using a variety of solidification techniques, which include stir, casting of a.mixtuie of liquid matrix with reinforcement [3], powder metallurgy [4], metal infiltration [5], and spray atomization and co-deposition [6], Among the techniques available, spray atomization and co-deposition is of interest as an attractive route to fabricate MMCs because of several advantages: first, its ability to expose the reinforcement to relatively low temperatures, thus minimizing any potential reactions between the matrix and the ceramic reinforcement, and second, because of its potential to synthesize difficult-to-form materials into near-net shapes, minimizing the costly joining and machining operations that are typically required after conventional forming [7], During spray atomization and co-deposition, the matrix material is disintegrated into a dispersion of droplets using high-velocity inert gas jets. Simultaneously, one or more streams of reinforcing ceramic;particles are injected into the atomized spray, and the mixture of matrix droplets with interdispersed ceramic particles is deposited onto a substrate, eventually collecting as" a coherent preform. As the deposited preform cools down from the deposition temperature to ambient temperature, residual stresses are developed in the composites as a result of the mismatch of the thermal expansion coefficient between reinforcement and matrix. The knowledge of thermal residual stress state in as-sprayed MMCs provides a basis for a better control of manufacturing components using spray atomization and co-deposition process.