Developments in Processing of Functionally Gradient Metals and Metal-Ceramic Composites: A Review

Functionally gradient/graded materials (FGMs), an emerging new class of materials, are the outcome of the recent innovative concepts in materials technology. FGMs are in their early stages of evolution and expected to have a strong impact on the design and development of new components and structures with better performance. FGMs exhibit gradual transitions in the microstructure and/or the composition in a specific direction, the presence of which leads to variation in the functional performance within a part. The presence of gradual transitions in material composition in FGMs can reduce or eliminate the deleterious stress concentrations and result in a wide gradation of physical and/or chemical properties within the material. Functionally graded metal-ceramic composites are also getting the attention of the researchers. Among the fabrication routes for FGMs such as chemical vapour deposition, physical vapour deposition, the sol gel technique, plasma spraying, molten metal infiltration, self propagating high temperature synthesis, spray forming, centrifugal casting, etc., the ones based on solidification route are preferred for FGMs because of their economics and capability to make large size products. The present paper discusses and compares various solidification processing techniques available for the fabrication of functionally gradient metals and metal-ceramic composites and lists their properties and possible applications. The other processing methods are briefly described.