In situ Composites: A Review

The review of the works on the fabrication-technology studies, patterns of structure formation, and properties of in situ composites is presented. The main advantage of in situ (natural) composites is the thermodynamic stability of their composition and the coherence (conjugation) of the lattices of the contacting phases. All these ones provide the composite with a high level of the physical and mechanical properties. As shown, composite materials of this type are formed in the process of directed phase transformations, such as eutectic crystallization, eutectoid decomposition, etc., caused by a temperature gradient, as well as a result of diffusional changes in composition. The conditions for the growth of in situ composites are formulated. The mechanisms of growth of composite structures of the eutectic type are considered. The factors influencing on the morphology of structures of the eutectic type are indicated. The considered technological methods make it possible to obtain materials with predetermined properties, in which the size, volumetric composition, and spatial arrangement of phases are characteristic of in situ composites. The paper provides a large number of examples of in situ composites: from low-melting Bi-based alloys to refractory eutectics based on Mo and W (Bi–MnBi, Cd–Zn, Al–Al3Ni, Al–Al4La, Al–Al10CaFe2, Al–Al9FeNi, Al–Al3Zr, Al–Al3Sc, Au–Co, Si–TaSi2, Cr–HfC, Cr–ZrC, Cr–NbC, Cr–NbC, Cr–TaC, Nb–Nb5Si3, Mo–ZrC, Mo–HfC, W–TiC, W–ZrC, W–HfC, etc.). Processes and aspects of structure formation are considered. The influence of additional doping on the structure and properties of composite materials of the eutectic type of binary systems, as well as the features of the structure formation of ternary colonies in the composite are considered.