In situ composites

The in situ formation of reinforcements, matrices, and interphases is a promising approach to decreasing the cost of high performance metal-ceramic composites. It develops high mechanical properties, and allows significant savings to be achieved by reducing or eliminating processing steps, reinforcing fibers, and reinforcement-matrix interfacial coatings. Several types of in situ composite materials are already being tested in real-world components, and others are expected to undergo such trials soon. Those closest to commercial application include in situ-toughened silicon nitride, in which high toughness comes from the development of high aspect-ratio grains during processing; some of the Lanxide materials, in which toughening phases (in the form of particles or metallic inclusions) are produced during processing; and the XD materials, notably {gamma}-TiAl intermetallics toughened by in situ-produced titanium diboride particulates, developed primarily by Martin Marietta. This article compares composites produced by in situ technologies with those produced by conventional means, and provides examples of several current and near-term applications of these materials.