In Situ Formed Whisker Reinforced SiC Composites

A program is proposed to establish the combination of materials and processing parameters which will lead to in situ-formed whisker reinforced SiC composites. The proposed program is based on three CERCOM-funded efforts: (1) A feasibility demonstration that in situ-formed beta silicon nitride whisker-reinforced SiC composites can be produced; (2) A demonstration that new processing approaches can be used to produce a new type of monolithic SiC with segregated grain boundaries, and; (3) An on-going analytical evaluation of materials and processing parameters as a function of physical, mechanical and microstructural properties. Preliminary CERCOM studies with in situ-formed beta silicon nitride whisker-reinforced SiC composites have indicated that the flexure strength and fracture toughness increased from 517 MPa and 3.44 MPa.m 1/2 to 940 MPa and 6.24 MPa.m 1/2, respectively. The proposed program builds upon the CERCOM studies to define the materials and processing parameters required to achieve optimum acicular grain growth and aspect ratio and define the requirements for the control of the interface bonding between acicular grains and the second phase. R-curve studies will be performed on the new SiC composites. Preliminary thermomechanical testing will be performced for selected materials at 1000 and 1200oC. Anticipated Benefits: It is anticipated that combinations of materials and process parameters will be identified which will yield new, reliable, tough, high strength SiC composites which can be used for high temperature structural applications such as components for internal combustion engines, thermal management structures, and other structures for use in extreme environments.