Processing of Metal Matrix Composites with Controlled Microstructures

Conventional composite processing techniques are presently unable to fabricate unidirectional fiber reinforced composites based on small diameter fibers, for example, ~5-20 um in diameter. The primary problem is one of infiltration of the matrix in between the fibers and maintaining a reasonably constant fiber spacing. An innovative MMC processing technique is proposed wherein, starting with a ceramic fiber tow, each fiber would be spread and individually coated with the matrix material by a plasma-assisted sputtering process. The continuous coated fiber can then be utilized in a variety of ways, such as fiber lay-up for uniaxial panels or weaving in 2 or 3 dimensional architecture, followed by hot consolidation to obtain advanced composites with desired fiber orientation. Such a composite processing technique is also amenable to tailoring of the fiber-matrix interface by the addition of a very thin coat of metals such as Cr or Ti (which improve adhesion of the matrix to the fiber) prior to deposition of the matrix in a single step. Further, the fiber volume fraction within the matrix can be varied by varying the thickness of the coating. By coating all the fibers to a given thickness, an uniform fiber spacing can be obtained in a hot-consolidated state. This composite processing technique is also flexible enough to accommodate a starting compliant/compensating layer, if necessary, to improve the thermal cycling performance of these composites (especially those based on relatively brittle matrices).