Whisker composites processing

Table 5 SiC whisker composite processing and room temperature mechanical properties.

G. Pezzotti, et al., Processing and Mechanical Properties of Dense Si3N4-SiC-Whisker Composites without Sintering Aids, J. Am. Ceram. Soc., 72[8], 1461-1464 (1989). 

With the development of some composite materials and the commercial success of some of these products, the demand for whiskers has increased. Numerous companies experimented with different whisker growth processes over the years and several patents have been issued in the area. At the present time, commercial sale of whiskers is limited to a few companies in the world with SiC whiskers the most predominant. In addition, whiskers ofTiC.TiN, Al203,mullite, Si3N4, and B4C have also been produced and studied. However, SiC remains the whisker of most interest and commercial success. 

Dufresne A, Cavaille JY, Helbert W (1997) Thermoplastic nanocomposites filled with wheat straw cellulose whiskers. Part II effect of processing and modeling. Polym Compos 18 199 Dufresne A, Kellerhals MB, Witholt B (1999) Transcrystallization in Mcl-PHAs/cellulose whiskers composites. Macromolecules 32 7396-7401 Dufresne A, Dupeyre D, Vignon MR (2000) Cellulose microfibrils from potato tuber cells processing and characterization of starch-cellulose microfibril composites. J Appl Polym Sci 76 2080-2092... 

The purpose of this work is to continue the investigation of the turbomilling process as a means of improved processing for SiC whisker-ceramic matrix composites and dispersion of matrix powders prior to composite processing. 

Figure 13 Development of a process for complex near net shape part fabrication (SisNa - 30 v/o SiC whisker composite—Forming injection molding Densification hot isostatic pressing)...

In addition, different coupling agents have different effects when calcium carbonate whiskers are processed. The impact strength of the composites filled by stearic acid modified calcium carbonate whiskers is better than that of the composite material filled by titanate coupling agent modified whiskers. ... 

Crack deflection models show it depends substantially on particulate geometry, Figure 3, with rod shaped particles being most desired. This mechanism, therefore, clearly, overlaps with that of short fibers. Effects of variation In particle dimensions and of spaclal distribution are not precisely known. Agglomeration, of particles or short fibers Is clearly detrimental and thus one of the particular challenges of processing whisker composites 1s to prevent or eliminate agglomerates. 

Limited work on HIPIng whisker composites has begun. Thus, Becher and Tleges HIPed (at 1600 C) some of the AI2O3-SIC whisker composites they sintered, but such efforts are limited by the limited levels of whiskers In composites that can be sintered to closed porosity for HIPIng. However, as discussed later, these restrictions do not necessarily apply to reaction processed matrices. 

Another use for CVD and processing of ceramic fiber or whisker composites is to coat the fibers or whiskers. Thus, for example, Rice and co11eagues 2 177) demonstrated significant benefits of coating ceramic... 

Metal-Matrix Composites. A metal-matrix composite (MMC) is comprised of a metal ahoy, less than 50% by volume that is reinforced by one or more constituents with a significantly higher elastic modulus. Reinforcement materials include carbides, oxides, graphite, borides, intermetahics or even polymeric products. These materials can be used in the form of whiskers, continuous or discontinuous fibers, or particles. Matrices can be made from metal ahoys of Mg, Al, Ti, Cu, Ni or Fe. In addition, intermetahic compounds such as titanium and nickel aluminides, Ti Al and Ni Al, respectively, are also used as a matrix material (58,59). P/M MMC can be formed by a variety of full-density hot consolidation processes, including hot pressing, hot isostatic pressing, extmsion, or forging. 

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