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Solid-state diffusion bonding of carbon-carbon (C-C) composites by using boride and carbide interlayers has been investigated. The interlayer materials used in this study were single-phase borides (TiB, or ZrB,), eutectic mixtures of borides and carbides (ZrB, + ZrC or TiB, + B,C), and mixtures of TiB, + S i c + B4C produced in situ by chemical reactions between B,C, Ti, and Si or between TIC, Si, and B. The double-notch shear strengths of the joints produced by solid-state reaction sintering of B,C + Ti + Si interlayers were much higher than those of joints produced with other interlayers. The maximum strength was achieved for C-C specimens bonded at 2000°C with a 2:l:l mole ratio of Ti, Si, and B,C powders. The reaction products identified in the interlayers, after joining, were TiB,, Sic, and Tic. The joint shear strength increased with the test temperature, from 8.99 MPa at room temperature to an average value of 14.51 MPa at 2000°C.

The feasibility of joining of 3-D carbon-carbon (C-C) comto produce strong joints by the method of graphite formation posites by using B and TiSi 2 interlayers has been investi-(which involves the formation of a metal carbide interlayer gated. The optimum temperature for joining with a B followed by its decomposition at elevated temperatures into the interlayer was determined to be about 1995؇C and that for metal and carbon and the subsequent evaporation of the metal) joining with a TiSi 2 interlayer was about 1490؇C. The shear have been less successful. 6 strengths of the joints made at these optimum temperaturesThe objective of the present work was to study the joining of were found to increase with the shear testing temperature C-C composites by using B and TiSi 2 interlayers. The effects up to a point, followed by a decrease at higher temperatures.of the joining process variables and the test temperature on For C-C specimens bonded at 1995؇C with a B interlayer, the strength and microstructural features of the joints have the maximum joint shear strength (average value 18.35 been investigated. MPa) was observed at the test temperature of 1660؇C. The shear strength of joints produced with a TiSi 2 interlayer II. Experimental Procedure showed a maximum at the test temperature of 1164؇C, with an average value of 34.41 MPa. The B interlayers reacted(1) Materials with C-C composite pieces during joining, and the product Rectangular C-C specimens (approximately 25.4 mm ϫ of reaction was identified as B 4 C. In specimens joined with 12.7 mm ϫ 6.3 mm thick) were cut from larger pieces of 3-D TiSi 2 interlayers, the reaction between TiSi 2 and C did not C-C composite material supplied by Lockheed Missiles and go to completion, and the bond interlayer contained TiC, Space Co. The specimens were machined in such a way that the SiC, and TiSi 2 .fiber planes were along the three rectangular directions and at least one 25.4 mm ϫ 12.7 mm plane coincided with the plane I. Introduction containing x-and y-direction fibers. These planes were used as the faying (joining) surfaces in all the specimens.C ARBON-CARBON (C-C) composites are attractive as candi-The TiSi 2 , amorphous B, and crystalline B powders, purdate structural materials for high-temperature aerospace chased from commercial sources, were, respectively, 99.4%, applications. This is because of their low density and high 99.0%, and 99.5% pure. Their particle sizes were 1-5 m, strength at elevated temperatures. Currently, these materials are Ͻ1 m, and Ϫ100 to ϩ200 mesh (ϳ75Ϫ125 m), respecused for the nose and leading edges of the wings of space tively. Characterization of the powders by X-ray diffraction shuttles, in turbine engine components such as combustor and revealed that the crystalline B was orthorhombic boron and that augmenter nozzles, for brakes and clutches in Formula I racing the TiSi 2 powder contained some free Si and possibly also some cars, etc. The applications of C-C composites are expected to TiSi. The X-ray diffraction pattern for the TiSi 2 powde...