Integration Technologies for Silicon Carbide-BasedCeramics for Micro-Electro-Mechanical Systems-LeanDirect Injector Fuel Injector Applications

Advanced joining approaches are critically needed for the fabrication and integration of silicon carbide-based micro-electro-mechanical systems lean direct fuel injectors for jet engines. Diffusion bonding of silicon carbide with titanium interlayers offers advantages such as uniform application/surface coverage and no flow of the interlayer or the reaction formed phases during joint processing. The resulting joints were uniform, stable, leak free, and had high strength. Titanium interlayers with 10 and 20 lm thicknesses were obtained from physical vapor deposition (PVD) and pure metallic foils. The effects of the interlayer type and thickness and processing time on the resultant microstructures were investigated. The joints and their reaction-formed phases were analyzed with electron microprobe analysis and scanning electron microscopy coupled with energy-dispersive spectroscopy, ultra-sonic immersion nondestructive evaluation method, and transmission electron microscopy. For the physical vapor deposition Ti interlayers, the 10 lm coating gave the best results yielding a joint that did not have intermediate phases or microcracking. For the Ti foil interlayers, the joint processed with a 4 h-hold time had more stable phases and less microcracking than those with 1 and 2 h-hold times. The average tensile strength of the diffusion bonds was 14.2 MPa which was 2–3 times higher than the application requirements. The diffusion bonding approach was shown to meet the requirements for SiC-based fuel injector fabrication.