Research On Process And Mechanism Of Self-propagating Reaction Joining Between C/C Composites And Tial Alloy

C/C composites and TiAl alloy posses broad application prospects, due to their lowdensity and excellent performance. In this study, a simple, efficient and energy-savingjoining method applied to join the two high-temperature structure materials, calledself-propagating reaction joining was systematically studied. Theoretical analysiscombined with experimental methods were carried out to optimize the composition of theinterlayer. In addition, the reaction mechanism of the interlayer was revealed. Theinterfacial microstructure, microstructure evolution and shear strength of the joints madeby self-propagating reaction joining were systematically analyzed by means of opticalscanning electron microscope(SEM) coupled with energy dispersive spectrometer (EDS),X-ray diffractometer(XRD), and strength tests. The effect of the process parameters onthe interfacial microstructure and the joining quality was investigated as well.Taking the materials to be joined into account, Ti-Al and Ti-Al-C interlayer werechosen as the joining media. Thermodynamic and kinetic analysis were conducted tocalculate the adiabatic temperature(Tad) of the interlayer, and the relationship betweenpreheating temperature and Tadwas also studied. Based on the results of theoreticalcalculations, ten Ti-Al-C interlayers with different composition for self-progatingreaction joining were determined. Besides, the apparent activation energy was calculated.Combined with differential thermal analysis(DTA), combustion frontquenching(CFQ) test and the analysis of products sythesised by self-propagation reaction,the reaction mechanism of the interlayer was revealed. The analysis for the Ti-Al-Csystem showed that the self-propagating reaction started with melting of the Al particlesin the system，ignited by Ti-Al reaction，and the reaction proceeded in dissolution-precipitation mechanism. Then, Ti-C reaction was induced. On this basis，self-propagating synthesis of Ti-Al intermetallics and their simultaneous joining to C/Ccomposites was studied. The elemental mutual diffusion was found at the interfacebetween Ti-Al-C interlayer and C/C composites.According to the simultaneous joining of Ti-Al-C interlayer to C/C composites, andthe weldability analysis, the indirect self-propagating reaction joining of C/C compositesand TiAl alloy was realized using Ti-Al-C interlayer and the optimized Ag-Cu-Ti brazingfiller metals. Relying on the reaction heat released by self-propagating synthesis of theinterlayer, Ag-Cu-Ti filler could able to melt below its melting point. Molten fillershowed good wetting and spreading at C/C composites surface and well infiltrated intothe whole Ti-Al-C interlayer. A TiAl2/TiAl3reaction layer was found on the side of TiAl,while the reaction product TiC formed at the C/C composites surface. Reaction zone in the middle formed owing to the interactions between the Ag-Cu-Ti filler and syntheticproducts of Ti-Al-C interlayer, including a ring structure with unreacted Ti as the core,small pieces of TiAl3, and widely dispersed TiC.The thickness and composition of Ti-Al-C interlayer had an obvious impact on themicrostructure and mechanical properties of the joints. Better interfacial bonding couldbe obtained using thinner interlayer on the premise of meeting the requirement forself-propagating reaction joining. With the increase of the heat release in the range ofselected interlayer, joining strength increased gradually. The maximum shear strength ofthe joints achieved under the optimum process conditions was17.59MPa using theTi35Al45C20interlayer, and the fracture took place at the C/C composites surface.