Study On Mechanism Of Self Propagating Reaction Assisted Diffusion Bonding Of TiAl To TiC Cermet

The joining between ceramic and metal always serves as one of the hot and difficult issues in the joining fields. It is difficult for the traditional joining method to achieve the sound joining between ceramic and metal. The investigation about self-propagating reaction assisted diffusion bonding (SADF) of TiAl to TiC cermt was carried out in this study. The experimental method was combined with theoretical method. The optimal design of the interlayer was performed and the analysis of the critical dimension in the joint for the powder interlayer was completed. The interfacial microstructure and microstructural evolution for this special joining method was systematically analyzed. The effect of the parameters on the joining quality and interfacial reaction was investigated.The optimal design of the interlayer, which consists of the selection of the interlayer element and interlayer composition, is the basic target for the SADF. The effect of the interlayer composition and preheating temperature on the adiabatic temperature was studied. The powder interlayer composition for joining of TiAl to TiC cermet was determined as Ti(17-47%),Al(13-25%),C(4-12%),Ni(28-54%)(wt.%). The analysis for the Ti-Al-C-Ni system showed that Ti-C reaction was ignited by Al-Ni reaction. The apparent activation energy was calculated by the measurement and analysis of combustion velocity. The analysis of reaction products confirmed the reaction mechanism. The quenching of self-propagating reaction in the interlayer was generated by the cold plate effect. The critical combustion temperature and velocity were determined using the apparent activation energy. The critical dimension of interlayer and substrate was determined considering the critical heat loss.The SADF of TiAl to TiC cermet was achieved using Ti-Al-C-Ni powder interlayer. The typical microstructure was: TiAl/TiAl3/(Al-Ni)+TiC/Ni-rich/TiC-Ni. The effect of the parameters on the joining process using powder interlayer was studied. The density of joint using assisted electromagnetic field was lower than using assisted electronic field. However, the crack tended to generate in the joint with assisted electronic field. The effect of powder granularity, joining pressure and post-heating treatment was analyzed. The optimal joining parameter was 500MPa pressure for compact, 40MPa joining pressure, 1050℃joining temperature, 60min holding time and assisted electronic field. The tensile strength of 128.1MPa was achieved with equal atomic percent of TiAlCNi interlayer. The fracture analysis showed that the main reason for the poor joining properties was the low density in the products.The microstructure and joining mechanism for self-propagating reaction assisted brazing was investigated. The content of filler metal was determined considering the thermal and porosity analysis in the products. The joining experiment for TiAl to TiC cermet was carried out. The filler metal was molten by the heat released in the interlayer. The molten filler metal filled in the porosity of reaction products and the joining properties was increased. The heating temperature of high-temperature filler metal was decreased to the ignited temperature of the self-propagating reaction in the interlayer. The joint could be applied in high-temperature condition. The further investigation was helpful for the utilization of self-propagating assisted joining.The SADF of TiAl to TiC cermet was accomplished using Al/Ni multilayer. No porosity was observed in the joint using Al/Ni multilayer. The typical microstructure was: TiAl/ TiAl+Ti3Al+NiAl2Ti /NiAl2Ti/Ni2AlTi/Ni3(AlTi)/AlNi/ AlNi3/TiC-Ni. The nanoindentation and strength test shows that the AlNi3 layer was the main reason affected the joining properties. The reaction characteristic, reaction products and interfacial microstructure using nano multilayer was compared with using micron multilayer. The better joining quality was achieved using nano multilayer. The temperature distribution for joining of TiAl to TiC cermet using nano multilayer was investigated. The investigation about quantitative heat effect of interlayer on the substrate generated the theoretical basement for the wide application of the multilayer in the joining fields.