Process And Mechanism Research On Laser Inducing Self-propagating Joining Between TiAl And C_f/Al

Self-propagating high-temperature synthesis joining was applied to join TiAlintermetallic and C_f/Al composites, to maintain the joining requirements in this study.Proper interlayer was obtained according to materials’ properties and theoretical analyses.Thermal analysis of interlayer’s self-propagating high-temperature synthesis reaction andjoining process, the microstructure of the joint achieved through laser inducing, and theinfluence of parameters on joining quality and interfacial reaction were investigated bymeans of scanning electron microscope (SEM), energy disperse spectroscopy (EDS),X-ray diffraction (XRD), differential thermal analysis (DTA) and strength test. Finally,forming mechanism of the joint was explained.Self-propagating high-temperature synthesis joining method was considered to bethe best way to join TiAl intermetallic and C_f/Al composites. Ni-Al powders interlayerwas chosen and adiabatic temperature of Ni-Al interlayer was calculated base on thethermodynamics and the interlayer design principles. By the mean of differential thermalanalysis, theoretical ignition temperature was determined to be640℃. Heat transfer issueof interlayer combustion and SHS joining process was also studied. The results shownthat, actual ignition temperature of Ni-Al interlayer was affected by specific surface area,and larger specific surface area caused the rising of ignition temperature. The heatquantity loss of unit area through heat conduction was larger than thermal radiation. Theenlargement of heat rate could slow down the heat loss of interlayer in the heatingprocess, which played a positive role of reducing interlayer ignition temperature. Addingthermal insulation materials between the base metal and fixture could make the heatmaximize for warming base metal and near interlayer, and promote the propagation ofcombustion wave propagation.TiAl intermetallic and C_f/Al composites were joined through the igniting theinterlayer by laser, and defects emerged in the joint achieved with Ni-Al interlayer.Ni-Al-Ti interlayer could decrease the defects and get perfect joint. The typical jointmicrostructure of the joint was: TiAl/γ/Ni3Al+NiAl residual phase at hightemperature/NiAl+Al rich-γ/Ni3Al+NiAl residual phase at high temperature/Ni2Al3/NiAl3/C_f/Al+NiAl3/C_f/Al. Increasing the content of Ti-Al system in the interlayer made thereaction product change from NiAl to NiAl+Al rich-γ, and a rising of joint density. Whenthe content of Ti-Al system was0.1, joint shear strength had the maximum of24.12MPa.Excessive or insufficient Ti-Al system would all increase the defects, and decrease thejoint shear strength. Preforming pressure’s increasing made the rising of joint density andjoint shear strength. Joining pressure also increased the joint density and decreased the interface tensile stress, which reduced the crack trend and played a role in promoting thejoint shear strength. However, when the joining pressure was excessive, flaws emerged inthe interlayer product and C_f/Al composites fractured, the joint strength decreased.Through the quenching experiment, the combustion mechanism of Ni-Al-Tiinterlayer and the forming mechanism of laser inducing self-propagatinghigh-temperature synthesis joining between TiAl and C_f/Al was investigated. when thejoining started, the interlayer was ignited by laser beam and produced NiAl+Al rich-γ,then a combustion wave was formed. Combustion wave propagated, local part of basemetals melted and formed NiAl3, Ni2Al3, γ-Ni0.35Al0.30Ti0.35layers. When the combustionwave propagated to the end, self-propagating high-temperature synthesis reactionfinished. The interlayer cooled to room temperature, interface reaction stopped and thejoint formed.