Mechanical milling of Ti–Ni–Si filler metal for brazing TiAl intermetallics

The Ti–Ni–Si filler metal was manufactured by mechanical milling of TiH2, Ni and Si powder mixture. The microstructure of the filler metal and TiAl brazed joint was analyzed by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The effect of milling time on the brazing powder was investigated. It was found that NiSi phase formed when the milling time exceeded 120 min. The typical microstructure of the TiAl brazed joint using Ti–Ni–Si filler metal was TiAl/Ti3Al/TiAlNi2/Ti3Al + Ti5Si3/TiAlNi2/Ti3Al/TiAl. The effect of Si on the microstructure was investigated and the result suggested that Si addition resulted in the aggregation of Ti and formation of Ti3Al phase in the middle of joint. The optimal parameters were brazing temperature of 1140 °C and holding time of 30 min. The fracture was brittle and propagated between the TiAlNi2 layer and Ti3Al + Ti5Si3 layer.