Microstructure and Properties of TiAl Alloy Joints Brazed with a Novel Ti-based Filler
TiH2-65Ni and TiB2 composite powder filler prepared by mechanical milling was employed to vacuum braze Ti-47Al-2Nb-2Cr-0.15B(at%)alloy under the brazing temperature of 1190-1250℃for 10 min.The interfacial microstructure of the TiAl alloy brazed joints and the effect of the brazing temperature on the microstructure and the room temperature shear strength of the joint were investigated.It is found that the TiAl brazed joint is divided into three layers and it mainly consists of α2-Ti3Al,τ3-Al3NiTi2 and TiB phases.With the increase of the brazing temperature,the formed continuous α2-Ti3Al layer barrier layer is broken,the dissolution of the filler element into the TiAl substrate and the the dissolution of the TiAl substrate are increased,which results in an increase of brazing seam thickness.With the brazing temperature increasing,the shear strength of the joint increases firstly and then decreases.When the brazing temperature is 1230℃,the aspect ratio and quantity of the TiB whiskers with good thermodynamic compatibility to the brazing seam matrix increase significantly,the microstructure of the layer Ⅲ is refined and the phase distribution is uniformly distributed.The joint presents the maximum shear strength of 332.87 MPa and it brittlely fractures in layer Ⅱ which mainly consists of τ3-Al3NiTi2 in quasi-cleavage mode.
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