Characteristics of reaction phases and effects of phases on mechanical properties of TiAl/42CrMo steel brazed joint

TiAl alloy and 42CrMo steel were vacuum brazed at temperature of 1 143-1 213 K for 120 s-1 500 s. The microstructure was analyzed using optical microscope,scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The thickness of the reaction layers was measured using an analysis software. The hardness of the reaction layers and phases was tested and compared using nano-indenter and traditional microhardness tester. In order to determine the weak phases or layers,the brazed joints were tensile tested with in-situ observation by SEM. The results show that TiC,AlCuTi,Ti₃Al and AlCu₂Ti phases had higher hardness but the Ag-based solid solution was much softer. The hardness values acquired using the nano-indenter were a little higher than those traditional microhardness tester. The tensile test results revealed that the Al-Cu-Ti ternary layer adjacent to the TiAl substrate was the weakest part. When subjected to tensile load,cracks easily occurred in this zone and resulted in failure.