The Research On Vacuum Brazing Ti(C,N)-based Cermets To Steel And Microstructure Of The Joints

Ti(C,N)-based cermets are a kind of particle reinforced composite, which have widely been used as cutting tools, wear-resistance parts and seal devices, due to their high high-temperature hardness, excellent wear resistance and corrosion resistance, very low friction coefficient to steel, etc.. However, when subjected to vibration and impact, Ti(C,N)-based cermets can break because of relative low strengthness and toughness. Besides, it is not suitable to produce large and complex structure parts. In order to widen application of Ti(C,N)-based cermets, the research on Ti(C,N)-based cermets bonding to steel plays a important role. In this paper, sound joints were achieved using Cu-based alloy filler welding of Ti(C,N)-based cermets to steel. Effect of brazing temperature and holding time on interface structure and mechanical properties of joints were performed by X-ray diffraction(XRD), scanning electron microscope(SEM), energy dispersive spectrometer(EDS) and shear strength tester.Ti(C,N)-based cermets holding superior performance was fabricated by composition adjustment and process optimization using powder metallurgy route. Transverse rupture strength(TRS) was 1800-2000 MPa and hardness was 89-91 HRA. Alloy foil was prepared with the thickness of 0.3 mm using proper constituent by powder metallurgy method.Sound joints were obtained by vacuum brazing of Ti(C,N)-based cermets to W9Mo3Cr4 V steel using Cu-Ag-Ti alloy filler. Maximum shear strength of 260 MPa was achieved at 910 °C for 30 min and with the thickness 0.3 mm of alloy filler. At the same time, the fracture of this joint was located in alloy filler and fracture morphology had visible plastic deformation, which belonged to toughness fracture. In addition, interface structure of joint was Cu-Ni-Ti(s.s.)/Cu(s.s.)+Ag(s.s.)+Ti2Cu3 compound+TiCu4 compound/Ti(s.s.)+TiFe compound from Ti(C,N)-based cermets to steel side.For the sake of decrement of the cost of alloy filler, Ti(C,N)-based cermets and steel were successfully brazed using Ag-free multielement Cu-Mn-Ni-Cr-Si alloy filler by vacuum brazing. The joint shear strength was obviously higher than that containing Ag alloy filler. When the brazing temperature was 1030 °C, holding time was 20 min and the thickness of alloy filler was 0.3 mm, the maximum shear strength was achieved, 301.5 MPa. Meanwhile, the fracture of this joint situated in alloy filler and belonged to toughness fracture. The interface structure of the joint was Ti(C,N)-based cermet/Cu(s.s.)/Cr(s.s.)+Ti(s.s.)/(Fe,Ni)(s.s.)/steel from Ti(C,N)-based cermets to steel side. The formation process of the joint interface can be divided into three stages. In the first stage, the interface between base metal and alloy filler can be fully contacted due to the melting of Cu-based alloy filler. In the second stage, counter-diffusion was occurred between base metal and alloy filler. In the third stage, the interface between Ti(C,N)-based cermets and alloy filler formed Cu(s.s.) and the interface between alloy filler and formed(Fe,Ni)(s.s.). Besides, Ti(s.s.) and Cr(s.s.) were formed in alloy filler.