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

Ti(C,N)-based cermets is a kind of high performance tool materials, and it has wide perspective in application. So the research of Ti(C,N)-based cermets/metals welding is very important. At present it is difficult to obtain nice welding joints by common welding technology. In this paper, by vacuum brazing and high-frequency induction brazing, we achieved firmly joints of Ti(C,N)-based cermets to steel. The relationship among brazing technology, microstructures and properties of brazing joints were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray detector (EDS), and bending / shear strength tester.The microstructure and properties of Ti(C,N)-based cermets, methods and processes of welding between ceramics and steel , the development of ceramic and steel brazing technology have been critically overviewed in the first part of the dissertation. And the purpose and significance of the dissertation have been set forth.In this paper, on the basis of preliminary study of research group, by adjusting the composition of cermet, the vacuum sintering process and forming agent, Ti(C,N)-based cermets material(Ni content of 25%) with good performance was prepared . The cermet is the mother material of brzing to steel. The hardness of prepared Ti(C,N)-based cermets is 89～92 HRA and the transverse rupture strength is 1850～2200 MPa.Ti(C,N)-based cermets and steel are successfully brazed using Ag45CuZn filler metal by vacuum brazing. Excellent diffusion layer and mutual solution layer which exist between the welding base materials and the filler metal is the main reason of achieving firm brazed joints. The brazing temperature of 850℃, holding time of 15 min and the thickness of filler metal of 0.4 mm are a set of optimum technological parameters, under which the maximum shear strength of brazing joints, 145.2 MPa, is achieved. Interface formation process of Ti(C,N)-based cermet/Ag45CuZn/45 steel can be divided into the following stages.(1) brazing interface physical contact; (2) start melting of filler metal; (3) atomic diffusion and reaction layer began to grow; (4) (Fe,Ni) solid solution and (Cu,Ni) solid solution began to grow; (5)precipitation of Ag(s,s) and Cu(s,s). The final product of interface, at the side of steel, the layer of sosoloid is Cu(s,s) and (Fe, Ni) solid solution, the layer of filler metal is Ag(s,s), Cu(s,s) and Ag-Cu eutectic. At the side of cermet, the main reaction products is (Cu, Ni) solid solution. The layer of diffusion is made up of intermetallic compound and Cu(s,s), include Cu₅Zn₈ and (Cu, Ni) solid solution.Ti(C,N)-based cermets and 45 steel, lCrl8Ni9Ti stainess steel are successfully brazed using Ag45CuZn and Ag25CuZn filler metal by high frequency induction brazing. Induction brazing strength can meet the general engineering application requirements. The Ti(C,N) based cermets and 45 steel were brazed using B-Ag25CuZn filler material and QJ102 flux by induction brazing. When the brazing temperature is 950℃, the joint shear strength and bending strength are the maximum 147.6MPa and 103.2MPa, respectively. The Ti(C,N) based cermets and lCrl8Ni9Ti stainless steel were brazed using B-Ag25CuZn filler material and YJ-6 flux by induction brazing at 1000℃, the joint shear strength and bending strength are the maximum 119.3MPa and 59.2MPa, respectively. Compared with vacuum brazing, there are some advantages for induction brazing, such as small effect on the micro structure and property, high brazing efficiency, low product cost, difficult to form brittle intermediate phase.Cu-based multi-alloy filler material has good wettability on the motherland, as a result, high joint strength can be obtained by vacuum brazing Ti(C,N) based cermets and steel, with these filler materials, the joint shear strength is significantly higher than that with Ag-based brazing. The Ti(C,N) based cermets and 45 steel were brazed by vacuum brazing with the prepared filler material of Cu50NiCrMnSi alloy. When the brazing temperature is 1150℃, holding time of 15min, the joint shear strength is the maximum 275.7MPa. The Ti(C,N) based cermets and 1Cr18Ni9Ti stainless steel were connected by vacuum brazing with the prepared filler material of 1Cr18Ni9Ti45 alloy. When the holding time is 15min, brazing temperature of 1180℃, the joint shear strength is up to the average of 312.5MPa. The effect of brazing temperature on the properties of motherland is obvious with multi-alloy filler materials. With the increase of brazing temperature, the bending strength and hardness of motherland decrease slightly. When the brazing temperature. When the brazing temperature is over 1200℃, the properties of motherland sharp decreased. Therefore, Ti(C,N) based cermets and steel brazing temperature generally should not exceed 1200℃.Based on the above study, Ti(C,N)-based cermets welding tools were produced by induction brazing. The joint of the welding tool is firm and reliable, no sealing-off, cracking happened in the cutting process. The cutting performance and wear analysis of the Ti(C,N)-based cermets welding tools were conducted. The results shown that the cutting performance of Ti(C,N)-based cermets welding tools is superior to that of WC-Co cemented carbides welding tools (YG8 and YT15), the average life Ti(C,N)-based cermets welding tools is longer than that of WC-Co cemented carbides welding tools 1～2 times, and the failure mode of Ti(C,N)-based cermets welding tools were mainly broken plastic deformation wear and edge collapse.