| Composite ceramics were paid more attention and application, due to their superior properties than the single composition. Al2O3-TiC composite ceramics have good application foreground in the field such as mechanism, metallurgy etc, for their high hardness, high wear resistance, high temperature resistance, corrosion resistance and antioxidant properties. Because it is difficult to be formed, with the poor toughness and impact resistance, Al2O3-TiC composite ceramics are bonded with the metal materials into composite components, it is one of the effective ways to get better performance. But it is difficult to obtain the interface with continuous performance between the ceramics and metals. Heat stress is produced in the ceramics-metal bonded joints, leading to welding cracks. Therefore, the welding research between Al2O3-TiC composite ceramics and metal materials is necessary.Transient liquid phase diffusion bonding of Al2O3-TiC composite ceramics to Q235low carbon steel or1Cr18Ni9Ti stainless steel was researched under vacuum, by using Ti/Cu/Ti multi-interlayer. The appropriate diffusion bonding parameters of the Al2O3-TiC/Q235steel is heating temperature of1120～1160℃, holding time30to60min, welding pressure10to15MPa, and shear strength of116-143MPa was achieved. The appropriate diffusion bonding parameters of Al2O3-TiC/18-8steel is heating temperature of1110～1150℃, holding time30to60min, welding pressure10-15MPa, and shear strength of101～125MPa was achieved. Scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray diffraction (XRD) is used to study microstructure, element distribution, phase structure and shear fracture mechanism of Al2O3-TiC/steel diffusion bonding joint to establish relations among welding parameters, microstructure of interfacial transition zone, the micro-cracks and the fracture mechanism, to reveal its inherent regularity.The interfacial transition zone is formed between Al2O3-TiC and steel, with different microstructure characteristics from the two substrates. The interfacial transition zone is composed of two regions, the interlayer diffusion reaction zone and the steel side diffusion reaction region. The interlayer diffusion reaction zone is produced by the elements between Ti/Cu/Ti and the both substrates diffusing into it; the diffusion reaction zone on the steel side locates in the steel substrate, formed by the elements (mainly Ti) of interlayer diffusing into the steel substrate for a certain distance, reacting with the elements in steel and changing elements distribution in the steel substrate, it is different from steel for microstructure.Analysis has been carried on elements distribution and phase structure characteristics of Al2O3-TiC/steel diffusion bonding joints. The results show that, oxides of Ti (TiO) and complex oxides (Cu3Ti3O, Fe3Ti3O and Ni3Ti3O) were formed close to the interface of Al2O3-TiC ceramic due to interdiffusion between Ti, Cu and the both substrate elements. The phase of TiO with metallic properties is produced by reaction of Ti with Al2O3, which can wet Al2O3-TiC ceramics. Complex oxides of Cu3Ti3O, Fe3Ti3O and Ni3Ti3O, formed from reaction of Cu, Fe and Ni with Ti and TiO phase, also has metallic properties and furthermore wet Al2O3-TiC ceramics, which promoting to achieve firm metallurgical joining of Al2O3-TiC and steel. Residual stress in the joints is relieved by residual Cu as solid solution in the interlayer reaction zone. Fe-Ti brittle intermetallic compounds in the interfacial transition zone are easy to cause a crack.Shear fracture in the diffusion welding joints of dissimilar materials between Al2O3-TiC and steel, performs for three fracture paths of interfacial fracture, mixed fracture and ceramic fracture. The strength is higher for mixed fracture than interfacial fracture and ceramic fracture. When fracture occurred in ceramics for the diffusion welding joints of dissimilar materials between Al2O3-TiC and steel, it presents as fracture morphology of mirror region, mist region and hackle region which is a typical brittle fracture. When mixed fracture occurs in the joint of Al2O3-TiC/Q235steel, the crack originates in the Cu-Ti intermetallic compound layer in the interlayer reaction zone, then propagates into Al2O3-TiC ceramic, and finally fractures. When mixed fracture occurs in the joint of Al2O3-TiC/18-8steel, fracture oriented to Ti-Fe intermetallic layer in the interlayer tearing which is close to the Al2O3-TiC ceramic.This article concentrates on the microstructure and shear fracture mechanism of the diffusion welded joint of Al2O3-TiC composite ceramic and steel. The research provides experimental foundation and theoretical basis for the Al2O3-TiC composite ceramic application. The research has laid an important foundation for further research of ceramic composites welding research including Al2O3-TiC composite ceramics.
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