| Titanium diboride (1182) has excellent properties, as high melting point, high hardness, corrosion stability, oxidation resistance , high bending strength, wear-resisting and so on. It also has excellent thermal and electricity conductivities. So that it has been used widely in areas of high-temperature structure materials, wear-resisting materials, corrosion stability materials and electric materials. But it is difficult to meet the need under special and harsh condition because of its intrinsic brittleness. It is arising much more interest of research in the preparation of high-temperature resistant and corrosion stability materials with the welding joined ceramics and metals. Because TiB2 has strong covalent bond, high melting point and chemical inertia so that it is hard to weld TiB2-metal with traditional welding technics such as diffusion welding and brazing. However, the process of combustion reaction seems to offer just the sort of innovative new method for welding of ceramics and metals. The combustion reaction offers many attractive features, some of which are quite unusual if not unique. The high temperatures needed to bond refractory materials can be achieved through internal heat generation rather than from external sources.Combustion reaction welding technic was used to weld TiBi and metals (Fe and Mo) in the thesis. The principle of the selection of intermedium was suggested. Ti+B+Fe and Ti+B+Mo were selected respectively as the intermediums of the two systems. The interfaces of the two systems were microcosmic observed and the residual stresses were analyzed. The bending strength and shear strength of the TiB2/Mo system were measured too.To the TiB2/Fe system, the intermediums were Ti+B+60wt%Fe and Ti+B+80wt%Fe, welding temperature was 1000, pressure was 30GPa. From the X-ray diffraction (XRD) analysis, it was concluded that when the content of Fe of the intermedium was 60wt%, the combustion reaction product was TiB2 when the content of Fe of the intermedium was 80wt%, there were TiB2 and TiBo The result of Electron Probe Microscope Analysis (EPMA) showed that there was diffusion of elements and transition layers in theinterfaces, so that TiB2 and Fe were welded together. And the joint with 80wt% Fe in the intermedium was better than the other. Temperature affects the joint, the intermediums change the state from solid to liquid when temperature rises from 800 to 1000, and the liquid results in the joint. The residual stress was analyzed by XRD, the results showed that the residual was tensile stress; the largest value was 206 MPa.To the TiB2/Mo , the intermediums were Ti+B+20wt%Mo, Ti+B+40wt%Mo, Ti+B+60wt%Mo and Ti+B+80wt%Mo. Combustion reaction products were analyzed by XRD. The results showed that the main products were TiB2 and MoB, when the content of Mo in the intermedium were 60wt% and 80wt%, the Mo would leave over. The results of EPMA showed that there were diffusion of elements and transition layers in the interfaces for all different intermediums, TiB2 and Mo could be welded by combustion reaction at 1500 and 30GPa. The micros hardness showed that the hardness of intermedium lies between the metal Mo and the TiB2 ceramics. From metal Mo layer to TiB2 ceramics, the hardness changes gradually increased. The residual stress was tensile stress, the largest value was 180-200 MPa.Temperature strongly affected the properties of the samples. The bending strength and shear strength were examined of the TiB2/Mo welded under 1500 , 1550 and 1600. The results showed that the bending strength and shear strength were different at different temperature even with the same compositions of the intermediums. And at the same temperature, the properties were different due to the different compositions of the intermediums. With the increasing of Mo content in the intermediums, the bending strength was enhanced. The largest value was the sample welded with 80wt% Mo in the intermedium at 1500. The shear strength increased with the increasing of the content of Mo in the intermedium at 1550, w... |
