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Investigation On Microstructure And Stress Distribution Of The Al2O3-TiC/W18Cr4V Diffusion Bonding Interface

Posted on:2011-03-18Degree:DoctorType:Dissertation
Country:ChinaCandidate:X Q ShenFull Text:PDF
GTID:1101360305950561Subject:Materials Processing Engineering
Abstract/Summary:PDF Full Text Request
ceramic matrix composites composed of Al2O3 matrix and TiC reinforcing particles have been widely used as cutting tools because of their high strength, hardness and fracture toughness. If the diffusion joining of Al2O3-TiC ceramic matrix composites and W18Cr4V high speed steel can be realized, it will be have important significance to perfect the stress distribution in the components and enhance the use range of Al2O3-TiC composites.In this paper, Al2O3-TiC ceramic and W18Cr4V steel was bonded together by vacuum diffusion bonding technology. Al2O3-TiC/W18Cr4V diffusion bonding joint with sufficient combination interface can be obtained by controlling heating temperature 1080℃~1l60℃, holding time 30-60min, bonding pressure 10-15MPa and vacuum degree 1.33x10-4~1.33x10-5 Pa.The microstructure feature of the Al2O3-TiC/W18Cr4V interface was investigated by optical microscope and scanning electron microscopy (JXA-840). The influence of diffusion bonding parameters on interface combining state and microstructure of Al2O3-TiC/W18Cr4V interface was studied. With the increase of heating temperature and prolong of holding time, the transition zone width of the Al2O3-TiC/W18Cr4V interface broadened and the microhardness in transition zone improved. The phase components in shear fracture surface of Al2O3-TiC/W18Cr4V joint were determined and analyzed by XRD. The results indicated that the phases near Al2O3-TiC interface were Al2O3, TiC, TiO and Ti3Al. And Al2O3, TiC, Cu, CuTi, CuTi2, Fe3W3C and FeTi phases were near W18Cr4V interface.The division on the transition zone of Al2O3-TiC/W18Cr4V diffusion bonding interface was put forward to include Al2O3-TiC/Ti interface reaction layer, Cu-Ti solid solution layer, Ti/W18Cr4V interface reaction layer near Ti side and reaction layer near W18Cr4V side. The elements in the Al2O3-TiC/Ti interface reaction layer are Ti, Al and O. The elements in the Cu-Ti solid solution layer are Cu and Ti. The elements in the Ti/W18Cr4V interface reaction layer near Ti side are Ti and C. The elements in the reaction layer near W18Cr4V side are Ti, Fe, W and C. Ti exists in almost of all the reaction layers of Al2O3-TiC/W18Cr4V transition zone and coexists with many kinds of elements. It indicates that Ti was the main controlling element of interface reaction in Al2O3-TiC/W18Cr4V interface.The formation of Al2O3-TiC/W18Cr4V interface includes four stages. Firstly, Ti-Cu-Ti multi-interlayer melted into Cu-Ti eutectic liquid and spread throughout Al2O3-TiC/W18Cr4V interface. Secondly, Ti in the Cu-Ti eutectic liquid diffused into Al2O3-TiC and W18Cr4V and the width of Cu-Ti liquid broaden. Thirdly, the Cu-Ti liquid solidified and reaction layers in Al2O3-TiC and W18Cr4V interface formed. Lastly, the components in all reaction layers homogenized. The non-symmetry for the process of Al2O3-TiC/W18Cr4V diffusion bonding was studied. The reaction mechanism of Al2O3-TiC/W18Cr4V interface was studied and the results indicated that phase structures in the interface are Al2O3-TiC/TiC+Tl3Al+TiO/CuTi+CuTi2+TiC/TiC+FeTi/Fe3W3C+a-Fe/W 18Cr4V.The distribution of axial stress and shear stress in Al2O3-TiC/W18Cr4V diffusion bonding joint was studied using finite element method (FEM).The influences of bonding parameters, interlayer, sample size and shape on stress distribution were investigated. The calculated results indicated that the gradient of the axial stress and shear stress are great near the joint edge and are flat near the center. The maximum axial tensile stress located in Al2O3-TiC side near the joint edge. The maximum shear stress located in Ti/W18Cr4V interface near the joint edge. With the decrease of the bonding temperature and the improvement of bonding pressure, the axial tensile stresses decrease. With Ti-Cu-Ti interlayer instead of Ti interlayer, the axial stress and the shear stress both decrease. Improving the diameter of the sample and decreasing the thickness of W18Cr4V can decrease the axial tensile stress in the joint. The axial tensile stress in square sample is higher than that in round sample with equal area.The propagation paths of interface cracks in Al2O3-TiC/W18Cr4V joint include interface fracture and mixed fracture which had higher strength than interface fracture. The fracture mode can be controlled by controlling diffusion bonding parameters. The shear fracture of Al2O3-TiC/W18Cr4V joint was mostly cleavage fracture with obvious cleavage step. The fracture position mainly located at the interface near Al2O3-TiC. The fracture was mostly transgranular cleavage.The microstructure, interface formation mechanism, stress distribution and interface fracture of Al2O3-TiC/W18Cr4V diffusion bonding joint were studied in this paper. The studies can provide experimental basis and theory foundation for the wide application of Al2O3-TiC ceramic and research method for joining of Al2O3 and other metals.
Keywords/Search Tags:Al2O3-TiC ceramic matrix composites, diffusion bonding, microstructure, stress distribution, fracture
PDF Full Text Request
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