Design And Fabrication Of TZ-3Y20A/Mo Multilayer Composite

Multilayer composite is a kind of obdurability material, which is imitative of the framework of shell in the nature. This kind composite is especially attractive because of its high toughness. The special superposition of the multiplayer composite makes the researcher can proceed designing the layers from the macro-aspect and synthesize the new composite with superior performance.The effect of the geometry parameter of the multiplayer composite on the stress intensity factor K1 has been analyzed by the MSC.Marc finite element method in the present dissertation. The results show that K1 decreases gradually with the increasing of the layer number when the thickness' ratio is fixed at 2. However, K1 increases at first, and then decreases gradually with the increasing of the thickness' ratio when the layer number is fixed at 31. The residual thermal stress of the TZ-3Y20A/Mo multiplayer composite has been forecasted by finite element method. The result illustrates that the residual thermal stress of the TZ-3Y20A/Mo multiplayer composite is less than the flexure strength of TZ-3Y20A ceramic at the same experimental condition when the layer number and layer thickness' ratio exceeds 27 and 2 respectively.The multilayer composite including a hard component TZ-3Y20A and a plastic soft component Mo has been fabricated by particle sedimentation method. By choosing appropriate settling parameters and dispersed medium, the TZ-3Y20A/Mo multilayer composite has been obtained via alternating deposition of TZ-3Y20A and Mo according to the design of individual layer thickness and layer thickness' ratio. Then the green sediment has been densified at 1773K under pressure of 20MPa in an Ar atmosphere furnace for an hour. The testing results of the flexure strength and fracture toughness of multilayer samples show that, the flexure strength of rectangular bars of samples achieves the maximum (737.1MPa) when the layer thickness of TZ-3Y20A is 200um and the layer thickness of Mo is 67um. The fracture toughness reaches the maximum (14.9MPa-m1/2) when thelayer thickness of TZ-3Y20A is 200m and the layer thickness of Mo is 80m, which increases 63 % compared to the monolithic TZ-3Y20A specimens. The microstmcture and crack propagation manner of the fracture specimens have been observed using Scanning Electron Microscopy (SEM) and optics microscope. The results indicate that the mechanisms to improve the toughness of the multipiayer composite include the crack deflection along the metal interfaces, the crack divarication and passivation, the ductile-phase bridging, stretched, sliding friction, pull-out and interface delamination.