Fabrication And Properties Of ZrC-Mo Functionally Gradient Materials

In aerospace materials field,ultra-high temperature and huge temperature difference create severe thermal stress inside the components,which could not be simultaneously satisfied by individual materials.Comparing with homogenous materials,functionally graded materials(FGM)adjust the structure and components in a continuous or stepwise gradient along the thickness direction.The graded properties and performances could be formed correspondently and eliminate the obvious interface.The thermal stress induced by temperature difference would be well relieved because the abrupt interface is abolished by gradient elemental distribution,which could satisfy the requirement of harsh operating conditions.In this paper,the ultra-high temperature ceramic ZrC powder and high temperature metal Mo powder are selected as the raw materials of the research system.According to the linear / nonlinear composition law,three kinds of ZrC Mo Multilayer functional gradient materials with different gradient components are designed and prepared.Through various material analysis and testing methods,the phase,micro morphology,mechanical properties and thermal shock ablation resistance of ZrC Mo gradient materials were studied,characterized and analyzed.The main results are as follows:By investigating the sintering behavior of ZrC/Mo composites with different contents,integrated preparation of ZrC-Mo multilayer graded materials can be achieved at 1900 ℃.Structural analysis shows that ZrC-Mo FGM exhibit dense and homogeneous morphology with no visible defects such as cracks and pores.In the direction perpendicular to the thickness,the continuous change of components can be obviously observed,and there is no obvious interface between layers in the gradient material.The prepared ZrC-Mo gradient material has Macro gradient characteristics and micro continuity.The mechanical test results of compression resistance and three-point bending resistance show that the quadratic function nonlinear gradient material with high molybdenum content shows better mechanical properties.When the ceramic rich layer is used as the pressure bearing surface,its compressive strength and bending strength are 1187 MPa and 863 MPa respectively,which is much higher than the test results when the metal rich surface is used as the pressure bearing surface.The interlaminar crack propagation experiment of gradient materials shows that the cracks from different directions will deflect at the interlaminar interface.It is revealed that the crack propagation mode at the interlayer interface is fracture deflection and bridging,which leads to the extension of crack propagation path and the increase of fracture energy consumption,so as to improve the anti crack propagation ability of the material.The results show that ZrC Mo FGM has certain design advantages in mechanical properties.Thermal shock ablation test of oxyacetylene indicate that the ZrC-Mo FGM could better maintain integrity and avoid catastrophic damage comparing with the homogeneous ZrC/Mo composites.Gradient design establishes an effective structure and performance transition,which can alleviate the thermal stress caused by the difference of thermal expansion coefficient between ceramic materials and metal materials,and provides a new idea and method for the application of ultra-high temperature materials.