Microstructure Design And Grinding Behavior Of The LaPO₄/Al₂O₃ Machinable Ceramics

The LaPO₄ coatedα-Al₂O₃ powders are successfully synthesized by the heterogeneous precipitation method, which changes the status of large amount of LaPO₄, uneven distribution of LaPO₄ and serious degradation of the mechanical properties. By the microstructure design, weak interfacial bond is introduced at the LaPO₄/Al₂O₃ interface, the requested amount of LaPO₄ has decreased to some extent and the overall performance of the materials is improved dramatically. The grinding damages and removal mechanisms of composite ceramics are investigated after being ground, which can provide beneficial proof for the preparation and processing of high-performance ceramic materials.The coated powders are characterized through X- Ray diffraction (XRD) and transmission electron microscopy (TEM) respectively. LaPO₄/Al₂O₃ machinable ceramics are prepared using the coated powders with 20% LaPO₄. The phase composition and fracture morphology of them are detected by XRD and scanning electron microscopy (SEM). It shows that the coated powders and composite ceramics consist of onlyα-Al₂O₃ and monoclinic LaPO₄, indicating their good chemical stability even at high temperature. LaPO₄ wrap aroundα-Al₂O₃ particles equably, forming distinct core-shell structure. This microstructure design can make the two phases of the composite ceramics combining more closely and distributing more uniformly, thereby reduces the content of soft phase LaPO₄ and improves the mechanical properties and machinability of composite ceramics. Besides, the fracture mode of composite ceramics changes dramatically. There are many dissociation of layered LaPO₄ when the intergranular fracture occurs at the same time. The binding energy of LaPO₄ itself is as small as the weak interface of it. This provides directions on grinding removal mechanisms of LaPO₄/Al₂O₃ machinable ceramics.In this paper the LaPO₄/Al₂O₃ machinable ceramics are ground by single stroke grinding method, grinding surface and side are observed with optical microscopy and SEM. Surface broken damage and surface/subsurface micro-cracks appear after ground, leaving about 15μm effective grinding damage layer. Grinding surface/subsurface micro-cracks damage model are established according to the internal structure characteristics of ceramics. Effective crack depth DC is made as evaluation index of grinding surface/subsurface crack damage. Combined with the surface morphology of plastic deformation and brittle fracture, using micro mechanical mechanism, clarifies the process and mechanisms of plastic deformation and brittle fracture. It is investigated that how the microstructure affects the generation and expansion of micro-cracks, and eventually decides to the grinding removal mechanism of composite ceramics. Finally, the mechanical properties of materials are tested after grinding. The results show that the mechanical properties of composite ceramics preparated by coated powers have been greatly improved than those of used traditional mechanical mixing method. However, the grinding damage on the material properties is still evident. As the grinding feed increased, the mechanical properties decrease about 10% to 20%, and find that the mechanical properties loss will become gentle when the grinding feed increases to a certain extent.