New Processes,Microstructures And Properties Of Zirconia Ceramic Materials

Zirconia ceramics,known as ceramic steel,are potential materials for medical cutting tools.3mol.%Yttria-stabilised tetragonal zirconia polycrystalline ceramics?3Y-TZP?has been widely studied and applied due to its ideal combination of strength and toughness.Compared with the commonly used stainless steel materials,the application of zirconia ceramic in medical drill has the following advantages:Excellent biocompatibility;Good corrosion resistance,suitable for complex surgical environment;High smoothness,not easy to be polluted;High hardness and good hole forming property;Low thermal conductivity,not easy to produce excessive local temperature and damage bone tissue;Good abrasion resistance and long service life of drills made of zirconia ceramics.However,due to the inherent brittleness of ceramic materials,the drills are easy to break during high-speed drilling,which limits the further development of zirconia ceramics.In order to solve the problems,3mol.%Y₂O₃-coated powders and conventional coprecipitated 3Y-TZP powders were prepared.Based on this,Fe₃Al was incorporated as a toughening phase.The influence of different powder preparation methods and the added intermetallic compound on fracture toughness of zirconia ceramics was studied.In addition,a sintering method for the preparation of zirconia ceramics by high power vacuum hot pressing sintering system?HPS?was developed.The relationship between sintering process parameters,microstructure and mechanical properties was discussed and the sintering process parameters were optimized.Scanning electron microscope?SEM?and energy spectrum were utilized to characteriz the as-prepared 3mol.%Y₂O₃-coated zirconia and conventional coprecipitated 3Y-TZP.The results show that the distribution of yttrium oxide stabilizers in the lattice is obviously different.The non-uniform Y³⁺distribution and wide grain size distribution make the metastable tetragonal zirconia?t-ZrO₂?in Y₂O₃-coated zirconia more sensitive to phase transition.Therefore,Y₂O₃-coated zirconia shows a higher fracture toughness than coprecipitated zirconia.XRD,the result shows that the volume fraction increment of monoclinic zirconia(m-ZrO₂)in the fracture interface of the Y₂O₃-coated zirconia is greater after fracture,which proves that Y₂O₃-coated zirconia has higher phase transition sensitivity compared with the coprecipitated zirconia.The relationship between microstructure and mechanical properties of ceramic materials was investigated.The grain size distribution of Y₂O₃-coated zirconia is wider than coprecipitated zirconia but its density is lower.Compared with the coprecipitated zirconia,the fracture mode of Y₂O₃-coated zirconia changes from intergranular fracture to transgranular fracture,and the tendency of t-ZrO₂ to m-ZrO₂ transition is enhanced.Therefore,the fracture toughness of the Y₂O₃-coated zirconia increased⁹6%(from 4.41 MPa?m¹/2/2 to 8.64 MPa?m^1/2),and the hardness decreased⁴%,compared with that of the coprecipitated zirconia.Due to the low hardness of Fe₃Al,it will reduce the hardness of the Fe₃Al/ZrO₂ composite.However,the ductile fracture deformation and pull-out of Fe₃Al during fracture will consume more energy and help to improve the fracture toughness of the composites.As a result,the fracture toughness of the 20wt.%Fe₃Al/ZrO₂ composite increased by¹3%(from 8.64 MPa?m^1/2 to9.78 MPa?m^1/2),and the hardness decreased by⁷%,compared with that of the Y₂O₃-coated zirconia.