A Study On Preparation, Properties Of Al₂O₃ Ceramic And Machining Of Femoral Head For Partial Hip Joint Prostheses

The preparation, mechanical properties of alumina material and machining of femoral head for bioceramic-metal articulated partial hip joint prostheses were studied in this paper, which provided the research results being worth theoretical reference and practical use for the solving of technical problems of sintering and machining of alumina ceramic.In this paper, the alumina ceramic was prepared under normal pressure and low temperature, the mechanical properties, micromorphology, microstructure of grain boundary and phase composition of the alumina ceramic, and the precision shaping and cold processing of the femoral head were systematically studied; the effects of the additives, the relation between microstructure and mechanical strength, the sintering mechanism of the material and the influence factors of the structure and properties of the alumina ceramic were discussed also.Firstly, high purity a-Al2O3 micro-powder and MgO-ZrO2(Y2O3) composite additives were mixed with the method of ammonia precipitating-enwrapping, which made the additives well distributed in the matrix of raw material. Then the dehydrated and baked mixing material was calcined at 1280℃ to completely decompose the hydroxide in the mixing material and get powder of good sintering activity. The powder was pressed through molding and cold isostatic pressure, which increased the density and decreased the uneven distribution of stress inside the briquet to make the ceramic briquet equally compact. To meet the processing requirements before sintering, the pressed briquet was pre-calcined at 1150℃ to make it possess adequate processing strength at first and then was shaped through precise turning on the numerical control lathe according to the design diagram of the femoral head prostheses of partial hip joint. The shaped briquet was sintered at 1600℃ for 2.5 hours under normal pressure and at certain heating rate in Si-mo electric furnace. Tests showed that the comprehensive mechanical properties of the prepared alumina ceramic were excellent. The micromorphology and grain boundary microstructure of the material were studied with SEM and TEM; the grain boundary phase composition of the material were analyzed with EDS and X-ray. At last, the surface of the alumina femoral head was grade-polished with SiC micropowder and diamond grinding cream, the join part was trimmed with specificinstrument, which made the surface of the alumina femoral head reach the degree of approximating mirror finish and match the femoral stem well. The artificial partial hip joint prostheses was finally got by articulating the alumina femoral head with Ti alloy femoral stem coated with bioactive coating.The research on the effects of the composite additives and the studies on the microstructure and mechanical properties of the alumina ceramic showed that the MgO-ZrO2(Y2O3) composite additives could effectively promote the sintering of the material, restrain the abnormal growth of the grain and increase the toughness, thus to improve the mechanical properties of the alumina ceramic. When the content of MgO-ZrO2(Y203) was 4% and the mass ratio of MgO to ZrO2(Y203) was 1:1, sintered under normal pressure and at the low temperature of 1600, the main crystal phase of the material was a-Al2O3, the open porosity approximated zero, the average grain diameter was 2.58um, the biax bending strength reached 261.79 MPa, the fracture toughness attained 5.46 MPa m1/2, the abrasion amount was 0.098mm ; the grains of the material were small and uniform, no abnormal grown grains were found, and no obvious pores, remnant glass phase and cracking existed on the grain boundary. MgO and Al2O3 can form MgAl2O4 existing mainly on the grain boundary through solid phase reaction, which limited the migration of the grain boundary and thereby inhibited the abnormal growth of the alumina grain. Toughening mechanism of ZrO2(Y2O3) to alumina ceramic came from the phase change of t-ZrO2 on the grain boundary. With the content augmentation of ZrO2(Y2O3), the fracture toughness of the alu...