Study Of Al₂O₃ Ceramic Composite By Centrifugation-SHS And Abradability

Al₂O₃ ceramic composite lined steel pipe was made by the way of Centrifugation-SHS with powders of Al (industrial), SiO₂ (A.R), Fe₂O₃ (A,R) and Fe₂O₃ (industrial). Relative wear-resistant was tested by zero-G test and the microstfucture was tested by analysis method such as SEM, XRD. The wearing mechanism of materials was researched. The results indicate as follows. The experiment uses the aluminothermics-centrifugal to prepare the pad compound steel pipe with the ceramics inner of Al₂O₃. Melt induced phase separation by the centrifugal force in the processing of reaction. The lighter Al₂O₃ ceramics form the inner layer on the outside of melt, whereas the heavier FeAl2O4 and Fe form the mid-transition layer near the inner of steel pipe. The microstructure analysis indicates that the Al₂O₃distribution is determined by the fineness of the Fe₂O₃raw material. If the fineness is high, the ceramics layer presents a branch-crystal structure, if the fineness is low; the ceramics layer presents the net structure. Since the melt point of Al₂O₃ ceramics is high, it may crystallize first. And then it may form the branch-crystal framework in the direction of radial. The melt point of FeAl2O4 and Fe is lower. It fills up the inner of the Al₂O₃branch-crystal. Ceramic layer is mainly composited by (a-Al₂O₃ and FeAl₂O₃spinel, SiO₂ addition agent and foreign substance existed in the a-Al₂O₃ branch-crystal grain boundary. The melt point of Al₂O₃ceramics is higher; it may freeze first, while Fe layer freezing later. The ceramic cannot contract freely in the inner of the steel pipe. It induce axial crack in the ceramic layer because of the axial tensile stress between ceramic and transition layers. Abrasive experiment express, the abrasion of the surface layer AI2O3 ceramics form for micro-split and abrasion particulate to wear away, existent blemish, micro-crack of the ceramics layer the circumambience makes the intensity of its surroundings material lower, causing material abradability to lower. The pure degree of the material that the ceramics inner pad preparation the steel pipe is higher, then wear-resistance better; whereas the worse. Because of the existence of bug, micro-crack, pore in the AI2O3ceramic layer, the strength decrease. Then it makes the abradability of the material decrease. The abrasion particle may get touch on with the AI2O3ceramic. It also glides on the ceramic, and it may result some impress on the touch point. In the same time it also produce some micro-crack in the surface of the ceramic. This micro-crack may spread in the inner side of the material, whose center is border of touch point. This micro-crack come across with each other, then it make the ceramic brittle fracture. This may make the ceramic induce micro-avalanche area, then it result the abrade of AI2O3 ceramic.