Research On The Extrusion Infiltration Model Of Al₂O_3p/Steel Matrix Composites Based On Activated Preform

During the fabrication process of the Al2O3p/steel composites with liquid metal infiltration, the steel liquid has the poor infiltration motivation. This is mainly because the capillary force is the infiltration resistance due to the poor wettability of Al2O3 particles and steel liquid. The preform can be infiltrated by the steel liquid during squeeze casting. However, the increase of the infiltration depth is not obvious. The research shows that the Al2O3p/steel composites were fabricated by a modified squeeze casting with a 13mm thick heat-insulation layer inserted in the inner surface of the casting die and the active element added in the perform. The fabricated method can significantly increase the infiltration depth of the composites. So, the modeling of infiltration is established according to analyse the infiltration mechanism. The modeling of infiltration is amended from three aspects which include the external pressure, the preform preheat temperature and activation substances.In this work, the Si powder was mixed into the Al2O3 preform, squeeze casting technology was applied to fabricate the Al2O3p/40Cr composites. The Image-Pro Plus software was applied to measure the infiltration depth of the composites with different infiltration conditions. Then infiltration model was amended and validated.Firstly, the relationship between the infiltration depth and time is derived theoretically. This model is applicable to the system in wich the equivalent capillary radius is not the same in the infiltration direction and the viscosity resistance and the solidification resistance are considered in the infiltration process. The modeling of infiltration indicates that the infiltration depth is proportion to the quarter of the infiltration time. It is based on the temperature distribution in the infiltration direction is inversely proportional to the square of the infiltration depth, which is simulated by ProCAST.Secondly, the modeling of infiltration is amended according to fit the experiment datas. The infiltration depth of the composites was measured under different pressures. The result shows that the infiltration depth will increase with the increase of pressure, but its increase rate become smaller when the pressure is higher than 90 MPa. The modeling of infiltration was amended with the coefficient K1=2.27×10-5 according to fit the experiment datas by the Belehradek function. Then the infiltration depth of the composites was measured with different content of Si. The result shows that with the increase of the added Si, the infiltration depth of the composites increased significantly. Especially when the content of Si increased from 10%to 15%, the infiltration depth increased from 7.0mm to 14.4mm, increased by 105%. The contact angles between the steel liquid with different content of Si and Al2O3 particulates were measured. The result shows that the contact angle is 125°without adding Si. When the content of Si is 5%,10%,15%,20% and 25%, the contact angle is 118°,114°,111°,107° and 105°, respectively. So, The modeling of infiltration was amended with the coefficient K,=5.79X 10-3 and K2=30.89 by fitting the datas. The infiltration depth of the composites was measured with the different preform preheat temperature. The result shows that with the increase of the preform preheat temperature, the infiltration depth increase. The modeling of infiltration was amended with the coefficientK1;=-8.34X 10"5 and b1=-2.42 by fitting the experimental datas. Finally, the infiltration depth of the composites was validated by adding the Cr into the preform. The result indicates that the infiltration depth is 6.9mm in theoretically, and the actual infiltration depth is 7.1mm, which the error is 2%.In this work, the Si was mixed into the Al2O3 preform, squeeze casting technology was applied to fabricated the harrowing teeth. The XRD and element surface scanning were used to observe and analyse the microstructure. The result shows that there is no Si phase in the composites and the Si element is uniformly distributed in the steel matrix. The Vickers hardness tester was applied to check the microhardness of the composites. The checked result shows that with the increase of Si content, the microhardness of the ferrite first increased and then decreased, and final increased slowly, but the microhardness of the pearlite first increased and then decreased. In order to characterize the performance of the harrowing teeth, the wear volume of the composites was measured under the condition of the impact-abrasive wear. The result shows that with the increase of the Si content, the wear volume of the composites first decreased, and then increased. The wear volume of 10% Si composite is 63.64% less than the wear volume of the metal matrix.