The Research On Infiltration Casting Technology On Copper Substrate And The Properties Of The Infiltrated Layer

Copper alloy are the important metal materials in industry owing to its excellent conductibility and mechanical properties. The cost of copper parts would rise further because the copper rise obviously in price in recent years. The servicing requiments for most parts are wear resistance, heat resistance and corrosion resistance. Therefore, the surface modification is an effective method that prolongs the life span of parts and makes the costs of parts decreasing. A number of methods to improve its surface properties have been developed, including electroplating, vapor deposition and heat treatment. The surface coating often cracks or peels off owing to the residual stress, and some times the coating was too thin to reach the expected results of surface modification. These problems could be solved through casting infiltration technology. But this technology was limited to surface modification for iron and steel. The excellent thermal conductivity of copper makes it nearly impossible to modify surface performance using casting infiltration technology. The heat conducted ratio of copper is five times as large as that of steel or iron. Surface infiltrated layer on copper substrate were investigated in this paper. Ni-based surface infiltrated layer, Fe-based surface infiltrated layer and Ni/Al₂O₃ surface infiltrated layer were fabricated through vacuum infiltration casting technology. The processing parameters of infiltrated layer, micro-structure and properties were tested and discussed.All kinds of processing parameters that affected the formation and the quality of the infiltrated layer were investigated firstly. The studying results indicated that there are many parameters affecting the formation of infiltrated layer. They are vacuum degree, pouring temperature, bond, modulus of the casting, preheating temperature, grain size of alloying powder and the thickness of the preformed layer. The most important factors affecting formation of infiltrated layer are the vacuum degree, then pouring temperature and particle size. The rest parameters are not the main factors, while it would impose positive effect on forming and improving the quality of the infiltrated layer.There are three sub-layers from substrate to surface of the whole infiltrated layer from the microcosmic appearance for Ni-based infiltrated layer. That is the surface sintering layer, metallurgical fusing layer and diffusion solid solution layer. The infiltrated layer is mainly composed of Ni-based solid solution, CrB, Cr₃Ni₂ and Cu-based solid solution. The forming mechanism of the infiltrated layer is melting-metallurgical-fusion. The surface macro-hardness is HRC 55.0, and the micro-hardness distribution of infiltrated layer presents the gradient variation. Three point bending tests suggest that the bonding strength between the infiltrated layer and substrate be higher than that fabricated by plating and chemical plating. The oxidation resistance of Ni-based infiltrated layer was improved twice comparing to the substrate. The chilling cycles could reach beyond 130 times ranging from 800°C to 10°C for sample with infiltrated layer. The surface of Ni-based infiltrated layer appeared some micro-crack and oxidation to different extent. But the surface infiltrated layer could not peel off.The microstructure is uniform for Fe-based infiltrated layer. Particles that melted partly, strengthening phase formed during the formation of surface infiltrated layer, and solid solution are the main structures in the layer. The main composition of infiltrated layer is Ni-Fe, Ni-Cr-Fe alloy, Al-Si eutectic, Cu-based solid solution and hypereutectic ledeburite with carbide. The forming mechanism of the infiltrated layer is part-melting-metallurgical-fusion. The surface macro-hardness is HRC 55.0, and the micro-hardness distribution of infiltrated layer presents the gradient variation. The bending strength of samples with infiltrated layer was improved to different extent comparing with the substrate. The oxidation resistance of Fe-based infiltrated layer has not improved comparing with substrate. The thermal cycling is beyond 80 times ranging from 800°C to 10°C for sample with Fe-based infiltrated layer. Its thermal property was not improved comparing with the Ni-based infiltrated layer. There were many vertical micro-cracks on the surface of Fe-based infiltrated layer, and then produced horizontal micro-crack along the interface between the infiltrated layer and substrate during the process of thermal cycling.The Ni/ Al₂O₃ surface composite includes two sub-layers that are surface composite and the transition layer between the surface composite and substrate. Al₂O₃, Ni₃₁Si₁₂, Ni₃B, Ni-Cr-Fe alloy, Ni-based solid solution and Cu-based solid solution are the main composition within the infiltrated layer of Ni/ Al₂O₃ composite. The formingmechanism of the infiltrated layer is that the Ni-based powder melted and surrounded the ceramic particles. The surface macro-hardness can reach HRC 65.0, and the micro-hardness distribution of infiltrated layer presents gradient variation. The maximum micro-hardness is different, but the variation trend is similar for different Al₂O₃ content. The three-point test results indicated that there are two circumstances for the destroying of infiltrated layer. The vertical crack that was from the surface of the infiltrated layer to substrate appeared and extended to substrate for samples that the surface infiltrated layer with Al₂O₃ content was less than 20%. The vertical crack extended to the interface would then produce the horizontal crack that was along the interface for samples with Al₂O₃ content being beyond 30%.The vacuum infiltration casting technology has been applied on the tuyere of blast furnace and guides and guards for obtaining excellent surfacial properties. The results investigated that the main processing parameters affecting the infiltrated layer are pouring temperature, processing technics of preformed layer and pouring system. This would be the foundation for the application of this technology on other copper parts.