【作者】 周永欣；

【导师】 赵西成； 吕振林；

【作者基本信息】 西安建筑科技大学 ， 材料学， 2007， 博士

【摘要】 磨损是机械零部件失效的主要原因，约有80％是由于磨损造成的。随着生产设备的大型化发展，对材料的耐磨性提出了更高的要求，但目前传统金属材料性能提高有限，难以满足这一要求。近几年发展起来的颗粒增强钢铁基复合材料由于既保持了金属热稳定性好、延展性好的优点，同时又具有陶瓷颗粒的耐腐蚀、抗高温氧化和耐磨损等特点而备受瞩目。本文以承受低应力严重冲蚀磨损的泥浆泵、渣浆泵等的易磨损零部件为研究背景，采用负压铸渗法制备SiC／钢基表面复合材料，研究了SiC预制体膏块的组配和负压铸渗工艺参数对SiC／钢复合质量的影响。通过对该复合材料的宏观、微观以及界面结合组织和成分的分析，进而确定了最佳的SiC颗粒／钢基表面复合的负压铸渗制备工艺。在自制的浆料射流式冲蚀磨损试验机上研究了SiC／钢基表面复合材料、Q235钢、高铬铸铁、低铬铸铁等材料的浆料冲蚀磨损性能，并对各自的冲蚀磨损机理进行了分析。采用负压铸渗工艺技术，以35钢为基体，600μm～850μm SiC粒子为增强体，2％的高纯粘土为粘结剂和2％氟化钠+2％硼酸为添加剂，通过控制浇铸温度，加以合理的负压铸渗工艺成功制备了SiC／钢基表面复合材料。SiC粒子与钢基体之间形成结合良好的表面铸渗复合层，并存在明显的复合层、过渡区和基体区。对负压铸渗过程进行了热力学、动力学分析，推导出铸渗速度和铸渗复合层厚度的表达式。确定了影响负压铸渗速度和深度的主要因素，即：SiC粒子的大小、钢液的表面张力、钢液与SiC粒子间的润湿性、钢液的静压头、铸型的真空度、钢液处于液态的时间和钢液的粘度等。理论上得出钢液浇注过程中SiC粒子一定会分解的热力学依据。提出通过改变试验条件和工艺参数，进而控制反应的动力学过程，可以延缓和阻止碳化硅分解速度。探讨了各种粘结剂、熔剂及其加入量对负压铸渗表面复合质量的影响规律，确定了SiC／钢表面复合材料的最佳制备工艺参数。提出了当铸件厚度与预制体厚度之比(λ值)在4～8时，可以获得良好的SiC／钢基表面复合材料的负压铸渗效果和表面质量。分析了铸渗表面复合层的微观组织、成分、SiC粒子与钢基体的界面结合状况。SiC／钢表面复合材料复合层组织为SiC粒子+钢基体+石墨，SiC粒子分布均匀、排列比较紧密，无聚集成团现象，界面结合状况良好，其与钢基体之间呈冶金结合，具有较高的结合强度。钢基体主要为铁素体，在一定条件下也可出现珠光体组织。SiC颗粒周围的基体显微硬度值随着与SiC颗粒中心的距离的增加而逐渐减小，SiC颗粒的加入提高了复合材料的整体硬度。由于存在过渡层，从铸渗复合层到基体有一个渐降的硬度梯度，复合层的硬度也呈梯度分布，这种渐降的硬度梯度有利于提高复合材料的冲蚀磨损抗力。通过调整SiC预制体的添加物组配，可以既保证钢液的浸渗，又防止SiC粒子的分解。SiC粒子与钢基体界面处的反应产物为氧化物和复杂的复合氧化物。界面反应层的形成改善了SiC颗粒与钢基体的结合强度，并减小由于SiC颗粒与钢基体之间弹性模量和热膨胀系数差异而引起的热应力。综合运用机械设计制造、流体力学原理及水工原理等知识，研制了一台造价低廉、操作方便可用于料浆冲蚀磨损试验的料浆冲蚀磨损试验装置。试验表明：该试验机冲蚀磨损数据重现性好，适合于耐磨材料对比选择以及料浆冲蚀磨损机理的研究。SiC／钢基表面复合材料的冲蚀磨损试验表明：低角度冲蚀磨损时，SiC／钢基表面复合材料的冲蚀磨损机理和塑性材料的冲蚀磨损机理相似，为切削和犁削，45°冲蚀角下复合材料的相对冲蚀磨损性最好，其冲蚀耐磨性为Q235钢的4.03倍；当冲蚀角在60°～90°之间时，钢基体对SiC颗粒的“支撑效应”和SiC颗粒对钢基体的“保护效应”使复合材料的磨损量随着冲蚀角的增大而降低，冲蚀磨损机理为冲击断裂和切削；850μm SiC粒子要比600μm SiC粒子增强SiC／钢基表面复合材料的冲蚀磨损性能好。随料浆中石英砂冲蚀粒子的增大，SiC／钢基表面复合材料的冲蚀磨损率也随着增大。高铬铸铁的冲蚀磨损性能随冲蚀角度的增大先增大后减小，在60时出现峰值，冲蚀磨损机理为脆性断裂和薄片剥落；低铬铸铁在冲蚀角度小于45°时表现出了良好的冲蚀耐磨性，冲蚀磨损机理为切削、犁削；Q235钢的冲蚀磨损耐磨性一般，冲蚀磨损机理为切削磨损和冲击磨损。更多还原

【Abstract】 Approximately 75%-80% failures of parts are caused by wear in the application, wear is the main reason to result in the failure of components. With the development of huge production equipment, there are more stringent requirements for the wear resistance to the materials. However, it is very limited for the traditional materials to improve the properties, and it is difficult to meet this stringent requirements. Recently, more attentions have been paid to the particles reinforced metal matrix composites since they combine good thermal stability and good ductility of metals with good erosion resistance, high temperature oxidation resistance and wear resistance of ceramic particles. In the present investigation, the research background is that these easily worn components, such as slurry pump and dreg pump, are usually used in working conditions with low stress and erosion wear. The SiC particle reinforced steel matrix surface composite was prepared by expandable pattern casting and casting infiltration process, the effect of the constituents of prefabricated SiC loaf and the parameters of expandable pattern casting and infiltration on the compound quality of SiC/steel is studied. The optimum vacuum evaporative pattern casting (V-EPC) infiltration preparation technology of the SiC particle reinforced steel matrix surface composite was determined through the analysis of the macro/micro-structure, bonding interface structure and composition. The slurry erosion wear performances of the SiC particles reinforced steel matrix surface composite, Q235 steel, high chromium as-cast iron and low chromium as-cast iron were studied on the self-made slurry inject erosion wear machine, and their erosion and wear mechanisms were analyzed.The SiC particles reinforced steel matrix surface composite was prepared successfully by the vacuum evaporative pattern casting (V-EPC) infiltration technology on the substrate of 35 steel with the SiC particle 600μm to 850μm in diameter, 2wt% high purity clay as adhesive, and additives of 2wt%NdF and 2wt% boric acid, and through controlling casting temperature and proper vacuum evaporative pattern casting (V-EPC) infiltration. The good surface casting-infiltration layers are formed between SiC ceramic particles and substrate, there are obvious composite layers, transitional zone and substrate zone. The expression of casting-infiltration velocity and casting-infiltration layer thickness was deduced from the analysis of thermodynamic and kinetics of casting-infiltration process. The main factors affecting vacuum casting-infiltration velocity and depth are the size of SiC particles, surface tension of molten steel, wettiability between molten steel and SiC particle, the static pressure of molten steel, the mold vacuum, the holding time of molten steel and the viscosity of steel et al. The thermodynamic evidence that SiC must be decomposed during the pouring process of molten steel was obtained from theory. It is proposed that the reaction kinetics process can be controlled by changing experimental conditions and technological parameters, thus retard the decomposition rate of SiC. The effect of various adhesives, flux and the addition contents on the quality of vacuum casting infiltration surface composite was investigated, and the optimum preparation parameters of the SiC particle reinforced steel matrix surface composite was determined.The necessary condition of preparing SiC particles reinforced steel matrix surface composite by vacuum evaporative pattern casting (V-EPC) infiltration was put forward, that is, X value, the ratio of casting thickness and the perform thickness. When X is between 4 and 8, the good SiC particle reinforced steel matrix surface composite can be obtained.The microstructure, composition of casting-infiltration surface compound layer and the bonding interface between SiC particles and matrix were analyzed. The main microstructure of casting-infiltration compound layer is consisted of SiC particles, steel matrix and graphite, the SiC particles are distributed uniformly and arranged tightly without agglomeration, the SiC casting-infiltration compound layer has a metallurgical bonding with steel matrix, thus has a larger bonding strength. The matrix of steel is mainly ferrite, but pearlite also appears under certain conditions. The microhardness of matrix around SiC particles decreases with increasing the distance from the centre of SiC particles, the addition of SiC particles enhances the whole hardness of the composite. Due to the existence of transition zone, there is a gradually decreased hardness gradient from the compound layer to the matrix, the hardness of compound layer is distributed in gradient as well. The gradually negative hardness gradient is beneficial to enhance the slurry erosion wear resistance.The reasonable adjustment of additive constituents of prefabricate SiC loaf can not only guarantee the steel infiltration, but also prevent the decomposition of SiC particles. The reaction products in the interface between SiC particles and steel matrix are oxides and complex compound oxides. The formation of interface reaction layer improves the bonding strength between SiC particles and steel matrix, and decreases the thermal stress caused by the difference of elastic modulus and thermal expansion coefficient.An inexpensive and conveniently operated slurry erosion wear test apparatus was researched and developed ultilizing the knowledge of machine design and manufacturing, hydromechanics principle and the hydraulic engineering principle etc. The test results show that slurry erosion data of the apparatus is repeatable, and the test machine is a reliable apparatus which is suitable for abrasive material selection and erosion wear mechanism research. The slurry erosion wear tests show that the wear mechanism of the SiC particles reinforced steel matrix surface composite is cutting and ploughing when the jet angle is low. The SiC particles reinforced steel matrix surface composite has the best relative erosion wear property of at 45°jet angle, which is 3.03 times than that of the Q235 steel. The erosion wear rate of composite decreases with increasing the jet angle in the range of 60°～90°due to the supporting effect of the matrix on the reinforced particles and the protecting effect of the SiC particles on the matrix. The wear mechanisms of the SiC particles reinforced steel matrix surface composite are impact fracture and cutting. The SiC steel matrix surface composite reinforced with 850um SiC particles has better slurry erosive wear property than that reinforced with 600um SiC particles. The erosion wear rate of SiC steel matrix composite increases with increasing size of quartz particles in the slurry.With increase of jet angle, the erosion wear property of the high chromium cast iron first increases and then decreases, the peak value appears at 60°. Its wear mechanisms are brittle fracture and flaking. The low chromium cast iron has excellent slurry erosion wear resistance when the jet angle is less than 45°. Its erosive wear mechanisms are cutting and ploughing. The slurry erosion wear resistance of Q235 steel has plain property and its erosive wear mechanisms are cutting and impact wear.更多还原