【作者】 董洪峰；

【导师】 路阳；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2013， 博士

【摘要】 粉末冶金金属基金刚石复合材料工磨具以其近净成形、锋利、生产效率高等特点被广泛用于加工石材、陶瓷、半导体等脆硬材料,并且随着科技特别是航空航天、电子、通信等高端领域的快速发展,对工磨具材料的精细化方面提出了更高要求。为降低金属基金刚石工磨具材料的制备成本,并保证工磨具材料的优良机械性能、界面结合性能和摩擦性能,本文对胎体成分设计、烧结工艺优化、界面热力学／动力学、磨头的摩擦磨损几个方面进行研究,以达到材料的组织结构、成分、性能、工艺方法的一体化。为降低工磨具的厚度和提高加工精度,本文亦对金属基金刚石复合材料超薄切锯进行试制,并研究超薄切锯的组织、机械性能和界面特性。得到的结论如下：首先用混合实验和极端顶点设计法建立响应曲面模型,以模型的12个顶点和任意两个面的质心为试验点制备试样。用Excel回归分析得到的方程复相关系数趋近于“1”,因此其可用于预测胎体性能。与实验值相比,回归方程的预测值最大误差分别为2.8%、3.4%、2.9%,能可靠预测胎体性能。各元素的最佳含量范围是：Fe60-66wt.%,Cu20.30wt.%和66.68wt.%,Co0-1wt.%,Sn0-O.8wt.%和7-8wt.%；根据所得到的最优胎体组分,对Cu/Fe基金刚石复合材料磨头的烧结工艺正交试验结果进行极差分析,可知工艺参数对胎体相对密度、抗弯强度、布氏硬度和弹性模量的影响显著性各异。Cu/Fe基金刚石磨头的最优工艺参数范围是：烧结温度700-740℃、压力17-21MPa、保温时间2-4min：用标准反应热效应理论计算930K、970K、1010K烧结温度和下Cr与金刚石C及石墨C反应吉布斯自由能变化,可知在热力学上碳化物形成元素Cr与金刚石C和石墨C反应可自发生成Cr3C2、Cr7C3、Cr23C6。根据经典热力学理论,在烧结温度930K、970K、1010K和烧结压力13MPa、17MPa、21MPa条件下,金刚石在热力学上满足石墨化转变。通过实验验证可知,在烧结温度740℃、压力21MPa、保温时间4min条件下,Cu基金刚石复合材料磨头的金刚石表面出现剥落／粘着层,胎体和金刚石的界面形成冶金结合,没有发生石墨化,与理论一致；通过对三种烧结工艺金刚石磨头进行摩擦性能测试可知,烧结温度和压力与Cu/Fe基金刚石磨头的力学性能和摩擦性能密切相关。Cu基金刚石磨头胎体的主要摩擦形式为粘着磨损和磨粒磨损,金刚石的磨损形式为磨粒磨损,随着烧结温度升高或烧结压力增大,摩擦性能提高；Fe基金刚石磨头胎体主要为粘着磨损和磨粒磨损,随着温度的升高或压力的增大,金刚石依次发生严重磨粒磨损、轻微磨粒磨损和热蚀磨损；在740℃/13MPa/6min工艺条件下,Fe基金刚石磨头具有最优的耐磨匹配性,摩擦性能最好；根据Cu/Fe基金刚石超薄切锯的冷压工艺研究结果,单轴模压条件下,冷压坯的高径比很小,导致轴/径向的压坯组织存在各向异性。随着冷压力的增大,冷压坯中粉末的变形不均匀、粉间摩擦力不断变化,均决定冷压坯的致密化过程。不同冷压加载速率条件下的粉末变形时间不同,较低的加载速率导致低压下的Cu、Ni粉末变形很大,造成后续变形困难,压坯的孔隙率较高。较高的加载速率使粉末变形不充分,造成脱模弹性后效,压坯组织粉末间存在间隙。随着保压时间的延长,Cu/Fe基冷压坯组织更加致密,粉末变形量增加。烧结胎体的合金化、组织和力学性能受冷压坯组织和密度制约,烧结Cu/Fe基胎体的拉伸端口形貌包括解理、塑坑、沿颗粒脆性断口。Cu基胎体的最优冷压工艺为：冷压力187MPa、加载速率0.1mm/min、保压时间2mmin；Fe基胎体的最优冷压工艺为：168MPa、0.15mm/min、4min;冷压-烧结Cu/Fe基金刚石复合材料超薄切锯的界面分别富集Cr、Fe元素,Cu基超薄切锯断口的界面出现缝隙,Fe基超薄切锯断口的界面结合较好。由金刚石的静应力计算公式得到烧结Cu/Fe基超薄切锯中金刚石的静应力分别为-645、-387MPa,远小于热应力计算值,其主要由于界面碳化物的产生、胎体的冷却塑性变形及冷却相变均可释放应力。更多还原

【Abstract】 P/M metal-based diamond composite tools possess self-sharpening, near-net-forming, and of much higher production efficiency, have been widely used to saw and grind hard-brittle materials such as stone, ceramic, semiconductor. What’s more, recent advances in the field of aerospace, electron, communication and so on raise a higher claim to the refining of tools. To reduce the preparation costs of metal based diamonds tools and ensure the excellent machine, interface and friction peoperties, the design of matrix component, optimizing of sintering process, interfacial thermodynamics and dynamics, friction and wear of segments were studied. Then the unified of microstructure, composition, properties and process will be reached. To reduce the thickness and improve the machining precision, the trail-produce, microstructure, mechnical properties and interface of diamond ultra thin sawing were also performed.A response surfaces model, whose12vertices and any two centroids are used for the experimental points, has been successfully established by the mixture experiment and extreme vertices design method (EVD). It can be concluded that the mixture experiment and EVD can be usded to calculate the matrix performance because the multiple correlation coefficient solved by regression analysis using Excel. The regression equations, whose calculation errors are2.8、3.4、2.9%compared with experimental value, can reliablely predict the matrix performance. The optimal contents of each component are:Fe60-66wt.%, Cu20-30wt.%and66-68wt.%, Co0-1wt.%, Sn0-0.8wt.%and7-8wt.%;According to the optimal matrix component and extreme difference analysis of orthogonal test results for Cu/Fe based diamond composite segments, it can be drawn the conclusion that the process parameters effects on density, hardness, bending strength and elastic modulus of segments are different. The optimal parameter ranges of Cu/Fe based diamond segments are sintering temperature700-740℃, pressure17-21MPa, dwelling time2-4min;Thermodynamics analyses show that the Gibbs free energy change of Cr7C3, Cr3C2and Cr23C6by reactions between Cr and diamond/graphite, and diamond graphitization are both negative at specific experimental conditions, indicating that the Cr3C2, Cr7C3and Cr23C6carbides reactions and diamond graphitization can automatically proceed in the experimental condition. According to the experimental verification, it can be seen that the surface of diamond sintered exist adhesive/spalling layers and the diamond graphitization not occurs and the metallurgy interfaces between matrix and diamond are formed, which are cinsistent with the throry;According to friction analysis results of diamond segments in there kinds of process, the relationship between sintering temperature, pressure, mechanical and friction properties is much closed. The Cu based diamond segments, whose matrix wear modes are adhensive and abrasive and whose diamonds are abrasive wear modes, are more wear-resisting with increasing sintering temperature or pressure. The wear modes of diamond in Fe based diamong segments are serious abrasive wear, mild abrasive wear and thermal erosion wear. The wear matching and friction properties of Fe based diamond segments are the best in the condition of740℃/13MPa/6min;The axial and radial microstructures of green are anisotropy because of much smaller aspect ratio during cold uniaxial compaction (CUC). With increasing pressure, the green densification is affected by non uniform deformation and changing inter-powder force. The deformation time is different at different loading rate, the green prosity is higher because of more deformation at low pressure when the loading rate is lower and the spring back occurs at higher loading rate. The densification is improved with longer dwelling time. The fracture morphologies, containing dimples, cleavages and brittleness along with iron rich particles, are dependent on the lattice types and interfacial bonding of matrix phases which are affected by the microstructure of green samples. The optimal cold compaction process of Cu based matrixes are pressurel87Mpa, loading rate0.1mm/min, dwelling time2min and Fe168Mpa,0.15mm/min,4min;The Cr and Fe are enrichment in the interface of Cu/Fe based diamong ultra thin sawing during cold compaction sintering respectively and the interface bonding of Fe based is better than Cu based. According to2D hydrostatic equation of diamond, stress values of diamond in hot pressed Cu/Fe based diamong ultra thin sawing are-645,-387MPa which are much lower than thermal stress because of stress release by carbide, plastic deformation and phase transition during cooling.更多还原