压力铸造法制备陶瓷纤维增强铝基复合材

关键词：陶瓷纤维，铝基复合材料，压力铸造，耐磨性能，界面，纤维体积分数

摘要正文：为了拓宽MMC在汽车制造业的应用，本研究尝试用压力铸造法（die－casting）制备陶瓷短纤维增强铝基复合材料并得出最佳的压铸工艺参数：压射比压为80Mpa，铝合金液填充速度为15～20m/s，铝合金液浇注温度为680°C～700°C，预制件预热温度为400～700°C，压铸模预热温度为150～200°C。并在上述工艺参数下成功地压铸出体积分数为5%～50%复合材料试块。对压铸复合材料的微观组织、硬度、抗拉强度及耐磨性能进行了研究和分析。结果表明：铝合金液体较好地浸渗陶瓷纤维预制件，增强纤维在基体里分布比较均匀，与基体结合较好，但仍存在微孔，当体积分数很大时微孔数量较多；复合材料增强区和未增强区界面结合较好；复合材料布氏硬度高于基体，且硬度值随纤维体积分数增加而增高；复合材料在高温（300oC）下仍具有一定的抗拉强度，导致复合材料抗拉强度值不太高的主要原因是:压铸复合材料中存在微气孔、夹杂及复合材料的体积分数过大而造成的纤维不均匀分布；在油润滑条件下，所制备的铝基复合材料具有优异的耐磨性，其耐磨性远优于基体。干摩擦条件下，复合材料有两个磨损稳定但是磨损率不同的阶段，称之为：滑动磨损和磨粒磨损阶段，两个阶段过渡时的滑动路程称为临界点。滑动磨损阶段复合材料的耐磨性远优于基体，当转变为磨粒磨损阶段时复合材料磨损加剧，磨损率超过了基体。

Title: Ceramic Fiber Reinforced Aluminum Matrix Composites Made by Die-casting Technique

 Key words: ceramic fiber, aluminum matrix composite, die-casting, wear behaviors, interface, fiber volume fraction.

Abstract: In order to broaden the application of MMC on auto industry, die-casting technique were（is） adopted to fabricate ceramic short fiber reinforced composites in this research and the suitable process parameters of die-casting were（are） acquired as following: the pressure applied is about 80MPa, filling velocities of alloy liquid range from 15 to 20m/s, warm-up temperature of the preform is 400°C~700°C, and warm-up temperature of the mould is 150°C ~200°C. Composite specimens with 5 percent to 50 percent fiber volume fraction were fabricated by die-casting technique under the condition of process parameters above. The microstructure, hardness, tensile strength and wear behaviors of composites made by die–casting technique were （are）investigated and analyzed. The results showed that aluminum alloy liquid could be preferably dipped into ceramic fiber preform, and that the fiber distributes in the matrix relatively evenly and combines well with the matrix. But pores usually exist specially when fiber volume fraction is very high. The interfacial bonding between reinforced areas and unreinforced areas is well in the composite, whose overall hardness (HB) is higher than that of matrix and increases with the amount addition(increasing) of fiber volume fraction. A certain existence of tensile strength remains even under high temperature (300°C or so).The main reason leading to the limitation of composite tensile strength is the existence of pores, inclusions and unevenly distribution of fiber as high fiber volume fraction. The fabricated aluminum matrix composites have much better wear behaviors than that of the matrix when lubricated with oil. Under dry friction condition, there are two phases named sliding abrasion and grinding-particle abrasion.

原位合成熔铸法制备TiC颗粒增强2Cr13钢基复合材料显微组织、性能及工艺研究

    关键词：TiC 2Cr13不锈钢 复合材料 显微组织 常规力学性能 耐磨损性能 耐腐蚀性能

   本文利用原位合成熔铸法制备了TiC颗粒增强2Cr13钢基复合材料，并采用合理的热形变和热处理工艺改善了复合材料铸锭的组织。利用OM、SEM、XRD、碳硫仪等多种现代分析手段研究了复合材料的显微组织和TiC颗粒的形貌和分布，并测试了复合材料的常规力学性能、耐磨损性能和耐腐蚀性能。对熔炼工艺的研究表明，原位合成熔铸法制备TiC/2Cr13复合材料在工艺上是完全可行的。熔体中的Ti和C在高温下发生原位合成反应，可以在基体中形成稳定存在的TiC颗粒。铬元素、钛元素和TiC颗粒的含量基本到位。本文采用的生产性工艺，可以在大气中大炉量地制备TiC颗粒分布均匀的复合材料。对复合材料的热变形和热处理工艺的研究表明，锻、轧等热形变工艺和均匀化退火、淬火回火等热处理工艺可以在很大程度上的改善基体的组织，从而提高复合材料的性能。空冷淬火和油冷淬火均可使基体获得马氏体组织。随着回火温度的降低，复合材料的强度和硬度提高，塑性下降。在500－550℃温度范围回火时，2Cr13基体会出现回火脆性。随着回火温度的变化，复合材料的耐磨损性能无大的变化。对复合材料显微组织的研究表明，当TiC颗粒的含量为3wt%和4wt%、预制块中钛碳原子比为1:1和3:2时，TiC颗粒在基体中分布均匀，与基体结合良好，界面干净，具有很高的热稳定性。TiC颗粒大小在5-10μm左右，呈现为不规则多边形状。高温（660℃）回火后，复合材料的组织为细小均匀的回火索氏体上分布着TiC颗粒。低温（250℃、350℃）回火后，基体的组织则为回火马氏体。当TiC颗粒的含量达到5wt%，预制块中钛碳原子比达到2:3时，基体中的TiC颗粒发生了一定程度的团聚。高温（660℃）回火后，复合材料的显微组织除了回火索氏体和TiC颗粒外，还有因偏析形成的莱氏体和块状碳化物，以及大量细小弥散的析出碳化物。对复合材料常规力学性能的研究表明，TiC颗粒的引入提高了基体的室温抗拉强度和屈服强度。本文中以引入4wt%TiC、预制块中钛碳原子比为1:1的复合材料的强度最高，但塑性和韧性有一定程度的下降。当TiC颗粒的含量为3wt%和4wt%、预制块中钛碳原子比为1:1和3:2时，复合材料的塑性和韧性下降幅度不大。对复合材料耐磨损性能的研究表明，TiC颗粒的引入极大地减少了基体产生犁沟和显微切削的几率，使得复合材料的耐磨损性能较之基体有了显著的提高。对复合材料耐腐蚀性能的研究表明，在本文的腐蚀试验条件下，复合材料的耐腐蚀性优于基体。随着TiC颗粒含量和预制块中碳量的增加，复合材料的耐腐蚀性能下降。 TiC含量在3wt%-4wt%范围内、预制块中钛碳原子比在3:2到1:1范围内的复合材料配比是合理的、成功的。将复合材料的热处理工艺定为1000℃油淬，350℃回火可以使复合材料的硬度、韧性、耐蚀性、耐磨性等性能最好的满足刀口材料的使用要求。在本文的磨损试验条件下，不同热加工、热处理状态下的3% 1:1复合材料的耐磨损性能都明显优于812硬质Co合金。

Fabrication, Microstructure and Mechanical Properties of TiC Particles Reinforced 2Cr13 Matrix Composite

Key words: TiC, 2Cr13 stainless steel, composites, microstructure, mechanical properties, wear resistance

 TiC particles reinforced 2Cr13 matrix (TiCp/2Cr13) composites have been processed by in-situ solidification technology in this thesis. After appropriate themomechanical processing and heat-treatment, the composites have been successfully produced. The microstructures of composites, the distribution and morphology of TiC particles have been investigated by using OM, SEM, XRD and some other modern instruments. The mechanical properties, wear and corrosion resistance of the composites have also been investigated. The in-situ solidification technology has been proved to be successful for（to） the fabrication of the TiCp composites. Reaction of titanium with carbon in the melt occurs at（in） high temperature, which resulted in the formation of TiC particles with high thermal stability. The large-scale ingots can also been produced by using the techniques developed in（from） the present work The study on the techniques of thermomechanical processing and heat-treatment has shown that forging, rolling, annealing, quenching and tempering are helpful to the improvement of the microstructures and properties of the composites. The martensite microstructure has been observed in the samples of composites quenched in air as well as in oil. With the decrease of tempering temperature, the tensile strength, yield strength and hardness of the composites increase, but the elongation decreases. The matrix alloy (2Cr13) shows temper embrittlement when tempered at 500-550℃. The wear resistance of the composites changes a little when tempered at different temperatures. Microstructural observations on the composites have shown that when the fraction of TiC in the composite was 3wt% and 4wt% and the ratio of titanium to carbon in the add was 1:1 and 3:2, TiC particles have a uniform distribution and the size of the TiC particles has ranged from 5 to 10μm. When the fraction of TiC is 5wt%, or the ratio of titanium to carbon in the pre0form is 2:3, the segregation of the TiC particles occurs. Tests of the mechanical properties of the composites have shown that the addition of TiC particles improves the tensile strength and yield strength at room temperature. The composite with 4wt%TiC and a 1:1 ratio of titanium to carbon in the preform has the highest tensile strength and yield strength, however, the elongation and toughness of the composites is lower than that of the matrix alloy. The wear resistance of the composites has improved remarkably because of the TiC addition. With the increase of TiC fraction, the wear resistance of the composites increases. The corrosion resistance of the composites is better than that of 2Cr13, however,it decreases with the increase of TiC fraction and the content of carbon in the preform. When the content of TiC is 3wt% and 4wt% and the ratio of titanium to carbon in the preform is 1:1 and 3:2, the composites have excellent comprehensive properties. The composites tempered at 350℃ could meet the requirement of the blade material. Under the water lubrication friction conditions, the composites show a better wear resistance than the 812 Co alloy.