【作者】 李月英；

【导师】 刘勇兵；

【作者基本信息】 吉林大学 ， 材料学， 2004， 博士

【摘要】 铁基粉末冶金材料是发展迅速和具有巨大应用潜力的工程材料。近年来，由于具有优异的技术经济性，铁基粉末冶金材料逐渐取代部分传统的锻铸材料在机械、航天、农机，特别是汽车工业得到广泛的应用，制造像汽车齿轮、齿类零件（如带轮、链轮和齿毂等）和凸轮轴等几何形状复杂，加工困难或加工成本高的部件。但是，粉末冶金材料特有的孔隙的存在制约了其强度指标和摩擦学性能，使其急速上升的应用势头减慢。为了进一步扩大其应用领域，必须在提高粉末冶金材料密度级别的基础上，进一步改善其摩擦学特性。本试验制备出不同合金成分的铁基粉末冶金材料，并对其采用高频感应淬火和宽带激光淬火两种工艺进行表面处理，得到了高硬度和耐磨性的表面功能层，从而扩大了粉末烧结技术的应用领域，改善了烧结部件的性能。本试验采用普通压制烧结方法制备出不同合金成分的C-Cr-Ni-Mo-Cu系铁基粉末冶金材料，其密度级别达到6.7g/cm3。其中设计的合金成分变化范围为：C0.45～0.55%、Cr0.5～2.5%、 Ni1～3%、Mo0.85%、Cu1%～3%。并对制备过程中的压制压力、烧结温度和烧结时间等工艺参数对材料密度、硬度和组织的影响进行了研究。通过对制备工艺过程的分析，最终确定出优化后的制备工艺参数为：压制压力为600MPa，烧结温度为1200℃，烧结时间为60分钟。为了进一步提高材料的使用性能，本实验对制备出的铁基粉末冶金材料进行了两种表面淬火处理工艺：高频感应淬火和宽带激光淬火。对两种工艺下工艺参数对显微硬度的影响进行了研究，最终确定出优化后的表面处理工艺参数为：高频淬火装置输出功率为26.1kW；激光淬火装置的输出功率为3.2kW，扫描速度为8mm/s。材料的性能决定于其内部的组织结构，因此我们对铁基粉末冶金材料的组织和常规性能进行了系统的研究，并对两种表面处理工艺的强化机理进行了讨论。通过研究表明：烧结态铁基粉末冶金材料的组织为铁素体+珠光体组织。表面强化铁基粉末冶金材料的组织表现为层状组织，最表层为完全淬硬<WP=111>层，组织为淬火马氏体和残余奥氏体；第二层为过渡层，组织为马氏体、铁素体和渗碳体的混合组织。；第三层为基体，组织为铁素体和珠光体。本实验通过对表面强化铁基粉末冶金材料的常规性能进行研究表明，在本实验条件下，激光淬火后的硬化层硬度高达HV0.3 690～849，厚度约为1.2～1.9mm。而高频淬火后的硬化层硬度为HV0.3 598～678，厚度约为0.7～1.3mm，比激光淬火的硬化层硬度低，厚度也略薄。本研究表明硬化层形成残余压应力、马氏体晶粒细小、马氏体含量较多及弥散强化是材料高频感应淬火后硬度大幅度提高的主要原因；晶粒超细化，高的马氏体含量，马氏体高位错密度和高的固溶含碳量是材料经激光热处理后获得超高表面硬度的主要原因。作为减摩耐磨材料使用时，铁基粉末冶金材料的耐磨性及其影响规律的确定是非常重要的。因此本实验对该系列材料的摩擦磨损特性进行了系统的研究，对其在摩擦磨损过程中的磨损机理进行了详细的讨论。本试验铁基粉末冶金材料的摩擦磨损特性是在MG-2000型高温高速磨损试验机上进行的，摩擦形式采用销-盘式干滑动摩擦。影响摩擦磨损试验的因素主要有合金成分、试验载荷、滑动速度和磨损时间。本试验中分别测试了在这些参量影响下铁基粉末冶金材料在三种状态下（烧结态、高频淬火和激光淬火）的摩擦磨损曲线。试验结果表明：铁基粉末冶金材料经表面处理后摩擦磨损性能有了显著的改善，磨损量与摩擦系数比未淬火处理材料明显降低；并且宽带激光淬火铁基粉末冶金材料的摩擦磨损性能略优于高频感应淬火材料。通过对表面处理铁基粉末冶金材料摩擦磨损特性曲线的综合分析，我们得出在本试验成分范围内符合摩擦学设计的材料组成为：C0.45～0.55％；Cr1.0～1.5%；Ni2.0%；Cu2～2.5％；Mo0.85%。在本试验摩擦过程中，铁基粉末冶金材料的摩擦表面形成一表面层，该摩擦表面层的形成是由于加工硬化在摩擦表面产生塑性变形引起的。该表面层具有高的硬度，可有效阻止亚表层裂纹向表面的扩展，从而提高表面的耐磨性。在该表面层的最表面还覆盖着一层表面膜，该表面膜的存在可以起到降低摩擦系数和磨损率的作用。在较高载荷下由于该表面膜遭到破坏，从而影响了其减磨作用的发挥。通过对该表面膜进行结构分析得知其是由Fe、Fe3O4、Fe2O3和Fe4Cu3等物质组成的混合膜。在不同的试验条件下，摩擦表面膜的氧化物类型有所不同。在较低试验载荷（50N）和滑动速度（1.01m/s）下，摩擦表面膜中的氧化物类型主要是Fe2O3,摩擦表面呈砖红色。在中、高试验载荷（120N）和滑动速度（3.14m/s）下，摩擦表面膜中的氧化物主要为FeO，<WP=112>摩擦表面呈黑亮色。在二者之间的试验条件下（本试验中试验载荷为80N，滑动速度为2.04m/s），摩擦表面膜中的氧化物主要为Fe3O4，摩擦表面呈黑色。磨损过程中主要产生三种形状的磨屑：片状磨屑、块状磨屑和条状磨屑。在不同的试验条件下，磨屑的形态分布也有所变化。在较低试验载荷和滑动速度下，磨屑以块状磨屑为主，且粒度较小，一般在几百纳米到几微米之间。在较高试验载荷和滑动速度下，磨屑以片状磨屑为主，且较大，一般更多还原

【Abstract】 Ferrous powder metallurgical materials possess enormous potential market and have been developed rapidly. Recently, the more and more ferrous P/M materials instead of a part of wrought steels and casting irons are used to manufacture high performance structure components, such as automotive gears, camshafts and connecting rods, which would be difficult and expensive to generate by machining. However, the tribological and mechanical properties of P/M materials are limited by their residual porosity. To widen application field of P/M materials, it is very essential to improve its tribological properties based on increasing its density level. In this paper, ferrous P/M materials with different composition were prepared, and their surfaces treated by high-frequency induction quenching and wide-band laser hardening techniques. As a result, surfaces with high hardness and good wear resistance were obtained. The application field of powder metallurgical technology is widened and properties are improved. In this work, we prepared different composition C-Cr-Ni-Mo-Cu series ferrous P/M materials with density 6.7g/cm3 by common pressing-sinter technique. The designed range of component is C0.45～0.55%, Cr0.5～2.5%, Ni1～3%, Mo0.85%, Cu1%～3%. We studied the effect of suppress pressure, sinter temperature and sinter times on density, hardness and structure of the materials in the course of preparation. Ultimately, we obtained optimal processing parameter: suppress pressure 600MPa, sinter temperature 1200℃, sinter times 60 minutes. In order to improve surface properties of the materials, high-frequency induction quenching and wide-bond laser quenching techniques were used in this test. We studied the effect of processing parameter of the two surface treatment techniques on microhardness. Finally, we obtained optimal surface treatment processing parameter: high-frequency induction quenching output power 26.1kW; laser quenching output power 3.2kW, scanning speed 8mm/s.The properties of materials are decided by their inner structure. So we studied the structure and general properties of ferrous P/M materials, and discussed the strengthen mechanism of <WP=114>the two surface treatment processing. The results show that the metallographic structure of sintered state ferrous P/M materials is ferrite, pearlite. Surface strengthened ferrous P/M materials show a kind of layered structure. From the surface to the center, surface quenched materials can be divided into three layer. The first layer is complete hardened layer made up of fine martensite and remained austenite. The second layer is the transition layer which microstructures are martensite, ferrite and cementite. The third layer is matrix which microstructure is ferrite and pearlite. The study also showed that the microhardness and thickness of hardened layer for laser quenching ferrous P/M materials reaches HV0.3 690～849 and 1.2～1.9mm; the microhardness and thickness of hardened layer for high-frequency induction quenching ferrous P/M materials reaches HV0.3 598～678 and 0.7～1.3mm which are lower laser quenching materials. The primary reasons of high-frequency induction quenching strengthen are the formation of remained press-stress in the hardened layer, fine martensite grain, more martensite content and dispersion strengthen. The mostly reasons of laser surface quenching strengthen are superfine grain, high martensite content, martensite containing high dislocation density and high carbon content.For use in tribological applications，it is very important that make certain the wear resistance of ferrous P/M materials and the influence rules on it. So friction and wear properties of ferrous P/M materials were studied emphatically in this test，and its wear mechanisms were discussed in detail. Dry sliding wear tests were performed using a MG-2000 type pin-disk wear apparatus. The factors affecting the friction and wear tests of ferrous P/M materials are mostly alloy composition, the experimental loads，sliding speeds and times. The curves of friction and wear of ferrou更多还原