GCr15接触疲劳亚表面损伤机制研究

发布时间：2018-05-29 01:12

本文选题：GCr15轴承钢 + 滚道接触疲劳　；参考：《兰州理工大学》2017年硕士论文

【摘要】：GCr15轴承钢是一种广泛应用于制造轴承、齿轮等滚动零部件的高碳铬钢,通常情况下服役的轴承承受的是循环载荷,包括径向压缩应力和周向摩擦力。在这种复杂工况下的轴承实际寿命往往低于设计寿命。虽然对轴承钢的接触疲劳性能研究已久,但是对其失效机制仍存在分歧。由于机械设备常常在高温、高速、高载荷的条件下运行,因此接触疲劳又成为众多学者研究的热点问题。本文用试验模拟轴承的工作环境,研究不同载荷和滚滑比下试样接触表面磨损形貌以及亚表面损伤机制,为追溯疲劳本源和延长轴承的服役寿命提供理论依据。本文以GCr15轴承钢材料为试验对象,采用MJP-20型滚动接触疲劳试验机进行线接触滚动疲劳试验,通过改变载荷、滚滑比等试验参数研究材料接触疲劳亚表面损伤机制。试验前在同一热处理状态下获得均匀的组织,对加工试样材料的原始组织形貌以及成分含量进行了分析;试验后利用光学显微镜(OM)和扫描电镜(SEM)对接触表面的磨损形貌、裂纹和亚表面组织形貌进行观察,利用透射电镜(TEM)观察微区组织结构变化,最后使用纳米压痕仪对白色蚀刻区(WEA)和附近基体材料的硬度进行测量对比。通过以上对接触表面形貌、亚表面裂纹及微观组织变化的分析。得到结论为:(1)GCr15轴承钢试样在不同的接触压力和滚滑比下表面磨损形貌存在很大区别,试验表明载荷和滚滑比是影响表面磨损程度的共同因素。裂纹是导致轴承等工件剥落失效的直接原因。裂纹的不定向扩展会使材料产生多种失效模式,如点蚀、剥落和断裂等。(2)滚动接触疲劳是一个复杂的过程,在多个因素的影响下,疲劳裂纹的长大是连续或不连续扩展的一个过程,并且疲劳裂纹的扩展方向随着工况的改变而改变。裂纹内的磨屑是裂纹面相对运动及摩擦的结果。在裂纹内部还出现了扭曲和旋转的微观结构,因此赫兹接触是一个复杂的多轴应力状态。(3)WEA在接触压力和滚滑比的共同作用下形成且WEA在不同的接触压力产生。在WEA中已不存在碳化物且WEA和基体之间存在明显的界面。在靠近WEA的基体中出现拉长的晶粒和大量的位错簇。越靠近界面的位置,晶粒细化程度越高。由于晶粒细化,WEA的硬度比基体材料的硬度有明显的升高。(4)滚动接触疲劳引起微观结构变化有两种方式:纳米结晶和非晶化。于是,WEA可被分为变形WEA和转化WEA。变形的WEA主要包含纳米晶,而转化WEA是非晶相和纳米晶的共存体。这两种类型的微观结构变化均由塑性变形的累积程度决定。
[Abstract]:GCr15 bearing steel is a kind of high carbon chromium steel which is widely used in manufacturing rolling parts such as bearings gears and so on. Usually the bearing in service is subjected to cyclic load including radial compression stress and circumferential friction. The actual life of bearing under this complex working condition is often lower than the design life. Although the contact fatigue properties of bearing steels have been studied for a long time, there are still differences on the failure mechanism of bearing steels. Contact fatigue has become a hot issue for many scholars because the mechanical equipment often runs under high temperature, high speed and high load. In this paper, the contact surface wear morphology and subsurface damage mechanism of the specimens under different load and rolling slip ratio are studied by simulating the working environment of the bearing, which provides a theoretical basis for tracing the fatigue source and prolonging the service life of the bearing. In this paper, GCr15 bearing steel is used as experimental object. Linear contact rolling fatigue test is carried out with MJP-20 rolling contact fatigue tester. The mechanism of contact fatigue subsurface damage is studied by changing load, rolling slip ratio and other test parameters. The uniform microstructure was obtained in the same heat treatment state before the test. The original microstructure and composition content of the processed samples were analyzed. After the test, the wear morphology of the contact surface was observed by optical microscope (OM) and scanning electron microscope (SEM). The microstructures were observed by TEM and TEM. Finally, the hardness of white etched area was measured and compared with that of the matrix material by nano-indentation. Based on the above analysis of the contact surface morphology, sub-surface cracks and microstructure changes. It is concluded that the wear morphology of GCr15 bearing steel under different contact pressure and rolling slip ratio is very different. The test results show that the load and the rolling slip ratio are the common factors affecting the wear degree of the bearing steel. Crack is the direct cause of spalling failure of bearing and other workpieces. The unorientated propagation of cracks will lead to a variety of failure modes, such as pitting, denudation and fracture. Rolling contact fatigue is a complicated process, and under the influence of many factors, Fatigue crack growth is a process of continuous or discontinuous growth, and the direction of fatigue crack growth changes with the change of working conditions. The wear debris in the crack is the result of the relative movement and friction of the crack surface. There are also twisting and rotating microstructures inside the crack, so Hertz contact is a complex multiaxial stress state. WEA is formed under the combined action of contact pressure and roll slip ratio, and WEA is produced at different contact pressure. There are no carbides in WEA and obvious interface between WEA and matrix. Elongated grains and a large number of dislocation clusters appear in the matrix near WEA. The closer the interface is, the higher the grain refinement degree is. Because the hardness of WEA is obviously higher than that of matrix material, there are two ways to change the microstructure of WEA: nanocrystalline and amorphous. Therefore, WEA can be divided into transformed WEA and transformed wea. The deformed WEA mainly contains nanocrystalline, while the transformed WEA is the coexistence of amorphous phase and nanocrystalline. Both types of microstructure change are determined by the cumulative degree of plastic deformation.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.1

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