汽油发动机气门座圈和气门导管的失效分析

发布时间：2018-12-11 14:12

【摘要】：借助金相显微镜、X射线衍射仪、扫描电镜和能谱仪等,本文研究了V531、V571材质气门座圈和Yc1.8、1528材质气门导管的热疲劳裂纹萌生和扩展机理,分析了硫化膜的成分、组织结构和硫化腐蚀过程的机理,测量了相应失效气门座圈和气门导管的物理和力学性能,对失效产生原因进行了分析。结果表明：V531的裂纹萌生和扩展速率大于V571的裂纹萌生和扩展速率,1528的裂纹萌生和扩展速率大于Yc1.8的裂纹萌生和扩展速率。温度降低,裂纹的萌生和扩展速率均降低。主裂纹主要在边缘孔隙和凹陷处开始萌生,在孔隙间进行扩展。裂纹在珠光体中的扩展路径取决于拉伸应力与珠光体片层之间的位向关系；在硬质相内,裂纹的扩展路径近似直线。MoS2中的S与Fe反应生成FeS, FeS分布于基体中,促进裂纹的萌生和扩展。氧化腐蚀与热疲劳裂纹扩展相互促进。四种材质样品的硫化膜中均含有CuFe2S3、FeS、CuS、CuFeS2等硫化物,而V571的硫化膜中还存在NiS和CoS2。在硫化腐蚀开始阶段,Fe、Cu、Ni离子迅速迁移,与S离子反应生成硫化物,随着硫化腐蚀的不断进行,Cr的硫化物对Fe、Cu、Ni、Co离子的迁移的产生阻碍但作用有限,硫化腐蚀程度不断加深。V571的耐腐蚀性优于V531的耐腐蚀性,Yc1.8的耐腐蚀性优于1528的耐腐蚀性,同种材质气门座圈或气门导管在HNO3溶液中的耐腐蚀性优于在H2SO4溶液中的耐腐蚀性。硬质颗粒的聚集将导致硬度分布不均。孔隙率过高是造成硬度过低和切削困难的主要原因,铜残留于工件表面将导致工件之间相互粘结。碳含量过低将导致严重磨损失效,而碳含量过高则会使得压溃强度过低。铜片重量会对渗铜效果产生直接影响,而原料粉末碳含量过低、粉末搬运过程中的扬起和露点温度、保护气氛流量等产品生产工艺参数均可能导致产品的碳含量过低。本文最后针对各失效形式和原因提出了相应的改善措施。
[Abstract]:By means of metallographic microscope, X-ray diffractometer, scanning electron microscope and energy spectrometer, the thermal fatigue crack initiation and propagation mechanism of valve seat ring and Yc1.8,1528 valve tube made of V531 and V571 were studied, and the composition of vulcanization film was analyzed. The physical and mechanical properties of the corresponding failure valve seat ring and valve tube were measured and the causes of failure were analyzed. The results show that the crack initiation and propagation rate of V531 is higher than that of V571, and the crack initiation and propagation rate of 1528 is higher than that of Yc1.8. The rate of crack initiation and propagation decreased with the decrease of temperature. The main crack mainly begins to germinate at the edge pore and the depression, and propagates between the pores. The propagation path of crack in pearlite depends on the potential relationship between tensile stress and pearlite lamellar. In the hard phase, the propagation path of the crack is approximately straight line. The S in MoS2 reacts with Fe to form a FeS, FeS distribution in the matrix, which promotes the initiation and propagation of the crack. Oxidation corrosion and thermal fatigue crack growth promote each other. The sulfides such as CuFe2S3,FeS,CuS,CuFeS2 were found in the vulcanization films of four kinds of materials, while NiS and CoS2. also existed in the vulcanization films of V571. At the beginning of sulphide corrosion, Fe,Cu,Ni ions migrate rapidly and react with S ions to form sulfides. With the continuous sulphide corrosion, Cr sulphide hinders the migration of Fe,Cu,Ni,Co ions, but its effect is limited. The corrosion resistance of V571 is better than that of V531, and the corrosion resistance of Yc1.8 is better than that of 1528. The corrosion resistance of valve seat ring or valve tube of the same material in HNO3 solution is better than that in H2SO4 solution. The accumulation of hard particles will lead to uneven distribution of hardness. High porosity is the main cause of low hardness and difficult cutting. Copper residues on the surface of the workpiece will lead to mutual bonding between the workpieces. Too low carbon content will lead to serious wear failure, and too high carbon content will lead to too low crushing strength. The weight of copper sheet has a direct effect on the effect of copper infiltration, while the carbon content of raw material powder is too low, the raising and dew point temperature during powder handling, the flow rate of protective atmosphere, and so on, may lead to the low carbon content of the product. At the end of this paper, the corresponding improvement measures are put forward for each failure form and reason.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK413

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