ISSN   1004-0595

CN  62-1224/O4

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粉末粒径对激光熔覆修复EA4T钢拉压微动疲劳行为影响研究

Effect of Powder Particle Size on Tensile-Compressive Fretting Fatigue Behaviour of EA4T Steel Repaired by Laser Cladding

  • 摘要: 高铁轮轴配合面在压装过程中产生的异物拉伤会大大降低服役安全可靠性. 本文中以EA4T钢为研究对象,使用50、100和150 μm这3种粒径NiCrMo合金粉末对预损伤试样进行激光熔覆修复,开展拉压微动疲劳试验探究不同粉末粒径对材料修复后微动疲劳行为的影响. 结果显示,EA4T钢的拉压微动疲劳S~N曲线呈倾斜的“Z”字形特征,同一疲劳载荷条件下,3种粒径粉末修复试样疲劳寿命相比未修复试样均呈现略微下降,但仍保持较高的疲劳寿命. 修复前后材料疲劳失效断口均属于正断型穿晶断裂. 1×105次循环条件下接触损伤区均可见倾斜于接触面方向的疲劳裂纹,50 μm粒径试样损伤区存在因激光熔覆过程吸收过多热量而产生的凝固裂纹. 损伤区磨损形貌均表现为不规则椭圆形,损伤机理主要为黏着磨损、氧化磨损、磨粒磨损以及剥层;1×105次循环条件时,50、100和150 μm粒径试样磨损体积分别为2.43×106、1.94×106和3.29×106 μm3,2×105次循环条件时,50、100和150 μm粒径试样磨损体积分别为4.32×106、3.86×106和5.64×106 μm3,100 μm粒径试样接触区心部剥层现象较轻微,磨损体积较小;随着循环次数的增加,100 μm粒径修复试样晚于150 μm粒径修复试样进入裂纹扩展阶段,50 μm粒径修复试样会因凝固裂纹扩展过早断裂,100 μm粒径修复试样疲劳寿命相对较高.

     

    Abstract: The surface of high-speed rail wheel axles may attract damage caused by foreign matter during the press-fitting process, which could impact or even reduce the service reliability and safety. This study explored the use of NiCrMo alloy powder particle in three sizes (50, 100 and 150 μm) for laser cladding repair of pre-damaged EA4T steel, the undamaged specimen and repaired specimen were taken as the research object. The article investigates the influence of varying powder particle sizes on the fretting fatigue behavior after material repair through tensile-compressive fretting fatigue repeat tests. The results indicated that the tensile-compressive fretting fatigue S~N curves of the substrates displayed a slanted 'Z-shaped' feature. Despite a slight decrease in fatigue lifespan under the same load conditions of repaired specimens which compared to the substrate specimen, but all of the repaired specimens still showed an overall higher fatigue life in general. The fracture surface of both the undamaged specimens and repaired specimens exhibited a normal transgranular fracture type. Fatigue cracks tilted towards the contact surface direction were visible in the contact damage area after 1×105 cycles. Solidification cracks appeared in the damaged region of the 50 μm particle size specimen result from excessive heat absorption during laser cladding repair process. Shape of all the wear areas appeared as an irregular elliptical, with adhesive wear, oxidation wear, abrasive wear, and delamination being the normal primary damage mechanisms. The wear volume of 50, 100 and 150 μm particle size laser cladding repair specimens were measured at 2.43×106 μm3, 1.94×106 μm3, and 3.29×106 μm3 respectively after 1×105 cycles of fretting fatigue test. After 2×105 cycles of fretting fatigue test, the wear volumes for the same particle sizes powders were 4.32×106 μm3, 3.86×106 μm3, and 5.64×106 μm3. In the case of the 100 μm particle size specimen, there was a slight delamination phenomenon observed in the contact center, resulting in a small wear volume. As the number of cycles about fretting fatigue test increases, the 100 μm particle-repaired specimen crack propagation was delay compared to the 150 μm particle-repaired specimen. Conversely, the 50 μm particle-repaired specimen occurred premature fracture due to the solidification crack propagation. The fatigue lifespan of the 100 μm particle-repaired specimen was relatively longer than the other two kinds of laser cladding repair specimens with 50 μm and 150 μm particle sizes.

     

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