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激光金属沉积成形304不锈钢的疲劳断裂机理分析

Fatigue fracture mechanism of 304 stainless steel manufactured by laser metal deposition

  • 摘要: 激光金属沉积是一种应用广泛的激光增材制造技术,文中对激光金属沉积成形304奥氏体不锈钢进行疲劳试验,并对其疲劳断裂机理进行了分析. 根据试验结果绘制激光金属沉积成形304奥氏体不锈钢的应力-寿命(S-N)曲线,结果表明,应力幅的大小对疲劳断口形貌有着至关重要的影响. 应力幅越大,疲劳断口越粗糙,在较高的应力幅作用下,断裂试样表面存在随机分布的孔洞和裂纹,材料缺陷如氧化物夹杂和孔洞是导致疲劳裂纹萌生的主要原因,而在较大的应力幅(如275 MPa)作用下,较大的局部塑性变形也是导致疲劳裂纹萌生原因之一,随着应力幅的增大,疲劳条带更加清晰,在较高的应力幅作用下,多个滑移系的相交导致疲劳条带不在同一平面内扩展,并且裂纹扩展区内出现轮胎压痕. 随着应力幅的增大,由于疲劳裂纹扩展区内塑性变形量的增大导致疲劳裂纹扩展区中二次裂纹数量增加.

     

    Abstract: Laser metal deposition is a widely used laser additive manufacturing technology. The fatigue tests of 304 austenitic stainless steel manufactured by laser metal deposition are carried out and the fatigue fracture mechanism is studied. According to the experimental results, the S-N curve of 304 austenitic stainless steel manufactured by laser metal deposition is drawn. The results show that the stress amplitude has an important effect on the fatigue fracture morphology. The larger the stress amplitude is, the coarser the fatigue fracture is. Under the higher stress amplitude, there are randomly distributed holes and cracks on the surface of the fracture specimen. Material defects such as oxide inclusions and pores are the main causes of fatigue crack initiation, and large local plastic deformation under the large stress amplitude (such as 275 MPa) is also one of the causes of fatigue crack initiation. With the increase of stress amplitude, the fatigue bands become clearer. Under the higher stress amplitude, the intersection of multiple slip systems leads to the expansion of fatigue bands in different plane, and the tire indentation appears in the crack propagation zone. With the increase of stress amplitude, the number of secondary cracks increases due to the increase of plastic deformation in the fatigue crack propagation zone.

     

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