摘要不锈钢与铌的复合焊接结构在航空航天领域具有广阔的应用与发展前景。本课题采用了激光焊接的方法，在不同的参数条件下对304不锈钢板与铌板进行焊接，实现了两种材料的连接。使用金相显微镜观察接头横截面的宏观形貌与微观组织，使用EDS确定了焊接接头的化学元素组成，使用XRD确定了焊接接头的相组成。通过拉伸试验衡量焊接接头的力学性能。87009

激光焊接可以实现304不锈钢与铌的连接。除了20号试样焊后断裂，其他试样均没断裂。观察试样的显微照片，大部分试样上无明显的缺陷，有几组试样上存在裂纹，气孔，断裂现象，均出现在铌与焊缝交界处，且焊接速度过大的试样容易出现缺陷，说明在钢/铌激光焊接中较大的焊接速度不利于得到良好的焊接接头。焊缝区域完全由树枝状的γ相组成。在铌侧附近的焊缝存在金属间化合物，出现裂纹与断裂等现象均出现在该区域。金属间化合物层由μ-Fe7Nb6和少量的Cr2Nb，Ni8Nb组成。焊接接头的抗拉强度最大可达193MPa，具有一定的力学性能。通过正交试验法分析焊接速度，偏束距离，焊接功率对焊接接头抗拉强度的影响规律。其中焊接速度的影响最大，偏束距离的影响其次，激光功率的影响最小。焊接速度越小，焊接接头的抗拉强度越高；激光束光斑偏向不锈钢侧，焊接接头的抗拉强度变高。使用低焊速，向钢侧偏束的焊接参数可以提高焊接接头的抗拉强度。焊后断裂发生在铌侧界面处。

毕业论文关键词：钢/铌焊接;激光焊接;金属间化合物

Abstract The composite welding construction of stainless steel and niobium has an extraordinarily broad application and development prospect in airspace field。 In this thesis, with the application of laser welding, 304 stainless steel plate and niobium plate have been welded under different parameters and finally come to the connection of the two materials。 Metallurgical microscope has been used to observe the macroscopic morphology and microstructure of joint cross section。 SEM and XRD has been used accordingly to analyze the chemical elements compositions and phase compositions of the welding joint separately。 With the application of the tensile test, the mechanical properties can be measured。

Laser welding can be used to achieve the connection of 304 stainless steel and niobium。 except for the rupture of the 20 aliquot after welding, others show no sign of rupture。 When observing the micrograph of aliquots, most of them show no obvious defects while cracks, pores and ruptures exist in niobium and welding seam。 It turns out that higher welding speed can bring defects to the aliquot easier which suggests that high welding speed can not help to get qualified welding seam in this experiment。 The welding seam is totally consisted of austenite and appears as γ phase similar to the branch of a tree。 There are intermetallic compounds in areas of welding seam near the niobium where cracks and fractures are all found。 The intermetallic compounds consist of mostly μ-Fe7Nb6 and slightly some Cr2Nb and Ni8Nb。 The tensile strength of the welding joint can be as high as 193 MPa with certain mechanical properties。 By building mathematical models through orthogonal test, the analysis can be made about the influences of welding speed, partial beam distance and welding capacity towards the tensile strength of the welding joint。 Among them, the effect of speed comes the first, the partial beam the second and the capacity the least。 Low speed of welding brings high tensile strength。 When the laser beam light spot moves to the stainless steel side, the tensile strength turns higher。 Using the parameter of the low welding speed and partial beams of steel side can turn up the tensile strength。 Ruptures after welding take place in the welding seams near niobium。