High Strength, Ductile Braze Repairs for Stationary Gas Turbine Components: Part 1
High Strength, Ductile Braze Repairs for Stationary Gas Turbine Components: Part 1
复制标题
固定燃气轮机部件的高强度、延展性钎焊修复：第 1 部分
DOI：
10.1115/gt2008-51133
复制
发表时间：
2008
影响因子：
3.6
通讯作者：
M. Toit
中科院分区：
文献类型：
--
作者：
W. Miglietti;M. Toit
航空和陆基涡轮部件，如叶片/喷嘴、燃烧室、衬里和过渡件，在使用中经常退化和破裂。与其更换新的部件，创新的维修可以帮助降低大修和维护成本。这些成分由FSX-414等钴基固溶体高温合金或IN738等镍基伽马素析出强化高温合金铸造而成。其名义成分分别为Co-29.5Cr-10.5Ni-7W-2Fe[max]-0.25C-0.012B和Ni-0.001B-0.17C-8.5Co-16Cr-1.7Mo-3.4Al-2.6W-1.7Ta-2Nb-3.4Ti-0.1Zr，。扩散钎焊用于修复这类部件上的裂纹和退化已有40多年的历史。通常，用于部件修复的钎料是含有B和/或Si作为熔点降低剂的镍基和钴基钎料。特别是在修复工业燃气轮机部件上常见的宽裂纹时，这些熔点降低剂会形成脆性的金属间化合物和硅化物相，影响机械性能，如低循环和热疲劳。这项工作的目的是调查和评估过共晶Ni-Cr-Hf和Ni-Cr-Zr钎料的使用，其中熔点降低剂不再是B，而是Hf和/或Zr。通常，如果接头间隙或裂纹宽度小于0.15 mm，则可以单独使用钎料。对于大于0.15 mm的裂纹，将高温合金粉末与钎料混合，使宽裂纹能够被成功地钎焊修复。作为扩散钎焊修复合格的一种手段，进行了冶金性能和机械性能的评估。金相评价包括光学显微镜、扫描电子显微镜和微探针分析。扩散钎焊区由细小的等轴晶组织组成，碳化物相、γ[伽马]枝晶、花状/玫瑰花状γ-γ‘[伽马素]共晶相和Ni7Hf2、Ni5Hf或Ni5Zr金属间化合物相弥散分布在晶间和晶内。硬度测试表明，Ni-Hf和Ni-Zr金属间化合物相的硬度范围为250Hv~400Hv，而典型的铬-硼化物相的硬度范围为800Hv~1000Hv。因此，Ni-Hf和Ni-Zr金属间化合物相的硬度比铬-硼化物金属间化合物相的硬度低2.5-3.2倍。结果表明，大间隙Ni-Cr-Hf和Ni-Cr-Zr钎料的低周疲劳性能均优于Ni-Cr-B钎料。机械性能评估包括室温和高温拉伸测试，760°C-1093°C的应力断裂测试，最后是低周疲劳[LCF]测试，后者是最重要和最严格的测试之一，因为修复的裂纹是热疲劳驱动的。在最佳的钎焊热循环下，所获得的力学测试结果最低为80%，有时与母材的性能相当。版权所有©2008由ASME
Both aviation and land based turbine components such as vanes/nozzles, combustion chambers, liners, and transition pieces often degrade and crack in service. Rather than replacing with new components, innovative repairs can help reduce overhaul and maintenance costs. These components are cast from either Co-based solid solution superalloys such as FSX-414, or Ni-based gamma prime precipitation strengthened superalloys such as IN738. The nominal compositions of FSX-414 and IN738 are Co-29.5Cr-10.5Ni-7W-2Fe [max]-0.25C-0.012B and Ni-0.001B-0.17C-8.5Co-16Cr-1.7Mo-3.4Al-2.6W-1.7Ta-2Nb-3.4Ti-0.1Zr, respectively. Diffusion brazing has been used for over four decades to repair cracks and degradation on these types of components. Typically, braze materials utilized for component repairs are Ni and Co-based braze fillers containing B and/or Si as melting point depressants. Especially when repairing wide cracks typically found on industrial gas turbine components, these melting point depressants can form brittle intermetallic boride and silicide phases that effect mechanical properties such as low cycle and thermal fatigue. The objective of this work is to investigate and evaluate the use of hypereutectic Ni-Cr-Hf and Ni-Cr-Zr braze filler metals, where the melting point depressant is no longer B, but Hf and/or Zr. Typically, with joint gaps or crack widths less than 0.15mm, the braze filler metal alone can be utilized. For cracks greater than 0.15mm, a superalloy powder is mixed with the braze filler metal to enable wide cracks to be successfully brazed repaired. As a means of qualifying the diffusion braze repair, both metallurgical and mechanical property evaluations were carried out. The metallurgical evaluation consisted of optical and scanning electron microscopy, and microprobe analysis. The diffusion brazed area consisted of a fine-grained equiaxed structure, with carbide phases, γ [gamma] dendrites, flower shaped/rosette γ-γ′ [gamma-gamma prime] eutectic phases and Ni7 Hf2 , Ni5 HF, or Ni5 Zr intermetallic phases dispersed both intergranularly and intragranularly. Hardness tests showed that the Ni-Hf and Ni-Zr intermetallic phase only has a hardness range of 250Hv to 400Hv; whereas, the typical Cr-boride phases have hardness ranges from 800Hv to 1000Hv. Therefore the hardness values of the Ni-Hf and Ni-Zr intermetallic phases are 2.5–3.2 times softer than the Cr-boride intermetallic phases. As a result the LCF properties of the wide gap Ni-Cr-Hf and Ni-Cr-Zr brazed joints are superior to those of the Ni-Cr-B braze filler metals. The mechanical property evaluations were tensile tests at both room temperature and elevated temperature, stress rupture tests from 760°C–1093°C and finally low cycle fatigue [LCF] tests, the latter being one of the most important and severe tests to conduct, since the cracks being repaired are thermal fatigue driven. At the optimum braze thermal cycle; the mechanical test results achieved were a minimum of 80% and sometimes equivalent to that of the base metals properties.Copyright © 2008 by ASME