钎料合金BCo46的抗热腐蚀性能

HOT CORROSION RESISTANCE OF FILLER ALLOY BCo46

采用涂盐方法研究了新型钴基钎料BCo46的抗热腐蚀性能,并与BNi-2和基材合金DZ468进行了对比.评估了完全热处理后的采用BCo46钎焊DZ468合金接头的抗热腐蚀性能.研究表明,BCo46合金的热腐蚀抗力优于DZ468和BNi-2合金,热腐蚀过程中3种合金都发生了氧化膜溶解和硫化物析出,合金的腐蚀进程可以用硫化-酸碱熔融的热腐蚀模型解释;钎焊接头中形成的硼化物会显著降低合金的热腐蚀抗力,完全热处理后的钎焊接头组织均匀,接头抗热腐蚀性能与DZ468合金相当.

DZ468 alloy is a promising candidate in turbine blade serving in marine atmosphere because of its superior mechanical properties and good hot corrosion resistance. And brazing technology is indispensable to produce turbine blade because of its complicated hollow structure. Therefore, for accelerating the application of DZ468 superalloy, a new type Co-based filler named BCo46 was developed. Due to serving in marine atmosphere, the attack of hot corrosion can be inevitable. Frequently, the quality of turbine blade depends on the joining region, and the joining region has a lot to do with the filler used to braze the base alloy. Therefore, in this work, the hot corrosion behavior and mechanism of BCo46 alloy in the mixture of 75%Na2SO, ＋ 25%NaC1 （mass fraction） at 900 ~C was investigated, and compared with a common Ni-based filler BNi-2, and the base alloy DZ468. Moreover, the hot corrosion resistance of the joint bonded with BCo46 was evaluated. XRD, SEM, EDS and ICP spectrograph were employed to study the corrosion products of the tested alloys. The results show that the hot corrosion processes of BCo46, BNi-2 and DZ468 alloys are all accompanied with the dissolution of oxide scale and the formation of sulfide, which support the model of sulfidation-（acid-based） melting model. For filler alloy BCo46, Cr203, Co3BO~ and （Ni, Co）CrzO~ mainly exist in the outer corrosion layer and some CrS is formed in the inner corrosion layer; the external corrosion products of BNi-2 are NiO, （Ni, Co）Cr20,, Ni2FeBO5 and Cr203, and the internal precipitation is Ni2S3. The hot corrosion resistance of filler alloy BCo46 is superior to DZ468 superalloy and BNi-2 filler, it is because （1） BCo46 contains 22% Cr which can form dense and continuous oxide scale Cr^O3; （2） the diffusion rates of O and S are slower in Co- than Ni-based alloy; （3） Co can increase the adhesion of the oxide scale-base metal; （4） collaboration dissolution doesn＇t occur in BCo46. Furthermore, the formation of boride can deteriorate the hot corrosion resistance of alloy by forming oxides of boron which can dissolve oxide scale, consume Cr and increase phase interracial area to accelerate the diffusion of S and O. The joint after heat treatment can reach the level of the hot corrosion resistance of the base metal DZ468.