摘要:
针对严苛高温服役工况下零件腐蚀磨损失效严重的问题，本文利用激光定向能量沉积（laser directed energy deposition，LDED）的方法制备了不同Cr含量的低熔点镍基合金试样，进而研究Cr含量对合金组织性能与抗高温腐蚀性能的影响。采用SEM、XRD、EPMA等对合金的显微组织进行分析，同时讨论了合金组织与硬度及抗高温熔盐腐蚀性能间的内在联系。结果表明：激光定向能量沉积制备的高Cr低熔点镍基合金组织主要由γ-Ni、CrB和Cr5B3组成；随着Cr含量增加，合金中硼化物含量相应升高，且块状Cr5B3相逐渐向粗大条状转变，菊花状（γ-Ni+CrB）共晶相消失，出现层片状的（γ-Ni+Cr5B3）共晶相。合金的硬度随Cr含量不断升高，最高达到360.8 HV，主要由于基体相硬度的升高和硼化物硬质相含量的升高。与TP347H不锈钢相比，新型高Cr低熔点镍基合金的抗高温熔盐腐蚀性能更加优异，且随Cr含量增加，合金的抗高温腐蚀性能明显提高；Cr40合金试样表现出最优的抗腐蚀性能，比TP347H提高约15倍。在高温腐蚀过程中，合金表面形成致密的富Cr氧化膜，可有效阻碍腐蚀反应侵入；另一方面，Cr元素可发挥固硫作用，使得高Cr低熔点镍基合金表现出优异的抗高温熔盐腐蚀性能。
Abstract:
In view of the serious corrosion and wear failure of parts under harsh and high-temperature service conditions, low-melting nickel base alloy samples with different Cr content were prepared by laser directed energy deposition (LDED). The effects of Cr content on the microstructure and high-temperature corrosion resistance of the alloy were investigated. The microstructure of the alloy was analyzed by SEM, XRD and EPMA, and the relationship between the microstructure, hardness and resistance to high temperature molten salt corrosion was discussed. The results show that the microstructure of high Cr and low melting point nickel base alloy prepared by LDED is mainly composed of γ-Ni, CrB and Cr5B3. With the increase of Cr content, the boride content in the alloy increases correspondingly, and the coarse Cr5B3 phase changes from block to coarse strip gradually, The Daisy (γ-Ni+CrB) eutectic phase disappeared, and lamellar (γ-Ni+Cr5B3) eutectic phase appeared. The hardness of the alloy increases with the Cr content, reaching up to 360.8 HV, mainly due to the increase of matrix phase hardness and boride hard phase content. Compared with TP347H stainless steel, the new high Cr and low melting point nickel base alloy has better resistance to high temperature molten salt corrosion, with the increase of Cr content, the high temperature corrosion resistance of the alloy is obviously improved. Cr40 alloy samples show the best corrosion resistance, which is about 15 times higher than TP347H. During the high temperature corrosion process, a dense Cr-rich oxide film is formed on the alloy surface, which can effectively prevent the corrosion reaction from invading. On the other hand, Cr element can play the role of sulfur fixation, so that the high Cr low melting point nickel-based alloy shows excellent resistance to high temperature molten salt corrosion.
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