690合金中三晶交界及晶界類型對碳化物析出形貌的影響

690合金中三晶交界及晶界類型對碳化物析出形貌的影響EFFECTS OF TRIPLE JUNCTION AND GRAIN BOUNDARY CHARACTERS ON THE MORPHOLOGY OF CARBIDE PRECIPITATION IN ALLOY 690

利用SEM和EBSD技術(shù)研究了鎳基690合金在715 ℃時(shí)效15 h后不同類型的三晶交界附近三個(gè)晶界上碳化物的析出形貌。結(jié)果表明：對于不同類型三晶交界處，Σ3c晶界上析出的碳化物的形貌存在明顯的差異，碳化物按照Σ3-Σ3-Σ9、Σ3-Σ9-Σ27、Σ3-Σ27-R、Σ3-R-R三晶交界順序逐漸增多增大。Σ3i和Σ9晶界上析出的碳化物的形貌在不同類型的三晶交界附近基本相似。Σ27晶界上碳化物的析出形貌在三晶交界處與晶界內(nèi)部存在一定差異，三晶交界處析出的碳化物相對于晶界內(nèi)部離散且大。當(dāng)兩條隨機(jī)晶界與Σ3或Σ9晶界相連時(shí)，其中一條隨機(jī)晶界上析出的碳化物比另一條上的小。

The nickel based Inconel Alloy 690 (Ni-30Cr-10Fe, mass fraction %) was developed as a replacement material for Inconel Alloy 600 in the steam generator tube of pressurized water reactors nuclear power plants. Intergranular corrosion and intergranular stress corrosion cracking were the main failure reasons for steam generator tubes, which were related to the precipitation of grain boundary carbides. Hence, the precipitation of carbide at the grain boundaries and triple junctions with different characters is worthy to be studied. The morphology of carbide precipitated on grain boundaries at triple junctions with various characters in grain boundary engineering (GBE) treated nickel base Alloy 690 aged at 715 ℃ for 15 h were investigated by SEM and EBSD. The results show that, there are obvious differences in the morphology of carbides precipitated on the Σ3c grain boundary near different types of triple junction. The size of carbide precipitated at Σ3c grain boundary increased by the order of Σ3-Σ3-Σ9、Σ3-Σ9-Σ27、Σ3-Σ27-R、Σ3-R-R triple junctions. But the morphology of carbides precipitated at the Σ3i and Σ9 grain boundaries were independent of the nearby triple junction characters. The precipitation morphology of carbides precipitated on the Σ27 grain boundary near the triple junction is different from that precipitated on the internal grain boundary, for example, the carbides precipitated near triple junction was more discrete and bigger than that precipitated on internal grain boundary. When the triple junction contain two random grain boundaries and one Σ3 grain boundary or Σ9 grain boundary, the size of carbide precipitated on one of random grain boundary is smaller than that of precipitated on the other one.

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