基于團簇模型設計的鎳基單晶高溫合金(Ni, Co)-Al-(Ta, Ti)-(Cr, Mo, W)及其在900 ℃下1000 h的長期時效行為

基于團簇模型設計的鎳基單晶高溫合金(Ni, Co)-Al-(Ta, Ti)-(Cr, Mo, W)及其在900 ℃下1000 h的長期時效行為The Influence of the “Ni-Co Replacing” and “Ti-Ta Repalcing” for the 1st Generation Nickel-based Single Crystal Superalloys About Long Term Ageing Based on the Cluster-Plus-Glue-Atom Model

本文利用團簇加連接原子模型，通過“Ni-Co替換”和“Ti-Ta替換”對第一代鎳基單晶高溫合金進行成分設計。對于“Ni-Co替換”合金，Co元素的變化不影響鎳基單晶高溫合金的密度和初熔點。隨Co含量增加，合金的γ′體積分數升高，γ′尺寸減小。在900℃/1000h長期時效過程中，Co提高元素擴散系數的同時降低γ′形成元素在基體中的濃度，因此Co的變化不影響斜率K ([(at/2)3-(a0/2)3]1/3=Kt1/3)，也不影響錯配度。對于“Ti-Ta替換”合金，Ta的密度和熔點均高于Ti，因此隨Ta的增加(Ti的降低)，合金的密度和初熔點均升高。Ta元素的增加(Ti元素降低)雖然縮小了負錯配度，但合金900℃/1000h長期時效過程中依然保持負錯配度，抑制了γ′的粗化并提高了合金的結構穩定性。

It has been recently pointed out that the compositions of nickel-based single crystal superalloys are originated from cluster-plus-glue-atom structure units. The Co atom substitutions for the Ni atom and the Ta substitutes for Ti, under the two cases, this paper raises two groups (Group (a) and Group (b)) for nickel-based single crystal superalloys with the cluster-plus-glue-atom model. Group (a) is the [Al-Ni12-xCox](Al1Ti0.25Ta0.25Cr1W0.25Mo0.25), with x = 1.5, 1.75, 2, and 2.5 (the corresponding weight percents of Co are respectively 9.43 Co, 11Co, 12.57Co, and 15.71Co). Group (b) is the [Al-Ni11Co1](Al1Ti0.5-yTayCr1W0.25Mo0.25), with y=0, 0.25 and 0.5 (the corresponding weight percents of Ti and Ta are respectively 0Ta (2.65Ti), 4.82Ta (1.26Ti) and 9.32Ta (0Ti)). For the Co atom taking the placing of Ni at the shell sites, both the density and the incipient melting point do not change too much. As the content of Co increases, the mean size of the γ' precipitates reduces and the γ' volume fraction increases. For the 900℃/1000h long term ageing, the slope K ([(at/2)3-(a0/2)3]1/3=Kt1/3) is not too much change while the Co is increasing. Because the Co is able to promote the diffusion and reduce the concentration of the γ' forming elements. The misfit is not change too much when the Co replace the Ni. For the Ta substitutions for the Ti at the glue sites, with the Ta increases (the Ti reduces), both the density and the incipient melting point are increasing for the nickel-based single crystal superalloys. However, the negative misfit is shrinking when the Ta increases (the Ti reduces) because the lattice parameter of the γ' is increasing. But lower negative misfit exists after 900℃/1000 hours long term ageing. In the other words, the existing of negative misfit is able to resistant the γ' coarsening. In other words, when the Ta increases (the Ti reduces), the micro-structure stability is also improved because of Ta increasing (Ti reducing).

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