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| ROLE OF SOLUTION TREATMENT IN IMPROVING THE CREEP STRENGTH OF A DIRECTIONALLY SOLIDIFIED NICKEL-BASE SUPERALLOY |
| Lin Dongliang(Ling Tung-liang) (Shanghai Jiaotong University) |
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Cite this article:
Lin Dongliang(Ling Tung-liang) (Shanghai Jiaotong University). ROLE OF SOLUTION TREATMENT IN IMPROVING THE CREEP STRENGTH OF A DIRECTIONALLY SOLIDIFIED NICKEL-BASE SUPERALLOY. Acta Metall Sin, 1981, 17(1): 26-124.
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Abstract The effect of high temperature solution treatment on the structure and properties of a directionally solidified high strength nickel-base superalloy has been investigated. The size and amount of fine γ' particle in the ahoy increased with the increase of solution temperature. Creep rupture life τ_f was increased and secondary creep rate (?) decreased with the increase of the solution temperature. As the alloy was undergone 1210 to 1250℃ solution and 900℃, 16 h aging, a two-fold increase in creep rupture life was obtained at 760℃ under 66 kgf/mm~2 load, however, the secondary creep rate apparently decreased. The relationship between τ_f and (?) can be expressed as (?)~mτ_f =c, where m≈1, c≈8.0. It is thus regarded that the improvement of rupture life at intermediate temperature (760℃) is due primarily to a fall in secondary creep rate, and in turn to an extension in secondary stage of creep. The secondary creep rate is strongly dependent upon the size, a, and volume fraction, ν_f, of the fine γ' and (?)∞α/ν_f~(2/3).The dislocation substructure during secondary stage of creep has been examined by TEM. At a creep temperature of 760℃, there were a number of dense 3-dimensional dislocation networks in γ matrix, but only a few superlattice dislocation pairs appeared in γ'. When the temperature was increased to 980℃, the γ-γ' interface was found to be covered with 2-dimensional dislocation networks. A mechanism for secondary stage creep has been proposed according to the climbing model.
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Received: 18 January 1981
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