Effect of solution heat treatment on microstructures and stress rupture properties of a third generation Ni-based single crystal superalloy
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Abstract:
Effect of solution heat treatment on microstructures and stress rupture properties of a third generation Ni-based single crystal superalloy with content of 6.5%(mass fraction) Re has been investigated. The experimental results show that the as-cast alloy exists significant solidification segregation and a large percentage of (γ+γ') eutectic. During the solution heat treatment, the (γ+γ') eutectic initially solves rapidly when the temperature is higher than 1 335℃. However, the solidification segregation especially the segregation of Re is not significantly reduced until solution heat treatment temperatures exceed 1 360℃. The micropore content after solution heat treatment at 1 365℃ is about 0.21%(volume fraction), which is 5.2 times of that before heat treatment. The stress rupture properties of the as-cast alloy and the alloys after different solution heat treatment at 1 360℃ and 1 365℃ are investigated respectively at the conditions of 1 080℃/190 MPa, 1 100℃/140 MPa and 1 150℃/83 MPa. The results show that the heat treatment significantly improves the stress rupture properties, and the higher solution heat treatment temperature is, the longer the stress rupture lives are. During the process of high temperature stress rupture, most of cracks distribute in the interdendritic and cracks initiat from the (γ+γ') eutectic in the as-cast alloy. The alloy with solution heat treatment at 1 360℃ has some cracks which distribute both in the dendritic core and interdendritic area. A large amount of TCP(topologically close-packed) precipitation distributes in the dendritic core possibly due to the residual segregation of Re. However, as the alloy with solution heat treatment at 1 365℃, there is less TCP precipitation.
