The effect of secondary dendrite orientation on thickness debit effect of nickel-based single-crystal superalloy with tubular samples

Abstract

Secondary dendrite orientation and wall thickness considerably affect the stress rupture life of thin-walled samples. However, the effect of the secondary dendrite orientation on the thickness debit effect of nickel-based single-crystal superalloys has not been thoroughly investigated until now. Owing to geometrical constraints, typical sheet samples cannot reveal the mechanism responsible for the thickness debit effect in turbine blades. This study examined the effect of secondary dendrite orientation on the thickness debit effect of nickel-based single-crystal superalloys at 1100 °C/137 MPa in tubular samples. As the wall thickness decreased from 1.5 mm to 0.3 mm, the stress rupture life decreased from approximately 170 h to 64 h, demonstrating a noticeable thickness debit effect. Among the different secondary dendrite orientation areas, the variation in plastic deformation difference increased from 7 % (1.5 mm) to 45 % (0.5 mm) and subsequently decreased to 4 % (0.3 mm). In thinner samples, the thickness contraction and microstructure evolution were more pronounced in the [100] areas than that in the [110] and [210] areas. The theoretical calculation quantitatively indicated that for the effective stress increased, the contribution of plastic deformation (45 %) was slightly lower than that of oxidation (55 %) in 0.3 mm samples; nevertheless, plastic deformation played a prominent role in 0.5, 0.8, 1, and 1.5 mm samples and increased from 61 % (0.5 mm samples) to 85 % (1.5 mm samples). In thinner samples, the larger plastic deformation in the secondary dendrite orientation of the [100] areas and oxidation increased the effective stress, resulting in a shorter rupture life. These findings are conducive to the structural optimization and performance improvement of turbine blades.