Microstructure and Stress-Rupture Property of Large-Scale Complex Nickel-Based Single Crystal Casting

doi:10.1007/s40195-018-0716-6

Abstract

Abstract:

The microstructure and stress-rupture property of the large-scale complex single crystal (SX) casting DD10 were investigated in high-rate solidification process. It is found that the primary dendrite arm spacing (PDAS) does not increase monotonically with the height increase. When across the platform, the temperature gradient increases due to the effect of platform, and the corresponding PDAS decreases. The distribution of eutectic volume fraction in large-scale complex SX casting is affected by PDAS, solid back diffusion, and the development of high order dendrites. The eutectic volume fraction contained in the sample taken below the platform decreases with the height increase. While the eutectic volume fraction contained in the sample taken upper the platform increases gradually with the height increase. After heat treatment, most of the γ/γ′ eutectics are eliminated and the components are distributed uniformly. The similar stress rupture properties of the samples at different heights in the same direction are obtained.

Key words: Large-scale single crystal, Platform, Primary dendrite arm spacing, Eutectic volume fraction, Stress-rupture property

Min Huang, Gong Zhang, Dong Wang, Jia-Sheng Dong, Li Wang, Lang-Hong Lou. Microstructure and Stress-Rupture Property of Large-Scale Complex Nickel-Based Single Crystal Casting[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(8): 887-896.

Figures/Tables 11

Table 1 Nominal chemical composition (wt%) of experimental alloy DD10 in present work

Cr	Co	Mo	W	Al	Ti	Ta	Ni
12.5	4.0	0.2	5.0	3.6	4.0	5.0	Bal.

Fig. 1 Schematic diagram of large-scale single crystal casting with platform. A, B, C, D, and E represent the samples at different heights for microstructural analysis. F, F′, H, I, and J are the samples taken for the stress rupture experiments.

Fig. 2 Transverse dendrite morphologies of samples at different heights in as-cast large-scale single crystal casting DD10 with platform: a 44 mm; b 124 mm; c 154 mm; d 234 mm; e314 mm; f distribution of PDAS in large-scale single crystal casting DD10 with platform

Fig. 3 Transverse γ/γ′ eutectic morphologies of samples at different heights in as-cast large-scale single crystal casting DD10 with platform: a 44 mm; b 124 mm; c 154 mm; d234 mm; e 314 mm; f distribution of eutectic volume fraction in as-cast large-scale single crystal casting DD10 with platform

Fig. 4 Transverse dendrite morphologies of samples at different heights in heat-treated large-scale single crystal casting DD10 with platform: a 44 mm; b 124 mm; c 154 mm; d234 mm; e 314 mm

Table 2 Element segregation coefficients (k) of large-scale single crystal casting DD10 with platform in as-cast and heat-treated conditions

Sample	Co	Al	Cr	Ti	Ni	Mo	Ta	W
As-cast	1.050	0.984	0.979	0.569	1.000	0.779	0.894	1.720
Heat-treated	1.030	0.964	1.020	0.960	0.984	0.894	0.915	1.320

Fig. 5 Transverse γ/γ′ eutectic morphologies of samples at different heights in heat-treated large-scale single crystal casting DD10 with platform: a 44 mm; b 124 mm; c 154 mm; d234 mm; e 314 mm; f distribution of eutectic volume fraction in heat-treated large-scale single crystal casting DD10 with platform

Table 3 Stress rupture properties of large-scale single crystal casting DD10 with platform

Sample	Rupture life (h)
F	37.3
F′	38.3
H	82.6
I	81.6
J	82.1

Fig. 6 Fractographies of samples from different positions: F a; F′ b; H c; I d; J e

Fig. 7 Crack morphologies of different samples in longitudinal section from stress rupture experiments: a sample F; b sample F′; c sample H; d sample I; e sample J

Fig. 8 a Schematic diagram of large-scale single crystal castings without platform (A, B, C, D, and E represent the samples at different heights for microstructural analysis), bDistribution of PDAS at different heights in large-scale single crystal castings without platform

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