Effect of grit blasting and subsequent heat treatment on stress rupture property of a Ni-based single-crystal superalloy SGX3

doi:10.1007/s40195-020-01051-x

Abstract

Abstract:

In the present study, the effect of grit blasting and subsequent heat treatment on the stress rupture properties of a third-generation nickel-based single-crystal superalloy SGX3 sheet was studied. It was found that the stress rupture life of alloy SGX3 sheet at 980 °C/250 MPa was reduced by about 60% by only vacuum heat treatment at 1100 °C for 200 h and further reduced by 20% and 70% respectively with grit blasting of 0.3 MPa/1 min and 0.5 MPa/2 min before heat treatment. The microstructure analysis results indicated that the degradation of stress rupture life of alloy SGX3 sheet by vacuum heat treatment was mainly attributed to the variation of γ/γ′ microstructure, i.e., the decrease in γ′ volume fraction and the coarsening of γ′ precipitates. Furthermore, such degradation by grit blasting and subsequent vacuum heat treatment should be attributed to the formation of cellular recrystallization with different thicknesses at the surface of alloy SGX3 sheet, which not only acts as the vulnerable site for cracks to initiate and propagate but also reduces the effective loading area.

Key words: Ni-based single-crystal superalloy, Creep life, Degradation, Recrystallization

Jinshan He, Zhengrong Yu, Longfei Li, Xitao Wang, Qiang Feng. Effect of grit blasting and subsequent heat treatment on stress rupture property of a Ni-based single-crystal superalloy SGX3[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(12): 1681-1688.

Figures/Tables 12

Fig. 1 Geometry of creep rupture testing specimen (mm)

Table 1 Specimens with different grit blasting

No	Standard heat treatment	Grit blasting	Vacuum heat treatment
SH	√
VH	√		1100 °C/200 h
GH1	√	0.3 MPa/1 min	1100 °C/200 h
GH2	√	0.5 MPa/2 min	1100 °C/200 h

Fig. 2 Microstructures of different specimens before stress rupture tests: a specimen SH; b specimen VH; c specimen GH1; d specimen GH2

Table 2 Statistical analysis of microstructures for different specimens

Specimen	Thickness of cellular recrystallization μ (μm)	Area of cellular recrystallization (×10⁵ μm²)	Effective loading area (%)	Volume fraction of γ′ (vol.%)
SH	0±0	0	100	64.0
VH	0±0	0	100	40.6
GH1	18.4±1.9	1.5	96.1	40.1
GH2	49.6±4.2	4.0	89.4	40.0

Fig. 3 Rupture life values for specimens with different heat treatments and grit blasting

Fig. 4 Microstructures of longitude sections with 4 mm away from fracture surfaces for different specimens after stress rupture tests: a specimen SH; b specimen VH; c specimen GH1; d specimen GH2

Fig. 5 Microstructures of longitude sections near fracture surfaces for different specimens after stress rupture tests: a specimen SH; b specimen VH; c specimen GH1; d specimen GH2 (the insets are of small magnifications)

Fig. 6 Morphologies of retained cracks and corresponding loading direction inverse pole figure maps for different specimens after stress rupture tests: a specimen VH, b specimen GH2

Fig. 7 Effects of grit blasting and subsequent heat treatment on stress rupture property of alloy SGX3 sheet

Fig. 8 Illustration of surface recrystallization on stress rupture life for different Ni-based superalloys

Table 3 Chemical composition (wt%) of alloys in Refs.[8, 14, 17, 19, 27]

References	Ni	Cr	Co	W	Mo	Al	Ti	Ta	C	B	Nb	Hf
[8]	Bal	8.5	5	9.5	-	5.5	2.2	2.8	0.02	-	-	-
[14]	Bal	8	5	5	2	6	2	3	-	-	-	-
[17]	Bal	8-10	9-11	11.5-12.5	-	4.75-5.25	1.75-2.25	-	0.12-0.16	0.01-0.02	0.75-1.25	1-2
[19]	Bal	8.9	10	11.7	-	5	2	1	-	0.014	1	1.8
[27]	Bal	9	10	7	2	5	3.5	4	0.1	0.01	-	-

Table 4 Creep information of alloys in Refs.[8, 14, 17, 19, 27]. The normalized stress rupture life is defined as the ratio of the stress rupture life time of a specimen over that of the same alloy without recrystallization at the same creep condition

References	Alloy	Creep condition	Recrystallization type	Effective loading area (%)	Normalized stress rupture life
[19]	Directionally solidified	980 °C/235 MPa	Not indicated	1	1±0.18
				0.98	0.99±0.06
				0.96	0.84
				0.88	0.44
				0.8	0.3
[27]	Directionally solidified	955 °C/255 MPa	Equiaxed	1	1
[27]	Directionally solidified	955 °C/255 MPa	Equiaxed	0.95	0.68
[8]	Single crystal	1000 °C/195 MPa	Equiaxed	1	1
				0.92	0.56
				0.91	0.5
				0.88	0.48
				0.87	0.45
				0.86	0.36
				0.85	0.34
[14]	Single crystal	950 °C/240 MPa	Equiaxed	1	1
				0.96	0.71
				0.93	0.5
				0.89	0.365
[17]	Single crystal	1000 °C/195 MPa	Not indicated	1	1
				0.92	0.5
				0.876	0.474
				0.851	0.34

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