Low-Cycle Fatigue Properties of Nickel-Based Superalloys Processed by High-Gradient Directional Solidification

doi:10.1007/s40195-017-0563-x

Abstract

Abstract:

The low-cycle fatigue (LCF) properties of DD10 (single-crystal) and DZ53 (columnar-grained) superalloys solidified by liquid-metal cooling (LMC) and high-rate solidification (HRS) processes have been systematically investigated. It was found that the LCF life of DZ53 solidified by LMC was obviously better than that solidified by HRS. In contrast, for DD10, LMC showed no remarkable influences on LCF properties at high temperature and only improved LCF properties at intermediate temperature. Microstructure examination showed that the cracks generally initiated at micropores in the subsurface at intermediate temperature. However, the cracks occurred on the surface due to oxidation, or persistent slip bands near script-MC at high temperature. Therefore, the benefits of LMC technique can be attributed to both of the reduced casting defects which significantly affect the LCF properties at intermediate temperature and the improved microstructural homogeneity which was strongly correlated to the LCF properties of alloys at high temperature.

Key words: Superalloys, Rapid solidification, Low-cycle fatigue, Microstructure

Z. D. Fan, D. Wang, C. Liu, G. Zhang, J. Shen, L. H. Lou, J. Zhang. Low-Cycle Fatigue Properties of Nickel-Based Superalloys Processed by High-Gradient Directional Solidification[J]. Acta Metallurgica Sinica (English Letters), 2017, 30(9): 878-886.

Figures/Tables 11

Table 1 Nominal chemical compositions of DD10 and DZ53 alloys (wt%)

Alloy	Re	W	Mo	Ta	Cr	Co	Al	Ti	C	Ni
DD10	-	4	0.5	5	12	6	4	4	0.03	Bal.
DZ53	3	9	2	7	6	9	6	1	0.1	Bal.

Table 2 Fatigue properties of DD10 solidified by HRS at 1253 and 1033 K

Total strain range (%)	Fatigue life	Deviation from [001] (°)	Fatigue life	Deviation from [001] (°)
Total strain range (%)	1253 K		1033 K
2.4	114	3	20	5
2.0	226	6	444	6
1.8	-	-	1204	5
1.6	348	7	2360	4
1.4	-	-	10,344	6
1.2	1144	6	-	-
1.0	2174	7	-	-
1.0	2964	5	-	-
0.8	7534	3	-	-
0.8	5960	8	-	-

Table 3 Fatigue properties of DD10 solidified by LMC at 1253 and 1033 K

Total strain range (%)	Fatigue life	Deviation from [001] (°)	Fatigue life	Deviation from [001] (°)
Total strain range (%)	1253 K		1033 K
2.4	100	5	100	3
2.4	67	7	100	3
2.0	236	7	764	5
1.8	-	-	1356	5
1.6	426	8	5400	2
1.4	582	3	11,356	4
1.2	1312	8	-	-
1.2	842	8	-	-
1.0	1768	3	-	-
1.0	2028	7	-	-
0.8	5620	4	-	-

Fig. 1 OM micrographs of DD10 and DZ53 alloys after heat treatment: a DD10 alloy solidified by HRS, b DD10 alloy solidified by LMC, c DZ53 alloy solidified by HRS d DZ53 alloy solidified by LMC

Fig. 2 Comparison of the morphologies of script carbides in DZ53: a HRS, b LMC

Fig. 3 Images of micropores in DD10 and DZ53 alloys after heat treatment: a DD10 alloy solidified by HRS, b DD10 alloy solidified by LMC, c DZ53 alloy solidified by HRS, d DZ53 alloy solidified by LMC

Fig. 4 LCF properties of DD10 and DZ53 alloys solidified by HRS and LMC techniques at different temperatures: a DD10 alloy at 1253 K, b DD10 alloy at 1033 K, c DZ53 alloy at 1253 K

Table 4 Quantitative comparison of PDAS, eutectics and microporosity

Alloy	DS process	PDAS (μm)	Remaining eutectics (%)	Volume fraction of microporosity (%)	Maximum equivalent radius of microporosity (μm)
DD10	HRS	360 ± 27	No	0.2	20
DD10	LMC	155 ± 10	No	0.08	15
DZ53	HRS	345 ± 21	0.51 ± 0.1	0.45	28
DZ53	LMC	145 ± 12	0.02 ± 0.006	0.1	16

Fig. 5 LCF fractographs of DD10 alloy under total strain range of 1.2%: a a low-magnification fractograph of HRS alloy at 1253 K, b a low-magnification fractograph of LMC alloy at 1253 K, c longitudinal section microstructure of HRS alloy at 1253 K, d a low-magnification fractograph of HRS alloy at 1033 K, e a high-magnification fractograph of HRS alloy at 1033 K, f a low-magnification fractograph of LMC alloy at 1033 K, g a high-magnification fractograph of LMC alloy at 1033 K

Table 5 Tensile properties of DD10 and DZ53 alloys solidified by HRS and LMC techniques

Alloy	DS process	Temperature (K)	0.2% YS (MPa)	UTS (MPa)	Elongation (%)
DD10	HRS	1033	1110	1330	13.2
	LMC	1033	1121	1310	14.2
	HRS	1253	392	636	24.7
	LMC	1253	405	640	25.1
DZ53	HRS	1253	815	597	12.5
DZ53	LMC	1253	844	613	23.6

Fig. 6 LCF fractographs of DZ53 alloy under total strain range of 1.2% at 1253 K: a a low-magnification fractograph of HRS alloy, b a low-magnification fractograph of LMC alloy, c a high-magnification fractograph of HRS alloy, d a high-magnification fractograph of LMC alloy, e, f longitudinal section microstructure of HRS alloy

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