Microstructure and Mechanical Properties of a Spray-Formed Superalloy

doi:10.1007/s40195-014-0121-8

Abstract

Abstract:

The microstructural evolution and mechanical properties of a spray-formed superalloy were studied in this paper. Based on a better understanding of the microstructural evolution of the spray-formed superalloy during solution treatment, an optimum solution treatment process was obtained, namely, at 1,140°C for 6 h, and air cooling (AC). The effects of the ageing treatments on the mechanical properties of the post-solution-treated spray-formed superalloy were evaluated using ageing harden curves and tensile testing. The results indicated that the maximum hardness value was achieved at 850°C for 8h, AC. Due to co-precipitation of primary and secondary γ′ precipitates during the heat treatment, the spray-formed superalloy obtained an excellent combination of yield strength (YS=1,110 MPa), ultimate tensile strength (UTS=1,503 MPa), ductility (elongation, EL=21%) and excellent stress rupture properties at 650°C (UTS=1,209 MPa, EL=15.8%). The heat treatment also improved the rupture life at 650°C/950 MPa and 750 °C/539 MPa up to 140h without rupturing. The tensile-fractured surfaces exhibit ductile transgranular failure feature. The optimum heat treatment process was determined to be 1,140°C/6h+850°C/8h+AC.

Key words: Spray-formed superalloy, Microstructure, Ageing harden, Mechanical properties

Kang Fuwei, Cao Fuyang, Zhang Xuemin, Yue Hongyan, Feng Yicheng. Microstructure and Mechanical Properties of a Spray-Formed Superalloy[J]. Acta Metallurgica Sinica (English Letters), 2014, 27(6): 1063-1069.

Figures/Tables 9

Fig. 1 Schematic diagram of spray-forming set-up

Fig. 2 Calculated phase diagram of the as-HIPed spray-formed superalloy

Fig. 3 Optical image a, SEM image b showing the microstructures of the as-HIPed spray-formed alloy

Fig. 4 SEM micrographs of spray-formed superalloy under different solution treatment conditions: a 1,120 °C/2 h + WQ, b 1,130 °C/6 h + AC, c 1,140 °C/6 h + AC, d 1,150 °C/4 h + AC

Fig. 5 Hardness of the post-solution-treated spray-formed superalloy under different ageing time and ageing temperatures

Fig. 6 Hardness versus radius of γ′ precipitates of spray-formed superalloy under the heat treatment condition of 1,140 °C/6 h + 850 °C/8 h + AC

Fig. 7 Optical image a, SEM image b showing the microstructures of the spray-formed superalloy the heat treatment condition of 1,140 °C/6 h + 850 °C/8 h + AC

Table 1 Comparison of mechanical properties of spray-formed and conventional Samples at different conditions

Sample	UTS (MPa)	YS at RT (MPa)	EL (%)	Rupture life (h)
	RT	650 °C		RT	650 °C	650 °C/950 MPa	750 °C/539 MPa
Spray formed	1,503	1,209	1,110	21	15.8	>140	>140
Wrought [20]	1,275	1,150	8,53	14	14	100	100

Fig. 8 SEM images of heat treatment spray-formed superalloy after tensile tests at room temperature a, 650 °C b

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