Re-recognition of the Effects of Phosphorus and Boron on the γ″ and γ′ Phases in IN718 Alloy

doi:10.1007/s40195-018-0786-5

Abstract

Abstract:

The effects of P and B on the matrix strength and precipitations of γ′ and γ″ phases in the grain interior were re-recognized in this study. The combination addition of P and B markedly accelerated the precipitations of γ′ and γ″ phases and strengthened the matrix of IN718 alloy when air-cooled from high temperature, while made no difference when water-quenched from high temperature. The effect of single addition of P on the precipitations of γ″ and γ′ phases was the same with that of the combination addition of P and B, while the single addition of B had no effect on the precipitations of the two phases. Therefore, it was P rather than B which accelerated the precipitations of γ′ and γ″ phases. P could take part in the precipitations of γ′ and γ″ phases, which was revealed by electrochemical extraction and quantitative analysis of chemical composition. It also revealed that P atoms were dissolved in the γ matrix to a relatively high degree at the temperature that γ′ and γ″ phases began to precipitate, and consequently the precipitations of γ′ and γ″ phases were accelerated. The first-principle calculation indicated that P decreased the formation enthalpies of γ′ and γ″ phases when it occupied the Ni lattice sites in the two phases, which explained the effect of P on the γ′ and γ″ phases.

Key words: IN718 superalloy, Phosphorus and boron, γ″ and γ′ phases;, Hardness

An-Wen Zhang, Yang Li, Sha Zhang, Fang Liu, Wei-Hong Zhang, Lian-Xu Yu, Wen-Ru Sun. Re-recognition of the Effects of Phosphorus and Boron on the γ″ and γ′ Phases in IN718 Alloy[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(3): 372-380.

Figures/Tables 13

Table 1 Analyzed concentrations of the three master ingots (mass%)

Master alloy no.	Ni	Fe	Cr	Al	Ti	Nb	Mo	C
A	52.7	Bal.	19.18	0.64	1.11	5.22	3.05	0.058
B	52.6	Bal.	19.12	0.50	0.86	4.99	3.01	0.46
C	52.3	Bal.	19.15	0.48	0.90	5.30	3.08	0.043

Table 2 Analyzed compositions of the six alloys

Alloy no.	P (mass%)	P (atomic%)	B (mass%)	B (atomic%)
A1	0.001	0.002	0.0046	0.024
A2	0.017	0.031	0.009	0.048
B1	0.001	0.002	0.004	0.022
B2	0.001	0.002	0.010	0.054
C1	0.001	0.002	0.005	0.026
C2	0.015	0.028	0.005	0.026

Fig. 1 Sketch maps of γ′ and γ″ lattices. Reproduced with permission from [15]

Fig. 2 Typical microstructures of the alloys: a the as-cast alloy; b the homogenized alloy; c the homogenized alloys performed by “Tag” method

Fig. 3 HV micro-hardnesses of the alloys A1 and A2 cooled by WQ and AC after homogenization

Fig. 4 Alloys A1 and A2 cooled by WQ after homogenization, dark-field images of γ″ and γ′ phases and the SAED patterns with [001] zone axis: a Alloy A1, viewed along a (0 1 0) direction; b Alloy A1, viewed along a (1 1/1221/122 0) direction.; c Alloy A2, viewed along a (0 1 0) direction; d Alloy A2, viewed along a (1 1/1221/122 0) direction

Fig. 5 Alloys A1 and A2 cooled by AC after homogenization, dark-field image of γ″ and γ′ phases and the SAED patterns with [001] zone axis: a Alloy A1, viewed along a (0 1 0) direction; b Alloy A1, viewed along a (1 1/1221/122 0) direction.; c Alloy A2, viewed along a (0 1 0) direction; d Alloy A2, viewed along a (1 1/1221/122 0) direction

Fig. 6 HV micro-hardnesses of the alloys B1 and B2 cooled by WQ and AC after homogenization

Fig. 7 Bright-field images and corresponding SAED patterns of the alloys B1 and B2 cooled by AC after homogenization: a alloy B1; b alloy B2

Fig. 8 HV micro-hardnesses of the alloys C1 and C2 cooled by WQ and AC after homogenization

Fig. 9 Bright-field images and corresponding SAED patterns of the alloys C1 and C2 cooled by AC after homogenization: a alloy C1; b alloy C2

Table 3 Effect of P on the formation enthalpies of γ″ and γ′ phases calculated by first-principle calculations

Phase	Supercell	?_fH (eV/atom)
Ni₃Al (γ′)	Ni₂₄Al₈	- 0.475
	Ni₂₄Al₇-P	- 0.461
	Ni₂₃Al₈-P	- 0.508
Ni₃Nb (γ″)	Ni₂₄Nb₈	- 0.329
	Ni₂₄Nb₇-P	- 0.314
	Ni₂₃Nb₈-P (Ni-1)	- 0.339
	Ni₂₃Nb₈-P (Ni-2)	- 0.308

Fig. 10 X-ray diffraction pattern of the extractions of the alloy C2

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