Design and development of a high-performance Ni-based superalloy WSU 150 for additive manufacturing

doi:10.1016/j.jmst.2020.01.041

Abstract

Abstract:

This research proposes a design and development strategy of a new nickel-based superalloy for additive manufacturing. A new Ni-based superalloy has been developed by the application of the combinatorial alloy development technique coupled with CALPHAD based solidification modeling by effectively suppressing the precipitation kinetics. The suppression of precipitation during processing paved a way for prevention of cracks during deposition. The new alloy “WSU 150″ revealed excellent room temperature mechanical properties with a yield strength of 867 MPa, an ultimate tensile strength of 1188 MPa, and an elongation of 27.9% in the as-deposited condition. The mechanical properties of the heat-treated alloy were improved significantly to 1114 MPa yield strength, 1396 MPa ultimate tensile strength, and an elongation of 16.1%. Improvement in the mechanical properties is attributed to the additional precipitation and coarsening of γ' and carbides during heat-treatment. Microstructural investigation of the alloy revealed spherical γ' with a rippled size distribution from the center to the interdendritic region. The average size of the γ' particles in the as-deposited condition was found to be around 48 nm in the interdendritic region. Heat-treatment promoted the coarsening of γ' which is explained in the paper.

Key words: Ni-based superalloys, Additive manufacturing, Laser metal deposition, Ripple pattern microstructure, Alloy development, Mechanical properties

Praveen Sreeramagiri, Ajay Bhagavatam, Abhishek Ramakrishnan, Husam Alrehaili, Guru Prasad Dinda. Design and development of a high-performance Ni-based superalloy WSU 150 for additive manufacturing[J]. J. Mater. Sci. Technol., 2020, 47: 20-28.

Figures/Tables 13

Fig. 1. Robotic laser metal deposition (LMD) equipment developed at Wayne State University. (a) Robotic arm with a nozzle attached through the optical fiber, (b) Image demonstrating the combinatorial alloy development technique with LMD.

Fig. 2. SEM images of the as-deposited gradient samples showing the microstructural morphology of γ? particles. (a → h) Showing the increasing trend of size and volume fraction of γ? with the increase of high γ? alloy content in the sample.

Table 1 Chemical composition of the new WSU 150 alloy powder.

Element (Wt%)	Ni	Cr	C	Mo	Co	W	Cb (Nb)	Ti	Ta	Al
WSU150	59.64	17.83	0.09	5.3	9.29	1.33	0.45	2.75	0.9	2.44

Table 2 Process parameters used for the deposition of WSU 150.

Alloy	Laser Power (Watt)	Scan Speed (mm/min)	Powder Flow Rate (gm/min)	Shaping Gas (ft³/hr)	Powder Carrier Gas (ft³/hr)
WSU 150	750	720	14.5	15	15

Fig. 3. (a) Block deposited for the tension test coupons, (b) Tension test sample dimensions in accordance with ASTM E8 standards, (c) Tension test sample prepared according to (b).

Fig. 4. (a) CALPHAD based solidification modeling for WSU 150, (b) Schiel based elemental segregation model for WSU 150 from start to the end of solidification.

Fig. 5. SEM analysis of as-deposited WSU 150. (a) Low magnification image showing the dendrite (gray contrast) and interdendritic region (lighter region), (b-c) Dendrite with different cores, (d) γ? particles at the center of the dendrite, (e) Transition zone of two cores with a different precipitate size distribution, and (f) Magnified view of (c) showing different cores and size distribution of γ? particles.

Fig. 6. SEM analysis of WSU 150 aged at 760 °C for 4 h, (a) Transition from one core to other core, (b) Dendrite and interdendritic region with carbides in the interdendritic region, (c) Dendrite and interdendritic region, (d) Magnified view of (a) showing different cores and size distribution of γ? particles.

Fig. 7. (a-b) Locations of EDS analysis performed on the WSU 150 alloy.

Table 3 The EDS analysis on the sample referenced to Fig. 7.

(a)
Location	1	2	3
Element	Wt.%	Wt.%	Wt.%
Al	19.59	2.81	2.73
Ta	1.32	1.84	1.72
W	2.98	2.5	2.79
Mo	5.26	5.28	5.31
Ti	2.02	2.32	2.29
Cr	14.83	17.6	17.64
Co	7.87	9.46	9.91
Ni	46.13	58.18	57.62
(b)
Location	1	2	3
Element	Wt.%	Wt.%	Wt.%
Al	2.84	2.83	2.91
Ta	1.91	1.83	1.98
W	2.37	2.73	2.53
Mo	5.02	5.21	5.43
Ti	2.38	2.56	2.79
Cr	17.75	17.81	17.5
Co	9.24	9.03	8.97
Ni	58.5	58.01	57.9

Fig. 8. X-ray diffraction pattern of the as-deposited and heat-treated WSU 150 samples.

Table 4 Mechanical properties of the as-deposited and the heat-treated WSU 150.

Condition		AD	HT @760 °C/4 h
Name	Units	WSU150
Young’ Modulus ‘E’	GPa	191.32	201.84
Yield Strength	MPa	867	1113.84
Ultimate Tensile Strength ‘UTS’	MPa	1188	1396
Engineering Strain at UTS	%	27.57	16.05
% Elongation	%	27.9	16.1
Fracture Stress	MPa	1164.04	1386.32

Fig. 9. (a) Tension test results of WSU 150 conducted in as-deposited and different heat-treated conditions, (b) Bar chart representing strength and ductility of various as-deposited and heat-treated conditions.

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