Laser dissimilar welding of CoCrFeMnNi-high entropy alloy and duplex stainless steel

doi:10.1016/j.jmst.2021.02.003

Abstract

Abstract:

High entropy alloys (HEAs) have superior mechanical properties that have enabled them to be used as structural materials in nuclear and aerospace applications. As a dissimilar joint design is required for these applications, we created a dissimilar joint between CoCrFeMnNi-HEA and duplex stainless steel (DSS) through laser beam welding; a technique capable of producing a sound joint between the two materials. Microstructure examination using SEM/EBSD/XRD analysis revealed that the weld metal (WM) exhibits an FCC phase regardless of the postweld heat treatment (PWHT) temperature (800 and 1000 °C) without forming detrimental intermetallic compounds or microsegregation. The heat-affected zone of the CoCrFeMnNi-HEA showed CrMn oxide inclusions while that of the DSS showed no inclusions. Moreover, a lower hardness was recorded by the WM compared to the base metal after welding. After PWHT, the hardness of the WM, CoCrFeMnNi-HEA, and DSS decreased with an increase in the PWHT temperature. However, the decrease in the hardness of the HEA was more significant than in the WM and DSS. The cause for this reduction in hardness was attributed to recrystallization and grain growth. In addition, a strength of 584 MPa with low ductility was recorded after welding. The obtained strength was lower than that of the BMs, but comparable to that of the welded CoCrFeMnNi-HEA. The application of PWHT resulted in over a 20% increment in ductility, with only a marginal reduction in strength. The deformation mechanism in the as-weld joint was mainly dominated by dislocation while that for the PWHT joint was twinning. We propose laser beam offset welding as a technique to improve the mechanical properties of the dissimilar joint, which will be the subject of future studies.

Key words: High entropy alloys, Welding, Duplex stainless steel, Post-weld heat treatment

Nana Kwabena Adomako, Giseung Shin, Nokeun Park, Kyoungtae Park, Jeoung Han Kim. Laser dissimilar welding of CoCrFeMnNi-high entropy alloy and duplex stainless steel[J]. J. Mater. Sci. Technol., 2021, 85: 95-105.

Figures/Tables 16

Fig. 1. (a) Schematic diagram of the experimental setup. (b) Observation positions of the microstructure specimens and microhardness test.

Fig. 2. (a) Microstructures of CoCrFeMnNi-HEA before and after PWHT. (b) Microstructure of DSS before and after PWHT. Red arrows point to the CrMn oxides.

Fig. 3. SEM/EDS line scan and mapping image of (a) as-welded joint, (b) PWHT joint at 800 °C, and (c) PWHT joint at 1000 °C.

Fig. 4. SEM/EDS mapping image of the HAZ with the as-welded joint at the (a) CoCrFeMnNi-HEA and (b) DSS side. (c) XRD data showing patterns of the CoCrFeMnNi-HEA, DSS, as-welded joint, and PWHT joint at 800 °C and 1000 °C. EBSD phase map of the (c-i) as-welded joint, (c-ii) PWHT joint at 800 °C, and (c-iii) PWHT joint at 1000 °C.

Table 1 EDS analysis of the different regions in the FZ of the as-welded joint in Fig. 3(a).

	Chemical Composition (wt.%)						Cr-equivalents = %Cr + %Mo + 1.5%Si + 0.5%Nb + 2%Ti	Ni-equivalents = %Ni + 30%C + 0.5%Mn
Region	Fe	Cr	Ni	Co	Mn	Si	Cr-equivalents = %Cr + %Mo + 1.5%Si + 0.5%Nb + 2%Ti	Ni-equivalents = %Ni + 30%C + 0.5%Mn
①	50.0	19.9	10.6	9.9	9.5	0.14	20.11	15.35
②	45.3	20.8	11.4	9.6	12.6	0.21	21.12	17.70
③	52.2	19.1	9.8	9.3	9.4	0.17	19.36	14.50

Fig. 5. Graph of the Schaeffler diagram [33] showing points (①, ②, and ③) marked on the FZ of the joint.

Fig. 6. EBSD IPF maps and texture analysis in the FZ for the (a) as-welded joint, (b) PWHT joints at 800 °C, and (c) PWHT joints at 1000 °C.

Table 2 Grain size analysis in the joints.

	Regions and average grain size (μm)
Sample	HEA-HAZ	FZ-HEA Side	FZ-DSS side	DSS-HAZ
As-weld	21.5 ±6	140.3 ± 47	414.8 ± 130	37.4 ±12
PWHT at 800 °C	22.6 ± 7	327.9 ± 81	365.7± 100	31.1±10
PWHT at 1000 °C	69.0±24	315.5 ± 102	268.0 ±93	32.4 ± 10

Fig. 7. Microhardness distribution profiles of the various joint interfaces.

Table 3 The hardness of the welded joint and parent metal before and after PWHT.

	Average micro-hardness value (HV)
Samples	CoCrFeMnNiHEA	CoCrFeMnNi HEA (HAZ)	FZ	DSS (HAZ)	DSS
As-welded	320	230	170	240	250
PWHT at 800 °C	150	150	160	235	240
PWHT at 1000 °C	120	120	150	225	230

Fig. 8. (a) Stress-strain curve of the parent metal and welded joints. (b) An optical image and schematic diagram of the fractured welded samples.

Fig. 9. Fracture surface of the (a) as-weld, (c) PWHT at 800 °C, and (c) PWHT at 1000 °C joints.

Table 4 Tensile properties of the weld joint before and after PWHT.

Samples	Ultimate Tensile Strength (MPa)	Yield Strength (MPa)	Ductility (%)
As-welded	584	397	8.2
PWHT at 800 °C	515	252	23.5
PWHT at 1000 °C	492	186	36.1

Fig. 10. Strain hardening rate as a function of the true strain of the as-weld and PWHT joints.

Fig. 11. ECCI and EBSD (IPF and KAM) images of the tip of the fracture specimen of the (a) as-weld, (b) PWHT at 800 °C, and (c) PWHT at 1000 °C joints.

Table 5 Tensile strength of welded CoCrFeMnNi-HEA from the literature.

Welding method	Materials joined	Tensile strength (MPa)	Failure region	References
Electron beam	Rolled HEA	565	FZ	[25]
Gas Tungsten Arc	Rolled HEA	530	FZ	[34]
Electron beam	Rolled HEA	617	FZ	[34]
Gas Tungsten Arc	Rolled HEA	519	FZ	[42]
Laser beam	Rolled HEA	640	FZ	[26]
Laser beam	Cast and Rolled HEA	360	Cast BM	[19]

References 44

[1]	B. Gludovatz, A. Hohenwarter, D. Catoor, E.H. Chang, E.P. George, R.O. Ritchie, Science 345 (2014) 1153-1158. DOI PMID
[2]	B. Cantor, Entropy 16 (2014) 4749-4768. DOI URL
[3]	N.K. Adomako, J.H. Kim, Y.T. Hyun, J. Therm. Anal. Calorim. 133 (2018) 13-26. DOI URL
[4]	H.S. Cho, S.J. Bae, Y.S. Na, K.S. Lee, J.H. Kim, D.G. Lee, J. Alloy. Compd. 821 (2020), 153526. DOI URL
[5]	Y. Zhang, T.T. Zuo, Z. Tang, M.C. Gao, K.A. Dahmen, P.K. Liaw, Z.P. Lu, Prog. Mater. Sci. 61 (2014) 1-93. DOI URL
[6]	J.H. Kim, Y.S. Na, Met. Mater. Int. 25 (2019) 296-303. DOI URL
[7]	J.H. Kim, K.R. Lim, J.W. Won, Y.S. Na, H.S. Kim, Mater. Sci. Eng. A 712 (2018) 108-113. DOI URL
[8]	S.W. Kim, J.H. Kim, Mater. Sci. Eng. A 718 (2018) 321-325. DOI URL
[9]	K. Jin, C. Lu, L.M. Wang, J. Qu, W.J. Weber, Y. Zhang, H. Bei, Scr. Mater. 119 (2016) 65-70. DOI URL
[10]	A. Ayyagari, R. Salloom, S. Muskeri, S. Mukherjee, Materialia 4 (2018) 99-103. DOI URL
[11]	N.A.P.K. Kumar, C. Li, K.J. Leonard, H. Bei, S.J. Zinkle, Acta Mater. 113 (2016) 230-244. DOI URL
[12]	T. Egami, M. Ojha, O. Khorgolkhuu, D.M. Nicholson, G.M. Stocks, JOM 67 (2015) 2345-2349. DOI URL
[13]	L.R. Owen, N.G. Jones, J. Mater. Res. 33 (2018) 2954-2969. DOI URL
[14]	J.D. Tucker, M.K. Miller, G.A. Young, Acta Mater. 87 (2015) 15-24. DOI URL
[15]	Y.Q. Wang, B. Yang, J. Han, F. Dong, Y.L. Wang, Procedia Eng. 36 (2012) 88-95. DOI URL
[16]	A.N. Ashong, M.Y. Na, H.C. Kim, S.H. Noh, T. Park, H.J. Chang, J.H. Kim, Mater. Des. 182 (2019), 107997. DOI URL
[17]	M.P. Groover, Fundamentals of Modern Manufacturing, fourth ed., 2008.
[18]	Z. Wu, S.A. David, Z. Feng, H. Bei, Scr. Mater. 124 (2016) 81-85. DOI URL
[19]	H. Nam, S. Park, E.J. Chun, H. Kim, Y. Na, N. Kang, Sci. Technol. Weld. Join. 25 (2020) 127-134. DOI URL
[20]	R. Sokkalingam, V. Muthupandi, K. Sivaprasad, K.G. Prashanth, J. Mater. Res. (2019) 1-12.
[21]	A. Aloraier, R. Ibrahim, P. Thomson, Int. J. Press. Vessel. Pip. 83 (2006) 394-398.
[22]	W. Chen, P. Ackerson, P. Molian, Mater. Des. 30 (2009) 245-251. DOI URL
[23]	F. Yusof, M.F. Jamaluddin, Compr. Mater. Process. (2014) 125-134.
[24]	S. Kou, Welding Metallurgy, Wiley Interscience, New Jersey, 2003.
[25]	Z. Wu, S.A. David, Z. Feng, H. Bei, Scr. Mater. 124 (2016) 81-85. DOI URL
[26]	H. Nam, C. Park, C. Kim, H. Kim, N. Kang, Sci. Technol. Weld. Join. 23 (2018) 420-427. DOI URL
[27]	E.J. Pickering, R. Muñoz-Moreno, H.J. Stone, N.G. Jones, Scr. Mater. 113 (2016) 106-109. DOI URL
[28]	Y.K. Kim, G.S. Ham, H.S. Kim, K.A. Lee, Intermetallics 111 (2019), 106486. DOI URL
[29]	A. Gali, E.P. George, Intermetallics 39 (2013) 74-78. DOI URL
[30]	C.S. Lee, R.S. Chandel, H.P. Seow, Mater. Manuf. Process. 15 (2000) 649-666. DOI URL
[31]	B.M. Sim, T.S. Hong, M.A.A. Hanim, E.J.N. Tchan, M.K. Talari, Materials 12(2019).
[32]	V. Raghavan, Metall. Mater. Trans. A 26 (1995) 237-242. DOI URL
[33]	A.L. Schaeffler, Met. Prog. 56 (1949) 680.
[34]	Z. Wu, S.A. David, D.N. Leonard, Z. Feng, H. Bei, Sci. Technol. Weld. Join. 23 (2018) 585-595. DOI URL
[35]	S.K. Dinda, M. Basiruddin Sk, G.G. Roy, P. Srirangam, Mater. Sci. Eng. A 677 (2016) 182-192. DOI URL
[36]	P.P. Bhattacharjee, G.D. Sathiaraj, M. Zaid, J.R. Gatti, C. Lee, C.W. Tsai, J.W. Yeh, J. Alloy. Compd. 587 (2014) 544-552. DOI URL
[37]	G. Laplanche, O. Horst, F. Otto, G. Eggeler, E.P. George, J. Alloy. Compd. 647 (2015) 548-557. DOI URL
[38]	Y.C. Huang, C.H. Su, S.K. Wu, C. Lin, Entropy 21 (2019) 297. DOI URL
[39]	H. Shahmir, J. He, Z. Lu, M. Kawasaki, T.G. Langdon, Mater. Sci. Eng. A 676 (2016) 294-303. DOI URL
[40]	G. Laplanche, O. Horst, F. Otto, G. Eggeler, E.P. George, J. Alloy. Compd. 647 (2015) 548-557. DOI URL
[41]	N. Park, B.J. Lee, N. Tsuji, J. Alloy. Compd. 719 (2017) 189-193. DOI URL
[42]	J.P. Oliveira, T.M. Curado, Z. Zeng, J.G. Lopes, E. Rossinyol, J. Min, N. Schell, F.M.B. Fernandes, H. Seop,Mater. Des. 189 (2020), 108505.
[43]	X. Zhao, Z. Shi, C. Deng, Y. Liu, X. Li, Metals 10 (2020) 1138. DOI URL
[44]	K.D. Ramkumar, R. Sridhar, S. Periwal, S. Oza, V. Saxena, P. Hidad, N. Arivazhagan, Mater. Des. 68 (2015) 158-166. DOI URL