Effects of trace calcium and strontium on microstructure and properties of Cu-Cr alloys

doi:10.1016/j.jmst.2021.08.080

Abstract

Abstract:

Cu-0.57Cr-0.01Ca and Cu-0.58Cr-0.01Sr (wt.%) alloys were fabricated and processed by thermo-mechanical treatment. Their mechanical and electrical properties and microstructure were investigated in detail and compared with those of a Cu-0.57Cr (wt.%) alloy. The results showed that the softening resistance of the Cu-Cr alloy was significantly improved by the additions of Ca and Sr elements. Compared with the Cu-Cr alloy, the deformation microstructure of the Cu-Cr-Ca and Cu-Cr-Sr alloys was more difficult to recrystallize at elevated temperatures, and the Cr precipitates in the Cu-Cr-Ca and Cu-Cr-Sr alloys were smaller in size and had an FCC structure at any given aging state. The high strengths of the Cu-Cr-Ca and Cu-Cr-Sr alloys were mainly attributed to the dislocation strengthening provided by high-density dislocations and the precipitate strengthening provided by fine Cr precipitates. First-principles calculation showed that the segregations of Ca and Sr atoms at interface between Cr precipitates and copper matrix were favorable in energetics. This segregation effectively hindered the growth of Cr precipitates and significantly enhanced the pinning effect on the motion of dislocations and subgrain boundaries, eventually leading to the improvement in the softening resistance of the Cu-Cr alloy.

Key words: Cu-Cr alloy, Softening resistance, Microstructure, Strengthening, Segregation

Muzhi Ma, Zhu Xiao, Xiangpeng Meng, Zhou Li, Shen Gong, Jie Dai, Hongyun Jiang, Yanbin Jiang, Qian Lei, Haigen Wei. Effects of trace calcium and strontium on microstructure and properties of Cu-Cr alloys[J]. J. Mater. Sci. Technol., 2022, 112: 11-23.

Figures/Tables 18

Table 1. Chemical compositions of the Cu-Cr, Cu-Cr-Ca and Cu-Cr-Sr alloys (wt.%).

Alloy	Cr	Ca	Sr	Cu
Cu-Cr	0.57	-	-.	Bal.
Cu-Cr-Ca	0.57	0.01	-	Bal.
Cu-Cr-Sr	0.58	-	0.01	Bal.

Fig. 1. Variations of Vickers hardness and electrical conductivity of the Cu-Cr, Cu-Cr-Ca and Cu-Cr-Sr alloys during isothermal aging treatment at (a, b) 400 and (c, d) 500 °C for different time.

Fig. 2. Stress versus strain curves of the Cu-Cr, Cu-Cr-Ca and Cu-Cr-Sr alloys after cold rolling and isothermal aging treatment at 400 °C for 3 h and 16 h.

Table 2. Mechanical properties of the Cu-Cr, Cu-Cr-Ca and Cu-Cr-Sr alloys after cold rolling and isothermal aging treatment at 400 °C for 3 h and 16 h.

Alloy	Aging time (h)	Yield strength (MPa)	Tensile strength (MPa)	Elongation (%)
Cu-Cr	0	396	407	18.1
	3	434	470	23.0
	16	173	330	48.0
Cu-Cr-Ca	0	398	409	18.2
	3	440	477	21.8
	16	362	447	30.9
Cu-Cr-Sr	0	398	412	18.4
	3	449	489	21.4
	16	431	466	22.1

Fig. 3. Inverse pole figure mappings of the transverse directions of the Cu-Cr, Cu-Cr-Ca and Cu-Cr-Sr alloys after (a-c) cold rolling and isothermal aging treatment at 400 °C for (d-f) 3 h and (g-i) 16 h.

Fig. 4. Fractions of deformed, substructured and recrystallized grains of the (a) Cu-Cr, (b) Cu-Cr-Ca and (c) Cu-Cr-Sr alloys after cold rolling and isothermal aging treatment at 400 °C for 3 h and 16 h.

Fig. 5. TEM images of the Cu-Cr alloy after isothermal aging treatment at 400 °C for 3 h: (a-c) BF images, (d) SAED image, (e) HRTEM and (f) corresponding RFFT images.

Fig. 6. TEM images of the Cu-Cr alloy after isothermal aging treatment at 400 °C for 16 h: (a), (b) BF images, (c) SAED image and (d-f) HRTEM images.

Fig. 7. TEM images of the Cu-Cr-Ca alloy after isothermal aging treatment at 400 °C for 3 h: (a-c) BF images, (d) SAED image, (e) HRTEM and (f) corresponding RFFT images.

Fig. 8. TEM images of the Cu-Cr-Ca alloy after isothermal aging treatment at 400 °C for 16 h: (a, b) BF images, (c) SAED image, (d, f) HRTEM and (e) corresponding RFFT images.

Fig. 9. TEM images of the Cu-Cr-Sr alloy after isothermal aging treatment at 400 °C for 3 h: (a-c) BF images, (d) SAED image, (e) HRTEM and (f) corresponding RFFT images.

Fig. 10. TEM images of the Cu-Cr-Sr alloy after isothermal aging treatment at 400 °C for 16 h: (a, b) BF images, (c) SAED image, (d, f) HRTEM and (e, g) corresponding RFFT images.

Table 3. Increases in electrical resistivity caused by solute atom, grain boundary, dislocation and second phase of the Cu-Cr, Cu-Cr-Ca and Cu-Cr-Sr alloys after cold rolling and isothermal aging treatment at 400 °C for 3 h and 16 h.

Alloy	Aging time (h)	${{c}_{\text{Cr}}}$ (at.%)	$\text{ }\!\!\Delta\!\!\text{ }{{R}_{\text{Cr}}}$ (10^-8 Ω m)	${{c}_{\text{Ca}}}$ (at.%)	$\text{ }\!\!\Delta\!\!\text{ }{{R}_{\text{Ca}}}$(10^-8 Ω m)	${{c}_{\text{Sr}}}$ (at.%)	$\text{ }\!\!\Delta\!\!\text{ }{{R}_{\text{Sr}}}$(10^-8 Ω m)	D (μm)	$\text{ }\!\!\Delta\!\!\text{ }{{R}_{\text{GB}}}$(10^-8 Ω m)	ρ (10¹⁴ m^-2)	$\text{ }\!\!\Delta\!\!\text{ }{{R}_{\text{D}}}$ (10^-8 Ω m)	F (%)	$\text{ }\!\!\Delta\!\!\text{ }{{R}_{\text{SP}}}$ (10^-8 Ω m)
Cu-Cr	0	0.397	2.239	-	-	-	-	10.77	0.003	10.3	0.028	0.29	0.004
	3	0.050	0.281	-	-	-	-	4.94	0.007	3.76	0.010	0.62	0.010
	16	0.022	0.123	-	-	-	-	4.37	0.008	0.31	0.001	0.65	0.010
Cu-Cr-Ca	0	0.405	2.284	0.016	0.004	-	-	10.67	0.003	10.1	0.027	0.28	0.004
	3	0.058	0.325	0.016	0.004	-	-	8.46	0.004	4.52	0.012	0.61	0.010
	16	0.034	0.190	0.016	0.004	-	-	8.03	0.005	2.62	0.007	0.64	0.010
Cu-Cr-Sr	0	0.409	2.304	-	-	0.002	0.001	10.74	0.003	10.2	0.028	0.29	0.004
	3	0.064	0.363	-	-	0.002	0.001	9.26	0.004	5.45	0.015	0.62	0.010
	16	0.038	0.215	-	-	0.002	0.001	9.10	0.004	4.75	0.013	0.65	0.010

Table 4. Calculated contributions of solid solution strengthening, grain boundary strengthening and dislocation strengthening on the increment of yield strengths of the Cu-Cr, Cu-Cr-Ca and Cu-Cr-Sr alloys after cold rolling and isothermal aging treatment at 400 °C for 3 h and 16 h.

Alloy	Aging time (h)	${{c}_{\text{Cr}}}$ (at.%)	${{c}_{\text{Ca}}}$ (at.%)	${{c}_{\text{Sr}}}$ (at.%)	D (μm)	$\bar{\theta }$ (°)	$L$ (μm)	${{\sigma }_{\text{SS}}}$ (MPa)	${{\sigma }_{\text{GB}}}$ (MPa)	${{\sigma }_{\text{D}}}$ (MPa)
Cu-Cr	0	0.397	-	-	10.77	5.33	1.06	1.7	43	275
	3	0.050	-	-	4.94	6.18	3.36	0.6	63	166
	16	0.022	-	-	4.37	6.51	42.72	0.4	67	48
Cu-Cr-Ca	0	0.405	0.016	-	10.67	5.30	1.07	4.9	43	272
	3	0.058	0.016	-	8.46	5.78	2.61	3.9	48	182
	16	0.034	0.016	-	8.03	5.86	4.58	3.7	49	139
Cu-Cr-Sr	0	0.409	-	0.002	10.74	5.25	1.05	2.8	43	274
	3	0.064	-	0.002	9.26	5.53	2.07	1.8	46	200
	16	0.038	-	0.002	9.10	5.62	2.42	1.6	46	187

Table 5. Calculated contributions of precipitate strengthening on the increment of yield strengths of the Cu-Cr, Cu-Cr-Ca and Cu-Cr-Sr alloys after cold rolling and isothermal aging treatment at 400 °C for 3 h and 16 h.

Alloy	Aging time (h)	d (nm)	f (%)	λ (nm)	${{\sigma }_{\text{P}\_\text{o}}}$ (MPa)	${{\sigma }_{\text{P}\_\text{m}}}$ (MPa)	${{\sigma }_{\text{P}\_\text{c}}}$ (MPa)	${{\sigma }_{\text{P}\_\text{s}}}$ (MPa)	${{\sigma }_{\text{P}\_\text{b}}}$ (MPa)	${{\sigma }_{\text{P}}}$ (MPa)
Cu-Cr	0	-	-	-	0	0	0	0	0	0
	3	7.5	0.343	139.0	420	252	1495	2167	126	126
	16	25	0.372	445.0	437	365	2837	3639	54	54
Cu-Cr-Ca	0	-	-	-	0	0	0	0	0	0
	3	5	0.352	91.4	26	79	12	118	168	118
	16	5	0.377	88.3	27	82	13	122	173	122
Cu-Cr-Sr	0	-	-	-	0	0	0	0	0	0
	3	3	0.349	55.1	26	69	10	104	227	104
	16	3	0.376	53.1	27	71	10	118	235	108

Fig. 11. Calculated and experimental yield strengths of the (a) Cu-Cr, (b) Cu-Cr-Ca and (c) Cu-Cr-Sr alloys after cold rolling and isothermal aging treatment at 400 °C for 3 h and 16 h.

Fig. 12. Models established for first-principles calculation: (a-c) {100}, {110} and {111} pure metal models, (d) {100} solid solution model, (e) {100} interface model and (f-h) {100}, {110} and {111} segregation models.

Fig. 13. Segregation energy of a Ca or Sr atom to segregate from different initial positions towards different sites of interfaces.

References 62

[1]	P. Zhang, Q. Lei, X. Yuan, X. Sheng, D. Jiang, Y. Li, Z. Li, Mater. Today Commun. 25 (2020) 101353.
[2]	P. Zhang, Y. Li, Q. Lei, H. Tan, R. Shi, J. She, S. Li, J. Zhu, X. Sheng, J. Zhang, Z. Li, J. Mater. Res. Technol. 9 (2020) 2299-2307. DOI URL
[3]	P. Zhang, J. Jie, Y. Gao, H. Li, T. Wang, T. Li, J. Mater. Res. 30 (2015) 2073-2080. DOI URL
[4]	S. Fu, P. Liu, X. Chen, H. Zhou, F. Ma, W. Li, K. Zhang, Mater. Sci. Eng. A 802 (2021) 140598. DOI URL
[5]	Y. Wang, H. Fu, J. Wang, H. Zhang, W. Li, J. Xie, J. Nucl. Mater. 526 (2019) 151753. DOI URL
[6]	M. Ma, Z. Li, Z. Xiao, H. Zhu, X. Zhang, F. Zhao, Mater. Sci. Eng. A 795 (2020) 140 0 01.
[7]	A. Popovich, V. Suﬁiarov, I. Polozov, E. Borisov, D. Masaylo, A. Orlov, Mater. Lett. 179 (2016) 38-41. DOI URL
[8]	S.C. Krishna, G.S. Rao, A.K. Jha, B. Pant, P.V. Venkitakrishnan, Mater. Sci. Eng. A 674 (2016) 164-170. DOI URL
[9]	Y. Liu, Z. Li, Y. Jiang, Y. Zhang, Z. Zhou, Q. Lei, J. Mater. Res. 32 (2017) 1324. DOI URL
[10]	M.Z. Ma, X. Zhang, Z. Li, Z. Xiao, H.Y. Jiang, Z.Q. Xia, H.Y. Huang, Crystals 10 (2020) 426. DOI URL
[11]	W.U. Shanjiang, W. Junfeng, Z. Shuwei, Z. Jianbo, W. Hang, Y. Bin, Chin. J. Mater. Res. 33 (2019) 552-560. DOI
[12]	Y. Sun, L. Peng, G. Huang, H. Xie, X. Mi, X. Liu, Mater. Sci. Eng. A 776 (2020) 139009. DOI URL
[13]	Z. Zhao, Z. Xiao, Z. Li, M. Ma, J. Dai, J. Alloy. Compd. 752 (2018) 191-197. DOI URL
[14]	G.A. Snyder, Periodic Table, Springer, Netherlands, 1998.
[15]	Y. Wang, S. Curtarolo, C. Jiang, R. Arroyave, T. Wang, G. Ceder, L.Q. Chen, Z.K. Liu, Calphad 28 (2004) 79-90. DOI URL
[16]	M.Z. Ma, Z. Li, W.T. Qiu, Z. Xiao, Z.Q. Zhao, Y.B. Jiang, J. Alloy. Compd. 788 (2019) 50-60. DOI URL
[17]	X. Guo, Z. Xiao, W. Qiu, Z. Li, Z. Zhao, X. Wang, Y. Jiang, Mater. Sci. Eng. A 749 (2019) 281-290. DOI URL
[18]	G. Kresse, J. Furthmuller, Phys. Rev. B 54 (1996) 11169-11186. DOI PMID
[19]	J.P. Perdew, Y. Wang, Phys. Rev. B 45 (1992) 13244-13249. PMID
[20]	J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865-3868. DOI PMID
[21]	H.J. Monkhorst, J.D. Pack, Phys. Rev. B 13 (1976) 5188-5192. DOI URL
[22]	M. Methfessel, A. Paxton, Phys. Rev. B 40 (1989) 3616-3621. PMID
[23]	K. Wang, K.F. Liu, J.B. Zhang, Rare Met. 33 (2014) 134-138. DOI URL
[24]	I.S. Batra, G.K. Dey, U.D. Kulkarni, S. Banerjee, J. Nucl. Mater. 299 (2001) 91-100. DOI URL
[25]	R. Seth, S. Woods, Phys. Rev. B 2 (1970) 2961. DOI URL
[26]	S. Nagarjuna, K. Balasubramanian, D.S. Sarma, Mater. Sci. Eng. A 225 (1997) 118-124. DOI URL
[27]	C. Xia, Y. Jia, W. Zhang, K. Zhang, Q. Dong, G. Xu, M. Wang, Mater. Des. 39 (2012) 404-409. DOI URL
[28]	Y.P. Li, Z. Xiao, Z. Li, Z.Y. Zhou, Z.Q. Yang, Q. Lei, J. Alloy. Compd. 723 (2017) 1162-1170. DOI URL
[29]	D. Risold, B. Hallstedt, L.J. Gauckler, H.L. Lukas, S.G. Fries, Calphad 20 (1996) 151-160. DOI URL
[30]	K.M. Mannan, K.R. Karim, J. Phys. F Met. Phys. 5 (1975) 1687-1693. DOI URL
[31]	P. Luo, D.T. McDonald, W. Xu, S. Palanisamy, M.S. Dargusch, K. Xia, Scr. Mater. 66 (2012) 785-788. DOI URL
[32]	J. Freudenberger, A. Kauffmann, H. Klauß, T. Marr, K. Nenkov, V.S. Sarma, L. Schultz, Acta Mater. 58 (2010) 2324-2329. DOI URL
[33]	P. Rodríguez-Calvillo, N. Ferrer, J.M. Cabrera, J. Alloy. Compd. 626 (2015) 340-348. DOI URL
[34]	S.Y. Chang, C.F. Chen, S.J. Lin, T.Z. Kattamis, Acta Mater. 51 (2003) 6291-6302. DOI URL
[35]	S. Arajs, G. Dunmyre, J. Appl. Phys. 36 (1965) 3555-3559. DOI URL
[36]	C. Michaelsen, C. Gente, R. Bormann, J. Mater. Res. 12 (1997) 1463-1467. DOI URL
[37]	M.Z. Ma, Z. Li, W.T. Qiu, Z. Xiao, Z.L. Zhao, Y.B. Jiang, Z.Q. Xia, H.Y. Huang, J. Alloy. Compd. 820 (2020) 153112. DOI URL
[38]	Y. Wu, Y. Li, J. Lu, S. Tan, F. Jiang, J. Sun, Mater. Sci. Eng. A 731 (2018) 403-412. DOI URL
[39]	P. Luo, D.T. McDonald, S.M. Zhu, S. Palanisamy, M.S. Dargusch, K. Xia, Mater. Sci. Eng. A 538 (2012) 252-258. DOI URL
[40]	N. Hansen, Scr. Mater. 51 (2004) 801-806. DOI URL
[41]	K. Ma, H. Wen, T. Hu, T.D. Topping, D. Isheim, D.N. Seidman, E.J. Lavernia, J. M. Schoenung, Acta Mater. 62 (2014) 141-155. DOI URL
[42]	D.A. Hughes, N. Hansen, Acta Mater. 48 (20 0 0) 2985-30 04. DOI URL
[43]	C. Booth-Morrison, D.N. Seidman, D.C. Dunand, Acta Mater. 60 (2012) 3643-3654. DOI URL
[44]	H. Wang, L.K. Gong, J.F. Liao, H.M. Chen, W.B. Xie, B. Yang, J. Alloy. Compd. 749 (2018) 140-145. DOI URL
[45]	D.N. Seidman, E.A. Marquis, D.C. Dunand, Acta Mater. 50 (2002) 4021-4035. DOI URL
[46]	M.C. Gao, Y. Suzuki, H. Schweiger, Ö.N. Do ˘gan, J. Hawk, M. Widom, J. Condens. Matter Phys. 25 (2013) 075402. DOI URL
[47]	G.Y. Guo, H.H. Wang, Phys. Rev. B 62 (20 0 0) 5136-5143. DOI URL
[48]	C. Booth-Morrison, D.C. Dunand, D.N. Seidman, Acta Mater. 59 (2011) 7029-7042. DOI URL
[49]	A.J. Ardell, Metall. Trans. A 16 (1985) 2131-2165. DOI URL
[50]	H. Wen, T.D. Topping, D. Isheim, D.N. Seidman, E.J. Lavernia, Acta Mater. 61 (2013) 2769-2782. DOI URL
[51]	Z. Zhao, Z. Xiao, Z. Li, W. Qiu, H. Jiang, Q. Lei, Z. Liu, Y. Jiang, S. Zhang, Mater. Sci. Eng. A 759 (2019) 396-403. DOI URL
[52]	J. Lee, J.Y. Jung, E.S. Lee, W.J. Park, S. Ahn, N.J. Kim, Mater. Sci. Eng. A 277 (1)(2000) 274-283. DOI URL
[53]	Y. Sun, L. Peng, G. Huang, X. Feng, H. Xie, X. Mi, X. Liu, Mater. Sci. Eng. A 799 (2021) 140144. DOI URL
[54]	J. Li, H. Ding, B. Li, Mater. Sci. Eng. A 798 (2020) 140413.
[55]	H. Peng, W. Xie, H. Chen, H. Wang, B. Yang, J. Alloy. Compd. 852 (2021) 157004. DOI URL
[56]	H. Zeng, H. Sui, S. Wu, J. Liu, H. Wang, J. Zhang, B. Yang, J. Alloy. Compd. 857 (2021) 157582. DOI URL
[57]	J. Li, H. Ding, B. Li, W. Gao, J. Bai, G. Sha, Mater. Sci. Eng. A 802 (2021) 140628. DOI URL
[58]	W. Wang, J. Zhu, N. Qin, Y. Zhang, S. Li, Z. Xiao, Q. Lei, Z. Li, J. Alloy. Compd. 847 (2020) 155762. DOI URL
[59]	L. Peng, H. Xie, G. Huang, G. Xu, X. Yin, X. Feng, X. Mi, Z. Yang, J. Alloy. Compd. 708 (2017) 1096-1102. DOI URL
[60]	S. Xu, H. Fu, Y. Wang, J. Xie, Mater. Sci. Eng. A 726 (2018) 208-214. DOI URL
[61]	J.Y. Cheng, F.X. Yu, B. Shen, Mater. Lett. 115 (2014) 201-204. DOI URL
[62]	Y.J. Hu, Y. Wang, W.Y. Wang, K.A. Darling, L.J. Kecskes, Z.K. Liu, Comput. Mater. Sci. 171 (2020) 109271. DOI URL