Diffusion behavior and reactions between Al and Ca in Mg alloys by diffusion couples

doi:10.1016/j.jmst.2017.10.007

Abstract

Abstract:

The diffusion behavior and reactions between Al and Ca in Mg alloys by diffusion couple method were investigated. Results demonstrate that Al₂Ca is the only phase existing in the diffusion reaction layers. The volume fraction of Al₂Ca in diffusion reaction layers increases linearly with temperature. The standard enthalpy of formation for intermetallic compounds was rationalized on the basis of the Miedema model. Al-Ca intermetallic compounds were preferable to form in the Mg-Al-Ca ternary system under the same conditions. Over the range of 350-400 °C, the structure of Al₂Ca is more stable than that of Al₄Ca, Al₁₄Ca₁₃and Al₃Ca₈. The growth constants of the layer I, layer II and entire diffusion reaction layers were determined. The activation energies for the growth of the layer I, layer II and entire diffusion reaction layers were (80.74 ± 3.01) kJ/mol, (93.45 ± 2.12) kJ/mol and (83.52 ± 1.50) kJ/mol, respectively. In layer I and II, Al has higher integrated interdiffusion coefficients $D ? i Int, layer$ ,layer than Ca. The average effective interdiffusion coefficients $D ? A l eff$ values are higher than $D ? Ca eff$ in the layer I and II.

Key words: Magnesium alloys, Diffusion behavior, Interface, Intermetallic compounds

Jiahong Dai, Hong Xiao, Bin Jiang, Hongmei Xie, Cheng Peng, Zhongtao Jiang, Qin Zou, Qingshan Yang, Fusheng Pan. Diffusion behavior and reactions between Al and Ca in Mg alloys by diffusion couples[J]. J. Mater. Sci. Technol., 2018, 34(2): 291-298.

Figures/Tables 16

Table 1 Chemical compositions (wt%) of Mg-40Al and Mg-20Ca Mg alloy.

Materials	Al	Ca	Si	Cu	Fe	Ni	Mg
Mg-40Al	39.37	-	0.0049	0.0063	0.0037	0.0011	Bal.
Mg-20Ca	-	18.78	0.0053	0.0042	0.0047	0.0028	Bal.

Fig. 1. BSE micrographs from (Mg-40Al)/(Mg-20Ca) diffusion couples (a) prior to annealing before, and annealed at (b) 350 °C, (c) 375 °C and (d) 400 °C for 72 h.

Fig. 2. X-ray diffraction patterns of the constitutive phases of the diffusion reaction layer after annealed at 400 °C for 72 h.

Fig. 3. High magnification images of (a) region 2 and (b) region 3 for in Fig. 1d, and EDS results of (c) position A in (a), and (d) position B in (b). V = 0.348T-183, where V is the volume fraction of Al2Ca in diffusion reaction layers, T is temperature.

Fig. 4. SEM/EDS maps of the region 1 in Fig. 1c, where the peak intensity reflect the atomic concentrations of Mg, Al and Ca, respectively.

Fig. 5. The volume fraction of Al2Ca in diffusion reaction layers at 350 °C, 375 °C, 400 °C for 72 h.

Fig. 6. Concentration profiles of (Mg-40Al)/(Mg-20Ca) diffusion couples annealed at (a) 350 °C, (b) 375 °C, (c) 400 °C for 72 h.

Fig. 7. A schematic diagram of diffusion process.

Fig. 8. Diffusion path of (Mg-40Al)/(Mg-20Ca) diffusion couple annealed at 400 °C.

Fig. 9. Formation enthalpies of the Mg-Al, Mg-Ca and Al-Ca binary systems.

Fig. 10. Gibbs free energies of the formation of Al4Ca, Al2Ca, Al14Ca13 and Al3Ca8 as the function of temperature.

Fig. 11. Thickness of layer I, layer II and entire diffusion reaction layer versus square root of diffusion annealing time at 350 °C, 375 °C and 400 °C.

Fig. 12. Arrhenius plots of the diffusion reaction layers growth.

Table 2 Growth constants, pre-exponential factors and activation energies of layer I, layer II and total layer.

Layer	T (°C)	k (m²/s)	k₀ (m²/s)	Q (kJ/mol)
Layer I	350	1.66(±0.37) × 10^-14	9.72(±0.53) × 10^-8	80.74 ± 3.01
	375	2.97(±0.14) × 10^-14
	400	5.29(±0.42) × 10^-14
Layer II	350	1.95(±0.28) × 10^-15	7.95(±0.49) × 10^-8	93.45 ± 2.12
	375	2.22(±0.47) × 10^-15
	400	4.55(±0.10) × 10^-15
Total	350	2.67(±0. 81) × 10^-14	2.66(±0. 34) × 10^-7	83.52 ± 1.50
	375	4.82(±0.71) × 10^-14
	400	8.85(±0.24) × 10^-14

Table 3 Integrated interdiffusion coefficients D?iInt, layer,Layerand activation energies of layer I, layer II and total layer.

Table 4 Average effective interdiffusion coefficients Q?ieff and activation energies of layer I and II.

References

[1]	F. Pan, X. Chen, T. Yan, T. Liu, J. Mao, W. Luo, Q. Wang, J. Peng, A. Tang, B. Jiang,J. Magnes. Alloys 4 (2016) 8-14.
[2]	X.J. Wang, D.K. Xu, R.Z. Wu, X.B. Chen, Q.M. Peng, L. Jin, Y.C. Xin, Z.Q. Zhang, Y.Liu, X.H. Chen, G. Chen, K.K. Deng, H.Y. Wang, J. Mater.Sci.Technol. 34(2018)245-247.
[3]	F. Pan, M. Yang, X. Chen, J. Mater.Sci.Technol. 32(2016) 1211-1221.
[4]	J. Swaminathan, U. Pillai, K. Guguloth, B.C. Pai, Mater. Sci. Eng. A 485 (2008)86-91.
[5]	D.G.L .Prakash, D. Regener, J.Alloys Compd. 461(2008) 139-146.
[6]	I.P. Moreno, T.K. Nandy, J.W. Jones, J.E. Allison, T.M. Pollock, Scripta Mater. 45(2001) 1423-1429.
[7]	J.R. TerBush, A. Suzuki, N.D. Saddock, J.W. Jones, T.M. Pollock,Scripta Mater.58(2008) 914-917.
[8]	B. Jiang, W. Liu, D. Qiu, M.-X. Zhang, F.Pan, Mater. Chem. Phys. 133(2012)611-616.
[9]	Z.T. Jiang, B. Jiang, Y. Xiao, Y. Tian, G.Y. Zhou, F.S. Pan, Mater. Res. Innov. 18source(2014) S 4-137 (S134-141).
[10]	Z. Jiang, B. Jiang, J. Zhang, J. Dai, Q. Yang, Q. Yang, F. Pan, T. Nonferr.Metal.Soc.26(2016) 1284-1293.
[11]	A. Suzuki, N.D. Saddock, J.W. Jones, T.M. Pollock, Scripta Mater. 51(2004)1005-1010.
[12]	L. Han, H. Hu, D.O. Northwood, Mater. Lett. 62(2008) 381-384.
[13]	A.V. Koltygin, V.E. Bazhenov, E.A. Belova, A.A. Nikitina, J. Magnes. Alloys 1(2013) 224-229.
[14]	D. Kevorkov, M. Medraj, J. Li, E. Essadiqi, P. Chartrand, Intermetallics 18 (2010)1498-1506.
[15]	Y. Zhong, J. Liu, R.A. Witt, Y.H. Sohn, Z.K. Liu, Scr. Mater. 55(2006) 573-576.
[16]	J. Gr?bner, D. Kevorkov, I. Chumak, R. Schmid-Fetzer, J. Mater.Res. 94(2003)976-982.
[17]	K. Ozturk, Y. Zhong, Z.K. Liu, A.A. Luo,JOM 55(2003) 40-44.
[18]	A. Janz, J. Gr?bner, H. Cao, J. Zhu, Y.A. Chang, R. Schmid-Fetzer, Acta Mater. 57(2009) 682-694.
[19]	J.S. Kirkaldy, L.C. Brown, Can. Metall. Quart. 2(1963) 89-115.
[20]	J.E. Morral, Metall. Mater. Trans. A 43 (2012) 3462-3470.
[21]	V. Raghavan, J. PhaseEquilib.Diffus. 32(2011) 52-53.
[22]	N. Dasa, J. Mittra, B.S. Murty, S.K. Pabi, U.D. Kulkarni, G.K. Dey, J. AlloysCompd. 550(2013) 483-495.
[23]	K. Ozturk, L.Q. Chen, Z.K. Liu, J. AlloysCompd. 340(2002) 199-206.
[24]	J. Dai, B. Jiang, X. Li, Q. Yang, H. Dong, X. Xia, F. Pan, J. AlloysCompd. 619(2015) 411-416.
[25]	M.A. Dayananda, Metall. Mater. Trans. A 14 (1983) 1851-1858.
[26]	M.A. Dayananda, Metall. Mater. Trans. A27 (1996) 2504-2509.
[27]	S. Brennan, K. Bermudez, N.S. Kulkarni, Y. Sohn, Metall. Mater. Trans. A 43a(2012) 4043-4052.