Precipitation Kinetics and Mechanism in Cu-7 wt% Ag Alloy

Djamel Hamana, Mohamed Hachouf, Leila Boumaza, Zine El Abidine Biskri

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DOI: 10.4236/msa.2011.27120                

Abstract

The discontinuous precipitation kinetics and mechanism of the α (Ag-rich) phase in Cu-7 wt% Ag alloy has been investigated using dilatometric and calorimetric anisothermal analysis, optical microscopy, scanning and transmission electron microscopy and X-ray diffraction. Dilatometric and calorimetric curves present at ~ 500°C an important effect related to the ? (Ag-rich) phase formation and consequently the matrix β (Cu-rich) depletion. The nucleation and growth of the precipitated phase show cells formation at initial grain boundaries; a fine lamellar structure is detected by SEM and TEM and consists of alternate lamellar of the α (Ag-rich) and β (Cu-rich)-solid solutions. Cellular precipitation leads to the simultaneous appearance of two diffraction peaks and occurs apparently according to the Fournelle and Clark’s mechanism. Obtained results give an Avrami exponent n = 2.0 ± 0.2 in agreement with an interfacial controlled process having an activation energy E_a equals to 99 ± 7 kJ/mol obtained from anisothermal analysis by using different isoconversion methods. This activation energy expresses the discrepancy between isoconversion methods and the analytical diffusive model. Moreover, the supersaturation rate has an effect on the lamella spacing of the precipitated cells.

Keywords

Cu-Ag alloy, Dilatometry, Calorimetry, Scanning Electron Microscopy, Discontinuous Precipitation

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	S. Hirth and G. Gottstein, “Misorientation Effects on Discontinuous Precipitation in Al-Ag-Ga,” Acta Material, Vol. 46, No. 11, 1998, pp. 3975-3984. doi:10.1016/S1359-6454(98)00061-5
[2]	I. Manna, S. K. Pabi and W. Gust, “Discontinuous Reactions in Solids,” International Meterials Reviews, Vol. 46, 2001, pp. 53-91. doi:10.1179/095066001101528402
[3]	K. Nakahigashi, H. Ishibashi, S. Minamigawa and M. Kogachi, “X-Ray Diffraction Study on Ultrafine Particles of Ag-Cu Alloys Prepared by Hydrogen Plasma-Metal Reaction Method,” Japanese Journal of Applied Physics, Vol. 31, 1992, pp. 2293-2298. doi:10.1143/JJAP.31.2293
[4]	W. Leo, “Elektronenmikroskopische Untersuchungen zur Ausscheidung in aush?rtbaren Sil Ber-Kupfer-Legierung- en,” Zeitschrift Für Metallkunde, Vol. 58, 1967, pp. 456- 461.
[5]	R. Wirth and H. Gleiter, “Is Discontinuous (Cellular) Precipitation an Effect of a Structural Transformation in the Migrating Phase Boundary?” Acta Metallurgical, Vol. 29, No. 11, 1981, pp. 1825-1830. doi:10.1016/0001-6160(81)90108-5
[6]	W. Gust, J. Beuers, J. Steffen, S. Stiltz and B. Predel, “Diffusion along Migrating and Stationary Grain Boun- daries in the Cu-Ag System,” Acta Metallurgica, Vol. 34, No. 8, 1986, pp. 1671-1680. doi:10.1016/0001-6160(86)90113-6
[7]	P. Gupta, “Kinetics of Discontinuous Precipitation and Dissolution in Cu-Ag Alloys,” Canadian Metallurgical Quarterly, Vol. 37, No. 2, 1998, pp. 141-159. doi:10.1016/S0008-4433(98)00014-7
[8]	D. Hamana and H. Choutri, “Effect of Plastic Deformation on the Kinetics and Mechanism of Cellular Precipitation,” Scripta Metallurgical and Material, Vol. 25, No. 4, 1991, pp. 859-864. doi:10.1016/0956-716X(91)90238-V
[9]	D. Hamana, M. Bouchear and A. Derafa, “Effect of Plastic Deformation on the Formation and Dissolution of Transition Phases in al-12 wt% mg Alloy,” Materials Chemistry and Physics, Vol. 57, No. 2, 1998, pp. 99-110. doi:10.1016/S0254-0584(98)00191-6
[10]	D. Hamana, M. Bouchear, M. Betrouche, A. Derafa and N. Ya. Rokhmanov, “Comparative Study of Formation and Transformation of Transition Phases in Al-12 wt% Mg Alloy,” Journal of Alloys and Compounds, Vol. 320, No. 1, 2001, pp. 93-102. doi:10.1016/S0925-8388(01)00923-9
[11]	D. Hamana, A. Azizi, M. Bouchear and M. Boufenghour, “Effect of the Presence of Phases on the Dilatometric Anomalies in Metallic Alloys,” Annals de Chimie- Scie- nces des Matériaux, Vol. 31, No. 5, 2006, pp. 501-511. doi:10.3166/acsm.31.501-511
[12]	D. Hamana and A. Azizi, “Low Temperature Post-Precip- itation after Precipitation of β′ and β Phases in Al-12 wt% mg Alloy,” Materials Science and Engineering A, Vol. 476, No. 1-2, 2008, pp. 357-365. doi:10.1016/j.msea.2007.04.120
[13]	L. Hadjadj, R. Amira, D. Hamana and A. Mosbah, “Characterization of Precipitation and Phase Transformations in Al-Zn-Mg Alloy by the Differential Dilatometry,” Journal of Alloys and Compounds, Vol. 462, No. 1-2, 2008, pp. 279-283. doi:10.1016/j.jallcom.2007.08.016
[14]	A. Hayoune and D. Hamana, “Structural Evolution during Non-Isothermal Ageing of a Dilute A-Cu Alloy by Dilatometric Analysis,” Journal of Alloys and Compounds, Vol. 474, No. 1-2, 2009, pp. 118-123. doi:10.1016/j.jallcom.2008.06.070
[15]	D. Hamana and L. Boumaza, “Precipitation Mechanism in Ag-8 wt% Cu alloy,” Journal of Alloys and Compounds, Vol. 477, No. 1-2, 2009, pp. 217-223. doi:10.1016/j.jallcom.2008.10.063
[16]	H. E. Kissinger, “Reaction Kinetics in Differential Thermal Analysis,” Analytical Chemistry, Vol. 29, No. 11, 1957, pp. 1702-1706. doi:10.1021/ac60131a045
[17]	M. J. Starink and P. Van Mourik, “Cooling and Heating Rate Dependence of Precipitation in an Al-Cu Alloy,” Materials Science and Engineering A, Vol. 156, No. 2, 1992, pp. 183-194. doi:10.1016/0921-5093(92)90150-Y
[18]	A. T. Adorno, R. A. G. Silva and T. B. Nevers, “Ag Precipitation and Dissolution Reactions in the Cu-3 wt% Al-4 wt% Ag Alloy,” Materials Science and Engineering. A, Vol. 441, No. 1-2, 2006, pp. 259-265. doi:10.1016/j.msea.2006.08.055
[19]	W. Scharfenberger, G. Schmitt and H. Borchers, “über die Kinetik der Diskontinuierlichen Ausscheidung der Silberlegierung mit 7, 5 Gew-%Cu,” Zeitschrift für Metallkunde, Vol. 63, 1972, pp. 553-560.
[20]	K. Matusita and S. Sakka, “Kinetic Study of Crystallization of Glass by Differential Thermal Analysis-Criterion on Application of Kissinger Plot,” Journal of Non-Cryst- alline Solids, Vol. 38, No. 2, 1980, pp. 741-746. doi:10.1016/0022-3093(80)90525-6
[21]	P. Papon, J. Leblond and P. H. E. Meijer, “Physique des Transitions de Phases,” Dunod, Paris, 1999, pp. 212-373.
[22]	D. Duly and Y. Brechet, “Nucleation Mechanism of Discontinuous Precipitation in Mg-Al Alloys and Relation with the Morphology,” Acta Metallurgical and Material, Vol. 42, No. 9, 1994, pp. 3035-3043. doi:10.1016/0956-7151(94)90400-6
[23]	R. A. Fournelle and J. B. Clark, “Genesis of the Cellular Precipitation Reaction,” Metallurgical and Materials Transactions B, Vol. 3, 1972, pp. 2757-2767.