Effect of Ag addition on phase transitions of the Cu–22.26 at.%Al–9.93 at.%Mn alloy

doi:10.1016/j.tca.2012.12.014

Thermochimica Acta

Volume 554, 20 February 2013, Pages 71-75

https://doi.org/10.1016/j.tca.2012.12.014 Get rights and content

Abstract

The phase transitions that occur in the Cu–22.26 at.%Al–9.93 at.%Mn and Cu–22.49 at.%Al–10.01 at.%Mn–1.53 at.%Ag alloys after slow cooling were studied using differential scanning calorimetry at different heating rates, microhardness changes with temperature, magnetization changes with temperature, scanning electron microscopy and energy dispersion X-ray spectroscopy. The results indicated that the presence of Ag does not modify the transition sequence of Cu–Al–Mn alloy, introduces a new transition due to the (Ag-Cu)-rich precipitates dissolution at about 800 K, and changes the mechanism of DO₃ phase dissolution. This mechanistic change was analyzed and a sequence of phase transitions was proposed for the reaction.

Highlights

► A kinetic mechanism for the dissolution of DO₃ phase is suggested. ► The intermediate phase interferes on the kinetics of the DO₃ phase dissolution. ► The presence of Ag changes the stability of intermediate phase.

Introduction

Alloys of the Cu–Al–Mn system are Hume–Rothery alloys. The phase stability of these materials is largely dominated by the average number of conduction electrons per atom, denoted as e/a. Within a certain range of compositions around the Cu-rich region (far from the Cu₂AlMn Heusler stoichiometry) the system undergoes a martensitic transition associated with shape-memory properties [1]. The Cu-rich portion of the Cu–Mn–Al system has been fully investigated at temperatures above 723 K. It was found that the addition of Mn expands the high temperature β phase field of the Cu–Al system. The β phase stability compositional range increases with temperature, and includes the composition of the well-known Heusler alloy Cu₂MnAl at temperatures above 923 K. At 673 K the equilibrium phases in these alloys are: Cu₃Mn₂Al, γ and β_Mn [2]. At temperatures lower than 600 K, a spinodal decomposition can occur between a non-magnetic (DO₃) Cu₃Al-rich phase and a (L2₁) Cu₂AlMn-rich phase, which orders ferromagnetically. The kinetics of this process is slow and this decomposition is avoided for typical cooling rates. Associated with this spinodal decomposition some authors have reported the appearance of superparamagnetism at low temperatures [3].

Silver additions to Cu–Al alloys increase its hardness [4], stress corrosion resistance [5] and modify the aging characteristics of the alloys [6], with no ternary intermediate phases being observed [7], [8]. It is expected that Ag additions to Cu–Al–Mn alloys present a similar effect, thus improving some properties of the system mainly its corrosion resistance, apart from allowing the study of the effect of Ag presence on the characteristics temperatures and mechanism of phase transitions. In this work, the influence of addition of 1.53 at.%Ag to the Cu–22.26 at.%Al–9.93 at.%Mn alloy was studied using differential scanning calorimetry (DSC) at different heating rates, microhardness changes with temperature, magnetization changes with temperature, scanning electron microscopy (SEM) and energy dispersion X-ray spectroscopy (EDXS). The purpose of this work is to study the phase transitions in the Cu–Al–Mn and Cu–Al–Mn–Ag alloys after slow cooling at about 5 K/h, correlating with the presence of Ag and its influence on the ternary system.

Section snippets

Experimental procedure

The Cu–22.26 at.%Al–9.93 at.%Mn and Cu–22.49 at.%Al–10.01 at.%Mn–1.53 at.%Ag alloys were prepared in an arc furnace under argon atmosphere using 99.95% copper, 99.97% aluminum, 99.995% manganese and 99.98% silver as starting materials. Cylindrical samples with 2.0 cm diameter and 6.0 cm length were cut in disks of 2.0 mm thickness. The samples were maintained for 120 h at 1123 K and then cooled at 5.0 K/h down to room temperature. The DSC curves were obtained using a DSC Q20 TA Instruments at different

Results and discussion

Fig. 1 shows the DSC curves obtained at different heating rates for the Cu–22.26 at.%Al–9.93 at.%Mn and Cu–22.49 at.%Al–10.01 at.%Mn–1.53 at.%Ag alloys. These alloys were initially maintained at 1123 K for 120 h and then cooled at 5.0 K/h down to room temperature. The curves of Fig. 1a, corresponding to the Cu–22.26 at.%Al–9.93 at.%Mn alloy, show three thermal events. The endothermic peak P₁, at about 520 K, is shifted to higher temperatures with the increase of the heating rate. This thermal event is

Conclusions

The phase transitions in the Cu–22.49 at.%Al–10.01 at.%Mn–1.53 at.%Ag alloy were analyzed and a kinetics mechanism for the DO₃ phase dissolution was suggested. The results indicated that the DO₃ phase interferes in the microhardness values of the Cu–22.49 at.%Al–10.01 at.%Mn–1.53 at.%Ag alloy. The α + T₃-Cu₃Mn₂Al + γ → β + γ + T₃-Cu₃Mn₂Al transition is dominant at lower heating rates while L2₁(p) → B2 transition is dominant at higher heating rates. The (Ag–Cu)-rich precipitates dissolution occurs in the same

Acknowledgments

The authors thank FAPESP (proc. 2011/11041-4), CNPq (proc. 482348/2010-0) and LME/LNLS for technical support during electron microscopy work (JSM-5900LV).

References (12)

M. Bouchard et al.
Phase transitions and modulated structures in ordered (Cu–Mn)₃Al alloys
Acta Metall.
(1975)
A.T. Adorno et al.
Influence of silver additions on the aging characteristics of the Cu–10.4 at.%Al alloy
J. Alloys Compd.
(1998)
G.J. Arruda et al.
Kinetics of eutectoid decomposition in Cu–Al and Cu–Al–Ag alloys
Mater. Lett.
(1997)
A.T. Adorno et al.
Activation energy for the reverse eutectoid reaction in hypo-eutectoid Cu–Al alloys
Thermochim. Acta
(2012)
S. Vyazovkin et al.
ICTAC kinetics committee recommendations for performing kinetic computations on thermal analyses data
Thermochim. Acta
(2011)
J. Marcos et al.
Kinetics of the phase separation in Cu–Al–Mn alloys and the influence on martensitic transformations
Philos. Mag.
(2004)

There are more references available in the full text version of this article.

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Effect of Ag addition on phase transitions of the Cu–22.26 at.%Al–9.93 at.%Mn alloy

Abstract

Highlights

Introduction

Section snippets

Experimental procedure

Results and discussion

Conclusions

Acknowledgments

Acta Metall.

J. Alloys Compd.

Mater. Lett.

Thermochim. Acta

Thermochim. Acta

Kinetics of the phase separation in Cu–Al–Mn alloys and the influence on martensitic transformations

Philos. Mag.