Influence of Manganese Content on Martensitic Transformation of Cu-Al-Mn-Ag Alloy

Abstract

The influence of manganese content on the formation of martensite structure and the final properties of a quaternary Cu-Al-Mn-Ag shape memory alloy (SMA) was investigated. Two alloys with designed compositions, Cu- 9%wt. Al- 16%wt. Mn- 2%wt. Ag and Cu- 9%wt. Al- 7%wt. Mn- 2%wt. Ag, were prepared in an electric arc furnace by melting of high-purity metals. As-cast and quenched microstructures were determined by optical microscopy and scanning electron microscopy equipped with EDS. Phases were confirmed by high-energy synchrotron radiation and electron backscatter diffractions. Austenite and martensite transformations were followed by differential scanning calorimetry and hardness was determined using the Vickers hardness test. It was found that the addition of silver contributes to the formation of the martensite structure in the Cu-Al-Mn-SMA. In the alloy with 7%wt. of manganese, stable martensite is formed even in the as-cast state without additional heat treatment, while the alloy with 16%wt. of manganese martensite transforms only after thermal stabilization and quenching. Two types of martensite, β1′ and γ1′, are confirmed in the Cu-9Al-7Mn-2Ag specimen. The as-cast SMA with 7%wt. Mn showed significantly lower martensite transformation temperatures, Ms and Mf, in relation to the quenched alloy. With increasing manganese content, the Ms and Mf temperatures are shifted to higher values and the microhardness is lower.

A Microstructural Study of Cu-10Al-7Ag Shape Memory Alloy in As-Cast and Quenched Conditions

“…This is typical behavior for Cu-SMA materials and is consistent with previous studies of SMAs. [11][12][13][14][37][38][39][40][41] The slight variance in the hardness between the tested values, in both as-cast and quenched conditions can be ascribed to the formation of mechanically induced martensite in stressed areas, occurring under high indentation loads [42].…”

“…This increased interest stems from the addition of manganese in binary Cu-Al alloys, which serves to stabilize the β-phase region and extend it towards lower aluminum concentrations. As a result, the β-phase exhibits increased stability against diffusive decomposition [8][9][10][11][12]. As the alloy cools, the β-phase undergoes transformations with disordered order and progresses from β(A2) to β 2 (B2) to β 1 (L2 1 ) [12][13][14][15][16].…”

“…Conversely, at lower aluminum concentrations, typically below 16%at., A2 transforms either into A1 (disordered face-centered cubic structure f.c.c.) or into a 2M structure [10][11][12]. Depending on the chemical composition, various martensite structures can be observed in Cu-based SMA, including hexagonal 2H and rhombohedral structures 9R, 18R, 6R and 3R [11,12,[17][18][19].…”

“…or into a 2M structure [10][11][12]. Depending on the chemical composition, various martensite structures can be observed in Cu-based SMA, including hexagonal 2H and rhombohedral structures 9R, 18R, 6R and 3R [11,12,[17][18][19].…”