Influence of Al and Ni concentration on the Martensitic transformation in Cu-Al-Ni shape-memory alloys

Abstract

The martensitic transformation temperatures and the types of martensitic phases have been determined in a wide concentration range of technological interest for Cu-Al-Ni shape-memory alloys (SMAs) A stability diagram of martensitic phases as a function of alloy concentration has been determined. It is found that when the aluminum content increases, the transformation changes from ␤ 3 ⇒ ␤ Ј 3 to ␤ 3 ⇒ ␥ Ј 3 , with an intermediate concentration range where both martensites coexist due to a ␤ 3 ⇒ ␥ Ј 3 ϩ ␤ Ј 3 transformation. On the other hand, an increase of nickel content stabilizes the martensite ␤ Ј 3 , changing from a mixed ␤ 3 ⇒ ␥ Ј 3 ϩ ␤ Ј 3 to a single ␤ 3 ⇒ ␤ Ј 3 transformation. Furthermore, linear relationships between M s and Al and Ni concentrations have been obtained for all types of martensitic phases.

Effect of (Al-Ni) & (Cu-Ni) Concentrations Ratios on the Hardness and Porosity of Ternary (CuAl-Ni) Smart Alloys

“…This type of martensite is brittle and causes heavy hardness that lead to it lose its ability to recover its original shape and confines to only limited applications at high temperatures as shown in the figure (1), (Recarte V., et al, 2002& Hautcoeur A., et al, 2015.…”

“…The four weight percentages of Cu-Al-Ni smart alloys to be studied with the weight percentage of the application (CN-250X), (Recarte V., et al, 2002& Hautcoeur A., et al, 2015.…”

“…The appearance of this phase causes heavy brittleness in the smart alloy and results in failure of shape restoration. The smart alloys possess a single martensitic transformation which should be selected especially for high temperature applications, because these alloys are thermally more stable and highly thermoelastic as shown in the figure 1 (Recarte V., et al, 2002).…”

Impact of Alloy Composition and Thermal Stabilization on Martensitic Phase Transformation Structures in CuAlMn Shape Memory Alloys

“…In 6,7 heat treatments above 1073 K and quenching are considered to improve the damping capacity. Small quenching rates and also low temperature ageing pins (by point defects) the system by increasing the amount of γ´3 which leads to reduced SME, damping capacity and increased martensite start (M S ) temperatures 8 . High amounts of Al and Mn are known for lowering M S temperature and exhibit excellent SME (above 12.8 wt.% Al 9 ), but limits usability due to extreme brittleness in polycrystalline systems 4,8,10,11 .…”

“…Zinc and nickel can be used as less effective substitutes for Al to reduce the M S . But if their amount got to high, they tend to increase the prowess to ageing at RT and brittleness 8,12,13 . The lately researched elements Be, Ag, Mg show some interesting influence in controlling the phase transformation temperatures and aging stabilisation, too 12,[14][15][16][17] .…”