Microstructure, mechanical properties and shape memory effect of Cu–Hf–Al–Ni alloys

Abstract

The influence of hafnium element's incorporation on a Cu– xHf–13.0Al–4.0Ni (wt-%) ( x = 0.5, 1.0 and 2.0) high-temperature shape memory alloy was investigated systematically. The results show that the matrix of Cu– xHf–13.0Al–4.0Ni ( x = 0.5, 1.0 and 2.0) alloys is 18R martensite, and an orthorhombic-structured Cu8Hf3 phase is formed and distributed at the grain boundaries. The grain size is significantly reduced with increasing Hf content. The mechanical properties of Cu– xHf–13.0Al–4.0Ni ( x = 0.5, 1.0 and 2.0) alloys are improved by Hf doping due to the combination of refinement strengthening, solid solution strengthening and second phase strengthening. After heating under pre-strain of 10%, the shape memory effect of the Cu–1.0Hf–13.0Al–4.0Ni alloy reaches 5.6%, which is obviously higher than that of the Cu–13.0Al–4.0Ni alloy.

Structural and Phase Transformations and Physical and Mechanical Properties of Cu-Al-Ni Shape Memory Alloys Subjected to Severe Plastic Deformation and Annealing

“…As was determined, hot deformation via forging of the studied Cu-based alloys permits refining of austenite grains down to 0.5–1 mm [ 54 , 55 ]. However, the further subsequent cooling in air entails (i) the decomposition by the scheme β→β 1 +γ 2 (at temperatures above the T ED close to 840 K) and (ii) eutectoid decomposition via β 1 →α+γ 2 (at temperatures below T ED ) ( Figure 1 a), which is in good correspondence with the known data from [ 2 , 24 , 35 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 ]. However, quenching of the alloys after their hot forging allows us to prevent the eutectoid decomposition.…”

“…In our works [ 35 , 51 , 52 , 53 , 54 , 55 , 56 , 57 ] it was found that a radical decrease in the grain size during SPD and, accordingly, an increase in the length of the grain boundaries permits us to make the level of embrittlement of SME β-copper alloys lower. Any other methods of refinement of the grain structure of these alloys using alloying additives, heat treatment, rapid quenching, powder metallurgy, and a number of other corresponding methods turned out to be generally unsuccessful [ 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 ]. The aim of this presented work was to study (i) the structure of the Cu-Al-Ni-based SMAs and (ii) the effect of the SPD by means of HPT and subsequent annealing on the grain sizes, structural phase transformations, mechanical properties, and hardness.…”

Effect of heat treatment on microstructure and mechanical properties of Cu–6.9Ni–2.97Al–0.99Fe–1.06Mn alloy

“…Figure 10 shows the tensile fracture morphology of the Cu–6.9Ni–2.97Al–0.99Fe–1.06Mn alloy after 6 h of ageing treatment. It can be seen from Figure 10(a) that the sample does not experience obvious necking during the stretching process, and the fracture is relatively flush, showing typical brittle material fracture characteristics [22]. It can be seen from Figure 10(b) that the macroscopic fracture of the aged alloy is polygonal in shape and composed of many crystal interfaces similar to that of a mass of rock candy, which is a typical intergranular fracture feature [23].…”

The Effect of Heat Treatment on the Structure and Mechanical Properties of Nanocrystalline Cu–14Al–3Ni Alloy Subjected to High-Pressure Torsion

“…deformation (SPD) and, therefore, the increase in the boundary length [8][9][10][11][12][13][14]. At the same time, other various methods used for refining the grain structure of the alloys [15][16][17][18][19][20][21] with application of alloying additions [17,21], heat treatment [15][16][17][18], rapid quenching [6], powder metallurgy and others [19,20], as a rule, were found to be ineffective. The aim of this study is to investigate the effect of heat treatment on the grain size, structural and phase transformations, mechanical properties, and hardness of the SMA Cu-14Al-3Ni alloy subjected to SPD.…”