Influence of Thermomechanical Treatment on Structural-Phase Transformations and Mechanical Properties of the Cu–Al–Ni Shape-Memory Alloys

• Published in: Russian physics journal Vol. 61; no. 9; pp. 1681 - 1686
• Main Authors: Svirid, A. E., Kuranova, N. N., Lukyanov, A. V., Makarov, V. V., Nikolayeva, N. V., Pushin, V. G., Uksusnikov, A. N.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.01.2019; Springer Nature B.V
• Subjects: ALUMINIUM; Aluminum; ANNEALING; AUSTENITE; Condensed Matter Physics; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Copper; Disintegration; Ductile fracture; Ductile-brittle transition; ELECTRON DIFFRACTION; ELECTRON MICROSCOPY; Elongation; Forging; FRACTURES; GRAIN BOUNDARIES; GRAIN SIZE; Grain structure; Hadrons; Heat treatment; Heavy Ions; Lasers; MARTENSITE; Martensitic transformations; Mathematical and Computational Physics; Mechanical properties; MECHANICAL TESTS; Nickel; Nuclear Physics; Optical Devices; Optics; PHASE TRANSFORMATIONS; Phase transitions; Photonics; Physics; Physics and Astronomy; QUENCHING; RECRYSTALLIZATION; SEGREGATION; Shape effects; Shape memory; Shape memory alloys; SHAPE MEMORY EFFECT; Substructures; TEMPERATURE RANGE 0273-0400 K; TENSILE PROPERTIES; Theoretical; Thermomechanical treatment; THERMOMECHANICAL TREATMENTS; Ultimate tensile strength; X-RAY DIFFRACTION; YIELD STRENGTH; martensitic phases; shape memory; thermomechanical treatment; mechanical properties; structure
• ISSN: 1064-8887; 1573-9228
• DOI: 10.1007/s11182-018-1587-z

Using the methods of optical and electron microscopy and electron and X-ray diffraction analyses, the influence of thermomechanical treatment on the mechanical properties, average grain size, and structural and phase transformations is investigated in the Cu–Al–Ni triple alloys exhibiting a shape memory effect. In the alloys under study with a fixed content of 3wt% Ni the concentration of aluminum was varied from 9 to 14 wt%. It is shown that in the alloys subjected to thermal treatment, including forging and homogenizing annealing using controlled recrystallization in the austenitic state followed by quenching, the grain-boundary disintegration and segregation disappear. It is found out that the microstructure of the alloys in the hot-forged and hardened states with the content of aluminum 9–10 wt%. consists of the grains of the average dimensions within 60–80 μm, with the content of aluminum 10–12 wt% – 100–350 μm, while in the alloys with the content of aluminum up to 14 12 wt% the average grain size reaches 1 mm. According to the data of mechanical testing at room temperature, with a decrease in the content of aluminum the ultimate tensile strength (σ UTS ), the yield strength (σ М ) and the relative elongation (δ) increase. An improvement of the mechanical properties of the alloys is attributed to the grain structure refinement of the β 2 -austenite and package substructure of the β' 1 -and γ' 1 -martensites as the content of aluminum in the alloys decreases. For instance, in the fine-grained alloys containing 9.2 and 9.5 wt% Al the value of relative elongation remains at a high level (>10%), while for the other alloys with 10–14 wt% Al it does not exceed 5%. As the content of aluminum in the alloys decreases, the character of the specimen fracture under uniaxial tension changes (from brittle to ductile).