Orientation dependence and tension-compression asymmetry of shape memory effect in Ti50Ni40Cu10 single crystals

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2022-01, Vol.832, p.142468, Article 142468
• Main Authors: Kireeva, I.V., Chumlyakov, Y.I., Pobedennaya, Z.V., Saraeva, A.A.
• Format: Article
• Language: English
• Subjects: Asymmetry; Crystal structure; Crystallography; Martensite; Martensitic transformations; Mechanical twinning; Orientation; Orientation dependence; Plastic flow; Shape effects; Shape memory alloys; Shape memory effect; Single crystals; Strain; Stresses; Tension-compression asymmetry; Ti50Ni40Cu10 single crystals
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2021.142468

Transformation strain under stress in Ti50Ni40Cu10 alloy single crystals, with a two-step B2–B19–B19′ martensitic transformation (MT), was investigated along three different crystallographic orientations, i.e., [1‾17], [011] and [1‾23], in order to reveal the orientation dependence and tension-compression asymmetry of the shape memory effect (SME) at different stress levels. It was shown that the SME depends on the crystal orientation and the deformation method (tension and compression). The maximum value of the SME εSME under tensile stresses turned out to be higher than the theoretical transformation strain resource ε0. In [1‾17]-oriented crystals, εSME = 6.1% exceeded ε0 = 3.4% by 2.7%; in [011]-oriented crystals εSME = 9.1% exceeded ε0 = 7.14% by 1.96%; in [1‾23]-oriented crystals εSME = 8.2% exceeded ε0 = 7.22% by 0.98%. Higher experimental values for εSME than the theoretical transformation strain resource ε0 at B2–B19–B19′ MT was found to be associated with elastic mechanical twinning along the {110}В19 planes of B19-martensite. Under compression, in the studied orientations, εSME was less than ε0 for the B2–B19–B19′ MT. This was due to lower stresses in the initial B2-phase and local plastic flow during development of an MT under stress at stresses of more than 200 MPa. •Shape memory effect was studied in Ti50Ni40Cu10 single crystals under external stresses.•Shape memory effect depends on the crystal orientation and the deformation method.•Shape memory effect under tensile stresses exceeds theoretical resource of the lattice strain.•Elastic mechanical {110}В19 twinning of B19-martensite leads to an increase in shape memory effect.