Microstructure and Mechanical Behavior of a TiNi Alloy during Multiple Martensitic Transformations and Annealing

—The effect of preliminary thermal cycling and annealing performed in the range of aging temperatures on the microstructure and mechanical behavior of a TiNi alloy is considered. The structure in the initial state consists of almost dislocation-free austenite grains. Equal-channel angular pressing r...

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Bibliographic Details
Published in:Russian metallurgy Metally 2022-07, Vol.2022 (7), p.727-734
Main Authors: Churakova, A. A., Kayumova, E. M.
Format: Article
Language:English
Subjects:
Aging
Aging (metallurgy)
Annealing
Chemistry and Materials Science
Crystal defects
Equal channel angular pressing
Grain size
Intermetallic compounds
Martensitic transformations
Materials Science
Mechanical properties
Metallic Materials
Microstructure
Nickel base alloys
Nickel compounds
Shape memory alloys
Tensile strength
Tensile tests
Thermal cycling
Titanium compounds
Yield strength
Yield stress
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Summary:—The effect of preliminary thermal cycling and annealing performed in the range of aging temperatures on the microstructure and mechanical behavior of a TiNi alloy is considered. The structure in the initial state consists of almost dislocation-free austenite grains. Equal-channel angular pressing results in an ultra-fine grained (UFG) structure consisting of equiaxed grains with an average size of 400 nm in the Ti 49 Ni 51 alloy. The maximum number of thermal cycles is n = 100. The yield strength decreases when the number of thermal cycles increases to n = 100, which can be attributed to a saturation effect. The significant decrease in the yield strength at n = 100 can be associated with a high density of defects and aging particles, which cause the fracture of samples at lower tensile strength values, making dislocation motion difficult. Thermal cycling and subsequent annealing at 400°C do not change the grain size. The results of tensile tests show that thermal cycling ( n = 100) and subsequent aging increase the tensile strength and yield strength in the UFG state.
ISSN:0036-0295
1555-6255
1531-8648
DOI:10.1134/S0036029522070035