The effect of Ru on Ti 50 Pd 50 high temperature shape memory alloy: a first-principles study
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.331
The effect of Ru on Ti50Pd50 high temperature shape memory alloy: a first-principles study R. G. Diale1, R. Modiba2, P. E. Ngoepe1, and H. R. Chauke1 1
Materials Modelling Centre, University of Limpopo, Private Bag X 1106, Sovenga, 0727, South Africa
2
Future Production: Manufacturing, CSIR, PO Box 395, Pretoria, 0001, South Africa
ABSTRACT
The stability of the Ti50Pd50-xRux alloy was investigated using first-principles density functional theory within the plane-wave pseudopotential method. Firstly, the Ti50Pd50 gave equilibrium lattice parameter and lowest heats of formation in better agreement with experimental data to within 3%. The heat of formation decreases with an increase in Ru concentration, consistent with the trend of the density of states which is lowered at the Fermi level as Ru content is increased which suggests stability. It was also found that from the calculated elastic constants the structures showed positive shear modulus above 20 at. % Ru, condition of stability. Furthermore, the addition of Ru was found to strengthen the Ti50Pd50-xRux system at higher concentrations. The thermal coefficients of linear expansion for the Ti50Pd31.25Ru18.75 are higher at low temperature, and that the TiPd-Ru system tends to expand more at low content of 18.75 at. % Ru than at higher content. Partial substitution of Pd with Ru was found more effective as a strengthening element and may enhance the martensitic transformation temperature of the Ti50Pd50 alloy.
INTRODUCTION Shape memory alloys (SMAs) are a group of metallic materials that can remember their original shape after being deformed or heated at a certain temperature. SMAs play an important role in industrial use because of their shape memory effects and pseudoelasticity [1]. The major application for SMAs is found in the medical sector, engineering, and technical field. This is mainly because the alloys are less expensive, high fatigue strength, and large-shape changing abilities [2]. Amongst SMAs, the Ti-Ni has been extensively studied and are useful because of their unique sufficient ductility and
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shape memory properties [2]. These alloys have limited temperature around 373 K and thus have limited application area. Recent studies focus on the development of hightemperature shape memory alloys (HTSMAs) based on TiPd, TiAu, and TiPt [3]. A lot of work has been done on TiPt recently to enhance their shape memory properties [4]. It has been reported that TiPt undergoes martensitic transformations from B2 in the austenite phase to B19 in the martensite phase [5], which renders the material as a possible candidate for high temperature applications. Particularly, considerations have been given to ternary alloying with various elements such as Zr, C
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