Structure and Properties of Ti 28 Ni 50 Hf 22 Powder Alloy
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Structure and Properties of Ti28Ni50Hf22 Powder Alloy S. S. Volodkoa, *, S. N. Yudinb, **, V. V. Cheverikinc, ***, A. V. Kasimtsevb, ****, G. V. Markovaa, *****, T. A. Sviridovac, ******, B. V. Karpovd, *******, S. S. Goncharova, ********, and I. A. Alimova, ********* a
Tula State University, Tula, 3000120 Russia b OOO Metsintez, Tula, 300041 Russia c National University of Science and Technology MISiS, Moscow, 119049 Russia d Research and Development Center, Center for Pressure Metal Treatment on the Base of National University of Science and Technology MISiS, Moscow, Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected] ****e-mail: [email protected] *****e-mail: [email protected] ******e-mail: [email protected] *******e-mail: [email protected] ********e-mail: [email protected] *********e-mail: [email protected] Received June 14, 2019; revised July 16, 2019; accepted July 19, 2019
Abstract—The effect of consolidation and thermal treatment on the structure, local chemical composition, and martensite transformation temperatures of the Ti28Ni50Hf22 powder alloy is studied. It is shown that, in the powder state, the alloy is characterized by an inhomogeneous distribution of Ti and Hf in the matrix, whose concentration spread may reach 27 at %. Vacuum sintering and homogenizing annealing lead to equalization of the chemical composition. During powder sintering, the spread of Ti and Hf concentrations reduces from 27 to 2 at %. Subsequent vacuum annealing at a temperature of 1000°C for 4 h for a sintered sample additionally reduces the spread of concentrations from 4 to 2 at %, while the increase in the annealing duration from 4 to 16 h does not affect the uniformity of the element distribution. It is established that, at a large inhomogeneity of the chemical composition, the differential scanning calorimetry (DSC) methods fail to record the occurrence of martensitic transformation in the melt. However, homogenization of the alloy leads to the appearance of endothermic peaks on the DSC curve upon heating, as well as to narrowing of the interval of reverse martensitic transformation. Keywords: calcium hydride synthesis, alloy with a high temperature shape memory effect, martensitic transformation, powder metallurgy, consolidation, thermal treatment, structure DOI: 10.1134/S2075113320050354
INTRODUCTION Shape memory alloys (SMAs) have been widely used in different areas of human activity owing to unique properties, such as a shape memory effect (SME) and superelasticity (SE). Currently, the development of nuclear power and the aerospace industry [1, 2] requires the use of alloys with a high-temperature shape memory effect in which the temperature interval of implementing the SME is above 100°C, typical of binary TiNi alloys that undergo thermoelastic martensitic transformation (TMT). Alloying of TiNi intermetallic with such elements as Hf or Zr is an effective method to increase the TMT of TiNi alloy to
300–500°C [1, 3]. Obtaining such
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