Annealing behaviour of nanocrystalline NiTi (50 at% Ni) alloy produced by high-pressure torsion

R. Singh, H. Rösner, E. A. Prokofyev, R. Z. Valiev, S. V. Divinski, G. Wilde

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

An equiatomic nanocrystalline NiTi alloy, deformed by high-pressure torsion (HPT), was investigated. The as-prepared bulk NiTi alloy consisted of both amorphous and nanocrystalline phases. Crystallization and structural changes during annealing were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). DSC thermograms and X-ray analyses revealed stress relaxation and partial crystallization below 500 K, while grain growth of the nanocrystals occurred predominantly after heating to temperatures above 573 K. Along with the amorphous phase crystallization, a continuous growth of pre-existing nanocrystals that are retained after HPT was observed. The DSC signals observed during continuous heating experiments indicate an unusually large separation between the crystallization and growth stages. A detailed analysis of the evolution of the enthalpy release upon annealing revealed reproducibly non-monotonous trends with annealing temperature that cannot be explained solely by nucleation and growth of crystalline volume fractions. Instead, the results can be rationalized by assuming a reverse amorphization process occuring during annealing at 523 K. This behavior, which also caused a large variation in nanocrystal size after annealing at higher temperatures, is discussed with respect to the nanoscale microstructural heterogeneity after initial deformation processing.

Original languageEnglish
Pages (from-to)3079-3092
Number of pages14
JournalPhilosophical Magazine
Volume91
Issue number22
DOIs
Publication statusPublished - Aug 1 2011

Fingerprint

torsion
annealing
crystallization
nanocrystals
heat measurement
scanning
thermograms
heating
stress relaxation
x rays
enthalpy
nucleation
trends
transmission electron microscopy
temperature
diffraction

Keywords

  • crystallization
  • grain boundary
  • nanocrystalline
  • NiTi
  • relaxation

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Annealing behaviour of nanocrystalline NiTi (50 at% Ni) alloy produced by high-pressure torsion. / Singh, R.; Rösner, H.; Prokofyev, E. A.; Valiev, R. Z.; Divinski, S. V.; Wilde, G.

In: Philosophical Magazine, Vol. 91, No. 22, 01.08.2011, p. 3079-3092.

Research output: Contribution to journalArticle

Singh, R. ; Rösner, H. ; Prokofyev, E. A. ; Valiev, R. Z. ; Divinski, S. V. ; Wilde, G. / Annealing behaviour of nanocrystalline NiTi (50 at% Ni) alloy produced by high-pressure torsion. In: Philosophical Magazine. 2011 ; Vol. 91, No. 22. pp. 3079-3092.
@article{7a7654bdd8834fa2a3f2721f56add8df,
title = "Annealing behaviour of nanocrystalline NiTi (50 at{\%} Ni) alloy produced by high-pressure torsion",
abstract = "An equiatomic nanocrystalline NiTi alloy, deformed by high-pressure torsion (HPT), was investigated. The as-prepared bulk NiTi alloy consisted of both amorphous and nanocrystalline phases. Crystallization and structural changes during annealing were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). DSC thermograms and X-ray analyses revealed stress relaxation and partial crystallization below 500 K, while grain growth of the nanocrystals occurred predominantly after heating to temperatures above 573 K. Along with the amorphous phase crystallization, a continuous growth of pre-existing nanocrystals that are retained after HPT was observed. The DSC signals observed during continuous heating experiments indicate an unusually large separation between the crystallization and growth stages. A detailed analysis of the evolution of the enthalpy release upon annealing revealed reproducibly non-monotonous trends with annealing temperature that cannot be explained solely by nucleation and growth of crystalline volume fractions. Instead, the results can be rationalized by assuming a reverse amorphization process occuring during annealing at 523 K. This behavior, which also caused a large variation in nanocrystal size after annealing at higher temperatures, is discussed with respect to the nanoscale microstructural heterogeneity after initial deformation processing.",
keywords = "crystallization, grain boundary, nanocrystalline, NiTi, relaxation",
author = "R. Singh and H. R{\"o}sner and Prokofyev, {E. A.} and Valiev, {R. Z.} and Divinski, {S. V.} and G. Wilde",
year = "2011",
month = "8",
day = "1",
doi = "10.1080/14786435.2011.566228",
language = "English",
volume = "91",
pages = "3079--3092",
journal = "Philosophical Magazine",
issn = "1478-6435",
publisher = "Taylor and Francis Ltd.",
number = "22",

}

TY - JOUR

T1 - Annealing behaviour of nanocrystalline NiTi (50 at% Ni) alloy produced by high-pressure torsion

AU - Singh, R.

AU - Rösner, H.

AU - Prokofyev, E. A.

AU - Valiev, R. Z.

AU - Divinski, S. V.

AU - Wilde, G.

PY - 2011/8/1

Y1 - 2011/8/1

N2 - An equiatomic nanocrystalline NiTi alloy, deformed by high-pressure torsion (HPT), was investigated. The as-prepared bulk NiTi alloy consisted of both amorphous and nanocrystalline phases. Crystallization and structural changes during annealing were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). DSC thermograms and X-ray analyses revealed stress relaxation and partial crystallization below 500 K, while grain growth of the nanocrystals occurred predominantly after heating to temperatures above 573 K. Along with the amorphous phase crystallization, a continuous growth of pre-existing nanocrystals that are retained after HPT was observed. The DSC signals observed during continuous heating experiments indicate an unusually large separation between the crystallization and growth stages. A detailed analysis of the evolution of the enthalpy release upon annealing revealed reproducibly non-monotonous trends with annealing temperature that cannot be explained solely by nucleation and growth of crystalline volume fractions. Instead, the results can be rationalized by assuming a reverse amorphization process occuring during annealing at 523 K. This behavior, which also caused a large variation in nanocrystal size after annealing at higher temperatures, is discussed with respect to the nanoscale microstructural heterogeneity after initial deformation processing.

AB - An equiatomic nanocrystalline NiTi alloy, deformed by high-pressure torsion (HPT), was investigated. The as-prepared bulk NiTi alloy consisted of both amorphous and nanocrystalline phases. Crystallization and structural changes during annealing were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). DSC thermograms and X-ray analyses revealed stress relaxation and partial crystallization below 500 K, while grain growth of the nanocrystals occurred predominantly after heating to temperatures above 573 K. Along with the amorphous phase crystallization, a continuous growth of pre-existing nanocrystals that are retained after HPT was observed. The DSC signals observed during continuous heating experiments indicate an unusually large separation between the crystallization and growth stages. A detailed analysis of the evolution of the enthalpy release upon annealing revealed reproducibly non-monotonous trends with annealing temperature that cannot be explained solely by nucleation and growth of crystalline volume fractions. Instead, the results can be rationalized by assuming a reverse amorphization process occuring during annealing at 523 K. This behavior, which also caused a large variation in nanocrystal size after annealing at higher temperatures, is discussed with respect to the nanoscale microstructural heterogeneity after initial deformation processing.

KW - crystallization

KW - grain boundary

KW - nanocrystalline

KW - NiTi

KW - relaxation

UR - http://www.scopus.com/inward/record.url?scp=79959350090&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=79959350090&partnerID=8YFLogxK

U2 - 10.1080/14786435.2011.566228

DO - 10.1080/14786435.2011.566228

M3 - Article

AN - SCOPUS:79959350090

VL - 91

SP - 3079

EP - 3092

JO - Philosophical Magazine

JF - Philosophical Magazine

SN - 1478-6435

IS - 22

ER -