Creep of binary Ni-rich NiTi shape memory alloys and the influence of pre-creep on martensitic transformations
-
G. Eggeler
,
J. Khalil-Allafi
Abstract
The present work represents an exploratory study of creep in a Ni-rich NiTi shape memory alloy (50.7 at.% Ni) in the temperature range 470 – 530 °C at stresses between 90 and 150 MPa. Creep of Ni-rich NiTi alloys is characterized by stress exponents of 2 (for the minimum creep rate data) and of 4.7 (for creep rates measured after 10% of accumulated strain). During creep, Ni4Ti3 precipitates (which nucleate and grow during heating under a small pre-load) coarsen. The interparticle spacing increases and this is why the resistance of the material to creep decreases. It was not possible to rationalize this creep softening on the basis of a traditional Orowan process. Instead a wrapping process, where particles were wrapped in by migrating sub-grain boundaries, was observed. The sharp minima in the creep curves and the strain dependence of the stress exponent as observed in the present study can be rationalized on the basis of an initial climb controlled bypassing of particles followed by this wrapping process, which becomes more intense as interparticle spacings increase. When comparing crept materials with materials which were aged at the same temperature for the same time there only is a small difference between the corresponding differential scanning calorimetry (DSC) charts. Therefore we conclude that the precipitation and coarsening of Ni4Ti3 particles during creep is more important in affecting DSC chart features than the evolution of a creep dislocation structure.
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Articles in the same Issue
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- Notifications/Mitteilungen
- Personal/Personelles
- Books/Bücher
- DGM Conferences/Training
Articles in the same Issue
- Frontmatter
- Editorial
- Editorial
- Articles/Aufsätze
- A model for the work hardening of WC–Co “hard metals”
- On the dispersion strengthening mechanisms in ODS materials
- Effect of hydrogen on the mechanical properties of the β titanium alloy Timetal® 21S
- Cyclic deformation behaviour of (α + β) titanium alloys under complex mechanical and physiological loading conditions
- Assessment of the influence of interdendritic shrinkage cavities on the thermo-mechanical fatigue behaviour of the nickel-base superalloy MAR-M247LC
- Effects of static strain aging on residual stress stability and alternating bending strength of shot peened AISI 4140
- On the possibilities to enhance the fatigue properties of ultrafine-grained metals
- New method of determining stress relaxation behavior in creep machines by controlled unloading
- Creep of binary Ni-rich NiTi shape memory alloys and the influence of pre-creep on martensitic transformations
- Interaction of high-cycle fatigue with high-temperature creep in superalloy single crystals
- A unified description of creep in pure and dispersion-strengthened copper
- A new interpretation of flow-stress measurements of high-purity NiAl below room temperature
- A mesoscopic plasticity model accounting for spatial fluctuations of plastic strains, internal stresses and dislocation densities
- Behavior of X-ray peak widths in the Wilkens model of a restrictedly random distribution of dislocations
- Dislocation structure and crystallite size distribution in hexagonal nanomaterials from X-ray peak profile analysis
- Werden gewichtsoptimiert konstruierte Bauteile durch die Verwendung von Leichtmetallen wirklich leichter?*)
- Strain-induced martensite formation in metastable austenitic steels with varying carbon content
- Isothermal bainitic transformation in low alloy steels: factors limiting prediction of the resulting material’s properties
- Fatigue damage evolution in a particulate-reinforced metal matrix composite determined by acoustic emission and compliance method
- Microstructure and modification mechanisms of Si phase in as-thixoformed alloy A356
- Influence of size effect on microstructural changes in cyclically deformed polycrystalline nickel
- Self-diffusion of 71Ge and 31Si in Si –Ge alloys
- On localised corrosive attack, stress corrosion cracking and corrosion fatigue effects in a hardmetal cutting-tool material
- The internal stress during growth of SiC single crystals
- Notifications/Mitteilungen
- Personal/Personelles
- Books/Bücher
- DGM Conferences/Training
