The effect of thermal cycling and stress-assistant ageing two-way shape memory effect in [123]-oriented Co40Ni33Al27 single crystals

The effect of thermal cycling through an interval of B2-L10 martensitic transformation (MT) under action of external stress and tensile stress-assistant ageing on the two-way shape memory effect in [bar 123]-oriented Co40Ni33Al27 (at.%) single crystals are investigated. For the first time it is experimentally established that tensile stress-assistant 100 MPa ageing at 573 K for 1 h along [bar 123]-direction of Co40Ni33Al27 single crystals creates the necessary conditions for two-way shape memory effect (TWSME) with the reversible strain up to epsilon=2.4 (±0.3)% at cooling/heating. The TWSME in quenched [bar 123]-oriented Co40Ni33Al27 single crystals can be induced by thermal cycling through an interval of B2-L10 MT under action of constant external stress 50 MPa with the reversible strain less than 1%

Investigation of the two-way shape memory effect in [001]-oriented Co35Ni35Al30 single crystals

For the first time, a study of the two-way shape memory effect (the TWSME) for the quenched and aged at 673 K for 0.5 h [001]-oriented Co35Ni35Al30 single crystals in compression was carried out. In the quenched CoNiAl crystals, the TWSME with a reversible strain of (-3.1 ± 0.3) % was induced by training procedure in the superelasticity temperature range. The physical reason of the TWSME is the creation of internal stress fields due to the formation of dislocations next to γ-phase particles, and an interface between the B2-matrix and the γ-phase in the quenched crystals. It was experimentally shown that aging at 673 K for 0.5 h under a compressive stress of 100 MPa along the [110] direction creates the conditions necessary for observing the TWSME, without additional training with a reversible strain of (+2.2 ± 0.3) %. The conditions for observing the TWSME are determined by the action of the internal stress fields of 25 MPa created by the oriented arrangement of the dispersed particles in the stress-assisted aged crystals. The TWSME is not observed in the stress-free aged crystals with non-oriented precipitation of particles, both before and after training

Stress-induced martensitic transformation in high-strength [236]-oriented Ni51Ti36.5Hf12.5 single crystals

The effects of heat treatment on the stress-induced B2-B19' martensitic transformations in the Ni51.0Ti36.5Hf12.5 single crystals oriented along [236] direction are studied. It is shown that in the annealed at 1323K for 4 h crystals, the temperature range of superelasticity increase almost twofold from 75K up to 135K as compared to the as-grown single crystal contained disperse particles of H-phase. The [236]-oriented Ni51.0Ti36.5Hf12.5 single crystals are characterized with high levels of applied compressive stress up to 1700 MPa in the as-grown state and 1900 MPa in annealed crystals for the completely reversible stress- induced B2-B19' martensitic transformation with reversible strain up to |εSE| =1.4%

The cyclic stability of rubber-like behaviour in stress-induced martensite aged Ni49Fe18Ga27Co6 (at.%) single crystals

In present work, the cyclic stability of the rubber-like behaviour (RLB) was investigated in Ni49Fe18Ga27Co6 (at. %) single crystals. Crystals were aged in the martensite phase at 423 K for 1 h under a compressive stress of 450 MPa, applied along the [110]B2[100]L10-direction. The RLB was induced by a preliminary chemical stabilization of the oriented L10-martensite during stress-induced martensite aging (SIM-aging) and following the reversible reorientation of martensitic variants under a compressive stress applied along the [001]B2[001]L10-direction. The high cyclic stability of the RLB was obtained in 200 loading/unloading cycles, due to the low reorientation stresses of the L10-martensite variants (no higher than 140 MPa) and the high strength properties of the L10-martensite (~1.6 GPa). The irreversible strain after 200 cycles did not exceed 0.6%. An increase in the number of cycles did not lead to the effect of destabilization of the L10-martensite

Elastocaloric effect in aged single crystals of Ni54Fe19Ga27 ferromagnetic shape memory alloy

In the present study, the effect of 0-phase dispersed particles on both the L21(B2)-10M/14ML10 martensitic transformations and the elastocaloric effect in aged Ni54Fe19Ga27 single crystals oriented along the [001]-direction was investigated. It was experimentally shown that aging strongly affects the elastocaloric properties of these crystals. The precipitation of semi-coherent 0-phase particles up to 500 nm in size in the crystals aged at 773 K for 1 h leads to a 1.4 times increase in the operating temperature range of the elastocaloric effect up to DTSE = 270 K as compared with the initial as-grown crystals (DTSE = 197 K). The adiabatic cooling values DTad are similar for the as-grown crystals DTad = 10.9 (0.5) K and crystals aged at 773 K DTad = 11.1 (0.5) K. The crystals containing temperature range of DTSE = 255 K with slightly smaller adiabatic cooling DTad below 9.7 (0.5) K. The aged [001]-oriented Ni54Fe19Ga27 single crystals demonstrate high cyclic stability: the number of cycles does not influence the adiabatic cooling values and parameters of loading/unloading curves regardless of the particle size. The ways to improve the elastocaloric cooling parameters and stability of the elastocaloric effect by means of dispersed particles in the NiFeGa ferromagnetic shape memory alloy were discussed.В ст. ошибочно: Nikita S. Suriko

The effect of thermal cycling and stress-assistant ageing two-way shape memory effect in [123]-oriented Co40Ni33Al27 single crystals

The effect of thermal cycling through an interval of B2-L10 martensitic transformation (MT) under action of external stress and tensile stress-assistant ageing on the two-way shape memory effect in [bar 123]-oriented Co40Ni33Al27 (at.%) single crystals are investigated. For the first time it is experimentally established that tensile stress-assistant 100 MPa ageing at 573 K for 1 h along [bar 123]-direction of Co40Ni33Al27 single crystals creates the necessary conditions for two-way shape memory effect (TWSME) with the reversible strain up to epsilon=2.4 (±0.3)% at cooling/heating. The TWSME in quenched [bar 123]-oriented Co40Ni33Al27 single crystals can be induced by thermal cycling through an interval of B2-L10 MT under action of constant external stress 50 MPa with the reversible strain less than 1%

Two-way shape memory effect in [001] B2-oriented Co-Ni-Al single crystals

In the present study, the necessary conditions for the two-way shape memory effect (TWSME) and its stress-free thermal cycling stability in the Co35Ni35Al30 single crystals, oriented along the [001]B2 direction, were investigated. The TWSME is attributed to the internal stress fields created through the generation of stable dislocation structures and retained martensite in two ways. First, the training involved 100 loading/unloading cycles at room temperature T=295 К with the maximum given strain of 6.0% in compression. Second, the ageing at T=423 К for 1.0 h under a stress of 500 MPa was applied to the martensitic state along the [001]B2[110]L10 direction. It was experimentally shown that the aged crystals demonstrated the best properties of the TWSME response when compared with the trained crystals: i.e., a higher operating temperature range (250-297 K), the high cyclic stability of the reversible strain εTWSME=(3.1±0.3)% during thermal cycles and the low value of the temperature hysteresis (ΔT=24 К). In contrast, in the trained crystals the operating temperature range of the TWSME is shifted towards a low temperature region (220-275 K), after 100 thermal cycles the reversible strain εTWSME is significant decreased from 3.0 to 2.0 % and the temperature hysteresis ΔT is increased from 33 to 50 K

Cyclic stability in superelasticity window for aged single crystals CoNiAl

The cyclic stability of superelasticity in a wide temperature range was investigated on aged at 573 K for 0.5 h Co35Ni35Al30 single crystals oriented along the [001]-direction in compression. Aged single crystals exhibited superelasticity in a wide temperature window from 223 to 548 K (SE = 325 K) with high cyclic stability compared with the initial quenched crystals SE = 175 K (from 373 to 548 K) due to the strengthening of the high-temperature B2-phase by nanoscale particles. It is shown that the aged single crystals demonstrate excellent cyclic stability of superelasticity at room temperature during 10 000 loading/unloading cycles without any significant degradation of reversible strain, critical stresses for the stress-induced martensitic transformations and stress hysteresis. The main mechanisms of the superelasticity degradation during cyclic tests have been determine

Two-way shape memory effect in [001] B2-oriented Co-Ni-Al single crystals

In the present study, the necessary conditions for the two-way shape memory effect (TWSME) and its stress-free thermal cycling stability in the Co35Ni35Al30 single crystals, oriented along the [001]B2 direction, were investigated. The TWSME is attributed to the internal stress fields created through the generation of stable dislocation structures and retained martensite in two ways. First, the training involved 100 loading/unloading cycles at room temperature T=295 К with the maximum given strain of 6.0% in compression. Second, the ageing at T=423 К for 1.0 h under a stress of 500 MPa was applied to the martensitic state along the [001]B2[110]L10 direction. It was experimentally shown that the aged crystals demonstrated the best properties of the TWSME response when compared with the trained crystals: i.e., a higher operating temperature range (250-297 K), the high cyclic stability of the reversible strain εTWSME=(3.1±0.3)% during thermal cycles and the low value of the temperature hysteresis (ΔT=24 К). In contrast, in the trained crystals the operating temperature range of the TWSME is shifted towards a low temperature region (220-275 K), after 100 thermal cycles the reversible strain εTWSME is significant decreased from 3.0 to 2.0 % and the temperature hysteresis ΔT is increased from 33 to 50 K