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%

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%

Stress-induced thermoelastic martensitic transformations and functional properties in [011]-oriented NiTiHfPd single crystals

The stress-induced martensitic transformation in the [011]-oriented Ni45.3Ti29.7Hf20Pd5 (at. %) single crystals in as-grown, homogenized and aged states were investigated in compression. It is experimentally shown that heat treatments of single crystals result in increase in martensitic transformation temperatures, two-fold decrease in reversible strain and increase in strain-hardening coefficient. As-grown single crystals demonstrate large temperature range of superelasticity (up to 140 K), large reversible strain (up to 4.3%) and large work output in comparison with homogenized and aged crystals

Effect of one variant of Ti3Ni4 particles on stress-induced martensitic transformations in <111>-oriented Ti49.2Ni50.8 single crystals

In the present study the effects of stress-assisted aging of the Ti49.2Ni50.8 single crystals oriented along [11] direction on the stress-induced B2-R-B19' thermoelastic martensitic transformations and superelasticity are investigated. It is experimentally established that aging at 823 K for 1h under compression stress of 150 MPa along [11] direction leads to the precipitation of one crystallographic variant of Ti3Ni4 particles of 350(±30) nm in size. Precipitation the single variant of Ti3Ni4 particle results in an appearance of homogeneous long-range internal stress field || ≈ 65 MPa, that defines the main features of stress-induced B2-R-B19' transformation and determines the increase in the characteristic temperatures of martensitic transformation and the existence of two-way shape memory effect

Elastocaloric effect in heterophase TiNi single crystals

The paper presents studies of the elastocaloric effect during the stress-induced B2–(R)–B19′ martensitic transformation depending on the microstructure and test temperature in Ni50.6Ti49.4 and Ni50.8Ti49.2 (at.%) single crystals oriented along the [001]B2 direction. The aging of TiNi single crystals at 573 and 823 K for 1–1.5 h improves the characteristics of superelasticity and elastocaloric effect. Precipitating large Ti3Ni4 particles with the size of ~ 400 nm aged at 823 K leads to an increase in the temperature range of elastocaloric effect and in the maximum adiabatic cooling ΔTad up to 24.2–25.3 K compared with quenched single crystals (ΔTad = 14.3 K). TiNi single crystals containing nanosized Ti3Ni4 particles smaller than 10 nm (aging at 573 K) have a distinguishing feature: two-stage reverse B19′–R–B2 martensitic transformation leads to staging on the elastocaloric effect temperature dependence. The maximum ΔTad in these single crystals is lower compared with single crystals aged at 823 K. It is equal to 16.8 K and 21.3 K in Ni50.6Ti49.4 and Ni50.8Ti49.2 alloys, respectively. However they demonstrate record coefficient of performance up to 27.8 in the Ni50.6Ti49.4, which characterizes them as promising for further use in solid-state cooling devices

The effect of subsequent stress‐induced martensite aging on the viscoelastic properties of aged NiTiHf polycrystals

This study investigated the effect of stress‐induced martensite aging under tensile and compressive stresses on the functional and viscoelastic properties in Ni50.3Ti32.2Hf17.5 polycrystals containing dispersed H‐phase particles up to 70 nm in size obtained by preliminary austenite aging at 873 K for 3 h. It was found that stress‐induced martensite aging at 428 K for 12 h results in the appearance of a two‐way shape memory effect of −0.5% in compression and +1.8% in tension. Moreover, a significant change in viscoelastic properties can be observed: an increase in internal friction (by 25%) and a change in elastic modulus in tensile samples. The increase in internal friction during martensitic transformation after stress‐induced martensite aging is associated with the oriented growth of thermal‐induced martensite. After stress‐induced martensite aging, the elastic modulus of martensite (EM) increased by 8 GPa, and the elastic modulus of austenite (EA) decreased by 8 GPa. It was shown that stress‐induced martensite aging strongly affects the functional and viscoelastic properties of material and can be used to control them

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

The effect of stress-induced martensite aging in tension and compression on B2–B19′ martensitic transformation in Ni50.3Ti32.2Hf17.5 high-temperature shape memory alloy

The present study investigates the high-temperature shape memory effect (SME) in heterophase Ni50.3Ti32.2Hf17.5 polycrystals with nanosized H-phase particles after stress-induced martensite (SIM) aging in tension and compression. SIM aging created the conditions for fully reversible two-way SME with a strain of up to 50% of the one-way shape memory strain. SIM aging altered the viscoelastic properties of material, in particular, the elastic moduli of austenite and martensite increased, as did internal friction. Increased interface mobility is suggested as the reason for internal friction growth

Orientation dependence of superelasticity in quenched high-nickel Ti51.8Ni single crystals

The orientation dependence of the functional and mechanical properties of quenched Ti-51.8at.%Ni single crystals, undergoing a strain-glass transition upon cooling/heating was investigated. It was found that a compressive stress above 800 MPa leads to the B2-B190 martensitic transformation (MT), regardless of orientation. In the high-strength [0 0 1]-orientation, superelasticity (SE) was observed at 203–248 K, with a reversible strain of 2.3%. Degradation of SE at deforming stresses r > 1000 MPa was associated with the formation of {1 1 3}B2 twins during the reverse MT. In the low-strength 1 1 1-orientation, the formation of stress-induced B190 -martensite occurred simultaneously with the plastic deformation of the B2-phase (due to the formation of reorientation bands and dislocation slip) and a reversible strain was not observed

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