Influence of particles on the functional properties of single crystals of high-strength ferromagnetic alloys

Single crystals of the ordered ferromagnetic Co49Ni21Ga30 (at.%) alloy with B2-L10 martensitic transformation and of the disordered iron-based Fe41Ni28Co17Al11.5X2.5 (X=Ta, Ti) (at.%) alloys, which undergo thermoelastic γ-a' martensitic transformations, were studied in terms of the influence of chemical composition, size and volume fraction of the dispersed γ'- phase particles on functional properties – shape memory effect and superelasticity. Single crystals of Co49Ni21Ga30 alloy showed that the precipitation of nanometric γ'-phase particles changes the martensitic transformation characteristic temperature, reduces the value of the shape memory effect and superelasticity, increases thermal and stress hysteresis, and leads to hardening of the high temperature phase, which promotes superelasticity at a wide temperature range and at high temperatures at T>373K compared with the crystals without particles. Single crystals of FeNiCoAlX (X=Ta, Ti) alloys have experimentally demonstrated that the precipitation of ordered γ'-phase particles at a size of d=5-10 nm during aging at T=973 K, 3 h, leads to the occurrence of the shape memory effect and superelasticity

EFFECT OF AGING ON FUNCTIONAL AND MECHANICAL PROPERTIES OF SINGLE CRYSTALS CONIGA ALLOY

На [001]-монокристаллах Co49Ni21Ga30 (ат, %) установлено, что выделение частиц γ'-фазы размером 3–5 нм после старения 623 К в течение 15 минут приводит к снижению температуры начала прямого мартенситного превращения на 150 К, уменьшению величины обратимой деформации в 2 раза, увеличению величин термического и механического гистерезисов в 1.5–3 раза и расширению температурного интервала проявления сверхэластичности на 80 К.On [001]-oriented Co49Ni21Ga30 (at,%) single crystals it was established that presipitation of γ'-phase particles in size of 3–5 nm after aging of 623 K for 15 minutes leads to a decrease in the start martensitic transformation temperature by 150 K, a decrease in the reversible strain in 2 times, an increase in the values of thermal and stress hysteresis in 1.5–3 times, and an expansion of the temperature range of the superelasticity on 80 K.Работа выполнена при финансовой поддержке гранта РФФИ № 16-38-00608

Superelasticity in quenched and aged FeMnAlNiTi oligocrystals under compression

The paper studies superelasticity in a 203–523 K temperature range of the 42.5Fe-34Mn-15Al-7.5Ni-1Ti at.% oligocrystals quenched and aged at 473 K for 3 hours. It is shown that the critical stress for the stress-induced α-γ' martensitic transformation slightly grows with the test temperature increasing in accordance with the Clausius–Clapeyron relation. The value of α = dσcr/dT characterizing this growth in quenched and aged oligocrystals, is close to 0.46 and 0.37 MPa/K, respectively. Regardless of the structural condition, superelasticity is observed within the whole mentioned temperature range. At room temperature, the maximum superelasticity is 6.0 and 6.8% of quenched and aged oligocrystals, respectively. A rapid degradation of the functional properties of oligocrystals is detected during the loading-unloading cycles at room temperature. After ten isothermal loading-unloading cycles, residual strain of 2.8 and 1.7% is observed in quenched and aged oligocrystals, respectively

Tension-compression asymmetry of the superelastic behavior of high-strength [001]-oriented FeNiCoAlNb crystals

Temperature dependence of the stressesrcrof stress-inducedc-a0martensitic transformations (MT) andsuperelasticity (SE) were studied in tension and compression on [001]-oriented Fe-27Ni-17Co-11.7Al-2.9Nb (FeNiCoAlNb) (at.%) crystals after two-step ageing (973 K, 0.5 h + 723 K, 3h). It was shown thatthea=drcr/dT value does not depend on the stress state (tension/compression) in the range of thestress-inducedc-a0MT. SE depends on the stress state and the maximum SE strain of 11.5% was observedin compression

The influence of heat treatmnet and stress state on functional and mechanical properties of [001]-oriented FeNiCoAlTi single crystals

The effect of γ'- and β-phase particles on the γ–α' thermoelastic martensitic transformation (MT) during heating/cooling and under stress in [001]-oriented single crystals of a Fe–28%Ni–17%Co–11.5%Al–2.5%Ti (at.%) alloy is studied in tension and compression. The influence of the ageing mode on the Ms temperature is shown. During a simultaneous precipitation of γ'- and β-phase particles following two-step ageing for 4+4 h at 873 K, a 100 K increase in the Ms temperature is observed compared to one-step ageing for 8 h. No differences (asymmetry) in the stresses σcr for the start of the stress-induced γ–α' MT nor in the values of α = dσcr/dT in tension and compression are observed in the crystals with γ'- and γ'+β-phase particles. The absence of asymmetry of σcr and α = dσcr/dT is due to close values of the shape memory effect (SME) and superelasticity (SE) in tension and compression. Upon precipitation of β-phase particles the values of SME and SE decrease

Influence of particles on the functional properties of single crystals of high-strength ferromagnetic alloys

Single crystals of the ordered ferromagnetic Co49Ni21Ga30 (at.%) alloy with B2-L10 martensitic transformation and of the disordered iron-based Fe41Ni28Co17Al11.5X2.5 (X=Ta, Ti) (at.%) alloys, which undergo thermoelastic γ-a' martensitic transformations, were studied in terms of the influence of chemical composition, size and volume fraction of the dispersed γ'- phase particles on functional properties – shape memory effect and superelasticity. Single crystals of Co49Ni21Ga30 alloy showed that the precipitation of nanometric γ'-phase particles changes the martensitic transformation characteristic temperature, reduces the value of the shape memory effect and superelasticity, increases thermal and stress hysteresis, and leads to hardening of the high temperature phase, which promotes superelasticity at a wide temperature range and at high temperatures at T>373K compared with the crystals without particles. Single crystals of FeNiCoAlX (X=Ta, Ti) alloys have experimentally demonstrated that the precipitation of ordered γ'-phase particles at a size of d=5-10 nm during aging at T=973 K, 3 h, leads to the occurrence of the shape memory effect and superelasticity