Reversible reorientation of martensite variants in stress-induced martensite aged Co35Ni35Al30 single crystals

The paper reports the temperature dependence of the reversible reorientation of martensite variants during loading/unloading along the [001](B2)||[001](L10)-direction in compression in stress-induced martensite (SIM) aged at 423 K for 0.5 h under a compressive stress of 500 MPa applied along the [110](B2)||[100](L10)-direction Co35Ni35Al30 single crystals. A wide temperature range of reversible strain from 203 K to 413 K (210 K) is observed due to the stabilisation of the tetragonal L1(0)-martensite variant V1 ([001](B2)||[001](L10)) during SIM-aging in these single crystals. The reversible strain in the range of 157 K (203 K<T-t<A(s)=A(f)=360 K) is because o(f) the reorientation of the L1(0)-martensite variants V1-V2/V3. The superelasticity at T-t>A(f)=360 K occurred due to the stress-induced B2-L1(0)(V2/V3) martensitic transformation (MT). Rubber-like behaviour develops in the range of 52 K (203 K<T-t<M-f*=255 K) and is characterised by a narrow stress hysteresis of 13 MPa and a reversible strain of -12.0 % due to the movement of the twinning boundaries (reversible twinning) in L1(0)-martensite. The reversible strain reaches -10.2 % in the temperature range from M-f*=255 K to A(s)=A(f)=360 K. This strain is associated with a new mechani(s)m of L1(0)-martensite variant reorientation, which occurs through a sequence of reverse and forward stress-induced L1(0)(V1)-B2-L1(0)(V2/V3) MTs and leads to the stages on the stress-strain curves. The reverse L1(0)(V1)-B2 MT at loading and forward B2-L1(0)(V1) MT at unloading on the first stage of the stress-strain curves are characterised by low critical stresses of 8-23 MPa, a narrow stress hysteresis of 3-19 MPa and a completely reversible strain of -6.0 %, which is stable for 100 loading/unloading cycles.