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

Abstract

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 L10-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<Tt<As=Af=360 K) is because of the reorientation of the L10-martensite variants V1-V2/V3. The superelasticity at Tt>Af=360 K occurred due to the stress-induced B2-L10(V2/V3) martensitic transformation (MT). Rubber-like behaviour develops in the range of 52 K (203 K<Tt<Mf*=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 L10-martensite. The reversible strain reaches −10.2 % in the temperature range from Mf*=255 K to As=Af=360 K. This strain is associated with a new mechanism of L10-martensite variant reorientation, which occurs through a sequence of reverse and forward stress-induced L10(V1)-B2-L10(V2/V3) MTs and leads to the stages on the stress–strain curves. The reverse L10(V1)-B2 MT at loading and forward B2-L10(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.