High temperature shape memory behavior of Ni50.3Ti25Hf24.7 single crystals

In this work we present the high temperature functional behavior of the new Ni50.3Ti25Hf24.7 shape memory alloy (SMA). Very high transformation strains were measured during isobaric experiments at temperatures up to Af = 420 °C. For the [111]B2 orientation in tension, we measured with digital image correlation (DIC) averaged transformation strain of 5.15%, while in small domains 7.74%. For the [011]B2 orientation in compression, we measured averaged transformation strain of 4.6%, locally 5.3%. The remarkable results in terms of actuation strains at T > 400 °C define the Ni50.3Ti25Hf24.7 alloy as one of the most promising shape SMA for high temperature applications

The effect of aluminium on mechanical properties and deformation mechanisms of hadfield steel single crystals

On single crystals of Hadfield steel (Fe-13Mn-1.3C, Fe-13Mn-2.7Al-1.3C, wt.%) the systematical investigations of deformation mechanisms - slip and twinning, stages of plastic flow, strain hardening coefficient depending on orientation of tensile axis have been carried out by methods of optical and electron microscopy, x-ray analysis. Is has been shown that the combination of low stacking fault energy ($\gamma_{\rm{SF}}=0.03$J/m$^2$) with high concentration of carbon atoms in aluminium-free steel results in development of the mechanical twinning at room temperature in all crystal orientations. The new type of twinning with formation of extrinsic stacking fault has been found out in [001] single crystals. Experimentally it has been established that alloying with aluminium leads to increase of stacking fault energy of Hadfield steel and suppresses twinning in all orientations of crystals at preservation of high values of strain-hardening coefficients $\theta$