The effect of mechanical cyclings on the stress-strain(S-S) curves was studied systematically using tensile tests over a wide temperature range. Two-stage yielding was observed in the temperature range between Ms and ...The effect of mechanical cyclings on the stress-strain(S-S) curves was studied systematically using tensile tests over a wide temperature range. Two-stage yielding was observed in the temperature range between Ms and the ultimate temperature to induce martensite, denoted by Md. The first stage was confirmed to be associated with stress-induced martensite(SIM) and the second stage was associated with the yielding of SIM. When the samples were mechanically cycled between Ms and Md, a stress-softening phenomenon was observed. The cyclings made the martensite amount increase, critical stress σc of SIM decrease according to exponential law, and the entropy(also enthalpy) of the parent to martensite transformation also decrease. The variations of SIM relative amount were determined by recording the changes of electrical resistances in the course of tension.展开更多
Snap-acting transformation and snap-acting two way shape memory (TWSM) effect have been obtained in NiTi alloy using the constrained effect of stress on the driving force of TWSM element. The TWSM strain of the snap-a...Snap-acting transformation and snap-acting two way shape memory (TWSM) effect have been obtained in NiTi alloy using the constrained effect of stress on the driving force of TWSM element. The TWSM strain of the snap-acting element made of Ni51Ti49 alloy finishes abruptly at certain temperature without any additional mechanism, within an interval less than 1 ms. A thermodynamic model is presented to account for these observations.展开更多
The effect of aluminium content and solution heat treatment in α+β phase region on the shape memory characteristics and mechanical properties of cold wrought Cu-Al-Ni-Mn-Ti alloy are studied in this paper. Results i...The effect of aluminium content and solution heat treatment in α+β phase region on the shape memory characteristics and mechanical properties of cold wrought Cu-Al-Ni-Mn-Ti alloy are studied in this paper. Results indicate that the transformation temperature (Tt) of Cu-Al-Ni-Mn-Ti alloy reduces obviously with the increase of the amount of α-phase. During aging at 623 K, Tt increases at first up to a peak value, then decreases with prolongation of aging time. Life time of heat resistance of the alloy at high temperatures is improved with increase of the amount of α-phase, this life time becomes poor with Bainite precipitation. When the amount of α-phase is less than 5%, the ratio of shape recovery brought about by the solution heat treatment in α+β phase region is almost not effected. However, plasticity of the alloy increases obviously as aluminium content decreases. We believe that improving cold workability of Cu-Al-Ni-Mn-Ti alloy and keeping good heat resistant property and shape memory effects are possible by means of reducing the content of aluminium and solulion heat treatment in α+β phase region.展开更多
文摘The effect of mechanical cyclings on the stress-strain(S-S) curves was studied systematically using tensile tests over a wide temperature range. Two-stage yielding was observed in the temperature range between Ms and the ultimate temperature to induce martensite, denoted by Md. The first stage was confirmed to be associated with stress-induced martensite(SIM) and the second stage was associated with the yielding of SIM. When the samples were mechanically cycled between Ms and Md, a stress-softening phenomenon was observed. The cyclings made the martensite amount increase, critical stress σc of SIM decrease according to exponential law, and the entropy(also enthalpy) of the parent to martensite transformation also decrease. The variations of SIM relative amount were determined by recording the changes of electrical resistances in the course of tension.
基金The project is supported by National Natural Science Fundation of China
文摘Snap-acting transformation and snap-acting two way shape memory (TWSM) effect have been obtained in NiTi alloy using the constrained effect of stress on the driving force of TWSM element. The TWSM strain of the snap-acting element made of Ni51Ti49 alloy finishes abruptly at certain temperature without any additional mechanism, within an interval less than 1 ms. A thermodynamic model is presented to account for these observations.
文摘The effect of aluminium content and solution heat treatment in α+β phase region on the shape memory characteristics and mechanical properties of cold wrought Cu-Al-Ni-Mn-Ti alloy are studied in this paper. Results indicate that the transformation temperature (Tt) of Cu-Al-Ni-Mn-Ti alloy reduces obviously with the increase of the amount of α-phase. During aging at 623 K, Tt increases at first up to a peak value, then decreases with prolongation of aging time. Life time of heat resistance of the alloy at high temperatures is improved with increase of the amount of α-phase, this life time becomes poor with Bainite precipitation. When the amount of α-phase is less than 5%, the ratio of shape recovery brought about by the solution heat treatment in α+β phase region is almost not effected. However, plasticity of the alloy increases obviously as aluminium content decreases. We believe that improving cold workability of Cu-Al-Ni-Mn-Ti alloy and keeping good heat resistant property and shape memory effects are possible by means of reducing the content of aluminium and solulion heat treatment in α+β phase region.
