Aleksandr E. Volkov

Influence of neutron irradiation on the martensitic transformations and shape-memory effect in a TiNi alloy

The paper reports measurements of the strains and electrical resistance of a TiNi shape-memory alloy under irradiation in the low-temperature helium circuit of a nuclear reactor. Irradiation of the alloy in martensitic state at 170 K revealed that the transition temperatures from cubic to rhombohedral and from rhombohedral to monoclinic phase decrease exponentially with increasing dose. No change in the shape-memory effects and transformation plasticity was observed up to a dose of 6.7×1022 n/m2. Keeping the sample at 340 K without irradiation restores (increases) partially the transition temperatures. The relations observed can be assigned to a change in the degree of long-range order in the lattice caused by neutron irradiation.

Simulation of Payload Vibration Protection by Shape Memory Alloy Parts

A system of vibroisolation under consideration consists of a payload connected to a vibrating housing by plane shape memory alloy (SMA) slotted elements. The calculation of the mechanical behavior of the SMA is based on a microstructural theory. Simulations of harmonic and of impact excitations are carried out. The results have shown that protective properties of this system depend on the SMA state. The maximum reduction of the acceleration amplitude for harmonic excitation is reached when the SMA is in the martensitic (pseudo-plastic) state or in the two-phase state. A variation of temperature allows changing the resonance frequency and thus escaping from the resonance and controlling a mode of vibration.

Simulation of Vibration Isolation by Shape Memory Alloy Springs Using a Microstructural Model of Shape Memory Alloy

A vibroisolation of a payload connected to a vibrating housing by two helical shape memory alloy (SMA) elements is considered. A microstructural theory is used for the simulation of the mechanical behavior of the SMA. The simulations have shown that the resonant frequency and the mitigation of the external vibrations depend on the shape memory alloy state. The maximum reduction of the acceleration amplitude for harmonic excitation is reached when the SMA is in the martensitic pseudoplastic state or in the two-phase state. Variation of temperature allows changing the resonance frequency and thus escaping from resonance. The acceleration of the payload at impact is the smallest when the SMA elements are in the pseudoelastic state.

Martensitic transformation in a copper-aluminum-nickel alloy single crystal after short-term neutron irradiation

The influence of neutron irradiation on the temperature kinetics of thermoelastic martensitic transformation in a Cu-Al(13.4%)-Ni(5%) alloy single crystal is investigated by measuring the electrical resistivity directly under irradiation of the sample in a nuclear reactor channel. It is revealed that, after irradiation of the crystal in a martensitic or two-phase state, the temperature of the phase transition upon heating becomes 25–30 K higher than that prior to irradiation. This shift in the transition temperature is observed only upon the first heating, and the kinetics of martensitic transformation is restored in subsequent thermocycles. The shift in the transformation temperatures after irradiation increases with an increase in the fluence. The experimental results are explained by a disturbance of coherence at the interfaces in the irradiated crystals.

Kinetics of radiation damage and martensitic transformations in TiNi alloys irradiated with neutrons

The variation of the temperatures of martensitic transformations and the rate of radiation damage in TiNi alloys were studied upon irradiation with reactor neutrons. The irradiation was performed at temperatures of 120 and 335 K. In the process of irradiation, electrical resistance of the alloys was measured continuously and thermal cycling through the temperature range of martensitic transformations was carried out. The transformation temperatures were shown to decrease at different rates with increasing irradiation fluence. The electrical resistance increases linearly with increasing neutron fluence to 6.7×1018 cm−2 irrespective of the irradiation temperature. Deviation from a linear dependence is only observed when the irradiation leads to a change in the phase state of the alloy. The rate of the resistance increase only slightly depends on the irradiation temperature. In martensite, it is greater by a factor of 2–4 than that in austenite. Mechanisms of irradiation-induced modification of the structure of TiNi alloys that explain the experimental data obtained are discussed.

Features of the strain hardening of nickel titanium in the region of thermoelastic martensite transformation

The inheritance of strain hardening in a nickel titanium (TiNi) alloy that possesses shape memory has been studied using a sample subjected to plastic deformation in the austenite state prior to a transition to the martensite state. The results show that the strain hardening created in the TiNi alloy in the austenite state is not inherited in the martensite state and the sample behaves as if there were no significant plastic deformation. It is suggested that this behavior can be related to the fact that the alloy lattice defects (primarily, dislocations generated during pre-deformation in the austenite state) are not effective obstacles to the motion of domain boundaries in the martensite state.

Effect of alternating-sign plastic straining on the shape memory effects in nickel titanium

The effects of shape memory, martensite transformation plasticity, and two-way shape memory in nickel titanium (TiNi) prestrained in an alternating-sign regime have been studied. The reversible deformation and the temperature-dependent deformation kinetics in the temperature interval of martensite transformation were independent of the degree of prestraining. It is concluded that an increase in the density of dislocations does not significantly influence the mechanical behavior of nickel titanium in the vicinity of the martensite transformation. The results of computer simulation based on the structural analytical theory are in satisfactory agreement with experiment.

Delay of reversible deformation in titanium nickelide after an incomplete transformation cycle

Characteristic features of the appearance of reversible shape memory in an equiatomic TiNi alloy were studied after a cycle in an incomplete range of martensitic transformation temperatures. It was observed that the establishment of reversible shape memory is accompanied by the SMART effect (Stepwise Martensite to Austenite Reversible Transformation) which is manifest as a temperature delay of the deformation under heating. The delay occurs at that temperature at which the transformation terminated in the preliminary thermal cycle and is 3 °C.