L. S. Bushnev

Structure and mechanical and electrochemical properties of ultrafine-grained Ti

A study is conducted into the microstructure and physico-mechanical properties of ultrafine-grained titanium produced by severe plastic deformation using the method of equichannel angular pressing. The effects of thermal and mechanical treatment on these characteristics are investigated. The possibility of forming mechanical properties in titanium that compare well with those of highly doped titanium alloys is shown.

Growth kinetics of precipitate-free zones near grain boundaries in Cu-Al-Co alloys

Transmission electron microscopy was used to study the growth kinetics of precipitate-free zones in aging Cu-Al-Co alloys. The formation of zones was associated with the precipitation of the CoAl intermetallic compound at grain boundaries and dissolution of metastable cobalt precipitates near the boundary. The growth of the zone width was found to be of a two-stage character. The activation energy of the zone growth process was determined and proved to be identical in both stages. The first stage is associated with the presence of a supersaturated solid solution of cobalt. The zone growth kinetics in the second stage at 600 and 650°C is nearly linearly dependent on time.

On the nature of the dispersion hardening of Cu-Al-Co alloys

The authors describe an investigation into the mechanism of strain hardening of Cu-8 at. % Al-2 at. % Co alloy strengthened by particles of the intermetallic compound CoAl. They show that within the range 77–573°K the temperature dependence of the yield point is determined by the temperature dependence of the shear modulus. At T > 573°K the reverse processes gain in importance and cause a sharp decrease in the coefficient of strain-hardening and a loss of plasticity. The investigation of the Bauschinger effect and its reversal showed that distant stresses, generated by Orowan loops, have a considerable effect on the strain-hardening process. The reversal processes and an increase in test temperature produced no qualitative change in the dislocation pattern.

Diffusive shape memory effect in the V-H system

The effect of cold plastic deformation on the occurrence of the diffusive shape memory effect in the V-H system due to redistribution of the β-phase arising from the Gorskii effect is investigated by means of three-point bending tests. The slight plastic deformation produced by the bending in the region of the α-solid solution gives rise to a diffusive shape memory effect when there is no load, whereas large deformations completely suppress the diffusive shape memory effect. It is suggested that the reason for the occurrence and disappearances of the diffusive shape memory effect is internal residual stresses of a different scale level which occur after cold plastic deformation.

Structure and properties of heat-resistant coatings based on a Ni-Cr-Al-Y alloy

A study was made of the effect of long high-temperature annealings on the evolution of the structure and properties of heat-resistant coatings of a nickel-chromium-aluminum-yttrium alloy. The coatings are used to protect heat-resistant nickel alloys from oxidation and corrosion.

SHAPE MEMORY EFFECT IN THE VANADIUM- HYDROGEN SYSTEM

The shape memory effect (SME) has been investigated in alloys of the V-H system at concentrations in the range 0.2–0.5 H/V. It is shown that SME occurs over the entire H/V range indicated, but the magnitude of the stresses, the reversibility of the deformation during heating, as well as the magnitude of the thermal hysteresis depend essentially on the hydrogen concentration. The conclusion is drawn that the transformation in this system is of a martensitic character.

Temperature dependences of the flow and critical shear stresses of dispersion-hardening alloys

A study was made of the temperature dependences of the flow stress σ0.1 (T) and of the critical shear stress τcr(T) of Cu-15% A1-(1–2)% Co, Cu-8% A1-(2–2.8)% Co, and Cu-4% A1–2% Co alloys containing noncoherent intermetallic particles. In the case of single crystals at temperatures 77–673° K there was a good agreement between the theoretically calculated values of the Orowan hardening and those found experimentally, so that the dependence τcr(T) was governed by the temperature dependence of the shear modulus G(T). For polycrystalline samples the usual dependence of the mechanical propertiesties on the grain size was not observed. At temperatures from 77 to 473–573°K the dependence σ0.1 (T) was similar to the dependence G(T) and a good agreement was observed between the theoretically calculated dispersion hardening effects with those found experimentally. At temperatures T > 473–573°K the deformation was influenced greatly by grain-boundary glide, which enhanced the dependence σ0.1 (T) compared with that expected theoretically.

Recrystallization of dispersion-hardened nickel alloys with a polygonalized substructure

Conclusions1.High-temperature annealing of dispersion-hardened nickel alloys, with a substructure specially polygonized by thermomechanical treatment, is accompanied by two competing processes: fast and slow recrystallization. The latter leads to a coalescence of hardener particles at moving boundaries.2.Both recrystallization processes are sensitive to changes in the dispersion level of hardener particles, within a rather narrow range of this variation. In dispersion-hardened nickel alloys there occurs a regular lowering of the recrystallization temperature and a transition from fast to slow recrystallization, all related to a decrease in the volume fraction of particles within the 500–1500 Å size range.3.An appreciable change in the degree of hardener dispersion in Ni-HfO2 (III), along with lowering of the recrystallization temperature, will accelerate the process of fast recrystallization.

Investigation of decomposition processes in alloy Cu-Ge-Ti

The process of the decomposition of alloy Cu-6 at.% Ge-2.8 at.% Ti in the 400–700°C temperature range was investigated by transmission electron microscopic methods and by a study of the kinetics of the change of electrical resistance. After quenching in water decomposition at 500–600° occurs in two stages. In the first stage the coherent phase precipitates as lamellae with habit plane 100. The second stage is associated with the occurrence of semicoherent lamellae of the same phase. The effect of hardening conditions of the character of decomposition is investigated.

Effect of vacancies on nucleation of a new phase in copper-base alloys

The effect of hardening conditions on the decomposition of alloys Cu-Al-Co was investigated by studying the kinetics of the change of electrical resistance, measuring the paramagnetic susceptibility, and by transmission microscopy. The data obtained indicated a considerable effect of hardening vacancies on the process of nucleation of the stable phase (CoAl). It is shown that nucleation of phase CoAl occurs on vacancion clusters.