A. N. Tyumentsev

Evolution of Structural and Phase States at Large Plastic Deformations of an Austenitic Steel 17Cr-14Ni-2Mo

We present the results of the investigation of the evolution of the defect substructure and phase transformations in the process of deformation by rolling and high-pressure torsion of a chromium-nickel steel 17Cr-14Ni-2Mo. Experimental evidences have been found in favor of the occurrence of γ → α(α′) → γ transformations as one of the mechanisms of plastic deformation and reorientation of the crystal lattice at large plastic deformations of the steel under study. It has been shown that the nanostructured states are formed in the process of interaction of localized deformation bands with microbanded twin structures. Mechanisms of deformation and reorientation of the crystal lattice upon the formation of the above-indicated states and possible mechanisms of phase transformations in the process of large plastic deformations of this steel have been discussed.

Substructure formation in high-strength dispersely strengthened alloys

ConclusionsAnalysis of new experimental laws of plastic flow observed in high-strength alloys with dispersional strengthening (such as the formation of substructure with high crystal-lattice curvature, high-temperature localization of deformation from the earliest stages, with reorientation of the localized-shear zones and the adjacent undeformed structural elements) leads to the conclusion that deformational point defects play an important role in the realization of collective deformational modes in the high-strength state.In conditions of high nonequilibrium concentration, deformational point defects, first, permit the inclusion of quasi-viscous diffusional mechanisms of crystal-lattice reorientation by point-defect drift in the local fields of high inhomogeneous stress and, second, by facilitating dislocational deformation mechanisms, may lead to local weakening of the shear zones, localization of the plastic flow, and stability loss, in particular, as a result of mutually consistent autocatalytic defect multiplication.

Structural—Phase transformations in metal alloys during high-dose ionic implantation

Data on phase and structural transitions in the surface layers of metal alloys as a function of the conditions of ionic implantation (ii) are reviewed. It is noted that ionic mixing of surface-absorbed active elements from the implantational gas medium plays an important role in forming the elementary and phase composition of the ion-doped layers. The dependence of these characteristics on the ii conditions is analyzed. The formation of high-energy defect structures and the dispersion of the implanted-layer crystal structure in the strong internal-stress fields generated by the highly nonequilibrium solid solutions and in the course of phase transformation are considered. New possibilities for microstructural modification in ii are identified, with the formation of high-energy defect (including nanocrystalline), heterophase, and other phase—structural states and their combinations in ion-doped layers of metallic alloys.

Influence of the temperature and structural state on the systematic features of plastic deformation in Mo-Re-based alloys

The salient aspects of the formation of a dislocation structure during plastic deformation of the alloys Mo-47 wt. % Re and Mo-47 wt. % Re-1 vol. % ZrO2 at T=300 K in previously recrystallized and polygonalized structural states have been studied with an electron microscope. The studies revealed the systematic features of rotational modes of plastic deformation in these alloys under conditions of substructural hardening and high-temperature grain-boundary slip. An analysis is made of the effect that the substructure and highly dispersed particles of the oxide phase have on the plastic deformation and mechanical properties of Mo-Re-based alloys at T=300-1500 K.

Crystal structure of oxides in internally oxidized alloys based on niobium and molybdenum

The paper presents the results of investigations on the crystal structure of zirconium and hafnium oxides in internally oxidized niobium and molybdenum alloys. It has been shown that the crystal structure of the oxides in the low-temperature range depends on the particle size. Particles of a size 2r>20 nm have a monoclinlc lattice, in accordance with the phase diagram. When the particle size is 2r<4 nm hct modifications of ZrO2 and HfO2 are observed, which is at variance with the phase diagram. In the range 4<2r<20 nm previously unknown orthorhombic modifications of the oxides were discovered. The change in the crystal lattice of the oxides as the particle size decreases is due exclusively to scale effects and can be explained by taking account of the contribution of the surface energy to the free energy of the particles.

Stability of zirconium oxides in Nb-Mo-ZrO2 alloy

The paper gives the results of investigations on the rate of coalescence of zirconium oxides in Nb-Mo-ZrO2 alloy. On the basis of experimental results and theoretical estimates, it is shown that the stability of zirconium oxides in a niobium matrix increases substantially when the oxygen content in the solid solution rises. A high stability of zirconium oxides in niobium, which ensures a considerable (up to T ≃1800°C) increase in the recrystallization temperature and enhancement of the mechanical properties of the alloys at T ⩽ 1100°C can be attained at an oxygen content C0 ≃0.2–0.5 at.% in the solid solution.

Temperature characteristics of the mechanical properties and of the dislocation structure of molybdenum-rhenium alloys

The temperature characteristics of the yield strength and of the dislocation structure of supersaturated molybdenum-rhenium alloys were studied over the 77–673°K temperature range. A lesser dependence of σ0.1 on the temperature was found to result from twinning. The mobility of screw dislocations was found to become much lower due to alloying with rhenium. An analysis of the peculiarities in the dislocation structure of the alloys under consideration here (plane pileup, screw dipoles, singularities of interaction between glissile dislocations) has led to the conclusion that the lower mobility of screw dislocations is a consequence of the lower energy of the packing defect in molybdenum alloyed with rhenium. The lattice resistance to a movement of screw dislocations (τp) at room temperature has been estimated from the distance between dislocations in screw dipoles and found to be τp≥16 kgf/mm2.

Discontinuous decomposition in quenched and deformed alloys

Discontinuous decomposition in quenched and deformed samples of the alloy Cu + 4.3% Ti has been studied by optical metallography and by electron metallography (with replicas and thin foils). The structure of the discontinuous-decomposition regions changes markedly during the continuous metastable decomposition in the matrix. Cells are nucleated within grains in the deformed samples at recrystallization nuclei.