V. I. Zel'dovich

About the Mechanism of Deformation at Martensite Transformation in the Fe-31 wt%Ni Alloy

The criterion of an estimation of a reality of the mechanism of deformation of a lattice at martensite transformation is proposed. The most real mechanism of deformation of a lattice in FeNi alloy with the twinned martensite is determined. The Kurdjumov-Sachs shear on a plane (111) fcc in a direction [11-2] fcc is the basic component of deformation of a lattice in the given mechanism.

Amorphization of Titanium Nickelide by means of Shear under Pressure and Crystallization at the Subsequent Heating

Transmission electron microscopy and X-ray diffraction were used to study structural changes in the Ti-50.5 at. % Ni alloy upon severe plastic deformation by shear under pressure and subsequent heating. An increase in the degree of deformation leads sequentially to a martensite transformation, twinning of martensite crystals, formation of reorientation bands, development of rotational modes of deformation, formation of a nanocrystalline structure, and finally amorphization. A scheme of the formation of amorphous structure of the alloy during deformation is suggested based on the observed structural changes. It has been found that a reverse martensitic transformation might be one of mechanisms of plastic deformation of the alloy. Therefore, as the degree of deformation increases, first forward and subsequently reverse martensitic transformations can occur. The formation of an amorphous structure starts as the degree of deformation reaches 4.2 (one revolution of Bridgman anvils); at a degree of deformation of 6.8 (5 revolutions of the anvils), the process is virtually completed. The crystallization of the amorphous alloy upon heating starts even at 200°C. However, upon heating up to 300°C (for 0.5-h holdings), the kinetics of crystallization is slow. After annealing at 350°C, the complete crystallization with the formation of a nanocrystalline structure with a grain size of 20-70 nm takes place

Influence of Aging and Strain on the Structure and Mechanical Properties of Chromium-Zirconium Bronze

The influence of aging and deformation by dynamic channel-angular pressing (DCAP) on the change of the structure and mechanical properties of Cu – 0.14 % Cr – 0.04 % Zr low-alloy chromium-zirconium bronze has been studied. It is shown that, under DCAP and subsequent aging, the studied bronze suffers the decomposition of the alpha-solid solution accompanied by the precipitation of nanosized particles of chromium and the copper-zirconium phase. This hardens the bronze and increases its thermal stability. A substantial increase in the mechanical properties of the bronze after DCAP and subsequent aging has been found. Thus, ultimate strength is increased 2.8 times and yield stress is increased 5.1 times as compared with the initial hardened condition, satisfactory plasticity being maintained.

Formation of bulk nanostructure metals under dynamic loading

Structural changes observed in samples of technical-purity titanium, copper, and aluminum alloy AMts (Al–Mn) after severe plastic deformation were studied and results of this investigation are presented. In experiments, materials were loaded with the help of a gun. Samples were accelerated up to the velocity of about 100–400 m/s and then directed into a special matrix consisting of two channels located at 90x to one another. These samples were deformed with the strain rate of y10 s; the stagnation pressure in the channel ranged from 2 to 5 GPa. Consideration is given to the relation between loading conditions and the specific nature of structure formation in materials. Under dynamic loading, the coarse-grained structure of the grain in the aluminum alloy becomes y400 nm, and the sub-grain structure with the size of 50–100 nm is formed in copper. Microhardness of materials increases 1.5–2 times.

Dynamic and Static Displacements of Atoms in B2-Phase of TiNi Alloy

We measured integrated intensities of 26 reflections of the B2-phase of titanium nickelide single crystal and determined structure factors for these reflections. Based on the structure factors, mean squares of displacements of Ni and Ti atoms with respect to the crystal-lattice sites have been determined. After that we determined the mean squares of atomic displacements Ni and Ti in temperature range of existence of the B2-pase, at temperatures Т1=328 K and T2=376 K. We separated the mean squares of atomic displacements Ni and Ti into static and dynamic ones. The mean squares of dynamic displacements of Ni and Ti atoms are identical, but the mean square of static displacements is greater by a factor of 4.7 for Ni atoms than for Ti atoms. The Debye temperature calculated from the mean squares of displacements of Ni atoms is 360 K; that calculated for Ti atoms in a similar way is 390 K. The large value of complete atomic displacements in TiNi is due to static rather than dynamic displacements of atoms, mainly due to static displacements of nickel atoms.

A study of transformations of β-solid solution in shape-memory alloys of the Cu-Zn-Al system

Conclusions1. The β → α transformation in high-temperature decomposition of alloys of the Cu - Zn - Al system has features of diffusion and martensitic transformations. The shapes of the crystals, their merging, and the change in the chemical composition characterize the β → α transformation as a diffusion one. The spatial distribution of rods of the α-phase within the original grain and the regular structure in particles of the α-phase indicate the shear nature of the β → α transformation.2. Plate bainite crystals that appear in the low-temperature transformation form groups of a “butterfly” type or a “cell” structure.3. The growing martensite crystals stop on particles of the α-phase and on plate bainite crystals in the “cells.” The “butterfly” groups of bainite crystals and individual bainite crystals do not hamper the growth of martensite crystals.