V. M. Gundyrev

High-strain-rate deformation of titanium using dynamic equal-channel angular pressing

Titanium samples were deformed using equal-channel angular pressing (ECAP). Structural changes upon the uniform and localized high-strain-rate deformation and specific features of the nucleation and propagation of cracks have been studied. A geometrical method of determining the amount of uniform shear strain upon equal-channel angular pressing has been suggested. The method is based on a metallographic examination of the spatial orientation of structural components. The localized deformation leads to the appearance of adiabatic-shear bands. Two band systems are formed: longitudinal and transverse, arranged at an angle to the longitudinal. The occurrence of recrystallization inside the bands indicates local heating of the material to 770–870 K. Specific features of the structure of the adiabatic-shear bands arising in this method of deformation is their large width (to 100 μ m) and a multilayer structure.

The ω-phase formation in titanium upon deformation under pressure

The ω-phase formation in titanium of the VT1-00 grade upon deformation under pressure has been investigated by X-ray diffraction analysis and diffraction electron microscopy. The deformation was effected by two methods: shear under a pressure of 6 GPa in Bridgman anvils and high-strain-rate equal-channel angular pressing at a pressure of about 2 GPa. Upon deformation under a pressure of 6 GPa, the ω phase is formed as grains that are isolated or clustered into groups. Upon deformation at a pressure of 2 GPa, this phase arises in the form of nanosized particles that are orientationally related to the α phase. After deformation by shear under pressure using one revolution of the anvils, new grains of the α phase up to 2–3 μm in size have been detected. The grains are nearly free of dislocations and have wavy boundaries. The origin of these grains is tracealle the reverse ω → α phase transformation that takes place upon pressure release and occurs via the “normal” rather than martensitic mechanism, at the expense of migration of the inter-phase boundaries. Upon heating, the reverse ω → α transformation at 100°C does not yet begin, whereas at 220°C the transformation proceeds almost completely. A temperature distribution in the titanium sample upon shear under pressure at a rate of 0.3 rpm has been calculated; according to this distribution, the maximum temperature rise is 12 K.

Crystallographic analysis of martensitic transformation in an iron-nickel alloy with twinned martensite

A variant of the crystallographic theory of martensitic transformations is proposed, based on a mechanism of lattice deformation in which the angle of rotation of a martensite plate is reduced to a minimum. In an iron-nickel alloy with twinned martensite, the least angle of rotation corresponds to the deformation of the austenite lattice by shear on the (111) plane in the

Structure of titanium subjected to dynamic channel-angular pressing

\left[ {11\bar 2} \right]

Crystallographic analysis of the FCC → BCC martensitic transformation in high-carbon steel

direction proposed by Kurdyumov and Sachs as the first shear in the two-shear theory of martensite formation in steel.

Effect of spherically converging stress waves on the phase composition, structure, and physicochemical transformations of the mixture of aluminum and quartz powders

A precision method for determining orientation relationships upon the B2 → B19′ transformation in titanium nickelide has been developed. The method is based on analyzing the martensite texture formed in the initial high-temperature B2 phase of a single crystal having a high degree of perfection. The orientation relationships between the B19′ lattice and the initial B2 lattice of the TiNi single crystal were established from the B19′ martensite texture formed in single crystals of titanium nickelide upon the B2 → B19′ transformation and from measurements of the lattice parameters. Crystal mechanism of B19′ martensite was proposed which included the shear in the (21-1) B2 plane in the direction [−11-1] B2 by 10°. Such a shear system is typical of the bcc crystals at deformation by twinning. Absolute shear values are in a ratio of 1:4 for B2 → B19′ transformation and for twinning, respectively. Martensite deformation at an invariant lattice is accompanied by small rotations of martensite crystals (±1.6°), that increases the quantity of martensite orientations from 12 to 24.

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

The microstructure of titanium after dynamic channel-angular pressing in two passes is studied by metallography and electron microscopy. This structure is compared to the structure of titanium after one-pass pressing. The high-rate deformation of titanium in this method consists of uniform deformation and localized deformation. Uniform deformation creates a submicrocrystalline structure. An increase in the number of passes from one to two leads to an increase in the grain-subgrain misorientation and the formation of a more homogeneous structure. Localized deformation causes the formation of adiabatic shear bands and cracks. An increase in the number of passes from one to two is accompanied by the accumulation of localized-deformation regions. The presence of regions with a martensitic structure in adiabatic shear bands in a sample deformed in two passes indicates heating of these regions above the α-β transition temperature. ω-phase particles are observed. The orientation relationships between the α and ω phases are such that the basal planes of their hexagonal crystal lattices are mutually perpendicular.

Crystallographic analysis of the B2 → B19′ martensite transformation in titanium nickelide

The fine structure of Ni–Mn–In alloys has been studied when manganese atoms are substituted for nickel atoms in an annealing state. The concentration dependence of the critical temperatures and the structures of the alloys have been discussed. It has been found that, as manganese atoms replace nickel atoms, the structure after annealing is changed from a two-phase (L21 + martensite) to single-phase L21 structure. The martensitic transformation in Ni47Mn42In11 alloy is accompanied by the formation of modulated 14M martensite.