Phase Naklep Research Articles

Hydrogen-phase naklep as a result of single isothermal hydride transformations

Hydrogen treatment of metallic materials is a promising area of controlled hydrogen action on metals and alloys in order to impart special properties to them. In this work, the changes in the mechanical properties of palladium during single hydride transformations, which are initiated in the initially non-nakleped palladium hydride, have been experimentally studied. Were investigated wire palladium samples with a purity of 99.98 %, a diameter of 0.5 mm and a length of 165 mm. Samples for research were preliminarily subjected to hydrogen treatment, and then mechanical tests were carried out. The mechanical properties of non-nakleped palladium hydride are presented. Hydrogen-phase naklep of palladium during hydrogen treatment has been studied. It is shown that palladium hydride is a plastic material with low strength characteristics. During the reverse hydride transformation, the hydrogen phase naklep of palladium develops. Experimental facts of the appearance of hydrogen-phase naklep during the interaction of hydrogen with other metals and alloys are discussed.

Effect of the Temperature of Shock-Wave Loading on Structure and Phase Transformations in Nitrogen-Containing Austenitic Cr–Mn–Ni Steel

This work has determined the peculiarities of structure and phase transformations at various initial temperatures (–129…548°С) and high deformation rates (448–530 m/s) of shock-wave loading in the austenitic nitrogen-containing steel KH20N6G11M2AFB (0.4N–20Сr–6Ni–11Mn–2Mo–V–Nb). The cyclic γ → e → γ transformation is observed in the course of shock-wave loading at 20–203°С, which causes the phase naklep of austenite and the possible occurrence of the shape memory effect in the regions of deformation localization.

Structural heredity in the U-6Nb alloy and conditions for its elimination

The conditions have been determined for the manifestation of structural heredity in the U-6 wt % Nb alloy with the restoration of the size and shape of grains of the initial high-temperature γ phase in the course of the forward γ → α″ martensitic transformation upon cooling and the reverse α″ → γ transformation upon heating. Contrary to iron-based alloys, the restored γ phase does not undergo recrystallization due to phase-transformation-induced deformation (phase naklep) upon subsequent high-temperature heating. The elimination of structural heredity with a noticeable grain refinement (by almost an order of magnitude, down to 10–20 μm) in the high-temperature γ phase occurs in the process of the repeated quenching from 700°C after the use of one of the preliminary heat treatments (cold deformation of the α″ martensite, the recrystallization of the deformed α″ phase, the high-temperature aging of the initial α″ martensite, and eutectoid decomposition).

Damage of the unalloyed-plutonium structure as a result of phase naklep and self-irradiation: An electrical-resistance study

Damage of the structure of the α phase of plutonium as a result of repeated α ↔ β phase recrystallization and prolonged self-irradiation was estimated based on the changes in the electrical resistance measured at room temperature before and after phase recrystallization. Samples with different time of storage were used. An analysis of the results showed that the electrical resistance of samples grows linearly depending on the number of cycles of phase recrystallization. It has been established that the slope of the dependences obtained is determined by the maximum temperature of the sample in the cycle. At a maximum temperature in the cycle equal to 170°C, an increase in the relative electrical resistance of the samples was ∼2.5%/cycle; when heating to 125°C, ∼0.3%/cycle. The variation of the electrical resistance of the samples stored for ∼20 years depending on the number of cycles of phase recrystallization exhibited a single feature, namely, a decrease in resistance in the first cycle of heating to 170°C rather than an increase observed in the experiments with the samples stored for ∼2.5 year. This decrease is connected with the influence of the possible beginning of migration of radiogenic helium. In the subsequent cycles, the change in the electrical resistance of samples upon prolonged storage was analogous to that of the samples with a short time of storage.

Effect of the austenite stability on the fracture mode and mechanical properties of aging nonmagnetic alloys after different strengthening treatments

Aging austenitic alloys with a stable (N26Kh5T3; Ms < −196°C) and metastable (N25Kh2T3; Ms = −130°C) austenite have been investigated after employing different methods of heat and thermomechanical treatments, namely, (1) aging at a temperature Ta = 600°C (A); (2) strengthening using phase-transformation-induced hardening (“phase naklep” (PN)) and subsequent aging at Ta = 600°C (PN + A); (3) deformation to 30% (D) at Td = 600°C after preliminary aging at the same temperature (A + D); and (4) PN + A + D. In this case, the alloy with stable austenite has not been strengthened by phase naklep. Structure, fracture mode, ultimate strength, yield strength, relative reduction of area, and relative elongation have been studied depending on the duration of aging τa upon these strengthening treatments. It has been established that the physicomechanical properties of the alloys depend not only on τa, but also on the testing temperature. It is shown that all above physicomechanical characteristics of the alloys under consideration are affected substantially by the austenite stability.

Effect of the structure of aging invars with a metastable austenite on the frequency dependence of their magnetic permeability

The effect of the generator current frequency f on the magnetic permeability μ of the N30K10T3 invar is studied for its various structural states formed upon the following treatments: phase naklep (i.e., the phase-transformation-induced hardening of austenite), cold plastic deformation, and cooling in liquid nitrogen. The ferromagnetic austenite of the alloy is metastable with respect to the γ → α martensite transformation upon cooling to temperatures below the temperature of the onset of the martensite transformation (Ms ≈ −80°C) and represents a supersaturated solid solution ageable during heating. The types of treatment are shown not to change the linear character of the μ(f) dependence in the frequency range under study (15–50 kHz) and to decrease μ to a certain extent.

10.1007/s11508-008-3008-y

Analysis is given of phase and structural transformations occurring upon ultrarapid laser heating in steels with different initial structures, namely, after annealing, after preliminary quenching, quenching and tempering, and after quenching with subsequent deformation and tempering. It is shown that a significant suppression of diffusion processes occurs during laser heating; this circumstance substantially affects the nature of the phase and structural transformations proceeding during laser processing. Special attention is given to studying the process of recrystallization and to the phenomenon of structural heredity during laser heating. The process of recrystallization during laser heating is considered as consisting of two stages, namely, an ordered lattice rearrangement (α-γ transformation) and the recrystallization of austenite that suffered phase-transformation-induced hardening (“phase naklep”). The effect of tempering and plastic deformation on the recrystallization of a preliminarily quenched steel consists in the intensification of the second stage, i.e., of the recrystallization of the transformation-hardened austenite. It is shown that the α-γ transformation during the laser heating of steels with the initial structure of lath martensite occurs by the “mechanism of recovery,” i.e., via the formation and growth of austenite nuclei. In steels with the initial structure of pearlite, the nucleation of austenite during laser heating can occur by a shear martensite-like diffusionless mechanism with the observance of characteristic orientation relationships between the initial ferrite and the newly formed austenite.

Changes in the grain and fine structures of palladium as a result of hydrogen phase naklep

Changes in the grain and fine structures of palladium that occur after the occurrence of reverse β → α hydride phase transformation in the metal are studied. It is shown that hydrogen treatment does not change the microstructure of palladium but strongly affects its fine structure.

Mechanical properties and fine structure of annealed and HPN-treated palladium

Strengthening of palladium using hydrogen-induced transformation hardening (“hydrogen phase naklep” (HPN)) in the course of the reverse β → α hydride phase transformation in palladium-hydrogen alloys has been studied. It has been shown that the degree of HPN is mainly determined by the difference of the specific volumes of the transforming phases. As the transformation temperature decreases and the difference of the specific volumes of the transforming phases increases, the degree of strengthening of palladium during HPN systematically increases and its plasticity decreases, which is accompanied by an increase in the dislocation density and magnitude of microdistortions and by a decrease in the dimensions of the mosaic blocks.

Hydrogen phase naklep influence on palladium grain and fine structures

The hydrogen phase naklep (cold work) of palladium in the result of hydride β → α phase transformations is described. It is shown that the palladium microstructure does not change, but its fine structure changes greatly as a result of the hydrogen treatment.

Hydrogen phase “naklep” and hydrogen treatment of niobium

The main idea of this investigation is to confirm the possibility of using hydrogen treatment based on hydrogen phase naklep (HPN) phenomenon for improving the structure and properties of niobium which is a nonpolymorphic metal sensitive to hydrogen embrittlement. Data are given for different schemes of hydrogen treatment of NbH x alloys. All these kinds of treatment result in controllable strengthening and changing of other physical properties. The possibility of getting a great variety of structures of treated alloys after HPN is shown. Finally, the influence of vacuum annealing on the recovery of mechanical and some physical properties of the HPN-treated NbH 0.03 alloy is studied. It was shown that HPN leads to formation of metastable hydrides in this alloy contributing both to strengthening and ductility by the hydride TRIP-effect mechanism. Two stages of structure and properties recovery have been determined.

Hydrogen treatment of niobium: Strengthening and structural changes

A review on the phenomenon of controllable hydrogen phase naklep and the prospects of its use in metal science and engineering was published in this journal in 1981. In the review we covered both the scientific and practical aspects of the new experimentally discovered phenomenon of the controllable transition of metals and alloys into a high strength state with special physical properties by charging them with hydrogen and causing α solid solution ⇌ hydride β phase transformations. We called this phenomenon “controllable hydrogen phase naklep” (HPN). The HPN phenomenon has been demonstrated in a limited number of metals and alloys under a variety of conditions. Palladium is the classic material for studying this phenomenon. We assume that HPN is a general phenomenon which may be exploited for many alloy systems. The main idea of this work is to confirm the HPN phenomenon in a specific material, i.e. niobium, which is very sensitive to embrittlement and is not a polymorphic material. This is why there are few possibilities to treat niobium, to change its structure and to improve its properties. First we consider the main features of the HPN phenomenon and the reasons why it is not correct to use the terms “cold work”, “strain hardening”, “cold hardening” and others for this new general phenomenon. Data are given for the special vacuum-hydrogen installation and the experimental technique of hydrogen treatment which causes controllable phase naklep of niobium with its plasticity preserved. This is followed by a review of hydrogen treatment results. The possibilities to have a great variety of structures and mechanical properties of niobium and niobium-hydrogen alloys after hydrogen treatment causing HPN are obvious. Finally, new ideas about the phenomenology and mechanism of the phenomenon are discussed.

The phenomenon of controllable hydrogen phase naklep and the prospects for its use in metal science and engineering

In this review we cover both the scientific and the practical aspects of the experimentally discovered phenomenon of the controllable transition of metals and alloys into a high strength state with special physical properties either during charging with hydrogen or after introduction of reversible phase transformations between α solid solutions and β hydrides (we call this phenomenon “controllable hydrogen phase naklep” (HPN)). We first consider the role of the polymorphism of metals as one of the foundations of physical metallurgy and the difficulty of treating metals which do not exhibit polymorphism. This is followed by hypothesis and experimental confirmation of the HPN phenomenon, which is proposed as a basis for new kinds of strengthening treatments for metals and alloys without polymorphism. Data are given on the technique of HPN treatment (palladium is the classic material for studying the HPN phenomenon), the hardening of metals by HPN treatment, hydride high plasticity of properly hardened palladium and the recrystallization of HPN-treated metal. This is followed by a review of the phenomenology and mechanism of the phenomenon and its use in engineering. Here the composition and properties of new HPN-hardening alloys for diffusion filters for production of high purity hydrogen are observed. Finally, new ideas are discussed. An attempt is made to formulate a new paradigm of strengthening based on the HPN. The possibilities of the wide use of hydrogen as an alloying element and external agent for the treatment of metals are associated with the development of nuclear hydrogen energy and technology.