Scanning and transmission electron microscopies are used to study the microstructure and phase composition of the surface layer of Zr–1

The intermetallic compound Al2Pt has potential of use in radiation sensing devices and selective solar absorbers, and is a promising protective coating of jet engine turbine blades. In our study, we demonstrate for the first time the possibility of forming nanocrystallites of the Al2Pt intermetallic compound in an Al-Pt disc produced by high pressure torsion (HPT) of elemental chips at cryogenic temperature. The composition of the Al + Pt mixture corresponds to the Al2Pt stoichiometry. Microhardness dependences against the distance from the disc center have been plotted and phase composition in the different points has been investigated. The formation of some high-strength phases was confirmed by a significant increase in microhardness near the edge of the cryodeformed Al-Pt disc. The Al2Pt intermetallic phase and amorphous phase were revealed both in XRD-scans and TEM-observations. The spread of Al2Pt crystallites sizes is wide and ranges from 10 to 200 nm. It was found that the amorphous phase had a composition of about 85Al-15Pt (at

The production of Al-based composites with high functional properties is an urgent scientific problem, the results of which may be of interest for practical application. That is why, there is an increasing interest in using the high pressure torsion (HPT) method to consolidate mixtures of aluminum with different metal powders and obtain new materials with promising properties. In the work, we obtained a novel metal-matrix composite, in which a soft Al-matrix is strengthened by hard and inert Pt-particles. The evolution of the phase composition and microhardness of the discs, which were produced by HPT of mixture Al+Pt chips, are investigated. Severe plastic deformation and large shear strain implemented under HPT lead to amorphization and solid solutions based on both Al and Pt. According to our estimation, near 5 at.% Al dissolved in Pt after the room-temperature HPT. Despite the fact that Pt is practically insoluble in Al, the XRD results of the Al-Pt disc suggest the formation of a non-equilibrium solid solution containing 2.1 at.% Pt in the Al matrix. The aluminum and platinum disks were also obtained and investigated. It was revealed, that the microhardness of the Al-Pt composite disc is between the microhardness values of Al- and Pt-discs.

Scanning and transmission electron microscopies are used to study the microstructure and phase composition of the surface layer of Zr-1% Nb alloy, which was subjected to treatment by nanosecond laser pulses. During laser treatment, a thin strengthened surface layer with the fine microstructure is found to form. The strengthening of the surface layer no less than 4 mu m thick is proved to be due to the formed twin micropackets consisting of martensite nanolamellas and nano-sized omega-Zr phase.

An innovative technology has been developed and implemented for the restoration and manufacturing of new mold copper plates for continuous casting machines (CCMs) using wear-resistant composite coatings. These copper plates significantly surpass the service life of imported copper plates featuring galvanic coatings, sometimes by up to 20 times. However, the pressing challenge of restoring the copper plates of molds once they have reached the minimum permissible thickness remains unresolved. This study aimed to explore the feasibility of restoring a plate composed of precipitation-hardening Cr–Zr bronze with the same material by employing friction stir lap welding (FSLW). The objectives were to examine the structure, quality, and hardness of the welded joint, alongside investigating the impact of heat treatment (quenching and aging). By utilizing multi-pass FSLW method with a rotating tool crafted from a heat-resistant alloy and overlapping (partially overlapping) successive passes, a welded joint with a thickness of ~5 mm was achieved, devoid of critical continuity flaws (cracks or voids). Within the bronze layer restored through FSW, a softening effect ranging from 85–105 HV1 was observed compared to the initial hardness of the bronze in its hardened and aged state while in service (116–126 HV1). This is attributed to recrystallization and overaging, specifically the coarsening of chromium particles within the Cr–Zr bronze due to the heating of the weld nugget (stir zone) to 600–700 °C. The observed softening effect during FSW can be effectively rectified through heat treatment involving dissolution of the hardening phases followed by aging, resulting in a hardness increase to approximately 120–150 HV1. The process of restoring copper plates to their original thickness via the progressive and environmentally friendly FSW method, followed be the subsequent application of wear-resistant composite coatings, presents the opportunity for an almost infinite operational cycle of molds. This advancement could potentially eradicate the necessity for Russia to rely on importing such molds copper plates.

We have studied the kinetics of the disorder → order (A1 → L10) transformation in Cu–56Au nonstoichiometric alloy at a temperature of 250°C. The disordered initial state of the alloy was produced by either quenching of samples from a high temperature or plastic deformation. The results demonstrate that the rate of atomic ordering in the quenched alloy is extremely low: the transformation needs approximately two months of annealing at a temperature of 250°C to reach completion. The rate of atomic ordering in predeformed samples is even lower. In both an as-quenched and an ordered state, the lattice parameters of the alloy under investigation slightly exceed those of the equiatomic alloy. Independent of the initial state of samples, their microhardness first rises in the course of atomic ordering and then falls off. The resistivity of Cu–56Au alloy in a well-ordered state has been shown for the first time to be ρ = 7.04 × 10–8 Ω m, which is far lower than was thought previously. The data we obtained have been used to assess the ratio of the phases present (order/disorder) in different stages of annealing.

— We have studied the kinetics of the disorder → order ( A 1 → L 1 0 ) transformation in Cu–56Au nonstoichiometric alloy at a temperature of 250°C. The disordered initial state of the alloy was produced by either quenching of samples from a high temperature or plastic deformation. The results demonstrate that the rate of atomic ordering in the quenched alloy is extremely low: the transformation needs approximately two months of annealing at a temperature of 250°C to reach completion. The rate of atomic ordering in predeformed samples is even lower. In both an as-quenched and an ordered state, the lattice parameters of the alloy under investigation slightly exceed those of the equiatomic alloy. Independent of the initial state of samples, their microhardness first rises in the course of atomic ordering and then falls off. The resistivity of Cu–56Au alloy in a well-ordered state has been shown for the first time to be ρ = 7.04 × 10 –8 Ω m, which is far lower than was thought previously. The data we obtained have been used to assess the ratio of the phases present (order/disorder) in different stages of annealing.

Проведено исследование кинетики фазового превращения беспорядок → порядок ( A 1 → L 1 0 ) в нестехиометрическом сплаве Cu–56 ат. % Au при температуре 250°C. Исходное разупорядоченное состояние формировали либо закалкой образцов от высокой температуры, либо сильной пластической деформацией. Установлено, что скорость атомного упорядочения закаленного сплава чрезвычайно мала и превращение заканчивается приблизительно через 2 мес. отжига при температуре 250°C. Скорость атомного упорядочения предварительно деформированных образцов еще ниже. Обнаружено, что как в закаленном, так и в упорядоченном состояниях кристаллическая решетка исследуемого сплава немного больше по сравнению с эквиатомным сплавом. Установлено, что вне зависимости от исходного состояния образцов их микротвердость в процессе атомного упорядочения сначала возрастает, а затем снижается. Впервые показано, что удельное электросопротивление сплава Cu–56Au в хорошо упорядоченном состоянии составляет ρ = 7.04 × 10 –8 Ом м, что намного ниже, чем считалось ранее. На основе полученных данных построена зависимость соотношения фаз (порядок/беспорядок) на различных этапах отжига.

40 mm thick coarse-grained (up to 10 - 20 mm) CuCrZr mold wall to 2 mm thick pure copper plate lap joint was performed using friction stir welding (FSW) operating a H13 die steel tool. The obtained defect-free joint indicates the potential of FSW to restore worn-out copper molds wall. FSW resulted in ultrafine microstructure (0.5 -1.0 mu m) of stir zone strengthened by chromium and Cu5Zr nanoparticles. Grain boundary and dispersion hardening increase the hardness of the stir zone up to 150 -190 HV1 compared to 110 -130 HV1 of the initial coarse-grained structure. Based on the results, friction stir welding and related friction stir processing technologies are proposed as a severe plastic deformation method to obtain an ultrafine-grained state of CuCrZr alloys.

Ni-Al alloys are considered the materials with high-temperature shape memory effect. However, being in coarse-crystalline state, Ni-Al alloys have low ductility. By performing grain refinement, it is possible to improve the alloys ductility. For example, it is possible to use the ultrarapid crystallization on revolving drum. The grain refinement will cause the structure dispersion. In this paper, the authors made an attempt to detect a 14M martensite in Ni-Al alloys - Ni 62,5 Al 37,5 , Ni­­ 64 Al 36 , Ni­­ 65 Al 35 and Ni 56 Al 34 Co 10 (at. %) - produced by melt spinning on the revolving steel drum. Tape samples having thickness of 30 µm and the grain-size of 0,5–4 µm were produced in the result of rapid crystallization. Using the resistometric measurement, the authors determined the temperatures of the direct and the reverse martensitic transformations in all alloys under examination. The authors could determine the martensitic transformation temperatures in Ni­­ 65 Al 35 and Ni 56 Al 34 Co 10 alloys only with the help of rapid heat at the rate of 75 ºС/min, as during the slow heat at the rate of 1–5 ºС/min the maraging with the А 5 В 3 (Ni 5 Al­ 3 ) type phase takes place, which causes the loss of martensitic transformation reversibility. The alloys’ structure is studied with the help of transmission electron microscopy. At room temperature, Ni­­ 62,5 Al 37,5 alloy stays in metastable austenitic condition with B2 lattice and Ni­­ 64 Al 36 , Ni 65 Al 35 and Ni 56 Al 34 Co 10 alloys go through martensitic transformation. The structure in Ni 65 Al 35 and Ni 56 Al 34 Co 10 alloys consists of plate martensite depleted of inner fine-scale twinning, whilst the Ni­­ 64 Al 36 alloy structure consists of thin-plate martensite and retained austenite. According to the microdiffraction data, martensite in three alloys is recognized as martensite with L1 0 lattice. Using the radiographic analysis, the authors determined in Ni­­ 64 Al 36 and Ni­­ 65 Al 35 alloys a small amount of 14M martensite as well as the major martensitic L1 0 phase and the retained austenite.

The metastable austenitic iron alloy with 31.3 wt % Ni (N31) has been used to show the possibility of the formation of a nickel-concentration inhomogeneity in a fine-grained austenite due to an α → γ trans-formation under the condition of a preliminary formation of a nickel-enriched intermediate nanocrystalline γ phase. The thermal expansion coefficients (TECs) in the range of −100 to +300°C have been estimated in concentrationally inhomogeneous steel N31 after various heat treatments. The conditions necessary to ensure the possibility of controlling the TEC in wide limits have been found.

Fe-32% Ni alloy subjected to slow heating to a temperature below A s at a rate of 0.01 K/min demonstrates the untwinning and appearance of an intermediate ɛ phase with an hcp lattice and lattice parameters a = 2.535, c = 4.132 Å, and c/a = 1.63. Slow heating to 430–490°C leads to the formation of nanocrystalline austenite enriched in nickel, which substantially increases the hardness of martensite. The formation of austenite in the Fe-32% Ni alloy, which is a mixture of martensite with 20–30% nanocrystalline austenite, during its rapid heating to 600°C occurs via the bulk mechanism with short-range atomic diffusion. In this case, the diffusion does not eliminate the concentration micro-inhomogeneity of the alloy in nickel but leads to the reorientation of γ-phase nanocrystals, almost eliminates the dislocation structure, and removes the strengthening by phase hardening.

Melt-quenched Ni 65 Al 35 and Ni 56 Co 10 Al 34 (at %) alloys are studied by electrical resistance measurement and electron microscopy. The effects of the isothermal holding time in the supersaturated β solid solution field and the heating rate during thermal cycling on the restoration of the reversibility of the martensitic transformation are investigated. After short-term aging in the B 2 austenite field followed by long-term aging in the L 1 0 martensite field, the melt-quenched Ni 65 Al 35 and Ni 56 Co 10 Al 34 alloys retain their high thermal stability of the reversibility of the martensitic transformation.

Resistometry and electron microscopy were used to study Ni65Al35 and Ni56Al34Co10 (at.%) alloys prepared by the method of accelerated melt spinning. Ribbon samples were studied during and after different heating–cooling cycles or different isothermal holding conditions at temperatures of up to 780°C. A method was proposed for improvement of the heat resistance of the supersaturated β solid solution and stabilization of the reversibility of the high-temperature martensitic transformation in alloys of the Ni–Al system. This method consists in a partial replacement of nickel by cobalt, accelerated melt spinning, and short-time stabilization annealing in the low-temperature range of the B2 austenite.

Six microcrystalline alloys rapidly quenched from the melt (Ni 64 Al 36 , Ni 65 Al 35 , Ni 66 Al 34 , Ni 56 Al 34 Co 10 , Ni 64 Al 32 Si 2 , and Ni 64 Al 32 Cr 4 , at %) have been investigated using polythermal and isothermal resistometry with a subsequent microstructural analysis. The absence of reversibility of the thermoelastic martensitic transformation for all these alloys (except for Ni 64 Al 36 and partly Ni 56 Al 34 Co 10 ), the reason for which is a strong tendency to a diffusive decomposition of the “fresh” (as-quenched) martensite of these alloys has been revealed. New regimes of stabilizing annealing that enable application of high-nickel alloys based on nickel-aluminum martensite as functional materials with a high-temperature shape-memory effect have been suggested.

Rapidly crystallized NiAl-based β-alloys − Ni64Al36, Ni65Al35, and Ni56Al34Co10 (at.%) – were studied by methods of resistometry and electron microscopy. The decomposition of the L10-martensite, which was accompanied by formation of Ni5Al3 particles, was observed in alloys whose reverse martensite start temperature was over 250°C. Formation of nanoparticles with the A5B3(Ni5Al3) superstructure in the martensite stabilized it against the reverse shear transformation up to a complete suppression of the thermoelastic β(B2)↔L10 transformation. The replacement of nickel by 10at.% cobalt in the Ni66Al34 alloy decreased the tendency to the formation of Ni5Al3 and Ni2Al particles.

Diagrams of the onset of decomposition of two functional microcrystalline alloys (Ni65Al35 and Ni56Al34Co10) with a thermoelastic reversible martensitic transformation prepared by ultrarapid quenching from the melt have been constructed based on the results of isothermal measurements of electrical resistance during various annealings. A multi-stage nature of the diffusive decomposition of a β solid solution supersaturated with Ni has been revealed, and the temperature range of its maximum thermal stability has been found. The retardation effect of cobalt on the decomposition of high-nickel martensitic Ni-Al alloys has been determined.

Alloys of the 37–39at.% Co–32–34at.% Ni–28–30at.% Al system, which were prepared by quick spinning-melt quenching and had a microcrystalline structure, were studied using electron microscopy, resistometry and magnetometry. It was shown that the temperature interval of the β(B2)→L10 martensitic transformation depended on the composition and the structural size of the alloys. When 1at.% Co and 1at.% Al were replaced by Ni, the temperature interval of the B2↔L10 martensitic transformation increased by 30–60 and 100–110K, respectively. The martensitic transformation hysteresis width was about 100K.