Submicrocrystalline Structure Research Articles

Influence of Copper Doping by Aluminum on the Parameters of the Submicrocrystalline Structure Formed During ABC Pressing

Influence of Copper Doping by Aluminum on the Parameters of the Submicrocrystalline Structure Formed During ABC Pressing

Formation of a submicrocrystalline structure in metastable austenitic steels during severe plastic deformation and subsequent heating

The structure and the mechanical properties of metastable austenitic steels after severe plastic deformation by four or six passes of equal-channel angular pressing (ECAP) at a temperature of 400°C are studied. It is shown that ECAP results in strain hardening mainly due to the formation of a submicrocrystalline structure, which is retained after subsequent heating to 500°C.

Structure and Properties of a Titanium Film – Aluminum Substrate System Alloyed by an Intense Pulsed Electron Beam

The structure and properties of a Ti film – Al substrate system alloyed by an intense pulsed electron beam are studied. It is shown that electron beam melting of this system provides the formation of a multiphase submicrocrystalline structure with high strength and tribological properties in the surface layer. Irradiation modes, which allow an increase in the microhardness of the material and a decrease in its wear rate, are defined. Physical substantiation of this phenomenon is given.

The Structure and Properties of Yttrium-Stabilized Zirconium Dioxide Ceramics Treated by Electron Beam

The high-intensity electron-beam treatment of the submillisecond duration is used to treat the surface layer of sintered zirconium dioxide ceramics partially stabilized by yttrium. The electron beam irradiation parameters are obtained allowing the structural modification under a rapid solidification. It is shown that the structural modification of ceramics under melting conditions with the subsequent rapid solidification is accompanied by the formation of a sub-microcrystalline structure that fosters a multiple magnification (≈ 2 times) of the modified layer hardness.

Investigation of structure, phase composition, and mechanical properties of Zr-2.5% Nb alloy after ECAP

The analysis of the structure, phase composition, and mechanical properties of the industrial Zr-2.5% Nb alloy after severe plastic deformation by ECAP method were investigated. ECAP of the alloy leads to the formation of a grain-subgrain submicrocrystalline structure. The average size of the structural elements was 190 and 250nm for the final temperature of ECAP of 350°C, and 400°C, respectively. ECA-pressing leads to a significant increase in the strength of the alloy while maintaining a sufficient reserve of plasticity and fully ductile dimple fracture. After ECAP, the alloy becomes single-phase (α-Zr). At temperatures above 570°C, the precipitation of the particles of the second phase (β-Nb) was observed.

Submicrocrystalline Austenitic Stainless Steel Processed by Cold or Warm High Pressure Torsion

The formation of submicrocrystalline structure during severe plastic deformation and its effect on mechanical properties of an S304H austenitic stainless steel with chemical composition of Fe – 0.1C – 0.12N – 0.1Si – 0.95Mn – 18.4Cr – 7.85Ni – 3.2Cu – 0.5Nb – 0.01P – 0.006S (all in mass%) were studied. The severe plastic deformation was carried out by high pressure torsion (HPT) at two different temperatures, i.e., room temperature or 400°C. HPT at room temperature or 400°C led to the formation of a fully austenitic submicrocrystalline structure. The grain size and strength of the steels with ultrafine-grained structures produced by cold or warm HPT were almost the same. The ultimate tensile strengths were 1950 MPa and 1828 MPa after HPT at room temperature and 400°C, respectively.

НАНОСТРУКТУРИРУЮЩИЕ КОМБИНИРОВАННЫЕ ФРИКЦИОННО-ТЕРМИЧЕСКИЕ ОБРАБОТКИ АУСТЕНИТНОЙ СТАЛИ 12Х18Н10Т

Corrosion-resistant austenitic chromium-nickel steels have low strength properties that cannot be improved using thermal treatment. The application of frictional treatment as the finishing operation allows providing the increased wear resistance, effective strain hardening and high quality of work surface of 2Kh18N10T steel. During operation and processing, the austenic steel parts could be subjected to heating. In this paper, the authors used the methods of transmission electronic microscopy, X-ray diffraction analysis, and microhardness testing to study the influence of heating in the temperature range of 100–750 °С on the structural-phase state and microhardness of 2Kh18N10T steel subjected to frictional treatment and to consider the possibilities of hardening of metastable austenic steel using combined frictional thermal treatment. It is determined, that during frictional treatment, 65 vol. % of strain-induced α'-martensite appears in the steel surface layer and the microhardness increases up to HV 0,025=690. Two-hour annealing at 450 °С ensures the retention of 65 vol. % of α'-phase in the structure and the additional increase of surface hardness up to HV 0,025=900 due to nanoscale Cr 23 C 6 carbides precipitation, and their application for hardening of nano- and sub-microcrystalline martensite-austenic structures formed in surface layer after the frictional treatment. In the result of heating up to 650 °С, the austenic submicro- and nanocrystalline structure with HV 0,025=630 hardness exceeding the initial hardness of austenic steel in hardened condition by about three times appears on the steel surface. Based on the results obtained, the authors proposed two regimes of nanostructuring combined strain-heat treatment, which involve frictional treatment and further annealings at the temperatures of 450 and 650 °С.

Деформация сдвигом методом кручения, осадки и прессования

Integrated process of metal deformation by Torsion, Upsetting and Press Forming serves to produce submicrocrystalline structure of large weight metal stocks. The performed work demonstrated efficiency of shear deformation with twist torsion. The most efficient is the use of indirect twist torsion allowing preparation of the stock metal structure for subsequent conventional conversion with the minimum time and economic costs. As compared to the known methods of nonmonotonic deformation, such as high pressure torsion, equal channel angular extrusion and twist extrusion, twist torsion allows solid stock processing. The new trend in the deformation domain will be particularly vital for extra strong metal production for aircraft engineering, space technologies, automotive industry, shipbuilding, bridge engineering and other industries. The developed process allowed comparing of the conventional upsetting and extrusion with shear deformation and determining its efficiency.

Dimensional stability of coarse-grained and submicrocrystalline TiNi shape memory alloy for medical use under quasistatic and cyclic bending

The paper reports on a comparative study of inelastic strain accumulation in coarse-grained and submicrocrystalline titanium nickelide (TiNi) under quasistatic and cyclic loads. It is shown that the formation of submicrocrystalline structure in TiNi by equal channel angular pressing provides a steep increase in its strain resistance under quasistatic and cyclic loads. The contribution of dislocation and martensitic mechanisms to residual strain accumulation under different loading conditions is analyzed.

On Regularities of Grain Refinement through Large Strain Deformation

The recent studies on grain refinement in austenitic stainless steels during large strain deformations are critically reviewed. The paper is focused on the mechanism of structural changes that is responsible for the development of submicrocrystalline structures that can be interpreted as continuous dynamic recrystallization developing under conditions of warm working. The final grain size that is attainable by large strain warm working can be expressed by a power law function of temperature compensated strain rate with an exponent of about -0.15. The development of submicrocrystalline structures is assisted by the deformation microbanding and dynamic recovery, which are characterized by opposite temperature dependencies. The grain refinement kinetics, therefore, are characterized by a weak temperature dependence for a wide range of warm working conditions.

Effects of Initial Microstructure and Deformation Method on Grain Refinement in a Cu-Cr-Zr Alloy

The development of submicrocrystalline structure in a Cu-0.3wt.%Cr-0.5wt.%Zr during multidirectional forging (MDF) and equal channel angular pressing (ECAP) was investigated in comparison. A large number of strain-induced subboundaries with low-angle misorientations appeared at early deformation. The subsequent straining led to an increase in the misorientations of these subboundaries, resulting in the formation of submicrocrystalline structure at sufficiently large strains. The process of microstructural evolution can be considered as continuous dynamic recrystallization. MDF provided faster kinetics of new ultrafine grain formation as compared to ECAP. The fraction of ultrafine grains with a size below 2 μm comprised 0.59 or 0.23 after MDF or ECAP to a total strain of 4, respectively. The grain refinement kinetics could be accelerated by the presence of second phase precipitates. The fraction of ultrafine grains after MDF to a strain of 4 achieved 0.36 or 0.59 in the solution treated or aged samples, respectively.

Formation of fully austenitic ultrafine-grained high strength state in metastable Cr–Ni–Ti stainless steel by severe plastic deformation

The present research establishes a possibility of producing nano- and submicrocrystalline structure in fully austenitic state of the metastable Cr–Ni–Ti steel after high pressure torsion (HPT) by raising the temperature of severe plastic deformation above the treshold value for strain-induced martensite transformation, and at room temperature by reducing the temperature of strain-induced martensite transformation with the grain size decreases during step-by-step decreasing HPT temperature.

Tribological and corrosion behaviors of warm-and hot-rolled Ti-13Nb-13Zr alloys in simulated body fluid conditions.

Development of submicrocrystalline structure in biomedical alloy such as Ti-13Nb-13Zr (in wt%) through warm-rolling process has been found to enhance mechanical properties compared to conventional thermomechanical processing routes including hot-rolling process. The present study investigated the tribological and corrosion behaviors of warm-rolled (WR) and hot-rolled Ti-13Nb-13Zr alloys which have not been studied to date. Both tribological and corrosion experiments were carried out in simulated body fluid conditions (Hank’s solution at 37°C) based on the fact that the investigated alloys would be used in a human body as orthopedic implants. The WR Ti-13Nb-13Zr demonstrated a submicrocrystalline structure that provided a significant enhancement in hardness, strength, and corrosion resistance. Meanwhile, there was no notable difference in wear resistance between the WR and hot-rolled samples despite the different microstructure and hardness. The present study confirmed the enormous potential of WR Ti-13Nb-13Zr with not only great mechanical properties but also high corrosion resistance in the simulated body fluid.

Optimization of strength, ductility and electrical conductivity of Cu–Cr–Zr alloy by combining multi-route ECAP and aging

Properties of Cu–Cr–Zr alloy with ultrafine-grained (UFG) structure produced by equal-channel angular pressing (ECAP) via different routes have been investigated. Special attention was paid to the optimization of multi-functional structural, thermal, electrical and mechanical properties of the alloy by aging of UFG one. Multi-pass ECAP via different routes gives rise to the formation of a deformation-induced submicrocrystalline structure with the grain (subgrain) sizes in the range of 200–300nm depending on applied routes which leads to high hardness and strength in the Cu–Cr–Zr alloy with reduced ductility. Amongst the applied routes, route-Bc was found to be the best processing path for achieving the lowest grain size, the highest hardness and strength. Aging of 8Bc-processed UFG samples increases the hardness and strength of Cu–Cr–Zr alloy while retaining an electrical conductivity comparable to that of aged coarse-grained (CG) one. A satisfactory electrical conductivity of 71%IACS without considerable loss of peak hardness was achieved after aging of 8Bc-processed UFG alloy at 425°C for 240min. The precipitation strengthened UFG alloy remains its stable behavior at elevated temperatures up to 450°C.

Structure of electroexplosive TiB2–Ni composite coatings after electron beam processing

High-intensity electron beam modification of electroexplosive TiB2–Ni composite coatings is conducted for the first time. The phase and elemental composition of the surface layer of steel Hardox 450 subjected to electroexplosive spraying (EES) of the TiB2–Ni composite coating and subsequent irradiation with a submillisecond high-intensity pulsed electron beam are studied. Electron beam processing (EBP) modes that provide the formation of dense glossy surface layers based on titanium diboride and nickel with a submicrocrystalline structure are revealed. It is shown that EBP of a layer subjected to EES conducted in a melting mode leads to the formation of a surface layer with homogeneous structure and concentration.

Influence of deformation during warm rolling on martensitic transformation temperatures and the value of superelasticity and shape memory effects in Ti49.2Ni50.8 (at %) alloy

The influence of the warm isothermal (723 K) rolling in grooved rolls on the grain structure, martensitic transformation temperatures, and inelastic properties of Ti49.2Ni50.8 (at %) alloy is investigated. It is shown that transition from initial coarse-grained structure to microand submicrocrystalline structures of samples occurs as a result of rolling with the intense deformation to 1.8. The inelastic properties (superelasticity and shape memory effects) are studied under torsion deformation. The value of the superelasticity effect (including the elastic deformation) was determined in isothermal (295 K) “loading–unloading” cycles. The value of the shape memory effect is equal to the recovery of inelastic deformation under heating of unloaded samples. The accumulated plastic deformation corresponds to the residual deformation after the completion of shape recovery under heating. The total inelastic deformation under torsions of rolled sample reaches 8.5–9.5% (99% of the degree of shape recovery), the shape memory effect is 5–6%, and the superelasticity effect is 3–4%.

Ultrasonic plastic deformation of steels

In the work we demonstrate the possibility of forming thin surface and near-surface layers with submicrocrystalline structure under ultrasonic plastic deformation of machined steels. Formation of fine gradient textures up to nanocrystalline allows significant changing physical and mechanical properties of machined steels. Ensures improvement of microstructure, produces internal compressive strains which improves the cyclic strength of machine parts.

The Influence of Pulsed Heat and Power Supply on the Structure and Properties of Welded Joint Metals and Surfaced Coatings

We have investigated the influence of the modes of adaptive pulse-arc welding and surfacing on the structure and physical-mechanical properties of welded joints of steel 09Mn2Si and the surfaced composition of this steel coated with a modified powder material of chromium carbide with the submicrocrystalline structure. It is shown that the pulsed mode of welding and surfacing can improve the homogeneity of the structure of the welded joint of steel and a surfaced coating and reduce the grain size of metals in both of them. Structural changes lead to an increase in ductility and toughness of the weld metal.

Effect of Heat Input Pulse on the Structure and Properties of Welded Joints of Steels Ferritic-Pearlitic Class, Operating Under Low-Frequency Temperature-Force Loading

We have investigated the influence of the modes of adaptive pulse-arc welding and surfacing on the structure and physical-mechanical properties of welded joints of steel 09Mn2Si and the surfaced composition of this steel coated with modified powder material of chromium carbide with the submicrocrystalline structure. It is shown that the pulsed mode of welding and surfacing can improve the homogeneity of the structure of the welded joint of steel and surfaced coating and reduce the grain size of metals in both of them. Structural changes lead to the increase in ductility and toughness of the weld metal.

Microstructure and anisotropy of the mechanical properties in commercially pure titanium after equal channel angular pressing with back pressure at room temperature

In this work, we report on the anisotropy of the mechanical properties and the results of in-depth microstructural analysis of commercially pure (CP) grade 2 titanium after severe plastic deformation. CP-Ti was successfully processed at room temperature via four consecutive passes of equal channel angular pressing (ECAP) with very high back pressure (BP). An ECAP-BP die with circular channel cross-section, channel angle φ=90° and arc curvature angle ψ=0° was used. A sub-microcrystalline structure with a grain size of ~150nm exhibits promising mechanical properties, as determined by hardness measurements and tensile and compression tests in different directions. We observed a significant mechanical anisotropy related to the strong texture. Considering the ID, ED and TD to be the insert, extrusion and transverse directions of the ECAP die, respectively, the highest compression strength was attained for samples with the major axis in the ID and in a direction inclined 22.5° from the ID toward the TD (σmax~1150MPa). In contrast, the lowest strength was observed in the ED and at 45° from the ID toward the ED (σmax~940MPa). Although a fracture occurred during compression of the samples tested along the ID, compression along the ED exhibited perfect plasticity with balanced hardening and softening mechanisms. Transmission electron microscopy (TEM) examination after ECAP-BP revealed a small amount of high-pressure hexagonal ω-phase. The occurrence of this phase was induced by a combination of severe plastic deformation and high pressure.