High-pressure Torsion Research Articles

Long term hydrogen storage properties of ZK60 Mg-alloy as processed by different methods of SPD

Hydrogen storage characteristics is studied in the Mg-alloy ZK60 after processing by different SPD (Severe Plastic Deformation) methods such as High Pressure Torsion (HPT) and Friction Stir Processing (FSP), applying various deformation extents and rates. The capacity and kinetics of hydrogen storage was investigated and analysed, up to 100 storage cycles. While the degree of SPD deformation is less important for the storage capacity, the SPD processing method itself matters, yielding about ~ 30% more capacity in FSP than in HPT. As shown by DSC and XRD analyses, it is the density of SPD-induced vacancy agglomerates which is significantly higher in FSP than in HPT (~ 10–3 instead of ~ 10–4) because of the enhanced dislocation slip activity. Thanks to their stabilization through Mg(Zn,Zr) precipitates, the vacancy agglomerates survive numerous cycles of hydrogen storage in spite of the high storage temperature of 350 °C, and can act as thermally stable heterogeneous nuclei for the hydrogenation. This latter mechanism was found in all SPD methods applied irrespective of the deformation extent, on the basis of Johnson–Mehl–Avrami-Kolmogorov analysis providing the Avrami exponent n = 1, already from the second up to the highest hydrogen storage cycles.

Possible Behavior of Shear Deformation under High-Pressure Torsion

Possible Behavior of Shear Deformation under High-Pressure Torsion

Refractory High‐Entropy Alloys Produced from Elemental Powders by Severe Plastic Deformation

A comparative investigation of two fundamentally different approaches for the synthesis, microstructure evolution, and mechanical properties of the refractory high‐entropy alloys (RHEA) HfNbTaTiZr and HfNbTiZr is performed. The two methods comprises conventional arc (button) melting and a powder route based on mechanical alloying and consolidation via severe plastic deformation. In particular, blended elemental powder is pre‐compacted and subjected to one or four passes of equal channel angular pressing (ECAP) at 500 °C and then 10 revolutions of high pressure torsion (HPT) at room temperature to an effective strain between 4 and 40. Some samples are then annealed at 500 °C for 1 h to investigate the thermal stability of the phases. The four ECAP passes at 500 °C do not result in the formation of the body‐centered cubic (BCC) phase typical for the program RHEAs despite the presence of interfacial zones between particles and defect‐driven diffusion. Nevertheless, a single ECAP pass is sufficient to create a solid bulk sample for subsequent HPT. After 10 HPT revolutions, in contrast to melting route resulting in a single BCC phase alloy, both alloys form new phases comprising a Nb‐rich BCC phase and a ZrHf‐rich HCP phase in both alloys.

Исследование усталостных свойств и трибологические испытания стали AISI 316 после кручения под высоким давлением

The effect of high-pressure torsion process in a new die on the fatigue properties of corrosion-resistant steel AISI 316 has been studied. The deformation was carried out at cryogenic and room temperatures. The number of deformation cycles was 8. The initial blank had a ring shape with a diameter of 76 mm, a width of 3.5 mm and a thickness of 3 mm. It is revealed that the fatigue strength of both samples increases due to structure refinement and twinning in austenite during high pressure torsion deformation, partial martensitic transformation and increase of the share of more angular boundaries during cyclic deformation. The main factor of higher fatigue limit of AISI 316 steel after cryogenic deformation in comparison with room temperature is more intensive grinding of microstructure and presence of increased share of large-angle boundaries and more complete martensitic transformation.

High-pressure-torsion-induced segregation, precipitation and grain refinement of Al-(Si, Mg and Cu) binary alloys

To uncover the effects of segregation and precipitation on grain refinement of metals under severe plastic deformation, high-pressure-torsion (HPT) processing is performed on three binary Al-(Si, Mg, and Cu) alloys with different stability and segregation characteristics. Atom probe tomography analysis reveals that HPT processing induces significant decomposition of Al-1 at% Si and Al-1 at% Cu alloys with coarse Si particles and fine Al2Cu (θ) precipitates formed, but no decomposition of Al-1 at% Mg alloy, with dislocations segregated with Si, Cu, and Mg, and grain boundaries (GBs) only segregated with Cu and Mg. The GB segregation of Cu is stronger than that of Mg and Si, with Cu excess in the range of 1.5–7.0 atoms/nm2, Mg excess in the range of 0–4.0 atoms/nm2, but no Si excess. Interestingly, some GBs without Mg segregation develop a Mg-depletion zone along a single side. All evidences demonstrate that GB segregation and precipitation are responsible for HPT-induced grain refinement of Al-1Mg and Al-1Cu alloys but coarsening of the Al-1Si alloy. Engineering solute distribution is of significance in controlling the ultrafine grain of the Al alloys.

Effect of Bimodal Quasicrystal Phase on the Dynamic Recrystallization of Mg–Zn–Gd Alloy during High-Pressure Torsion

Effect of Bimodal Quasicrystal Phase on the Dynamic Recrystallization of Mg–Zn–Gd Alloy during High-Pressure Torsion

Mechanical softening of CuX alloys at elevated temperatures studied via high temperature scanning indentation

The thermal stability and temperature dependent hardness of ultrafine-grained Cu-alloys CuSn5 and CuZn5 after high pressure torsion are investigated using the high temperature scanning indentation (HTSI) method. Fast indentations are carried out during thermal cycling of the samples (heating-holding-cooling) to measure hardness and strain rate sensitivity as a function of temperature and time. The microstructures after each thermal cycle are investigated to characterize the coarsening behaviour of both alloys.Results show that the thermal stability of the tested alloys can be expressed in terms of several temperature regimes: A fully stable regime, a transient regime in which growth of individual grains occurs, and finally a regime in which the microstructure is fully coarsened. The onset of grain growth is accompanied by high strain rate sensitivity on the order of 0.2–0.3. Furthermore, the obtained hardness and strain rate sensitivity values are in good agreement with continuous stiffness measurement (CSM) and strain rate jump (SRJ) experiments. This highlights the applicability of the HTSI method to the characterization of the thermomechanical properties of ultrafine-grained alloys.

Crystal-to-amorphous phase transformation in ternary shape memory alloys

This systematic study evaluates the role of important factors in crystal-to-amorphous phase transformation during severe plastic deformation in ternary shape memory alloys. Experiments coupled with thermodynamic calculations to obtain comprehensive interpretation on the amorphization in ternary shape memory alloys. Equiatomic binary NiTi together with ternary Ni–45Ti–5Hf and Ti–45Ni–5Cu (at%) alloys as alloy models were processed by high-pressure torsion (HPT) at room and cryogenic temperatures. The binary and Hf-added alloys revealed an amorphous structure with a few remaining nanocrystals, however, Cu-added ternary alloy showed resistance to the amorphization after HPT processing. The results revealed two key factors of preventing martensite-to-austenite transformation during deformation and the intrinsic potential of the material for amorphization drive crystal-to-amorphous phase transformation. Higher transformation temperatures, enthalpy and thermal hysteresis prevented martensite-to-austenite transformation, which therefore encouraged amorphization. In addition, a large negative heat of mixing, Gibbs energy for amorphization and a large atomic size mismatch are important factors in implementing crystal-to-amorphous phase transformation. This investigation is a step forward to a fundamental understanding of ternary or even compositionally complex shape memory alloys for microstructural engineering by providing a homogeneous ultrafine-grained structure due to amorphization and subsequent heat treatment to achieve superior shape memory effect and superelasticity.

Effect of high-pressure torsion on the structure and microhardness of biodegradable Fe-30Mn-5Si (WT.%) alloy

The effect of high-pressure torsion (HPT), including a new method of accumulative HPT (AccHPT), on the microstructure and mechanical properties of Fe-30Mn-5Si alloy is studied. It is shown that during HPT and AccHPT, stress-induced ε-martensite is predominantly formed, and a mixture of nanograined structure, nanosubgrained structure and highly-dislocated substructure after HPT, while predominantly nanograined structure after AccHPT, are obtained. The increase in the number of HPT revolutions results in a broadening of the X-ray diffraction lines and higher microhardness values. The highest values were achieved on samples after AccHPT.

Effect of deformation nanostructuring on ion-beam erosion of copper

The effect of deformation nanostructuring on ion-beam erosion of copper at high fluences of irradiation with 30 keV argon ions was experimentally studied. Deformation nanostructuring by high-pressure torsion was used to form an ultrafine grained structure with a grain size of ~0.4 µm in copper samples with an initial grain size about 2 µm. It was found that when a layer of thickness comparable to the grain size was sputtered, a steady-state cone-shaped relief was formed on the copper surface, the appearance of which did not change with increasing irradiation fluence. It has been shown that the smaller the grain size in copper, the greater the concentration and the smaller the cone height on the surface. The cone inclination angles, close to 82°, as well as the sputtering yield of 9.6 at./ion, practically does not depend on the copper grain size, the thickness of the sputtered layer, and the irradiation fluence. Calculations using the SRIM code showed that when taking into account the sputtering of atoms from the walls of the cones, the sputtering yield of a cone-shaped copper relief Үc, was 3.5 times less than the yield of a single cone, 1.2 times greater than the sputtering yield of a smooth surface, and the value of 9.25 at./ion was close to the experimentally measured one.

Possible behavior of shear deformation under high-pressure torsion

The mutual influence of the primary and secondary order parameters when torsion is applied under high pressure is studied. Equilibrium and nonequilibrium cases are considered. The first is realized with a continuous increase in torque, and the second when studying the transition from one state to another, described by a traveling wave. The consideration was carried out on the basis of Landau's thermodynamic theory.

Surface sliding revealed by operando monitoring of high-pressure torsion by acoustic emission

High-pressure torsion (HPT) is widely used as a key method for microstructure control through deformation processing across a broad range of materials. However, certain gaps in process control impact its efficacy. In this study, we investigate the acoustic emission (AE) signals generated during HPT by considering commercially pure molybdenum as an example. By employing the adaptive sequential k-means algorithm, we analyse the AE stream to categorise and identify its sources. By comparing the kinetics of AE signal evolution during HPT processing at pressures of 2 GPa and 5 GPa, two distinct signal types are identified: one linked to plastic deformation and the other to workpiece slippage over HPT anvil surfaces. This research demonstrates the potential of AE tools for operando monitoring of HPT stability and detection of workpiece slippage, thereby enhancing the processing efficiency.

Influence of grain refinement via high-pressure torsion on corrosion behavior of medium- and high-entropy alloys CoCrFeNi and CoCrFeMnNi with various chromium contents

Influence of grain refinement via high-pressure torsion on corrosion behavior of medium- and high-entropy alloys CoCrFeNi and CoCrFeMnNi with various chromium contents

Correlation between microstructure, magnetic properties and mechanical behavior of the Permimphy alloy after high-pressure torsion

Correlation between microstructure, magnetic properties and mechanical behavior of the Permimphy alloy after high-pressure torsion

Enhanced Microhardness and Corrosion Performance of Additively Manufactured Inconel 718 Specimens through Nanostructuring by Severe Plastic Deformation

Severe plastic deformation (SPD) processes, particularly high-pressure torsion (HPT) have been increasingly applied to metallic specimens fabricated by laser powder bed fusion (L-PBF) additive manufacturing (AM) for enhancing their mechanical and functional properties through nanoscale grain refinement (≤ 100 nm). In this study. L-PBF AM-fabricated Inconel 718 (IN 718) specimens are initially subjected to 10 HPT revolutions to produce nanosized grains. Subsequently, microstructural characterisation, as well as hardness and electrochemical tests are conducted to evaluate the evolution of microstructures, hardness, and corrosion performance of the as-received and HPT-processed specimens by using various microscopy, Vickers microhardness (HV) measurements, and corrosion performance, respectively. The results reveal an average grain size of ~ 46 nm, dense dislocation networks, and nanotwins after 10 HPT processing, which contribute to the two-fold hardness increase compared to the as-received condition. Such microstructures also contributed to the overall improved corrosion performance after 10 HPT processing, as quantified by the 83% and 73% reduction in corrosion rate and pitting potential, respectively.

Effect of processing Mg–6Zn–0.2Ce through high-pressure torsion on its use as a biomaterial

Effect of processing Mg–6Zn–0.2Ce through high-pressure torsion on its use as a biomaterial

Hybrid graphene nanoplatelets/multi-walled carbon nanotubes reinforced Cu/Ti3SiC2/C nanocomposites with high efficiency dispersal and strengthening through high-pressure torsion

It is widely accepted to use hybrid reinforcements to prepare metal matrix composites (MMCs). However, it still suffers from some side effects, especially when nano-carbon is used as the reinforcing phase, it tends to agglomerate and then affect its strengthening effects. In the present work, Cu/Ti3SiC2/C nanocomposites reinforced with graphene nanoplatelets (GNPs) as well as multi-walled carbon nanotubes (MWCNTs) achieved combined mechanical along with electrical properties through high-pressure torsion (HPT). For one nanocomposite with 0.8 % GNPs-0.2 % MWCNTs, after HPT, nano-grains were obtained with the average size of 0.57 μm, which notably achieved grain refinement. With increasing HPT turns, the microhardness and electrical conductivity at N = 5 T reached 260.02 HV and 68.3 % IACS, which increased by 62.5 % and 41.4 %, respectively, compared to the samples before HPT. The enhanced performance with HPT on the nanocomposites mainly comes from the homogenization and grain refinement of the microstructure, as well as well-bonded interfaces between Cu matrix and reinforcements. This work provides a reference for preparing composites with balanced mechanical and electrical properties with hybrid reinforcements.

Evaluating High‐Pressure Torsion Scale‐Up

Increasing sample dimensions in high‐pressure torsion (HPT) processing affects load and torque requirements, deformation distribution, and heating. Finite‐element modeling (FEM) and experiments are used to investigate the effect of technical parameters on the scaling up of HPT. Simulations confirm that axial load and torque requirements are proportional to the square and the cube of the sample radius, respectively. The temperature rise also displays a pronounced dependency on the radius. Decreasing the diameter‐to‐thickness ratio can cause heterogeneity in strain distribution along the thickness direction at the edges of the sample. Such heterogeneity is governed by friction conditions between the material and the lateral wall of the anvil depression. Simulation of HPT processing of ring‐shaped samples shows that it is possible to reach more homogeneous distribution of strain and flow stress in the processed material. Experiments using magnesium confirm a tendency for strain localization in the early stage of HPT processing but increasing the number of turns increases the homogeneity of the material. The embodied energy in HPT processing is discussed.

Coupling of surface and volume behaviors to understand the generation of TTS in pure magnesium proceeded by HPT

This study analyzes the formation of tribologically transformed structures (TTS) in pure magnesium (Mg) using high-pressure torsion (HPT) processing. Generally, studies conducted in such conditions do not focus on surface behaviors. The correlation between the friction and wear phenomena at the surface and the microstructural changes was investigated to supplement the knowledge on TTS formation during the first stage of rotation. An RHEOS apparatus was used to test the samples with an average grain size of 70 μm under a mean pressure of 1 GPa and a rotation speed of 0.5 rpm. The samples were conducted in an unconstrained setup at room temperature. Surface and microstructure changes were examined using optical microscopy, scanning electron microscopy (SEM), and the focused ion beam (FIB). Observation of surfaces shows that friction between the anvils and the surfaces of the sample was set to satisfy the sticking condition. Three different zones in surface contact are identified: the centre zone, the adhesion/sliding zones, and the edge zone, which generate consequently different behaviors. It was found that 0.5 turns of HPT produced a significant refinement in the grain size of the processed Mg. The TTS were considered a zone with a fine microstructure, where the initial grain size was reduced to the range of 300 nm to 1000 nm. The results show that TTS produced in these conditions are not homogenous. The deformation occurs differently, so the TTS were less or more refined. According to the different observations, a scenario of surface degradation was established. The accommodation mechanisms considered are the rupture and shear modes, which occurred, respectively, in the first material and the third body.

Nanostructuring of Ferritic Steel: A Review on Enhanced Surface Properties Using Ultrasonic Shot Peening

Nanostructuring of ferritic stainless steel refers to the process of intentionally reducing the grain size of the material at the nanoscale level. By manipulating the microstructure of the steel, it is possible to enhance its mechanical, physical, and chemical properties. Nanostructuring can significantly improve the strength, hardness, and wear resistance of ferritic stainless steel, while still maintaining its corrosion resistance. The increased density of grain boundaries and the complex dislocation network within the nanostructured material contribute to these improved properties. Moreover, the nanostructured ferritic stainless steel exhibits enhanced thermal stability, leading to better high-temperature performance and resistance to creep deformation. The small grain size also allows for increased precipitation of secondary phases, such as carbides, nitrides, or intermetallic compounds, which can further improve the material's properties. There are several methods to achieve nanostructuring in ferritic stainless steel, such as severe plastic deformation (SPD) techniques like high-pressure torsion, equal channel angular pressing, and accumulative roll bonding. These techniques impose extreme plastic deformation on the material. Leading to grain refinement below the micrometre range. Also, a novel method of surface nanostructuring ultrasonic shot peening (USP) is discussed in detail. Shot peening is a process in which small, spherical media, typically made of steel or ceramic, called "shots," are propelled onto the surface of a material at high velocities. Ultrasonic shot peening enhances the traditional shot peening process by introducing high-frequency vibrations to the shots. These vibrations are generated by an ultrasonic transducer, which is immersed in a bath of shots and liquid. The vibrations are transmitted through the liquid to the shots, causing them to collide with the surface of the ferritic steel at even higher velocities and energy levels than in traditional shot peening. In summary, nanostructuring of ferritic stainless steel offers great potential for tailoring the material's properties to meet specific application requirements, including improved strength, hardness, wear resistance, corrosion resistance, and high-temperature performance. USP is an effective surface treatment method for ferritic steel, offering advantages in terms of fatigue life, stress corrosion cracking resistance, surface hardness, and wear resistance.