Influence Of High Pressure Torsion Research Articles

An EBSD analysis of a commercial immiscible Cu43%Cr alloy after high-pressure torsion processing and annealing

ABSTRACT The influence of high-pressure torsion (HPT) and annealing on microstructure, texture and thermal stability of an immiscible composite Cu43%Cr alloy was studied using electron backscatter diffraction, X-ray diffraction and microhardness measurements. As-received alloy samples were subjected to HPT and subsequent annealing treatment in the range of 210–850°C for 1 h in order to develop ultrafine-grained (UFG) microstructures and highlight their thermal stability. The Cu and Cr grains were refined to ∼0.45 and ∼0.39 µm, respectively and exhibited equiaxed morphology. The crystallographic texture was of shear type in both Cu and Cr with the domination of C and F orientations, respectively. The UFG microstructure and texture were retained in the Cu43%Cr alloy up to 850°C. The global results show that the immiscible composite Cu43%Cr alloy exhibits a high thermal stability up to 850°C. The evolution of the microstructure, texture and thermal stability of the UFG Cu43%Cr alloy was compared to published data and available models.

The Influence of High-Pressure Torsion on the Free Volume and Shear-Band Formation during the Indentation of Vit105 Metallic Glass

The research on structural features, microhardness distribution, and deformation features of Vit105 bulk metallic glass (BMG) before and after high-pressure torsion (HPT), as well as after relaxing annealing, has been carried out. HPT n = 1 leads to an increase in free volume ΔV, and relaxing annealing leads to a decrease in ΔV and non-uniformity relative to the initial state of BMG. In the initial BMG and in the BMG after relaxing annealing, microhardness is uniformly distributed over the surface, while in the material subjected to HPT, the microhardness distribution is more heterogeneous. The bonded-interface indentation of the BMG has been conducted in different states. The formation of numerous concentric bands around the indenter is observed. The pattern of band distribution is more homogenous in Vit105 BMG alloy before HPT. In relaxed samples, the bands often have fractures and irregularities, as well as cracks that can be seen under the indents. After HPT, the formation of several intensity bands can be observed, as well as a number of low-intensity ones between the main intensity bands. The average distance between the bands in the initial BMG and BMG after HPT is close to identical, while the distance between the bands is smaller in the relaxed state, which reflects the lower plasticity of the material after annealing.

Влияние интенсивной пластической деформации на механические свойства чистого цинка

Biodegradable materials, which have the ability to resorb in the body, are new and promising materials for medical implants. Currently, scientists carry out the investigations according to three directions: Mg, Fe, and Zn alloys. Zinc-based alloys and zinc have good solubility in the body, which meets the clinical requirements of implants. However, pure zinc has low mechanical properties, including hardness and tensile strength. Therefore, at present, the world scientific community is seeking ways to improve the properties of pure zinc by alloying. Another known approach is the ultrafine-grained (UFG) structure formation by the severe plastic deformation (SPD) methods, which are based on the large plastic deformations under high pressure and relatively low homologous temperatures. In this work, the authors studied the influence of high pressure torsion of pure zinc with various numbers of revolutions. The paper presents calculations of shear deformation after SPD. The authors investigated the dependence of mechanical properties and microstructure on the deformation degree. Tension tests at room temperature were carried out, and microhardness was measured. The authors studied the structure using scanning electron microscopy and optics. The study identified that the use of high pressure torsion leads to an increase in the tensile strength of pure zinc up to 140 MPa and ductility up to 40 % resulting from dynamic recrystallization.

Influence of High-Pressure Torsion on the Microstructure and Microhardness of Additively Manufactured 316L Stainless Steel

High-pressure torsion (HPT) is known as an effective severe plastic deformation (SPD) technique to produce bulk ultrafine-grained (UFG) metals and alloys by the application of combined compressive force and torsional shear strains on thin disk samples. In this study, the microstructures and microhardness evolution of an additively manufactured (AM) 316L stainless steel (316L SS) processed through 5 HPT revolutions are evaluated at the central disk area, where the effective shear strains are relatively low compared to the peripheral regions. Scanning electron microscopy (SEM) analysis showed that the cellular network sub-structures in AM 316L SS were destroyed after 5 HPT revolutions. Transmission electron microscopy (TEM) observations revealed non-equilibrium ultrafine grained (UFG) microstructures (average grain size: ~115 nm) after 5 revolutions. Furthermore, energy dispersive x-ray spectroscopy (EDX) analysis suggested that spherical Cr-based nano-silicates are also found in the as-received condition, which are retained even after HPT processing. Vickers microhardness (HV) measurements indicated significant increase in average hardness values from ~220 HV before HPT processing to ~560 HV after 5 revolutions. Quantitative X-ray diffraction (XRD) patterns exhibit a considerable increase in dislocation density from ~0.7 × 1013 m−2 to ~1.04 × 1015 m−2. The super-high average hardness increment after 5 HPT revolutions is predicted to be attributed to the UFG grain refinement, significant increase in dislocation densities and the presence of the Cr-based nano-silicates, according to the model established based on the linear additive theory.

Influence of high pressure torsion on microstructure evolution and mechanical properties of AZ80/SiC magnesium matrix composites

The effect of applying 1, 5 and 10 turns of high pressure torsion (HPT) as a severe plastic deformation technique on the microstructural evolution, hardness, tensile and shear strength of an as-cast AZ80-SiC magnesium matrix composite is investigated in the present study. The results show that HPT at room temperature refines the microstructure of the as-cast material having an average grain size of 176 ± 58.9 μm to a fine grain structure with average grain sizes of 4.2 ± 4.1 μm and 2.5 ± 2.1 μm in 5 and 10 turns HPT samples, respectively. In addition, ultra-fine grained regions (grain size <1 μm) with volume fractions of about 12, 27 and 31 vol% are obtained in the samples processed by 1, 5 and 10 turns of HPT, respectively. Based on microstructural observations, it is concluded that 5 and 10 turns HPT samples are almost similar in terms of grain size, recrystallized fraction, low-angle grain boundary fraction, and recovered parts. The ultimate tensile and shear (achieved from shear punch tests) strengths of the as-cast sample are improved by applying HPT due to grain size and texture hardening mechanisms. The highest strength values are obtained after performing the first HPT turn due to the more significant effect of texture hardening in comparison to the 5 and 10 turns HPT-processed samples. Similar to the strength results, the hardness of the as-cast material is also enhanced from 66 ± 6 HV to about 123 ± 3 HV through HPT processing.

Influence of high-pressure torsion on the deformation nature of Vit105 metallic glasses during microhardness tests

Severe plastic deformation by torsion leads to a decrease in the microhardness of Zr-based BMG, while relaxing annealing, on the contrary, increases it. It was found that the microhardness and the nature of deformation near the indentation depend on the applied load. At low loads, the formation of shear bands is observed. With increasing load, the tendency towards homogeneous deformation increases.

Influence of HPT and Accumulative High-Pressure Torsion on the Structure and Hv of a Zirconium Alloy

The authors previously used the accumulative high-pressure torsion (ACC HPT) method for the first time on steel 316, β-Ti alloy, and bulk metallic glass vit105. On low-alloyed alloys, in particular, the zirconium alloy Zr-1%Nb, the new method was not used. This alloy has a tendency to α → ω phase transformations at using simple HPT. When using ACC HPT, the α → ω transformation can be influenced to a greater extent. This article studies the sliding effect and accumulation of shear strain in Zr-1%Nb alloy at various stages of high-pressure torsion (HPT). The degree of shear deformation at different stages of HPT was estimated. The influence of various high-pressure torsion conditions on the micro-hardness and phase composition by X-ray diffraction (XRD) of Zr-1%Nb was analyzed. It is shown that at high-pressure torsion revolutions of n = 2, anvils and the specimen significantly slip, which is a result of material strengthening. It was found that despite sliding, regular high-pressure torsion resulted in the high strengthening of Zr-1%Nb alloy (micro-hardness more than doubled), and after high-pressure torsion n = 10, up to 97% of the high-pressure ω-phase was formed in it (as in papers of other researchers). Accumulative high-pressure torsion deformation leads to the strongest transformation of the Zr-1%Nb structure and Hv and, therefore, to a higher real strain of the material due to composition by upsetting and torsion in strain cycles.

The Influence of HPT on Microstructure and Wear Resistance of Al-7wt%Si-2wt%Fe Alloy

An aluminum silicon-based alloy Al-7wt%Si-2wt%Fe, was processed by severe plastic deformation technique in high-pressure torsion (HPT) at room temperature under a pressure of 6.0 GPa and rotational speed of 1.0 rpm with various numbers of turns up to five. Microstructure evolution, especially iron-containing intermetallic phases, was observed using an optical microscope and a scanning electron microscope (SEM). The microstructure results demonstrate that the large strains introduced by HPT at ambient temperature cause fragmentation of iron-intermetallic particles. The degree of fragmentation increases with increasing numbers of turns so that the intermetallic particles decreased in size with increasing imposed strain. In addition, the wear properties were evaluated using ball-on-disc dry sliding testing for both the as-cast material and the alloy processed by HPT using micro-tribometer UMT-2 (CETR Co., USA) following the ASTM G99-05 (2010) standard. The wear tests were conducted on the surface of the samples at 1.5 mm from the disc center under a normal load of 5 N with a rotational speed of 60 rpm and sliding time of 10 min. The friction coefficient and wear volume loss were examined to evaluate the effect of HPT on wear resistance. The results show that the samples processed by HPT have lower average values for the COF and wear volume loss than that of unprocessed samples.

Influenceof high pressure torsion on magnetic properties Fe50Ni50 and Fe49Ni49Al2 alloys

Influenceof high pressure torsion on magnetic properties Fe50Ni50 and Fe49Ni49Al2 alloys

Influence of High-Pressure Torsion and Accumulative High-Pressure Torsion on Microstructure and Properties of Zr-Based Bulk Metallic Glass Vit105

Vit105 (Zr52.5Cu17.9Ni14.6Al10Ti5 at. %) bulk metallic glass samples were processed by high-pressure torsion and accumulative high-pressure torsion. By DSC, XRD and SANS methods it was shown that accumulative high-pressure torsion allows for achieving high real strains and leads to an increase in the free volume and significant transformation of the structure. Minor crystallization was detected after high-pressure torsion processing.

Influence of high-pressure torsion on microstructure, hardness and shear strength of AM60 magnesium alloy

The evolution of the microstructure, crystallographic texture and hardness of an AM60 magnesium alloy was studied in the center and the edge parts of disks processed by high-pressure torsion (HPT) technique at room temperature. In addition, the mechanical properties were also tested by shear punch test (SPT). The number of HPT turns varied between ½ and 10. It was found that the grain size of the initial extruded material (~16 μm) decreased to ~2 and ~0.8 μm at the disk center and edge, respectively, even after ½ turn of HPT. Ten turns of HPT resulted in further grain refinement to ~1 and ~0.23 μm at the disk center and edge, respectively. The dislocation density saturated even after ½ turn with the value of ~11 × 1014 m−2. The maximum value of the hardness was ~1300 MPa that was measured at the edge of the disk deformed for ½ turn. Despite the practically unchanged grain size and dislocation density, the hardness decreased between 3 and 10 turns which can be explained by texture softening. A good agreement was observed between the yield strength estimated as one-third of the hardness and the values calculated from the dislocation density, grain size and texture. The difference between the microstructure and hardness obtained for AM60 samples processed by HPT and equal channel angular pressing (ECAP) is discussed.

Formation of the ω Phase in the Titanium—Iron System under Shear Deformation

The effect of the phase composition on the α/β-Ti(Fe)→ω-Ti(Fe) transformation in the Ti-4 wt % Fe alloy under shear strain with high-pressure torsion (HPT) has been studied. For shear deformation by means of HPT, two initial states of the alloy were used, which significantly differed in the morphology of the phases and the concentration of iron atoms in the β phase. During HPT, a stationary state occurred in both sample series, which is characterized by the presence of a single ω phase containing 4 wt % Fe and by a grain size of about 200 nm. Thus, the HPT state is equifinal and independent of the initial phase composition of the samples. It was found that under the influence of HPT in Ti-4 wt % Fe alloys not only martensitic (shear) transformation into the ω phase occurs, but also a significant mass transfer of atoms of the alloying element. An analysis of the change in the torsion torque directly in the HPT process made it possible to estimate the rate of deformation-induced mass transfer. It is 18–19 orders of magnitude higher than the rate of conventional thermal diffusion at the processing temperature THPT = 30°C, while it is close to the diffusivity values at 700–800°C. This is because HPT increases the concentration of lattice defects, which in turn is equivalent to an increase in temperature. A similar combination of accelerated mass transfer during HPT and martensitic (shear) transformation was previously observed in copper-based shape memory alloys, but for the first time studied for the formation of ω-phase in titanium alloys.

Influence of plastic deformation by high-pressure torsion on the crystallization kinetics of a Pd40Ni40P20 bulk metallic glass

The influence of high-pressure torsion on the crystallization behavior of the pre-annealed Pd40Ni40P20 bulk metallic glass was investigated by differential scanning calorimetry and fluctuation electron microscopy. Calorimetry shows that deformation splits the single main crystallization peak into a two-step crystallization process including a primary and a main peak. This is in line with fluctuation electron microscopy, which shows a reduction of ordering upon deformation. The overall activation energy and the local activation energy of the crystallization were analyzed by the Kissinger and Kissinger-Akahira-Sunose methods, respectively. The primary crystallization peak occurs at a lower temperature but shows a higher activation energy due to the drastically accelerated atomic mobility. Deformation can accelerate the crystallization process by increasing the nucleation rate.

Phase transitions in copper–silver alloys under high pressure torsion

AbstractThe influence of high pressure torsion (HPT) on the formation and decomposition of solid solutions in the copper–silver system has been studied. The investigated Cu-8 wt.% Ag alloy was annealed at two different temperatures, 500 and 650°C, and quenched. The samples consisted of (Cu) solid solution in the matrix with (Ag) precipitates. During HPT a steady-state value of torsion torque was reached after about 1.5 anvil rotations. After HPT (5 anvil rotations) the composition of the (Cu) solid solution in both samples had become equal. In other words, the concentration of silver in the (Cu) matrix annealed at 650°C decreased and in the sample annealed at 500°C increased. Moreover, a similar process took place in (Ag) precipitates as well. The concentration of copper in (Ag) particles in the sample annealed at 650°C decreased and in the sample annealed at 500°C increased. Thus, the composition of (Cu) and (Ag) solid solutions reached at steady-state during HPT does not depend on that before HPT. The composition of the (Cu) and (Ag) solid solutions after HPT is as high as if the samples were annealed at a certain intermediate temperature about 600 ± 20°C.

Influence of High Pressure Torsion on structure and properties of Zr-Ti-Nb alloy synthesized from TiH2, ZrH2 and Nb powders

The effects of High Pressure Torsion (HPT) deformation on the microstructure and mechanical properties of a corrosion-resistant, low modulus Zr-Ti-Nb alloy, obtained by vacuum sintering of cold pressed powder are studied. It is shown that HPT treatment leads to the following effects: elimination of the residual chemical heterogeneity of the alloy, significant reduction of the porosity of the material and the pore size and improvement of mechanical properties. The phase composition of the alloy does not change during processing. The results show the potential of the HPT method for the production of alloys with a favorable combination of properties.

Influence of High Pressure Torsion on Thermoelastic and Thermoelectric Response of Pure Copper and Aluminum under Pulsed Laser Radiation

This work presents experimental studying the effect of processing by severe plastic deformation (SPD) on the thermoelastic and thermoelectric properties of pure aluminum and copper under pulsed laser radiation. The studies were carried out on technical aluminum AD1 (99.3%) and pure copper M1 (99.9%). High pressure torsion (HPT) was used for processing by SPD. After the HPT processing, the materials samples in the form of a plane disk were subjected to pulsed laser radiation focused on the disk center. Pulsed lasers with a wavelength of 1.06 micron and operating in the free laser oscillation mode with pulse duration of 100 microseconds or in the mode of a single pulse with duration of about 10 nanoseconds were used. The thermoelastic and thermoelectric responses of the materials were determined by measuring acoustic waves and the thermoelectric power. The disks with the initial coarse-grained material state were considered as a reference sample, and the disks of the materials after SPD processing were considered as a controlled object. The results demonstrated a very high sensitivity of the parameters of thermoelastic and thermoelectric response to structural changes in the materials. For example, the used HPT mode led to a reduction in the maximum thermoelectric power value for aluminum by 40% and for copper by 35%.

Texture and microhardness of Mg-Rare Earth (Nd and Ce) alloys processed by high-pressure torsion

The influence of high-pressure torsion (HPT) processing on the texture and microhardness of two binary Mg-RE (RE = Nd and Ce) alloys was investigated using X-ray diffraction and Vickers microhardness measurements. Disks cut from the alloys were processed by HPT at room temperature for up to 10 turns. The precipitation products of both alloys were identified using synchrotron radiation. The results show that both alloys exhibit a weak basal texture where the c-axis of most grains is shifted 15° from the shear direction. An Mg-1.44Ce (wt%) alloy showed a continuous decrease in the texture strength which may be due to the effect of second precipitation phases (Mg17Ce2 and MgCe2). The microhardness of both alloys increased significantly with increasing HPT turns but levelled-off beyond about one HPT turn. Maximum values of ~65 and ~96 Hv were achieved which are significantly higher than the hardness of the undeformed Mg-Ce and Mg-Nd alloys.

Influence of high-pressure torsion and hot rolling on the microstructure and mechanical properties of aluminum–fullerene composites

In this study, we investigate the impacts of working process, high-pressure torsion (HPT) and hot rolling (HR) on the microstructure and mechanical performance of aluminum-based nanocomposites containing fullerenes. HPT caused severe plastic deformations that generate numerous dislocations and lattice strains, and this stimulated the formation of aluminum carbides (Al4C3) and reduced the hardness during heat treatment. In contrast, the HRed specimens experienced dynamic recovery, and their initial dislocation densities and lattice strains were lower than those of the HPTed specimens. Thus, the HRed composites formed supersaturated aluminum phases as well as aluminum carbides during the heat treatment. The supersaturated phases provided high-density dislocations and severe lattice strains, resulting in an increase in the hardness during the heat treatment. This comparison suggests that the mechanical properties of aluminum–fullerene composites can be controlled by working processes in practical situations.

High-pressure torsion driven phase transformations in Cu–Al–Ni shape memory alloys

Severe plastic deformation (SPD) frequently induces phase transformations like decomposition of supersaturated solid solution, dissolution of precipitates, amorphization, nanocrystallization etc. Such diffusive phase transitions are combined with SPD-driven accelerated mass transfer. Displacive (or martensitic) phase transitions can also take place and in combination with diffusive ones have not been investigated in depth in severely deformed materials. The goal of this work is to investigate the combination of displacive (austenite↔martensite) and diffusive (decomposition of supersaturated solid solution) phase transitions in two different Cu–Al–Ni shape memory alloys under the influence of high-pressure torsion (HPT). After homogenization in the one-phase (austenitic) β-area of Cu–Al–Ni phase diagram and quenching, the first alloy was in martensitic state (mainly β′3 martensite with a small amount of γ′3 martensite), and the second one remained austenitic (β3 phase). The HPT of these alloys led to the precipitation of α1-phase in the first case and γ1-phase in the second one (as if they were annealed at an effective temperature Teff = 620 ± 20 °C). As a result of precipitation, the matrix in the first alloy was enriched and in the second one depleted in Al. After HPT, both alloys contained mainly β′3 martensite with a certain amount of γ′3 martensite. Thus, the HPT-driven diffusive transformations (precipitation of α1-and γ1-phase) influence the followed displacive (martensitic) transformation. Simultaneously, a dramatic grain refinement is obtained and the reported results open new possibilities to investigate the superelastic and shape memory effects in nanostructured Cu–Al–Ni alloys.

Influence of High-Pressure Torsion on the Microstructure and the Hardness of a Ti-Rich High-Entropy Alloy

High-Pressure Torsion (HPT) is one of the most effective severe plastic deformation techniques in grain refinement. The goal of this study was to investigate the influence of HPT on the microstructure and hardness of a Ti-rich High-Entropy Alloy (HEA). The evolution of the grain size due to 1 turn of HPT was studied by transmission electron microscopy. Besides the refinement of the microstructure, a phase transition also occurred during HPT, as revealed by X-ray diffraction. The initial bcc structure transformed into a martensitic phase throughout the material. The features of this phase transformation were studied on a sample compressed to low strain values. The hardness as a function of the distance from the center in the HPT-processed disk was measured and correlated to the microstructure.