The microstructure, phase state, and tensile properties of a bioresorbable Fe-30Mn-5Si alloy after high-pressure torsion (HPT) with n = 1 or 5 revolutions and post-deformation annealing (PDA) at 500 and 600 degrees C were investigated. HPT produced submicrograined structure (grain size of 200-500 nm) with nanosubgrained structure (subgrain size of 20-50 nm) inside grains, and highly-dislocated regions. Subsequent PDA is accompanied by growth of HPT-produced grains and subgrains, polygonization of highly-dislocated substructures and partial recrystallization. HPT with n = 5 followed by PDA at 600 degrees C resulted in the best tensile properties.

A high-pressure torsion (HPT) with a number of revolutions (n) of up to 10 and an advanced method of accumulative HPT (AccHPT), n = 10 with subsequent post-deformation annealing (PDA) at 500 and 600 °C, were applied to a biodegradable Fe-30Mn-5Si (wt.%) alloy. The effect of HPT, AccHPT and AccHPT with PDA on the microstructure, phase composition, microhardness and electrochemical behavior in Hanks’ solution was studied. HPT with n = 1 and 5 resulted in forming a mixed submicrocrystalline (SMCS) and nanocrystalline (NCS)structure, while HPT, n = 10 and AccHPT, n = 10 resulted in a predominant NCS with grain/subgrain sizes of 15–100 nm and 5–40 nm, respectively. PDA after AccHPT resulted in a mixture of SMCS and NCS. HPT, n = 5, n = 10 and AccHPT, n = 10 led to a transition from a two-phase (γ-austenite and ε-martensite) state after reference quenching, and HPT, n = 1 to a single-phase state (stress-induced and deformed ε-martensite), while the AccHPT, n = 10 with PDA results in a two-phase state of γ-austenite and cooling-induced ε-martensite, similarly to reference heat treatment (RHT). The increase in n resulted in the microhardness increasing up to its maximum after AccHPT, followed by a slight decrease after PDA. HPT and AccHPT led the biodegradation rate to decrease as compared to the initial state. PDA after AccHPT at 500 and 600 °C resulted in a two-phase state corresponding to an elevated biodegradation rate without significant material softening. The observed electrochemical behavior features are explained by changes in a combination of the phase state and the overall level of crystal lattice distortion.

The martensitic transformation and strain nanodomain were studied in the Ti40.7Hf9.5Ni44.8Cu5 shape memory alloy, whose grain size varied from 130 mu m to 160 nm. The largest average grain size (600 mu m in length and 130 mu m in diameter) was found in the CAST sample. The grains with the smallest size (160 nm) formed during the crystallisation of thin ribbons obtained by the melt spinning technique from the Ti40.7Hf9.5Ni44.8Cu5 ingot (labelled as RIBBON). The average grain size (16 mu m) was observed in the sample subjected to high-pressure torsion and post-deformation annealing (labelled as HPT). It was found that the CAST and HPT samples included the NiTi-based matrix and the Ti2Ni-type precipitates, whereas the RIBBON sample contained the NiTibased matrix only. Regardless of the grain size, all samples underwent the B2 <-> B19' transformation on cooling and heating. A decrease in grain diameter from 130 mu m to 160 nm decreased the transformation temperatures by more than 100 degrees C but did not affect the sequence of the transformation. The strain nanodomains formed in all samples on cooling prior to the forward martensitic transformation. The smaller the grain size, the larger the temperature range of the strain nanodomain existence. On heating of HPT and RIBBON samples, the B19 phase transformed to the B2 phase with strain nanodomains, which disappeared only on heating over 120 degrees C. The influence of grain size on the martensitic transformation and strain nanodomains was analysed from the thermodynamics approach.

In this study, the deformation behavior induced by micro-indention is investigated on Zr-based metallic glass in the melt-spun ribbon form. Further, melt-spun ribbon samples were severe plastically deformed using high pressure torsion method with variation in anvil rotations using a compressive pressure of 6 GPa. Calculation of free volume is performed on melt-spun ribbon and on deformed samples using x-ray diffraction analysis and is found to marginally increase in later. Formation of free volume influences the deformation mechanism through early initiation and propagation of shear bands in high-pressure-torsion-processed samples. The presence of amorphous structure after high pressure torsion process is an indication that glassy phase is retained in severe plastic deformed samples. The present research work aims to understand the role of high pressure torsion and its correlation with micro-indentation-induced deformation behavior in Zr 62 Cu 22 Al 10 Fe 5 Dy 1 metallic glass samples. Graphical abstract

Grain refinement and precipitation hardening play critical important role for stabilization and improving functional properties of shape memory alloys. However, the relationship between precipitation and nanocrystalline grain growth behavior in NiTiHf alloys is still unclear. This work aims to investigate the role of precipitation in the nanocrystalline grain growth behavior of HPT-processed Ni50Ti30Hf20 high-temperature shape memory alloy. An abnormally low grain growth rate (n = 0.08) was observed after post-deformation annealing (PDA) at 550 °C for 1 h. It was proposed that grain growth suppression may be caused by the presence of relatively large H-phase precipitates, which act as barriers to grain boundary movement. A detailed analysis of the grain growth kinetics during PDA suggests that the coarsening process is controlled by Ni diffusion. Additionally, the dependence of strength and transformation temperatures on grain size in NiTiHf alloy is found to follow the Hall-Petch relation with some exceptions due to H-phase precipitation. The results of this research may be useful for the development of methods and strategies to stabilize the nanocrystalline structure in metallic materials.

Grain refinement and precipitation hardening play critical important role for stabilization and improving functional properties of shape memory alloys. However, the relationship between precipitation and nanocrystalline grain growth behavior in NiTiHf alloys is still unclear. This work aims to investigate the role of precipitation in the nanocrystalline grain growth behavior of HPT-processed Ni50Ti30Hf20 high-temperature shape memory alloy. An abnormally low grain growth rate (n = 0.08) was observed after post-deformation annealing (PDA) at 550 degrees C for 1 h. It was proposed that grain growth suppression may be caused by the presence of relatively large H-phase precipitates, which act as barriers to grain boundary movement. A detailed analysis of the grain growth kinetics during PDA suggests that the coarsening process is controlled by Ni diffusion. Additionally, the dependence of strength and transformation temperatures on grain size in NiTiHf alloy is found to follow the Hall-Petch relation with some exceptions due to H-phase precipitation. The results of this research may be useful for the development of methods and strategies to stabilize the nanocrystalline structure in metallic materials.

(Ti54Ni34Cu12)90Nb10 alloy with initial two-phase structure of B19 martensite and β-Nb phase was subjected to high-pressure torsion (HPT) process at room temperature. HPT leads to the formation of nanocrystalline bands of β-Nb phase alternating with amorphous matrix. Nanocrystalline debris of B2 phase was found to be embedded into the amorphous matrix. Refinement of β-Nb phase upon HPT is much greater compared to that for pure Nb alloy.

We investigated the microstructure of the Zr–2.5%Nb zirconium alloy after subjecting it to equal-channel angular pressing (ECAP) and found that ECAP at 300 °C increases the strength by 140 to 180 %. Notably, unlike other studies, our alloy did not show complete dissolution of niobium particles, which may be due to the reduced diffusion rates at the lower deformation temperature of 300 °C. Pre-treatment involving quenching before severe plastic deformation was also studied, which developed a lamellar structure introducing additional boundaries that facilitated grain refinement during subsequent ECAP. The strength of the alloy was further enhanced by solid-solution hardening, achieved through the complete dissolution of the Nb particles into the matrix post-quenching. This process resulted in a 2.3-fold increase in yield strength after quenching plus ECAP compared to the initial coarse-grained state.

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.

This overview examines the results of a study of the effect of slippage in high-pressure torsion (HPT). A number of papers in this area and the works of the authors of this overview are considered. The authors used the method of the “joint HPT of the disk halves”. This method is the simplest and most illustrative method for evaluating slippage during HPT. The authors used 10 and 20 mm diameter anvils, with a groove on the lower anvil and a calculated pressure of 6 GPa. In the case of the HPT of solid bulk metal glass (BMG), slippage starts at the early stages of HPT and is total. Slippage may also be significant at the early stages of the HPT of such metallic materials as Ti, Ni, Fe-0.1%C, and Zr-2.5%Nb. Slippage increases with the number of revolutions, n. There is no slippage at the initial stages of the HPT of copper. However, after HPT Cu n = 10, slippage can be total. Nevertheless, studies show that the structure of samples using HPT, obtained by the authors, is similar to the nanostructure observed by other authors after using HPT with similar materials. Thus, notwithstanding slippage during HPT, deformation during HPT still occurs, and nanostructure formation occurs. Therefore, the formation of a nanostructure in samples during HPT is not proof of the absence of slippage. The authors provide a possible explanation for this. The authors propose a new method—“accumulative high-pressure torsion”—to achieve a high strain in various materials. In this procedure, several cycles are repeated, according to the following scheme: “HPT for n = 1 or 2 turns of the anvil → cutting the specimen into pieces → unstacking the stacked pieces on the anvil and subsequent HPT for n = 1 or 2”. Studies performed on a number of materials demonstrate that novel method transforms the structure more efficiently than regular HPT.

The Ti-18Zr-15Nb shape memory alloys are a new material for medical implants. The regularities of phase transformations during heating of this alloy in the coarse-grained quenched state and the nanostructured state after high-pressure torsion have been studied. The specimens in quenched state (Q) and HPT state were annealed at 300–550 °C for 0.5, 3, and 12 h. The α-phase formation in Ti-18Zr-15Nb alloy occurs by C-shaped kinetics with a pronounced peak near 400–450 °C for Q state and near 350–450 °C for HPT state, and stops or slows down at higher and lower annealing temperatures. The formation of a nanostructured state in the Ti-18Zr-15Nb alloy as a result of HPT suppresses the β→ω phase transformation during low-temperature annealing (300–350 °C), but activates the β→α phase transformation. In the Q-state the α-phase during annealing at 450–500 °C is formed in the form of plates with a length of tens of microns. The α-phase formed during annealing of nanostructured specimens has the appearance of nanosized particle-grains of predominantly equiaxed shape, distributed between the nanograins of β-phase. The changes in microhardness during annealing of Q-specimens correlate with changes in phase composition during aging.

The structure and properties of the Ti–18Zr–15Nb alloy subjected to equal channel angular pressing (ECAP) at 200°С (the number of ECAP cycles n = 1–4) and 500°С (the number of ECAP cycles n = 4 and n = 8) are studied. The main phase of the alloys in all the states is the bcc β phase. No clear presence of X-ray reflections belonging to the secondary α", ω, and α phases is found. The ECAP at 200°С leads to the formation of deformation macrobands that cut the entire sample. As ECAP temperature increases to 500°С, the deformation occurs without the formation of macrobands. According to optical microscopy data, after ECAP, the fragmentation occurs within grains outside of macrobands; microbands and deformation microband packets form. According to transmission electron microscopy data, ECAP results in refining the structure to submicron grains and deformation microbands. The ultimate strength increases as the number of ECAP cycles increases and reaches 960 MPa after ECAP at 200°С with n = 4; however, in this case, the plasticity decreases. The best combination of mechanical properties is achieved after ECAP at 500°С with n = 4; the ultimate strength is 825 MPa at the relatively high plasticity equal to δ = 16

A Ti-18Zr-15Nb (at%) shape memory alloy was subjected to a high-temperature thermomechanical treatment (HTMT) combining an equal channel angular pressing (ECAP) at 500 degrees C for n = 4-8 passes and a short-time post-deformation annealing (PDA) at 600 degrees C. The phase composition, microstructure, texture, mechanical and functional properties were studied. The functional fatigue behavior observed in this study was compared to that resulted from the reference low-temperature thermomechanical treatment (LTMT) by ECAP at 200 degrees C for 3 passes + PDA (600 degrees C for 5 min). The ECAP at 500 degrees C (n = 4) led to the formation of a highly deformed, dynamically polygonised substructure of beta-phase with a crystallographic texture close to the [101] direction. In this state, the alloy exhibited an excellent combination of the static functional and mechanical properties: a relatively high strength (UTS = 670 MPa), a sufficient ductility (delta = 13.3 %), a low Young's modulus (E < 40 GPa), and a high superelastic recovery strain (epsilon(se)(r)(max) = 3.1 %). An increase in the number of passes during ECAP to n = 8 led to a greater substructural hardening of the material, grain/subgrain refinement, and the release of alpha-phase. This significantly increased the alloy strength (UTS = 897 MPa), but reduced its ductility (delta = 5.9 %) and suppressed martensitic transformation. The alloy after both the HTMT (ECAP at 500 degrees C, n = 4) and TMT (ECAP at 200 degrees C, n = 3) processes exhibited an equally excellent functional fatigue resistance accompanied by a superior superelastic behavior with small accumulated strains. However, the HTMT process appears to be more technologically advanced, as it eliminates the need for PDA and reduces the risks of specimen cracking during processing.

Changes in the structure of amorphous alloys under deformation by high-pressure torsion, multiple-pass rolling, and pressure treatment have been studied using X-ray diffraction and scanning electron microscopy. It has been shown that under all types of deformation, shear bands are formed in amorphous alloys, which are regions of lower density compared to a surrounding undeformed amorphous matrix. Shear bands are regions of an increased free volume; the formation of bands results in steps occurring on the surface of samples. The number of shear bands and the surface morphology of deformed amorphous alloys are determined by the deformation type and physical properties of a material.

This paper is devoted to the study of the current density distribution effect on plasma electrolytic oxidation process and resultant coatings on a Zr-1Nb alloy. The influence of the distance between the plates simultaneously placed into an electrolyzer was evaluated to assess the throwing power of the PEO process. The current density on the facing surfaces of the plates decreases when the distance between them shrinks. This current density has a notable impact on the resultant PEO coating in terms of the surface morphology parameters and electrochemically evaluated corrosion resistance. The influence of this effect is low on the stages of anodizing and spark discharges (60–120 s of the PEO), and significantly increases on the stage of microarc discharges (120–360 s of the PEO). The coating obtained with a smaller distance between the plates, while having the same coating thickness as the others, exhibits higher wear resistance. New correlations between the current density, diffusion coefficient, time constant of nucleation and the coating thickness in the middle of the facing samples were established; in addition, a correlation of the coating morphology in this area with the roughness parameters RPc, RSm was shown. This study contributes to the development of optimized PEO processes for the simultaneously coated several devices of complex shape, e.g., orthopedic implants.

The paper analyzes the effect of severe plastic deformation on the structure, mechanical and thermal properties as well as crystallization process of a Zr62.5Сu22.5Al10Fe5 alloy. High pressure torsion (HPT) induces local atomic changes and accumulates the formation of inhomogeneous chemical regions. The mechanically treated alloy structure is generally complex. The residual glassy matrix contains nanocrystalline particles. The structural changes observed during the HPT process lead to significant changes in the crystallization process. The effect of shear strain on crystallization of the Zr62.5Сu22.5Al10Fe5 alloy and its properties was studied in detail using transmission electron microscopy (TEM), X-Ray diffraction (XRD), and differential scanning calorimetry (DSC) methods.

The team of the Sao Paolo University (Brazil) developed a new β-Ti alloy Ti10Mo8Nb6Zr, which is perspective as material for medical implants. The structure and micro-hardness of titanium alloy Ti10Mo8Nb6Zr after high pressure torsion were studied. The XRD analysis showed that β-phase was the main phase of Ti10Mo8Nb6Zr alloy in the initial state. After high pressure torsion, β-phase remains the main one. There is also an additional α-phase, but its amount is low (below 10%). The half-width of a primary X-ray line of β-phase is greatly increased after HPT. This testifies to an increased density of dislocations and refinement of grains during HPT. According to TEM, after HPT a nanosized structure is formed. The TEM studies show that the alloy after HPT n=0.5 and n=5 contains both sub-grains with low-angle sub-boundaries and grains with high-angle boundaries and a high density of dislocations. Even after HPT with a relatively low n (n=0.5) a rather fine structure is formed with a size of grains/sub-grains of about 200-500 nm. After HPT with n = 5, the microstructure of Ti10Mo8Nb6Zr alloy is additionally refined, but the size of grains/sub-grains is about 200-300 nm. HPT with a low number of revolutions n=0.5 leads to a substantial growth of HV from 326 to 400. Further increase in the number of revolutions leads to additional growth of microhardness. The HV increment after HPT of this alloy (about 20%) is much lower than that after HPT of titanium and α-Ti alloys.

The effect of thermal cycling on the structure of TiNi alloy in coarse-grained (CG) and ultrafine-grained (UFG) states is investigated. Thermodynamic aspects of martensitic transformations, changes in the entropy and energy of the process are considered. The change in the dissipation energy determines the change in the hysteresis of transformations in the CG and UFG states. It is noted that the UFG state is characterized by a larger increase in the elastic energy of martensite plates. The change in the elastic energy of defects is compared with the data on the structure obtained by the X-ray method. A larger increase in the density of dislocations in the CG state is a cause of an increase in the energy of defects. A slightly lower value of the dissipation energy in the UFG state and a decrease in its values in the CG state after thermal cycling confirms the data on the transformation hysteresis.