High Speed High Pressure Torsion Research Articles

Magnetic Shape Memory Nanocomposites Assembled with High Speed High Pressure Torsion.

When a severe plastic deformation (SPD) process is performed at high temperatures, it becomes more versatile. Designed originally for the bulk nanoconstruction of hard-to-deform alloys, high-speed high-pressure torsion (HSHPT) is an SPD method used in this research for assembling multiple layers of shape memory nanocomposites. Three hard-to-deform magnetic alloys in the cast state were used. Soft magnetic shape memory alloys, NiFeGa and FePdMn, and a potentially hard magnetic alloy, CoZr, were assembled in various composites. Both grain refinement and strong layer bonding were achieved in ZrCo/FePdMn and ZrCo/NiFeGa composites in seconds. The very short SPD time is specific to HSHPT because of the intense friction that occurs under high pressures, which generates huge amounts of heat. After SPD, the temperature rises in bulk material like a pulse, being dissipated mostly through heat conduction. The SPD parameters were carefully controlled with an advanced automation system using a programmable logic controller. Nevertheless, the major drawbacks of high-pressure torsion were overcome, and large SPD discs were obtained. Various investigation techniques (optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and atomic force microscopy) show well-defined interfaces as well as a fine and ultrafine structure.

Modeling of Severe Plastic Deformation by HSHPT of As-Cast Ti-Nb-Zr-Ta-Fe-O Gum Alloy for Orthopedic Implant.

The High Speed High Pressure Torsion (HSHPT) is the severe plastic deformation method (SPD) designed for the grain refinement of hard-to-deform alloys, and it is able to produce large, rotationally complex shells. In this paper, the new bulk nanostructured Ti-Nb-Zr-Ta-Fe-O Gum metal was investigated using HSHPT. The biomaterial in the as-cast state was simultaneously compressed up to 1 GPa and torsion was applied with friction at a temperature that rose as a pulse in less than 15 s. The interaction between the compression, the torsion, and the intense friction that generates heat requires accurate 3D finite element simulation. Simufact Forming was employed to simulate severe plastic deformation of a shell blank for orthopedic implants using the advancing Patran Tetra elements and adaptable global meshing. The simulation was conducted by applying to the lower anvil a displacement of 4.2 mm in the z-direction and applying a rotational speed of 900 rpm to the upper anvil. The calculations show that the HSHPT accumulated a large plastic deformation strain in a very short time, leading to the desired shape and grain refinement.

Conceptual Analysis on Severe Plastic Deformation Processes of Shape Memory Alloys: Mechanical Properties and Microstructure Characterization

Shape memory alloys (SMAs) are types of materials that can restore their original shape upon severe or quasi-plastic deformation, being exposed to specific external stimuli, including heating, electric current, magnetic field, etc. They are a category of functional materials that provides superelasticity as a significant material property. The roots of this unintentional discovery were in the 20th century, and later it attracted the attention of various industries, including aerospace, medical, mechanical, manufacturing industries, etc. Later developments mainly focused on improving the properties of these materials. One of the ways in which this is achieved is the application of intensive plastic strains on SMAs through severe plastic deformation (SPD) methods, leading to extreme grain refinement. Superelasticity is a key characteristic of SMAs and is known as the capacity of a polycrystalline material to display extremely high elongations before failure, in a typically isotropic way, with an approximate strain rate of 0.5. Utilization of SPD techniques can also affect and lead to superior superelasticity responses in SMAs. Several SPD methodologies have been introduced over the decades, to produce ultrafine-grained and even nanostructured materials, including constrained groove pressing, equal-channel angular pressing, high-speed high-pressure torsion, accumulative roll bonding, etc. This paper aims to present a clear view of the mechanical properties and microstructure evolution of shape memory alloys after processing by some SPD methods, and to show that SPD methods can be a great option for developing SMAs and expanding their industrial and technological applications.

Significance of strain rate in severe plastic deformation on steady-state microstructure and strength

The microstructure and mechanical properties of materials saturate to steady states after severe plastic deformation (SPD). Despite the well-known effect of temperature on the steady-state microstructure, there is no general agreement on the significance of strain rate and the applicability of the Zener-Hollomon parameter in this regard. In this study, several pure metals (aluminum, copper, titanium, and iron) and a Cu–30Zn (wt%) brass alloy have been processed by a high-speed high-pressure torsion (HPT) equipment with controllable rotation speeds in the range of 0.06–60 rpm. It is found that crystallite/grain size, dislocation density, microhardness and shear stress at the steady state are reasonably rate-independent for the von Mises strain rates in the range of 0.004–20 s−1. Because both rates of grain refinement and of dynamic recrystallization are proportional to the strain rate, it is suggested that their balance, which determines the steady state, is rate-independent.

Using High Speed High Pressure Torsion for Cu–13Al–4Ni Shape Memory Alloy Processing

Recently, severe plastic deformation (SPD) is recognized as a very efficient processing technique for the fabrication of bulk nanostructured (ns)/ultrafine-grained materials. High-speed high-pressure torsion (HSHPT) process, an SPD method, is used as a novel approach to produce ultrafine grains in memory materials. The influence of HSHPT process variables on some Cu-based shape memory alloys (SMAs) is explored and discussed. This paper also envisages providing a comparative study of significant microstructural evolutions and features that are introduced by HSHPT processing. The plastic deformation mechanisms of the copper-based SMAs are investigated from macrostructural and microstructural points of view using optical and scanning electron microscopic techniques. In addition, significant grain size reduction brought about by the process is attested by X-ray diffraction and transmission electron microscopy. The transition temperatures have been determined by differential scanning calorimetry.

Structural Characteristics of Multilayered Ni-Ti Nanocomposite Fabricated by High Speed High Pressure Torsion (HSHPT)

It is generally accepted that severe plastic deformation (SPD) has the ability to produce ultrafinegrained (UFG) and nanocrystalline materials in bulk. Recent developments in high pressure torsion (HPT) processes have led to the production of bimetallic composites using copper, aluminum or magnesium alloys. This article outlines a new approach to fabricate multilayered Ni-Ti nanocomposites by a patented SPD technique, namely, high speed high pressure torsion (HSHPT). The multilayered composite discs consist of Ni-Ti alloys of different composition: a shape memory alloy (SMA) Ti-rich, whose Mf > RT, and an SMA Ni-rich, whose Af < RT. The composites were designed to have 2 to 32 layers of both alloys. The layers were arranged in different sequences to improve the shape recovery on both heating and cooling of nickel-titanium alloys. The manufacturing process of Ni-Ti multilayers is explained in this work. The evolution of the microstructure was traced using optical, scanning electron and transmission electron microscopes. The effectiveness of the bonding of the multilayered composites was investigated. The shape memory characteristics and the martensitic transition of the nickel-titanium nanocomposites were studied by differential scanning calorimetry (DSC). This method opens up new possibilities for designing various layered metal-matrix composites achieving the best combination of shape memory, deformability and tensile strength.

The Influence of Severe Plastic Deformation on Microstructure and In Vitro Biocompatibility of the New Ti-Nb-Zr-Ta-Fe-O Alloy Composition.

In this work, severe plastic deformation (SPD) of the newly designed Ti-Nb-Zr-Ta-Fe-O GUM metal was successfully conducted at room temperature using high speed high pressure torsion (HSHPT) followed by cold rolling (CR) to exploit the suitability of the processed alloy for bone staples. The Ti-31.5Nb-3.1Zr-3.1Ta-0.9Fe-0.16O GUM alloy was fabricated in a levitation melting furnace using a cold crucible and argon protective atmosphere. The as-cast specimens were subjected to SPD, specifically HSHPT, and then processed by the CR method to take the advantages of both grain refinement and larger dimensions. This approach creates the opportunity to obtain temporary orthopedic implants nanostructured by SPD. The changes induced by HSHPT technology from the coarse dendrite directly into the ultrafine grained structure were examined by optical microscopy, scanning electron microscopy and X-ray diffraction. The structural investigations showed that by increasing the deformation, a high density of grain boundaries is accumulated, leading gradually to fine grain size. In addition, the in vitro biocompatibility studies were conducted in parallel on the GUM alloy specimens in the as-cast state, and after HSHPT- and HSHPT+CR- processing. For comparative purposes, in vitro behavior of the bone-derived MC3T3-E1 cells on the commercially pure titanium has also been investigated regarding the viability and proliferation, morphology and osteogenic differentiation. The results obtained support the appropriateness of the HSHPT technology for developing compression staples able to ensure a better fixation of bone fragments.

Structural Change in Ni-Fe-Ga Magnetic Shape Memory Alloys after Severe Plastic Deformation.

Severe plastic deformation (SPD) is widely considered to be the most efficient process in obtaining ultrafine-grained bulk materials. The aim of this study is to examine the effects of the SPD process on Ni-Fe-Ga ferromagnetic shape memory alloys (FSMA). High-speed high-pressure torsion (HSHPT) was applied in the as-cast state. The exerted key parameters of deformation are described. Microstructural changes, including morphology that were the result of processing, were investigated by optical and scanning electron microscopy. Energy-dispersive X-ray spectroscopy was used to study the two-phase microstructure of the alloys. The influence of deformation on microstructural features, such as martensitic plates, intragranular γ phase precipitates, and grain boundaries’ dependence of the extent of deformation is disclosed by transmission electron microscopy. Moreover, the work brings to light the influence of deformation on the characteristics of martensitic transformation (MT). Vickers hardness measurements were carried out on disks obtained by SPD so as to correlate the hardness with the microstructure. The method represents a feasible alternative to obtain ultrafine-grained bulk Ni-Fe-Ga alloys.

Achieving ultra-fine grained microalloyed steel by severe plastic process

Latterly, it is of interest to enhance combination of strength and toughness of steel for advanced products, therefor the objective of this research is to improve the mechanical properties of high strength low - or ultra - low alloy (HSLA) steels through grain refinement. The ultra-fine grained S420NL steel were produced by high speed high pressure torsion (HSHPT) at room temperature. This severe plastic deformation method was chosen because it is one of the most feasible and rapid ways for nanostructuring various metallic materials down to ultrafine grain range. The procedure key parameters of deformation are described in detail in the paper. The influence of severe plastic deformation applied in cast state steel on microstructure changes and deformation behaviour was investigated. Optical microscopy, SEM and energy dispersive x-ray spectroscopy (EDX) analysis carried out on the samples revealed that severe plastic deformation led to the subsequent formation of an ultrafine-grained microstructure. Sample hardness increased rapidly with progress of torsion deformation degree.

Formation of submicrocrystalline structure in a biodegradable Mg alloy

Magnesium alloy, as biodegradable material, are attracted increasing interest in the field of bone graft substitution due to their excellent biocompatibility and good corrosion resistance. The main clinical challenges of ZK60 Mg alloy remain requirements such as: straight, fracture resistance, work hardening mechanical shock and so on, concomitant with plasticity. According to the Hall-Petch theory, an effectively enhance strength of Mg alloys may be realized by grain refinement. This paper proposes a reliable approach to fabricate Mg cast alloys down to ultrafine-grain range within just a few seconds. Ultrafine grained (UFG) Mg alloy was produced by severe plastic deformation (SPD), using high speed high pressure torsion (HSHPT) procedures. The microstructure evolution of the as-cast and as-severely deformed Mg-Zn-Zr was characterized using electron microscopy and energy dispersive spectroscopy (EDX). X-ray diffraction analyses (XRD) was performed to study the impact of severe plastic deformation on internal structure changes. Micro hardness tests indicated significant increase with the progression of true strain. Results so far have been very encouraging in developing new solution for biodegradable applications.

A new application of Fe-28Mn-6Si-5Cr (mass%) shape memory alloy, for self-adjustable axial preloading of ball bearings

A new application of Fe-Mn-Si based shape memory alloys (SMAs) was developed under the form of truncated cone-shaped module, for self-adaptive axial preload control in angular contact bearings. The modules were processed by high-speed high-pressure torsion (HS-HPT), from circular crowns cut from axially drilled ingots of Fe-28Mn-6Si-9Cr (mass%) SMA. The specimens were mechanically tested in the hot rolled state, prior to HS-HPT processing, demonstrating free-recovery shape memory effect (SME) and high values for ultimate tensile stress and strain as well as low cycle fatigue life. The HS-HPT modules were subjected to static loading–unloading compression, without/with lubrication at specimen-tool interface, both individually and in different coupling modes. Dry compression cycles revealed reproducible stress plateaus both during loading and unloading stages, being associated with hardness gradient, along cone generator, caused by HS-HPT processing. Constrained recovery tests, performed using compressed modules, emphasized the continuous generation of stress during heating, by one way SME, at a rate of ∼9.3 kPa/%. Dynamic compression tests demonstrated the capability of modules to develop closed stress–strain loops after 50 000 cycles, without visible signs of fatigue. HS-HPT caused the fragmentation of crystalline grains, while compression cycles enabled the formation of ε hexagonal close-packed stress-induced martensite (ε), which is characterized by a high density of stacking faults. Using an experimental setup, specifically designed and manufactured for this purpose, both feasibility and functionality tests were performed using HS-HPT modules. The feasibility tests proved the existence of a general tendency of both axial force and friction torque to increase in time, favoured by the increase of initial preloading force and the augmentation of rotation speed. Functionality tests, performed on two pairs of HS-HPT modules fastened in base-to-base coupling mode, demonstrated the capacity of modules to accommodate high preloads while maintaining both axial force and friction torque at constant values in time. These preliminary results suggest that, for the time being, the modules can operate only as single use applications, more effective during the running-in period. This bevahior recommends HS-HPT modules as a new application of Fe-Mn-Si SMAs, with the potential to be used for the development of new temperature-responsive compression displacement systems.

A Versatile Method for Nanostructuring Metals, Alloys and Metal Based Composites

A new severe plastic deformation method based on High Pressure Torsion is described. The method patented as High Speed High Pressure Torsion (HSHPT) shows a wide scope and excellent adaptability assuring large plastic deformation degree on metals, alloys even on hard to deform or brittle alloys. The paper present results obtained on aluminium, magnesium, titan, iron and coper alloys. In addition capability of HSHPT to process metallic composites is described. OM SEM, TEM, DSC, RDX and HV investigation methods were employed to confirm fine and ultrafine structure.

Microstructural Evolution in Ultrafine Grained FeMnSiCr Shape Memory Alloy Modules

High speed high pressure torsion (HSHPT) processing technology, engineered to achieving (ultra) fine bulk metallic structure under high pressure (~ GPa) and torsion by applying supplementary elevated rotation speed of superior anvil. Coned-disk spring shape modules were processed from an as cast Fe-28Mn-6Si-5Cr (mass %) shape memory alloy (SMA). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies revealed that the structure of modules became submicron as an effect of HSHPT processing. After severe plastic deformation, a grain size gradient was obtained along the truncated cone generator, increasing from inner to outer areas, due to different deformation degrees in these zones. The mechanical and shape memory properties was performed in order to relate the structural changes caused by severe plastic deformation.

Effect of Severe Plastic Deformation on the Structure and Magnetic Behaviour of an Fe-Mn-Si Shape Memory Alloy

This work focuses on the relation between severe plastic deformation process via HSHPT and magnetic properties of an Fe–Mn–Si-Cr shape memory alloy. High speed high pressure torsion (HSHPT) was applied on cast state of alloy. Microstructure evolution of severe plastic deformed iron based alloy subjected to different deformation degree were investigated. The microstructure and phase compositions of alloy were characterized using optical microscopy, scanning electron microscopy and transmission electron microscopy. The magnetic properties are discussed on the basis of the severe plastic deformation process and the underlying martensitic transformation. Thermomagnetic curves, between 150 K and 390 K and magnetic hysteresis loops at 300 K temperatures were measured. The thermo-resistivity measurements were done by standard four-probe. The magnetic properties are interpreted and correlated with microstructure.

Investigations of a nanostructured FeMnSi shape memory alloy produced via severe plastic deformation

Low-cost iron-based shape memory alloys (SMAs) show great potential for engineering applications. The developments of new processing techniques have recently enabled the production of nanocrystalline materials with improved properties. These developments have opened avenues for newer applications for SMAs. The influence of severe plastic deformation induced by the high-speed high-pressure torsion (HSHPT) process on the microstructural evolution of an Fe–Mn–Si–Cr alloy was investigated. Transmission electron microscopic analysis of the alloy revealed the existence of nanoscale grains with an abundance of stacking faults. The high density of dislocations characteristic of severe plastic deformation was not observed in this alloy. X-ray diffraction studies revealed the presence of e-martensite with an HCP crystal structure and γ-phase with an FCC structure.

Effect of High Speed High Pressure Torsion Parameters on Grain Refinement of Coned Shape Fe Based SMA Active Elements

High Speed High Pressure Torsion (HS-HPT) refers to processing that involves a combination of high pressure with torsional straining. This technique allows the efficient grain refinement on shape memory alloy brittle (CuAlNi) or with very low plasticity (FeMnSiCr). HS-HPT involve slippage between anvils and sample this means the SPD occurs at specific temperature. The recrystallization during HS-HPT on shape memory alloys determines their functionality without supplemental heat treatments. The samples manufactured by HS-HPT are discs, rings or coned shaped, 20-40mm in diameter and 1mm - 0.2mm thickness. Varying HS-HPT parameters coned shaped elements with increasing deformation degree were produced from Fe28Mn6Si7Cr [mass %] shape memory alloy. Scanning electron microscopy (SEM) observations, highlighted ultrafine structure. Experiments show that the mechanical properties of the alloy can be enhanced by HS-HPT.

Investigation of microhardness evolution in an ultrafine grained NiTi alloy formed via high speed high pressure torsion (HSHPT)

An investigation was conducted so as to evaluate the homogeneity of microstructure and mechanical properties of an NiTi shape memory alloy subjected to high speed high pressure torsion (HSHPT). The alloy chosen for the study had 50.3 at.% of Ni in its composition and was supplied in the form of hot extruded rods of 9 mm diameter. The final shape achieved after severe plastic deformation was a disc, whose diameter and thickness measured 40 mm and 0.18 mm, respectively. The TEM studies and the microhardness determination using a Vickers hardness tester revealed the effect of dynamic recrystallisation, which is very unique to severe plastic deformation involving HSHPT. An analysis of the microhardness data shows that the disc-shaped element is essentially homogeneous. In addition, the microhardness increases with the increase in accumulated strain. The results are presented and discussed in detail in the paper..

A Comparative Study of Austenitic Structure in NiTi and Fe Based Shape Memory Alloys after Severe Plastic Deformation

The effect of high speed high pressure torsion (HS-HPT) was studied in NiTi and FeMnSiCr SMAs, by comparison. Severe plastic deformation was performed in austenite state for both types of alloys. The alloys subjected to HS-HPT, reduced their grain size due to microstructure fragmentation by compression and torsion. The active elements were achieved being able to support variable ranges of processing parameters like force, pressure, rotation speed and time of torsion. The evolution of microstructural refinement in the samples subjected to different deformation by HS-HPT, were studied by optical and scanning electron microscopy observation and the thermal effect was reveled using differential scanning calorimetry (DSC).

Effects of HSHPT on the martensitic transformation behaviour of an NiTi alloy

High speed high pressure torsion (HSHPT) is a novel severe plastic deformation technique that is used to produce bulk ultrafine-grained nickel-titanium shape memory alloys. In this study, the effect of grain refinement on phase transformation was investigated in a near equiatomic NiTi shape memory alloy subjected to processing by this technique. Phase transformations involving different degrees of deformation and stability of thermally-induced phase transformations were analyzed by differential scanning calorimetry (DSC). The measurements suggest that the martensitic transformation occurred even when the highest degree of deformation was applied. Optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations bring to light that the true strain applied controls the evolution of the microstructure. The results are presented and discussed in detail in this paper.

Hardness-gradient reversion in FeMnSiCr shape memory alloy modules produced by high-speed high pressure torsion

High pressure torsion (HPT) processing technology, consisting in the obtainment of (ultra)fine bulk metallic structure during 2–3 complete rotations of the superior anvil at low speed (~10-1 rpm) under high applied pressure (~ GPa) applied on the lower anvil, has been modified as to allow the application of elevated number of rotation numbers (~102 rpm). By high-speed high pressure torsion (HS-HPT), coned-disk spring shape modules were processed from an as cast Fe-28Mn-6Si-5Cr (mass %) shape memory alloy (SMA). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies revealed that the modules became nanostructured as an effect of HS-HPT processing. After processing, a hardness gradient was obtained along the truncated cone generator, increasing from inner to outer areas, due to different deformation degrees in these zones. After complete flattening, the measurements revealed that the hardness gradient maintained its value but reversed its variation sense.