Combination Of High-pressure Torsion Research Articles

Achieving ultra-high strength of Al-Cu-Li alloys by the combination of high pressure torsion and age-hardening

The combined strengthening effects of high pressure torsion (HPT) and age hardening on a recently developed 3rd generation Al-Cu-Li alloy was investigated. Solution treated samples were processed through HPT at room temperature, followed by low temperature artificial ageing (i.e. T4-HPT-AA). A micro-hardness of ∼ 240 Hv was achieved on ageing at 110 oC/60h after HPT. A further improvement in the hardness to ∼ 260 Hv was accomplished by a pre-ageing 110 oC/24h before HPT combined with a post-HPT ageing process at 110 oC for 180h (i.e. T6-HPT-AA). These novel multi-stage processes give rise to an increase in hardness by a factor of 2 as compared to the T4 condition (∼ 120 Hv). After HPT the grain size was dramatically refined to the ultrafine-grained (UFG) structure, accompanied by a large amount of dislocations. No long-range ordered precipitates were observed after HPT and subsequent ageing treatments. Instead, atom probe tomography (APT) provided clear evidence that Cu-Mg co-clusters were homogeneously distributed in the matrix of T4 and T6 processed samples and they segregate strongly to the grain boundaries (GBs) during HPT. Further ageing treatment after HPT leads to the segregation of clusters to dislocations. A strengthening model that incorporates dislocation hardening, grain boundary hardening, solid solution strengthening and a new short-range order strengthening mechanisms was used to predict the yield strength of the alloy. This model indicates that the combined effect due to all three types of Cu-Mg clusters (clustering in matrix, clustering at GBs and at dislocations) is dominant for the strength in all conditions.

Исследование выделений вторых фаз в наноструктурном технически чистом титане

The results of studies on the process of precipitation of dispersed second phases in commercially pure titanium Grade 4 and the effect of secondary precipitates on its structure and mechanical properties in two states, coarse-grained and nanostructured ones, are presented. The nanostructured state was obtained by high-pressure torsion (HPT) under a pressure of 6 GPa up to N =10 revolutions at room temperature. A particular consideration is given to the study of changes in the phase composition and microstructure of titanium subjected to deformation processing after annealing at an elevated temperature of 700°C for 30 minutes. In this work, by means of studies in a transmission electron microscope, it was shown that at a temperature of 700°C and higher, in the structure of the samples, nanoparticles of the second phases which differ in size and morphology are precipitated in both states. The nature of the observed particles was studied in SEM, by indexing the electron diffraction patterns taken from the particles, and by carrying out X-ray phase analysis by the “transmission” method. Particles of the second phases are modifications of the high-temperature β-phase of titanium. The HPT treatment of the alloy, according to the XRD data, leads to an increase in the volume fraction of precipitated particles after annealing and, as a result, to an increase in the microhardness of the states under study. The results of microhardness measurements at varying regimes of deformation and annealing are presented. Combination of HPT up to N = 5 revolutions and annealing at 700°C for 30 minutes followed by additional torsion straining also up to N = 5 revolutions provides the highest microhardness values in commercially pure titanium, which reaches 423 HV.

Achieving Ultra-High Strength of Al-Cu-Li Alloys by the Combination of High Pressure Torsion and Age-Hardening

The combined strengthening effects of high pressure torsion (HPT) and age hardening on a recently developed 3rd generation Al-Cu-Li alloy was investigated. Solution treated samples were processed through HPT at room temperature, followed by low temperature artificial ageing (i.e. T4-HPT-AA). A micro-hardness of ~240 Hv was achieved on ageing at 110°C/60h after HPT. A further improvement in the hardness to ~260 Hv was accomplished by a pre-ageing 110°C/24h before HPT in combination with a post-HPT ageing process at 110°C for 180h (i.e. T6-HPT-AA). These novel multi-stage processes give rise to an increase in hardness by a factor of 2 as compared to the T4 condition (~120 Hv). After HPT the grain size was dramatically refined to the ultrafine-grained (UFG) structure, accompanied by a large amount of dislocations. No long-range ordered precipitates were observed after HPT and subsequent ageing treatments. Instead, atom probe tomography (APT) provided clear evidence that Cu-Mg co-clusters were homogeneously distributed in the matrix of T4 and T6 processed samples and they segregate strongly to the grain boundaries (GBs) during HPT. Further ageing treatment after HPT leads to the segregation of clusters to the dislocations. A strengthening model that incorporates dislocation hardening, grain boundary hardening, solid solution strengthening and a new short-range order strengthening mechanisms was used to predict the yield strength of the alloy. This model indicates that the combined effect due to all three types of Cu-Mg clusters (clustering in matrix, clustering at GBs and at dislocations) is dominant for the strength in all conditions.

Achieving ultra-high hardness of nanostructured Mg-8.2Gd-3.2Y-1.0Zn-0.4Zr alloy produced by a combination of high pressure torsion and ageing treatment

A Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr (wt%) alloy is subjected to a series of thermal and mechanical treatments involving solution treatment, artificial ageing to peak hardness, high pressure torsion (HPT) and a second artificial ageing. During HPT precipitates dissolve and during the final post-HPT ageing, the supersaturated solid solution decomposes and solutes segregate at grain boundaries. By employing this T6 + HPT + T5 treatment, the hardness increases to 156 ± 1 HV, which is much higher than that achieved by any other reported combination of thermal and thermo-mechanical processing of Mg alloys. The ultra-high hardness is due to the combined effects of solute segregation, grain refinement and high dislocation density.

Combination of High-Pressure Torsion with Incremental Feeding for Upsizing Sample

Combination of High-Pressure Torsion with Incremental Feeding for Upsizing Sample

Using heat treatments, high-pressure torsion and post-deformation annealing to optimize the properties of Ti-6Al-4V alloys

Experiments were conducted to investigate the processing parameters that may be used to optimize the properties of Ti-6Al-4V alloys. The alloy was initially subjected to two different heat treatments leading to the formation of martensitic α′ and lamellar α+β microstructures and then both materials were processed by high-pressure torsion (HPT) for 10 turns at room temperature. This gave significant grain refinement to the nanometer range in both conditions and the occurrence of an allotropic hcp to fcc phase transformation in the martensitic alloy. These nanostructured alloys were subjected to post-deformation annealing (PDA) at temperatures in the range of 473–1023 K. The results show the hardness increases slightly to 773 K due to α′+fcc→α+β+fcc and α→α+β phase transformations in the martensitic α′ and lamellar α+β alloys and then decreases up to 1023 K due to recrystallization and grain growth. An optimum property of a very high yield strength (∼1120 MPa) and ultimate tensile strength (∼1200 MPa), together with excellent ductility (elongation to failure of ∼26%), was achieved in the Ti-6Al-4V martensitic alloy processed by a combination of HPT followed by PDA at 873 K for 60 min.

Strain induced hardening and softening behaviors of deformed Cu and Cu–Ge alloys

Abstract

Evolution of defect structures during cold rolling of ultrafine-grained Cu and Cu–Zn alloys: Influence of stacking fault energy

Samples of pure Cu, bronze (Cu–10 wt.% Zn) and brass (Cu–30 wt.% Zn) with stacking fault energies (SFE) of 78, 35, and 14 mJ/m 2, respectively, were processed by high-pressure torsion (HPT) and by a combination of HPT followed by cold-rolling (CR). X-ray diffraction measurements indicate that a decrease in SFE leads both to a decrease in crystallite size and to increases in microstrain, dislocation and twin densities for the HPT and HPT + CR processed ultrafine-grained (UFG) samples. Compared with processing by HPT, subsequent processing by CR refines the crystallite size of all samples, increases the twin densities of UFG bronze and brass, and increases the dislocation density in UFG bronze. It also decreases the dislocation density in UFG brass and leads to an unchanged dislocation density in UFG copper. The results suggest there may be an optimum stacking fault energy for dislocation accumulation in UFG Cu–Zn alloys and this has important implications in the production of materials having reasonable strain hardening and good tensile ductility.