Strengthening of Nickel Deformed by High Pressure Torsion

2008 ◽  
Vol 584-586 ◽  
pp. 417-421 ◽  
Author(s):  
Hong Wang Zhang ◽  
X. Huang ◽  
Niels Hansen ◽  
Reinhard Pippan ◽  
Michael Zehetbauer
Keyword(s):  
High Pressure ◽  
Cold Rolling ◽  
High Pressure Torsion ◽  
Structural Evolution ◽  
Longitudinal Section ◽  
High Angle ◽  
Microstructural Parameters ◽  
Transmission Electron ◽  
Structure Relationship ◽  
Von Mises

The strength of a deformed metal depends on the content of high angle boundaries, low angle dislocation boundaries and the dislocations between the boundaries. High angle boundaries contribute by Hall-Petch strengthening, whereas for the low angle dislocation boundaries and dislocations between boundaries the strengthening is proportional to the square root of the dislocation density. Based on an assumption of additivity of these contributions, the flow stresses of metals deformed by cold rolling have been calculated successfully. In the present investigation pure Ni (99.9%) has been deformed by high pressure torsion (HPT) to von Mises strains of 0.9, 1.7, 8.7 and 12. The strength of the HPT Ni has been determined by Vickers microhardness (HV) measurements and the microstructural parameters have been determined by transmission electron microscope (TEM) in the longitudinal section. HPT has been compared with deformation by cold rolling and torsion based on the structural evolution with strain and the stress-structure relationship. Based on an assumption of a linear additivity of boundary strengthening and dislocation strengthening, good agreement has been found between the calculated and the experimental flow stress.

High Pressure Torsion of Intermetallic Zr3Al

2008 ◽  
Vol 584-586 ◽  
pp. 553-558 ◽  
Author(s):  
David Geist ◽  
Christian Rentenberger ◽  
Hans Peter Karnthaler
Keyword(s):  
High Pressure ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
Structural Evolution ◽  
Nanocrystalline Structure ◽  
Temperature Dependent ◽  
Transmission Electron ◽  
Ordered Alloys ◽  
Grain Fragmentation ◽  
Shear Strains

The L12-structured intermetallic compound Zr3Al can be rendered amorphous easily by several techniques. In the present study the structural evolution during high pressure torsion (HPT) was investigated systematically by transmission electron microscopy (TEM) methods. Zr3Al samples were deformed at room temperature to different grades of deformation up to shear strains of 140 000%. TEM investigations revealed that the tendency to grain fragmentation, disordering and the formation of a nanocrystalline structure is weak compared to other L12 ordered alloys like Ni3Al. In addition, an amorphous phase has not been encountered. The present results differ strongly from previous ones obtained from ball-milled materials. Possible reasons for the different behavior are discussed on the basis of the temperature dependent dissociation scheme of the superlattice dislocations gliding in Zr3Al.

scholarly journals Crystallization of Cu60Zr20Ti20 bulk metallic glass by high pressure torsion

2019 ◽  
Vol 58 (1) ◽  
pp. 304-312
Author(s):  
Ádám Révész ◽  
András Horváth ◽  
Gábor Ribárik ◽  
Erhard Schafler ◽  
David J. Browne ◽  
...  
Keyword(s):  
High Pressure ◽  
Metallic Glass ◽  
Crystallite Size ◽  
Bulk Metallic Glass ◽  
High Pressure Torsion ◽  
Average Crystallite Size ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Microstructural Parameters ◽  
Profile Fitting

Abstract Bulk metallic glass of Cu60Zr20Ti20 composition has been synthesized by copper mold casting. Slices of the as-cast glass has been subjected to severe plastic deformation by high-pressure torsion for different whole turns. The microstructure and the thermal behavior of the deformed disks have been investigated by X-ray diffraction and differential scanning calorimetry. It was confirmed that the initial compression preceding the high pressure torsion induces crystallized structure, which shows only minor further changes upon the severe plastic shear deformation achieved by twisting the sample. The X-ray line profiles have been evaluated by the Convolutional Whole Profile Fitting algorithm in order to determine the evolution of the microstructural parameters, such as the median and variance of the crystallite size distribution, average crystallite size and dislocation density as a function of the number of revolutions. Hardness measurements by nanoindentation have also been carried out on the as-cast alloys and the deformed disks.

Hardening model of severe plastically deformed AA2024 by high-pressure torsion

2020 ◽  
Vol 11 (4) ◽  
pp. 591-603
Author(s):  
Fauziana Lamin ◽  
Ahmad Kamal Ariffin Mohd Ihsan ◽  
Intan Fadhlina Mohamed ◽  
Cheeranan Krutsuwan Nuphairode
Keyword(s):  
High Pressure ◽  
Simulation Model ◽  
High Pressure Torsion ◽  
Model Verification ◽  
Von Mises Stress ◽  
Rotational Axis ◽  
Content Type ◽  
Hardening Model ◽  
Von Mises ◽  
Stress Flow

PurposeThis paper aims to evaluate the validity of bilinear hardening model to represent the stress flow of high-pressure torsion (HPT)-strengthened lightweight material, AA2024.Design/methodology/approachFinite-element HPT simulation was performed by applying a simultaneous prescribed displacement on the axial and rotational axis that is equivalent to 4 GPa pressure and 30° torsion. The material behaviour incorporates plasticity attributes with a bilinear constitutive equation that consists of elastic and tangent modulus.FindingsAs a result, the von Mises stress generated from the simulation is in good agreement with the experiment, indicating that the assumptions of plasticity properties applied for the FEM simulation model are acceptable. The model verification confirms the anticipated plasticity parameters’ effect on the generated von Mises stress. The disc centre also evidenced an insignificant stress increment due to the limited shear straining.Research limitations/implicationsA reliable hardening model would assist in understanding the stress flow associated with mechanical properties enhancement.Practical implicationsThe bilinear hardening model exhibits a satisfactory stress estimation. It simplifies the ideal strain variable hardening procedures and lessens the total computation time that is valuable in solving severe plastic deformation problems.Originality/valueAn integration of well-defined input parameters, concerning the hardening behaviour and the plasticity properties, contributes to the establishment of a validated HPT simulation model, particularly for AA2024. This study also proved that perfectly plastic behaviour is inappropriate to represent hardening in the HPT-strengthened materials due to the remarkable stress deviation from the experimental data.

scholarly journals Microstructural Investigation of Nanocrystalline Hydrogen-Storing Mg-Titanate Nanotube Composites Processed by High-Pressure Torsion

Energies ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 563 ◽  
Author(s):  
Marcell Gajdics ◽  
Tony Spassov ◽  
Viktória Kovács Kis ◽  
Ferenc Béke ◽  
Zoltán Novák ◽  
...  
Keyword(s):  
High Pressure ◽  
Ball Milling ◽  
High Pressure Torsion ◽  
High Energy ◽  
Titanate Nanotubes ◽  
Microstructural Investigation ◽  
Microstructural Parameters ◽  
Preparation Conditions ◽  
Average Dislocation Density ◽  
Nanotube Composites

A high-energy ball milling and subsequent high-pressure torsion method was applied to synthesize nanocrystalline magnesium samples catalyzed by TiO2 or titanate nanotubes. The microstructure of the as-milled powders and the torqued bulk disks was characterized by X-ray diffraction. The recorded diffractograms have been evaluated by the convolutional multiple whole profile fitting algorithm, which provided microstructural parameters (average crystal size, crystallite size distribution, average dislocation density). The morphology of the nanotube-containing disks has been examined by high-resolution transmission electron microscopy. The effect of the different additives and preparation conditions on the hydrogen absorption behavior was investigated in a Sieverts’-type apparatus. It was found that the ball-milling route has a prominent effect on the dispersion and morphology of the titanate nanotubes, and the absorption capability of the Mg-based composite is highly dependent on these features.

Microstructure and Microhardness of Copper Subjected to High Pressure Torsion

2011 ◽  
Vol 194-196 ◽  
pp. 712-715 ◽  
Author(s):  
Zi Ling Xie ◽  
Lin Zhu Sun ◽  
Fang Yang ◽  
Xiao Bing Li
Keyword(s):  
High Pressure ◽  
High Pressure Torsion ◽  
Type Equation ◽  
Longitudinal Section ◽  
Dislocation Cell ◽  
Subgrain Structure ◽  
Structure Morphology ◽  
Evolution Of Microstructure ◽  
Equiaxed Grains ◽  
Variation Tendency

Experiments were conducted on copper subjected to High Pressure Torsion to investigate the evolution of microstructure and microhardness with shear strain, γ. Observations have been carried out in the longitudinal section for a proper demonstration of the structure morphology. An elongated dislocation cell/subgrain structure was observed at relatively low strain level. With increasing strain, the elongated subgrains transformed into elongated grains and finally into equiaxed grains with high angle grain boundaries. Measurements showed the hardness increases with increasing γ then tends to saturations when γ >5. The variation tendency of microhardness with γ can be simulated by Voce-type equation.

Microstructure Development and Precipitation Effects in Ultra Fine Grained Mg-3Tb-2Nd Alloy Prepared by High Pressure Torsion

2008 ◽  
Vol 584-586 ◽  
pp. 591-596 ◽  
Author(s):  
Jakub Čížek ◽  
Ivan Procházka ◽  
Bohumil Smola ◽  
Ivana Stulíková ◽  
Martin Vlach ◽  
...  
Keyword(s):  
High Pressure ◽  
Positron Lifetime ◽  
High Pressure Torsion ◽  
Creep Properties ◽  
Fine Grained ◽  
Transmission Electron ◽  
Highly Sensitive ◽  
Ideal Tool ◽  
Increasing Temperature

Mg-Tb-Nd ternary alloy represents a novel hardenable Mg-based alloy with enhanced strength and favorable creep properties. In the present work we studied microstructure of ultra fine grained (UFG) Mg-Tb-Nd alloy prepared by high pressure torsion (HPT). Lattice defects introduced into the specimen by the severe plastic deformation play a key role in physical properties of UFG specimens. It is known that positron lifetime (PL) spectroscopy is highly sensitive to open volume defects (like vacancies, dislocations, etc.). Therefore, PL spectroscopy is an ideal tool for defect characterizations in the HPT deformed specimens. In the present work we combined PL studies with transmission electron microscopy and microhardness measurements. After detailed characterization of the as-deformed structure, the specimens were step-by-step isochronally annealed and we investigated the development of microstructure with increasing temperature.

Aging and Precipitation Behavior in Supersaturated Al-2%Fe Alloy Produced by High-Pressure Torsion

2014 ◽  
Vol 794-796 ◽  
pp. 766-771 ◽  
Author(s):  
Jorge M. Cubero-Sesin ◽  
Masashi Watanabe ◽  
Makoto Arita ◽  
Zen Ji Horita
Keyword(s):  
High Pressure ◽  
High Pressure Torsion ◽  
Xrd Analysis ◽  
Aged Condition ◽  
Subsequent Aging ◽  
Transmission Electron ◽  
Fe Content ◽  
Average Grain Size ◽  
The Matrix ◽  
Peak Aged

The aging behavior of a cast Al-2 wt.% Fe alloy processed by High-Pressure Torsion (HPT) at room temperature was studied by subsequent aging treatments at 200 °C. Observations by Transmission Electron Microscopy (TEM) revealed that the microstructure after HPT processing reached an ultrafine-grained level with an average grain size in the Al matrix of ~120 nm. The initial eutectic structures were fragmented into particles with sizes of less than 400 nm and partially dissolved in the matrix up to a supersaturated Fe content of ~1% as confirmed by X-Ray Diffraction (XRD) analysis. The peak-age condition was achieved within 0.25 h of aging, which provides the maximum hardness of ~200 HV. Analyses by high-resolution S/TEM show that round particles of Al6Fe with sizes of ~5-10 nm and semi-coherent with the matrix are the dominant precipitates in the peak-aged condition. The hardness increases by aging for 12 h above the as-HPT-processed level of 185 HV. The dominant precipitate phase transforms to Al3Fe in the over-aged condition with a loss of coherency during growth. Enhanced precipitation kinetics was observed because of high density of lattice defects induced by the HPT processing, which were also confirmed by significant recovery in the electrical conductivity of the samples after aging.

scholarly journals Особенности упрочнения структурированного интенсивной пластической деформацией сплава Al-Cu-Zr

2021 ◽  
Vol 63 (10) ◽  
pp. 1572
Author(s):  
Т.С. Орлова ◽  
Д.И. Садыков ◽  
М.Ю. Мурашкин ◽  
В.У. Казыханов ◽  
Н.А. Еникеев
Keyword(s):  
High Pressure Torsion ◽  
High Strength ◽  
Coarse Grained ◽  
X Ray Diffraction ◽  
Microstructural Parameters ◽  
Transmission Electron ◽  
Ultrafine Grained ◽  
Preliminary Annealing ◽  
Coarse Grained State ◽  
Additional Hardening

The effect of small additions of copper on the microstructure and physic-mechanical properties of an ultrafine-grained Al-1.47Cu-0.34Zr (wt%) alloy structured by high pressure torsion after preliminary annealing at 375 °C for 140 h has been studied. As a result of processing, high values of strength characteristics (conditional yield strength 430 MPa, ultimate tensile strength 574 MPa) with an acceptable level of electrical conductivity (46.1% IACS) and ductility (elongation to fracture ~ 5%) have been achieved. On the basis of the microstructural parameters determined by X-ray diffraction analysis and transmission electron microscopy, hardening mechanisms responsible for such high strength have been analyzed. It was shown that Cu plays the key role in strengthening. The addition of copper significantly contributes to grain refinement and, consequently, to grain-boundary hardening. Alloying with copper leads to significant additional hardening (~ 130 MPa) in the ultrafine-grained alloy, which is not typical for coarse-grained state. Segregation of Cu at grain boundaries and the formation of Cu nanoclusters are the most probable reasons for this hardening.

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