Figure - available from: Journal of Materials Science
This content is subject to copyright. Terms and conditions apply.
The Hall–Petch relationship for the ultrafine-grained AZ91 alloy in the current work and for AZ31 and AZ61 alloys processed by HPT and ECAP
Source publication
An investigation has been conducted on AZ91 magnesium alloy processed in high-pressure torsion (HPT) at 296, 423 and 473 K for different numbers of turns. The microstructure has altered significantly after processing at all processing temperatures. Extensive grain refinement has been observed in the alloy processed at 296 K with apparent grain size...
Similar publications
Low-carbon steel (0.2 mass%) samples were austenitized and quenched at a cooling rate of 10°C/s under GPa level high pressure. The morphology, lattice constant, and order degree of C atom distribution of high-pressure quenching martensite were characterised and analyzed by TEM, EBSD, XRD, and Mössbauer. Besides, the transformation characteristics a...
TWIP steel Mechanical properties Grain size effect Texture Kernel average misorientation a b s t r a c t The development of microstructure and texture of twinning-induced plasticity (TWIP) steel sheet during ECAP at two temperatures (250 and 350) up to four passes were investigated. The high chromium content is the differential of this TWIP steel,...
Molecular dynamics (MD) Simulation
has been employed to study the compression
behaviour of twinned copper nanowires at fixed
strain rate of 1 x 10 10 s -1 . FCC structure of copper
nanowires are subjected to uniaxial compression at
0.1K temperature. Copper nanowires of varying
diameters have been chosen (2.88 nm and 5.76 nm).
Embedded Atom Model (E...
Molecular dynamics simulation is applied to study the crack propagation in austenitic steel containing precipitation. Based on the experimental results, models containing precipitation with two shapes and three volume fractions are constructed. The interactions of the crack with precipitation, dislocation, twin and stacking faults are investigated....
The present article studied the effect of ultrasonic surface rolling process (USRP) on the microstructure and wear behavior of a selective laser melted Ti-6Al-4V alloy. Surface characteristics were investigated using optical microscope, nano-indentation, scanning electron microscope, transmission electron microscope and laser scanning confocal micr...
Citations
... -dislocations theory [3,4], -pressure processing influence on metals and alloys structure and properties experimental data analysis results [5,6], -crystal lattice microscopic defects behavior under developed and limited plastic deformation [7,8] conditions modeling results, using phenomenological and other approaches to solving problems of deformation theory, etc. ...
Purpose. Based on existing criteria for predicting the suitability of metals and their alloys for manufacturing products from them by deformation or casting analysis develop a set of dimensionless parametric criteria and their quantitative scales. Their using will allow increasing the predicting accuracy of metals and alloys for their processing by pressure or casting suitability and feasibility. Methodology. The work uses phenomenological approach to systematic analysis results of metals and alloys mechanical and individual casting properties interpreting under uncertainty conditions, drawing on literature reference data, expert evaluation data and the authors’ own research results. The authors’ own data have been obtained experimentally using standard methods for mechanical properties determining and due to original authors’ method for technical purity metals and alloys based on them cast samples values of their absolutely hindered linear shrinkage determination during casting. Findings. The authors first proposed parametric dimensionless criteria and scales to them (criteria groups). Their application allows one, through such groups combinations, to assess suitability of any alloy or metal for its use possibility for products manufacturing by casting and/or pressure processing. Originality. For the first time dimensionless parametric criteria have been developed and proposed for use at initial stages of new alloys or technologies elaboration for products from them manufacturing as well as their quantitative scales for preliminary assessment (prognosis) of alloys processing feasibility by pressure or casting, regardless of their type and method. Practical value. Developed criteria and their quantitative scales using will allow alloys developers and specialized enterprises employees to save time and expenses both for alloy elaboration and for its implementation into production.
... The thin discs were formed by extruding the rod, resulting in initial thicknesses of 1.5 mm and ultimate thicknesses of 0.85 mm. The high-pressure and high-temperature (HPT) processing was carried out at temperatures of 296 K utilizing an HPT facility that has been extensively described in a recent publication [18]. The processing of HPT was performed at a rate of 1 revolution per minute, using 3.0 GPa as an applied pressure at different turns of one turn (N = 1) and ten turns (10 turns). ...
In this research, the nanoparticles (NPs) of magnesium alloy (Mg–Al-Zn) were prepared using a laser ablation technique in a solution and then deposited on porous silicon. The structural characterization, electrical, and spectral properties of the nanoparticles deposited on the porous silicon were investigated. Firstly, the initial alloy was made as a bulk nanostructured alloy using high-pressure torsion processing at a grain size of 100 nm and then subjected to laser ablation at different powers of 500, 600, 700, 800, and 900 mJ, to produce metallic nanoparticles at a minimum particle size of 5.6 nm. Secondly, metallic nanoparticles were deposited on the porous silicon. Porous silicon (PS) was fabricated by photo-electrochemical etching (PECE) on an n-type crystalline silicon (c-Si) wafer with (111) orientation An etching current density of 20 mA/cm² was applied for 15 min in an etchant medium of a 20% concentration of HF in the aforementioned etching process. The resultant particles were analyzed using the X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), and UV–visible spectrophotometry, as well as the electrical properties and photodetection studies were achieved here. The XRD data indicated the presence of Mg–Al-Zn NPs with a hexagonal wurtzite structure at a distinct diffraction peak at 28.5°. The morphological characteristics of Mg–Al-Zn nanoparticles deposited on the porous silicon indicated that the nanoparticle layer predominantly comprises particles with various shapes and sizes, randomly distributed on the porous silicon, with a relatively large particle size of an average of 24.15 nm when using a laser power of 500 mJ in the ablation process. The optical characteristics of the synthesized nanoparticles showed a rise in the value of the band gap with the augmentation of wavelength. Current–voltage (I-V) characterization showed there was an ohmic contact between deposited samples and electrodes. The photo-detector investigation yielded spectrum responsivity curves with three distinct zones. The initial region in the curve is ascribed to the assimilation of ultraviolet (UV) radiation by the Mg–Al-Zn NPs. The second region was attributed to the absorption of visible light by the PS layer, whereas the third peak resulted from the edge absorption of the Si substrate. The Mg–Al-Zn NPs/PS photodetector demonstrated a responsivity of 0.41 A/W when using a laser intensity of 900 mJ. The findings of this work open the way for future investigations to utilize such complex metallic systems as in Mg–Al-Zn NPs in photodetectors and optoelectronic devices utilizing complex metallic systems with advanced properties.
... Wrought alloys are considered to display the lowest workability of magnesium alloys at room temperature yet have the greatest strength. In this category, the magnesium-aluminum system is the most important in alloys such as AZ31, AZ61, Mg-8Al-1Zn, and AZ91 [19][20][21][22]. It is well known that increasing the Al content in Mg alloys will increase the strength of the alloys. ...
Mg–8Al–1Zn magnesium alloy was successfully processed using deferential speed rolling (DSR) at temperatures of 400 and 450 °C for thickness reduction of 30, 50, and 70% with no significant grain growth and dynamic recrystallization. Using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), the rolled microstructures were examined. Although the results indicate a slight reduction in grain size from the initial condition, the DSR processing of alloy at an elevated temperature was associated with a significant number of twins and a distribution of the fine particles of the second phase. The strength in terms of microhardness measurements and strain hardening in terms of shear punch testing was significantly improved in the rolled microstructure at room temperature. The existence of twins and widely distributed second-phase fine particles at twin boundaries reflected positively on the extent of the elongations in terms of shear displacements when microstructures were tested at elevated temperatures in the shear punch testing.
... [48][49][50][51] Therefore, the existence of relatively homogenous fine intermetallic particles within the alloy matrix hinders dislocation motion and grain growth at ambient and elevated temperatures, respectively, resulting in the improvement of the ambient temperature strength and superplastic behaviour at elevated temperatures. 25,52 These outcomes were supported by the current findings of highly-dispersed intermetallic nanosized particles, extensive grain refinement and considerable dislocation density in the severely plastic deformed Al-Si-Cu alloy in comparison with their additively manufactured and conventional counterparts. ...
Ultrafine-grained Al–9%Si–3%Cu alloy was achieved by a combination of laser powder bed fusion (LPBF) additive manufacturing and high-pressure torsion (HPT) processing in this investigation. The alloy was initially deposited layer-by-layer using a bi-directional scan strategy in LPBF with a scan rate of 1000 mms ⁻¹ , a layer thickness of 40 µm and a hatch spacing of 200 µm, leading to a melt pool morphology with an average width of 150 µm and differing lengths. This led to a grain size of 722 nm and a dislocation density of 1.1 × 10 ¹⁴ m ⁻² . This as-deposited alloy was then processed using HPT at room temperature using an applied pressure of 6.0 GPa and at a speed of one revolution per minute for different numbers of turns: half, one, five and ten turns. The alloy after HPT processing showed ultrafine grains with a grain size of 66 nm, well-dispersed nanosized intermetallic particles with sizes of 50–90 nm, the disappearance of the pool morphology and a notable dislocation density of about 6.2 × 10 ¹⁴ m ⁻² for the ten turns HPT-processed alloy. The as-deposited and subsequently HPT-processed samples were tensile tested at 298 and 573 K at different strain rates between 10 ⁻⁴ and 10 ⁻¹ s ⁻¹ . The elongation-to-failure and tensile strength were recorded and the fracture surfaces were also inspected using scanning electron microscopy and then correlated with the manufacturing, processing and tensile testing conditions. The alloy performance in tensile testing has been evaluated at ambient and elevated temperatures in terms of structural evolution and fractography for the first time. Ultrafine α-aluminium grains and nanosized eutectic silicon particles obtained by room temperature HPT-processing of the alloy have significantly improved the mechanical properties and microstructural stability at ambient and elevated testing temperatures for the HPT-processed additively manufactured alloy compared to the as-deposited additively manufactured and counterpart conventional alloys. The HPT-processed tensile samples showed a significant tensile strength of 700 MPa at 298 K and elongation-to-failure of 220% at 573 K, which is higher than that seen in the as-deposited tensile samples where 400 MPa and 106% are observed under the same testing conditions. Fractographic observations demonstrated that mixed brittle and shear ductile fractures dominated in the as-deposited tensile samples at 298 K, and tension ductile fracture dominated at 573 K. However, the HPT-processed tensile samples exhibited tension ductile and shear ductile fractures at 298 K, and tension ductile fracture at 573 K. The ultrafine-grained microstructure produced by the HPT application in the LBPF-manufactured alloy controls effectively the fracture mechanisms, dimple morphology and thus strength and elongation in comparison with the as-deposited additively manufactured microstructure.
... Severe plastic deformation (SPD) has been demonstrated as a feasible means to process Mg materials, resulting in refined microstructures and ultimately improved properties [4] . SPD techniques such as equal channel angular pressing (ECAP) [5] , multi-directional forging [6] , hydrostatic cyclic extrusion compression (HCEC) [7] , and high-pressure torsion (HPT) [8] are being used to process alloys of the Mg-Al system and successfully produce microstructures with fine or ultrafine grains and refined secondary phase particles. In this context, a new processing technique has been recently proposed for the SPD of lightweight materials, the constrained friction processing (CFP). ...
Constrained Friction Processing (CFP) is a novel solid-state processing technique suitable for lightweight materials, such Mg- and Al-alloys. The technique enables grain size refinement to fine or even ultrafine scale. In this study, the effect of CFP on the microstructural refinement of AM50 rods is investigated in terms of particle size and morphology of the eutectic and secondary phases originally present in the base material, in particular the eutectic beta-Mg17Al12 and Al-Mn phases. For that purpose, as-cast and solution heat-treated base material and processed samples were analyzed. The Al8Mn5 intermetallic phase was identified as the main secondary phase present in all samples before and after the processing. A notorious refinement of these particles was observed, starting from particles with an average equivalent length of a few micrometers to around 560 nm after the processing. The refinement of the secondary phase refinement is attributed to a mechanism analogous to the attrition comminution, where the combination of temperature increase and shearing of the material enables the continuous breaking of the brittle intermetallic particles into smaller pieces. As for the eutectic phase, the results indicate the presence of the partially divorced beta-Mg17Al12 particles exclusively in the as-cast base material, indicating that no further phase transformations regarding the eutectic phase, such as dynamic precipitation, occurred after the CFP. In the case of the processed as-cast material analyzed after the CFP, the thermal energy generated during the processing led to temperature values above the solvus limit of the eutectic phase, which associated with the mechanical breakage of the particles, enabled the complete dissolution of this phase. Therefore, CFP was successfully demonstrated to promote an extensive microstructure refinement in multiple aspects, in terms of grain sizes of the alpha-Mg phase and presence and morphology of the Al-Mn and eutectic beta-Mg17Al12.
... 59 The latter is in line with the Hall-Petch relation for hardness, which states that smaller grain sizes result in increased hardness. 60 Figure 8 represents the impact of some different SPD processes on the mechanical properties of AM60 alloy. The results show that the first pass of M-TCEE has a more pronounced impact on yield strength, ultimate tensile strength, and elongation compared to other methods. ...
The current study uses a modified tube cyclic expansion extrusion (M-TCEE) as a novel severe plastic deformation method to improve the microstructure and properties of AM60 magnesium alloy tubes. Employing a bulk rod-shaped punch in the M-TCEE process makes it feasible to apply greater pressing forces without worrying about the buckle of the punch, which is a problem encountered when using the traditional TCEE method that involves a hollow tubular punch. Consequently, this advancement allows for the manufacturing of tubes with increased length-to-diameter ratios. By undergoing the process, the initial large grains are refined and utilized to generate a bimodal grain structure that includes coarse cores encompassed by fine grains. The findings demonstrate that by performing the M-TCEE process, the yield strength increases by 78% compared to its initial value of 79 MPa, the ultimate tensile strength increases ~ 56% compared to its initial value of 147 MPa, and the ductility almost doubled (from ~ 2.7% to ~ 5.3%). Additionally, the microhardness rose from 56 HV to 82 HV. Also, the corrosion behavior of AM60 tubes is improved by the M-TCEE process, as indicated by the hydrogen evolution curves. Overall, the M-TCEE method has the potential to improve the microstructural, mechanical, and corrosion characteristics of AM60 tubular samples.
... This confirms that Mg-SiC gets harder as the number of HPT processing turns increases. However, the trend in the figure does not show that the increase is monotonic, apparently the curves flatten out towards higher strains, which indicates a tendency towards hardness saturation (Al-Zubaydi et al., 2016;Xu et al., 2008;Zhilyaev et al., 2007) in the HPT processed Mg-SiC. This shows that any HPT processing turns beyond 5 turns can be considered excessive especially when the gain acquired from an extra amount of hardness in the material does not warrant the amount of energy required to process the extra HPT turns. ...
... Another observation is that the specimen size (thickness and diameter) under the test conditions was small enough to yield almost uniform grain sizes and microhardness values throughout its radial distance at any given number of processing turns. Larger samples at moderate hydrostatic pressures and HPT turns tend to exhibit coarser grains at the centre than around the edges hence the microhardness values at the center also tend to be lower than at the edges (Al-Zubaydi et al., 2016;Zhilyaev et al., 2007). Other researchers (Huang et al., 2020) have however observed that HPT processed Al-0.1% Mg alloy exhibited lower hardness values at the disc edges than at its center after half, single and three turns, and that the size of the hard region in the disc center reduced as the number of turns increased from half to three turns. ...
Without a doubt, lightweight materials of high strength are in high demand in the automotive, aerospace, biomedical, and other industries that require such materials. Processing or manufacturing such materials has been a vital topic in contemporary research, as well as material development in the industry. A possible solution for the processing of lightweight materials of high strength is to target lightweight materials by nature such as magnesium and improve their mechanical properties such as stiffness, strength, and hardness. The aforementioned properties are sometimes achieved by processing soft and light materials through High-Pressure Torsion. In this work, Magnesium with Silicon Carbide nanoparticles (Mg-SiC) was strengthened and hardened through the High-Pressure Torsion (HPT) processing technique. The samples were compressed with a pressure of 6.0 GPa and twisted at the rotating speed of 1 rpm with varying numbers of turns N = 0, N = 1, N = 5 and N = 10 at a temperature of 23°C. The processed samples were prepared for the experimental investigation of microstructural characterization and hardness test examinations. Microstructural results showed that grain refinements of material can be achieved through HPT processing methods, which reduced the average grain sizes of unprocessed (N = 0) Mg alloy samples from 149.9 µm to 27.1 µm after processing ten turns. However, hardness test results do not indicate any significant improvement after one HPT processing turn although homogeneity is attained at five processing turns within the nanocomposites.
... 85,155,156) It can be seen that an AZ31 alloy subjected to HPT processing has several times smaller grain size (³100200 nm) compared to the alloy processed by ECAP at elevated temperatures (³0.99 µm, see Table 1), which is accompanied by a significant increase in hardness (³120 HV) 140,144,147,157) compared to ³87 after ECAP. 158) For the AZ91 alloy with a higher aluminium content, a spectacularly small grain size of about 35 nm was observed after HPT processing at ambient temperature, 159) which was reflected in an increase in hardness to 135 HV. A similar hardness value (130 HV) was obtained for the AM60 alloy after grain refinement from 16 µm to 800 nm after only 1/2 HPT turn. ...
Ultra-fine grained and even nanostructured magnesium alloys obtained by processing with methods of severe plastic deformation (SPD) are promising biomaterials for absorbable orthopaedic implants due to their enhanced mechanical properties, adequate corrosion resistance and biocompatibility. This paper presents an overview of the impact of the most important SPD methods – equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) – on microstructure refinement and improvement of the mechanical properties of magnesium alloys intended for medical implants. Several selected groups of magnesium alloys which have the potential for use as bioabsorbable implants are discussed. The presented results of many years of research indicate the beneficial effect of SPD methods on obtaining ultra-fine and even nanostructures of magnesium alloys with improved mechanical and better functional properties, which are necessary for bioabsorbable implants.
... It is now well recognized that high-pressure torsion (HPT) is one of the most efficient techniques of severe plastic deformation (SPD) that can produce materials with excellent grain refinement and outstanding mechanical properties at room temperature (RT). [1] Moreover, HPT processing allows materials having low crystal symmetry, such as magnesiumbased alloys having hexagonal close-packed (HCP) structures, to be deformed at RT. [2][3][4][5][6][7][8] Significant grain refinement, to the range of %110-250 nm, was reported using HPT processing in several Mg-based alloys. [4,5,[8][9][10][11][12] The mechanism responsible for grain refinement in these Mg-based alloys is dynamic recrystallization (DRX) due to the lack of a sufficient number of active slip systems. ...
... [1] Moreover, HPT processing allows materials having low crystal symmetry, such as magnesiumbased alloys having hexagonal close-packed (HCP) structures, to be deformed at RT. [2][3][4][5][6][7][8] Significant grain refinement, to the range of %110-250 nm, was reported using HPT processing in several Mg-based alloys. [4,5,[8][9][10][11][12] The mechanism responsible for grain refinement in these Mg-based alloys is dynamic recrystallization (DRX) due to the lack of a sufficient number of active slip systems. [13] Specifically, it is a discontinuous DRX process in which an array of new fine grains form along the original grain boundaries in a necklace-like structure in the process known as a strain-induced boundary migration (SIBM) mechanism. ...
High‐pressure torsion (HPT) processing is successfully applied to fabricate a novel hybrid material from separate discs of AZ31 (Mg–3Al–1Zn, wt%) and Mg–0.6Gd (wt%) alloys by straining through numbers of rotations, N, of 1/4, 1/2, 5, 10, and 20 turns at room temperature. The microstructure and texture are investigated near the bonding interface through the disc diameter using electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The microstructure exhibits two grain refinement regimes with the first occurring during an equivalent strain range, εeq, of ≈0.3–72 and the second during εeq from ≈72 to 517. The general texture changes from B‐fiber to Y‐fiber and C2‐fiber through the HPT processing. The resultant microstructures and textures of this hybrid alloy are examined separately for the AZ31 and Mg‐0.6Gd alloys and found controlled by the presence of twinning, slip systems, and second phases and the occurrence of different dynamic recrystallization mechanisms.
... The alloy rod was cut using a wire discharge machine into discshaped samples with diameters and thicknesses of 10 mm and 0.85 mm, respectively, to be placed between the HPT anvils for processing. Processing through HPT was carried out at room temperature through a quasi-constrained mode with 6.0 GPa as applied pressure and at different turns of 1/2, 1, 5, and 10 at speed of 1 revolution per minute [19]. The sample's thickness after 10 turns was about 0.7 mm. ...
The tensile properties of an ultrafine-grained Al–9%Si–3%Cu alloy deposited by the laser powder bed fusion process have been investigated in this work. The additively manufactured (AM) alloy was subjected to high-pressure torsion processing at room temperature successfully at different number of turns in HPT and then inspected through hot tensile testing at 298 and 573 K using strain rates ranging from 10–1 to 10–4 s⁻¹. The processed alloy showed extensive refinement and high dislocation density that was associated with considerable strength at ambient temperature. The as-deposited and processed samples of the alloy exhibited significantly higher tensile strength and elongation under hot deformation conditions compared with their cast counterpart alloys. The room temperature-HPT processing presented ultrafine α-Al and well-distributed nanosized eutectic Si particles which significantly improved the tensile behaviour and thermal stability of the processed microstructures. The formation of fibrous structures has enhanced the flow behaviour and cavitation resistance at the elevated testing temperature. The current work indicates the impact of room temperature-HPT processing on the mechanical performance of the controllable AM-deposited alloy to meet industrial needs without further heat treatments or alloying additions.
