Grain Growth Mechanism Research Articles

Electron Backscatter Diffraction Analysis of Low-Misorientation-Angle Boundary and High-Energy Boundary in the Hot-Rolled Plate of Grain-Orientated Silicon Steel

In order to study the texture evolution and the formation of an inhomogeneous microstructure in hot-rolled plate of grain-orientated silicon steel, Fe3C (hexagonal) and ferrite phases in the subsurface layer were studied using electron backscatter diffraction. The results indicate that fiber texture (ferrite) mainly composed of {441}<104> and (110)[001] Goss oriented grains was formed at a depth of 25% of the thickness of hot-rolled plate. Matrix grains in the subsurface layer were arbitrary separated into irregular large grains (≥40 μm) and fine grains (<40 μm), and the grain boundary characteristics and texture evolution of matrix grains were studied. The results indicated that the formation of the colonies of fine grains was the result of dynamic recrystallization, and high-frequency low-misorientation-angle boundaries (0~20°) were formed between large grains (≥40 μm) and fine grains (<40 μm), which can be considered as the irregularity of large grains caused by solid-state wetting. Due to the texture evolution of large grains (≥40 μm), a large number of high-energy boundaries (20~45°) were formed between irregular large grains (≥40 μm), resulting in rapid consumption between adjacent large grains and the elongation of large grains along the rolling direction. Therefore, it can be assumed that the migration of low-misorientation-angle boundaries (0~20°) under solid-state wetting and high-energy boundaries (20~45°) are important mechanisms for non-uniform grain growth in hot-rolled plate of grain-orientated silicon steel.

Investigating and correlating the photocatalytic activity of synthesised strontium titanate nanopowder with calcination temperature

In this study, SrTiO3 nanoparticles were synthesised in high yield using a simple and low-cost method, followed by calcination. The effect of the calcination temperature in the range from 700 to 1100 °C on the morphology, phase structure, crystallite size, and photocatalytic activity of SrTiO3 nanoparticles was investigated. Analysis of the morphology and structure of the synthesised samples revealed an increase in the average particle size from 70.4 to 361.72 nm as well as crystallite growth with increasing calcination temperature (from 800 to 1100 °C), likely due to the fusion of smaller crystallites into larger ones. A possible pathway for the growth mechanism of strontium titanate grains was also proposed. The SrTiO3 sample calcined at 800 °C exhibited the highest methylene blue (MB) photodegradation efficiency, achieving 100 % degradation within 30 min of irradiation. The pseudo-first-order reaction rate constant k for this sample was determined to be 0.156 min−1, which is almost 1.8 and 14.19 times higher compared to those of commercial P25 and SrTiO3, respectively. The analysis indicated that the high photoactivity of this sample was due to its high crystallinity, relatively small particle size, and optimal light absorption, which enhanced the separation and transport of the photogenerated charges and increased the number of active sites, thereby positively affecting the photocatalytic properties. Additionally, the effects of the initial dye concentration and amount of photocatalyst loaded on the photodegradation efficiency were investigated.

A potential mechanism for abnormal grain growth in Ni thin films on c-sapphire

Normal grain growth (NGG) of a (111) textured Ni film on c-sapphire and abnormal grain growth (AGG) of (100) grains at the expense of this (111) texture has been studied as a function of temperature with and without a capping layer. The grain boundaries (GBs) in the Ni film are controlled by the preferred orientation relationships (ORs) adopted by the Ni grains on the sapphire substrate. The 2 variants of a single OR, Ni(111)<11¯0>//Al2O3(0001)<11¯00>, form a (111) mazed bicrystal with Σ3 GBs. The (100) grains have a single OR, Ni(100)<010>//Al2O3(0001)<11¯00> with 3 variants; their GBs within the (111) grains have the (111)<11¯0>//(100)<010> misorientation.(100) AGG within the (111) mazed bicrystal of the 100 nm Ni film takes place above 1023 K. The orientation transition is driven by the biaxial elastic modulus anisotropy which favors the growth of (100) grains over (111) grains, as this reduces the elastic strain energy induced by the thermal mismatch between Ni and sapphire. (100) AGG is suppressed and the NGG of the (111) texture is slowed down when the film is covered by a 10 nm amorphous alumina layer aimed at inhibiting surface diffusion. Thus, it is proposed that as long as the surface can act as a sink for the point defects diffusing along the GBs, the movement of the GBs is correlated to the diffusivity of atoms and vacancies, which is a function of their misorientation and crystallographic GB structure.

Densification and properties of WC-CoCrFeNi/Co cemented carbide fabricated via spark plasma sintering

The spark plasma sintering (SPS) technique was used to employe WC-CoCrFeNi/Co cemented carbides, incorporating CoCrFeNi and Co as low-coercivity binder phases, resulting in the development of cemented carbides with exceptional mechanical properties. The densification mechanism varying with increasing sintering temperature and the effect of densification on the mechanical properties were investigated using the creep deformation model. In the temperature range of 1100 °C–1300 °C, the main factors contributing to densification behavior are particle rearrangement and grain boundary diffusion due to the viscous flow of the binder phase. The densification mechanism gradually transforms into dislocation climbing with increasing temperature. When the sintering temperature exceeded 1300 °C, the WC grain size increased significantly with increasing temperature and holding time, and the dominant mechanism for grain growth was grain boundary diffusion. The high densification resulted in a substantial increase in effective grain boundary area, thereby increasing both hardness and fracture toughness of the material. Benefiting from the fine grain strengthening effect of the high-entropy alloys (HEAs) and the excellent wettability of Co, a highly dense cemented carbide material with excellent hardness and fracture toughness is achieved at the sintering temperature of 1300 °C, characterized by a relative density of 99.3 %, a hardness of 2064.9 MPa, and a fracture toughness of 11.5 MPa m−2.

Enhanced cross-interfacial growth by thickening transition layers and tailoring grain size of columnar nanotwinned Cu films

Electrodeposited <111>-oriented nanotwinned Cu (NT-Cu) films consist of micron-scale columnar grains and they are thermally stable up to 400 °C. By adding nanoscale equiaxed Cu grains at the bottom of the NT-Cu films, anisotropic large grain growth could be triggered below 200 °C. The grains grew over 50 μm in bonded Cu–Cu films with 5.7 μm thick. Two main factors are identified for the low thermal stability and large grain growth behavior. The grain refining and transition layer thickening are effective to lower the thermal stability of the NT-Cu and reduce the required temperature for recrystallization and grain growth in the NT-Cu film. By increasing the fine-grained layer and refining the grain size of the columnar twinned grains, anisotropic grain growth can occur at 150 °C. The low thermal stability NT-Cu can be employed to completely eliminate the bonding interface at low temperatures in Cu–Cu joints. However, when the fine-grained layer is thicker than a threshold value, normal grain takes place and the bonding interface remains. The mechanism of anisotropic large grain growth was also proposed.

Simulation of recrystallization grain growth in AZ61 magnesium alloy based on GA and 3D CA

In this paper, the Arrhenius constitutive model (GA-Arrhenius) optimized by genetic algorithm (GA) is established, and the dynamic recrystallization (DRX) grain growth process of AZ61 magnesium alloy during hot deformation is simulated by three-dimensional cellular automata (3D CA), and the morphological evolution and grain boundary migration of recrystallized grains are reproduced. The results show that the GA-Arrhenius model accurately predicts the rheological behavior of the material, while the 3D CA model effectively describes the formation and growth mechanism of grains during DRX.

From nano to giant grains: Optimizing Pt thermistors for microbolometers

Pt is a suitable thermistor for use in microbolometers due to its high melting point, chemical inertness, and low 1/f noise. This work explores mechanisms of grain growth to fabricate Pt thin film thermistors for maximizing the temperature coefficient of resistance (TCR). The interplay between the microstructure and TCR is examined by varying Pt film deposition parameters, AlOX interlayer deposition technique, patterning technique, and annealing parameters. A smooth thin film morphology having giant grains of several hundreds of micrometers is achieved by abnormal grain growth, which is not attainable through normal grain growth. The fabrication of thermistor meanders is demonstrated through a combination of processes including Pt film deposition in O2/Ar environment, annealing at 1000 °C in Ar, and ion beam etching. Pt thermistors with a TCR (0 °C – 100 °C) of 0.371 ± 0.001 %/ °C are compatible with microbolometers utilizing carbon nanotube absorbers.

Improving the Magnetic Properties of Electrodeposited Fe-55wt%Ni Alloy via Abnormal Grain Growth Induced by Second-Phase Particles

In this study, pulse reverse current electrodeposition was employed to fabricate Fe-55 wt%Ni alloy. Abnormal grain growth induced by the precipitation of second-phase particles during annealing resulted in a coarse-grained electrodeposited Fe-55 wt%Ni alloy. The grain evolution process during annealing was investigated, and the temperature for abnormal grain growth was determined through the high-temperature confocal microscopy technique. Subsequently, the mechanism of abnormal grain growth was investigated. The results suggest that abnormal grain growth occurs at approximately 1003 K, attributed to the preferential growth of (110) oriented grains due to local strain energy changes caused by the precipitation and coarsening of the second-phase particles (MnS). The preferred orientation of the grains transitioned from (111) to (110). Annealing at 1073 K for 2 h resulted in an average grain size increase to approximately 200 μm. Under these conditions, the magnetic properties of the alloy reached optimal levels, with a magnetization saturation strength of 186.7 emu g−1 and a coercivity of less than 1 Oe. This research presents a novel approach to preparing coarse-grained electrodeposited Fe-Ni alloys, significantly enhancing their magnetic properties.

Exploring microfine magnesite based on thermal decomposition and sintering kinetics: A new direction in the one-step preparation of high-density sintered magnesia

The thermal decomposition and sintering kinetics of microfine magnesite were investigated to inaugurate a new One-step process for preparing high-density sintered magnesia. The optimal parameters for the discharging particle size of magnesite through ball milling were determined using an orthogonal experiment and Three-Way Measures ANOVA. The model for the thermal decomposition process of microfine magnesite was established through TGA-DSC and nonlinear regression analysis. Meanwhile, by describing the sintering process of microfine magnesite in detail through microstructure and CTE, the kinetic mechanisms of grain growth at different sintering stages were obtained. The results revealed that increasing the ratio of ball to powder can quickly obtain microfine magnesite which the bulk density reaches 3.45 g·cm−3 after One-step sintering. The thermal decomposition process required an activation energy of only 124.98 kJ·mol−1, which is much lower than existing technology and followed the Two-dimensional phase boundary reaction mechanism R2. Additionally, the densification process was dominated alternatively by grain boundary diffusion and volume diffusion. This paper provided a detailed theoretical basis and leads a new direction in the One-step preparation of high-density sintered magnesia.

Directional heat treatment technique to prepare columnar grains in a TiAl alloy: Microstructure evolution and deformation behavior

Directional TiAl alloys show excellent comprehensive mechanical properties at high temperature (HT), and their notable attributes in high-temperature deformation resistance offer them promising application potential as structural materials in the aero engine industry. Directional heat treatment (DHT) is an effective local solid phase transformation technology in alloy processing and microstructure control. The directional Ti47Al2Nb2Cr alloys with columnar grains microstructure were fabricated via multiple DHT technology, where the HT deformation performance and corresponding deformation mechanism were both investigated. Results show that both the length in axial and width in radial are increasing with the increase of DHT time, together with the reduce of columnar grains amount, ultra-large columnar grains of 58.6 mm in length and 4.8 mm in width are even obtained, which makes it possible to realize the directional single crystals fabrication further, and the DHT-TiAl alloy may possess a tensile strength of 611.7 MPa at 800 ℃. For the first time, the mechanism of columnar grain growth is considered from the point of thermodynamics via analyzing the driving force of different DHT regions, which is thought to be greatly related to the temperature gradient, and the rule of preferred orientation choosing for columnar grains growth is discussed as well, then we defined the possible conditions of controlling columnar grains steady growth. Eventually, the detailed deformation mechanism of the multiple-DHT treated TiAl alloy was analyzed by transmission electron microscopy (TEM), which demonstrates that the twin intersections together with stress-induced γ variants within γ matrix, and the well-known long period stacking order (LPSO) structure 6 R and 9 R characterized by periodic stacking fault both found near α2 phase and γ twins/pseudo-twins further improved the plastic deformation accommodation and interface compatibility of DHT-TiAl alloy. This observed microstructure transformation and corresponding mechanical performance improvement demonstrate the potential of DHT technology in microstructure improving and properties strengthening for TiAl alloys during practical manufacturing process.

A Common Diffusional Mechanism for Creep and Grain Growth in Polymineralic Rocks: Application to Lower Mantle Viscosity Estimates

AbstractIn a previous study (Okamoto &amp; Hiraga, 2022, https://doi.org/10.1029/2022jb024638), we concluded that diffusion creep and grain growth in polymineralic rocks proceed by a common diffusional mechanism. Here, we built on that finding and estimated lower mantle grain size and viscosity during a single mantle convection cycle dominated by diffusion creep. We approximated the lower mantle as a two‐phase material consisting of bridgmanite + ferropericlase and post‐perovskite + ferropericlase, depending on depth. We used previously reported self‐diffusivities for bridgmanite and post‐perovskite. We predict a bridgmanite grain‐size of tens to hundreds of microns shortly after the phase transition at ∼660 km depth. This size remains relatively constant until the mantle material enters the post‐perovskite zone, which is marked by significant grain growth up to ∼9 mm just prior to upwelling. This size is sufficient to prevent further grain growth until the mantle material reaches the top of the lower mantle. These grain sizes combined with the diffusivities yield viscosities that vary laterally and with depth. At a lateral temperature difference of up to 800 K in the lower mantle, fine‐grained cold downwelling mantle is almost as viscous as, or more likely to be softer than coarse‐grained hot upwelling mantle. The lateral viscosity variations cannot be more than 2 orders of magnitude, and we estimated viscosities of 1018–1020 Pa · s in the upper lower mantle, 5 × 1020–5 × 1022 Pa · s in the lower bridgmanite zone, and 1017–1019 Pa · s in the post‐perovskite zone, which compare well with the values estimated in previous geophysical modeling studies.

Room Temperature Crystallized Phase-Pure α-FAPbI3 Perovskite with In-Situ Grain-Boundary Passivation.

Energy loss in perovskite grain boundaries (GBs) is a primary limitation toward high-efficiency perovskite solar cells (PSCs). Two critical strategies to address this issue are high-quality crystallization and passivation of GBs. However, the established methods are generally carried out discretely due to the complicated mechanisms of grain growth and defect formation. In this study, a combined method is proposed by introducing 3,4,5-Trifluoroaniline iodide (TFAI) into the perovskite precursor. The TFAI triggers the union of nano-sized colloids into microclusters and facilitates the complete phase transition of α-FAPbI3 at room temperature. The controlled chemical reactivity and strong steric hindrance effect enable the fixed location of TFAI and suppress defects at GBs. This combination of well-crystallized perovskite grains and effectively passivated GBs leads to an improvement in the open circuit voltage (Voc) of PSCs from 1.08V to 1.17V, which is one of the highest recorded Voc without interface modification. The TFAI-incorporated device achieved a champion PCE of 24.81%. The device maintained a steady power output near its maximum power output point, showing almost no decay over 280h testing without pre-processing.

Microstructure and properties of Al–Cu–Mg alloy welded by 14 μm single-mode laser small oscillation welding

In this paper, the 14 μm single-mode laser oscillation welding technique was adopted to achieve high-quality welding of 2A12 aluminum alloy. Specifically, its influence on the microstructure and mechanical properties of the joint and the formation mechanism were investigated. The results showed that the ultra-small spot laser (28 μm) was able to achieve sequential oscillation of the molten pool with small amplitude (0.1 mm). The increased frequency caused the average grain size to decrease and the grain boundary length increased in the fusion zone. Meanwhile, the average grain orientation difference increased, and the growth orientation was more dispersed and homogeneous. While reducing weld morphology defects and refining grain microstructure, there was little influence on the penetration and width morphology of the weld. Finally, successfully prepared welds with tensile strength up to 410.4 MPa and elongation simultaneously increased to 4.065 % at 200 Hz. Furthermore, the influence of keyhole oscillation on the molten pool flow at small amplitude was explained by high-speed camera observation, which explored the mechanism of grain growth in the oscillating joints and provided new ideas for the welding of 2xx aluminum alloys.

On the basic mechanism of grain growth: the role of texture on grain boundary migration rate

In this paper we will review some of the many achievements of Statistical Theory of Grain Growth (which is 40 years old, this year!), based on the classic law of grain growth. For instance, we will show that grain growth in presence of texture (which is the usual feature in a real microstructure) is not exclusively depending on the curvature of the grain boundary, as in this case the effect of curvature at the vertexes (in 2-D case) contributes as well (which, depending on the texture pattern, sometimes may be more relevant than curvature along the boundary). Such phenomenon requires a reformulation of Von Neuman’s equation in 2-D by involving, beside the different boundary mobilities, the different energies of the “third” grain boundary, which is pulling the vertex and inducing an extra curvature which is not balanced along the grain perimeter (for simplicity’s sake we are referring to a 2-D case, but the analysis can also be done in 3-D). We can then observe that boundary movement is not only depending on a couple of grains in contact (with the boundary curvature acting like in a bicrystal) but also includes the network of “third” grains operating at the vertexes. The overall consequence is that the growth kinetics and the grain size distribution shape are unique and variable for each texture component which contradicts classic growth laws as well as the expected results for the whole grain size distribution.

Preface

The 8th Conference on Recrystallization and Grain Growth (Rex&GG2023) was held simultaneously in Chongqing, China, and Copenhagen, Denmark during 15 – 19th May 2023. Following the tradition of the Rex&GG conference series, the conference focused on the latest progress in recovery, recrystallization, and grain growth research on a wide range of different materials. The conference sessions not only covered conventional research topics such as fundamental mechanisms of recovery, recrystallization, and grain growth, effects of deformation microstructure, and grain boundary structure, energy, mobility, and migration, but also covered relatively new research directions, including industrial online monitoring, additive manufacturing, and use of artificial intelligence. In total, the conference had 137 oral presentations and 69 posters. Among these, 40 presentations have been extended to full papers and are included in the proceedings of Rex&GG2023.The conference was originally planned to be held in 2022 and was eventually held in a two-site mode in May 2023 due to ongoing uncertainties and travel difficulties related to COVID-19. Chongqing hosted the main site as initially planned, and a second site was set up in in parallel in Copenhagen, for participants facing difficulties in traveling to Chongqing. Each conference site was run with fully joint sessions, with presentations on-site or remote from the other site, mixed within each session. Despite the travel difficulties, more than 300 attendees from 23 countries participated at one of the two conference sites. We greatly appreciated the active participation of all attendees in helping to ensure the success of the conference.Last but not least, on behalf of the international committee, and the local organizing committee, we would like to express our gratitude to all attendees, organizing staff, and volunteers in Chongqing and Copenhagen.List of Editors are available in this pdf.

Microstructure and performance optimization of Al2O3/TiC/TiB2/h-BN@Al2O3 self-lubricating ceramic tool materials

Based on the classical Monte Carlo (MC) model and grain growth theory, the model of h-BN@Al2O3 coated solid lubricant was designed and introduced into the simulation system. The Al2O3/TiB2/h-BN@Al2O3 self-lubricating composite ceramic tool model was designed, and the microstructure evolution of tool materials during hot pressing sintering was simulated. The effects of TiB2 and h-BN@Al2O3 content on the microstructure of ceramic materials were studied, and finally the optimized composition parameters were obtained. The effects of sintering temperature and sintering pressure on the microstructure of tool materials were studied, and reasonable sintering parameters were obtained. The experimental results show that under the sintering temperature of 1650℃ and sintering pressure of 32Mpa, the ceramic material with 10%volTiB2 and 5%volh-BN@Al2O3 has the best mechanical properties, that is, the bending strength is 610MPa, the hardness is 17.9GPa, and the fracture toughness is 5.17 MPa·m1/2. SEM analysis shows that the grain growth of the material is uniform, the solid lubricant is well combined with the matrix, and the material has a good microstructure. Comparing the simulation results with the previous experimental results, it is found that the results are in good agreement, which indicates that the designed MC model reliably reflects the physical process of material grain growth, and has certain guiding significance for further research on the mechanism of grain growth.

Self-toughening mechanism of the ZrO2 scale and the precipitation of Sn during the steam oxidation of ZIRLO™ at 1200 °C

The steam oxidation behavior of ZIRLO™ at 1200 °C was investigated using a thermogravimetric analyzer. The microstructure of the oxide was analyzed using SEM, EBSD, and FIB+TEM in depth. Very long “spaghetti-like” columnar oxide grains were formed owing to the intracrystalline diffusion of O2− and the high oxidation temperature. These grains extended from the oxide/matrix interface to a thin outer equiaxed grain layer. The special growth mechanism of the columnar grains determines the unique properties of the oxide scale, such that their structural integrity cannot be destroyed. Therefore, the oxidation kinetics followed a parabolic law throughout the oxidation process without breakaway behavior. Observations revealed the presence of twins, slip bands, and subgrains within the ZrO2 grains, which were identified as the primary manners of oxide deformation under stress. The residual stress and phase distribution along the thickness of the oxide were investigated using synchrotron radiation X-ray diffraction. The oxide was almost completely transformed into a m phase after oxidation. The compressive stress inside the oxide was relatively low, indicating that the stress was relaxed. Transformation toughening, plastic deformation, densely arranged columnar grains, and the absence of grain boundaries parallel to the direction of compressive stress constitute the self-toughening mechanism of the ZrO2 scale. Zr5Sn3, ZrSn2, and β-Nb second phase particles were observed at the ZrO2 grain boundaries and inside the ZrO2 grains. The outward diffusion of Sn in the liquid state and the peritectic reaction can result in the formation of voids at the edges of the second phase particles.

Comparison of (K0.5Na0.5)NbO3 Single Crystals Grown by Seed-Free and Seeded Solid-State Single Crystal Growth.

(K0.5Na0.5)NbO3-based piezoelectric ceramics are of interest as a lead-free replacement for Pb(Zr,Ti)O3. In recent years, single crystals of (K0.5Na0.5)NbO3 with improved properties have been grown by the seed-free solid-state crystal growth method, in which the base composition is doped with a specific amount of donor dopant, inducing a few grains to grow abnormally large and form single crystals. Our laboratory experienced difficulty obtaining repeatable single crystal growth using this method. To try and overcome this problem, single crystals of 0.985(K0.5Na0.5)NbO3-0.015Ba1.05Nb0.77O3 and 0.985(K0.5Na0.5)NbO3-0.015Ba(Cu0.13Nb0.66)O3 were grown both by seed-free solid-state crystal growth and by seeded solid-state crystal growth using [001] and [110]-oriented KTaO3 seed crystals. X-ray diffraction was carried out on the bulk samples to confirm that single-crystal growth had taken place. Scanning electron microscopy was used to study sample microstructure. Chemical analysis was carried out using electron-probe microanalysis. The single crystal growth behaviour is explained using the mixed control mechanism of grain growth. Single crystals of (K0.5Na0.5)NbO3 could be grown by both seed-free and seeded solid-state crystal growth. Use of Ba(Cu0.13Nb0.66)O3 allowed a significant reduction in porosity in the single crystals. For both compositions, single crystal growth on [001]-oriented KTaO3 seed crystals was more extensive than previously reported in the literature. Large (~8 mm) and relatively dense (<8% porosity) single crystals of 0.985(K0.5Na0.5)NbO3-0.015Ba(Cu0.13Nb0.66)O3 can be grown using a [001]-oriented KTaO3 seed crystal. However, the problem of repeatable single crystal growth remains.

Abnormal grain growth behavior and mechanism of 6005A aluminum alloy extrusion profile

Peripheral coarse grain (PCG) structure is a common microstructural defect appearing in the aluminum alloy extrusion process, which seriously affects the mechanical properties of the profiles. In this work, a series of extrusion experiments and numerical simulations were conducted to investigate the influence of billet temperature and ram speed on the microstructure, mechanical properties and thickness of PCG layers of 6005A aluminum alloy profiles. The mechanism of abnormal grain growth (AGG) occurring on the surface and in the core of profiles was revealed. The result showed that lower ram speed could suppress the formation of coarse grains. The AGG on the surface of the profiles was activated by the shear deformation and lattice distortion derived from the friction on the interface between the profile and die. When the billet was heated to a relatively high temperature, dynamic recrystallization (DRX) was dominant, and the Cube{100}<100> and R-Cube{100}<110> grains underwent abnormal growth to form surface coarse grains. When the billet was heated to a relatively low temperature, the degree of static recrystallization (SRX) became stronger, and the Goss{110}<100> and R-Cube{100}<110> grains underwent abnormal growth to form surface coarse grains. The AGG in the core of profiles was activated by the large grain boundary misorientation and a strain gradient formed because the Cube{100}<100> recrystallized grains were surrounded by the Copper{112}<111> and Brass{110}<112> deformed grains. The second phases in the 6005A aluminum alloy extrusion profiles were mainly β (Mg2Si) and AlFeMnCrSi. As the billet temperature increased, more β phases dissolved into the aluminum matrix, thus enhancing the strength and hardness of the profiles. As the ram speed decreased, the thickness of PCG layers reduced, thus resulting in higher strength and hardness of the profiles. Due to the integrated effect of solution strengthening and grain refinement strengthening mechanisms, the combination of extrusion parameters for the profile to obtain the best mechanical properties was determined as 540 °C × 0.5 mm/s.

Nanotwin stability in alloyed copper under ambient and cryo-temperature dependent deformation states

Nanometer size grains, solid solution strengthening, low temperatures, and a high density of nanotwins can provide significant strengthening to a material. Nevertheless, under loading the microstructure may evolve altering the effect of grain size, twin density, etc. on this strengthening. In some cases, these effects can be coupled as in detwinning, which is a mechanism for cryogenic grain growth. In this work, a series of copper nanotwinned columnar grains are solid solution alloyed with aluminum and subject to ambient and cryogenic (−196 °C) environments during mechanical indentation, with the influence of alloying on the detwinning evolution studied. Under indentation, at a lower aluminum solute content (2 at.%), the columnar grains bent corresponding to a loss of twins. At a higher aluminum solute content (8 at.%), the grains shear and retain the nanotwins. Atomistic-scale simulations reveal an increase in the incoherent twin boundary velocity with decreasing temperature, but this boundary velocity is reduced with increasing alloy solute content. The coupling of solid solution strengthening and nanotwin stabilization is then used to explain the microstructural stability as a function of indentation at different temperature conditions.