Ultrafine-grained Alloy Research Articles

Comprehensive evaluation of corrosion resistance and biocompatibility of ultrafine-grained TiMoNb alloy for dental implants

To address the limited wear resistance observed in traditional titanium alloys, we have developed an ultrafine-grained equiatomic TiMoNb compositionally complex alloy (CCA) with exceptional wear resistance. However, there is a significant lack of in vitro and in vivo evaluation of the TiMoNb CCA for biomedical applications. In this study, we comprehensively evaluate the corrosion behavior, tribo-corrosion performance, biocompatibility, and osseointegration of the TiMoNb alloy. Our findings indicate that the alloy exhibits strong corrosion resistance and stable tribo-corrosion behavior, attributed to the presence of Ti-rich nanoscale precipitates that impede tribo-corrosion-induced shear deformation, along with a protective nanoscale oxide layer. Furthermore, in vitro and in vivo evaluations demonstrate the excellent biocompatibility of the TiMoNb alloy and reveal its ability to promote the regeneration of defective femurs and its favorable bone osseointegration capability. Overall, our study underscores the potential of the TiMoNb alloy as a promising material for dental implants and provides valuable insights into the tribo-corrosion mechanisms of ultrafine-grained alloys.

Achieving superior strength and ductility synergy in bulk ultrafine grained Al-Mg-Sc-Zr alloy via powder pre-aging

Introducing high density of nano-precipitates to recrystallized ultrafine grains is helpful to realize strength-ductility synergy but is a challenging task, because recrystallization and precipitate growth/coarsening usually concur. Here we develop a pre-aging powder metallurgy processing route to achieve such microstructure in Al-Mg-Sc-Zr alloy. During the pre-aging stage, atomic clusters including short-range order are formed within the grains, which provide new sites for the nucleation and enable the formation of fine Al3(Sc, Zr) precipitates. Subsequent high-temperature sintering and hot extrusion lead to grain recrystallization. The nano-precipitates not only further strengthen the ultrafine-grained alloy by Orowan mechanism, but also greatly enhance the strain-hardening rate by dislocation-precipitate interaction, resulting in excellent strength-ductility synergy. The utilization of digital image correlation (DIC) analysis allows for the observation of dynamic strain aging during the tensile process, whereby the strain demonstrates a distinctive step-like transition coinciding with the passage of the Portevin-Le Chatelier (PLC) band. This work provides a new path for improving the mechanical properties of the same type of metallic materials.

Influence of ultrafine-grained structure of Ti-42Nb-7Zr alloy on energy dissipation and storage under quasi-static tension

The ultrafine-grained (UFG) structure and plastic deformation of the Ti-42Nb-7Zr alloy have been investigated using infrared thermography. The initial stage occurs at a constant temperature when the total energy of plastic strain absorbed by the alloy is 1.75 times higher for the UFG alloy, than for the alloy with a coarse-grained structure. This fact is due to substructural strengthening caused by severe plastic deformation and dispersion hardening with ω-phase nanoparticles. The amount of heat released before the UFG alloy fracture is 2 times larger than the amount of stored energy, and this results in localized softening of the UFG alloy prior to its fracture.

Underwater friction stir welding of ultrafine-grained laminated composites produced through accumulative roll bonding process

In this work, ultrafine-grained (UFG) plates of AA2024/AA5083 laminated composite with alternating layers of heat-treatable aluminum AA2024 and strain-hardening aluminum AA5083 were fabricated through accumulative roll bonding (ARB) technique and were subsequently joined using underwater friction stir welding (UFSW). Friction stir welding (FSW) is a solid-state welding method which is suitable for the joining of similar and dissimilar UFG alloys of AA2024 and AA5083, which are mainly used in aerospace and aviation industries. Welding variables, such as pin profile, rotational speed, welding speed, and tilt angle were optimized using the Taguchi optimization technique. Different zones of UFSWed joints including stir zone (SZ), thermo-mechanically affected zone (TMAZ), and heat affected zone (HAZ) were investigated through OM, TEM, and SEM. The results showed that the tapered cylindrical pin, 1000 rpm rotational speed, 110 mm.min−1 welding speed, and 2.5° tilt angle were the optimal welding variables in terms of tensile strength. The microstructural results showed the formation of nano-size, recrystallized equiaxed grains with a size of 500 nm (the same size as that in the UFG base metal) in the optimal sample. The hardness in the weldment of the optimal UFSW sample decreased slightly, so that the efficiency of 85% was presented and the minimum hardness location (MHL) disappeared. The ultimate tensile strength (UTS) of 425 MPa and 64% efficiency were observed in the optimal conditions. Due to the presence of very fine grains and large dislocations, and the uniform distribution of precipitates in the underwater state, high strength and elongation were obtained.

Mechanical softening of CuX alloys at elevated temperatures studied via high temperature scanning indentation

The thermal stability and temperature dependent hardness of ultrafine-grained Cu-alloys CuSn5 and CuZn5 after high pressure torsion are investigated using the high temperature scanning indentation (HTSI) method. Fast indentations are carried out during thermal cycling of the samples (heating-holding-cooling) to measure hardness and strain rate sensitivity as a function of temperature and time. The microstructures after each thermal cycle are investigated to characterize the coarsening behaviour of both alloys.Results show that the thermal stability of the tested alloys can be expressed in terms of several temperature regimes: A fully stable regime, a transient regime in which growth of individual grains occurs, and finally a regime in which the microstructure is fully coarsened. The onset of grain growth is accompanied by high strain rate sensitivity on the order of 0.2–0.3. Furthermore, the obtained hardness and strain rate sensitivity values are in good agreement with continuous stiffness measurement (CSM) and strain rate jump (SRJ) experiments. This highlights the applicability of the HTSI method to the characterization of the thermomechanical properties of ultrafine-grained alloys.

Effect of ultrafine-grained structure and chromium addition on corrosion resistance of Ni-Cr-Al alloys

The present work aims to understand the various scientific aspects related to the corrosion behavior of the ultrafine-grained (UFG) and coarse-grained (CG) Ni-(10,20)Cr-10Al (wt%) alloys in 3.5 wt% NaCl solution based on the passive layer formation on the alloys. In this regard, UFG and CG Ni-(10, 20)Cr-10Al (wt%) alloys were synthesized and characterized. Results of corrosion studies reveal that the UFG structure of the alloys is favorable to enhance the corrosion performance due to their high grain boundary density, which provides nucleation sites for rapid and effective passivation of the alloys by the formation of external Cr2O3 layer instead of mixed oxides/hydroxides. Besides, the Cr addition to the alloys also fosters the Cr-containing passive layer formation. The superior corrosion behavior of the UFG alloys is supported by scanning electron microscopy, electrochemical impedance spectroscopy, and Raman spectroscopy.

Effect of severe plastic deformation on the structure and properties of the Zn–1%Li– 2%Mg alloy

Through the optimization of processing parameters, including pressure, temperature, and deformation degree, a high pressure torsion (HPT) regime was identified. This regime allows for the creation of a unique microstructure in the biodegradable Zn–1%Li–2%Mg alloy, which exhibits exceptional physical and mechanical properties. Following 10 revolutions of HPT treatment (resulting in an accumulated deformation degree, γ = 571) at the temperature of 150 °C and an applied pressure of 6 GPa, the Zn–1%Li–2%Mg alloy displayed notable mechanical characteristics, including a high yield strength (~385 MPa), ultimate tensile strength (~490 MPa), and ductility (44 %) during tensile tests. To elucidate the underlying reasons for these remarkable mechanical properties, an examination of the alloy’s microstructure was conducted employing electron microscopy and X-ray phase analysis (XPA). The study revealed the formation of a distinct microstructure characterized by alternating bands of the α-phase Zn, a mixture of Zn and ~LiZn3 phases, as well as the α-phase Zn containing Mg2Zn11 particles, as a consequence of HPT treatment. Additionally, it was observed that HPT treatment induced a dynamic strain aging process, leading to the precipitation of Zn particles in the LiZn3 phase and the precipitation of Mg2Zn11 and β-LiZn4 particles in the Zn phase. These precipitated particles exhibited a nearly spherical shape. The application of the XPA method helped to confirm that the Zn phase becomes the predominant phase during HPT treatment, and microscopy data showed the formation of an ultra-fine grained (UFG) structure within this phase. A comprehensive analysis of the hardening mechanisms, based on the newly acquired microstructural insights, revealed that enhanced strength and ductility of the Zn–1%Li–2%Mg UFG alloy can be attributed primarily to the effects of dispersion, grain boundary, and heterodeformation-induced hardening, including dislocation strengthening.

MECHANICAL PROPERTIES AND FRACTURE OF ULTRAFINE-GRAINED NEAR β TITANIUM ALLOY UNDER THREE-POINT BENDING

Comparative studies are conducted on the structure and mechanical properties of the ultrafine-grained Ti-5Al-5V-5Mo-1Cr-1Fe alloy obtained by abc pressing and radial shear rolling with subsequent aging. It is shown that the ultrafine-grained structure formed by these methods provides increased strength properties both in tension and in three-point bending compared to the initial coarse-grained state. At the same time, the alloy obtained by abc pressing demonstrates a higher resistance to fracture during three-point bending compared to the alloy obtained by radial shear rolling + aging due to its enhanced ductility. This also determines the ductile pattern of fracture of the ultrafine-grained alloy obtained by abc pressing during three-point bending in contrast to brittle-ductile fracture of the alloy obtained by radial shear rolling + aging.

Precipitation kinetics of precipitates with different orientations and segregation in an ultrafine grained Al–Cu–Mg alloy

The precipitation kinetics of precipitates with different orientations and segregation in an ultrafine grained (UFG) Al–Cu–Mg alloy (AA2024) aged at 210 °C have been investigated using situ small angle X-ray scattering (SAXS), situ wide angle X-ray (WAXS) and Transmission Electron Microscopy (TEM). For UFG alloy, the number and size of (111) S'/S phases are larger than those of (130) S'/S phases on the whole, because spacing of slip plane near (111) S'/S phases is larger than that near (130) S'/S phases, resulting in solute atoms are easier to diffusion near (111) S'/S phases, and (111) S'/S phases are easier to grow, meanwhile, resulting in the critical shear stress for dislocation moving near (111) S'/S phases is smaller than that near (130) S'/S phases, further leading to the dislocation density near (111) S'/S phases is 1.07–1.19 times larger compared to that near (130) S'/S phases during ageing process, which provides more nucleation sites for (111) S'/S phases. After ageing for 10–40 min, the segregation degree of Cu and Mg atoms near dislocations and grain boundaries is increased in UFG alloy, while after ageing for 80 min, the segregation of Cu atoms is decreased and Mg atoms continue to increase, the segregation of Mg atoms begin to decrease after ageing for 120 min.

Preparation of ultrafine-grained Mg–Mn–Ce alloy with high ductility and energy absorption by coupling extrusion and forging

An ultrafine-grained (UFGed) Mg–0.9Mn–0.5Ce (wt.%) alloy with high compressive ductility and energy absorption was developed using a low-temperature deformation method of coupling extrusion and forging. Specifically, the alloy was extruded at 150 °C with an extrusion ratio of 12:1, followed by forging at 200 °C to a true strain of 1.2 along the extrusion direction. The microstructure and plastic mechanism were uncovered using optical microscopy, scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. The microstructure was found to consist of ultrafine dynamically recrystallized (DRXed) grains and fragmented unDRXed grains, exhibiting an average grain size of 1.9 μm after low-temperature extrusion. After forging, new UFGs were gradually generated, a uniform UFGed microstructure with an average grain size of 2.7 μm was obtained, and the texture intensity was decreased as well. The homogenous UFGs and basal slip collaboratively contributed to better comprehensive performance of the UFGed alloy, such as a high compressive ductility of 45.0% and a high energy absorption of 122.72 MJ/m3.

Microstructural modification and mechanical improvement of ultrafine-grained Ti alloy through electron wind force: An innovative approach

This study focuses on the effect of high-density pulsed electric current (HDPEC) on the microstructure and mechanical properties of ultrafine-grained (UFG) Ti–6Al–7Nb (mass%) alloy. After the UFG Ti alloy prepared by high-pressure torsion (HPT), the samples exhibit high tensile yield strengths of 1200 MPa with total elongation of ∼20 %. Interestingly, an unusual improved elongation of ∼33 % with a yield strength of 1100 MPa was obtained in samples processed by HPT plus HDPEC. Quantitative evaluation shows that the improved ductility is attributed to the decreasing of dislocation density. The electron wind force played an important role to promote the movement of dislocation easier with the assistance of local Joule heating during HDPEC processing. It is shown that the bimodal structure with a low dislocation density leads to the high strength and high ductility. It indicated that HDPEC give an effective method to improve the ductility in UFG alloys.

Machinability Features of Ti-6Al-4V Alloy with Ultrafine-Grained Structure

Titanium alloys are widely used in various industries. The most common and well-known titanium alloy is titanium alloy with aluminum and vanadium (Ti-6Al-4V). This alloy is used, for example, in the manufacture of aircraft engines. As part of the development of technologies and the emergence of the evolving requirements for materials, Ti-6Al-4V alloys with ultrafine grains less than 1 μm may become promising. This modification of the alloy has excellent strength characteristics, such as increased fatigue resistance. However, manufacturers are aware of the machinability problem of titanium alloys. To date, a sufficiently high level of understanding of this problem has already been achieved. But, there is practically no information about the machinability of ultrafine-grained alloys and their comparison, in this regard, with the usual coarse-grained version. This study presents the results of experimental studies on the influence of cutting parameters (cutting speed, V, m/min; feed rate, Fz, mm/rev) on the roughness and microstructure of the surface of Ti-6Al-4V samples with coarse-grained and ultrafine-grained structures produced via equal-channel angular pressing. It is shown that turning at a low cutting speed (V = 48 m/min) results in a better surface roughness, Ra, for the coarse-grained sample compared to its ultrafine-grained alloy counterpart. When the cutting speed is increased by 1.5 times (up to V = 72 m/min), on the contrary, the ultrafine-grained sample has a lower surface roughness, Ra, compared to the coarse-grained sample. The differences in the morphology and microstructure of the chips, depending on the microstructure type of the processed alloy, are discussed: the presence of plastic flow lines in the chip microstructure of the turned ultrafine-grained sample and the formation of shear bands, cleavages, and microcracks in the chips of the turned coarse-grained alloy.

Effect of Deformation-Induced Plasticity in Low-Alloyed Al-Mg-Zr Alloy Processed by High-Pressure Torsion

The influence of additional deformation heat treatments (DHTs), implemented by two regimes: (1) annealing and small additional deformation by high-pressure torsion (HPT) at room temperature (RT) and (2) HPT at elevated temperature to 10 turns and small additional HPT at RT, has been studied on the microstructure, mechanical properties and electrical conductivity of ultrafine-grained (UFG) Al-0.53Mg-0.27Zr (wt.%) alloy structured by HPT to 10 turns at RT. As is shown, both types of additional DHT lead to a substantial increase in plasticity (2–5 times) while maintaining high electrical conductivity (~53% IACS) and strength comprising 75–85% of the value in the pre-DHT state of the UFG alloy. The possible physical reasons for the revealed changes in the physical and mechanical properties are analyzed. Comparison of the strength and plasticity changes with the microstructure evolution after DHT of both types indicates that the increase in the density of introduced grain boundary dislocations is the most probable factor providing a tremendous increase in plasticity while maintaining a high level of strength in the UFG alloy under study. An outstanding combination of high strength (370 MPa), high elongation to failure (~15%) and significant electrical conductivity (~53% IACS) was achieved for the Al-Mg-Zr alloy. This combination of properties exceeds those obtained to date for this system, as well as for a number of other commercial conductor alloys based on the Al-Zr system.

Modeling the Effect of Grain Boundary Segregations on the Fracture Toughness of Nanocrystalline and Ultrafine-Grained Alloys

A theoretical two-dimensional (2D) model is proposed that describes the effect of grain boundary (GB) segregations on the fracture toughness of nanocrystalline or ultrafine-grained alloys. It is shown that GB segregations can lead to crack curvature, providing both crack surface roughness and crack deflection near the crack tip. Within the model, the growth of cracks along GBs under the action of a tensile load is considered. The effects of brittle GB segregations on the crack surface roughness and crack deflection near the crack tip are analyzed, and the associated increase in the fracture toughness of the material is calculated. It is shown that toughening can be achieved if segregations are very brittle and occupy a moderate proportion of GBs. In particular, a sufficiently large (up to 50%) fraction of GBs containing very brittle segregations can increase the fracture toughness by 30–35%. The results of the model can be applied to thin nanocrystalline or ultrafine-grained films.

A comprehensive study on size-effect, plastic anisotropy and microformability of aluminum with varied alloy chemistry, crystallographic texture, and microstructure

Fabrication of microparts with large aspect-ratio and complex shapes remains a huge challenge for industries and microforming is a potential solution to manufacture such microparts. However, similarity in specimen-deformation and microstructural length scales during microforming results in size effect, leading to unpredictable plastic behavior and increased process scatter. One approach to counter size effect is by engineering suitable microstructure in the material. In the present work, three grades of Al (AA1070, AA5083, AA2014) with unique alloy chemistry and microstructural profile are processed by cryorolling (CR) to 95% thickness reduction. By imparting controlled postprocess annealing on the CR materials, three distinctive microstructures – (i) ultrafine grained (UFG) with average grain size around 1 μm, (ii) fine grained (FG) with average grain size near to 5 μm, and (iii) coarse grained (CG) with approximate average grain size of 20 μm are engineered. The influence of alloy chemistry, grain boundary engineering and crystallographic texture on microformability are studied. For pure Al (AA1070), the UFG and FG microstructures show superior microformability than the CG counterparts. The equiaxed UFG grains present in these microstructures mitigate the size effect abnormalities by increasing the number of grains in the deformation volume and uniformly distributing the complex microforming strain via grain boundary mediated plasticity. Their corresponding texture containing strong Copper mixed with scattered Cube elements promotes in-plane strain condition and high resistance to localized thinning. Also, the material shows near-zero planar anisotropy that leads to a homogenous in-plane strain distribution. Unlike pure Al, the UFG and FG Al alloys suffer from increased strain localization due to presence of solute clouds and nanoprecipitates. They influence strain-aging (Portevin–Le Chatelier effect), strain gradient hardening phenomenon, and shear propensity during failure of the Al alloys. A composite texture consisting of a combination of Brass, Dillamore, S, and β-fiber elements in the Al alloys is found to be detrimental to their microformability. The Dillamore texture is contributed by formation of adiabatic shear bands during deformation of Al alloys.

Corrosion Resistance of the Welded Joints from the Ultrafine-Grained Near-α Titanium Alloys Ti-5Al-2V Obtained by Spark Plasma Sintering

A solid-phase diffusion welding of coarse-grained and ultrafine-grained (UFG) specimens of titanium near-α alloy Ti-5Al-2V used in nuclear power engineering was made by Spark Plasma Sintering. The failure of the welded specimens in the conditions of hot salt corrosion and electrochemical corrosion was shown to have a preferentially intercrystalline character. In the case of the presence of macrodefects, crevice corrosion of the welded joints was observed. The resistance of the alloys against the intercrystalline corrosion was found to be determined by the concentration of vanadium at the titanium grain boundaries, by the size and volume fraction of the β-phase particles, and by the presence of micro- and macropores in the welded joints. The specimens of the welded joints of the UFG alloy are harder and have a higher resistance to hot salt corrosion and electrochemical corrosion.

Preparation of powder by electrical discharge erosion and sintering of ultrafine WC-5TiC-10Co alloy with high hardness

In this work, studies were carried out on obtaining a powder by electrical discharge erosion (EDE) of a WC-5TiC-10Co cemented carbide, sintering an ultrafine-grained alloy from the obtained powder, and studying the microstructures and properties of the obtained particles and alloys. We have established that with an increase in the pulse energy from 0.5 J to 10 J, the EDE productivity increases linearly. At the same time, energy consumption decreases and tends towards a constant value (3.4–4.2 kWt*h/kg). It has been established that an undesirable change in the carbon content in the resulting powder from the liquid pyrolysis is proportional to the product of the specific energy consumption and the difference in the mole fractions of carbon and oxygen in the liquid. Excess carbon was removed by heat treatment in the appropriate volume of CO2. It has been established that EDE results in a complete dissolution of tungsten in cubic carbide (Ti,W)C, which is retained in the formed particles. During further heat treatment and sintering, new plate-like ultrafine WC grains grow from a supersaturated (Ti,W)C solution. An increased concentration of tungsten is retained during sintering in ultrafine-grained grains of a supersaturated (Ti,W)C solid solution. By reducing the average diameter of the WC grains from 1.45 μm to 0.42 μm and increasing the carbide content (Ti,W)C, the hardness of the obtained alloys increases from 1410 HV in the original alloy to 1650 HV in the sintered alloy. Fracture toughness increases due to formation of lamellar WC grains from 12.9 mPa*m1/2 to 14.1 MPa*m1/2.

Effect of the Texture of the Ultrafine-Grained Ti-6Al-4V Titanium Alloy on Impact Toughness.

In this work, the strength properties and impact toughness of the ultrafine-grained (UFG) Ti-6Al-4V titanium alloy produced by severe plastic deformation (SPD) in combination with upsetting were studied, depending on the direction of crack propagation. In the billets processed by equal-channel angular pressing (ECAP), the presence of anisotropy of ultimate tensile strength (UTS) and ductility was observed, conditioned by the formation of a metallographic and crystallographic texture. At the same time, the ECAP-processed UFG alloy exhibited satisfactory values of impact toughness, ~0.42 MJ/m2. An additional upsetting of the ECAP-processed billet simulated the processes of shape forming/die forging and was accompanied by the development of recovery and recrystallization. This provided the "blurring" of texture and a reduction in the anisotropy of UTS and ductility, but a difference in impact toughness in several directions of fracture was still observed. It is shown that texture evolution during upsetting provided a significant increase in the crack propagation energy. The relationship between microstructure, texture and mechanical properties in different sections of the material under study is discussed.

Low-Temperature Superplasticity and High Strength in the Al 2024 Alloy with Ultrafine Grains.

This study aims to achieve an ultrafine-grained (UFG) Al 2024 alloy superplasticity at temperatures lower than the traditional ones for commercial Al alloys (400-500 °C). The UFG structure with a mean grain size of 100 nm produced in the alloy by high-pressure torsion at room temperature provided a very high strength-microhardness (HV0.1) of 286 ± 4, offset yield strength (σ0.2) of 828 ± 9 MPa, and ultimate tensile strength (σUTS) of 871 ± 6 MPa at elongation to failure (δ) of 7 ± 0.2%. Complex tensile tests were performed at temperatures from 190 to 270 °C and strain rates from 10-2 to 5 × 10-5 s-1, and the values of flow stress, total elongation and strain rate-sensitivity coefficient were determined. The UFG alloy was shown to exhibit superplastic behavior at test temperatures of 240 and 270 °C. For the first time, 400% elongation was achieved in the alloy at an unusually low temperature of 270 °C (0.56 Tm) and strain rate of 10-3 s-1. The UFG 2024 alloy after superplastic deformation was found to have higher strength (150-160 HV) than that after the standard strengthening heat treatment T6.

Effect of Sc, Hf, and Yb Additions on Superplasticity of a Fine-Grained Al-0.4%Zr Alloy

This research was undertaken to study the way deformation behaves in ultrafine-grained (UFG)-conducting Al-Zr alloys doped with Sc, Hf, and Yb. All in all, eight alloys were studied with zirconium partially replaced by Sc, Hf, and/or Yb. Doping elements (X = Zr, Sc, Hf, Yb) in the alloys totaled 0.4 wt.%. The choice of doping elements was conditioned by the possible precipitation of Al3X particles with L12 structure in the course of annealing these alloys. Such particles provide higher thermal stability of a nonequilibrium UFG microstructure. Initial coarse-grained samples were obtained by induction casting. A UFG microstructure in the alloys was formed by equal-channel angular pressing (ECAP) at 225 °C. Superplasticity tests were carried out at temperatures ranging from 300 to 500 °C and strain rates varying between 3.3 × 10−4 and 3.3 × 10−1 s−1. The highest values of elongation to failure are observed in Sc-doped alloys. A UFG Al-0.2%Zr-0.1%Sc-0.1%Hf alloy has maximum ductility: at 450 °C and a strain rate of 3.3 × 10−3 s−1, relative elongation to failure reaches 765%. At the onset of superplasticity, stress (σ)–strain (ε) curves are characterized by a stage of homogeneous (uniform) strain and a long stage of localized plastic flow. The dependence of homogeneous (uniform) strain (εeq) on test temperature in UFG Sc-doped alloys is increasing uniformly, which is not the case for other UFG alloys, with εeq(T) dependence peaking at 350–400 °C. The strain rate sensitivity coefficient of flow stress m is small and does not exceed 0.26–0.3 at 400–500 °C. In UFG alloys containing no Sc, the m coefficient is observed to go down to 0.12–0.18 at 500 °C. It has been suggested that lower m values are driven by intensive grain growth and pore formation in large Al3X particles, which develop specifically at an ingot crystallization stage.