Alloy Phase Research Articles

Antiferromagnetism and Phase Stability of CrMnFeCoNi High-Entropy Alloy.

It has long been suspected that magnetism could play a vital role in the phase stability of multicomponent high-entropy alloys. However, the nature of the magnetic order, if any, has remained elusive. Here, by using elastic and inelastic neutron scattering, we demonstrate evidence of antiferromagnetic order below ∼80 K and strong spin fluctuations persisting to room temperature in a single-phase face-centered cubic (fcc) CrMnFeCoNi high-entropy alloy. Despite the chemical complexity, the magnetic structure in CrMnFeCoNi can be described as γ-Mn-like, with the magnetic moments confined in alternating (001) planes and pointing toward the ⟨111⟩ direction. Combined with first-principles calculation results, it is shown that the antiferromagnetic order and spin fluctuations help stabilized the fcc phase in CrMnFeCoNi high-entropy alloy.

3D morphological evolution of the Fe-Rich phase and mechanical properties of the recyclable A356 alloy

Efficient utilisation of recycled aluminium promotes low-carbon and green manufacturing in the aluminium industry. However, the low tolerance of Al for Fe content limits its application. The morphological evolution of the Fe-rich phase and the mechanical properties of recycled A356 alloys with varying Fe contents were investigated using optical microscopy (OM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), synchrotron radiation X-ray computed tomography (SRXCT), and Thermo-Calc thermodynamic calculations. The results show that with increasing Fe content, the morphology of the Fe-rich phase transformed from fine-granular and short rod-like structures into coarse needle-like and Chinese-script. In three dimensions (3D), the larger Fe-rich phases displayed a multibranched structure composed of rod-like and plate-like phases rather than a single morphology. Notably, at an Fe content of 0.4 %, the Fe-rich phases presented Chinese-script and short rod-like shapes in sections but did not significantly change the 3D morphology or type of the Fe-rich phase. However, the Fe-rich phases in the 0.4 %Fe alloy exhibited higher thickness and sphericity, which improved the ductility of the alloy. Thermodynamic calculations indicate that the initial formation temperature of the Fe-rich phase in the 0.4 % Fe alloy overlaps with that of the Al-Si eutectic reaction, which is referred to as the critical Fe content. At the critical Fe content, the ternary eutectic reaction of Al-Si-(AlFeSi) suppressed the rapid growth of the Fe-rich phase and mitigated their negative impact on ductility.

The effect of pre-heat parameters and final-heat parameters on microstructure evolution and mechanical properties of Mg-Gd-Y-Zn-Zr alloy

In this study, an ultra-high strength Mg-13Gd-4Y–0Zn-0.5Zr (wt.%) alloy with tensile yield strength (TYS) of 456 MPa and ultimate tensile strength (UTS) of 486 MPa was prepared by using different pre-heat parameters and subsequent final-heat treatment combined with backward extrusion (BE) deformation process. It was shown that the pre-heat teratment could significantly enhance the UTS and TYS of the secondary backward extruded (BEed) alloy compared with none treatment. The reason was that the pre-heat treatment promoted the particle stimulated nucleation (PSN) mechanism and continuous dynamic recrystallization (CDRX), significantly increasing the fraction of dynamic recrystallization (DRX). The strengthening of the secondary BEed alloy was attributed to the unique microstructure characteristics: (I) the fine DRXed grains pinned by dynamic precipitates, (II) the dense dynamic precipitation phases, (III) the effect of the fine-grain strengthening. However, the overly densely distributed second phase, which increased the local dislocation density due to the narrower spacing, made it difficult to prevent crack propagation and caused premature fracture of the alloy. In addition, the subsequent final-heat treatment also facilitated the precipitation of the second phases of the secondary BEed alloys and brought in the ultra-high mechanical properties.

Effect of cooling rates and heat treatment time on Si phase of AlSi10Mg alloy manufactured by selective laser melting: Microstructure evolution and strengthening mechanism

As a processing technique to change the organization and properties of materials, heat treatment was widely used to strengthen metallic materials. This study examines the impact of varying cooling rates and heat treatment durations on the mechanical properties and microstructure of AlSi10Mg alloys produced through Selective laser melting (SLM). The heat treatment process was Solution Heat Treatment (SHT, 525 °C), and the heat treatment time includes 1 h, 2 h, and 3 h. Cooling methods consist of Refrigerant Cooling (RC), Water Cooling (WC), Air Cooling (AC), Oil Cooling (OC), and Furnace Cooling (FC). As the cooling rate decreases and the heat treatment time increases, the size of the formed Si phase particles varies from small to large, and the distribution deviates from inhomogeneous to homogeneous. In addition, the number of precipitated particles increases and then decreases. To investigate the impact of cooling rates and heat treatment time on the mechanical properties of AlSi10Mg alloys, quasi-static tensile and compression tests were performed. On the other hand, the tensile strength of the heat-treatment samples decreases while the ductility increases, and the Vickers hardness of the samples also decreases with decreasing cooling rate and increasing heat treatment time. The results of the study showed that the cooling rate and heat treatment time of the material had a greater effect on its tensile properties than on its compressive properties. The samples treated at 525 °C - 2 h - AC exhibited the highest tensile and compressive properties. Finally, the analysis of the strengthening mechanism of AlSi10Mg alloys through the presence of Si phase particles of varying sizes was conducted using transmission electron microscopy.

Au-induced crystallization of amorphous Ge thin films: An indication of the existence of a recrystallization process during growth at deep subeutectic temperature

The influence of Au catalyst microstructure on the crystallization behavior of Ge thin films obtained by Au-induced crystallization method is studied. By improving the Au catalyst crystallinity by pre-annealing, the hole mobility of Ge thin film crystallized at 200°C is improved to nearly 150 cm2/Vs thanks to the increase in Ge grain size, which is fairly high for a Ge film as thin as 10 nm. It is found that the increase in Ge grain size originates from the recrystallization process at deep subeutectic temperature. This is attributed to the existence of a metastable AuGe alloy phase surrounding crystalline Ge, which is kinetically stabilized by a continuous flow of Ge atoms through the alloy phase and realizes a solution-like growth. The process using a kinetically stabilized metastable phase will open up the possibility to realize a novel cost-effective and low-temperature process to fabricate high-performance semiconductor devices on plastic substrates.

Effects of Co/CoNi ratio on elemental occupancy tendencies and lattice misfit of γ/γ′ phases in precipitation-strengthened alloys

Occupancy tendencies of elements significantly differ in precipitation-strengthened Ni-based, CoNi-based, and Co-based alloys, which further affect the γ/γ′ lattice misfit and mechanical properties, but relevant research is lacking. In this work, occupancy tendencies of doping elements (Ta, W, Cr, Fe, Mo, Re, Ti, V) and lattice misfit of γ and γ′ phases in precipitation-strengthened alloys dependent on Co/CoNi ratios have been systematically studied through first-principles calculations. The results show that the tendency of all eight elements to occupy the γ′-Al sublattice site increases with the increase of the Co/CoNi ratio, and the tendency to occupy the γ-Ni/Co site all decreases. The occupancy tendencies of these elements exhibit a strong correlation with the Co/CoNi ratio. Lattice misfit gradually increases as the Co/CoNi ratio is raised. Notably, element Ta has the greatest influence on lattice misfit. The appropriate Co/CoNi ratio is conducive to synergistically enhancing high entropy effects and lattice distortion effects for matrix and Ni3Al precipitate phase, and regulating reasonable lattice misfit, which is beneficial for the design of precipitation-strengthened alloys with excellent strength-ductility balance.

Hot-dip galvanizing process and coating corrosion behavior of fe-mn-al-c steel

The temperature of the zinc bath and the immersion duration are critical factors that significantly impact the surface quality and adhesion of batch hot-dip galvanizing coatings. This study focuses on the influence of different zinc bath temperatures (460, 490, and 520 °C) and immersion duration (1, 3, 5, and 10 min) on the hot-dip galvanized coatings of Fe-Mn-Al-C lightweight steel, which were characterized using scanning electron microscopy and energy dispersive X-ray analysis. The results demonstrate that with the increasing zinc bath temperature and immersion duration, the coating thickness and bond strength initially increase and then decrease. The inhibition layer in the coating gradually fractures and thickens with the rising temperature, leading to changes in the alloy phases within the coating. The optimal batch hot-dip galvanizing condition for the experimental steel is immersing at 490 °C for 3 min. Furthermore, we conducted a neutral salt spray corrosion test on the specimens under the optimal batch hot-dip galvanizing condition to study their corrosion behavior and mechanism and evaluate the impact of batch hot-dip galvanizing on the corrosion resistance of Fe-Mn-Al-C steel.

Significantly improved strength of the TiC/TA19 composites via interface and dislocation strengthening

For titanium matrix composites (TMCs) with a dual-phase structure, yield strength (YS) is typically governed by the hard α phase rather than the soft β phase in the matrix alloy. Therefore, by controlling the precipitation of nanoscale secondary α phases (αs) within the β phase, lattice distortion can be induced, leading to dislocation pile-ups at the αs/β phase interface, thereby achieving strengthening of the matrix interface. Herein, TiC/TA19 composites were fabricated using spark plasma sintering, and induced the dispersion and pinning of nanoscale αs phases from the β phase at the αs/β phase interface through multi-pass cumulative rolling, achieving super high strength. In particular, the nanoscale αs phase exhibits two typical Burgers orientation relationships with the β phase, i.e. (0001)αs//(110)β & [11 2− 0]αs//[1− 11]β and (0001)αs//(01 1−)β & [11 2− 0]αs//[1− 11]β, respectively. Compared with the yield strength of sintered composites, when the rolling reduction was 75 %, the YS of TiC/TA19 composites increased by 33.7 %, reaching 1368 MPa, and the elongation was 3.6 %, only 0.7 % lower than that of sintered composites (4.3 %). The enhanced strength is mainly attributed to the αs precipitation for αs/β interface strengthening and dislocation strengthening derived from the TiC and nanoscale αs precipitates. The volume fraction of dynamic recrystallization grains in TiC/TA19 composites increased with the rolling reduction, and more pyramidal <c+a> slip systems were activated to coordinate the plastic deformation of the composites. This study offers a promising route to fabricating superior high-strength TMCs and provides new insights into balancing strength and ductility.

The mechanical coupling effect of α and β phases in Ti6Al4V alloy undergoing laser shock peening: A molecular dynamics study

In the dual- or multi-phase metallic materials, the influence of different microstructural constituents on the plastic strain/stress distribution is still an area of great controversy. Herein, the heterogeneous deformation behavior of α and β phases in Ti6Al4V duplex titanium alloy undergoing laser shock peening (LSP) has been investigated by molecular dynamics simulations, and the corresponding typical microstructural features are characterized at varied strains. Also, the relationship between the theoretical microstructural morphologies and the micro stress is revealed. It evidently indicates that, the grain refinement process can be summarized as: (i) dislocation motions1 interacting with deformation twins in α phases, (ii) a combination of dislocation propagations and the deformation-induced phase transition from β phase to α phase. In addition, unlike the α single-phase titanium alloy, the representative stress – strain curve of α + β titanium alloy presents a gentle fluctuation trend with smaller amplitude value, suggesting an occurrence of the coupling deformation behavior between α and β phases. The initial interfacial dislocation nucleation prefers to site in the α/α interface rather than the α/β interface, then emitting to the interior of α grains. Features of dislocation slip, twin growth, stacking fault, and phase transformation dominate the release of LSP-generated micro stress, while grain and interphase boundaries, as well as dislocation locks, contribute to the increment of the LSP-generated micro stress.

Synthesis and evaluation of thermal and optical properites of Fe2AlB2 phase alloy for thermal control in space applications

Ternary laminated Fe2AlB2 alloy holds its significance in displaying high strength, damage tolerance, oxidation and radiation cracking resistance. It is synthesized through a pressureless sintering route from elemental powders. Synthesis of Fe2AlB2 is studied from two different molar ratios (2/1/2 and 2/1.5/2) and three different sintering temperatures (1100°C, 1150 °C and 1200 °C). Phase analysis is carried out through an x-ray diffractometer and scanning electron microscopy (SEM). In addition, thermal decomposition, thermal conductivity and absorbance spectra are examined. Fe2AlB2 begins to decompose at 1169 °C into borides and aluminides. Thermal conductivity and diffusivity of Fe2AlB2 decreases with increase in temperature. Lower solar reflectivity and high thermal emittance of Fe2AlB2 implies the thermal control and optical behavior that can be expected for extreme space environments.

First Principles Calculation of the Effect of Cu Doping on the Mechanical and Thermodynamic Properties of Au-2.0Ni Solder.

To meet the demands for high-temperature performance and lightweight materials in aerospace engineering, the Au-Ni solder is often utilized for joining dissimilar materials, such as Ti3Al-based alloys and Ni-based high-temperature alloys. However, the interaction between Ti and Ni can lead to the formation of brittle phases, like Ti2Ni, TiNi, and TiNi3, which diminish the mechanical properties of the joint and increase the risk of crack formation during the welding process. Cu doping has been shown to enhance the mechanical properties and high-temperature stability of the Au-Ni brazed joint's central area. Due to the difficulty in accurately controlling the solid solution content of Cu in the Au-Ni alloy, along with the high cost of Au, traditional experimental trial-and-error methods are insufficient for the development of Au-based solders. In this study, first principles calculations based on density functional theory were employed to analyze the effect of Cu content on the stability of the Au-2.0Ni-xCu (x = 0, 0.25, 0.5, 0.75, 1.0, 1.25 wt%) alloy phase structure. The thermal properties of the alloy were determined using Gibbs software fitting. The results indicate that the Au-2.0Ni-0.25Cu alloy exhibits the highest plastic toughness (B/G = 5.601, ν = 0.416, Cauchy pressure = 73.676 GPa) and a hardness of 1.17 GPa, which is 80% higher than that of Au-2.0Ni. This alloy balances excellent strength and plastic toughness, meeting the mechanical performance requirements of brazed joints. The constant pressure specific heat capacity (Cp) of the Au-2.0Ni-xCu alloy is higher than that of Au-2.0Ni and increases with Cu content. At 1000 K, the Cp of the Au-2.0Ni-0.25Cu alloy is 35.606 J·mol-1·K-1, which is 5.88% higher than that of Au-2.0Ni. The higher Cp contributes to enhanced high-temperature stability. Moreover, the linear expansion coefficient (CTE) of the Au-2.0Ni-0.25Cu alloy at 1000 K is 8.76 × 10-5·K-1, only 0.68% higher than Au-2.0Ni. The lower CTE helps to reduce the risk of solder damage caused by thermal stress. Therefore, the Au-2.0Ni-0.25Cu alloy is more suitable for brazing applications in high-temperature environments due to its excellent mechanical properties and thermal stability. This study provides a theoretical basis for the performance optimization and engineering application of the Au-2.0Ni-xCu alloy as a gold-based solder.

Micro-galvanic corrosion behaviour of Mg−(7,9)Al−1Fe−xNd alloys

The localized micro-galvanic corrosion process and the kinetic information of Mg−(7,9)Al−1Fe−xNd alloys were investigated by in situ observation under electrochemical control and in situ atomic force microscopy (AFM) in an electrolyte environment. The results revealed that the formation of the Nd-rich phase in alloys resulted in a decrease in the Volta potential difference from ~400 mV (AlFe3/α-Mg) to ~220 mV (Nd-rich/α-Mg), reducing the corrosion products around the cathodic phase and corrosion current density of the microscale area. The addition of Nd significantly improved the corrosion resistance, mainly due to the suppression of the micro-galvanic corrosion between the second phases and substrate. Finally, the corrosion mechanism of Mg−(7,9)Al−1Fe−xNd alloys was discussed based on in situ observations and electrochemical results.

The influence of heat treatment on AlSi-polymer abradable coating

Abstract Abradable coatings, as one of the most important technologies for aero and industry gas turbine engines, have an extremely significant influence on engine performance. The macro-hardness of AlSi-Polyester for low-pressure compressor and as-sprayed coating degradation mechanism has been investigated by heat treatment process in imitation service condition. SEM (Scanning Electron Microscope) and OM (Optical Microscope) were used to observe the morphology of powder and coating microstructure in cross-section, respectively. Rockwell hardness tester was used to measure the macrohardness of coatings before and after heat treatment. It shows that AlSi-Polyester powder has an approximately spherical shape and uniform microstructure with alloy phase and polyester phase distribution in the coating prepared by air plasma spraying. Oxidation of the alloy phase and reduced polyester, as well as macrohardness in the as-sprayed coating, occur after the heat treatment process.

The enhanced aging hardening behavior in Si-containing Al-5Zn-1Mg-1Cu alloys

Abstract The ageing behaviour and phase transformation of a range of Si-microalloyed low Mg/Zn ratio Al-5.0Zn-1.0Mg-Cu alloys were investigated at a temperature of 150°C by using TEM and microhardness tests. Adding Si had a important influence on the proportion of precipitates and microhardness. As Si content increased, the precipitated phase underwent a gradual transition from the T+η precipitates to the fine GPB-II precipitates. Concurrently, the microhardness exhibited a notable enhancement from 120 HV to 150 HV when the alloys were subjected to 150°C aging. Existence of small and even GPB-II phases in the Si-adding alloy was identified as underlying cause of this result. This GPB-II phase exhibited a bilayer microstructure. In core region predominantly comprise Zn, Si and Mg, and the shell region primarily consist of Zn and Cu. This structure effectively inhibited phase growth, maintaining the phases at a smaller scale and enhancing the alloy’s hardening effect.

Rapid dissolution kinetic of the second phases in high-strength aluminum alloy by electroshock treatment

Rapid dissolution kinetic of the second phases in high-strength aluminum alloy by electroshock treatment

Effects of Co and Mo on the microstructure properties of GH4282 and the mechanical properties of metal bellows

Abstract In the present study, a new type of Ni-Cr-Co-Mo (GH4282) precipitation-hardening superalloy was prepared on the basis of GH4202 alloy. By adding Co and Mo elements to enhance the solution-strengthening effect, good creep resistance and toughness were obtained. The results show that the strength and microstructure stability of GH4282 alloy are significantly higher than those of traditional GH4202 alloy under the condition of 700~900°C. The precipitated phase of GH4282 alloy is dominated by γ′ phase, which contains M23C6, MC, and a small amount of M6C carbide. The precipitation is mainly distributed along the grain boundaries, and has good stability at temperatures below 900°C, which can effectively pin the grain boundaries. The thermal stability of the alloy is increased. The metal bellows made of GH4282 alloy have significantly higher fatigue life and high-temperature stability, the increase of Co and Mo element content leads to the enhancement of precipitation, and the combined effect of solution strengthening and precipitation strengthening leads to the above results.

A new rhombohedral phase and its 48 variants in β titanium alloy

A new rhombohedral phase (termed R′) in a solution−aging-treated titanium alloy (Ti−4.5Al−6.5Mo−2Cr− 2Nb−1V−1Sn−1Zr, wt.%) was identified. Its accurate Bravais lattice parameters were determined by a novel unit cell reconstruction method based on conventional selected-area electron diffraction (SAED) technique. The orientation relationship between R′ phase and BCC phase was revealed. The results show that the R′ phase is found to have 48 crystallographically equivalent variants, resulting in rather complicated SAED patterns with high-order reflections. A series of in-situ SAED patterns were taken along both low- and high-index zone axes, and all weak and strong reflections arising from the 48 variants were properly explained and directly assigned with self-consistent Miller indices, confirming the presence of the rhombohedral phase. Additionally, some criteria were also proposed for evaluating the indexed results, which together with the Bravais lattice reconstruction method shed light on the microstructure characterization of even unknown phases in other alloys.

Study on solidification organization and phase formation of Fe-6.5wt.%Si high silicon steel by arc melting and heat treatment

Abstract The solidification microstructure and phase formation behavior of Fe-6.5wt.%Si high silicon steel was investigated using arc melting and heat treatment. The alloy phase composition and microstructure were analyzed by XRD and SEM. The magnetic performance was measured at a high- and low-temperature vibration sample magnetometer. The results show that the temperature gradient causes alloy ingot to be roughly divided into three layers. With the decrease in temperature, from the bottom to the top, the phase morphology is fine crystals, columnar internal dendrites, and isoaxial internal dendrites. In the annealing ring ingot, the inner dendrites disappeared, and from the bottom to the top of the sample, the microstructure changed from fine crystal, columnar crystal, and isoaxial crystal, to micro-cracks, which first increased and then reduced. The hysteresis loop curve width of the alloy is narrow, the slope is large, the hysteresis is 0.126 emu/g, and the magnetic utilization after annealing decreases to 0.0667 emu/g, but the coercive force increases to 2.8 Oe/g, and the annealed alloy is more sensitive to the magnetic field and has a high magnetic conductivity coefficient.

Gd Added Mg Alloy for Biodegradable Implant Applications.

Microstructure, mechanical, in vitro and in vivo behavior of extruded Mg alloys with varying Zn/Gd ratios, Mg-2Gd-2Zn-0.5Zr (Zn/Gd = 1), Mg-2Gd-6Zn-0.5Zr (Zn/Gd = 3), and Mg-10Gd-1Zn-0.5Zr (Zn/Gd = 0.1) were investigated. The results revealed that the major secondary phases such as W (Mg3Zn3Gd2), (Mg,Zn)3Gd, LPSO (Long period stacking order) and I (Mg3Zn6Gd) phase in alloys depended on Zn/Gd ratio. These second phases influenced the mechanical as well as biological characteristics of the alloys. Among studied alloys, Mg-10Gd-1Zn-0.5Zr alloy showed the highest yield strength and tensile strength of 270 (±9.29) and 330 MPa (±15.8), respectively, with a reasonably good elongation of 12% (±2.36). The presence of Gd2O3 in the degradation film of Mg-10Gd-1Zn-0.5Zr enhanced the resistance offered by the film, which resulted in its lowest biodegradation, better viability, and cell proliferation under in vitro condition. The short term (subcutaneous implantation in rats for 1 month) in vivo studies showed that the alloy Mg-10Gd-1Zn-0.5Zr degraded at a rate of 0.35 mm/y (±0.02) and did not induce any toxicity to the vital organs.

Effect of Fe-Co catalysis on the temperature field distribution during the growth of 3C-SiC fibers synthesised by microwave heating

Microwave heating produce local hot spots on materials, which result in uneven heating and other issues. Regulate the microwave temperature field using different catalyst combinations such as Fe (NO3)3·9H2O and Co (NO3)2·6H2O. The electromagnetic and temperature field distributions of 3C–SiC fibers and the molecular dynamics of the SiC interfacial growth process and interfacial oxidation reaction during microwave heating in the presence of a catalyst were simulated and calculated respectively. The results show that the combination of Fe and Co at 9 wt% catalyst concentration can effectively improve the electromagnetic loss capability of SiC fibers. The Fe and Co bimetallic catalysed synthesis of 3C–SiC fibers follows a vapor–liquid–solid growth mechanism. The Fe–Si and Fe–Co–Si alloy phases can induce 3C–SiC growth along (111) crystal faces. The simultaneous exothermic reactions provide a highly catalytically active growth environment that facilitates the enhancement of microwave temperature field uniformity. This phenomenon facilitated the synthesis of 3C–SiC fibers.