Supersaturated Solid Solution Research Articles

Interface Characteristics, Erosion Behavior, and Thermal Shock Resistance of Al–Ta Alloy Coatings Produced by Arc Spraying

The pure aluminum coatings of physical vapor deposition chambers used in current semiconductor processes offer insufficient protection against ion bombardment. In this study, the arc spraying process was used to produce Al–Ta alloy coatings to replace pure aluminum coatings. The microstructure, mechanical properties, and particle erosion properties of these coatings were investigated at 1% and 3% Ta content and compared with those of pure Al. The surface and surface morphologies of the three coatings were similar. However, Ta was uniformly dispersed to form a supersaturated solid solution in the 1Ta and 3Ta coatings. The tensile results indicated that the adhesion of the three coatings was similar. According to particle erosion results, cohesive strength and erosion resistance apparently increased. Moreover, the thermal shock effect caused by the extreme thermal cycle in these chambers causes coating degradation. So, this study compared the thermal shock properties of the Al–Ta alloy coatings with Y2O3 ceramic coating. The 1Ta and 3Ta coatings did not differ considerably from pure Al coating in terms of thermal shock resistance, and all three were higher than that of the Y2O3 coating. The aforementioned results indicate that the produced Al–Ta alloy coatings can offer superior chamber protection ability.

Structure formation and peculiarities of crystallisation of lead-free tin – zinc alloys obtained by rapid solidification

The results of the study of the microstructure of lead-free alloys of the tin – zinc system obtained by rapid solidification at a cooling rate of at least 105 K/s are presented. In tin and zinc alloys with concentrations of 1.2–2.0 wt. % Zn and 1.5 wt. % Sn, respectively, during rapidly cooling of the melt, the alloying element is captured. The formed solid solutions are supersaturated and at room temperature disintegrate according to the mechanism of formation and growth of nuclei of a new phase. The average size of zinc and tin precipitates after holding the foil for two days does not exceed 0.5 μm. Melts of compositions Sn – 4.4–15.0 wt. % Zn after rapidly cooling are supercooled and supersaturated by two components and experience spinodal decomposition (stratification) followed by the formation of supersaturated solid solutions based on tin and zinc, which disintegrate at room temperature. The average size of zinc precipitates in non-equilibrium eutectic does not exceed 2 μm. In rapid solidificated foils of alloys containing 50–80 wt. % Zn, a two-phase structure is formed from solid solutions based on tin and zinc. The average size of tin precipitates does not exceed 1 μm. As the crystallisation front moves away from the contact surface of the foil with the surface of the mold, the tin particles become larger and the specific surface of the interphase boundary decreases.

A novel GP-Li precursor and the correlated precipitation behaviors in Al-Cu-Li alloys with different Cu/Li ratio

Aluminum-lithium (Al–Li) alloys have become an essential material for aircraft skin in the aerospace industry owing to their high strength and low density. An optimized coherent Cu/Li ratio and well controlled precipitation sequence are critical to upgrade the desired properties. In this study, we systematically evaluate the effect of the Cu/Li ratio (ranging from 0.5 to 1.4) on the aging hardening and precipitation behavior of Al–Cu–Li alloys with specific rare earth elements (Sc, Zr, and Ce). Using state-of-the-art aberration-corrected transmission electron microscopy equipped with super-energy-dispersive X-ray spectroscopy (EDS) and atomic scale spatially resolved electron energy loss spectroscopy (EELS) with K3 camera, classical strengthening phases, such as Cu containing precipitates T1 (Al2CuLi), θ′ (Al2Cu) and Li-rich phase δ′ (Al3Li), have been identified during the artificial aging and natural aging treatment. A new Li-rich phase (namely, the GP-Li zone) with a hexagonal shape has been identified in alloys with Cu/Li ratios of 0.5 and 1. High density GP-Li zones are formed after five months natural aging, which are found fully coherent with the Al matrix. The discovery of GP-Li zones shows a new precipitation path for Li atoms in the supersaturated solid solution. Besides, the GP-Li zone stimulates the nucleation of T1 and θ′ phase at the interfaces indicating that there is an alternative approach for the nucleation mechanism of T1 and θ′. The crossover between the suppression of δ′ phase formation and the acceleration of T1 and θ′ precipitation occurs when the Cu/Li ratio is increased during the artificial aging process, resulting in a decrease in the aging hardening ability at first, followed by a large recovery in aging hardening. The findings of this study provide a strategy to design high strength Al–Li alloys through the manipulation of Cu/Li ratios and the newly identified GP-Li phase.

Sustainable nanoporous gold with excellent SERS performances

A low-cost Nanoporous Gold (NPG) has been successfully produced by utilizing the simple method of chemical dealloying. Ribbons of a supersaturated solid solution Au33Fe67 were obtained by rapid solidification using melt-spinning technique. Chemical dealloying of the ribbons was achieved in 1 M HNO3 at 70 °C for varying lengths of time. The as-quenched ribbon and as-dealloyed samples have been structurally and compositionally investigated using XRD, FESEM and EDS techniques. The obtained NPG is homogeneous with tunable ligament size and shape, easy-to-handle and free-standing. NPG has been successfully applied as substrate for Surface-Enhanced Raman Scattering (SERS) using 4,4′-bi-pyridine probe molecule. An impressive enhancement in the SERS effect has been observed. The detection limit is recorded to be as low as 10−15 M. The NPG sample shows great potential as an economical and highly sensitive SERS-active substrate for life science applications and ultrasensitive instrumentation. Catalytic properties have been explored demonstrating a high activity of the material. Most notably, a metastable precursor has been favourably obtained from an immiscible Au–Fe system. Usage of critical raw materials has been avoided. A cost-effective starting material has been used in the form of an Fe-rich precursor by pairing abundant and cheap Fe with Au. Then, an elegant and rapid dealloying procedure makes the overall production of NPG an inexpensive and sustainable process.

Effect of process parameters and heat treatment on the microstructure and properties of CuCrZr alloy by selective laser melting

Complex CuCrZr alloy parts with well-matched conductivity and strength can be prepared by adjusting the process parameters of selective laser melting (SLM). Thus, in this study, SLM was used to prepare CuCrZr alloys, and their structure, electrical conductivity, and mechanical properties were analyzed. Moreover, effect of aging treatment on the alloy structure was investigated. With the laser power of 400 W, scanning speed of 300 mm/s, and scanning distance of 80 μm, an CuCrZr alloy sample with a maximum relative density of 99.15% and elongation of 71.7% was obtained by SLM. After direct age hardening (DAH) at 480 °C for 2 h, the conductivity and strength of the alloy increased significantly. In particular, the conductivity increased from 22.16%IACS to 72.8%IACS, indicating an overall increase of 228.5%. Meanwhile, the strength increased from 265.5 to 612.0 MPa. From the backscatter diffraction analysis, the small-angle grain boundaries increased after aging, and the crystal orientation changed from <101> to <111>. During direct aging, a large amount of nanoscale Cr phase was precipitated from the supersaturated solid solution, which increased the strength of the alloy. Further, precipitation strengthening was determined to be the main alloy strengthening mechanism. Moreover, the reduction in the solid solution content reduced the electron scattering effect and increased the overall conductivity of the alloy.

Microstructure evolution and strengthening mechanism analysis of novel Mg-RE-Ag alloy during heat treatment

Precipitation strengthening is crucial for Mg-RE alloys to achieve excellent mechanical properties. Herein, the high-strength Mg-6Gd-2Y-1.5Ag-1Nd-0.4Zn-0.5Zr alloy was designed and developed by building multi-orientated nano-precipitates. The corresponding microstructure and strengthening mechanism were comprehensively investigated utilizing XRD, OM, SEM, TEM, Brinell hardness and tensile tests under various heat treatment conditions. The results indicated that the as-cast alloy consisted of the primary α-Mg matrix and Mg5(Gd,Y,Nd,Ag,Zn)-type eutectic phase at the grain boundaries. With the increase of solid solution temperature and time, the grain size of the alloy gradually increased. After solution treatment at 510 °C for 10 h, solute atoms from the eutectic phase fully diffused into the matrix, and the supersaturated solid solution was obtained. The solution-treated alloy was subsequently aged, and multiple types of nanoscale precipitates formed in the matrix. The precipitation evolution can be divided into three distinct stages. At the early aging stage, the fine solute clusters were the primary precipitates. And then a mass of basal γ'' and prismatic β′ phases occurred uniformly in the matrix at the peak-aged stage. After reaching the over-aged stage, the primary precipitates further transformed into coarse γ and β phases. The alloy achieved outstanding mechanical properties at both room and high temperatures after the peak-aged treatment, which was mainly related to the synergistic strengthening of the multi-orientated β′ and γ'' nano-precipitates. The peak-aged alloy's ultimate tensile strength, yield strength, and elongation were 370 MPa, 335 MPa, 2.8% at room temperature, and 258 MPa, 215 MPa, 11.8% at 300 °C, respectively.

Microstructure and resistivity of Au-B supersaturated solid-solution films prepared by sputter deposition

• A series of Au–B films was deposited by magnetron sputtering. • Au-B supersaturated solid solutions without AuB 2 compounds confirmed in the films. • The microstructure of the Au–B supersaturated solid-solution films was studied. • The relationship between the resistivity and b content in the films was revealed. • The Au–B supersaturated solid-solution films were stable at room temperature. Au-B films are of interest for superconductor and hohlraums materials. A series of gold-boron (Au-B) films with different B contents has been deposited by magnetron sputtering of Au-B pseudo-alloy targets in an Ar atmosphere. The B atomic concentration of the Au-B films was varied by adjusting the B contents of the Au-B targets and sputtering pressure. The composition, microstructure and resistivity of the Au-B films were investigated by X-ray photoelectron spectrometry, X-ray diffraction and the four-probe method. Due to the mutually immiscibility of Au and B, non-equilibrium supersaturated solid solutions of B in Au with nanocrystalline microstructures instead of AuB 2 metal diboride were observed in the as-deposited films. With increasing B content, the average grain size of the films decreased and the d -spacing of Au (111) increased. The resistivity of the Au-B supersaturated solid-solution films was linearly related to the B content and no superconductivity was observed. The structure of the Au-B films was stable at room temperature for a long time, while annealing caused phase transition.

Effect of multiple thermal cycles on the microstructure evolution of GA151K alloy fabricated by laser-directed energy deposition

The microstructure and mechanical properties of high-performance Mg-RE (Magnesium rare earth) alloys prepared through laser-directed energy deposition (LDED) are worthy of an in-depth study, due to their excellent application perspectives in the aviation industry. In this work, a nominal Mg-15Gd-1Al-0.4Zr wt% (GA151K) alloy was fabricated by LDED, and the solid phase transformation induced by the application of multiple thermal cycles was investigated in detail. Moreover, in the last deposited layer, fine α-Mg grains, particle-like secondary phases, and intergranular island-like phases were observed. In addition, in the second layer from the top, α-Mg grains grew slightly by 1.4 ± 1.0 µm and the fraction of the intergranular island-like phase was significantly decreased by 9.3 ± 2.1%. As the deposition process progressed, the pre-solidified layers experienced additional thermal cycles, and two solid phase transformations occurred. One of the recorded transformations was that of the intergranular phase from Mg 3 Gd to Mg 5 Gd, while the other one was the precipitation of β′-Mg 7 Gd within the α-Mg matrix from the supersaturated solid solution. Here, the thermal cycles acted as an incomplete solution and aging treatment, leading to the unique morphology of the as-built GA151K alloy. The microhardness was improved by 6.9 ± 5.0 HV 0.2 with the application of consecutive thermal cycles. This work established a simplified relationship between the process parameters, the microstructure, and the mechanical properties of LDED Mg-Gd alloys, which is expected to promote the development and application of LDED high-performance Mg-RE alloys. • The transformation of intergranular phase from Mg 3 Gd to Mg 5 Gd and precipitation of β′ in AM Mg-Gd alloys are firstly reported. • The microstructure evolution principle of LDED GA151K under the influence of thermal cycles is studied in detail. • The importance of in situ precipitation strengthening to AM Mg-RE alloy is proposed.

Effect of solid solution process on the structure and properties of Cu-Cr-Mg alloy in the aging state

In this study, Cu-Cr-Mg alloy wires were prepared by up-drawing continuous casting and multi-pass drawing. The effect of the solid solution process on the strength and electrical conductivity of the Cu-Cr-Mg alloy was investigated. The solid solution degree of Cu-Cr-Mg alloys with different solid solution processes was evaluated by XRD. The types and morphologies of nanoprecipitates of the two alloys during different thermomechanical treatments were compared by selected area electron diffraction in TEM, and the degree of recrystallization of the peak-aged Cu-Cr-Mg alloy was analyzed by EBSD. The results showed that the degree of supersaturated solid solution of the as-cast Cu-Cr-Mg alloy was comparable to that of the as-cast Cu-Cr-Mg alloy after holding at 950 ℃ for 1 h and water quenching. Meanwhile, the strength of the as-cast Cu-Cr-Mg alloy was 52.2 MPa higher than that of the solution-treated Cu-Cr-Mg alloy, and the decrease in conductivity was only 6.3% IACS. The microstructure results showed that a large number of dispersed nanoscale precipitates existed in the matrix of both alloys, and the precipitates were close in size. The results of the strengthened model calculations are also close to the experimental results.

Mechanical spectroscopy study of as-cast and additive manufactured AlSi10Mg

The AlSi10Mg alloy produced by casting (AC) and additive manufacturing (AM) technology of laser powder bed fusion (L-PBF) has been investigated through mechanical spectroscopy (MS). In addition to the grain boundary peak PGB the Q−1 curves of both materials exhibit two other relaxation peaks, P1 (H = 0.8 ± 0.05 eV; τ0 = 10−11±1 s) and P2 (H = 1.0 ± 0.05 eV; τ0 = 10−13±1 s), depending on the interaction of dislocations with solute elements (Si and Mg). Relaxation strengths of P1, P2 and PGB of AM alloy are greater than those of the AC one owing to the finer structure of Al cells and the higher amount of Si and Mg in supersaturated solid solution induced by the rapid solidification typical of the L-PBF process. After successive MS test runs relaxation strengths of P1 and P2 peaks in both the examined materials decrease due to the precipitation of Si atoms and dislocation density recovery. Such decrease is more pronounced in AM alloy where change of cell shape and increase of cell size is observed. Dynamic modulus of AM alloy exhibits an anomalous trend in the first test run that is no more present in successive runs. The irreversible process giving rise to such anomalous behavior is the closure of pores of nanometric size.

Development of a high strength Zr/Sc/Hf-modified Al-Mn-Mg alloy using Laser Powder Bed Fusion: Design of a heterogeneous microstructure incorporating synergistic multiple strengthening mechanisms

Laser Powder Bed Fusion (L-PBF) provides great advantages in creating supersaturated solid solutions due to its intrinsic ultrafast cooling and high solidification rate, which is particularly desired for enhanced solid solution strengthening and precipitation strengthening. In the present work, a novel high strength Zr/Sc/Hf-modified Al-Mn-Mg alloy with a good L-PBF processability is investigated. The as-built alloy exhibits a heterogeneous microstructure featuring a bi-modal grain structure with coarse columnar and fine equiaxed grains and heterogeneously distributed nanometer and submicrometer-sized cuboid-shaped primary Al3(Sc,Zr,Hf) particles. The Al3(Sc,Zr,Hf) phase, exhibiting a homogeneous elemental distribution of Zr, Sc, and Hf, adopts a cubic L12 structure with a lattice parameter of 0.4044 ± 0.009 nm, showing a good coherency with α-Al. Additionally, the rapid L-PBF solidification enables the formation of submicrometer-sized elongated and globular primary Al6Mn and a supersaturated Al matrix with a high dislocation density. This results in a good combination of strength (yield strength of 438 ± 3 MPa and ultimate tensile strength of 504 ± 2 MPa) and ductility (elongation at fracture of 10.9 ± 1.4 %), with a moderate work hardening strength of 113 ± 12 MPa. Direct-ageing at 325 °C for 10 h promotes the formation of a large amount of rod-shaped Al6Mn precipitates and a few spherical Al3(Sc,Zr,Hf) nanoprecipitates. The heat treatment increases the hardness from 166 ± 2 HV in as-built condition to 173 ± 4 HV and enhances the tensile strength (yield strength of 487 ± 2 MPa and ultimate tensile strength of 542 ± 3 MPa) but slightly reduces the ductility to 7.4 ± 0.7 %. The high strength was achieved by the synergistic effect of grain boundary strengthening, solid solution strengthening, and Orowan strengthening mechanisms.

Microstructural Study of CrNiCoFeMn High Entropy Alloy Obtained by Selective Laser Melting.

The high entropy alloy (HEA) of equiatomic composition CrNiFeCoMn and with FCC crystal structure was additively manufactured in a selective laser melting (SLM) process starting from mechanically alloyed powders. The as-produced alloy shows fine nitride and σ phase precipitates, which are Cr-rich and stable up to about 900 K. The precipitates increase in number and dimensions after long-period annealing at 900–1300 K, with a change in the HEA mechanical properties. Higher aging temperatures in the furnace, above 1300 K, turn the alloy into a single FCC structure, with the disappearance of the nitride and σ phase precipitates inside the grains and at the grain boundaries, but still with the presence of a finer Cr-rich nitride precipitation phase. These results suggest that the as-produced HEA is a supersaturated solid solution at low and intermediate temperature with nitrides and σ nanostructures.

A study on the mechanical and electrical properties of high-strength CuCrZr alloy fabricated using laser powder bed fusion

Copper-chromium-zirconium (CuCrZr) is tailored using additive manufacturing, particularly laser powder bed fusion (LPBF). Due to high thermal conductivities and high reflectivity of infrared laser irradiation, it is still challenging to fabricate copper alloys using the LPBF technique. To address the issue, a short wavelength laser (515 nm) was employed in the LPBF process. In this work, the CuCrZr alloys were built with optimized building parameters such as powder of 485 W, scanning speed of 400 mm/s, and hatching distance of 0.09 mm. The relative density of the samples was found to be 98.07 %. The as-built samples exhibit good mechanical properties with ultimate tensile strength (UTS) of 447 ± 13 MPa, yield strength (YS) of 400 ± 11 MPa, total failure elongation (EL) of 10 ± 3 %, and Vickers hardness of 130 ± 15 HV). However, the electrical property is poor with 30 ± 1 %IACS. The high tensile stress and low electrical conductivity may attribute to the dislocation cells. Moreover, the dissolved Cr atoms result in poor conductivity. By direct aging treatment at 500 °C for 1 h, excellent mechanical properties (UTS = 566 ± 18 MPa, YS = 487 ± 13 MPa, EL = 15 ± 1 %, Vickers hardness = 161 ± 15 HV) were achieved while maintaining a good conductivity (64 ± 3 % IACS). The main contribution to the increase in YS is attributed to (I) the nanoscale Cr precipitated homogeneously in the copper matrix during the direct aging treatment and (II) the remaining high dislocation density near the dislocation cells. The enhancement of the electrical conductivity is attributed to the decomposition of the supersaturated solid solution.

Precipitation behavior of Cu-NiAl nanoscale particles and their effect on mechanical properties in a high strength low alloy steel

The precipitation behavior of Cu-NiAl nanoscale particles in a high strength low alloy steel and their effect on mechanical properties are studied systemically by atom probe tomography and tensile testing. The results display that the Cu-rich zones will nucleate firstly from the supersaturated solid solution for the experimental high strength low alloy steel tempered at 500 °C for 0.08 h, which will transform into Cu-rich particles and also promote the heterogeneous nucleation of isolated NiAl particles. The precipitation sequence in the studied high strength low alloy steel can be expressed as: supersaturated solid solution → Cu-rich zones → Cu-rich particles + isolated NiAl → Cu-NiAl + isolated NiAl. With increasing tempering time, the NiAl (Cu-NiAl + isolated NiAl) particles will coarsen continuously and the Cu-NiAl particles have larger radius and higher number density than the isolated NiAl particles. The tensile testing results reveal that NiAl particles exhibit strong precipitation strengthening and result in a strength plateau of about 1423–1486 MPa at 2–310 h. With tempering time increasing, the elongation decreases firstly and attains the minimum value of about 7.5% in the 5 h tempered condition due to the high number density (1.95 × 10 24 m −3 ) of NiAl particles, and then the elongation increases gradually to 13.0% at 310 h. Obviously, the sample tempered for 310 h displays a beneficial combination of yield strength (1423 MPa) and elongation (13.0%). Schematics of the precipitation behavior of Cu-NiAl co-precipitates for the experimental steel tempered at 500 °C. • The Cu-rich zones will nucleate firstly from the supersaturated solid solution. • The precipitation sequence can be shown as: Cu-rich zones → Cu-rich particles + isolated NiAl → Cu-NiAl + isolated NiAl. • The precipitation strengthening of NiAl particles is studied thoroughly. • The steel exhibits a beneficial combination of yield strength and elongation for the sample tempered at 500 °C for 310 h.

Effect of oxide dispersoids on precipitation-strengthened Al-1.7Zr (wt %) alloys produced by laser powder-bed fusion

Binary Al-1.7 wt % Zr (Al-0.5 at % Zr) alloys, with and without 1 wt % (0.7 vol %) Al2O3 nanoparticle additions (80–100 nm), are fabricated by laser powder-bed fusion (L-PBF) from blends of Al, Zr, and Al2O3 powders. Elemental Zr, which is ~80 % dissolved in the melt pool, forms primary L12-Al3Zr precipitates upon solidification and is also retained in a supersaturated solid solution in the Al matrix. The primary L12-Al3Zr phase takes three forms: (i) discrete, micron-sized precipitates that nucleate fine Al matrix grains, (ii) elongated “strings” of submicron precipitates forming in highly enriched Zr regions, and (iii) < 100 nm precipitates within fine Al-grains. The Al2O3 nanodispersoid additions are either lost to slag or entrapped within Al-grains as oxide dispersoids, resulting in an oxide concentration of 0.46 wt % for the modified ODS alloy. Al2O3 nanoscale dispersoids (0.28 wt %) are also observed in the unmodified alloy, and are assumed to originate from (i) native oxides from the surface of the Al powder particles, and/or (ii) reaction with trace amounts of oxygen in the processing environment. The hardness upon aging at 400 °C reaches a peak value of ~750–850 MPa after 1.5 h, consistent with precipitation of secondary L12-Al3Zr nanoprecipitates. Upon overaging, hardness slowly decreases to 500 MPa (the as-processed value) after 1,500 h at 400 °C, with no difference observed between the Al-Zr and Al-Zr-Al2O3 alloys. Strengthening mechanisms combines Hall-Petch strengthening from micron-sized grains, Zr solid-solution strengthening, and secondary L12-Al3Zr precipitate strengthening, with slow precipitate coarsening and effective grain pinning by Al3Zr precipitates and oxide dispersoids located at grain boundaries. Creep resistance is comparable for both alloys, which show threshold stresses of ~15 and 6 MPa, at 300 and 400 °C respectively. Oxygen content analysis is recommended for all Al-based alloys fabricated via L-PBF due to the potential for non-reproducible nanoscale oxide inclusions (from native oxide on Al powders and from reaction with residual oxygen), which may affect the mechanical properties of the alloys, but are difficult to observe via SEM or TEM analysis.

Phase-Field Simulation of Spinodal Decomposition in Mn-Cu Alloys

The spinodal decomposition was studied in the aged Mn-40 at. %Cu, Mn-30 at. %Cu, Mn-20 at. %Cu alloys using a phase-field model based on the Cahn–Hillard equation, considering a subregular solution model and the energy contribution of the magnetic behavior. The simulations were performed at aging temperatures of 300, 400, and 500 °C for times from 1 to 240 min. The growth kinetics of the Mn concentration profiles with time indicated clearly that the phase decomposition of the supersaturated solid solution γ into a mixture of Mn-rich γ′ and Cu-rich γ phases occurred by the spinodal decomposition mechanism. Moreover, the phase decomposition at the early stages of aging exhibited the characteristic morphology of spinodal decomposition, an interconnected and percolated microstructure of the decomposed phases. The most rapid growth kinetics of spinodal decomposition occurred for the aging of Mn-20 and 30 at. %Cu alloys because of the higher driving force. The presence of the phase decomposition is responsible for the increase in hardness, as well as the improvement of the damping capacity of Mn-Cu alloys.

Crystal nucleation and growth processes in Cu-rich glass-forming Cu-Zr alloys.

The glass formation ability of an alloy depends on two competing processes: glass-transition, on one hand, and crystal nucleation and growth, on the other hand. While these phenomena have been widely studied before in nearly equiatomic Cu-Zr alloys, studies are lacking for solute/solvent-rich ones. In the present work, molecular dynamics simulations show that the addition of a small amount of Zr (1-10 at. %) to Cu drastically increases the incubation time and slows down crystal growth, thus, leading to an improved glass forming ability. The crystal nucleation and growth processes of a competing face-centered cubic (FCC) Cu crystalline phase are analyzed in detail. In particular, the values of the critical cooling rate, incubation period for crystallization, and growth rate of FCC Cu crystals in these Cu-rich alloys are obtained. The growth of a supersaturated FCC Cu solid solution is found to be polymorphic at the interface (except for alloys with 9 and 10 at. % Zr) though a Zr concentration gradient is observed within growing crystals at high enough Zr content. The crystal growth rate before crystal impingement is nearly constant in all alloys, though it decreases exponentially with the Zr content. Crystallization kinetics are also analyzed within the existing theories and compared with the experimental values available in the literature.

Magnetoresistive behaviour of ternary Cu-based materials processed by high-pressure torsion

Severe plastic deformation using high-pressure torsion of ternary Cu-based materials (CuFeCo and CuFeNi) was used to fabricate bulk samples with a nanocrystalline microstructure. The goal was to produce materials featuring the granular giant magnetoresistance effect, requiring interfaces between ferro- and nonmagnetic materials. This magnetic effect was found for both ternary systems; adequate subsequent annealing had a positive influence. The as-deformed states, as well as microstructural changes upon thermal treatments, were studied using scanning electron microscopy and X-ray diffraction measurements. Deducing from electron microscopy, a single-phase structure was observed for all as-deformed samples, indicating the formation of a supersaturated solid solution. However, judging from the presence of the granular giant-magnetoresistive effect, small ferromagnetic particles have to be present. The highest drop in room temperature resistivity (2.45% at 1790 kA/m) was found in Cu62Fe19Ni19 after annealing for 1 h at 400 °C. Combining the results of classical microstructural studies and magnetic measurements, insights into the evolution of ferromagnetic particles are accessible.

Enhanced cryogenic and ambient temperature mechanical properties of CoCuFeMnNi high entropy alloy through controlled heat treatment

Dedicated thermal treatments can improve the mechanical behaviour of high entropy alloys (HEAs) by producing nanostructured microstructures with improved characteristics. Herein, the inherent metastability of an equiatomic CoCuFeMnNi alloy was exploited to induce the formation of secondary phases upon ageing treatment. Advanced characterization techniques, namely high resolution synchrotron X-ray diffraction and aberration corrected scanning transmission electron microscopy, allowed to describe the decomposition of the supersaturated solid solution. Nanometric rounded Cu-rich clusters in the solution-treated alloy and coherent, regularly oriented Cu-rich discs in the peak-aged condition were possibly produced by spinodal decomposition. An almost 100% enhancement of mechanical strength was obtained thanks to the modulation of composition. Moreover, mechanical behaviour at cryogenic temperature was improved by ageing, both in terms of strength and ductility. Plastic deformation took place by dislocation slip, regardless of the testing temperature. • CoCuFeMnNi high entropy alloy was subjected to solution treatment and ageing • The alloy’s inherent instability leads to decomposition of the supersaturated matrix. • The nanostructured microstructure led to improved mechanical behaviour.

A Critical Review on Al-Co Alloys: Fabrication Routes, Microstructural Evolution and Properties

Al-Co alloys is an emerging category of metallic materials with promising properties and potential application in various demanding environments. Over the years, different manufacturing techniques have been employed to fabricate Al-Co alloys, spanning from conventional casting to rapid solidification techniques, such as melt spinning, thus leading to a variety of different microstructural features. The effect of the fabrication method on the microstructure is crucial, affecting the morphology and volume of the precipitates, the formation of supersaturated solid solutions and the development of amorphous phases. In addition, the alloy composition has an effect on the type and volume fraction of intermetallic phases formed. As a result, alloy properties are largely affected by the microstructural outcomes. This review focuses on highlighting the effect of the fabrication techniques and composition on the microstructure and properties of Al-Co alloys. Another goal is to highlight areas in the field that are not well understood. The advantages and limitations of this less common category of Al alloys are being discussed with the scope of future prospects and potential applications.