Structure and corrosion behavior of FeCoCrNiMo high-entropy alloy coatings prepared by mechanical alloying and plasma spraying

FeCoCrNiMox composite powders were prepared using the mechanical alloying technique and made into high-entropy alloy(HEA)coatings with the face-centered cubic phase using plasma spraying to address the element segregation problem in HEAs and pre-pare uniform HEA coatings.Scanning electron microscopy,transmission electron microscopy,and X-ray diffractometry were employed to characterize these coatings’microstructure and phase composition.The hardness,elastic modulus,and fracture toughness of coatings were tested,and the corrosion resistance was analyzed in simulated seawater.Results show that the hardness of the coating is HV0.1606.15,the modulus of elasticity is 128.42 GPa,and the fracture toughness is 43.98 MPa·m^(1/2).The corrosion potential of the coating in 3.5wt%NaCl solution is-0.49 V,and the corrosion current density is 1.2×10^(−6)A/cm^(2).The electrochemical system comprises three parts:the electrolyte,the adsorption and metallic oxide films produced during immersion,and the FeCoNiCrMo HEA coating.Over in-creasingly long periods,the corrosion reaction rate increases first and then decreases,the corrosion product film comprising metal oxides reaches a dynamic balance between formation and dissolution,and the internal reaction of the coating declines.

Spark Plasma Sintering of Mg-based Alloys:Microstructure,Mechanical Properties,Corrosion Behavior,and Tribological Performance

Within the past ten years,spark plasma sintering(SPS)has become an increasingly popular process for Mg manufacturing.In the SPS process,interparticle diffusion of compressed particles is rapidly achieved due to the concept of Joule heating.Compared to traditional and additive manufacturing(AM)techniques,SPS gives unique control of the structural and microstructural features of Mg components.By doing so,their mechanical,tribological,and corrosion properties can be tailored.Although great advancements in this field have been made,these pieces of knowledge are scattered and have not been contextualized into a single work.The motivation of this work is to address this scientific gap and to provide a groundwork for understanding the basics of SPS manufacturing for Mg.To do so,the existing body of SPS Mg literature was first surveyed,with a focus on their structural formation and degradation mechanisms.It was found that successful Mg SPS fabrication highly depended on the processing temperature,particle size,and particle crystallinity.The addition of metal and ceramic composites also affected their microstructural features due to the Zener pinning effect.In degradative environments,their performance depends on their structural features and whether they have secondary phased composites.In industrial applications,SPS'd Mg was found to have great potential in biomedical,hydrogen storage,battery,automotive,and recycling sectors.The prospects to advance the field include using Mg as a doping agent for crystallite size refinement and using bulk metallic Mg-based glass powders for amorphous SPS components.Despite these findings,the interactions of multi-composites on the processing-structure-property relationships of SPS Mg is not well understood.In total,this work will provide a useful direction in the SPS field and serve as a milestone for future Mg-based SPS manufacturing.

Transformation of long-period stacking ordered structures in Mg-Gd-Y-Zn alloys upon synergistic characterization of first-principles calculation and experiment and its effects on mechanical properties

Based on experiments and first-principles calculations,the microstructures and mechanical properties of as-cast and solution treated Mg-10Gd-4Y-xZn-0.6Zr(x=0,1,2,wt.%)alloys are investigated.The transformation process of long-period stacking ordered(LPSO)structure during solidification and heat treatment and its effect on the mechanical properties of experimental alloys are discussed.Results reveal that the stacking faults and 18R LPSO phases appear in the as-cast Mg-10Gd-4Y-1Zn-0.6Zr and Mg-10Gd-4Y-2Zn-0.6Zr alloys,respectively.After solution treatment,the stacking faults and 18R LPSO phase transform into 14H LPSO phase.The Enthalpies of formation and reaction energy of 14H and 18R LPSO are calculated based on first-principles.Results show that the alloying ability of 18R is stronger than that of 14H.The reaction energies show that the 14H LPSO phase is more stable than the 18R LPSO.The elastic properties of the 14H and 18R LPSO phases are also evaluated by first-principles calculations,and the results are in good agreement with the experimental results.The precipitation of LPSO phase improves the tensile strength,yield strength and elongation of the alloy.After solution treatment,the Mg-10Gd-4Y-2Zn-0.6Zr alloy has the best mechanical properties,and its ultimate tensile strength and yield strength are 278.7 MPa and 196.4 MPa,respectively.The elongation of Mg-10Gd-4Y-2Zn-0.6Zr reaches 15.1,which is higher than that of Mg-10Gd-4Y0.6Zr alloy.The improving mechanism of elastic modulus by the LPSO phases and the influence on the alloy mechanical properties are also analyzed.

A new insight into LPSO phase transformation and mechanical properties uniformity of large-scale Mg-Gd-Y-Zn-Zr alloy prepared by multi-pass friction stir processing

A large-scale fine-grained Mg-Gd-Y-Zn-Zr alloy plate with high strength and ductility was successfully prepared by multi-pass friction stir processing(MFSP)technology in this work.The structure of grains and long period stacking ordered(LPSO)phase were characterized,and the mechanical properties uniformity was investigated.Moreover,a quantitative relationship between the microstructure and tensile yield strength was established.The results showed that the grains in the processed zone(PZ)and interfacial zone(IZ)were refined from 50μm to 3μm and 4μm,respectively,and numerous original LPSO phases were broken.In IZ,some block-shaped 18R LPSO phases were transformed into needle-like 14H LPSO phases due to stacking faults and the short-range diffusion of solute atoms.The severe shear deformation in the form of kinetic energy caused profuse stacking fault to be generated and move rapidly,greatly increasing the transformation rate of LPSO phase.After MFSP,the ultimate tensile strength,yield strength and elongation to failure of the large-scale plate were 367 MPa,305 MPa and 18.0% respectively.Grain refinement and LPSO phase strengthening were the major strengthening mechanisms for the MFSP sample.In particularly,the strength of IZ was comparable to that of PZ because the strength contribution of the 14H LPSO phase offsets the lack of grain refinement strengthening in IZ.This result opposes the widely accepted notion that IZ is a weak region in MFSP-prepared large-scale fine-grained plate.

Structural characteristics and magnetic properties of bulk nanocrystalline Fe_(84)Zr_2Nb_4B_(10) alloy prepared by mechanical alloying and spark plasma sintering consolidation

Magnetic properties of Fe84Zr2Nb4B10 sample were investigated. The sample was produced from nanocrystalline powders made by the mechanical alloying (MA) and consolidation using the spark plasma sintering (SPS) technique. Effects of milling time on phase transformation, structural characteristics, and magnetic properties of powders were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and physical property measure system (PPMS), respectively. Results show that nanostructured α-Fe supersaturated solid solution is obtained in the final MAed products. The saturation magnetization (Ms) increased with increasing milling time and became constant at 130 h, but the coercivity (Hc) increased firstly and then decreased. The consolidated bulk sample exhibited a high density of 6.893 g·cm-3, there was no phase change during SPS process, and the saturation magnetization and susceptibility of the SPSed bulk sample improved in comparison with the milled powders. The variation of magnetic parameters can be explained by nano-scale effect and Herzer model.

Microstructure, thermal properties, and corrosion behaviors of FeSiBAlNi alloy fabricated by mechanical alloying and spark plasma sintering

An equiatomic FeSiBAlNi amorphous high-entropy alloy （HEA） was fabricated by mechanical alloying （MA）. A fully amorphous phase was obtained in the FeSiBAlNi HEA after 240 h of MA. The bulk FeSiBAlNi samples were sintered by spark plasma sintering （SPS） at 520 and 1080℃ under a pressure of 80 MPa. The sample sintered at 520℃ exhibited an amorphous composite structure comprising solid-solution phases （body-centered cubic （bcc） and face-centered cubic （fee） phases）. When the as-milled amorphous HEA was consoli- dated at 1080℃, another fcc phase appeared and the amorphous phase disappeared. The sample sintered by SPS at 1080℃ exhibited a slightly higher melting temperature compared with those of the as-milled alloy and the bulk sample sintered at 520℃. The corrosion behav- iors of the as-sintered samples were investigated by potentiodynamic polarization measurements and immersion tests in seawater solution. The results showed that the HEA obtained by SPS at 1080℃ exhibited better corrosion resistance than that obtained by SPS at 520℃.

Mechanical alloying and phase transformation in Fe-Si alloy

The Fe-Si mechanical alloying and its transformation are investigated to evaluate whether mechanical alloying is a useful process for producing Fe-Si alloy. The mechanical alloying process of Fe-Si powders is studied by SEM（ scanning electron microscopy）, EDS（energy dispersive spectrometer）and XRD（X-ray diffraction）. The results show that the ball milling process first makes tough Fe powder a lump structure and brittle Si powder a small particle, and then as the mill power increases, the tough powder of iron with a lamellar structure forms and the Si particles lies on or between the Fe lamellas. Finally, the Fe and Si powders are mechanically alloyed through atom diffusion. So the Fe and Si powders can be alloyed by 15 h ball milling at a speed of 400 r/min and with a ball-to-powder ratio of 40 ： 1. After heating at 1 243 K for 1 h, the milled powders transform to α-FeSi2, and after heating at 1 243 K for 1 h, then cooling to 1 073 K for 1 h, the milled powders transform to β-FeSi2. Therefore, the monophase α-FeSi2 or β-FeSi2 can be obtained by heat treatment of mechanically alloyed Fe-Si powders.

Fabrication of Ti_3AlC_2 ceramic material by mechanical alloying

Ti3AlC2 has the properties of ceramics and metals. These excellent properties indicate that Ti3AlC2 is a very promising material to extensive applications. Ti3AlC2 ceramic material was prepared by mechanical alloying. The effects of milling time and sintering temperature on the fracture, microstmctttre and mechanical properties of Ti3AlC2 ceramic material were analyzed by laser particle analyzer, X-ray diffraction, and scanning electron microscopy. The experimental results showed that Ti3AlC2 had the best comprehensive properties after the composite powder was milled for 3 h and sintered at 1630℃ for 2 h. The relative density, bending strength, and hardness of the sample reached 92.23%, 345.2 MPa, and HRA 34.1, respectively. The fracture surface indicated that the fracture of the material belonged to ductile rapture.

Influence of B source materials on the synthesis of TiB_2-Al_2O_3 nanocomposite powders by mechanical alloying

An Al2O3-TiB2 nanocomposite was successfully synthesized by ball milling of Al, TiO2 and two B source materials of B2O3 （system （1）） and H3BO3 （system （2））. Phase identification of the milled samples was examined by Xray diffraction. The morphology and microstructure of the milled powders were monitored by scanning electron microscopy and transmission electron microscopy. It was found that the formation of this composite was completed after 15 and 30 h of milling time in systems （1） and （2）, respectively. More milling energy was required for the formation of this composite in system （2） due to the lubricant properties of HaBO3 and also its decomposition to HBO2 and B2O3 during milling. On the basis of X-ray diffraction patterns and thermodynamic calculations, this composite was formed by highly exothermic mechanically induced self-sustaining reactions （MSR） in both systems. The MSR mode took place around 9 h and 25 h of milling in systems （1） and （2）, respectively. At the end of milling （15 h for system （1） and 30 h for system （2）） the grain size of about 35-50 nm was obtained in both systems.

Influence of mechanical alloying time on the properties of Fe_3Al intermetallics prepared by spark plasma sintering

The Fe3Al-based intermetallics were prepared by mechanical alloying and spark plasma sintering （SPS）, and the influence of milling time on the properties of materials was investigated. The phase identification was investigated by X-ray, and the surface morphology and fractography were observed by scanning electron microscope （SEM）. The mechanical properties such as bending strength, strain, and microhardness were tested. The results show that Fe reacts with Al completely to form Fe3Al during short SPS processing time. The relative densities of the sintered samples were nearly 100%. The mechanical properties of the sintered samples can be improved along with the milling time. The representative values are the bend strength of 1327 MPa and the microhardness of 434.

Microstructure Design of High-Entropy Alloys Through a Multistage Mechanical Alloying Strategy for Temperature-Stable Megahertz Electromagnetic Absorption

Developing megahertz(MHz)electromagnetic wave(EMW)absorption materials with broadband absorption,multi-temperature adaptability,and facile preparation method remains a challenge.Herein,nanocrystalline FeCoNiCr_(0.4)Cu_(0.2) high-entropy alloy powders(HEAs)with both large aspect ratios and thin intergranular amorphous layers are constructed by a multistage mechanical alloying strategy,aiming to achieve excellent and temperature-stable permeability and EMW absorption.A single-phase face-centered cubic structure with good ductility and high crystallinity is obtained as wet milling precursors,via precisely controlling dry milling time.Then,HEAs are flattened to improve aspect ratios by synergistically regulating wet milling time.FeCoNiCr_(0.4)Cu_(0.2) HEAs with dry milling 20 h and wet milling 5 h(D20)exhibit higher and more stable permeability because of larger aspect ratios and thinner intergranular amorphous layers.The maximum reflection loss(RL)of D20/SiO_(2) composites is greater than-7 dB with 5 mm thickness,and EMW absorption bandwidth(RL<-7 dB)can maintain between 523 and 600 MHz from-50 to 150℃.Furthermore,relying on the“cocktail effect”of HEAs,D20 sample also exhibits excellent corrosion resistance and high Curie temperature.This work provides a facile and tunable strategy to design MHz electromagnetic absorbers with temperature stability,broadband,and resistance to harsh environments.

Alloying behavior and characterization of(CoCrFeNiMn)_(90)M_(10)(M=Al,Hf)high-entropy materials fabricated by mechanical alloying

The alloying behavior and microstructures of the(CoCrFeNiMn)_(90)M_(10)(M=Al,Hf)high-entropy alloy(HEA)powders fabricated by mechanical alloying were studied.The CoCrFeNiMn)_(90)Al_(10) powders have duplex solid-solution structures.In contrast,nanocrystalline HfNi_(3) anchoring in amorphous structures is found in the(CoCrFeNiMn)_(90)Hf_(10) powders.The(CoCrFeNiMn)_(90)Al_(10) powders show better ferromagnetic behaviors,mainly explained by the facilitated motion of the magnetic domain induced by the coherent interface between duplex phases.Combined with our previous work,the rules of forming solid-solution and amorphous phase in as-milled HEA powders are preliminarily proposed.It is found that,compared with the as-cast HEA reported previously,the variation range of mixing enthalpy with atomic size difference of the solid-solution formed in as-milled HEA powders is broader.Moreover,the variation ranges between mixing enthalpy and entropy with atomic size difference of the amorphous phase in HEA powder become wider than those of high-entropy bulk metallic glass.

Formation mechanism of Ti_5Si_3 powder by mechanical alloying

The formation mechanism of stoichiometry Ti_5Si_3 by mechanical alloying (MA)from elemental powders has been investigated. The results of XRD and SEM analyses of the powdershow that Ti_5Si_3 can be synthesized by MA in a planetary mill with two different formationmechanisms. Ti_5Si_3 was formed gradually with the mechanical collusion reaction (MCR) mechanismunder a lower impact energy, and the Ti_5Si_3 was formed abruptly with the self-propagatinghigh-temperature synthesis (SHS) formation mechanism under a higher impact energy.

Enhanced thermal stability and mechanical properties of high-temperature resistant Al-Cu alloy with Zr and Mn micro-alloying

The high temperature(HT)thermal stability and mechanical properties of Al-5%Cu(AC)and Al-5%Cu-0.2%Mn-0.2 Zr%(ACMZ)alloys from 573 to 673 K were systematically studied.The results displayed that micro-alloying additions of Zr and Mn elements have presented a significant role in stabilizing the main strengthening metastableθ′precipitates at a temperature as high as 573 K.Simultaneously,the HT tensile test demonstrated that ACMZ alloy retained their strength of(88.6±8.8)MPa,which was much higher than that of AC alloy((32.5±0.8)MPa)after the thermal exposure at 573 K for 200 h.Finally,the underlying mechanisms of strength and ductility enhancement mechanism of the ACMZ alloy at HT were discussed in detail.

Structure and Magnetic Properties of Fe1-xCx Solid Solution Prepared by Mechanical Alloying

Supersaturated solid solutions Fe1-xCx （0≤x≤0.9 ） of wide composition range have been prepared by mechanical alloying process. Nanocrystalline phase was formed for 0 ≤ x ≤ 0.67 and a large grain phase for 0.75 ≤ x ≤ 0.9. The large fraction of graphite volume puts off formation of nanocrystalline phase for high carbon content. In the large grain phase, magnetization follows simple magnetic dilution, and eoereivity He is mainly due to dissolution of carbon at grain boundaries. In the nanocrystalline phase the alloying effect of carbon is revealed by a distinct reduction of average magnetic moment. The increasing lattice constant with increasing carbon content is observed for x ≤ 0.5, suggesting that the high carbon concentration may enhance diffusion of carbon into the Fe lattice. It shows a discontinuity in the Hc variation with a grain size D of nanocrystalline phase. For small grain D below the critical value, Hc increases with D. For a large grain D, Hc decreases with increasing D. The solubility limit of carbon in a-Fe extended by nanocry- stalline phase formation is discussed.

Role of alloying and heat treatment on microstructure and mechanical properties of cast Al-Li alloys:A review

Due to the prominent advantages of low density,high elastic modulus,high specific strength and specific stiffness,cast Al-Li alloys are suitable metallic materials for manufacturing complex large-sized components and are ideal structural materials for aerospace,defense and military industries.On the basis of the microstructural characteristics of cast Al-Li alloys,exploring the role of alloying and micro-alloying can stabilize their dominant position and further expand their application scope.In this review,the development progress of cast Al-Li alloys was summarized comprehensively.According to the latest research highlights,the influence of alloying and heat treatment on the microstructure and mechanical properties was systematically analyzed.The potential methods to improve the alloy performance were concluded.In response to the practical engineering requirements of cast Al-Li alloys,the scientific challenges and future research directions were discussed and prospected.

A molecular dynamics study on mechanical performance and deformation mechanisms in nanotwinned NiCo-based alloys with nano-precipitates under high temperatures

Molecular dynamics simulations are performed to investigate the mechanical behavior of nanotwinned NiCo-based alloys containing coherent L12 nano-precipitates at different temperatures,as well as the interactions between the dislocations and nano-precipitates within the nanotwins.The simulation results demonstrate that both the yield stress and flow stress in the nanotwinned NiCo-based alloys with nano-precipitates decrease as the temperature rises,because the higher temperatures lead to the generation of more defects during yielding and lower dislocation density during plastic deformation.Moreover,the coherent L12 phase exhibits excellent thermal stability,which enables the hinderance of dislocation motion at elevated temperatures via the wrapping and cutting mechanisms of dislocations.The synergistic effect of nanotwins and nano-precipitates results in more significant strengthening behavior in the nanotwinned NiCo-based alloys under high temperatures.In addition,the high-temperature mechanical behavior of nanotwinned NiCo-based alloys with nano-precipitates is sensitive to the size and volume fraction of the microstructures.These findings could be helpful for the design of nanotwins and nano-precipitates to improve the high-temperature mechanical properties of NiCo-based alloys.

Evaluation of the microstructure,thermal and mechanical properties of Cu/SiC nanocomposites fabricated by mechanical alloying

Nano-sized silicon carbide(SiC:0wt%,1wt%,2wt%,4wt%,and 8wt%)reinforced copper(Cu)matrix nanocomposites were manufactured,pressed,and sintered at 775 and 875℃in an argon atmosphere.X-ray diffraction(XRD)and scanning electron microscopy were performed to characterize the microstructural evolution.The density,thermal expansion,mechanical,and electrical properties were studied.XRD analyses showed that with increasing SiC content,the microstrain and dislocation density increased,while the crystal size decreased.The coefficient of thermal expansion(CTE)of the nanocomposites was less than that of the Cu matrix.The improvement in the CTE with increasing sintering temperature may be because of densification of the microstructure.Moreover,the mechanical properties of these nanocomposites showed noticeable enhancements with the addition of SiC and sintering temperatures,where the microhardness and apparent strengthening efficiency of nanocomposites containing 8wt%SiC and sintered at 875℃were 958.7 MPa and 1.07 vol%^(−1),respectively.The electrical conductivity of the sample slightly decreased with additional SiC and increased with sintering temperature.The prepared Cu/SiC nanocomposites possessed good electrical conductivity,high thermal stability,and excellent mechanical properties.

Microstructure and Properties of W-15Cu Alloys Prepared by Mechanical Alloying and Spark Plasma Sintering Process

W-15Cu composite powders prepared by mechanical alloying （MA） of raw powders were consolidated by spark plasma sintering （SPS） process at temperature ranged 1 230-1 300 ℃ for 10 min and under a pressure of 30 MPa. By using high energy milling, particles containing very fine tungsten grains embedded in copper, called composite particles, could be produced. The W grains were homogeneously dispersed in copper phase, which was very important to obtain W-Cu alloy with high mechanical properties, fine and homogeneous microstructure. The microstructure and properties of W-15Cu alloys prepared by SPS processes at different temperature were researched. The results show that W-15Cu alloys consolidated by SPS can reach 99.6 % relative density, and transverse rupture strength （TRS） is 1 400.9 MPa, Rockwell C hardness （HRC） is 45.2, the thermal conductivity is 196 W/m-K at room temperature, the average grain size is less than 2 μm, and W-15Cu alloy with excellent properties, homogeneous and fine microstructure is obtained.

Thermal stability of nanocrystalline Mg-based alloys prepared via mechanical alloying

Thethermal stability and the kinetics of grain growth of nanocrystalline Mg-6Al-1Zn and Mg-6Al-1Zn-1Si alloys prepared via mechanical alloying were investigated. It started with elemental powders, using a variety of analytical techniques including differential scanning calorimetry （DSC）, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and energy dispersive spectrometry. The kinetics of grain growth in isothermal annealing was investigated. The XRD results show that, although the grain sizes of both material systems increase as the annealing temperature rises, the Si-containing system displays a relatively smaller grain size, i.e., 60 nm compared with 72 nm in Mg-6Al-1Zn system, after being exposed to 350 ℃ for 1 h. The second-phase intermetallic particle Mg2Si formed during the isothermal annealing of Mg-6Al-1Zn-1Si system could influence not only the activation energy but also the exponent of kinetic equation. Higher hardness values obtained in the Si-containing system would be due to the formation of Mg2Si intermetallic phase.