Clean production of Fe-based amorphous soft magnetic alloys via smelting reduction of high-phosphorus iron ore and apatite

Separated preparation of prealloys and amorphous alloys results in severe solidification-remelting and beneficial element removal-readdition contradictions,which markedly increase energy consumption and emissions.This study offered a novel strategy for the direct production of FePC amorphous soft magnetic alloys via smelting reduction of high-phosphorus iron ore(HPIO)and apatite.First,the thermodynamic conditions and equilibrium states of the carbothermal reduction reactions in HPIO were calculated,and the element content in reduced alloys was theoretically determined.The phase and structural evolutions,as well as element migration and enrichment behaviors during the smelting reduction of HPIO and Ca_(3)(PO_(4))_(2),were then experimentally verified.The addition of Ca_(3)(PO_(4))_(2)in HPIO contributes to the enrichment of the P element in reduced alloys and the subsequent development of Fe_(3)P and Fe_(2)P phases.The content of P and C elements in the range of 1.52 wt% -14.63 wt% and 0.62 wt% -2.47 wt%,respectively,can be well tailored by adding 0-50 g Ca_(3)(PO_(4))_(2)and controlling the C/O mole ratio of 0.8-1.1,which is highly consistent with the calculated results.These FePC alloys were then successfully formed into amorphous ribbons and rods.The energy consumption of the proposed strategy was estimated to be 2.00×10^(8) kJ/t,which is reduced by 30% when compared with the conventional production process.These results are critical for the comprehensive utilization of mineral resources and pave the way for the clean production of Fe-based amorphous soft magnetic alloys.

Formation and corrosion behavior of Fe-based amorphous metallic coatings prepared by detonation gun spraying

Amorphous metallic coatings with a composition of Fe48Cr15Mo14C15B6Y2 were prepared by detonation gun spraying process. Microstructural studies show that the coatings present a densely layered structure typical of thermally sprayed deposits with the porosity below 2%. Both crystallization and oxidation occurred obviously during spraying process, so that the amorphous fraction of the coatings decreased to 54% compared with fully amorphous alloy ribbons of the same component. Corrosion behavior of the amorphous coatings was investigated by electrochemical measurement. The results show that the coatings exhibit extremely wide passive region and low passive current density in 3.5% NaCl (mass fraction) and 1 mol/L HCl solutions, which illustrates excellent ability to resist localized corrosion.

Fabrication and microstructure of Fe-based amorphous composite coatings by laser cladding

Fe-based amorphous composite coatings were fabricated on AISI 1045 steel by laser cladding. The results of the X- ray diffraction and transmission electron microscopy analyses .show the coating is composed of an amorphous phase in majority and a nanocrystaUine phuse in m,inority. Phase composition of the coating changes along the depth of the coating. The reasonable scanning speed for fabricating an amorphous composite coating is 3 500 mm/min when the laser power is 4 800 W and the laser beam diameter is 2 mm. If the scanning speed is lower than 3 500 mm/min, the intensity of the two main diffraction peaks in X-ray diffraction patterns of the coatings decreases with the scanning speeds increasing. At the same time, a broad halo peak emerges and enlarges. High laser power and fast scanning speed are the essential conditions of amorphization. The coating exhibits high microhardness.

Fe-based amorphous coating prepared using high-velocity oxygen fuel and its corrosion behavior in static lead-bismuth eutectic alloy

The Fe_(949.7)Cr_(18)Mn_(1.9)Mo_(7.4)W_(1.6)B_(15.2)C_(3.8)Si_(2) amorphous coating was deposited on T91 steel substrate by using the high-velocity oxygen fuel(HVOF)spray technique to enhance the corrosion resistance of T91 stainless steel in liquid lead-bismuth eutectic(LBE).The corrosion behavior of the T91 steel and coating exposed to oxygen-saturated LBE at 400℃ for 500 h was investigated.Results showed that the T91 substrate was severely corroded and covered by a homogeneously distributed dual-layer oxide on the interface contacted to LBE,consisting of an outer magnetite layer and an inner Fe-Cr spinel layer.Meanwhile,the amorphous coating with a high glass transition temperature(Tg=550℃)and crystallization temperature(T_(x)=600℃)exhibited dramatically enhanced thermal stability and corrosion resistance.No visible LBE penetration was observed,although small amounts of Fe_(3)O_(4),Cr_(2)O_(3),and PbO were found on the coating surface.In addition,the amorphicity and interface bonding of the coating layer remained unchanged after the LBE corrosion.The Fe-based amorphous coating can act as a stable barrier layer in liquid LBE and have great application potential for long-term service in LBE-cooled fast reactors.

Effect of Kerosene Flowing Rate on Microstructure and Wearing Properties for Fe-based Amorphous Coatings

The effects of kerosene flow rate on the microstructure and wearing properties were investigated for Fe-based amorphous coatings sprayed by High Velocity Oxygen Fuel (HVOF).The microstructures and wearing properties of the Fe-based amorphous coatings were analyzed with scanning electron microscope (SEM),X-ray diffraction analyzer (XRD),and ball-on-disc tribometer (CFT-1),respectively.The experimental results show that the well interfacial bonding can be observed between the amorphous coating layer and the substrate,and the porosity in amorphous coating layer is less to 1%.Only some crystalline a-Fe and FeO phases can be detected by XRD in the amorphous coatings,while the amorphous content is up to 99.4%.The wearing coefficient is near to 0.15,which is superior to SUS316 of 0.28.As the increasing of wearing loads,the failure mode is changed from oxidation wear to the composite of oxidation and abrasive wear.

Microstructure of Cu-based Amorphous Composite Coatings on AZ91D Magnesium Alloy by Laser Cladding

To improve the sliding wear resistance of AZ91D magnesium alloy, Cu-based amorphous composite coatings made of CuaTTi34Zr11Nis and Cu47Ti34Zr11Ni8＋20 wt pct SiC powders were fabricated on AZ91D magnesium alloy by laser cladding, respectively. SEM （scanning electron microscopy）, EDS （energy dispersive X-ray spectroscopy）, XRD （X-ray diffraction） and TEM （transmission electron microscopy） techniques were employed to study the phases of the coatings. The results show that the coatings mainly consist of amorphous phase and different intermetallic compounds. The reason of formation of amorphous phase and the function of SiC particles were explained in details.

ELECTRODEPOSITION OF AMORPHOUS Ni-P ALLOY COATINGS

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Amorphous coatings deposited on aluminum alloy by plasma electrolytic oxidation

Amorphous [Al-Si-O] coatings were deposited on aluminum alloy by plasma electrolytic oxidation (PEO). The process parameters, composition, micrograph, and mechanical property of PEO amorphous coatings were investigated. It is found that the growth rate of PEO coatings reaches 4.44 μm/min if the current density is 0.9 mA/mm2. XRD results show that the PEO coatings are amorphous in the current density range of 0.3 - 0.9mA/mm2. EDS results show that the coatings are composed of O, Si and Al elements. SEM results show that the coatings are porous. Nano indentation results show that the hardness of the coatings is about 3 - 4 times of that of the substrate, while the elastic modulus is about the same with the substrate. Furthermore, a formation mechanism of amorphous PEO coatings was proposed.

Formation and mechanical properties of ductile Fe-based amorphous alloys using a cast iron with minor addition of B and Al

Fe-based amorphous alloys with ductility were synthesized using the commercial cast iron QT50 (denoted as QT) with the combining minor addition of B and Al by single roller melt-spinning. The melt-spun (QT1-xBx)99Al1 (x is from 0.006wt% to 0.01wt%) amorphous alloys exhibit onset crystallization temperatures and Curie temperatures of 759-780 and 629-642 K respectively, and whi- ch increase with B content. The amorphous ribbons are ductile and can be bent 180° without breaking. With the increase in B content from 0.006wt% to 0.01wt%, the Vickers microhardness of the amorphous alloys increases from Hv 830 to Hv 1110. The effects of the additional B and Al elements on the glass forming ability and mechanical properties were also discussed.

Ab initio molecular dynamics simulations of nano-crystallization of Fe-based amorphous alloys with early transition metals

The addition of early transition metals(ETMs)into Fe-based amorphous alloys is practically found to be effective in reducing theα-Fe grain size in crystallization process.In this paper,by using ab initio molecular dynamics simulations,the mechanism of the effect of two typical ETMs(Nb and W)on nano-crystallization is studied.It is found that the diffusion ability in amorphous alloy is mainly determined by the bonding energy of the atom rather than the size or weight of the atom.The alloying of B dramatically reduces the diffusion ability of the ETM atoms,which prevents the supply of Fe near the grain surface and consequently suppresses the growth ofα-Fe grains.Moreover,the difference in grain refining effectiveness between Nb and W could be attributed to the larger bonding energy between Nb and B than that between W and B.

Ferromagnetic Fe-based Amorphous Alloy with High Glass-forming Ability

A ferromagnetic amorphous Fe73Al4Ge2Nb1P10C6B4 alloy with high glass-forming ability was synthesized by melt spinning. The supercooled liquid region before crystallization reaches about 65.7 K. The crystallized structure consists of alpha -Fe, Fe3B, FeB, Fe3P and Fe3C phases. The Fe-based amorphous alloy exhibits good magnetic properties with a high saturation magnetization and a low saturated magnetostriction. The crystallization leads to an obvious decrease in the soft magnetic properties.

Effects of C/B4 C ratio on microstructure and property of Fe-based alloy coatings reinforced with in situ synthesized TiB2 -TiC

The Fe-based alloy coatings reinforced with in situ synthesized TiB2-TiC were prepared on Q235 steel by reactive plasma cladding using Fe901 alloy, Ti, B4C, and graphite （C） powders us raw materials. The effects of C/B4C weight percentage ratio （0 - 1. 38 ） on the microstructure , microhardness , and wet sand abrasion resistance of the coatings were investigated. The results show that the coatings consist of （ Fe, Cr ） solid solution, TiC, TiB2, Ti8C5 , and Fe3 C phases. The decrease of C/B4 C ratio is propitious to the formation of TiB2 and Tis C5. Increasing the C/B4 C ratio can help to refine the microstructure of the coatings. However, the microhardness of the middle-upper of the coatings and the wet sand abrasion resistance of the coatings degenerate with the increase of C/B4C ratio. The coating exhibits the best wet sand abrasion resistance at C/BaC =0 and its average mass loss rate per unit wear distance is 0. 001 2%/m. The change of the wet sand abrasion resistance of the coatings with the C/B4C ratio can be mainly attributed to the combined action of the changes of microhardness and the volume percentage of the ceramic reinforcements containing titanium in the coatings.

Molybdenum based amorphous and nanocrystalline coatings prepared by high velocity oxy-fuel spraying

The high velocity oxy-fuel(HVOF) based thermal spray process has developed as a potential advantageous approach for fabricating various kinds of functional coatings.In this article,the coatings of Mo-based alloy were synthesized using the HVOF process.The microstructure and the mechanical properties of the HVOF-processed coatings were investigated using SEM,TEM,XRD,and hardness and wear tests.Annealing treatment was applied to the as-sprayed coatings to develop the microstructure and its effect on the microstructure and mechanical properties of the coatings was examined.It is found that the HVOF-processed Mo-based alloy coatings are comprised of an amorphous splat matrix embedded with nano-sized crystalline particles.Annealing at temperatures over 950 ℃ results into crystallization of the amorphous matrix.The mechanical properties of the as-sprayed coatings are enhanced with annealing temperature up to 750 ℃ and from 950 to 1050 ℃,keeps constant between 750 and 950 ℃,and reduce over 1050 ℃.The change of the mechanical property with the microstructure was illustrated in the study.

Wear Properties of Plasma Transferred Arc Fe-based Coatings Reinforced by Spherical WC Particles

Fe-based coatings reinforced by spherical WC particles were produced on the 304 stainless steel by plasma transferred arc(PTA) to enhance the surface wear properties. Three different Fe/WC composite powder mixtures containing 0 wt%, 30 wt%, and 60 wt% of WC were investigated. The microstructure and phase composition of the Fe/WC composite PTA coatings were evaluated systemically by using scanning electron microscope(SEM) and X-ray diffraction(XRD). The wear properties of the three fabricated PTA coatings were investigated on a BRUKER UMT TriboLab. The morphologies of the worn tracks and wear debris were characterized by using SEM and 3 D non-contract profiler. The experimental results reveal that the microhardness on the cross-section and the wear resistance of the fabricated coatings increase dramatically with the increasing adding WC contents. The coating containing 60 wt% of WC possesses excellent wear resistance validated by the lower coefficients of friction(COF), narrower and shallower wear tracks and smaller wear rate. In the pure Fe-based coating, the main wear mechanism is the combination of adhesion and oxidative wear. Adhesive and two-body abrasive wear are predominated in the coating containing 30 wt% of WC, whereas threebody abrasion wear mechanism is predominated in the coating containing 60 wt% of WC.

FORMATION OF GRADIENT COATING OF Fe-BASED ALLOY WITH RARE EARTHS BY PLASMA SURFACING

A gradient coating of Fe-based alloy was manufactured with rare earths (RE) by plasma surfacing on Q235 steel substrate. The coatings were studied by using X-ray diffraction(XRD), scanning electron microscope(SEM), differential thermal analyzer(DTA), and electron probe micro-analyzer (EPMA). The results show that the phases of the two kinds of coatings(with and without RE) both include α-Fe, Fe7C3, Fe3C, Cr2B, Fe2B and FeB. The microstructure of F314 coating is mainly hypereutectic, the pro-phases Cr7C3 and Cr2B are loose, crassi, spiculate and contain microcracks. The brittleness of the coating is high, and the average hardness is 787 HV. When 0.8wt% RE was added into the F314 alloy, the microstructure varied from hypoeutectic to hypereutectic continuously, The hardness appears as gradient distribution with the highest value of 773 HV, meanwhile, the brittleness decreases significantly. The formation of gradient structure depends on the fallowing factors: (i) the conversion of RE. The addition of RE lowers the elements point and Fe-C eutectic temperature, thus the base metal melting acutely. (ii) the heating of plasma arc. Graded temperature results in directional solidification, thus the gradient structure forms easily. The main reasons for the hardness decrease with RE addition in the alloy are the ratio of hard phase lowering and the hardness of the hard phase decreasing.

Process-structure-property relationship for plasma-sprayed iron-based amorphous/crystalline composite coatings

This study explores the fabrication of Fe-based amorphous/crystalline coating by air plasma spraying and its dependency on the coating parameters(plasma power,primary gas flow rate,powder feed rate,and stand-off distance).X-ray diffraction of the coatings deposited at optimized spray parameters showed the presence of amorphous/crystalline phase.Coatings deposited at a lower plasma power and highest gas flow rate exhibited better density,hardness,and wear resistance.All coatings demonstrated equally good resistance against the corrosive environment(3.5wt%NaCl solution).Mechanical,wear,and tribological studies indicated that a single process parameter optimization cannot provide good coating performance;instead,all process parameters have a unique role in defining better properties for the coating by con-trolling the in-flight particle temperature and velocity profile,followed by the cooling pattern of molten droplet before impingement on the substrate.

Long-term corrosion behavior of HVOF sprayed FeCrSiBMn amorphous/nanocrystalline coating

A FeCrSiBMn amorphous/nanocrystalline coating with 700 μm in thickness and 0.65% in porosity, was prepared by high velocity oxygen fuel(HVOF) spraying process. The long-term corrosion behavior of the FeCrSiBMn coating was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) tests in a 3.5% NaCl solution with a hard chromium coating as a reference. The FeCrSiBMn coating exhibited higher corrosion potential and lower corrosion current density than the hard chromium coating. The pore resistance(Rp) and charge transfer resistance(Rct) of FeCrSiBMn coating were higher than those of the hard chromium coating. In addition, after immersion in the Na Cl solution for 28 d, only small pores in the FeCrSiBMn coating were observed. All the results indicated that the FeCrSiBMn coating held superior corrosion resistance to the hard chromium coating. This could be attributed to the dense structure, low porosity and amorphous/nanocrystalline phases of the FeCrSiBMn coating.

Influence of laser scanning speed on Cu-Zr-Al composite coatings on Mg alloys

To improve the surface properties of magnesium alloys, a study was conducted on Cu-Zr-A1 composite coatings on AZ91HP magnesium alloy by laser cladding. The influence of laser scanning speed on the microstructures and properties of the coatings was discussed. The coatings consist of amorphous phase, CusZr3, and Cul0ZrT. With the increase of laser scanning speed, the amorphous phase content of the coatings increases and reaches 60.56wt% with the laser scanning speed of 2.0 m/min. Because of the influence of laser scanning speed on the amorphous and crystal phases, the coatings show the maximum elastic modulus, hardness, and wear resistance at the laser scanning speed of 1.0 m/min. At the laser scanning speed of 2.0 m/min, the coatings have the best corrosion resistance.

Hot corrosion behaviors of 921A alloy and HVAF-sprayed Fe-based amorphous coating covered with KCl-ZnCl_(2) salts

Hot corrosion behaviors of the 921A alloy and Fe-based amorphous coating induced by KCl-10% ZnCl_(2) and KCl-55% ZnCl_(2) salts at 450℃ in air for 40 h were investigated.Results show that the 921A alloy suffers more serious corrosion damage than the coating and KCl-55% ZnCl_(2) salts are more corrosive than KCl-10% ZnCl_(2) salts.In the two salts,an Fe_(2)O_(3) layer is formed on the 921A alloy surface,while an outer Fe-rich oxide layer and an inner Cr-rich oxide layer are formed on the surface of the coating.Moreover,a certain amount of metal chloride can be found at the oxide/alloy(coating)interface,which can be explained by "active oxidation".However,the corrosion resistance of the Fe-based amorphous coating did not achieve the desired results,probably because the intersplats in the coating serve as corrosion diffusing channels,which facilitate the corrosion damage rate.Nevertheless,the coating is still in amorphous state after hot corrosion exposure.

Stability of electrodeposited amorphous Ni-Fe-P alloys

The stability of the electrodeposited amorphous Ni-Fe-P alloys was studied by DTA,DSC,XRD and improved four-ball wear tester in order to clear its applied scope.The results show that the element content has influence on the stability of amorphous Ni-Fe-P alloy,in which the crystallization temperature increases with Fe content,and the increase of P content delays the appearance of stable crystallization phases and recrystallization.There exist 6 exothermal reactions during heating the amorphous Ni69Fe8P23 alloy continuously.The activation energies of exothermal reactions at 248,303,322,350,376 and 442 ℃ are 131.5,111.6,237.8,253.6 and 238.5 kJ/mol,respectively.The amorphous Ni60Fe22P18 alloy crystallizes when the heating temperature is beyond 250 ℃.The stable crystallization phases consist of Ni(Fe)and Ni3P-type compounds Ni3P,Fe3P,(Fe,Ni)3P.The pressure and fraction have influence on the stability of amorphous alloy.Rubbing above the critical pressure crystallization will take place on the fractional surface.The crystallization phases due to pressure and fraction are different from those due to heating.It is the crystallization that increases the wear resistance of Ni-Fe-P coating under higher pressure.