Composition,structure and crystallite size of raney catalysts proceeding from several NiAl and FeAl Intermetallic phases

The intermetallic phases NiAl₃, Ni₂Al₃, (Ni_1?xFe_x)₂Al₃, FeAl₃ and Fe₂Al₅, are obtained as single phase, then they are used to prepare Raney catalysts. Composition, structure and crystallite size of Ni, Fe and (NiFe) catalysts are determined by chemical analysis and X-Ray diffraction. For Raney Ni, the composition results show the residual Al content to be higher in the catalysts proceeding from the intermetallics with the lower Al content. For the Raney (Ni,Fe) catalyst, the Fe/Ni ratio is of the same order than in the (Ni_1?xFe_x)₂Al₃ master alloy. From the structure results, a second phase, likely NiAl, is found beside fcc Ni in the catalysts with high residual Al content. The crystallite size of the various catalysts is in the range 3–15 nm; the surface area obeys a linear relationship versus the reciprocal of crystallite size.     

Novel high-entropy and medium-entropy stainless steels with enhanced mechanical and anti-corrosion properties

ABSTRACT

Novel high-entropy and medium-entropy stainless steels (MESS), containing a high amount of alloying elements, were designed and prepared by arc melting. These high-entropy and MESS possess a simple phase constitution, mainly solid solution phases, and noticeably exhibit excellent anti-corrosion properties in sulphuric acid. In particular, an austenitic Fe₆₅Cr₁₃Co_4.75Mn_4.75Mo_4.75Ni_4.75Cu₃ (at.-%) alloy has a higher hardness of 182 HV and better corrosion resistance than those of the 00Cr19Ni14Mn2 austenitic stainless steel prepared under the same condition; a ferritic precipitation hardening Fe₆₅Cr₁₃Al_3.167Co_3.167Mn_3.167Mo_3.167Ni_3.167Ti_3.167Cu₃ (at.-%) alloy was also developed, with a higher hardness of 584 HV and even better corrosion resistance.     

Microstructure and Mechanical Properties of Al25 − xCr25 + 0.5xFe25Ni25 + 0.5x (x = 19, 17, 15 at%) Multi‐Component Alloys

A series of Al_{25 ? x}Cr_{25 + 0.5x}Fe₂₅Ni_{25 + 0.5x} (x = 19, 17, 15 at%) multi‐component alloys are prepared by arc‐melting and rapid solidification of copper molds. The technique of thermal‐mechanical processing is further applied to the master alloys to improve their mechanical properties. These alloys consist of face‐centered cubic (FCC) and body‐centered cubic (BCC) structure. The volume fraction of the BCC phase increases as Al content increase and Cr and Ni contents decrease, accompanied with a microstructural evolution from dendritic structure to lamella‐like structure. Due to the increase of volume fraction of BCC phase, the master alloys exhibit an increased strength and a declined ductility as Al content increases. The rapid solidified alloys have more BCC phase compared with the master alloys, which enhances the strength and decreases the ductility. After homogenization, hot‐rolling, and annealing at 1000 °C, the Al₈Cr_33.5Fe₂₅Ni_33.5 alloy displays excellent combination of strength (yield strength is ～635 MPa and fracture strength is ～1155 MPa) and ductility (tension strain is ～11%).

     

Effect of Ni addition on formation of amorphous and nanocrystalline phase during mechanical alloying of Al-25 at.%Fe-(5,10) at.%Ni powders

Al-Fe-Ni ternary powder mixtures containing 25 at.%Fe-5 at.%Ni and 25 at.%Fe-10 at.%Ni were mechanically alloyed by a high-energy planetary ball mill. Structural evolution of these powders during milling was investigated by X-ray diffraction technique and transmission electron microscopy. Almost complete amorphous phase in Al₇₀Fe₂₅Ni₅ system is observed at the early milling stage. The amorphous phase transforms into metallic compound Al₅(Fe,Ni)₂ and then the compound changes to ordered Al(Fe,Ni) phase. The last milling products in Al₇₀Fe₂₅Ni₅ system are amorphous phase plus nanocrystalline of the disordered Al(Fe,Ni) phase changed from the ordered Al(Fe,Ni) phase. During milling of Al₆₅Fe₂₅Ni₁₀ system, α-Al and α-Fe solid solutions formed at the early stage change to the ordered Al(Fe,Ni) compound and at last the ordered phase changes to the disordered Al(Fe,Ni) phase. Ten percent of Ni addition promotes retardation of the formation of the amorphous phase.     

Ab initio calculations of Fe–Ni clusters

The clusters of Fe, Ni, and Fe–Ni are investigated computationally using a density functional approach. The geometries of clusters are optimized under the constraint of well-defined point group symmetries at the UB3LYP/LanL2DZ level. The equilibrium geometries and binding energies are presented and discussed, together with natural populations and natural electron configurations. In addition, the binding energies of Fe_n−xNi_x clusters are found to generally decrease by successive substitutions of Ni atoms for Fe atoms. For Fe_n−xNi_x clusters, the comparisons on total energies between isomers indicate that Ni atoms energetically prefer clustering in the mixed Fe–Ni clusters. The calculations for Fe_n−xNi_x clusters show that the clustering leads to a segregation of Ni atoms from Fe atoms.     

New understanding on metal recovery of Fe,Ni and Cr during carbon-thermal reduction of stainless steel dust

Stainless steel dust is a typical solid waste from iron and steel smelting. In this study, valuable metal components were recovered from stainless steel dust by carbon-thermal reduction. The effect of reduction conditions on the recovery of Fe, Ni and Cr was studied. The restrictive steps of Fe, Ni and Cr in the reduction process were clarified by XRD and SEM. The results show that the reduction temperature has a great influence on the reduction of metal Fe, Ni and Cr in stainless steel dust, and the increase of reduction temperature, reduction time and appropriate carbon ratio promoted the recovery of metal. The intermediate phase fayalite (Fe,Ni)₂SiO₄ and magnesiochromite Cr₂MgO₄ in the reduction process are the restrictive factors that cause the low recovery of Fe, Ni and Cr metals. In the process of carbon-thermal reduction, with the increase of reduction time, Fe²⁺ and Ni²⁺ in mesophase (Fe, Ni)₂SiO₄ were replaced by Mg²⁺ and Ca²⁺ in MgO and CaO, and finally reduced to MgCaSiO₄; Cr³⁺ in the mesophase Cr₂MgO₄ was replaced by Al³⁺ in Al₂O₃ and finally reduced to Al₂MgO₄, which improves the recovery of metal Fe, Ni and Cr.     

X-ray microanalysis and properties of multicomponent plasma-borided layers on steels

The structure and chemical composition of composite and multicomponent borided layers obtained by a new method that combines the chemical electroless and plasma boriding techniques are described. Quantitative X-ray microanalysis examinations show that on the surface of nickel–phosphorus coated steel borided at 923 K three boride phases of the type (Ni _x Fe_{1 – x} )₄B₃, (Ni _x Fe_{1 – x} )₂B and (Fe _x Ni_{1 – x} )B formed, whereas in the samples borided at 1123 K only two borides (Fe_{1 – x} Ni _x )B and (Fe_{1 – x} Ni _x )₂B are present. The shape and the distribution of the phases depends on the thickness of the Ni–P layer deposited on the steel substrate before boriding. The thicknesses of boride zones obtained on nickel coated steels are much greater than those obtained on the same steel without nickel coating. Also the diffusion zone between the Ni–P layer and the steel increases during boriding, which improves the adhesion of the layer to the substrate. The composite layers obtained show a high wear resistance, with their resistance to corrosion being markedly greater than that of uncoated and only borided steel.     

The preparation of ductile high strength Fe-base filaments using the methods of glass-coated melt spinning

High toughness glass-coated metallic fibres show great promise for use in composite materials as reinforcement for brittle matrixes such as fine ceramics. This paper describes the glass-coated melt spinning of austenitic steel and Fe-B base alloys in order to prepare a ductile high strength filament. The toughness was estimated from the area of the stress-strain curves of the filament obtained. Continuous high toughness steel filament, which had a maximum toughness of 6600 MPa% with a tensile strength of 3050 MPa and an elongation of 3.1% was obtained from the molten state at 1600 K for a winding speed of 7.95 m sec^–1. The filament was 3×10^–6m diameter and polycrystalline with a grain size of 1000×10^–10m. The crystal structure of the filament was a single b c c phase and the phase transformed into a stable f c c structure by heat treatment at 1073 K for 600sec. Ductile filaments of Fe_78-x Co₅Ni₅Cu₂B₁₀M _x (M _x Cr_5–20, Cr₅Si₃, Cr₅Co₅, Cr₅Ni₅, Cr₁₀Mo_0.5, Cr₁₀Nb_0.5) alloys were also successfully produced. The Fe_67.5Co₅Cr₁₀Ni₅Cu₂B₁₀Mo_0.5 filament had the highest toughness of 13 900 MPa% with tensile strength of 3760 MPa and an elongation of 4.8%. The filament had a single b c c phase.     

Role of Fe substitution and quenching rate on the formation of various quasicrystalline and related phases

We have investigated Fe substituted versions of the quasicrystalline (qc) alloy corresponding to Al₆₅Cu₂₀(Cr, Fe)₁₅ with special reference to the possible occurrence of various quasicrystalline and related phases. Based on the explorations of various compositions it has been found that alloy compositions Al₆₅Cu₂₀Cr₁₂Fe₃ and Al₆₅Cu₂₀Cr₉Fe₆ exhibit interesting structural phases and features at different quenching rates. At higher quenching rates (wheel speed ～ 25 m/sec) all the alloys exhibit icosahedral phase. For Al₆₅Cu₂₀Cr₁₂Fe₃ alloy, however, both the icosahedral and even the decagonal phases get formed at higher quenching rates. At higher quenching rate, alloy having Fe 3 at % exhibits twobcc phases,bccI (a = 8.9 å) andbccIIa = 15.45 å). The orientation relationships between icosahedral and crystalline phases are: Mirror plane ∥ [001] _bcc I and [351] _bcc II, 5-fold ∥ [113] _bcc II and 3-fold ∥ [110]inbcc II. At lower quenching rate, the alloy having Fe 6 at % exhibits orthorhombic phase (a = 23.6 å,b = 12.4 å,c = 20.1 å). Some prominent orientation relationships of the orthorhombic phase with decagonal phase have also been reported. At lower quenching rate (～ 10 m/sec), the alloy (Al₆₅Cu₂₂Cr₉Fe₆) shows the presence of diffuse scattering of intensities along quasi-periodic direction of the decagonal phase. For making the occurrence of the sheets of intensities intelligible, a model based on the rotation and shift of icosahedra has been put forward.     

Microstructure,phase formation and properties of rapid solidified Al–Fe–Cr–Ti alloys

Improvements in the mechanical strength of Al–Fe–Cr–Ti alloys have been demonstrated when non-equilibrium microstructures are developed. This paper investigated the effect of cooling rate and composition on the phase formation, microstructure and properties of new Al_96.6Fe_1.5Cr_1.7Ti_0.2 and Al_91.6Fe_4.9Cr_2.2Ti_1.3 (at.-%) alloys. Wedge-shaped samples produced by suction casting were characterised by optical, scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, energy dispersive X-ray spectroscopy and microhardness. The results showed that the morphology and size of the phases precedent of the flower-like phases change from small, spherical particles to large flower-like phases with decreasing the cooling rate. The presence of intermetallic phases Al₁₃Fe₄, Al₁₃Cr₂ and Al₃Ti in the Al_91.6Fe_4.9Cr_2.2Ti_1.3 alloy, resulted in a hardness 1.6 times higher compared to the Al_96.6Fe_1.5Cr_1.7Ti_0.2 alloy.     

Irreversible enthalpy relaxation of amorphous (Fe1−x Ni x )83P17(x=0–1) alloys

This paper deals with the changes in exothermic enthalpy relaxation behaviour and Curie temperature of amorphous Fe₃₃Ni₅₀P₁₇ alloy upon annealing, and the compositional effect (i.e. the change with Fe/Ni ratio) on the magnitude of exothermic reactions during continuous heating of (Fe_1–x Ni _x )₈₃P₁₇ (x=0–1) alloys, in order to clarify the thermal relaxation behaviour with irreversibility of metal-metalloid type amorphous alloys. For Fe₃₃Ni₅₀P₁₇ alloy, the exothermic reaction showed two distinctive peaks at about 480 and 580 K and the low-temperature peak had a very strong correlation with the change in Curie temperature. Furthermore it was observed that for (Fe_1–x Ni _x )₈₃P₁₇ alloys the magnitude of the low-temperature peak was nearly proportional to the number of Fe-Ni atom pairs. However, the high-temperature one was almost independent of the changes in Curie temperature and the ratio of Fe to Ni. These results suggest that the exothermic enthalpy relaxation peak at temperatures far below T _g (or T _x) originates from the local rearrangement of metal-metal interactions of different species, while the high-temperature peak is due to the rearrangement of metal-metalloid bonding. This separation into two stages is interpreted as due to the difference of bonding forces between metal-metal and metal-metalloid pairs in amorphous Fe-Ni-P alloys.     

Obtainment of the Fe0.70?xCrxAl0.3/Al2O3 nanocomposite by the method of SHS of mechanoactivated Cr2O3 + Fe + Al mixtures

Applying M?ssbauer spectroscopy methods, we have studied the structure of nanocomposites obtained by a technique combining the preliminary mechanical activation of an 8.1 wt % Cr₂O₃ + 65.9 wt % Fe + 25 wt % Al mixture and self-propagating high-temperature synthesis (SHS). It has been found that, at the stage of mechanical activation, an Fe/Al/Cr₂O₃ composite with a low impurity of the Fe₂Al₅ intermetallide is formed. At the stage of SHS, the interaction between activated components of the mixture leads to the formation of the Fe_{0.7 − x} Cr _x Al_0.3 (x = 0 − 0.2)/Al₂O₃ composite. Original Russian Text ? T.Yu. Kiseleva, A.A. Novakova, T.L. Talako, T.F. Grigor’eva, A.N. Falkova, 2009, published in Neorganicheskie Materialy, 2009, Vol. 45, No. 7, pp. 892–896.     

Characterization of crystallization in Metglas 2826 MB alloy

The crystallization behaviour of the Metglas 2826 MB alloy (Fe₄₀Ni₃₈Mo₄B₁₈) has been studied using resistance measurements and X-ray diffraction techniques. Three annealing sequences were used to follow the process. Samples were annealed isothermally (a) at 780° C in a vacuum of 2×10^–5 torr for times in the range 1 sec to 4 h, (b) for 2 h in an argon atmosphere at temperatures where the resistance curve indicated phase changes to occur, and (c) for 300 h in 100 torr of helium at 400, 600, 700 and 850° C. From these annealing sequences it was found that the alloy did not crystallize below 410° C and followed a crystallization process of: amorphous Fe₄₀Ni₃₈Mo₄B₁₈ Fe _x Ni_23–x B₆ (cubic)+glassy matrix Fe _x Ni_23–x B₆+(Fe, Ni) (FCC) (Fe, Ni)₃B(bct). This series of transformations was followed for Sequences (a) and (c) above, but was slightly different for Sequence (b). An orthorhombic (Fe, Ni)₃ B phase was found in the samples annealed in a vacuum of 2×10^–5 torr.Trademark of Allied Chemical Co.     

Formation and microstructure of quasicrystals in suction cast Al‐6 wt.% Mn alloys with additions of nickel and iron elements

The formation and microstructure of quasicrystals in suction cast Al‐6 wt.% Mn‐2 wt.% TM (TM = Ni, Fe) alloys were investigated by transmission electron microscopy, scanning electron microscopy, energy dispersive spectrometry, and X‐ray diffraction. The suction cast Al‐6 wt.% Mn‐2 wt.% Ni alloy consists of a single decagonal phase of Al₅₆Mn₁₁Ni₂, whereas the Al‐6 wt.% Mn alloy with 2 wt.% iron addition comprises a primitive icosahedral phase and a decagonal phase of Al₄₀Mn₇Fe₂. Thus, the addition of nickel or iron favors quasicrystal formation in the suction cast Al‐6 wt.% Mn alloys. Based on a 4 : 1 matching ratio of aluminum atoms to heavier atoms, the approximate electron to atom ratio is 1.85 in two decagonal phases of Al₅₆Mn₁₁Ni₂ and Al₄₀Mn₇Fe₂. Various morphologies of quasicrystals with a size of more than 5 μm were observed in the microstructure of suction cast Al‐6 wt.% Mn‐2 wt.% TM (TM = Ni, Fe) alloys. The decagonal Al₄₀Mn₇Fe₂ phase nucleates epitaxially and grows on the icosahedral phase.     

Effect of micro-alloying chromium on the corrosion resistance of nanocrystalline nickel aluminide intermetallic produced by mechanical alloying process

In this study, Ni₅₀Al_50 − xCr_x nanocrystalline intermetallic compound was synthesized by using the high energy mechanical milling of pure Ni, Al and Cr elemental powders for 16 h. The morphological investigation was done by using the optical and scanning electron microscope. The corrosion behavior of the samples was studied by using the electrochemical impedance spectroscopy in 3.5% NaCl solution. The results showed that when the micro-alloying Cr content is increased, the particles distribution is modified and the size of particles is decreased. Therefore the passive film which is formed on the surface of samples is less porous, so the corrosion resistance is increased.     

The effect of Fe on the crystallization behavior of Al–Mm–Ni–Fe amorphous alloys

The crystallization behavior and thermal stability of Al₈₆Mm₄Ni_10–x Fe _x alloys were investigated as a function of Fe content. Alloys, produced by a single roll melt-spinner at a circumferential speed of 52 m/s, revealed fully amorphous structures. The thermal stability of the present amorphous alloys increased with the increase of Fe content. The activation energy for crystallization of -Al increased as the Fe content increased. This increase of activation energy resulted in the simultaneous precipitation of -Al and intermetallic phase observed especially in Al₈₆Mm₄Ni₅Fe₅ and Al₈₆Mm₄Ni₂Fe₈ alloys. The glass transition was observed in DSC thermogram only after proper annealing treatment. The effect of alloy composition on the thermal stability could be explained in terms of the atomic structure of the amorphous alloy.     

Transformation of the quasicrystalline phase Al-Cr-Fe induced by rapid solidification

A quasicrystalline phase, Q, with icosahedral symmetry was detected by X-ray diffraction and transmission electron microscopy in Al-3Cr-xFe (x=0 1 or 3 at %) alloys elaborated by hot extrusion of rapidly solidified powders. Chemical microanalysis showed the average composition of this phase to be 75 ± 0.5% Al, 12 ± 1%Cr, 12 ± 1% Fe. Annealing treatments led to its transformation into the equilibrium phases Al₁₃Cr₂ and Al₁₃Fe₄, directly at high temperature, or through a metastable and unknown phase, X, at intermediate temperature. This transformation was followed by X-ray diffraction, calorimetry and in situ electron microscopy. The convergent-beam technique was used for characterization of the X phase.     

Structure and properties of coatings on Ni base deposited using a plasma jet before and after electron a beam irradiation

Experimental results for structure, morphology, phase composition and measurements of nano- and microhardness, wear resistance, and adhesion of coatings on a Ni base, which were deposited using a plasma jet, before and after pulsed plasma jet and high-current electron beam melting are presented. Newly formed phases like Cr₃Ni₂ and CrB and intermetallic compounds with molybdenum like Fe₇Mo₆, Fe₃Mo and possibly Fe Mo were found. We also found an effect of phase composition, changed grain dimension and smoothed relief resulting in a factor of three increase in micro- and nanohardness, almost a factor of 20 increase in friction wear resistance and several times increase in coating to substrate adhesion.     

Effect of microstructure on the mechanical properties of as-cast Ti–Nb–Al–Cu–Ni alloys for biomedical application

The correlation between the microstructure and mechanical behavior during tensile loading of Ti_68.8Nb_13.6Al_6.5Cu₆Ni_5.1 and Ti_71.8Nb_14.1Al_6.7Cu₄Ni_3.4 alloys was investigated. The present alloys were prepared by the non-equilibrium processing applying relatively high cooling rates. The microstructure consists of a dendritic bcc β-Ti solid solution and fine intermetallic precipitates in the interdendritic region. The volume fraction of the intermetallic phases decreases significantly with slightly decreasing the Cu and Ni content. Consequently, the fracture mechanism in tension changes from cleavage to shear. This in turn strongly enhances the ductility of the alloy and as a result Ti_71.8Nb_14.1Al_6.7Cu₄Ni_3.4 demonstrates a significant tensile ductility of about 14% combined with the high yield strength of above 820 MPa already in the as-cast state. The results demonstrate that the control of precipitates can significantly enhance the ductility and yet maintaining the high strength and the low Young's modulus of these alloys. The achieved high bio performance (ratio of strength to Young's modulus) is comparable (or even superior) with that of the recently developed Ti-based biomedical alloys.     

Tensile properties of the Cr–Fe–Ni–Mn non-equiatomic multicomponent alloys with different Cr contents

A series of Fe₄₀Mn₂₈Ni_32 − xCr_x (x = 4, 12, 18, 24 (at.%)) multicomponent alloys was prepared by vacuum arc melting. The Fe₄₀Mn₂₈Ni₂₈Cr₄, Fe₄₀Mn₂₈Ni₂₀Cr₁₂ and Fe₄₀Mn₂₈Ni₁₄Cr₁₈ alloys were ductile single phase fcc solid solutions. The Fe₄₀Mn₂₈Ni₈Cr₂₄ alloy had intermetallic sigma phase matrix and was extremely brittle after homogenization. The tensile properties of the Fe₄₀Mn₂₈Ni₂₈Cr₄, Fe₄₀Mn₂₈Ni₂₀Cr₁₂ and Fe₄₀Mn₂₈Ni₁₄Cr₁₈ solid solution alloys were examined in recrystallized condition with average grain size of ~ 10 μm. The yield strength increased from 210 MPa of the Fe₄₀Mn₂₈Ni₂₈Cr₄ alloy to 310 MPa of the Fe₄₀Mn₂₈Ni₁₄Cr₁₈ alloy. The elongation to fracture of the alloys decreased from 71% to 54%, respectively. Solid solution strengthening by the constitutive elements of the alloys was calculated using Labush approach. Strong solid solution strengthening by Cr was predicted. Gypen and Deruyttere approach was used to estimate solid solution strengthening of the Fe₄₀Mn₂₈Ni_32 − xCr_x alloys. Good correlation between predicted solid solution strengthening and the experimental yield strength values was found.