Effect of Mo on microstructure and mechanical properties of bulk nanocrystalline Fe3Al materials prepared by aluminothermic reaction

Abstract

Bulk nanocrystalline Fe₃Al based materials with 5, 10 and 15 wt-%Mo were prepared by aluminothermic reaction. The microstructure and mechanical properties of the materials were investigated. It was shown that the materials consisted of a nanocrystalline matrix phase that was composed of Fe, Al and Mo and a little Al₂O₃ contamination phase. The nanocrystalline phase had a disordered bcc crystal structure. Average grain sizes of the nanocrystalline phase of the materials with 5, 10 and 15 wt-%Mo were 19, 31 and 24 nm respectively and that of the material with 5 wt-%Mo was the smallest. The materials with 10 and 15 wt-%Mo exhibited brittle behaviour in compression, whereas the material with 5 wt-%Mo had a large plastic deformation. The material with 5 wt-%Mo had the highest bending strength and the lowest compressive yield strength.     

Effect of annealing on microstructure and mechanical properties of bulk nanocrystalline Fe3Al alloy with 5 wt.% Cu prepared by aluminothermic reaction

Microstructure and mechanical properties of bulk nanocrystalline Fe₃Al based alloy with 5 wt.% Cu prepared by aluminothermic reaction before and after annealed at 873, 1073 and 1273 K for 8 h were investigated. Microstructures of the alloy before and after the annealing consisted of a Fe-Al-Cu matrix, a little Al₂O₃ sphere and Fe₃AlC_x fiber phases. The matrix of the alloy before the annealing was composed a nanocrystalline phase with disordered bcc crystal structure and a little amorphous phase. The amorphous phase disappeared after the annealing and Fe₃Al phase with ordered DO₃ structure appeared in the alloy after annealed at 1073 and 1273 K in the matrix of the alloy. Size of the Fe₃AlC_x fiber phase increased with the annealing temperature. The alloy after the annealing had better plasticity, higher yield strength than that of the alloy before the annealing, and the alloy after annealed at 1273 K had the highest yield strength.     

合金元素对块体纳米晶Fe3Al材料磁学性能的影响

为了研究合金元素对块体纳米晶Fe3Al材料磁学性能的影响,通过铝热反应熔化法制备了纳米晶Fe3Al以及分别含Ni质量分数10%、Cr质量分数10%、Mn质量分数10%和含Ni质量分数10%-Cu质量分数2%的块体纳米晶Fe3Al.在振动样品磁强计(VSM)上测得合金的磁滞回线,分析其磁性能,采用X射线衍射仪进行结构分析和平均晶粒尺寸计算.结果表明:各样品的磁滞回线呈倾斜状且狭长,磁滞损耗很小;含Ni质量分数10%的样品饱和磁化强度Ms较大,剩余磁化强度Mr和矫顽力Hc较其他样品最小,具有较好的软磁性能;添加合金元素后几种材料的晶粒尺寸变小,磁性能有较大变化,合金元素对纳米晶Fe3Al块体材料的磁性能影响明显.     

Large electrical resistivity and high saturation magnetization nanocrystalline Fe86B13Cu1 alloy prepared by hot isothermal pressing

The effects of hot isothermal pressing (HIP) on the microstructures and magnetic properties of nanocrystalline Fe₈₆B₁₃Cu₁ ribbons were studied. It is shown that the precipitation of Fe₃B phase is suppressed and the grain size of α-Fe phase decreases to 13.2 nm when amorphous Fe₈₆B₁₃Cu₁ ribbons are annealed by HIP under the pressure of 150 MPa. A high electrical resistivity and high saturation magnetization nanocrystalline soft magnetic material is prepared by HIP owing to the suppression of the precipitation of Fe₃B phase and a marked decrease in the grain size of α-Fe phase. The prepared sample exhibits a large electrical resistivity of 183 μΩ cm, a high saturation magnetization of 1.94 T and a low coercive force of 12 A/m.     

Effect of Nb2O5 on the microstructure and mechanical properties of TiAl based composites produced by hot pressing

In situ composites of TiAl reinforced with Al₂O₃ particles are successfully synthesized from an elemental powder mixture of Ti, Al and Nb₂O₅ by the hot-press-assisted reaction synthesis (HPRS) method. The as-prepared composites are mainly composed of TiAl, Al₂O₃, NbAl₃, as well as small amounts of the Ti₃Al phase. The in situ formed fine Al₂O₃ particles tend to disperse on the matrix grain boundaries of TiAl resulting in an excellent combination of matrix grain refinement and uniform Al₂O₃ distribution in the composites. The Rockwell hardness and densities of TiAl based composites increase gradually with increasing Nb₂O₅ content, and the flexural strength and fracture toughness of the composites have the maximum values of 634 MPa and 9.78 MPa m^1/2, respectively, when the Nb₂O₅ content reaches 6.62 wt.%. The strengthening mechanism was also discussed.     

Some observations on the hydrogen embrittlement of Fe3Al-Fe3AlC intermetallic compounds

Effects of carbon on the hydrogen embrittlement behaviour of Fe₃Al intermetallic compounds were observed by revealing its microstructure. In low-carbon content (0.05 wt.%) alloy embrittlement was found in the Fe₃Al phase, in moderate level of carbon content (0.14-0.5 wt.%) there was no embrittlement in the alloy, whereas in high level of carbon content (1 wt.%) embrittlement was found in the interdendritic region.     

Microstructure and mechanical properties of nanostructure multilayer CrN/Cr coatings on titanium alloy

Five different nanostructured, multilayer coatings (CrN/Cr)x8 with different thickness ratio of Cr and CrN layers were deposited by PAPVD (Plasma Assisted Physical Vapour Deposition) vacuum arc method on Ti6Al4V titanium alloy. The microstructure, chemical and phase composition of the CrN and Cr sub-layers were characterized by SEM with EDX and Cs-corrected dedicated STEM on cross-sections prepared by focus ion beam. Besides, hardness and Young's modulus of the (Cr/CrN)x8 coatings has been measured. The adhesion has been tested by scratch test method. The obtained (CrN/Cr) multilayer coatings, 5-6 μm in thickness, have homogeneous and nanocrystalline structure, free of pores and cracks. The microstructures of Cr and CrN layers consist of columnar grains below 100 nm in diameter. The hardness and Young's modulus of these coatings depend linearly on thickness ratio of Cr and CrN layers. The decrease of the thickness ratio Cr/CrN 0.81 to 0.15 results in the increase of hardness from 1275 HV to 1710 HV and Young's modulus from 260 GPa to 271 GPa.     

A study of the nanostructure and hardness of electron beam evaporated TiAlBN Coatings

TiAlBN coatings have been deposited by electron beam (EB) evaporation from a single TiAlBN material source onto AISI 316 stainless steel substrates at a temperature of 450 °C and substrate bias of − 100 V. The stoichiometry and nanostructure have been studied by X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy. The hardness and elastic modulus were determined by nanoindentation. Five coatings have been deposited, three from hot-pressed TiAlBN material and two from hot isostatically pressed (HIPped) material. The coatings deposited from the hot-pressed material exhibited a nanocomposite nc-(Ti,Al)N/a-BN/a-(Ti,Al)B₂ structure, the relative phase fraction being consistent with that predicted by the equilibrium Ti-B-N phase diagram. Nanoindentation hardness values were in the range of 22 to 32 GPa. Using the HIPped material, coating (Ti,Al)B_0.29N_0.46 was found to have a phase composition of 72-79 mol.% nc-(Ti,Al)(N,B)_1 − x+ 21-28 mol.% amorphous titanium boride and a hardness of 32 GPa. The second coating, (Ti,Al)B_0.66N_0.25, was X-ray amorphous with a nitride+boride multiphase composition and a hardness of 26 GPa. The nanostructure and structure-property relationships of all coatings are discussed in detail. Comparisons are made between the single-EB coatings deposited in this work and previously deposited twin-EB coatings. Twin-EB deposition gives rise to lower adatom mobilities, leading to (111) (Ti,Al)N preferential orientation, smaller grain sizes, less dense coatings and lower hardnesses.     

Synthesis and mechanical properties of high-purity Cr2AlC ceramic

High-purity and dense Cr₂AlC has been successfully fabricated by hot-pressing, using Cr, Al and graphite as raw materials. Delamination, kink bands, monolamellar kink, transgranular crack and transgranular fracture of bulk Cr₂AlC are found during the room-temperature test. The density, Vickers hardness, flexural strength, Young's modulus, compressive strength and fracture toughness of the Cr₂AlC are 5.17 g/cm³, 4.9 GPa, 469 ± 27 MPa, 282 GPa, 949 ± 22 MPa and 6.22 ± 0.26 MPa m^1/2, respectively. The strength of Cr₂AlC could be greatly improved by second phase of Cr₇C₃. And the slipping of basal planes and slip system cold be hindered by Cr₇C₃, thus resulting in a lower toughness.     

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.     

Annealing effects on microstructure and mechanical properties of sputtered multilayer Cr(1 − x)AlxN films

Multilayer Cr_(1 − x)Al_xN films with a total thickness of 2 μm were deposited on high-speed steel by medium frequency magnetron sputtering from Cr and Al-Cr (70 at.% Al) targets. The samples were annealed in air at 400 °C, 600 °C, 800 °C and 1000 °C for 1 hour. Films were characterized by cross-sectional scanning electron microscopy and X-ray diffraction analysis. The grain size of the as-deposited multilayer films is about 10 nm, increasing with the annealing temperature up to 100 nm. Interfacial reactions have clearly changed at elevated annealing temperatures. As-deposited films' hardness measured by nanoindentation is 22.6 GPa, which increases to 26.7 GPa when the annealing temperature goes up to 400 and 600 °C, but hardness decreases to 21.2 GPa with further annealing temperature increase from 600 to 1000 °C. The multilayer film adhesion was measured by means of the scratch test combined with acoustic emission for detecting the fracture load. The critical normal load decreased from 49.7 N for the as-deposited films to 21.2 N for the films annealed at 1000 °C.     

Effect of V content on the microstructure and mechanical properties of Mo2FeB2 based cermets

Four series of cermets with V content between 0 and 7.5 wt.% in 2.5 wt.% increments were studied by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The transverse rupture strength (TRS), hardness (HRA) and fracture toughness (K_IC) were also measured. It was found that the grain size was affected by the V content. The cermets with 2.5 wt.% V addition exhibited the smallest grain size. An increasing V content decreased the wettability of the binder on the Mo₂FeB₂ hard phase, and accordingly resulted in the increase of porosity and aggregation of ceramic grains. EDS results showed that V addition occurred primarily in the hard phase, with a little amount in the Fe alloy binder. In addition, the content of Mo element in the binder decreased with increasing V content. The cermets with 2.5 wt.% V addition showed the highest TRS, hardness and fracture toughness of 2350 MPa, HRA 90.6 and 15.1 MPa m^1/2, respectively.     

Effects of calcium on the microstructures and tensile properties of Mg-5Li-3Al alloys

The as-cast Mg-5Li-3Al-xCa (x = 0, 0.5, 1, 1.5 wt.%) was prepared with vacuum induction melting furnace, then processed by hot extrusion. The microstructures and tensile properties were investigated. The results show that the grains of as-cast alloys were refined gradually with the increase of Ca content from 0.5 wt.% to 1 wt.%, while the Ca content increases to 1.5 wt.%, the grain size increases. The microstructures of investigated alloys were further refined after hot extrusion. Both as-cast and as-extruded Mg-5Li-3Al-0.5Ca alloys have the highest mechanical properties, which is mainly attributed to the grain refinement caused by the addition of Ca and the formation of strengthening phase, Al₄Ca. When the addition of Ca is up to 1-1.5 wt.%, the tensile properties of alloys are worsened due to the excessive (Mg, Al)₂Ca eutectic phase forming at grain boundary.     

A nanometre-sized porous phase in iron-carbon-boron system

A porous phase is detected in a Fe-0.28 wt.%C-0.1 wt.%B alloy. The porous phase is mainly located at the grain boundary region and the pore size ranges from about 10 nm to 500 nm. The chemical composition of the porous phase is very close to Fe₃(B_0.7C_0.3) with an orthorhombic lattice. The result shows an opportunity to produce bulk steel matrix composites with a porous second phase.     

Synthesis of CuCr and CuCrAg alloy with nano-ceramic dispersion by mechanical alloying and consolidation by laser assisted sintering

Cu-4.5Cr and Cu-4.5Cr-3Ag (in wt%) alloys without or with 10 wt% nanocrystalline Al₂O₃ and ZrO₂ dispersion have been synthesized by mechanical alloying or milling and consolidated by laser assisted sintering in Ar atmosphere. Microstructural characterization by scanning and transmission electron microscopy and phase analysis by X-ray diffraction suggest that the alloyed matrix undergoes significant grain growth after sintering while the dispersoids retain their ultrafine size and uniform distribution in the matrix. The dispersion of nano-Al₂O₃ is more effective than that of nano-ZrO₂ in enhancing the mechanical properties due to the smaller initial particle size of Al₂O₃ than that of ZrO₂. In general, laser sintering of mechanically alloyed Cu-4.5Cr and Cu-4.5Cr-3Ag alloys with 10 wt% nanocrystalline Al₂O₃ at 100 W laser power and 1-2 mm s⁻¹ scan speed yields the optimum combination of high density (7.1-7.5 mg m⁻³), hardness (165-225 VHN), wear resistance and electrical conductivity (13-20% IACS).     

Effect of aluminum content on solidification microstructure and properties of Fe‐Cr‐B‐Al alloys

The microstructures and mechanical properties of eight kinds of Fe‐Cr‐B‐Al alloys containing X wt.%Al‐0.35 wt.%C‐10.0 wt.%Cr‐1.4 wt.%B‐0.6 wt.%Si‐0.8 wt.%Mn (X = 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0) were studied by means of optical microscopy (OM), scanning electron microscopy (SEM), X‐ray diffraction (XRD), Rockwell hardness and Vickers micro‐hardness testers. The results indicate that the as‐cast microstructure of aluminium‐free sample consists of the martensite, austenite and eutectic borocarbides, and the eutectic borocarbides are the mixture of (Fe, Cr)₂B and (Cr, Fe)₇(C, B)₃, and its hardness reaches 65 HRC. When a small amount of aluminium element (Al ? 1.0 wt.%) is added, the phase composition has no significant change, and the hardness excels 65 HRC. When the concentration of aluminium reaches 1.5 wt.%, the matrix of Fe‐Cr‐B‐Al alloy becomes pearlite and δ‐ferrite, leading to a sharply decrease of the hardness. The proportion of ferrite goes up along with increasing aluminium concentration, and the hardness of Fe‐Cr‐B‐Al alloy has slight decrease.     

Heteroepitaxial growth of Fe2Al5 inhibition layer in hot-dip galvanizing of an interstitial-free steel

This work presents characterization results on inhibition layers formed on a TiNb-stabilized interstitial-free steel after short time galvanizing. The Fe-Al and steel interface was free from oxide, so that the Fe-Al intermetallic compound could directly nucleate on ferrite grains. Electron diffraction performed in a transmission electron microscope showed that only Fe₂Al₅ was formed and it had a well-defined orientation relationship of [110]_{Fe(sub/2)Al(sub/5)}// [111]_Fe, (001) _{Fe(sub/2)Al(sub/5)}//(01?1)_Fe and (11?0) _{Fe(sub/2)Al(sub/5)}//(21?1?)_Fe with Fe substrate. The structure of the interfaces between Fe₂Al₅ and Fe is discussed. The epitaxially nucleated Fe₂Al₅ grains on Fe substrate had very small grain size, 20 nm or less, and several variants were intimately mixed. The grains grew rapidly to hundreds of nanometers toward the Zn side.     

Relationship between microstructure,hardness and corrosion resistance in 20 wt.%Cr, 27 wt.%Cr and 36 wt.%Cr high chromium cast irons

The microstructures, hardness and corrosion behavior of high chromium cast irons with 20, 27 and 36 wt.%Cr have been compared. The matrix in as-cast 20 wt.%Cr, 27 wt.%Cr and 36 wt.%Cr high chromium cast irons is pearlite, austenite and ferrite, respectively. The eutectic carbide in all cases is M₇C₃ with stoichiometry as (Cr_3.37, Fe_3.63)C₃, (Cr_4.75, Fe_2.25)C₃ and (Cr_5.55, Fe_1.45)C₃, respectively. After destabilization at 1000 °C for 4 h followed by forced air cooling, the microstructure of heat-treatable 20 wt.%Cr and 27 wt.%Cr high chromium cast irons consisted of precipitated secondary carbides within a martensite matrix, with the eutectic carbides remaining unchanged. The type of the secondary carbide is M₇C₃ in 20 wt.%Cr iron, whereas both M₂₃C₆ and M₇C₃ secondary carbides are present in the 27 wt.%Cr high chromium cast iron. The size and volume fraction of the secondary carbides in 20 wt.%Cr high chromium cast iron were higher than for 27 wt.%Cr high chromium cast iron. The hardness of heat-treated 20 wt.%Cr high chromium cast iron was higher than that of heat-treated 27 wt.%Cr high chromium cast iron. Anodic polarisation tests showed that a passive film can form faster in the 27 wt.%Cr high chromium cast iron than in the 20 wt.%Cr high chromium cast iron, and the ferritic matrix in 36 wt.%Cr high chromium cast iron was the most corrosion resistant in that it exhibited a wider passive range and lower current density than the pearlitic or austenitic/martensitic matrices in 20 wt.%Cr and 27 wt.%Cr high chromium cast irons. For both the 20 wt.%Cr and the 27 wt.%Cr high chromium cast irons, destabilization heat treatment gave a slight improvement in corrosion resistance.     

Fabrication and evaluation of mechanical and tribological properties of boron carbide reinforced aluminum matrix nanocomposites

In this study, fabrication and characterization of bulk Al–B₄C nanocomposites were investigated. B₄C nanoparticles were mixed with pure Al powder by ball milling to produce Al–B₄C powder. Al–B₄C powders containing different amounts of B₄C (5, 10 and 15 wt.%) were subsequently hot pressed to produce bulk nanocomposite samples. Consolidated samples were characterized by hardness, compression and wear tests. Results showed that the sample with 15 wt.% B₄C had the optimum properties. This sample had a value of 164 HV which is significantly higher than 33 HV for pure Al. Also, ultimate compressive strength of the sample was measured to be 485 MPa which is much higher than that for pure Al (130 MPa). The wear resistance of the nanocomposites increased significantly by increasing the B₄C content. Dominant wear mechanisms for Al–B₄C nanocomposites were determined to be formation of mechanical mixed layer on the surface of samples.     

Effect of chromium substitution on structure and magnetic properties of Bi2Fe4O9

Orthorhombic Bi₂Fe_4 − xCr_xO₉ (x = 0.0, 0.25, and 0.75) nanoplatelets were synthesized by a simple hydrothermal method. The structure, morphology, and magnetic properties of the obtained powders have been characterized. Calculation of the lattice parameters of Bi₂Fe_4 − xCr_xO₉, as well as bond lengths and angles, was carried out by X-ray diffraction Rietveld refinement. The volumes of the metal-oxygen tetrahedra and octahedra were calculated to be sequentially increasing as the Cr doping level increases. The samples undergo an antiferromagnetic transition at 250 ± 5 K. The magnetic moments of the samples increase with higher Cr doping level. The 3d electron spin state for Fe³⁺ in the as-prepared samples is different, which is possibly due to the distortion of Fe-O tetrahedra and octahedra in the crystal structure after chromium substitution.