Effect of Al and C on structure and mechanical properties of Fe–Al–C alloys

Abstract

Effect of aluminium and carbon content on the microstructure and mechanical properties of Fe–Al–C alloys has been investigated. Alloys were prepared by combination of air induction melting with flux cover (AIMFC) and electroslag remelting (ESR). The ESR ingots were hot forged and hot rolled at 1373 K. As rolled alloys were examined using optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to understand the microstructure of these alloys. The ternary Fe–Al–C alloys containing 10·5 and 13 wt-%Al showed the presence of three phases: FeAl with disordered bcc structure, Fe₃Al with ordered DO₃ structure and Fe₃AlC_0·5 precipitates with L′1₂ structure. Addition of high concentration of carbon to these alloys resulted in excellent hot workability and superior tensile at room temperature as well as tensile and creep properties at 873 K. An increase in Al content from 9 to 13 wt-% in Fe–Al–C alloys containing the same levels of carbon has no significant influence on strength and creep properties at 873 K, however resulted in significant improvement in room temperature strength accompanied by a reduction in room temperature ductility.     

Mechanical Alloying of Co and Al Powders

1.IntroductionMechanical alloying is one of the effec-tive methods to prepare amorphous alloys[1].This method was first used by Koch etal.to prepare the Ni_(60)Nb_(40)amorphous alloy[2].Since then many other amorphousbinary alloys have been prepared by the     

Dilatometric Sintering of Ti-2Al and Ti-5Al Elemental Powders

The effect of Al addition （2 and 5 at. pct） on sintering kinetics of Ti power were investigated. Al reduces the sintering rates, sinter density, increases activation energy of sintering and accelerates the grain growth. Sintering was controlled by mixed mode, i.e. transient liquid phase sintering, formation of intermetallics, and Ti grain boundary diffusion in TiAl2 and other intermetallics.     

Synthesis and microstructural characterization of Al–Ni3Al composites fabricated by press-sintering and shock-compaction

Aluminum matrix composites reinforced with nanocrystalline Ni3Al intermetallic particles, were synthesized using powder metallurgy techniques. Nanocrystalline Ni3Al was obtained by mechanical alloying of Ni75–Al25 stoichiometric mixture from elemental powders after 900 ks of milling with a 5 nm grain size average. Mixture powders of aluminum with 0.007, 0.02 and 0.04 volume fractions of Ni3Al intermetallic particles were compacted using two different compaction methods, the cold isostatic press and sintered at 873 K and the shock-compaction technique. Microstructure of shock-compacted composites showed fine particles of a few microns and also coarse particles less than 100 μm homogeneously distributed on the matrix, also the presence of micro-cracks and low porosity. However the nanoscale features of intermetallic was retained. On the other hand, the press and sintered composites showed good densification. The densities of the composites were about 90% and 94% of the theoretical density for the shock-compacted and press-sintered process, respectively. Finally, the results of hardness measurements showed that the nanocrystalline Ni3Al reinforcement improves the hardness of Al matrix for all conditions. The highest hardness was obtained for the Al–4 vol.%Ni3Al shock-compacted composite.     

Corrosion Behavior and Protection Efficiency of 2024Al and SiCp／2024Al Metal Matrix Composite

The corrosion resistance of 2024 Al and SiC particle reinforced 2024 Al metal matrix composite(SiCp/2024Al MMC) in 3.5% NaCl solution was investigated with electrochemical method and immersion test, and the corrosion protection of sulfuric acid anodized coatings on both materials was evaluated by electrochemical impedance spectroscopy.The results showed that the SiCp/2024AlMMC is more susceptible to corrosion than its matrix alloy in 3.5% NaCl.For 2024Al,the anodized coating provides excellent corrosion resistance to 3.5%NaCl.The anodized coating on the SiCp/2024Al provides satisfactory corrosion protection,but it is not as effective as that for 2024Al because the structure of the anodized layer is affected by the SiC particulates.     

Eutectic spacing and faults of directionally solidified Al–Al3Ni eutectic

The Al–Al₃Ni eutectic was directionally solidified at a thermal gradient of 4.5 K/mm in a vacuum Bridgman–type furnace in order to study eutectic spacing selection criterion.The microstructure was examined in transverse and longitudinal sections and the interrod spacings were measured at different growth velocity. It has been shown that the interrod spacing is not unique and displays a limited range for rodlike Al–Al₃Ni eutectic alloy. The initial growth velocities are not responsible for the eutectic spacing range, while such faults as branching, endingand diameter change have a significant influence on the eutectic spacing adjustment.     

Eutectic spacing and faults of directionally solidified Al–Al3Ni eutectic

The Al–Al₃Ni eutectic was directionally solidified at a thermal gradient of 4.5 K/mm in a vacuum Bridgman-type furnace in order to study eutectic spacing selection criterion. The microstructure was examined in transverse and longitudinal sections and the interrod spacings were measured at different growth velocity. It has been shown that the interrod spacing is not unique and displays a limited range for rodlike Al–Al₃Ni eutectic alloy. The initial growth velocities are not responsible for the eutectic spacing range, while such faults as branching, ending and diameter change have a significant influence on the eutectic spacing adjustment.     

Synthesis and characterisation of nanostructured Al–Al3V and Al–(Al3V–Al2O3) composites by powder metallurgy

In this study, the formation and characterisation of Aluminium (Al)-based composites by mechanical alloying and hot extrusion were investigated. Initially, the vanadium trialuminide (Al₃V) particles with nanosized structure were successfully produced by mechanical alloying and heat treatment. Al₃V–Al₂O₃ reinforcement was synthesised by mechanochemical reduction during milling of V₂O₅ and Al powder mixture. In order to produce composite powders, reinforcement powders were added to pure Al powders and milled for 5?h. The composite powders were consolidated in an extrusion process. The results showed that nanostructured Al-10?wt-% Al₃V and Al-10?wt-% (Al₃V–Al₂O₃) composites have tensile strengths of 209 and 226?MPa, respectively, at room temperature. In addition, mechanical properties did not drop drastically at temperatures of up to 300°C.     

Synthesis and Characterization of Mixed Al+AlN Nanoparticles

Mixed Al+AlN nanoparticles were synthesized by an active plasma-metal reaction method. Mean particle size of the mixed Al+AlN nanoparticles is about 30-50 nm. Defects were found in some AlN particles. Moreover, the AlN ratio and its particle size in mixed Al+AIN nanoparticles obtained in different atmospheres (N2+Ar) increase with increasing N2 particle pressure, and the specific sudece areas of the mixed Al+AlN nanoparticles increase with the AlN ratio. The surface degradation of the Al+AlN exposed to air is estimated by the infrared absorption spectra     

Influence of retrogression and reaging on microstructure and properties of 8090 Al–Li alloy

Abstract

An investigation was made into the influence of a retrogression and reaging treatment on the microstructure, tensile properties, and stress corrosion cracking resistance of 8090 Al–Li alloy. The results show that retrogression of the material at 230°C for 40 min or 325°C for 1·5 min, and then reaging to the peak aged condition, can result in an improved combination of tensile strength and stress corrosion cracking resistance. Through retrogression and reaging treatment, the alloy almost achieves the strength of the peak aged state and the stress corrosion cracking resistance of the overaged state. Transmission electron microscopy indicates that the δ′ phase dissolves during retrogression and reprecipitates during reaging, thus increasing the strength. The T₂ phase precipitates and grows during both retrogression and reaging, which results in the increase of stress corrosion cracking resistance.

MST/1670     

Influence of Alternative Magnetic Field on the Diffusion of Al and Mg

The influence of an alternative magnetic field on the diffusion of Al and Mg in AI-Mg diffusion couple is studied. The diffusion zone is composed of two intermediate phases, namelyβ and γ phase. Thickness of each intermediate phase is examined. The results show that the alternative magnetic field increases the thicknesses of βand γ phase zone and the layer growth ofβ and γphase obeys the parabolic rate law. The growth rate of the β and γ phase are increased with the application of the alternative magnetic field. This change is manifested through a change in the frequency factor k0 and not through a change in the activation energy Q. The frequency factor k0 for intermediate phase growth with an alternative magnetic field is 39.95 cm2/s for 7 phase and 2.84×10-4 cm2/s for β phase compared with those without the magnetic field is 22.4 cm2/s for 7 phase and 1.53×10-4 cm2/s for β phase.     

Critical and Impeding Pressures of Al Evaporation during ISM Processing of NiAl

In this paper, the critical pressure pcrit and impeding pressure pimpe of the elemental evaporation were defined and studied based on the calculation of the relationship between the evaporation loss rate Nm and the chamber pressure p during melting of NiAl alloys. When the chamber pressure is lower than pcrit or higher than Pimpe Nm tends to be the maximum or minimum value and remains almost unchanged. However, declines sharply with the increase of the chamber pressure when pcrit相似文献   

Microstructure and Mechanical Properties of Rapidly Solidified Hypereutectic Al–Si and Al–Si–Fe Alloys

The microstructure and mechanical properties of rapidly solidified Al–18 wt% Si and Al–18 wt% Si–5 wt% Fe alloys were investigated by a combination of optical microscopy, scanning electron microscopy, transmission electron microscopy, x-ray diffraction, tensile testing, and wear testing. The centrifugally atomized binary alloy powder consisted of the -Al (slightly supersaturated with Si) and Si phases and the ternary alloy powder consisted of the -Al (slightly supersaturated with Si), silicon, and needle-like metastable Al–Fe–Si intermetallic phases. During extrusion the metastable -Al₄FeSi₂ phase in the as-solidified ternary alloy transformed to the equilibrium -Al₅FeSi phase. The tensile strength of both the binary and the ternary alloys decreased with a high-temperature exposure, but a significant fraction of the strength was retained up to 573 K. The specific wear gradually increased with increasing sliding speed but decreased with the addition of 5 wt% Fe to the Al–18 wt% Si alloy. The wear resistance improved with annealing due to coarsening of the silicon particles.     

Development of Some Fundamental Research of SiC_W/Al Composites in HIT PartⅠ Microstructure and SiC/Al Interface of SiC_W/Al Composites

The microstructure of SiC whisker reinforced aluminium alloy (SiC_w/Al) composite is reviewed,andthe SiC-Al interface in SiC_w/Al composite is especially discussed,The main contents aremorphology of the aluminium matrix in SiC_w/Al composite;microstructures and defects of SiCwhiskers in SiC_w/Al composite and bonding mechanisms of the SiC-Al interface in SiC_w/Al com-posite.     

Effect of alumina particle size and thermal condition of casting on microstructure and mechanical properties of stir cast Al–Al2O3 composites

Abstract

Metal matrix composites are considered as a distinct category of the advanced materials, which have low weight, high strength, high modulus of elasticity, low thermal expansion coefficient and high wear resistance. Among them, Al–Al₂O₃ composites have achieved significant attention due to their desired properties. In the present research, Al–Al₂O₃ composites with 5 vol.-% alumina were produced by stir casting at a temperature of 800°C. Two different particle sizes of alumina were used as 53–63 and 90–105 μm. The microstructure of the samples was evaluated by SEM. In addition, the mechanical properties of the samples were measured, and hence, the optimum temperature and particle size of alumina to be added to the Al matrix were determined. The results demonstrated the positive effect of alumina on improving the properties of Al–Al₂O₃ composites.     

Processing and properties of Al–Li–SiCp composites

Al–Li–SiC_p composites were fabricated by a modified version of the conventional stir casting technique. Composites containing 8, 12 and 18 vol% SiC particles (40 mm) were fabricated. Hardness, tensile and compressive strengths of the unreinforced alloy and composites were determined. Ageing kinetics and effect of ageing on properties were also investigated. Additions of SiC particles increase the hardness, 0.2% proof stress, ultimate tensile strength and elastic modulus of Al–Li–8%SiC and Al–Li–12%SiC composites. In case of the composite reinforced with 18% SiC particles, although the elastic modulus increases the 0.2% proof stress and compressive strength were only marginally higher than the unreinforced alloy and lower than those of Al–Li–8%SiC and Al–Li–12%SiC composites. Clustering of SiC particles appears to be responsible for reduced the strength of Al–Li–18%SiC composite. The fracture surface of unreinforced 8090 Al-Li alloy (8090Al) shows a dimpled structure, indicating ductile mode of failure. Fracture in composites occurs by a mixed mode, giving rise to a bimodal distribution of dimples in the fracture surface. Cleavage of SiC particles was also observed in the fracture surface of composites. Composites show higher peak hardness and lower peak ageing time compared with unreinforced 8090Al alloy. Macroand microhardness increase significantly after peak ageing. Ageing also results in considerable improvement in strength of the unreinforced 8090Al alloy and its composites. This is attributed to formation of δ^' (Al₃Li) and S^' (Al₂CuMg) precipitates during ageing. Per cent elongation, however, decreases due to age hardening. Al–Li–12%SiC, which shows marginally lower UTS and compressive strength than the Al–Li–8%SiC composite in extruded condition, exhibits higher strength than Al–Li–8%SiC in peak-aged condition.     

Structure and microstructure of leached Raney-type Al–Ni powders

The structure and microstructure of some leached Raney-type Al–Ni alloys of different compositions have been investigated by neutron diffraction and by small-angle neutron scattering. It was found that all alloys contain a crystalline face-centred cubic (fcc) Ni phase as well as an Al₃Ni₂ phase, the amount of which is decreasing with increasing Al content of the initial alloy. Both the Ni and the Al₃Ni₂ phases are conjectured to be non-stoichiometric. There is no indication of any other crystalline phase. The size of the Ni crystallites in all leached alloys has been found to be of the order of 30 Å, whereas the size of the Al₃Ni₂ ones varies with initial alloy composition and is found to be in the range of 100–250 Å. The change in structure by doping the initial alloys with small amounts of Ti and Cr is after leaching marginal.     

Optical Properties of Liquid Aluminum and Al–Ce Alloy

The Beattie ellipsometric method is used to investigate the index of refraction and the absorption coefficient of liquid aluminum and Al–3 at. % Ce alloy in the wavelength range from 0.44 to 2.3 m at a temperature of 1173 K. The experimental results are used to calculate the dispersion dependences of light conductance, reflectivity, and functions of characteristic loss of electron energy. The results of measurements in the infrared (IR) spectrum are used to determine the concentration of conduction electrons, plasma frequency, relaxation frequency, and the limiting light conductance. It turns out that an addition of 3 at. % Ce to aluminum causes almost no change in the concentration of charge carriers, whereas the relaxation frequency increases, which leads to a decrease in the electrical conductivity of the liquid alloy.