Effects of Al content on porous Fe–Al alloys

Abstract

Porous Fe–Al alloys with the nominal composition ranging from Fe–20 wt-%Al to Fe–60 wt-%Al have been fabricated by Fe and Al elemental powder reactive synthesis. The effects of the Al content on the pore properties of resultant porous Fe–Al alloys were systematically studied. It has been found that the volume expansion, the open porosity and the permeability can be manipulated by varying the Al content and that their maximum values are reached at Fe–45 wt-%Al. Their mechanical properties suggest that they are strong enough for the filtration applications.     

Influence of Al4C3 Particles on Grain Refinement of Mg–3Al Alloys

Al?CSi/Al₄C₃ master alloy has been developed by reacting the SiC particles in Al melt. The extent of SiC conversion to Al₄C₃ in the Al?CSi/Al₄C₃ master alloy has been calculated using optical emission spectroscopy. Experimental results indicated that only 70?% of SiC particles have been converted into Al₄C₃ after the reaction between Al and SiC in Al/5?wt% SiC_p composites at 900?°C. The grain refining efficiency of Al?CSi/Al₄C₃ master alloy has been assessed by adding this into the Mg?C3Al alloy. Grain size of Mg?C3Al alloy has been significantly refined from 480 to 220???m by the addition of 0.07?wt% of Al₄C₃ particles in the form of Al?CSi/Al₄C₃ master alloy.     

Hot-tearing susceptibility of Al–Zn alloys

The modern concepts of the causes of hot tearing are considered and the influence of the solid fraction growth rate of an alloy is studied. The hot-tearing susceptibility (HTS) of binary Al–(5–73) wt % Zn alloys is investigated using backbone tests. The HTS is found to be maximal at ~25 wt % Zn. This maximum cannot be explained by a change in the effective solidification range, since this range of the alloys decreases monotonically with increasing zinc content. The calculations of nonequilibrium solidification by the Scheil–Gulliver model and the solid fraction growth rate of the alloys under study demonstrate that the increase in the HTS induced by an increase in the zinc content from 5 to 25 wt % is related to the decrease in the solid fraction growth rate at the final stages of solidification. The decrease in the HTS at >25 wt % Zn is associated with an increase in the fraction of eutectic in the alloys (the solid fraction growth rate during the eutectic reaction tends toward infinity) and with a change in its morphology.     

Effect of B4C Particle Size on the Properties of Al/(Al–B4C)/Al Functionally Gradient Material

Powder Metallurgy and Metal Ceramics - The functionally gradient material (FGM), consisting of pure Al outer layer and Al–B4C inner layer, was fabricated by semi-continuous casting with...     

Anomalous coarsening behavior of small volume fractions of Ni3Al precipitates in binary NiAl alloys

The kinetics of coarsening of γ′ precipitates in binary NiAl alloys containing nominally 5.72, 5.74 and 5.78 wt% Al and aged at 630°C were investigated by transmission electron microscopy and magnetic analysis. The alloys were each pre-aged at a temperature just below its solvus prior to re-aging at 630°C. The volume fractions of γ′ were low between 0.02 and 0.03. the pre-aging treatment produced microstructures containing precipitates that nucleated heterogeneously on dislocations and grain boundaries, leaving empty matrix areas in which coherent γ′ precipitates subsequently nucleated and coarsened. Measurements were made only on these precipitates. The coarsening kinetics are anomalous in that the rate constant decrease with increasing volume fraction, in contradiction with all the theories of this process. Furthermore, the increase is quite large, exceeding a factor of four over a range of volume fractions that increased by less than 40%. Additionally, the rate constants exceed the values expected from the literature by factors of 10–40. The distributions of particles sizes were measured, and with few exceptions were found to agree with those of earlier investigations. It is suggested that elastic interactions among the γ′ precipitates play a pivotal role in decelerating the kinetics of coarsening, overpowering the expected accelerating effect of increasing volume fraction.     

Isothermal Solidification of an Al–Zn Alloy

In diffusion brazing, a brazing alloy layer thickness introduced into the gap between brazed parts is very small, which hinders the study of the isothermal solidification process. In this work, the isothermal solidification of an Al–Zn alloy is investigated at large volume and mass of the initial liquid that takes part in isothermal solidification. Zinc cylinders are caulked in the holes bored in aluminum cubes. The samples thus assembled are held at 500 ± 10°C for different times. The volume fraction of isothermal solidified crystals has been determined, and the growth rate of isothermal crystals is shown to decrease upon holding. The crystals formed during isothermal solidification width are up to 380 μm and length more than 1 mm. They are observed in the samples that are held more than 2 days. The zinc content in the isothermal solidified crystals corresponds to its mean content in the aluminum solid solution at 490–510°C, according to the Al–Zn phase diagram. The composition of the former liquid that surrounded the crystals during isothermal solidification coincides with the equilibrium composition of the liquid in the Al–Zn system at a temperature of 490–510°C.     

Phase Diagram of the Al ― Rh System

Phase equilibria in the Al Rh system over the range 15-50 at.% Rh were investigated by the methods of scanning electron microscopy, x-ray diffraction and electron-probe microanalysis.     

Mechanical properties of porous Fe–Al intermetallics

Abstract

The effects of Al content and porosity on the mechanical properties of porous Fe–Al intermetallics, particularly at high temperatures, were determined using scanning electron microscopy, X-ray diffraction and mechanical properties testing. Results show that the optimal mechanical properties are achieved at 20 to 30 wt-%Al content. The tensile and bend strengths decrease with increasing Al content at 35 to 60 wt-%Al content. The quantitative relationship between porosity and strength for porous Fe–Al intermetallics can be described as σ_b?=?181(1?θ)^3.3. The strength of porous Fe–Al intermetallics increases at medium temperature with the increase in temperature from room temperature. The maximum tensile strength (50.2 MPa) is achieved at 600°C, which is almost 36.8% higher than that at room temperature.     

Internal oxidation of NiAl and NiAlSi alloys at the dissociation pressure of NiO

NiAl and NiAlSi alloys were internally oxidized at temperatures of 1073–1273 K by the Rhines Pack method. For the NiAl alloy, the oxidation process follows parabolic law and the oxidation front was flat with severe integranular oxidation occurring at 1073 K and extensive grain boundary sliding at 1273 K. As for NiAlSi alloys, the oxidation rate increased with increase of Si content at 1073 K but the rate decreased at higher temperatures due to total or partial continuous oxide layer formation at the internal oxidation front. The depth of intergranular oxidation was also greatly reduced. For all samples, nickel was found to be transported out to the surface with the amount proportional to the Si content. Lattice diffusion (Nabarro-Herring creep) was believed to be the main cause for nickel transport in the NiAl alloy while dislocation pipe diffusion is the mechanism for NiAlSi alloys.     

Effect of modification on the solidification of Al–Si aluminum alloys

The solidification of the AK12 alloy processed by a standard flux and a combined modifying flux, which significantly increases the mechanical properties of the alloy at a significant increase in the modifying effect time, is studied. The experimental results are simulated using the ProCAST software package.     

A Study on Hot Tearing Susceptibility of Al–Cu,Al–Mg,and Al–Zn alloys

The present investigation deals with the hot tearing susceptibility of A206, A518, and A713 alloys. The hot tearing tests of the mentioned alloys were conducted at three different pouring temperatures using sand mold casting. Metallic cores designed to facilitate constrained radial contraction of the aforementioned alloys were used for casting. Macroscopic cracks were found in all the samples except in A518 alloy. It was observed that pouring temperatural and grain size have significant effect on crack susceptibility. Among the investigated alloys, A713 was found to be extremely prone to hot tearing. The microstructure characteristics of the alloys were studied using optical and scanning electron microscopy. Relationships between the pouring temperature, grain size and crack lengths of the alloys were also established.     

Microstructure and Element Profile of Rare Earth Permeating Layer of Al Bronze

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Evaluation of Microstructural Features of HVOF Sprayed Ni–20Al Coatings

The present study evaluates the microstructural features of high velocity oxy-fuel (HVOF) sprayed Ni–20Al coatings with liquefied petroleum gas (LPG) as fuel. The Ni–20Al coatings are commonly used for bond coat applications and as high temperature oxidation resistant coating. The quality of the deposited coating has been evaluated in terms of porosity, oxide content, surface roughness, micro-hardness, composition and morphology (surface and cross-sectional). The results indicate that, it is possible to develop dense Ni–20Al coatings with low oxide and porosity content along with high surface roughness using HVOF technology. Importantly, HVOF sprayed Ni–20Al coatings show better quality as compared to air plasma spray and can be used as an alternative to VPS in terms of quality to cost ratio for bond coat applications.