Pressure infiltration of molten aluminum for densification of environmental barrier coatings

Environmental barrier coatings (EBCs) effectively protect the ceramic matrix composites (CMCs) from harsh engine environments, especially steam and molten salts. However, open pores inevitably formed during the deposition process provide the transport channels for oxidants and corrosives, and lead to premature failure of EBCs. This research work proposed a method of pressure infiltration densification which blocked these open pores in the coatings. These results showed that it was difficult for aluminum to infiltrate spontaneously, but with the increase of external gas pressure and internal vacuum simultaneously, the molten aluminum obviously moved forward, and finally stopped infiltrating at a depth of a specific geometry. Based on the wrinkled zigzag pore model, a mathematical relationship between the critical pressure with the infiltration depth and the pore intrinsic geometry was established. The infiltration results confirmed this relationship, indicating that for a given coating, a dense thick film can be obtained by adjusting the internal and external gas pressures to drive a melt infiltration.

Numerical Study of the Effect of Workpiece Thickness on the Interfacial Behavior of a Molten Aluminum Droplet on a Zinc-coated Steel Sheet

In brazing, the interfacial conditions between the molten filler material and the solid workpiece are important, yet they cannot be observed experimentally. A two-dimensional axisymmetric simulation was conducted to analyze the behavior of a single droplet of molten aluminum on zinc-coated steel sheet as a simplified brazing process. The simulation models were verified through a comparison with experimental results in terms of bead shape, zinc distribution, and molten metal behavior. The results show that Young’s equation was not valid in explaining the wetting behavior because of the instant solidification. In this respect, the effects of the workpiece thickness and wetting angle on the bead width were negligible. Two periods of time, namely the times for the temperature difference and solidification, and their ratio (interface number) were defined to analyze the temperature behavior at the interface over time as well as the effects of workpiece thickness. The interfacial temperature behaviors tended to be divided into three regions: linear (or inversely proportional), singular, and convergence. The interface number converged to a value of one with the increase in the thickness.

Preparation Process and Phase Transformation of Al-5Ti-0.25C Master Alloy Adopting Ti Machining Chips

The refining performance of Al-Ti-C master alloys is substantially compromised by the inferior wettability between graphite and molten aluminum. In this paper, the Al-5Ti-0.25C master alloy was successfully prepared by reacting Ti machining chips, graphite, and molten aluminum. In order to determine a simple method of improving the wettability, the optimal preparation process and phase transformation of the Al-5Ti-0.25C master alloy were investigated using an optical microscope, X-ray diffractometer, and scanning electron microscope equipped with an energy dispersive spectrometer. The results show that the feeding method using a prefabricated block made from Ti chips, Al chips, and graphite effectively improves the wettability between graphite and molten aluminum and increases the recovery rate of graphite. When the reaction temperature is low (1223 K), the agglomeration of TiAl3 is caused. When the reaction temperature is high (1373 K), the morphology of TiAl3 changes from block-like to needle-like and increases its size. Further, a short reaction time (30 min) results in the incomplete dissolution of the Ti chips, while a long reaction time (90 min) causes the TiAl3 to transform into needle-like morphologies. The microstructural observation of undissolved Ti chips shows that TiAl3 and TiC are formed around it, which proves the transformation of Ti chips to TiAl3 and TiC. In addition, the enrichment of TiC and Al4C3 was observed in the vicinity of TiAl3, and a reaction model for the formation of TiC from the reaction of Al4C3 and TiAl3 was presented.

Ni-5wt% Al Coatings Deposited by Twin Wire Arc Spraying for Molten Aluminum Attack Protection

Nickel-aluminum alloys are widely used in harsh environments due to their corrosion resistance, high melting temperature, and thermal conductivity. In this work, Ni-5wt%Al coatings were deposited by twin-wire arc spraying (TWAS) on tool steel using a design of experiments approach to study the effect of process parameters on coating microstructure and performance. Test results presented in the form of process maps show how N2 pressure, stand-off distance, and current affect in-flight particle velocity and temperature as well as coating thickness and oxide content. Using this information, optimized coatings were then deposited on test substrates and subjected, along with uncoated tool steel, to several hours of molten aluminum attack. The coated samples showed no signs of physical or chemical damage, whereas the uncoated substrates experienced oxidation, aluminum infiltration, and formation of Fe-Al intermetallics.

Aluminum Slag Separation Process Analysis Through a Vibratory Machine in the Foundry Process

A The aluminum smelting industry has some challenges, due to the characteristics of the alloy that cause reactions that should be controlled. During the foundry process, the alloy is oxidized by contact of the molten aluminum with the ambient air. Oxide films forming on the surface of the molten metal must be removed during the cleaning of the furnaces in order to avoid contamination of the alloy to be used in the production of parts. Analyzing the melting process of a metallurgy at the industrial complex in Manaus, we saw that during the cleaning of the furnaces a metal tool is used to remove the slag, which brings with it a high level of aluminum brought about by the mechanical drag of the tool. As the company in question does not have resources to recover the metal aluminum contained in the slag, it is destined for the other institution which carried out the processing through the process of refusion of the slag and extraction of aluminum. The high level of losses in the process due to the discarding of slag generates considerable financial damage to the institution, reflected directly in the cost of manufacturing the products. In this way, the aim of the present work was to develop equipment for the extraction of the metal aluminum contained in the slag and consequently to reduce the losses in the process. The design of the equipment was chosen through a product development methodology, which made it possible to define the design specification, which can count on a container for the receipt and separation of the slag by means of the vibration brought on by motorvibrators installed at its ends, followed by a slingshot drawer responsible for the storage of the metal after the solidification and support/translate cars of the containers.