Date of Award

5-2022

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Committee Chair/Advisor

Dr. Hongseok Choi

Committee Member

Dr. Xin Zhao

Committee Member

Dr. Garret Pataky

Abstract

Metal foams have shown an excellent promise for usage as multifunctional material concerning research & development in the last 20 years. They provide remarkable mechanical as well as physical properties being lightweight. Open-cell metal foams have already been used in sound and noise absorption. Open-cell metal foams are outstanding for use in heat exchangers, filters, and many more applications, while closed-cell foams show excellent characteristics in impact energy absorptions. Closed-cell metal foams have higher energy absorption than their solid parent metal as they convert most of the impact energy into deformation energy. Metal foams have been used as prominent safeguard measures in crash-box devices, bumpers, roofs, etc.

Primarily the metal foams are manufactured from metallic melts or metal powder. The processing of metal foams through melts is known as the melt route process. This process is widely used because of the low cost of the overall process and is easy for volume production. In the melt route, the foams are manufactured either by injecting gas or incorporating blowing agents (like CaCO3, TiH2) into the melts. Blowing agents decompose in the melt, producing gas that induces foaming.

In the case of the conventional melt route process with the incorporation of a foaming agent, also known as stir casting, the melt is prepared in a furnace at a suitable temperature in a crucible; a thickening agent is added to the mixture in the appropriate quantity and stirrer with a mechanical stirrer. A thickening agent provides stability to foams as it lowers the liquid drainage in the foams, leading to uniform pores and pore boundaries. After a consistent viscosity of the melt is achieved, the foaming agent is added to the mixture, and stirring is continued until the mixture is foamed. After foaming, the crucible with the foamed mixture is held in the furnace, later removed, and cooled to obtain metal foam.

However, the challenge lies in the understanding effect of process parameters, as the pore distribution of metal foams due to the stir casting process is random. This processing, in turn, significantly affects the mechanical properties of foams. This research used calcium carbonate (CaCO3) as the foaming agent. The effect of various parameters such as stirring time, CaCO3 addition, stirring speed, and holding time are studied. Firstly, the L8 Taguchi array was developed to check the most influential parameters. Circularity shape factor (CSF) and pore distribution factor (PDF) were output parameters. Image-Pro was used to characterize the foam. Two levels of each parameter were considered, and stirring time, CaCO3 wt.%, were the most significant parameters.

A response surface model (RSM) was developed to optimize the two influential parameters. Twenty-six experiments (13 experiments with two replicates) were performed, and a quadratic polynomial equation was developed for CSF and PDF. Later, optimum values of process parameters were found to be stirring time 60s and 1.89 wt.% CaCO3. The result was validated by performing experiments with optimum parameters, and results were found to be within suggested limits.

Finally, foaming agent with added SiC nanoparticles was developed. Calcium acetate was dissolved in water with and without 0.1 wt.% SiC, and sonicated. Later, the water is evaporated, and the powder mixture is heated to obtain a foaming agent by decomposition of calcium acetate. Aluminum foam is manufactured using optimum parameters with the produced foaming agent. Upon analysis, it can be said that foaming agent integrated with nanoparticles can be used to control pore morphology.

Available for download on Saturday, April 22, 2023

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