PRODUCTION OF HIGHLY POROUS AL-NI FOAMS BY POWDER METALLURGY USING DOLOMITE AS A FOAMING AGENT

In this study, metal foams were fabricated using Al-Ni combined with dolomite(CaMg(CO_3 )_2) as an alternative foaming agent via the powder metallurgy (PM) route. For first-time dolomite, a dual carbonate (magnesium-calcium) was found to be a highly effective foaming and an excellent stabilizing agent. It has a gradual decomposition and at different temperatures produces oxides, improving foaming conditions and expansion performance. The experimental findings showed that the addition of 7wt% of dolomite is the optimal amount for the development of well-formed pores with uniform cell distribution, spherical shape, and thick cell walls. The addition of Ni to the mixture increased the melting temperature and decreased the difference between the alloying melting point and dolomite decomposition temperature. Specific Al-Ni compositions showed appropriate viscosities for enclosing the gas as it was released. Al-10Ni and Al-15Ni were found the optimum combinations to form intermetallics which further helped stabilize the foams. Moreover, as a result of this investigation, a modification of the powder metallurgy technique was proposed, by partial-sintering the precursors before the foaming process (i.e. raising the temperature of the precursor for a period of time prior to foaming). This step allowed the formation of particle sintering, enhancing foam expansion, leading to more homogeneous porosity, cell morphology and microstructure. The following thesis is based in one paper, which has been submitted to the journal, Advanced Engineering Materials