Dynamic Collapse Mechanisms in Metal Foam Expansion

Abstract

The study provides insight into decomposition of titanium hydride as foaming agent for powder metallurgically produced aluminum foams. Decomposition is characterized using thermal and kinetic analysis, allowing prediction of decomposition reactions. Such predictions are made for various time–temperature cycles, which are experimentally evaluated in parallel foaming experiments. A new explanation of foam collapse is derived from the results, which interprets hints at a maximum gas release rate, limiting maximum expansion, in terms of the existence of a maximum cell wall stretching rate and expanding foam can sustain. Thus a dynamic collapse criterion is added to existing static ones.

Multi-phase-field simulation of microstructure evolution in metallic foams

“…When two bubbles come into close contact, depending on forces which act upon them, they may undergo coalescence or remain separate. In the present model, the possibility for this bifurcation in dynamic behavior, which plays a key role in structure evolution in multi-bubble systems, is controlled via inequality (15). This issue is addressed in Fig.…”

“…4. Test of the coalescence condition, inequality (15). In panel (a) bubbles remain separated throughout the entire process of growth and deformation because, in addition to choosing a high σ SS , the phase fields representing the two bubbles are not allowed to merge into a single one.…”

“…In panel (a) bubbles remain separated throughout the entire process of growth and deformation because, in addition to choosing a high σ SS , the phase fields representing the two bubbles are not allowed to merge into a single one. In (b) and (c), however, this possibility is introduced via the coalescence condition, inequality (15). The only difference between (b) and (c) is the use of different initial bubble-densities.…”

“…Apparently, the system minimizes its free energy by keeping the bubbles apart. Starting with the same configuration as in panel (a), simulations are repeated using the coalescence condition, inequality (15). Two very similar cases that differ only in the initial gas density are considered.…”

Mechanical performance of structurally optimized AlSi7 aluminum foams – an experimental study

“…The latter have been obtained by means of blowing agents adapted in their thermal decomposition characteristics via thermal treatments. The details and effects of such treatments have been described by various authors, including those of the present work . Likewise, the impact of such measures on foam formation has been discussed in detail in several studies .…”