Khaled Morsi

The Ni-Al system contains five intermetallic compounds, out of which NiAl and Ni₃Al have received the vast majority of scientific and industrial interest over the past few decades. Ni₃Al is of major interest due to its unique properties, including a yield strength that increases with temperature. The combustion synthesis (CS) process for producing Ni₃Al from elemental powders of nickel and aluminum offers a low thermal budget and rapid processing, as well as purer products. This paper reviews the fundamentals of CS as applied to Ni₃Al and its composites, and focuses on research over the past 25 years, including mechanically and electrically activated combustion synthesis and combined combustion synthesis and bulk deformation processes to produce high-density products. Several new directions are suggested for future research in the field.

The powder metallurgy route (PM route) for producing aluminum closed-cell foams has recently attracted significant scientific and industrial interest. The process involves mixing a blowing agent powder (e.g., TiH₂) with aluminum powder, then compacting the mixture to produce a high-density bulk foamable precursor (BFP). The BFP is then heated above the melting point of aluminum, where the hydrogen released from TiH₂ particles forms bubbles in the molten aluminum, which become closed pores (cells) upon solidification. Despite metal powder agglomeration being an important factor in powder metallurgy research that can significantly influence processing, it has surprisingly received little to no attention in the powder-based foaming of metals. To the best of our knowledge, this paper is the first to address aluminum powder agglomeration within the context of powder-based metallic foams. Results show that significant aluminum powder agglomeration not only leads to an inhomogeneous distribution of the TiH₂ particles within the BFP, but also to the formation of locally higher than nominal concentrations of TiH₂ particle-rich regions, which greatly influence foaming characteristics. The work, for the first time, highlights the need to seriously consider metal-powder agglomeration (even partial agglomeration) in future foaming research via the PM route, and its effect on foaming characteristics.

The powder metallurgy (PM) route for the production of closed-cell metallic foams has recently received a significant amount of attention. One of the major issues is the non-uniform and non-spherical nature of the cells produced, which can negatively affect the mechanical behavior. The current paper uses the PM route to process metallic foams for the first time using novel Al-TiH₂ foamable precursor “particles” (FPPs). The effect of FPP content (0–10 wt.%) on the developed foam structure of aluminum and its mechanical properties is investigated. An increase in FPP content results in a decline in product density by forming uniform and near-spherical cells. The main advantage of the FPPs is the localization of the blowing agent TiH₂ particle content within Al-TiH₂ composite particles (i.e., giving rise to a higher local TiH₂ content), which has led to the production of pores with relatively high circularities even at very low overall TiH₂ contents. The foams produced displayed energy absorption capacities of 10–25 MJ/m³ at 50% strain, and maximum energy absorption efficiencies ranging from 0.6–0.7 (for 40–60% closed cell content)

The production of closed-cell metallic foams has been of interest to the scientific community and industry for decades, owing to their unique properties, which include high specific strength and stiffness, buoyancy, shock absorption, and crash worthiness. One of the approaches for their fabrication relies solely on the use of powders and is manifested in what has been referred to as the powder metallurgy (PM) route. This review discusses the underlying fundamentals of the process, and recent developments together with our current understanding. The effect of process parameters on the developed foam structure is reviewed for a range of metals, alloys, and metal matrix composites. Fundamental foaming mechanisms and characteristics are discussed.

The present study investigates the fabrication of Ni₃Al-carbon nanotube (CNT) nanocomposite using electrically activated reaction synthesis (EARS) and its effects on the mechanical properties of the nanocomposite. The effect of initial nickel (Ni) particle size and mechanical milling time of Ni-CNT/Al hierarchical composite powder on reaction characteristics, product microstructure and properties was investigated for the first time. An increase in mechanical milling time was found to result in a decline in ignition temperature and time to ignition for the two investigated initial nickel particle sizes (4–8 µm and 45–90 µm). The smaller initial nickel particle size and longer milling times had a major influence on the homogeneity, decreasing porosity, and increasing hardness of the reacted compacts.