Phase Transformation Induced Self-Healing Behavior of Al-Ag Alloy

Abstract

Self-healing alloys are promising materials that can decrease the consequences of accidents. To detect crack formation in a material is simple task that can be performed by e.g., sonic or ultrasound detection, but it is not always possible to immediately replace the damaged parts. In this situation, it is very advantageous to have the chance to heal the crack during operation, which can be done e.g., by annealing. In this paper, self-healing behavior was proven by TEM (Transmission electron microscope) observation of crack healing after annealing. The crack was observed in the rapidly solidified Al-30Ag alloy with non-equilibrium phase composition formed by a minor amount of Ag2Al and a supersaturated solid solution of Ag in an fcc-Al matrix (fcc = face centered cubic). After annealing at 450 °C, equilibrium phase composition was obtained by forming a higher amount of Ag2Al. This phase transformation did not allow the crack to be healed. Subsequent annealing at 550 °C caused recrystallization to a supersaturated solid solution of Ag in fcc-Al, followed by a return to the mixture of fcc-Al and Ag2Al by cooling, and this process was accompanied by the closing of the crack. This observation proved the self-healing possibilities of the Ag2Al phase. Practical application of this self-healing behavior could be achieved through the dispersion of fine Ag2Al particles in a structural material, which will enrich the material with self-healing properties.

Agro waste reinforcement of metal matrix composites, a veritable sustainable engineering achievement, or an effort in futility? A critical review

“…Kevlar and Nomex represent notable examples of aramid fibers, prized for their flame-retardant properties, abrasion and impact resistance, and exceptional strength-to-weight ratios, making them indispensable for protective clothing, ballistic armour, and aerospace applications. Meanwhile, metallic reinforcements like Al, Ni, Ti, carbides (SiC, TiC, WC), borides (BN, TiB 2 , ZrB 2 , HfB 2 , B 4 C), oxides (SiO 2 , Al 2 O 3 , MgO, K 2 O, Y 2 O 3 ), carbon (CNTs), steel particulates, or fibers are frequently employed in metal matrix composites (MMCs) to enhance attributes like crack healing [81,85,86], thermal stability [87,88], solar absorbance [89,90], and mechanical properties including toughness, strength, wear, and corrosion resistance.…”

Microstructural Transformations in Solid-State Annealed Al/Ag/Al Diffusion Couples Examined via High-Voltage Electron Microscopy (HVEM)

“…In contrast, the middle phase among the three intermediates is identified as the δ phase. The intermediate phase on the Al-rich side aligns with an unknown phase, which we define as φ, unaccounted for in the binary Ag-Al phase diagrams [7,8,14,27].…”

A Review of Self-healing Metals: Fundamentals, Design Principles and Performance

“…Hautakangas et al observed the autonomous healing of strain-induced defects in aluminum alloys via the precipitation of mobile Cu atoms at the defects with the help of positron annihilation spectroscopy [15]. Michalcova and coworkers discovered the crack-healing phenomenon caused by the precipitation of supersaturated Ag solutes in Al [16]. While fruitful research results have been gained in self-healing aluminum alloys, current research is mainly aimed at commonly used heatresistant aluminum alloy systems (AA2XXX series), and the selection of candidate elements for self-healing agents is limited to commonly used alloying elements, such as Cu.…”