Anna Knaislová

High-Pressure Spark Plasma Sintering (HP SPS): A Promising and Reliable Method for Preparing Ti–Al–Si Alloys

Ti–Al–Si alloys are prospective material for high-temperature applications. Due to low density, good mechanical properties, and oxidation resistance, these intermetallic alloys can be used in the aerospace and automobile industries. Ti–Al–Si alloys were prepared by powder metallurgy using reactive sintering, milling, and spark plasma sintering. One of the novel SPS techniques is high-pressure spark plasma sintering (HP SPS), which was tested in this work and applied to a Ti–10Al–20Si intermetallic alloy using a pressure of 6 GPa and temperatures ranging from 1318 K (1045 °C) to 1597 K (1324 °C). The low-porosity consolidated samples consist of Ti5Si3 silicides in an aluminide (TiAl) matrix. The hardness varied between 720 and 892 HV 5.

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

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.