The Deformation of Expanded Clay Syntactic Foams during Compression Characterized by Acoustic Emission

The deformation and failure mechanisms in syntactic foams with different metal matrices were investigated in this study. The syntactic foams were produced by the infiltration method using lightweight expanded clay particles (LECA) as a space holder and commercially pure Al or eutectic Al-12%Si alloy for the matrices. The samples were compressed at room temperature; simultaneously, the acoustic emission (AE) response and the surface deformation were monitored and collated with the deformation curves. In the case of the Al foam, ductile behavior with long plateau stress was observed. During this plateau regime, multiple active shear bands were detected. In contrast, the AlSi12 foam exhibited more brittle deformation behavior. At the end of the quasi-linear stage, the localization of the strain started within one large shear band, accompanied by a significant stress drop. The AE analysis revealed that the deformation was mostly governed by the fracture of LECA particles and the plastic deformation of the matrix material for both types of foams. After strain localization, in the case of the AlSi12 foam, the fracture of the matrix became significant, causing the deterioration of the sample. As for the Al foam, besides the fracture of the LECA particles, the plastic deformation of the matrix played an important role in preventing the foam from falling apart

Influence of Parameters of Quenching and Partitioning Process on Microstructure and Fraction of Retained Austenite

Certain amount of retained austenite can increase ductility of steels because of the TRIP phenomenon during plastic deformation. One method for achieving this is partitioning of carbon into austenite to stabilize it at room temperature. The quenching and partitioning (Q&P) heat treatment leads to a microstructure consisting of martensite and stabilized retained austenite between martensite plates, which provides a better combination of strength and ductility. In this study, the effect of parameters of Q&P process (quenching temperature, partitioning temperature and partitioning time) on the microstructure and retained austenite volume fraction of a low alloy medium carbon steel was investigated. The results showed that the high increase in partitioning time causes the disappearance of martensite blades and reduction of austenite volume fraction. However, increasing of partitioning temperature made the retained austenite films become thicker and its volume fraction increase. On the other hand, by increasing the quenching temperature, carbon content of retained austenite increased sharply