B.W. Chua

Influence of SiC particles on mechanical properties of Mg based composite

AZ91 magnesium alloy reinforced with different sizes of SiC particulates has been fabricated using powder metallurgy route. Mechanical properties of the specimens have been studied. Yield and ultimate tensile stresses show a decrease with the increase in the size of SiC particulates. The influence of thermal shock between 400°C and 30°C on the mechanical properties was also investigated. The results show a decrease in yield stress and elongation to fracture with the number of thermal shock cycles.

Improvement of microstructure and mechanical properties of AZ91/SiC composite by mechanical alloying

AZ91 magnesium alloy reinforced with SiC particulates was fabricated via powder metallurgy technique as well as mechanical alloying process where a planetary ball mill was employed. Microstructure and mechanical properties of the fabricated AZ91 composites had been evaluated. Microstructural study showed that grain size of the material was refined and SiC particulates were well distributed after mechanical alloying. Mechanical tests of the composite showed an enhanced yield and ultimate tensile strengths for the mechanically alloyed samples compared with those prepared via the powder metallurgical route.

Deformation behaviour of ultrafine and nanosize-grained Mg alloy synthesized via mechanical alloying

Bulk Mg–5Al alloys were consolidated from powders that had been mechanically alloyed over different milling durations. The microstructural evolution, and physical and mechanical properties of the alloys were investigated. Mechanical measurements revealed a change in deformation behaviour after certain milling durations. At short milling duration, high yield strength was obtained through dislocation strengthening mechanisms predominantly by grain refinement and to a lesser extent by solid solution strengthening and particle dispersion strengthening. However, at longer milling durations, low yield strength was observed and the strengthening mechanisms at work in short milling durations appeared to be no longer effective. Enhanced ductility with no work hardening behaviour was observed in samples with a mean grain size of 45 nm. It appeared that the significantly large increase in the grain boundary regions played an important role in the room temperature deformation of the alloys. The possibility of a diminishing effect of the dislocation strengthening mechanisms and the onset of grain boundary deformation modes for the softening phenomenon and the absence of work hardening at some nanoscale grain sizes are discussed.

Processing of thermally stable doped perovskite PZT ceramics

Abstract In this paper, various methods of synthesizing lead zirconium titanate (PZT) ceramics with high Curie temperature (Tc) and thermal stability are discussed. Perovskite PZT variants were synthesized from stoichiometric oxide ratios of Pb, Zr, Ti and dopant element. The oxide powders were mixed mechanically and calcinated, and then sintered for the desired perovskite phase to form. Varied mixing and sintering parameters allowed investigation of the optimum settings required for proper densification with enhanced material properties. The piezoelectric properties and relative permittivity of doped PZT ceramics were analyzed using the resonant frequency method. Pure and Mg-doped PZT samples were subjected to thermal shock and cyclic test and the material properties of these samples were compared to verify the extent of degradation. Results were investigated for PZT ceramics’ viability in high temperature applications. Differential scanning calorimetry (DSC) was used to evaluate the Tc for various dopants, and thus to identify the ideal dopant that yields highest Tc and operational temperature with appreciable piezoelectric properties.

From waste to high strength alloy - recycling of magnesium chips

Abstract Ultrafine grained magnesium alloy was synthesized via mechanical milling of AZ91 chips. Mechanical property measurement revealed enhanced yield strength of 470 MPa after mechanical milling. The increase in yield strength is associated with reduction in grain size which restricts twining and dislocation gliding. The present investigation demonstrates that magnesium alloys can be cost-effectively recycled through the process of mechanical milling.