Volume 44, Issue 8

The crushed and rounded ferroboron (FeB) powders of Fe-18.8B-0.2C-0.5Si-0.8Al (wt.%) were deposited onto an aluminum substrate by atmospheric DC plasma spraying to improve its tribological properties. Hexagonal boron nitride (h-BN) powders which have excellent lubricating properties similar to graphite were incorporated into the boride powders as a solid lubricant by a sintering process to obtain protective coatings with a low friction coefficient. As-sprayed coatings are composed of mainly FeB, iron matrix supersaturated with boron owing to the rapid solidification of molten droplets flattened on a substrate. The friction and wear behaviour of each coating were evaluated using a ring-on-disk type wear tester in paraffin based oil with an air atmosphere. It was found that sintering of iron boride powder with h-BN powder (5 wt.%) is an acceptable method for producing a protective composite coating against friction and wear. The evaluation of friction and wear results shows that iron boride coatings exhibit high seizure load and good anti-wear performance.

The revealing of the materials microstructure using Ar + Ion Etching by a Precision Etching and Coating System (PECS TM ) and Focus Ion Beam (FIB) techniques is described and discussed. The advantages and disadvantages of both methods in respect to materials preparation and characterisation are demonstrated on selected samples. Different kinds of materials were chosen for investigations to give a better overview on the both methods possibilities. FIB technique is very useful for the visualisation of crystallographical defects with high disorientation angle like twins, whereas PECS reveals even small crystallographical differences (subgrains, dislocation walls) induced through plastic deformation. For the optimum performance (etching and visualisation) the knowledge of the precise etching and visualisation parameters is necessary.

Alumina ceramics are one of readily available and cost-effective materials for ceramic-based ballistic applications. As impact velocity is most important parameter in armor design, ceramic microstructures have key role for better understanding of the ballistic penetration. Dry pressed alumina tiles bonded to fiberglass laminate backings have been tested in the ballistic experiments for low and high impact velocities. The microstructural changes and damage mechanisms have been characterized by scanning electron microscopy (SEM). Radial and conical types of cracks have been observed in the alumina ceramics tested. The damage mechanisms have changed in accordance with the impact velocity