In situ laser irradiation of WC-Co hardmetals inside an SEM. Part 1. General features of surface modification.

Abstract

Samples of WC-6% Co hardmetals were irradiated with a pulsed CO2 laser inside a scanning electron microscope in order to study the mechanisms and development of surface modification in microscopic detail. The photon emission of the irradiated surface was measured simultaneously. Samples with surfaces prepared in different ways were irradiated in a multiple pulse regime. The laser power density was somewhat lower than that which would lead to a melting of the polished surface. It is shown that under such irradiation conditions the decisive step in surface modification is the successive solution of the carbide in the lower melting binder phase. Above a critical number of laser pulses, in the order of a thousand, this leads to the onset of large-scale melting, pointing to a marked rise of absorbency. These alterations of surface state are well reflected in the photon emission measurements. The influence of the original binder distribution within the surface layer, changed by grinding or p olishing, is investigated