QUANTITATIVE IMAGE ANALYSIS OF MICROSTRUCTURE EVOLUTION DURING SOLID STATE SINTERING OF W-Cu

The microstructure evolution of W-Cu composites during solid state sintering at 1050°C is studied on samples quenched after different sintering times. The microstructure is formed by 3 phases: tungsten (W), copper (Cu) and pores. During the process, the initial mixture of W- and Cu-powder is transformed by migration of Cu and rearrangement of W particles. These microstructural changes are studied to identify the underlying phenomena and to control the material properties. Based on experiments performed with two different W powders, this paper deals with various aspects of the quantitative analysis of the observed evolution. A careful preparation of the images is necessary. The porous samples are impregnated with a resin under vacuum before being cut and carefully polished. Low voltage (<10 kV) is used during image acquisition on a scanning electron microscope. Area fraction measurements are used to check the quality of the images and the segmentation process. Classical measurements are used to study the spreading of Cu onto the surface of W particles: surface area of each phase, area of contact between phases, chord length distributions. New measurements based on classical methods are also developed to distinguish between two mechanisms of Cu migration in the microstructure : Cu spreading on W surface (wetting of the surface), and capillary penetration in the inter-W channels. An analysis of the location of Cu and pores in the space between W particles (inter-W space) is performed using a granulometry based on 2D openings. It evidences the mechanism of capillary penetration of Cu in the inter-W space in the case of small W-particles.