Abstract
Heavy tungsten alloy with composition 93W:3Ni:2Fe:2Co was successfully prepared through gaseous reduction technique. Starting from tungsten, nickel, iron, and cobalt oxides, a mixture of these oxide powders was reduced by treatment in hydrogen. The course of reduction was followed up by measuring the weight loss as a function of time in the temperature range of 850-1000 degrees C. Afterward, samples were subjected to sintering process in reducing atmosphere (Ar/49% H-2) at different temperatures (1300-1500 degrees C) and dwell times (30, 90 min) to investigate the microstructural changes occurring during sintering. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the reduced samples. The microhardness of the sintered samples was measured and correlated to sintering temperature and dwell time. It was found that the heavy tungsten alloy can be synthesized from metal oxide at reduction temperatures above 850 degrees C. The reduction rate increased with temperature. The values of the apparent activation energy were calculated from Arrhenius plots and correlated with the reduction mechanism. Considering the activation energy values, the course of reduction is most likely controlled by interfacial chemical reaction mechanisms. With increase of sintering temperature and dwell time, transition from solid-state diffusion to liquid-phase sintering took place, which led to rapid densification of the alloy together with formation of tungsten solid phase. Increase of densification was also coupled with increase of hardness.