Circular economy and urban mining for the sustainable development of the production of hardmetals based on tungsten Carbide-Cobalt (WC-Co)

Abstract

The recovery of hardmetal residues and the replacement of Co and WC are research trends for environmental sustainability in developing new products within class of materials. The proposal for phase II is based on the promising results obtained in the PIPE project concluded in its phase I, "Circular Economy and Urban Mining for the sustainable development of the tungsten carbide and cobalt-based carbide production chain (WC- Co)" - process 2019/08927-2. Phase I was very successful about the reuse of carbide grinding residue (grinding sludge), using the conventional process, that is, conditioning (physically and chemically) the sludge, followed by compaction and sintering (99.5% relative density and 88.4 HRA hardness), as described in the Phase I scientific reports. During phase I, new forming techniques were also explored, such as gelcasting and 3D printing (direct and indirect processes), using firstly virgin raw materials to establish a reference and, later, mixtures of virgin raw materials with residue. Unlike the conventional process (compaction and sintering), these new processes allow the production of components with dimensions and shapes closer to the final ones, reducing manufacturing costs. Additionally, as these processes occur in a liquid medium (suspensions), they allow the use of dispersants and more intense de-agglomeration processes, which favors obtaining more homogeneous microstructures with improved performance. Some exploratory tests conducted with these two processes in phase I indicate that they can be used to manufacture products that cannot be obtained by the conventional process, which are limited in terms of complex shapes. Additionally, PBF-L/M (powder bed melting - laser) was tested, both for virgin raw materials and for conditioned grinding sludge, and a feeding system was developed so that the powder bed is uniform and homogeneous.In this phase II of the project, the proposal will be to advance in the conventional compaction process, expanding the classes of waste to be recycled (grinding sludge, lathe waste and sintered parts), in addition to evolving new conformation techniques: gelcasting, and 3D printing (extrusion and GMP-L). An important topic for this phase II is the production of suspensions with suitable characteristics for each of the processes that use slurry, which includes increasing the solids concentration, reducing the sedimentation rate and flocculation tendency, in addition to adjusting the rheological behavior. Similarly, it is intended to evolve in the PBF-L process, improving the flowability of the powders by means of atomization in spray dryer followed by pre-sintering to obtain spherical agglomerates, in addition to using a feeding system specially developed for this process. (AU)