Impurity characterization of zinc-recycled WC-6 wt.% Co cemented carbides

• Recycled powders have 99% purity levels or higher.
• 70% zinc recycled mining scrap grade had excellent, homogeneous Co distribution.
• The main source of impurities is production process and not zinc recycling process.
• Micro-PIXE is an excellent characterization tool for impurity detection in hard metals.
• Micro-PIXE can detect subtle differences between microstructures.

The impurity levels of three WC-6 wt.% Co grades produced using new and zinc recycled powders, were characterized using several analytical techniques. One of the grades was produced from 70% mining scrap material which was subjected to the zinc reclamation process, while a second grade was produced from 100% zinc recycled powder of a new, un-used alloy. The spray dried granules and the sintered alloys were characterized using ICP–OES (inductively coupled plasma/optical emission spectrometry), XRD (X-ray diffraction), SEM/EDS (scanning electron microscopy/energy dispersive X-ray spectrometry), and micro-PIXE (proton induced X-ray emission). All grades had high purity levels of approximately 99%. Iron was found to be the main impurity in all the grades and was predominantly concentrated in the Co binder phase. The main source of the impurities was found to be the production processes and not the zinc reclamation process. The 70% mining scrap zinc recycled grade had the most homogeneous Co binder distribution, while the grade produced from new powders had the least homogeneous Co distribution. This difference is due to the additional levels of crushing and milling which the mining scrap grade underwent. The micro-PIXE analysis clearly demonstrated that powder production conditions, powder homogeneity, and recycling directly impact the microstructures of the sintered materials, and that production process contamination can be detected, quantified, and mapped within the microstructures to a depth approaching 30 μm.