Cobalt has been the most suitable and most commonly used binder for tungsten carbide based hardmetals. The most important factor in favour of cobalt (Co) is its excellent wetting behaviour for tungsten-carbide (WC).
Due to the poor corrosion resistance of Co, its high cost and environmental toxicity, substantial research has been devoted to find suitable alternative binders for WC systems. The aim is to reduce the amount of Co, or possibly, to completely replace Co binder. Two promising alternatives are described and utilised in this project, the first one is a mixture of iron (Fe), nickel (Ni) and cobalt (Co) and the second alternative is composed of iron (Fe) and manganese (Mn). Compared to cobalt, Fe and Mn are very cheap and non toxic.
A literature review was performed on different relevant aspects covering the field of hardmetals, powder preparation methods, powder metallurgy and nanomaterials. The submicron/nano-structured composite powders were prepared by the mechanical alloying method using both planetary ball and high-energy ball milling processes.
A series of experiments were performed with the planetary ball mill by varying milling time (2.5, 5, 10 hrs) and rotation speed (250, 400rpm) parameters to process WC-10wt%Co, WC-10%FeNiCo and WC-10%FeMn. It was noticed that as the milling time increased (above 2.5 hours for 150rpm) the amount of elements (Fe, Cr) picked up from the stainless steel vial inner wall increased. The contamination level increased further at a rotation speed of 400rpm. This indicates that both speed and time should be kept low to minimise contamination or a hard steel vial should be utilised. For that, additional powders were prepared using the high-energy ball mill.
The grain size of WC phase was calculated using the Scherer equation and the corresponding X-ray diffraction peaks while the WC particle size was evaluated using scanning electron microscopy images. Composite powders were successfully made in which fine WC particles (submicron down to about 200nm size) were distributed within the matrix (Co, FeNiCo or FeMn).
The next step would be to compact such powder for a subsequent sintering process. For that appropriate compaction dies were designed using Inventor CAD software. A die to produce cylindrical samples for microstructural and hardness analyses was designed as well as another die to produce samples for 3-point bending tests. Both dies were designed according to ASTM standards.
The aim of our final thesis project was to prepare submicron/nano-structured powders from WC-Co system and replace Co with suitable alternatives. This project was accomplished at the University of Wolverhampton (UK) in line with our Master Degree Industrial Sciences.
First of all, we would like to thank everybody who helped to bring our final thesis to a good end. A special word of thanks goes to our supervisor Dr. ir. T. Laoui and to S. Hewitt, of the University of Wolverhampton, for enriching us with the knowledge they have and the daily good care for us.
Further, we would like to thank Dr. ir. A. Van Bael, of the XIOS Hogeschool Limburg, for allowing us the opportunity to accomplish our training in Wolverhampton and for reading our final thesis project and Ms. Bauwens for helping us arrange the paperwork involving our stay in Wolverhampton.
We would also like to thank our parents, for giving us the opportunity to do our thesis project abroad.
Last word of thanks to everybody, especially our parents and girlfriends, for supporting us in the difficult times we sometimes had.
Our stay at the UK was part of a project in the Erasmus framework.