Layer Growth in Co(W)-Zn Systems at Hard Metal Recycling

Abstract

The influence of W content on the Co(W)Zn system and the behavior of individual elements was investigated. Cobalt is a so-called critical element and is one of the main parts in hard metal products. Because of its toxicity, it requires special care in handling. Further optimization of hard metal recycling, especially by the zinc process, is needed to use scrap as a secondary resource. In this work, Co(W) materials were put in contact with liquid zinc and held at specific temperatures, giving insight into the formation of intermetallic Co-Zn phases by varying the temperature, duration,and W content. Lower temperatures led to a minimum layer width, and increasing temperatures and W contents resulted in greater thicknesses of the intermetallic phases. The element distribution analyses show that W diffuses from the base material through the intermetallic Co-Zn layer and accumulates at detached Co-Zn phases, forming thin, enriched filaments. This can be attributed to the fact that the intermetallic Co-Zn phases and Zn have no solubility in W. Consequently, the latter is located on the outside of these phases. The combination of practical experiments and statistical analyses will ultimately provide a possibility for improving recycling processes.