Oxidation behavior of functionally graded cemented carbides with CoNiFeCr multi-principal-element alloy binder

The oxidation behavior of the WC-CoNiFeCr functionally graded cemented carbide (FGCC) has been investigated by isothermal oxidation and composition characterization. The results showed that the oxidation of cemented carbide was closely related to the oxidation temperature and oxidation time, and the oxidation of different elements had a clear sequential order. The Cr element was first selectively oxidized to Cr2O3, followed by the oxidation of other composing elements of the multi-principal-element alloy (MPEA) binder to MxOy and MWO4. The WC was then oxidized to WO3, and WO3 and MxOy were thereafter reacted to form MWO4. The binder composition, structural distribution, and WC grain size were the three key factors that affected the oxidation resistance of the cemented carbides. Fine-grained and graded cemented carbides, with CoNiFeCr MPEA binder, had the highest anti-oxidation properties. The FGCC showed lower oxidation of the binder at 600 degrees C, a denser MWO4 distribution at 700 degrees C, and a smaller volume expansion at 800 degrees C, as compared with the non-graded cemented carbide (CC). Compared with the coarse-grained cemented carbide, the fine-grained cemented carbide had more grain boundaries between the WC and the binder, which resulted in a denser distribution of the binder oxides. WC-20CoNiFeCr had a higher energy barrier for the oxidation reaction and more stable oxidation products than WC-20Co. The results did not only provide theoretical guidance for the understanding of the anti oxidation mechanism of WC-CoNiFeCr, but they also expanded a new approach for the preparation of cemented carbides with high oxidation resistance.