Macro- to nano-scale analysis of an amorphous carbon coating on cemented carbides

Abstract

This study characterizes a novel amorphous carbon coating on two cemented carbide substrates with fine (6CoF) and medium-sized (6CoM) tungsten carbide grains, both containing 6 wt% of cobalt binder. These materials are critical as drilling and milling tools in the manufacturing industry due to their exceptional hardness and fracture toughness balance. Samples of the coating-substrate interface were prepared using a focused ion beam and analyzed with advanced transmission electron microscopy techniques. Raman spectroscopy verified the amorphous nature of the coatings, discarding potential FIB-induced amorphization. Energy-dispersive X-ray spectroscopy, selected area electron diffraction, and 4D scanning transmission electron microscopy were employed to analyze the chemical composition and crystallographic structure. While the coatings were predominantly amorphous, the 6CoM sample exhibited a polycrystalline region containing diamond and graphite. Additionally, a ∼ 40 nm thick amorphous layer rich in tungsten was identified at the coating-substrate interface in both samples, providing a complete characterization of this important coating-substrate system for the tooling industry.