Microstructural analysis and ASTM B611-21 wear testing of novel binder hardmetals for future percussive drilling applications

Abstract

Since their discovery exactly one hundred years ago, WC-Co hardmetals (cemented carbides) have been a well-established composite material. They are extensively used in multiple fields of industry such as cutting applications, drilling, mining, and milling, due to the combination of high hardness and toughness. In recent years the partial or complete substitution of Co as the metallic binder has been a central topic of hardmetal research for economical, legal, ethical, and health-related reasons. The presented work focuses on the complete substitution of Co as the binder element in hardmetals that in the future could be used in percussive drilling applications. Other suitable metallic elements have been used combination with Ni as the binder basis to strengthen the binder via the well-known principle of solid solution strengthening. Four alternative binder grades were selected, and various sintering experiments were conducted to determine the influence of maximum sintering temperature (Tmax), atmosphere, and annealing treatment. HV50, KIc via indentation fracture toughness, microstructure, magnetic saturation as well as differential thermal analysis (DTA) and dilatometry (DIL) were investigated. To simulate the high-stress and abrasive conditions in percussive drilling to a certain degree, wear tests in the form of a modified ASTM B611–21 test were conducted. The results were compared with industrially available reference grades and show that completely Co-free, Ni-based alloys can compete with Co when used as the binder matrix in hardmetals and upon further optimisation may very well be viable candidates for Co replacement.