Assessment of fracture toughness of cemented carbides by coupling introduction of artificial flaws via laser ablation with quantitative fractography

Abstract

Cemented carbides are widely used in structural and tooling applications where high mechanical reliability is essential. Owing to their inherently brittle nature, fracture in these materials is typically governed by the propagation of microstructural or processing-induced flaws. Developing a robust and practical methodology for accurately determining their fracture toughness is therefore critical to ensure safe, reliable, and efficient performance in demanding service conditions. This study proposes to assess fracture toughness by means of a strategy that couples controlled introduction of artificial flaws via nanosecond-pulsed laser ablation with post-mortem analysis of broken surfaces through quantitative fractography. Two fine-grained WC-Co cemented carbide grades, differing in binder content, were selected to examine the proposed approach. Artificial microdimples, designed to control failure initiation sites, were created under optimized laser conditions and subjected to monotonic and cyclic loading in four-point bending. Fractographic analysis provided key parameters, flaw size and mirror radius, for fracture toughness estimation based on mirror-mist-hackle geometry. To validate the approach, additional measurements were carried out using two other methods: indentation fracture toughness and flexural testing of single-edge notched and pre-cracked beams. Statistical analysis showed that the combined controlled defect-quantitative fractography method yields reliable fracture toughness values. They closely match the reference baseline values determined by using tests involving specimens with well-defined through-thickness sharp cracks, and confirm the toughness overestimation often observed in tougher grades when implementing the indentation method.