Hard and super hard composites are used as cutting tool materials as they offer superior wear resistance in the precision machining of automotive and aerospace components. However, the wear properties of these materials are dependent on their microstructure (i.e. grain size and binder percentage), hardness and fracture toughness characteristics, limiting the application of one material to the machining of specific workpieces.

This project aims to develop a laser-based process for the localised control of cutting tool materials microstructure to respond to the specific characteristic of a targeted workpiece. The goal is to develop a system which allows adaptive cutting tool reconditioning (recrystallisation, enhanced hardness and fracture toughness) for tailored wear/chemical performances.

Methods used throughout the research included both:

• Laser in-situ finishing: maintaining surface integrity without using thermo-protective coating or medium (achieved Ra=140 nm)
• Laser surface engineering: functionalised changes of the chemical properties of the coated/uncoated tools, change of microstructure (phase-binder distribution) to enhance hardness/fracture toughness characteristics, to improve wear resistance and enhance thermal stability

Our solution proposes an unconventional low-energy laser process (3.78 J cm^-2) able to promote grain recrystallisation affecting dislocation movement, hence, by reducing the crystallite size more grain boundaries are formed impeding dislocation movements, affecting yield strength and promoting enhanced hardness. The result agrees with the Hall-Petch strengthening mechanism: by changing the average crystallite size it is possible to strengthen polycrystalline materials.

The method and its relationship to Hall-Petch strengthening effect is explained in our recent article.