Pulsed laser deposition of AlMgB14 on carbide inserts for metal cutting

Nanocrystalline AlMgB14 containing 0–30 mol% additives are a family of new superhard materials with hardness comparable to that of TiB2 on the lower end and to that of cubic BN on the higher end. Compared with diamond and cubic BN, AlMgB14 is an equilibrium material with excellent electrical conductivity, high chemical stability, and lower density. The projected cost of manufacture of the boride is 10% of the cost of diamond and cubic BN. AlMgB14 materials appear to be congruently melting/evaporating, which would allow them to be processed with techniques such as pulsed laser deposition (PLD). In this work, the feasibility of PLD for synthesizing thin films of baseline AlMgB14 (0% additive) is demonstrated and compared with TiB2. A 248-nm, 23-ns KrF excimer laser was used to prepare baseline boride thin films on cemented carbide (ANSI C-5 and C-2) tool inserts. The films were dark blue, continuous and fairly uniform with few particulates. An impact fracture test showed that adhesion of the films to the substrate was excellent. The deposition rate was 0.08 nm per pulse at an energy density of 7 J/cm2. Nanoindentation hardness tests revealed that the films exhibited hardness 60% higher than the carbide substrate. Lathe turning tests with cold-drawn 1045 steel bars indicated that C-5 tools coated with 0.5 μm baseline AlMgB14 have an average flank wear reduction of 12% compared to uncoated C-5 tools. Further machining tests on C-2 tools showed that the tools coated with baseline boride have much better flank (23% reduction) and nose wear resistance (26% reduction) compared with TiB2 coated tools. In addition, multilayer composite coating of AlMgB14 and TiB2 outperformed single layer boride coating in minimizing the tool wear. This pioneering work sets the stage and serves as a catalyst for rapid and innovative advances in the development of new boride materials for numerous tool and hard coating applications, including bulk cutting tools, hard and erosion-resistant coatings, wear-resistant electrical switch contacts, and conductive thin films for MEMS.