Effect of boron concentration on the mechanical, tribological and corrosion properties of Ta–B–N films by reactive magnetron sputtering

Abstract

A practical design approach in improving the mechanical and corrosion characteristics of nitride-based films is by the synthesis of nanocomposites, and we have fabricated tantalum boron nitride (Ta–B–N) nanocomposite films by a reactive magnetron sputtering process.

The deposited Ta–B–N coatings were found to exhibit a nanocomposite structure consisting of nanocrystalline TaN and amorphous BN phase coexisting. The incorporation of boron into the films modified the microstructure from columnar to fine grain with a face-centred cubic (fcc) TaN (200) preferred orientation. However, the hardness increased to a maximum value of ∼33.3 GPa when the boron concentration was 1.5 at.%. The increase in hardness was due to both grain refinement and the increase in compressive residual stress. More so, the wear rate of the film initially improved upon the addition of boron but later deteriorated when the boron concentration was further increased; however, the coefficient of friction values decreased monotonically when the content of boron was increased. The initial improvement in the wear performance was due to the increased hardness.

Furthermore, potentiodynamic polarisation analysis shows that the film with the highest boron content had the best corrosion resistance properties. This improvement is as a result of the evolution of the film's microstructure by the introduction of boron.