Fabrication and tribological behavior of sputtering TaN coatings

Abstract

Tantalum nitride, TaN, coatings with crystalline and amorphous microstructure features are fabricated by magnetron reactively sputtering through Ar/N2 gas flow control. The high Ar/N2 flow ratio of 18/2 sccm/sccm enhances the formation of crystalline fcc TaN phase, while amorphous structure with excess N content in the TaN coating is obtained under a low ratio of 12/8. The multilayer coating with alternating stacking of the amorphous and crystalline TaN nanolayers, i.e., heterostructural a-TaN/c-TaN, is deposited for comparison. The c-TaN exhibits higher hardness and modulus around 21 and 232GPa, respectively, as compared to the a-TaN. The a-TaN/c-TaN multilayer coating possesses hardness and modulus between those of a-TaN and c-TaN layers. Tribological behavior, including scratch and wear, of various TaN coatings are evaluated. The single TaN coatings, either with amorphous or crystalline structure, show an early stage severe cracking and chipping in scratch results. The brittle failure along the scratch scars of the single-layer TaN coatings is suppressed by the multilayer feature. Similar brittle failure modes are found for the a-TaN and c-TaN single-layer coatings under the pin-on-disc wear test. Smooth wear scar edge and limited delamination of the multilayer a-TaN/c-TaN coating are observed, indicating a tougher mechanical behavior and stronger adhesion of the multilayer coating as compared to single TaN layers.