Development of graded Cr-Ti-N coatings

Multicomponent coatings developed recently have much higher hardness than traditional hard coatings such as TiN and CrN. However, alloyed nitrides coated directly on substrates usually suffer from decreased adhesion strength. Compositional grading is one approach to achieve both high hardness and high adhesion for tribological applications. This paper reports the development of graded Cr-Ti-N coatings using an unbalanced magnetron sputtering technique. The mechanical properties of the coatings were determined by nanoindentation and scratch tests. The tribological properties were evaluated by a pin-on-disk tribometer. The structure and mechanical properties of the coatings were found to depend strongly on substrate bias and the relative content of the titanium to chromium. Under optimized deposition conditions, the graded Cr-Ti-N coatings showed very high elasticity (an elastic recovery of ca 80% was observed), which is desirable for tools coatings. The hardness increased by a factor of 2 and the adhesion strength was also improved compared with those of CrN or TiN, resulting in a significant enhancement of wear resistance. These improvements were attributed to a combination of alloy-hardening and grading effects through an intermediate compound.