DEVELOPMENT OF GRADED CR-TI-N COATINGS

Multicomponent coatings developed recently have much higher hardness t han traditional hard coatings such as TiN and CrN. However, alloyed ni trides coated directly on substrates usually suffer from decreased adh esion strength. Compositional grading is one approach to achieve both high hardness and high adhesion for tribological applications. This pa per reports the development of graded Cr-Ti-N coatings using an unbala nced magnetron sputtering technique. The mechanical properties of the coatings were determined by nanoindentation and scratch tests. The tri bological properties were evaluated by a pin-on-disk tribometer. The s tructure and mechanical properties of the coatings were found to depen d 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% w as observed), which is desirable for tools coatings. The hardness incr eased by a factor of 2 and the adhesion strength was also improved com pared with those of CrN or TiN, resulting in a significant enhancement of wear resistance. These improvements were attributed to a combinati on of alloy-hardening and grading effects through an intermediate comp ound. (C) 1998 Elsevier Science S.A.