Structure and properties of CrSiCN coatings deposited by pulsed dc magnetron sputtering for wear and erosion protection

• Trimethylsilane (TMS) was used as a source of Si and C for reactive sputtering deposition of CrSiCN coatings.
• Solid solution hardening and grain boundary strengthening contributed to hardness enhancement.
• The optimum Si and C contents were in the range of 1.7–5 at.% and 5–9.6 at.%, respectively.
• Strong connections between H/E⁎ and H3/E⁎2 ratios and wear and SPE resistance of the coatings.

CrSiCN nanocomposite coatings were deposited by sputtering a chromium (Cr) target in a gas mixture containing argon, nitrogen, and trimethylsilane (TMS) using middle frequency pulsed dc magnetron sputtering (PDCMS). The coatings with different silicon (Si) and carbon (C) contents were obtained by varying the TMS flow rate from 0 to 12 sccm. Uniform depositions and high deposition rates (8–10 μm per hour) have been achieved. The microstructure of the coatings was studied by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. The lattice parameter of the coatings first increased with the addition of a small amount of Si (1.7 at.%) and C (5 at.%) by the formation of cubic solid solution, and then decreased with a further increase in the Si and C contents. The microstructure of the coating changed from columnar grains to interconnected fine grains, and finally to nanocomposite structure as the Si and C contents increased, in which cubic Cr(Si, C)N nanocrystallites were surrounded by an amorphous matrix consisting of SiCx, amorphous C, SiNx, and CNx. The volume fraction of amorphous phases increased as the Si and C contents increased. The mechanical properties, dry sliding wear resistance, and solid particle erosion (SPE) resistance of the coatings were analyzed using nanoindentation, ball-on-disc test, and air jet sand erosion test, respectively. As compared to the baseline CrN coating, the addition of a small amount of Si (1.7–5 at.%) and C (5–9.6 at.%) effectively improved the hardness and the H/E⁎ and H3/E⁎2 of the coatings. The strengthening mechanisms include solid solution hardening and grain boundaries strengthening via the formation of a thin amorphous layer. The improved mechanical properties contributed to excellent wear resistance and SPE resistance of the coatings against alumina at both 30° and 90° incident angles. However, as the Si and C contents were increased respectively to above 10.3 at.% and 16 at.%, the mechanical properties and wear and SPE resistance of the CrSiCN coatings all decreased.