Four nitride coatings, TiN, TiAlN, AlTiN and CrAlN were deposited on YG6 (WC + 6 wt.% Co) cemented carbide by cathodic arc-evaporation technique. The friction and wear properties were investigated and compared using ball-on-disc method at high speed with SiC ball as a counter material. The tests were evaluated by scanning electron microscopy, X-ray diffractometer, energy dispersive X-ray, micro hardness tester and an optical profilometer. The results showed that TiN and TiAlN coatings presented lower friction coefficient and lower wear rate, and that high Al content AlTiN and CrAlN coatings didn't present better anti-wear properties in this test. Oxidation and abrasive wear were the main wear mechanism of TiN coating. In spite of the observation of micro-grooves and partial fractures, TiAlN possessed perfect tribological properties compared with the other coatings. High Al content increased the chemical reactivity and aroused severe adhesive wear of AlTiN coating. CrAlN coating presented better properties of anti-spalling and anti-adhesion, but abundant accumulated debris accelerated wear of the coating under this enclosed wear environment.

Friction and wear properties of TiN, TiAlN, AlTiN and CrAlN PVD nitride coatings

Current status of materials development of nuclear fuel cladding tubes for light water reactors

The metalcutting process, which includes turning, milling, drilling, and other methods for shaping metals, generates large mechanical forces and high temperatures at the point of contact between the cutting tool and workpiece material. The cutting tool is damaged substantially in these severe service conditions and has to be replaced when the tool cannot produce the desired product at the specified tolerances. To improve the lifetime for which it functions properly, the cutting tool has to be protected, often by coatings that are specifically designed to prevent certain damage modes that occur in particular applications. In fact, over 90% of all cemented carbide inserts are currently coated using chemical vapor deposition, CVD, physical vapor deposition, PVD, or their combination. This paper will present PVD coatings that are specially designed to protect the cutting tool and extend its functionality (lifetime). The paper is organized in two parts. First, it will briefly describe the metalcutting process, the resulting challenges to the cutting edge and the components of a functional tool. The second and the main part will present and discuss the key PVD architectures employed to protect the tool: monolithic, multilayer and nanostructured coatings. The paper will conclude with a summary and outlook on the development of new PVD coatings for cutting tools.

Architecture of PVD coatings for metalcutting applications: A review

CrN, CrTiN, CrAlN and CrTiAlN coatings were deposited on Si (100) wafers, and their microstructure, mechanical properties, fracture toughness and adhesive strength were investigated via X-ray diffraction (XRD), nanoindentation and micro-scratch tests. Besides an F.C.C. crystal structure, TiN0.3 (004) and AlN (222) phases were found in the CrTiN and CrAlN coatings while the crystallinity of the CrTiAlN coating decreased. The hardness of the CrN (14.5 GPa), CrTiN (13.9 GPa) and CrAlN (17.7 GPa) coatings was determined by their grain sizes while the CrTiAlN coating with the most compact morphology exhibited the highest hardness of 22.0 GPa. In addition, CrTiN (KIc = 2.73 MPa· m ), CrAlN (KIc = 2.70 MPa· m ) and CrTiAlN coatings showed a stronger crack resistance than the CrN coating (KIc = 1.06 MPa· m ), especially the CrTiAlN coating without any radial cracks. However, the CrTiAlN coating encountered circumferential cracks and premature delamination (Adhesive energy Gc = 70 J/m2) because of its highest compressive stress (4.64 GPa). Based on the results here, it is concluded that a decent compressive stress of 3.0 GPa is expected to help thin films prevent from radial and circumferential cracks simultaneously.

Y.C. Chim

Papers

Oxidation resistance of TiN, CrN, TiAlN and CrAlN coatings deposited by lateral rotating cathode arc