Authors: Z. Cai, P. Zhang
Affilation: Academy of Armored Force Engineering, China
Pages: 53 - 59
Keywords: Ion plating, CrTiAlN composite coatings, microstructure, tribological properties, hardness
In order to improve the life of piston rings, a multicomponent CrTiAlN composite coatings with different chemical composition are deposited on the surface of 65Mn steels by multi-ion plating technology in a gas mixture of Ar+N2. The Metallic ratio of Cr, Ti, and Al was varied by adjusting the currents of different TiAl target. The coatings were characterized by means of energy dispersive spectrum, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electronic microscopy, nano hardness tester and ball-on-disc tribometer, respectively. The experimental results show that the deposition velocity of CrTiAlN coatings increased with the increasing of TiAl target current. When the TiAl target current was 60A, the deposition velocity of CrTiAlN coatings reached maximum value, about 72nm/min. With the addition of Ti and Al elements, the resulting CrTiAlN coatings crystallize in the cubic B1-NaCl structure with a preferential growth orientation changing from CrN (111) to CrN (200) (Fig.1). The surface morphology of CrAlTiN films are compact and dense. And the cross-section morphology appears as fibrous columnar crystals structure(Fig.2). The metallic elements in the coatings react with nitrogen to form nitride phases such as CrN, TiN and AlN. No Cr2N phase can be detected (Fig.3). The optimised CrTiAlN hard coatings with hardness of 35 GPa are found to have superior wear performance at high-temperature as compared to Cr plating and CrN coatings. And the abrasive wear was the main wear mechanism. The specific wear rate can reach as low as 2.2×10−4 mm3, which is about 2.75 times lower than that of Cr electroplating(Fig.4). The CrAlTiN composite films performs better than binary CrN as well as the Cr plating in teams of hardness and wear resistance at high temperature. Then the tribological mechanisms at high temperature for the above three kinds of coatings was discussed. It is expected that these advantageous properties can enable the CrTiAlN coatings for a wide range of applications the surface of piston rings.