Tribological Properties of Diamond– like Carbon Films Deposited by PECVD

The microstructure and mechanism of fatigue crack initiation of 2024–T3 and 2524–T34 Al alloys were investigated. Four–point bending and tension –tension fatigue tests on the tested alloys with a frequency of 15 Hz, R=0.1 along the rolling direction were conducted at room temperature. It was found that the flat grain was elongated along the rolling direction, showing the laminar grain structure. The amount of coarse and irregular particles and the density of secondary particles distributed in 2024 were much higher than that in 2524. Particles in 2524 distributed stripped along the rolling direction. The majority of fatigue cracks of 2524 were initiated on the coarse β phase second particle, containing Fe, a few of them formed on sites of material defects or slip bands. The intrusion and extrusion induced by slip band in the Al cladding layer provided principal fatigue crack initiation sites for 2024 and 2524 Al–cladding aluminum alloys.