An Accelerated Wear Test Method to Evaluate Lubricant Thin Films on Magnetic Hard Disks
X H. Zhang, Richard S. Gates, S Anders, Stephen M. Hsu
A high speed ball-on-inclined plane test method has been successfully used to evaluate the lubrication effectiveness of nanometer thick lubricant films on magnetic hard disks. The test evaluates the durability of the lubricant film and the carbon overcoat under sliding conditions. The test uses a polished ruby (Al2O3) ball without suspension to simulate the head material. The ball slides over a section of the disk surface at 2.0 m/s linear velocity. The disk sample is inclined at an angle of 0.055 ± 0.005 degrees} to allow for a geometric interference loading in addition to the preset load of the ball. Friction force of the contact is continuously monitored and recorded. Repeated sliding passes between the ball and the disk sample eventually leads to a dramatic increase in friction. Post-test analysis suggests that the increase in friction is due to the loss in lubrication effectiveness of the lubricant/carbon overcoat. The number of cycles to failure defines the durability of the lubricating layers. Test repeatability is about 10 %, depending on the nature of the lubricant, film thickness, and the surface roughness of the ball. Absence of any lubricant on the carbon overcoat results in rapid increase in friction in very short cycle time. The test can be used to evaluate different lubricant chemistries as well as different carbon overcoats.
durability, lubricant, lubrication, magnetic hard disks, monolayer, Zdol