April_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 0 4 4 iTSSe TSS iTSSe TSS FEATURE SPECIALIZED COATINGS FOR EXTREME ENVIRONMENTS Triboglide coatings offer enhanced wear resistance in applications like air foil bearings, actuators, and wear components where oil-based lubrication is scarce. Satish Dixit Director of Engineering/R&D Plasma Technology Inc., Torrance, California D uring the 1990s, a high temperature lubricant called Triboglide was developed as a derivative of the NASA 200 series coating system. The new lubricant was the re- sult of a collaboration between Plasma Technology Inc. (PTI), EG&G Pressure Science Inc., and NASA. As another outcome of this project, a thermal spray specification data sheet was de- veloped by PTI and EG&G. This specification covers a family of thermal sprayed, high velocity oxygen fuel (HVOF) coatings consisting of a chrome-carbidematrix with a nickel binder and a eutectic calcium-barium fluoride solid lubricant. The coating was rated for high temperatures from 800 ° to 1300 ° F for slid- ing type use. The composition of the new coating contained a 70 wt% hard CrC phase in an 18 wt% Ni binder with a 12 wt% eutectic CaF 2 -BaF 2 component. During development, parametric studieswere conducted and changes in spraying distance, angle, powder particle size, feed rates, and test temperature were correlated with tribo- logical performance using various percentages of solid lubri- cants. The initial block-on-ring wear test conducted by EG&G on Triboglide, Inconel 718, and NiCrAlY clearly indicated that Triboglide showed no signs of micro- crackingwhile Inconel andNiCrAlYex- hibited smearing and microabrasion. These tests indicate that the HVOF technique is the preferredmethod for applying Triboglide coatings. With renewed interest from companies such as Honeywell and Boeing, PTI has reexplored Tribo- glide as a hard, wear resistant, and low friction coating for applications like air foil bearings, actuators, and wear components where oil-based lubrication is scarce. Rotor shafts, actuators, and other parts working in high temperature and high speed en- vironments tend to wear faster due to rapiddegradation of lubricant oil (Fig. 1). Therefore, there is a need for sol- id lubrication that does not compro- mise on the high temperature wear and friction coefficient. COATING PROCESS Triboglide coatings were developed using the HVOF Jet Kote process. The HVOF thermal spray process is primarily the same as combustion spray except that the HVOF process 10 Fig. 2 — Cross section photos of different Triboglide coatings and NASA’s PS 304 coating. Fig. 1 — Micrograph of NASA PS 304 coating on a titanium shaft.