such surface treatments while monitoring other durability consequences。   The motivation

of this study is to provide an experimental evaluation of a number of surface roughness reduction methods and a chemical deposition type surface coating in terms of their friction, scuffing (including cases when the contacts are starved of lubricant) and wear performance in comparison to the baseline case of hard ground surfaces。 This experimental study will employ a rolling contact (two-disk) test methodology for such evaluations as well as a spur gear set-up for the resultant efficiency consequences。

In line with the intended applications of the Sponsor, both ground vehicle and aerospace gear and bearing contact conditions will be considered。 A typical automotive gear steel (AISI 5120) and an axle lubricant (80W90) will be used for the evaluations intended for ground vehicles, and AISI 9310 steel and MIL-PRF-23699 for the evaluations intended for aerospace applications will be used。 Measured traction (friction coefficient), wear and scuffing performances of surface treatment under both automotive and aerospace conditions will be compared to provide guidelines on their potential application to actual machine elements。

Based on the results of the two-disk experiments, these surface treatment methods will selectively be applied to actual spur gears and evaluated for their impact on spin and mechanical power losses of gears operating under speed, temperature and torque conditions representative of actual operating conditions。

Potential applications of these evaluated technologies are ground vehicle and aviation power trains, ground vehicle diesel engines, electric generators as well as ground vehicle and aviation turbine engines。 This research and its objectives are of interest to the Sponsor  due  to  its  potential  for  increases  in  efficiency  of  propulsion  systems。

Improvements in efficiency and/or fatigue characteristics of gear components will benefit by increasing the reliability, availability, and therefore the safety of ground and air vehicles。 Improvements will also impact the Sponsor’s logistical footprint through a reduction in the consumption of petroleum, oil, and lubricant products, as well as through a reduction in the consumption of expendable parts。 Therefore, the results of  this research provide the potential for a reduction in hazardous materials, environmental emissions, and cost。

1。2 Literature Review

The impact of contact surface conditions on various aspects of gear and bearing contacts have been a topic of various studies。 As-machined surfaces (shaved, shaped, broached, hard ground or honed) typically have roughness amplitudes that  are comparable to the minimum lubricant film thickness, resulting in ratios (ratio of the minimum film thickness to root-mean-square surface roughness amplitude) that are often very small ( 1)。 As demonstrated in a study by Li and Kahraman [1] through a mixed EHL model [2], contact conditions with 1 results in breakdown of fluid film in the contact interface to cause metal-to-metal (asperity) contact of surfaces。 Such asperity contacts not only reduce efficiency of components significantly but also impact their durability through scuffing, wear, pitting or micro-pitting。

Two logical ways to increase ratio at a given contact operating condition are (i) to use a lubricant with a higher viscosity to increase film thickness, and (ii) reduce the roughness   amplitudes   of   contact   surfaces   through   various   polishing   techniques。

Experimental literature contains a number of gear or roller test studies that attempted to quantify the impact of one or more of these methods on performance of lubricated contacts。