1。3 Thesis Objectives

It is clear from the literature review that there is not a comprehensive study on the various effects of engineered surface techniques on friction, wear and scuffing performance of lubricated contacts under both aerospace and automotive conditions。 All of the studies on surface roughness effects considered a certain single-level of polished surfaces to as-machined surfaces。 These studies fail to relate basic two-disk type tests to actual gear experiments。 Coatings considered for gear contact applications are typically thin-film coatings applied through PVD techniques with some significant cost penalty。

There is no study on chemically deposited coatings。 This study is aims at filling some of these gaps in the literature。

The specific technical objectives of this study are as follows:

• Quantify the improvements to friction of ground surfaces that can  be achieved through application of surface polishing techniques and NiB coating of sliding roller contacts and gears。

• Determine the ability of the NiB coating to retain critical dimensions of roller and the gear teeth while providing required wear resistance。 Investigate the compatibility of the NiB coating with approved aerospace and ground lubricants。

• Investigate the surface wear consequences of polishing and NiB coating treatments considered。

• Assess the improvements to contact scuffing performance with the NiB coating and surface polishing under both normal and loss-of-lube conditions。

This study will be kept limited to two gear steels, 9310 for aerospace applications and 5120 for automotive applications to go with MIL-PRF-23699 and 80W90 oils, respectively。 A two-disk setup and a four-square type gear test set-up will be devised and gear and roller specimens with desired surface treatments will be fabricated and tested。

1。4 Thesis Outline

In Chapter 2 of this report, the two-disk test methodology will be explained。 Details of each test set-up and procedures developed for the traction, wear and scuffing tests will be provided。 Test matrices defined for each type of test will be introduced。 Chapter 3 presents all of the two-disk test results and discusses them in terms of performance of each surface treatment。

Chapter 4 describes a gear test machine including specimens and instrumentation and measurement procedures。 A gear efficiency test matrix is defined and gear power loss results are presented and discussed。

The last chapter summarizes the test results, draws the major conclusions and recommends future work that can be done to further characterize performance of each surface finish technique。

CHAPTER 2

TWO-DISK TEST METHODOLOGY

2。1  Two-Disk Test Machine

A two-disk test machine shown in Figure 2。1 was used in this study to evaluate the friction coefficient, wear, and scuffing performance of roller specimens made from two different gear steels with four different engineered surfaces。 The schematic of the test machine is shown in Figure 2。2。 This test machine allows a pair of disks to be pushed against each other and operated at given values of rolling and sliding speeds。

Desired speed conditions were achieved by independently controlling the rotational speeds of the roller (smaller of the two disk specimens) and the disk (larger of the two disk specimens) independently。 Both drive units, powering the roller and the disk, were 10 HP, 3-phase AC vector motors, connected to 2:1 ratio timing belt as illustrated schematically in Figure 2。2。 These drives were controlled by a LabVIEW script。  This program was able to independently drive each motor to set roller and   disk