Wear characterization of Ti–6Al–4V under fretting–reciprocating sliding conditions
Introduction
Fretting wear occurs when two contacting surfaces slide against each other with oscillatory motion. It results from undesirable vibration as well as misalignment between the mating bodies. Further, the surface damage is produced due to fretting action, which can be the result of several wear mechanisms acting individually or in combination, and these are corrosion, adhesion, and/or abrasion [1]. For instance, as the surfaces slide back and forth, adhesion will clean substrate and expose the underlying material to oxidation and corrosion [1]. Oxidized debris, broken free from the surfaces, can act as an abrasive and initiate three-body wear [1]. The surface damage produced by fretting is a function of the type of relative slip: partial or gross, however, the maximum wear damage is found to occur under gross slip [2], [3].
The capability to predict the geometry of fretting and reciprocating wear scars, such as the scar's width and depth, would be a valuable tool when designing mechanical components. For example, the prediction of the depth of a wear scar is important to estimate the life of a protective coating, which depends on the thickness of the coating [4], [5]. It may be noted that the contact geometry of the components undergoing fretting and sliding wear will be modified. It would also affect significantly the contact stresses (both normal and shear stresses) which could then reduce the fretting life. Therefore, the worn components may no longer be able to meet the design specifications due to changes in component geometry and stress state.
Therefore, the characterization of wear behavior for various materials under different fretting and sliding conditions is needed, and there have been several studies in this direction [2], [3], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. The present study investigates the fretting–reciprocating wear behavior of titanium alloy in contact with titanium alloy (both Ti–6Al–4V). This material is widely used in aerospace and biomedical industry due to its superior mechanical properties and relatively low density. One such application is the dovetail contact region of blade/disk attachments in gas turbines where fretting fatigue-induced damages, both cracking and wear, are commonly seen. There have been several studies on the fretting fatigue as well as fretting wear behavior of Ti–6Al–4V [3], [8], [14], [18], [19], [20], [21], [22]. The present study is an extension of previous similar studies, however, characterizes the wear under reciprocating conditions in the presence of cyclic load on the substrate (specimen) unlike the previous studies where substrate (specimen) had no direct load. This phenomenon is referred to as the fretting–reciprocating sliding condition in this study unlike the conventional plain reciprocating sliding condition. Furthermore, the present study involved a large amount of wear damage. These aspects were the main focus of the current study and are directed towards the design of the blade/disk attachments in gas turbines. For this purpose, four series of tests were conducted to characterize the effects of different sliding and loading parameters on the wear behavior under cylinder-on-flat contact configuration; and these parameters were relative slip, normal contact load, number of cycles, and bulk cyclic stress. In addition, the evolution of shapes of wear scar under these different test conditions were documented and analyzed.
Section snippets
Background
A brief summary of the related previous studies will be presented before the details of the present investigation are presented.
Experimental procedure
This section describes the experimental setup, material, specimen details, and the techniques used to measure the test variables such as tangential force, Q, normal contact load, P, relative slip, δ, and wear volume, WV. The details of the test plan are also included.
Wear scar shape
Shapes of the wear scars were determined using the profilometric technique as discussed earlier. Two- and three-dimensional profiles of the worn surfaces were generated. Fig. 4, Fig. 5 show the typical three-dimensional views of the wear scars on the specimen and the corresponding pad surfaces, respectively from a test in the “baseline” series (Table 1) after an application of 1000 fretting cycles. The pad and specimen scars almost fit together like the two pieces of a jigsaw puzzle, and it was
Conclusions
The purpose of this study was to investigate the wear behavior of Ti–6Al–4V subjected to fretting–reciprocating sliding condition. Four series of fretting–reciprocating tests were conducted to analyze the effects of contact load, relative slip, number of cycles, and alternating axial stress on wear volume and scar shape development for the cylinder-on-flat contact. The following conclusions are drawn based on this work:
- 1.
The cyclic axial stress on the specimen increased the relative slip through
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