Test parameters selected for the ball-cratering wear experiments.
The purpose of this work is to study the influence of the micro-abrasive wear modes on the behaviors of the volume of wear (V) and of the coefficient of friction (μ) of thin films submitted to micro-abrasive wear. Experiments were conducted with thin films of TiN, TiAlN, TiN/TiAlN, TiHfC, ZrN, and TiZrN, using a ball of AISI 52100 steel and abrasive slurries prepared with black silicon carbide (SiC) particles and glycerine. The results show that the abrasive slurry concentration affected the micro-abrasive wear modes (“grooving abrasion” or “rolling abrasion”) and, consequently, the magnitude of the volume of wear and of the coefficient of friction, as described: (i) a low value of abrasive slurry concentration generated “grooving abrasion,” which was related to a relatively low volume of wear and high coefficient of friction, and (ii) a high value of abrasive slurry concentration generated “rolling abrasion,” which was related to a relatively high volume of wear and low coefficient of friction.
- micro-abrasive wear
- grooving abrasion
- rolling abrasion
- thin films
- volume of wear
- coefficient of friction
The micro-abrasive wear test by rotating ball (“ball-cratering wear test”) is an important method adopted to study the micro-abrasive wear behavior of metallic, polymeric, and ceramic materials. Figure 1 presents a schematic diagram of the principle of this micro-abrasive wear test, in which a rotating ball is forced against the tested specimen in the presence of an abrasive slurry, generating, consequently, the called “wear craters” on the surface of the tested material.
Initially, the development of the ball-cratering wear test aimed to measure the thickness of thin films (Figure 2a and b) , which can be made using the equations detailed in Ref. . Because of the technical features, this type of micro-abrasive wear test has been applied to study the tribological behavior of different materials [3, 4, 5], for example, in the analysis of the volume of wear (
As a function of the abrasive slurry concentration, two micro-abrasive wear modes can be usually observed on the surface of the worn crater: “grooving abrasion” is observed when the abrasive particles slide on the surface, whereas “rolling abrasion” results from abrasive particles rolling on the specimen’s surface. Figure 3a [11, 12] and Figure 3b presents, respectively, images of “grooving abrasion” and “rolling abrasion.”
Many works on coefficient of friction (
Analyzing and studying important researches regarding to tribological behavior of materials submitted to micro-abrasive wear test conditions [7, 8, 9, 26], the purpose of this work is to report the influence of the micro-abrasive wear modes on the behaviors of the volume of wear (
2. Equipment, materials, and methods
2.1 Ball-cratering wear test equipment
A ball-cratering wear test equipment with free-ball mechanical configuration (Figure 4 ) was used for the micro-abrasive wear tests, which has two load cells: one load cell to control the “normal force” (
Experiments were conducted with thin films of:
The abrasive material was black silicon carbide (SiC) with an average particle size of 3 μm; Figure 5  presents a micrograph of the abrasive particles (Figure 5a) and the particle size distribution (Figure 5b). The abrasive slurries were prepared with SiC and glycerine.
Table 1 presents the values of the test parameters defined for the micro-abrasive wear experiments.
The normal force value defined for the wear experiments was
All tests were
3. Results and discussion
Figures 6 and 7 show examples of worn surfaces obtained in the experiments; in all wear craters, the maximum depth (
The actions of the micro-abrasive wear modes showed an important influence on the volume of wear and on the coefficient of friction of the thin films studied in this research. A significant increase in the volume of abrasive particles from
Figures 8 and 9 show the behaviors of the volume of wear (
The values of the volume of wear reported under conditions of “rolling abrasion” (high-abrasive slurry concentration,
The values of the coefficient of friction reported under “grooving abrasion” (low-abrasive slurry concentration,
The results obtained indicated the conclusions:
The concentration of abrasive slurry affected the occurrence of “grooving abrasion”—under low concentration—or “rolling abrasion,” under high concentration.
The volume of wear increased with the increase of the abrasive slurry concentration.
With the low concentration of abrasive slurry, “grooving abrasion” and, consequently, high values of coefficient of friction were reported. In this situation, the abrasive particles were incrusted on the counter-body, hindering their movements and generating high tangential forces.
On the other hand, when the high concentration of abrasive slurry was used, “rolling abrasion” occurred. In this case, the abrasive particles were free to roll along the surface of the thin film, causing a low coefficient of friction.
abrasive slurry concentration—in volume, [% SiC + % glycerine] diameter of the wear crater, [mm] diameter of the ball, [mm] depth of the wear crater, [μm] coefficient of wear, [mm3/N m] ball rotational speed, [rpm] normal force, [N] radius of the ball, [mm] tangential force, [N] volume of wear, [mm3] coefficient of friction
abrasive slurry concentration—in volume, [% SiC + % glycerine]
diameter of the wear crater, [mm]
diameter of the ball, [mm]
depth of the wear crater, [μm]
coefficient of wear, [mm3/N m]
ball rotational speed, [rpm]
normal force, [N]
radius of the ball, [mm]
tangential force, [N]
volume of wear, [mm3]
coefficient of friction