**3.1. Morphology and roughness**

After grit blasting, the substrate surface is nonmetal shiny and matte-like. The surface morphology of as-obtained grit-blasting steel substrate was shown in **Figure 1**. It can be seen that surface roughness of the steel substrate was enlarged obviously than the polished samples.

**Figure 1.** The morphology of grit-blasting steel substrate.

However, there are not clearly defects and concave pits in the substrate surface. The average Ra value of steel substrate and polished samples are 7.5 and 0.03 μm. Grit-blasting substrate was larger than that of polished sample.

The surface morphology of ion plating TiN film covered a grit-blasting substrate is shown in **Figure 2**. Compared with the surface morphology before covered TiN films, there is not notable difference for surface morphology of TiN-covered samples. The average Ra value of as-prepared TiN film covered grit-blasting steel substrate was 8.2 μm, which is similar to that of grit-blasting substrate. The film thickness of TiN film is 4 μm, which is measured with the profile meter.

The average friction coefficients of TiN film and grit-blasting steel substrate sliding against steel ball were 0.125 and 0.135, respectively, which reduced by 7%. For zirconia ball, the average friction coefficients of TiN film and grit-blasting steel substrate were 0.125 and 0.155,

**Figure 3.** Histogram of average friction coefficient of grit-blasting steel substrate and TiN film sliding against with

Effects of Different Materials on the Tribological Performance of PVD TiN Films under Starved…

http://dx.doi.org/10.5772/intechopen.75842

105

The tribological properties of grit-blasting steel and TiN film against four different upper balls were carried out by a rotating tribometer with ball-on-disk of configuration. The coefficient of friction of grit-blasting steel substrate was shown in **Figure 4**. For different upper balls, their friction behaviors are different. The friction duration of alumina balls is worse than steel, zirconia, and silicon nitride balls. The friction duration was only 2 min when the coefficient of friction is over the limited value. During the alumina ball sliding against grit-blasting steel disk, its coefficient of friction was 0.13 and increased drastically after 1 min. Its friction duration was very shorter than other balls. For other different upper balls of steel, silicon nitride and zirconia balls, they exhibited the similar trend that the coefficient of friction elevated gradually and reached the steady value of 0.17. However, the friction duration of three different upper balls is as long as 120 min, the reaching time of steady-state friction coefficient is different. The coefficient of friction raised to steady state for steel ball after 50 min. For silicon nitride and zirconia balls, the times to reach the steady-state friction coefficient are 10 and 25 min, respectively.

The real-time friction coefficients of TiN films covered grit-blasting steel substrate against four different upper balls are shown in **Figure 5**. The friction coefficient of TiN film against alumina ball elevated drastically and over the limited value of friction coefficient for a very short time, which was similar with the trend of grit-blasting steel substrate against alumina ball. For three other upper balls, the friction duration of TiN films can last with a steady-state friction coefficient until friction experiment ended up. However, the undulations of friction coefficient of TiN films sliding against silicon nitride, steel, and zirconia balls are smaller than

respectively, which reduced by 19%.

different upper balls.

those of grit-blasting steel disks.

### **3.2. Friction test results**

The histogram of average friction coefficient of grit-blasting steel substrate and TiN films sliding against with different upper balls was shown in **Figure 3**. Because of the shorter friction duration for only few minutes, the average friction coefficient of alumina ball is not presented in the figure. For three other different balls, the average friction coefficient of silicon nitride ball against grit-blasting steel substrate is as same as that of silicon nitride ball sliding against TiN films. The average friction coefficients of TiN films were lower than those of gritblasting steel substrate for steel ball and zirconia ball under the same lubrication conditions.

**Figure 2.** Surface morphology of ion plating TiN film covered the grit-blasting substrate.

Effects of Different Materials on the Tribological Performance of PVD TiN Films under Starved… http://dx.doi.org/10.5772/intechopen.75842 105

**Figure 3.** Histogram of average friction coefficient of grit-blasting steel substrate and TiN film sliding against with different upper balls.

However, there are not clearly defects and concave pits in the substrate surface. The average Ra value of steel substrate and polished samples are 7.5 and 0.03 μm. Grit-blasting substrate

The surface morphology of ion plating TiN film covered a grit-blasting substrate is shown in **Figure 2**. Compared with the surface morphology before covered TiN films, there is not notable difference for surface morphology of TiN-covered samples. The average Ra value of as-prepared TiN film covered grit-blasting steel substrate was 8.2 μm, which is similar to that of grit-blasting substrate. The film thickness of TiN film is 4 μm, which is measured with the

The histogram of average friction coefficient of grit-blasting steel substrate and TiN films sliding against with different upper balls was shown in **Figure 3**. Because of the shorter friction duration for only few minutes, the average friction coefficient of alumina ball is not presented in the figure. For three other different balls, the average friction coefficient of silicon nitride ball against grit-blasting steel substrate is as same as that of silicon nitride ball sliding against TiN films. The average friction coefficients of TiN films were lower than those of gritblasting steel substrate for steel ball and zirconia ball under the same lubrication conditions.

**Figure 2.** Surface morphology of ion plating TiN film covered the grit-blasting substrate.

was larger than that of polished sample.

**Figure 1.** The morphology of grit-blasting steel substrate.

104 Lubrication - Tribology, Lubricants and Additives

profile meter.

**3.2. Friction test results**

The average friction coefficients of TiN film and grit-blasting steel substrate sliding against steel ball were 0.125 and 0.135, respectively, which reduced by 7%. For zirconia ball, the average friction coefficients of TiN film and grit-blasting steel substrate were 0.125 and 0.155, respectively, which reduced by 19%.

The tribological properties of grit-blasting steel and TiN film against four different upper balls were carried out by a rotating tribometer with ball-on-disk of configuration. The coefficient of friction of grit-blasting steel substrate was shown in **Figure 4**. For different upper balls, their friction behaviors are different. The friction duration of alumina balls is worse than steel, zirconia, and silicon nitride balls. The friction duration was only 2 min when the coefficient of friction is over the limited value. During the alumina ball sliding against grit-blasting steel disk, its coefficient of friction was 0.13 and increased drastically after 1 min. Its friction duration was very shorter than other balls. For other different upper balls of steel, silicon nitride and zirconia balls, they exhibited the similar trend that the coefficient of friction elevated gradually and reached the steady value of 0.17. However, the friction duration of three different upper balls is as long as 120 min, the reaching time of steady-state friction coefficient is different. The coefficient of friction raised to steady state for steel ball after 50 min. For silicon nitride and zirconia balls, the times to reach the steady-state friction coefficient are 10 and 25 min, respectively.

The real-time friction coefficients of TiN films covered grit-blasting steel substrate against four different upper balls are shown in **Figure 5**. The friction coefficient of TiN film against alumina ball elevated drastically and over the limited value of friction coefficient for a very short time, which was similar with the trend of grit-blasting steel substrate against alumina ball. For three other upper balls, the friction duration of TiN films can last with a steady-state friction coefficient until friction experiment ended up. However, the undulations of friction coefficient of TiN films sliding against silicon nitride, steel, and zirconia balls are smaller than those of grit-blasting steel disks.

**Figure 4.** The coefficient of friction of grit blasting steel-disk sliding against different upper balls.

The surface morphology of wear track in TiN film and wear scar in upper silicon nitride ball were shown in **Figure 7**. It is seen that there is not obvious wear and more smooth pits in the wear track of TiN film. There is a wear scar with the diameter of 0.37 mm in the upper silicon nitride ball. Although both titanium nitride and silicon nitride are very hard materials, the micro-bulge in the lower rough disk could be deformed under high pressure. This resulted in the bigger real contact area, which means the friction force of among all the micro-bulge with upper ball increased. It is confirmed that the real-time friction coefficient raised during the later stage of the friction tests. The surface morphology of wear track in TiN film and wear scar in upper zirconia ball are shown in **Figure 8**. It is also seen that there is not obvious wear and more smooth pits in the wear track of TiN film, which is similar with the wear track of TiN film sliding against silicon nitride ball. There is a wear scar with the diameter of 0.32 mm in the upper zirconia ball. Very small pores can be found in the wear scar of upper ball. These pores could absorb the lubricating oils on the surface of lower disk. During the sliding process, the absorbed oils in the pores can improve tribological properties by avoiding the direct contact of rubbing surface. So, the

**Figure 6.** The morphology of wear track in TiN film and wear scar in upper steel ball after friction tests under the starve

Effects of Different Materials on the Tribological Performance of PVD TiN Films under Starved…

http://dx.doi.org/10.5772/intechopen.75842

107

was steady.

The surface morphology of wear track of TiN film and wear scar in upper alumina ball is shown in **Figure 9**. Compared with the negligible wear of other different ball, there is obvious wear trace from the low-resolution figure and bigger smooth contact area from the highresolution figure in the TiN film. The bigger the contact area is, the bigger the friction force between the contact interface. So, the friction coefficient increases during the sliding process. There is a very small wear scar in the alumina ball as compared to the wear scars in the other different upper balls. It means that the material in the smooth contact area is from the lower

friction coefficient of TiN film against ZrO<sup>2</sup>

lubrication regime.

disk and lubricating oil, not upper ball.

**Figure 5.** The coefficient of friction of TiN films sliding against different upper balls.

#### **3.3. Surface analysis**

**Figure 6** shows the surface morphology of wear track in TiN film and upper steel ball under the starve lubrication regime. It is not seen that there is notable wear trace in the track from the low-resolution figure, which amplification is 100. However, there is some smooth pit in the wear track from the high-resolution figure, which amplification is 500. It can be attributed to the transfer phase from the upper steel ball and the plastic deformation of micro-bulge in the lower steel substrate. Because TiN is much hard than the soft steel ball, so the TiN film covered the grit-blasting steel substrate plays a similar role of sandpaper for upper steel ball. It is confirmed from the surface morphology of upper steel ball that there is a round wear scar with the diameter of 0.63 mm in the upper steel ball. The bigger wear scar of steel ball can result in reduced normal pressure, so the friction coefficient of TiN film against steel ball was steady.

Effects of Different Materials on the Tribological Performance of PVD TiN Films under Starved… http://dx.doi.org/10.5772/intechopen.75842 107

**Figure 6.** The morphology of wear track in TiN film and wear scar in upper steel ball after friction tests under the starve lubrication regime.

The surface morphology of wear track in TiN film and wear scar in upper silicon nitride ball were shown in **Figure 7**. It is seen that there is not obvious wear and more smooth pits in the wear track of TiN film. There is a wear scar with the diameter of 0.37 mm in the upper silicon nitride ball. Although both titanium nitride and silicon nitride are very hard materials, the micro-bulge in the lower rough disk could be deformed under high pressure. This resulted in the bigger real contact area, which means the friction force of among all the micro-bulge with upper ball increased. It is confirmed that the real-time friction coefficient raised during the later stage of the friction tests.

The surface morphology of wear track in TiN film and wear scar in upper zirconia ball are shown in **Figure 8**. It is also seen that there is not obvious wear and more smooth pits in the wear track of TiN film, which is similar with the wear track of TiN film sliding against silicon nitride ball. There is a wear scar with the diameter of 0.32 mm in the upper zirconia ball. Very small pores can be found in the wear scar of upper ball. These pores could absorb the lubricating oils on the surface of lower disk. During the sliding process, the absorbed oils in the pores can improve tribological properties by avoiding the direct contact of rubbing surface. So, the friction coefficient of TiN film against ZrO<sup>2</sup> was steady.

**3.3. Surface analysis**

106 Lubrication - Tribology, Lubricants and Additives

**Figure 6** shows the surface morphology of wear track in TiN film and upper steel ball under the starve lubrication regime. It is not seen that there is notable wear trace in the track from the low-resolution figure, which amplification is 100. However, there is some smooth pit in the wear track from the high-resolution figure, which amplification is 500. It can be attributed to the transfer phase from the upper steel ball and the plastic deformation of micro-bulge in the lower steel substrate. Because TiN is much hard than the soft steel ball, so the TiN film covered the grit-blasting steel substrate plays a similar role of sandpaper for upper steel ball. It is confirmed from the surface morphology of upper steel ball that there is a round wear scar with the diameter of 0.63 mm in the upper steel ball. The bigger wear scar of steel ball can result in reduced normal pressure, so the friction coefficient of TiN film against steel ball was steady.

**Figure 4.** The coefficient of friction of grit blasting steel-disk sliding against different upper balls.

**Figure 5.** The coefficient of friction of TiN films sliding against different upper balls.

The surface morphology of wear track of TiN film and wear scar in upper alumina ball is shown in **Figure 9**. Compared with the negligible wear of other different ball, there is obvious wear trace from the low-resolution figure and bigger smooth contact area from the highresolution figure in the TiN film. The bigger the contact area is, the bigger the friction force between the contact interface. So, the friction coefficient increases during the sliding process. There is a very small wear scar in the alumina ball as compared to the wear scars in the other different upper balls. It means that the material in the smooth contact area is from the lower disk and lubricating oil, not upper ball.

**Figure 7.** Morphology of wear track in TiN film and wear scar in upper silicon nitride ball after friction tests under the starve lubrication regime.

> The tribological performance of friction pairs is attributed to many factors, such as the natural lubricating characteristic, the physic-chemical properties of different materials, the content of lubricating oil, experiment conditions, and so on. In this paper, however, the average oil thickness is 3 μm before the test, the real oil content about the contact area is more as compared to before the test because of the aggregation effect of lubricating oil caused by the surface free

> **Figure 9.** The morphology of wear track in TiN film and wear scar in upper aluminia ball after friction tests under the

Effects of Different Materials on the Tribological Performance of PVD TiN Films under Starved…

http://dx.doi.org/10.5772/intechopen.75842

109

For the four kinds of upper balls, the lubricating abilities are different. Both zirconia and silicon nitride could exhibit better self-lubricating performance than alumina and steel. So, the friction durations of zirconia and silicon nitride are longer than alumina when they slid with TiN film under starved lubrication conditions. For one steel ball, its hardness is much smallest

One thick TiN film was prepared by ion-plated technology on the grit-blasted steel substrate. The tribological performance was evaluated with four upper balls made up of different materials under the starved lubrication regime. Compared with their higher friction coefficients for grit-blasting steel against different balls, the friction coefficients for TiN films on the gritblasting steel were lower and steady. It was due to the hardness of TiN film and small contact

in all of the test balls. And the steel ball was worn in the sliding process.

energies of different materials.

starve lubrication regime.

**4. Conclusion**

**Figure 8.** The morphology of wear track in TiN film and wear scar in upper zirconia ball after friction tests under the starve lubrication regime.

Effects of Different Materials on the Tribological Performance of PVD TiN Films under Starved… http://dx.doi.org/10.5772/intechopen.75842 109

**Figure 9.** The morphology of wear track in TiN film and wear scar in upper aluminia ball after friction tests under the starve lubrication regime.

The tribological performance of friction pairs is attributed to many factors, such as the natural lubricating characteristic, the physic-chemical properties of different materials, the content of lubricating oil, experiment conditions, and so on. In this paper, however, the average oil thickness is 3 μm before the test, the real oil content about the contact area is more as compared to before the test because of the aggregation effect of lubricating oil caused by the surface free energies of different materials.

For the four kinds of upper balls, the lubricating abilities are different. Both zirconia and silicon nitride could exhibit better self-lubricating performance than alumina and steel. So, the friction durations of zirconia and silicon nitride are longer than alumina when they slid with TiN film under starved lubrication conditions. For one steel ball, its hardness is much smallest in all of the test balls. And the steel ball was worn in the sliding process.
