#
Friction of Tungsten-Based Coatings of Steel under Sliding Contact^{ †}

^{†}

## Abstract

**:**

## 1. Introduction

## 2. Experimental Approach

## 3. Test Plan

## 4. Test Results

#### 4.1. Steel–Steel

#### 4.2. Steel–${\mathrm{WS}}_{2}$

#### 4.3. WC–Steel

#### 4.4. WC–${\mathrm{WS}}_{2}$

#### 4.5. Heavy Grease WC–${\mathrm{WS}}_{2}$

## 5. Optical Profilometer Measurements

## 6. Conclusions

## Funding

## Acknowledgments

## Conflicts of Interest

## Abbreviations

COF | Coefficient of Friction |

HVOF | High Velocity Oxygen Fuel |

LG | Light-Grease |

HG | Heavy-Grease |

ASTM | American Society for Testing and Materials |

WS${}_{2}$ | Tungsten Disulfide |

WC | Tungsten Carbide |

RMS | Root Mean Square |

Ra | Roughness Average (Arithmetical Mean Roughness) |

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**Figure 1.**A demonstration of the effect of the true contact area ratio versus apparent contact area. Each of the dots represents a given asperities height, determined with an algorithm to represent such an arbitrary shape [25]. The average asperity height was a nanometer (nm), whereas the average distance separating the surface means was 15 nm. Under these conditions that are typical of smooth, lubricated solid contact, only 11 out of 100 of the top surface asperities contacted the lower asperities, representing the true contact area ratio of 11%.

Grease | Material | Load (N) | Speed (r/min) | COF${}_{\mathbf{min}}$ | COF${}_{\mathbf{avg}}$ (900 s) | Scar (mm) |
---|---|---|---|---|---|---|

LG | Steel–Steel | 128 | 200 | 0.5787 | 0.65125 | 1.0563 |

LG | Steel–Steel | 461 | 200 | 0.3212 | 0.4802 | 0.8293 |

LG | Steel–Steel | 128 | 1200 | 0.3307 | 0.42015 | 1.6949 |

LG | Steel–Steel | 461 | 1200 | 0.1091 | 0.17155 | 0.9847 |

Grease | Material | Load (N) | Speed (r/min) | COF${}_{\mathbf{min}}$ | COF${}_{\mathbf{avg}}$ (900 s) | Scar (mm) |
---|---|---|---|---|---|---|

LG | Steel–${\mathrm{WS}}_{2}$ | 128 | 200 | 0.4251 | 0.5832 | 1.0499 |

LG | Steel–${\mathrm{WS}}_{2}$ | 461 | 200 | 0.248 | 0.339 | 0.8184 |

LG | Steel–${\mathrm{WS}}_{2}$ | 128 | 1200 | 0.3068 | 0.50195 | 1.3511 |

LG | Steel–${\mathrm{WS}}_{2}$ | 461 | 1200 | 0.1170 | 0.23415 | 1.2672 |

Grease | Material | Load (N) | Speed (r/min) | COF${}_{\mathbf{min}}$ | COF${}_{\mathbf{min}}$ (300–900 s) | COF${}_{\mathbf{avg}}$ (900 s) | Scar (mm) |
---|---|---|---|---|---|---|---|

LG | WC-Steel | 128 | 200 | 0.1052 | 0.4950 | 0.4997 | 0.7089 |

LG | WC-Steel | 461 | 200 | 0.1427 | 0.2532 | 0.2843 | 0.838 |

LG | WC-Steel | 128 | 1200 | 0.3166 | 0.3166 | 0.40205 | 1.186 |

LG | WC-Steel | 461 | 1200 | 0.1176 | 0.1176 | 0.15785 | 1.1885 |

Grease | Material | Load (N) | Speed (r/min) | COF${}_{\mathbf{min}}$ | COF${}_{\mathbf{min}}$ (300–900 s) | COF${}_{\mathbf{avg}}$ (900 s) | Scar (mm) |
---|---|---|---|---|---|---|---|

LG | WC–${\mathrm{WS}}_{2}$ | 128 | 200 | 0.0883 | 0.4075 | 0.47085 | 0.75742 |

LG | WC–${\mathrm{WS}}_{2}$ | 128 | 1200 | 0.2189 | 0.2189 | 0.37805 | 0.74092 |

LG | WC–${\mathrm{WS}}_{2}$ | 461 | 200 | 0.1355 | 0.2218 | 0.23365 | 1.21125 |

LG | WC–${\mathrm{WS}}_{2}$ | 461 | 1200 | 0.1149 | 0.1149 | 0.16895 | 1.4375 |

LG | WC–${\mathrm{WS}}_{2}$ | 981 | 200 | 0.1983 | 0.1983 | 0.2429 | 1.0042 |

LG | WC–${\mathrm{WS}}_{2}$ | 981 | 1800 | 0.0415 | 0.0415 | 0.0859 | 1.12225 |

Grease | Material | Load (N) | Speed (r/min) | COF${}_{\mathbf{min}}$ | COF${}_{\mathbf{avg}}$ (900 s) | Scar (mm) |
---|---|---|---|---|---|---|

HG | WC–${\mathrm{WS}}_{2}$ | 128 | 200 | 0.0201 | 0.02485 | 0.26533 |

HG | WC–${\mathrm{WS}}_{2}$ | 128 | 1200 | 0.0301 | 0.0375 | 0.2535 |

HG | WC–${\mathrm{WS}}_{2}$ | 128 | 1800 | 0.0101 | 0.0172 | 0.3005 |

HG | WC–${\mathrm{WS}}_{2}$ | 461 | 200 | 0.0700 | 0.07325 | 0.419 |

HG | WC–${\mathrm{WS}}_{2}$ | 461 | 1200 | 0.0692 | 0.0758 | 0.56125 |

HG | WC–${\mathrm{WS}}_{2}$ | 461 | 1800 | 0.0652 | 0.0762 | 0.67375 |

HG | WC–${\mathrm{WS}}_{2}$ | 981 | 200 | 0.0899 | 0.06685 | 0.461083 |

HG | WC–${\mathrm{WS}}_{2}$ | 981 | 1200 | 0.0646 | 0.09125 | 1.0535 |

HG | WC–${\mathrm{WS}}_{2}$ | 981 | 1800 | 0.0600 | 0.07795 | 0.651 |

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**MDPI and ACS Style**

Marko, M.D.
Friction of Tungsten-Based Coatings of Steel under Sliding Contact. *Lubricants* **2019**, *7*, 14.
https://doi.org/10.3390/lubricants7020014

**AMA Style**

Marko MD.
Friction of Tungsten-Based Coatings of Steel under Sliding Contact. *Lubricants*. 2019; 7(2):14.
https://doi.org/10.3390/lubricants7020014

**Chicago/Turabian Style**

Marko, Matthew David.
2019. "Friction of Tungsten-Based Coatings of Steel under Sliding Contact" *Lubricants* 7, no. 2: 14.
https://doi.org/10.3390/lubricants7020014