**7. Conclusions**

126 Tribology in Engineering

0

Si3N4 ceramic ball)

2

4

Wear rate (10-4

mm3/Nm)

6

8

10

0 200 400 600 800 1000

 Coating AISI 321 steel

Temperature/C

**Figure 14.** Wear rates of the Ni3Al-based composite coating at temperatures ranging from room temperature to 1000 °C in air (tested at an applied load of 20 N and sliding speed of 0.2 m/s against

20 40 60 80 100

2(°)

Ni3 Al

Ag Mo BaF2 CaF2

**Figure 15.** XRD patterns of the sintered Ni3Al-based self-lubricating composite coating

 

There is no doubt that search for newer and better high temperature self-lubricating materials will continue in coming years, since the application conditions of future mechanical systems will undoubtedly be much more demanding than the current ones.

To fulfill engineering application, a general design appraisal of high temperature selflubricating material can be proposed as follows: low friction (friction coefficient < 0.2); high wear resistance (wear rate < 10-6 mm3/Nm); and wide temperature range (from room temperature to high temperature of above 1000 °C).

To meet these requirements, matrix and solid lubricant selected are essential for novel high temperature self-lubricating material.

Intermetallic alloys own the comprehensive mechanical properties for industrial applications by micro- or macro-alloying process. They are now serious candidates for structural applications requiring reduced density, excellent fatigue strength, corrosion/oxidation resistance, and service at temperatures up to 1000 °C. Intermetallic alloys have attracted the attention of many researchers as promising tribomaterials for mechanical components operating under severe or hostile environments.

It should be realized by designers and engineers that there is no "universal lubricant" that can operate at a broad temperature range conditions. A synergetic lubricating action, a mixture of two or more solid lubricants, is one of promising approaches to fabricate high temperature self-lubricating materials. Furthermore, research on novel solid lubricant is also a response to the requirements.
