Ultra-high performance of DLC-coated Si3N4 rings for mechanical seals

✍ Scribed by M. Vila; J.M. Carrapichano; J.R. Gomes; S.S. Camargo Jr.; C.A. Achete; R.F. Silva

• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 303 KB
• Volume: 265
• Category: Article
• ISSN: 0043-1648
• DOI: 10.1016/j.wear.2008.01.007

✦ Synopsis

Silicon nitride (Si 3 N 4 )-based ceramics are useful materials for tribological purposes due to their superior mechanical properties. One of their applications is as mechanical face seals. However, Si 3 N 4 rings failed as self-mated systems, leading to fluid leakage and catastrophic failure under high-sealing loads. In order to improve the tribological behaviour and to provide efficient full-sealing conditions, the coating of the Si 3 N 4 surfaces with a solid lubricating diamond-like carbon (DLC) film is here proposed. Plasma-enhanced chemical vapour deposition (PECVD) DLC coatings with approx. thickness of 1.5 m were deposited on Si 3 N 4 rings by conventional RF glow discharge taking only pure methane or a 95:5 methane/silane mixture, under an applied self-bias voltage of -800 V. After 419 h of continuous work (4300 km), the self-mated pure DLC ring-on-ring tribosystem proved its outstanding performance in sealing of 2 bar of internal pressure of water, at 4 m s -1 , in the range 0.48-1 kN of applied normal load, without any signs of surface damage and a super low-friction coefficient value less than 0.001. The Si-DLC coatings have a slightly worse performance, with a running-in period and a steady-state friction coefficient of about 0.02.