Tribological Performance Evaluation of Complex Bonded Coatings

Transcription

1 Tribological Performance Evaluation of Complex Bonded Coatings C. Lorenzo-Martin, O. O. Ajayi, *A. Korenyi-Both Energy Systems Division Argonne National Laboratory * Tribologix Inc STLE Annual Meeting, May 18-22, 2014 Lake Buena Vista, FL.

2 Introduction Coatings (various kind) are used to enhance tribological performance under a variety of conditions. Dry, lubricated, vacuum, high temperatures,.. Deposited by a variety of techniques, e.g. PVD, CVD, Spray, electrochemical, etc Often coatings are optimized for some tribological performance attributes, e.g. Friction reduction: Solid lubricants such as MoS2, WS2, DLC, etc.. Wear protection: Hard thin films, nitrides, DLC, etc Vast majority of current coatings have operational limitations e.g. DLC coatings have thermal limits MoS 2 coatings have environmental limits. Ceramic thin-films such as TiN could make lubricant additives ineffective. It is always desirable to have coatings that can be tribologically effective over a wide range of operating conditions, such as temperature, environment, etc... Such coatings may require multiple constituents that are effective under different conditions. 2

3 Introduction Recently, a class of complex bonded coatings (CBC) with multiple active components were developed. (Now commercially available) Evolved from early work of composite spray coatings developed by NASA (PS series) Employed the new and emerging nano composite coating technology Designed for dry, vacuum and space application and well as wide temperature range from cryogenic to elevated This paper present an experimental assessment of tribological performance of a CBC coating under different tribological contact configurations. Exploration of off-label performance evaluation 3

4 Coating description Ambient conformal vapor deposition process Thickness approx. 2-3 microns Designed for dry sliding under different conditions: cryogenic, vacuum, ambient, high temperature up to 350 C Nano-composite of lamellar materials like MoS 2, C and Sb 2 O 3 Roughness: Sa=157 nm Thickness: 3.4 microns 4

5 Friction and Wear Performance evaluation Three different type of tribological performance evaluation: 1.- Sliding Friction and Wear Ball on flat contact configuration in unidirectional sliding Ball: ½ diameter Steel (62 Rc, Ra 60nm) Flat: 1.5 x2 x1/ steel, ( 62 Rc and Ra 19 nm) Temperature: ambient Duration: 60 minutes Dry Contact: Load: 5N and 10N (σmax=0.69 GPa and 0.87 GPa) Speed: 2cm/s Ball-on-flat Configuration Lubricated contact with PAO4 Load 10N and 50N (σmax=0.87 GPa and 1.48 GPa) Speed: 1cm/s 5

6 Friction and Wear Performance evaluation 2.- Lubricant Regime Transition Ball-on-flat Configuration Ball on flat contact configuration in unidirectional sliding Ball: ½ diameter Steel (62 Rc, Ra 60 nm) Flat: 1.5 x2 x1/ steel, ( 62 Rc and Ra 19 nm) Temperature: ambient Duration: 60 minutes Load 5N Fully Flooded with PAO4 Track: 20mm Ø track, Speed: variable (0.04 cm/sec 26.2 cm/sec) (0.04 rpm to 250 rpm) 6

7 Friction and Wear Performance evaluation 3.- Scuffing Performance Evaluation Block-on-ring Contact Configuration Block: H60 Steel (61 Rc, Ra 0.25 µm) Ring: 4620 steel, internal diameter (60 Rc, Ra 0.25 µm) Temperature: ambient RT Increase in temperature during the test duration Fully Flooded with PAO4 Speed: 1000 rpm Block-on Ring Configuration Procedure : Sample is loaded with an initial load of 50N and afterwards the load is increased at 25N/min. The test is terminated when scuffing occurs, indicated by: Sudden rise in friction accompanied by vibration and noise. 7

8 Results- Unidirectional Sliding (POD) CBC coatings showed remarkably low friction under dry contact 8

9 Wear measurements Wear Volume is determined by the average of wear/length in 4 different location and total wear volume calculated for entire track

10 Wear Results (POD) * * 10

11 Wear Surface Characterization 11

12 Results- Lubrication Regimes Friction and Speed is continuously monitored during testing RPM Lineal Speed m/s Duration (min) h = AA (ηη 0UU ee ) 0.71 αα 0.57 RR 0.4 EEE 0.03 WW 0.11 λ = h/σ 12

13 Results- Lubrication Regimes (POD) Clear transition lubrication regime Viscous losses increase of hydrodynamic regime often not seen in in point contacts Steel Friction Coefficient Lambda (initial) 13

14 Results- Lubrication Regimes (POD) Slight increase in friction only observed at very low lambda max. friction increases with number of cycle Otherwise, friction inversely proportional to lambda CBC 1 Friction Coefficient λ (initial) 14

15 Results- Lubrication Regimes (POD) Clear transition in lubrication regimes Friction noisier at very low lambda coating delamination Ni-PTFE Friction Coefficient λ (initial) 15

16 Lubrication Regime- SEM Steel CBC CBC Ni-PTFE Ni-PTFE 16

17 Scuffing Performance- BOR Typical Friction Load plot scuffing indicated by sudden rise in friction 17

18 Scuffing Performance- Summary Average Scuffing Load Steel NiPTFE CBC Scuffing Load (N) Uncoated ring/coated flat Coated ring/uncoated flat Coated ring/coated flat 18

19 Scuffing Mechanisms- SEM Steel Flat - Steel Ring Steel Flat - CBC Ring

20 Scuffing Mechanisms- SEM CBC Flat - Steel Ring CBC Flat - CBC Ring 20

21 Summary Tribological performance evaluation was conducted for composite bonded coating (CBC) designed with adaptable tribological performance attributes. The coating showed remarkably low friction under dry unidirectional sliding contact condition. Under oil lubricated condition, the CBC friction behavior is similar to that of other commercial non-vacuum based low-friction coating (Ni-PTFE). The CBC coating was effective in suppressing large frictional variation with changes in lubrication regime. The scuffing performance attributes of the CBC coating is again comparable to Ni-PFTE coating, both of which are better than the scuffing of uncoated surfaces. 21

22 Acknowledgement Work supported by U.S. Department of Energy, Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, under contract DE-AC02-06CH11357 Questions? 22