Why the atmosphere matters
Friction and wear are not intrinsic material properties. They belong to the whole tribosystem, and the surrounding gas is part of that system. Water vapour adsorbs on surfaces within seconds, oxygen drives oxidation and tribochemical films, and both are present in room air in amounts that vary with season, weather and laboratory. A coating qualified on a dry winter day can behave differently on a humid summer one.
Controlling the atmosphere makes results repeatable from day to day and lab to lab, and it lets the effect of humidity be measured deliberately rather than suffered as noise.
How the module works
The contact is enclosed in a chamber connected to a humidity controller, which sets relative humidity anywhere from 10% to 90% and holds it to within ±1%. The same enclosure can instead be fed with inert gas to purge oxygen and moisture. Rotational, linear and scratch tests run inside it as normal; block-on-ring and ring-on-ring can be enclosed as custom configurations.
A typical study runs the same test at several humidity set points (for example 10%, 30% and 60% RH) and compares friction curves, wear rates and wear morphology.
DLC: a material defined by its environment
Diamond-like carbon is the classic environment-sensitive coating. In NANOVEA’s DLC humidity study against a silicon nitride ball:
- at 10% RH, COF stayed around 0.05 throughout the test;
- at 30% RH, COF settled around 0.1;
- above 50% RH, a distinct run-in stage appeared over the first 2000 revolutions.
The ball’s wear scar was smaller at low humidity. In dry conditions a stable DLC transfer layer built up on the ball, so the coating slid against its own transfer film, which acted as an efficient solid lubricant.
Coatings that must survive the weather
Exterior coatings meet a wide humidity range in service. NANOVEA tested self-cleaning glass coatings at 30% and 60% RH against a WC ball. At 30% RH, uncoated glass started at COF ~0.45 and climbed to ~0.6, while both coatings started below 0.2; one stayed near 0.25 and the other rose sharply partway through the test. Testing at more than one humidity revealed differences in durability that a single room-air test would not.
Measuring the wear
After the test, the wear track is measured by chromatic confocal 3D non-contact profilometry. It handles transparent and highly reflective surfaces such as glass and DLC, and gives the worn volume for the specific wear rate K = V / (F × s) at each humidity.
