Abstract
The authors have studied the tribological behaviour of hureaulite coating previously modified by annealing. Hureaulite is a manganese phosphate used as an anti-friction coating on steel parts in relative motion. This coating possesses no intrinsic lubricating characteristics and must therefore be used in combination with a lubricant. It is the response of the tribosystem ‘coating-lubricant’ which is discussed. Using a friction test to determine the seizure resistance, it is shown that the modifications of the coating (dehydration, new phases and new compounds forming) lead to a great improvement in the resistance to seizure whose value is 5 to 10 times higher according to the annealing temperature. The micrographs show that these modifications generate cracks through the crystals; these cracks are perpendicular to the surface and do not lead to scaling phenomenon. They act like lubricant traps and so delay the seizure. Annealing temperatures ranging from 100 to 700°C and treatment duration from 1 to 100 min are studied. The possibility of reducing temperature while reasonably increasing time is shown so the heat treatment does not affect the steel substrate and could be industrialised.
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