ANNEALING IMPROVEMENT OF TRIBOLOGICAL PROPERTIES OF MANGANESE PHOSPHATE COATINGS

The authors have studied the tribological behaviour of hureaulite coat ing previously modified by annealing. Hureaulite is a manganese phosph ate 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 resp onse 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 comp ounds forming) lead to a great improvement in the resistance to seizur e whose value is 5 to 10 times higher according to the annealing tempe rature. The micrographs show that these modifications generate cracks through the crystals; these cracks are perpendicular to the surface an d do not lead to scaling phenomenon. They act like lubricant traps and so delay the seizure. Annealing temperatures ranging from 100 to 700 degrees C and treatment duration from 1 to 100 min are studied. The po ssibility of reducing temperature while reasonably increasing time is shown so the heat treatment does not affect the steel substrate and co uld be industrialised. (C) 1998 Elsevier Science S.A. All rights reser ved.