Proceedings of SerbiaTrib '13

Figure 4.Wearresistance of Ni coatings without and withnanoparticles without and with heat treatment3.3 Analysis of the experimental resultsThe presence of nanodiamond particles affectsthe value and the character of the abrasive wear.This influence becomes more complicated alongwith the heat treatment of the coating.For size of nanoparticles 4 nm and 100 nmcoatings with heat treatment show higher wear, andfor size 200 and 250 nm the opposite effect isobserved – wear is lower than that of the casewithout heat treatment.The dependence of wear on nanodiamondparticles size is of nonlinear character, and thevarious coatings show different duration of therunning-in process.The boundary number of cycles N*, where thewhole coating is worn, is always bigger forcoatings without heat treatment.The highest wearresistance show Ni coatingswith nanodiamond particles of the size δ = 100 nmwithout heat treatment.4. STARTING CONTACT FRICTION4.1 TheoryFrom the point of view of process history, or intime cross-section of the process, tribosystemundergo three friction stages: starting, kinetic andpathological friction. The starting friction, knownas static friction in the classical mechanics, is doneunder conditions of preliminary microdisplacementin the contact zone and the tribosystem performsthe transition between static state (at rest) andmovement. Kinetic is the friction when the body ismoving upon the counterbody.The kinetic friction matches the stationary andthe pathological regimes of contact joint operation.The pathological friction is characterized byabrupt increase of friction with wear and seizure incontact.Figure 5. Variation of friction force and frictioncoefficient with displacementThe difference between starting friction force Т оand sliding friction force ТT To T(1)gives the jump in the friction force during systemtransition from state at rest and state of movement,and corresponds to the jump in the frictioncoefficient, i.e. o (2)The work of the starting friction force is givenby:A T T S PS (3)s o o o o oAnd the work of the kinetic friction force is:A T TS PSpLet present the ratio AsTo ApToPSo PS s .100 .100A T PSsooo(4)Then: s 100,%(5)oThe parameter s is called relative change ofthe starting friction; it is the ratio between the jumpof friction and the starting friction coefficient.Similarly, for the relative change of the kineticfriction p is obtained the expression: AsTo ApToPSo PS p .100 .100 .100A TPSorp p 100,%(6)4.2 Procedure and experimental resultsThe parameters of starting friction have beenstudied using a test rig with functional scheme asshown in Figure 5.34 13 th International Conference on Tribology – Serbiatrib’13