Friction reactions induced by selective hydrogenation of textured surface under lubricant conditions

The passivation of hydrogen atoms and the conformation of textured surfaces under oil-lubricated conditions are effective strategies to obtain amorphous carbon(a-C)films with extremely low friction.It is critical to understanding the influence mechanism of selective surface hydrogenation on the tribological behaviors of textured a-C film under oil-lubricated conditions.In particular,the interactions of hydrogen atoms and lubricants are confusing,which is enslaved to the in situ characterization technique.The reactive molecular dynamics(RMD)simulations were conducted to analyze the friction response of textured a-C films with selective hydrogenation surfaces under oil-lubricated conditions.The results indicate that the existence of hydrogen atoms on specific bump sites significantly decreases the friction coefficient(μ)of textured a-C film,which is highly dependent on the surface hydrogen content.The repulsion between hydrogen atoms and lubricant molecules prompts the formation of a dense lubricant film on the surface of the mating material.Interestingly,with the enhancement of the surface hydrogen content,the passivation of the friction interface and the repulsion between hydrogen atoms and lubricants play dominant roles in reducing the friction coefficient instead of hydrodynamic lubrication.

Structure,tribological properties,and the growth mechanism of in-situ generated TiC in titanium cermet

Titanium cermet combining metallic toughness with ceramic wear resistance has been proven to be a potential candidate for implanted joint material.In this work,titanium cermet was synthesized by means of the elevated temperature solid carburizing technology.The Ti_(13)Nb_(13)Zr alloy surface was found to be converted into TiC ceramic layer combined with a carbon strengthened diffusion zone underneath.The overall thickness of the carburized region grew to about 100 um after 120 min carburization at 1,500 K.In order to clarify the growth behaviors of TiC ceramic layer,a growth mechanism is proposed.At the beginning of carburizing process,carbonaceous gas decomposed from carburizer due to high temperature and then converted to free atomic carbons through reduction reaction.Then,in-situ generated TiC ceramic layer possessing certain thickness formed on the surface,meanwhile,the inner carbon diffusion zone also grew inwards due to physical diffusion of carbon,and finally forming a gradient carbon distribution.In addition,the tribological behaviors of the new materials were evaluated through reciprocating ball-on-plate sliding wear tests in bovine calf serum.Although there was an increase in friction coefficient,the wear rate decreased by 59.6%due to the formation of the wear-resistant TiC ceramic layer.The wear mechanisms evolved from severe abrasive wear for bare Ti_(13)Nb_(13)Zr alloy to mild adhesive wear for titanium cermet.