Page 141 - 《摩擦学学报》2021年第6期

926 摩 擦 学 学 报 第 41 卷

of the PAI coating, and their influence trend was consistent with the changes in micro-hardness and elastic modulus.
The enhancement mechanisms of Ag 2 S nanoparticles to mechanical properties was that, firstly, the presence of Ag 2 S
nanoparticles produces a stress concentration effect in the process of material deformation, and the surrounding resin
matrix was yielded, which can absorb a large amount of deformation and effectively strengthen the strength and
toughness of the coating. Secondly, the presence of rigid Ag 2 S nanoparticles also inhibited the cracks propagation during
coating deformation, and promoted the passivation and termination of cracks. The reason for crack passivation or
termination was that the inorganic Ag 2 S nanoparticles would not cause large elongation deformation. Under the action of
large tensile stress, the part interface between the Ag 2 S nanoparticles and the matrix debonded to form a gap, so that the
crack was passivated and ceased to develop into a destructive crack. In addition, the interface debonding caused by yield
and stress concentration consumed more energy, thereby enhancing the mechanical toughness and resistance to plastic
deformation of the coating. When the Ag 2 S nanoparticle weight fraction reached 5.0%, this stress concentration effect
and yield deformation effect reached the maximum, therefore, it showed a more significant enhancement to the
mechanical properties.
Under dry friction conditions, the friction and wear behaviors of the in-situ synthesized Ag 2 S nanoparticles reinforced
composite coatings were further studied. The initial friction coefficient of pure PAI coating was relatively large (about
0.245) and quite unstable as the friction coefficient curve fluctuated greatly. After 700 s, the friction coefficient began to
rise significantly and wear failure began. At the end of the friction test, the friction coefficient increased to 0.375.
Compared with the pure resin system, the in-situ introduction of Ag 2 S nanoparticles significantly reduced the friction
coefficient of the nanocomposite coating, and the dynamic friction coefficient curve became relatively stable, and there
was no sudden failure during the friction test. As the content of Ag 2 S nanoparticles gradually raised, the average friction
coefficient of the nanocomposite coating increased first and then decreased. For the 5.0% Ag 2 S nanoparticle reinforced
nanocomposite coating, the average friction coefficient was the lowest (0.210) and the friction coefficient curve was the
−4 3
best stable. In addition, the pure PAI coating exhibited the highest wear rate, i.e. 1.80×10 mm /(N·m). By introducing
in-situ synthesized Ag 2 S nanoparticles with different contents, the wear rate of the nanocomposite coating was
significantly reduced. As the content of Ag 2 S nanoparticles increased, the wear rate of the nanocomposite coating
showed a similar trend to the friction coefficient, and the nanocomposite coating reinforced with 5.0% Ag 2 S
−5 3
nanoparticles also displayed the lowest wear rate of 9.24×10 mm /(N·m), which reduced by 47.78% than that of the
pure PAI coating. These tribological performance test results showed that Ag 2 S nanoparticles synthesized in-situ in the
coating by this method can significantly improve the lubricating performance and wear resistance of the polymer
coating, and there was an optimal addition amount to offer the best reinforcement effect.
The micro-scale morphologies of the worn surface and the wear scars of dual ball were observed and analyzed to
explore the enhancement effects of in-situ synthesized Ag 2 S nanoparticles to the tribological properties of the PAI
coating. The friction contact area on the pure PAI coating surface was severely worn with a large number of large cracks
and worn pits. The counterpart ball was worn more severely as the larger wear scar area, and no transfer film was formed
on the counterpart surface. The Ag 2 S nanoparticles introduced in-situ significantly inhibited the generation and
propagation of defects and cracks on the worn surface, greatly slowed down wear damage of the nanocomposite coating.
The worn surface became flat and compact, and the worn spot area of the corresponding dual ball was also reduced. It is
worth noting that the nanocomposite coating material transferred at the friction interface, and a friction transfer film was
formed on the corresponding dual ball. When less Ag 2 S nanoparticles were added (less than 5.0%), the increase of their
content can be more conducive to enhancing the wear resistance of the coating. The wear degree of corresponding worn
surfaces decreased as the cracks and defects gradually reduced. When their content exceeded 5.0% and further increased,
the worn surface cracks and defects of the coating intensified, and more obvious furrows appeared. This was caused by
the agglomeration of the excessive Ag 2 S nanoparticles. When the Ag 2 S nanoparticle weight fraction was 5.0%, the
nanocomposite coating exhibited the most excellent wear resistance, its worn surface was polished and crack defects
were significantly reduced, and the corresponding worn spot area on the dual ball was also smaller, which was attributed
to the improvement of mechanical strength of the coating and the formation of the friction transfer film on counterpart
ball.
Key words: nanoparticles; in-situ synthesis; size control; mechanical properties; tribological properties; transfer film

纳米粒子较大的比表面积使其具有较高的表面 自由能，在制备过程中倾向于形成较大尺寸的颗粒且