Zhihai Wang

Tribological Behavior of NiAl–1.5 wt% Graphene Composite Under Different Velocities

The progress in aerospace field requires a new NiAl matrix composite that can stand against wear and decrease the energy dissipation through decreasing friction. In this study, the tribological behavior of NiAl–1.5 wt% graphene composite is investigated at room temperature under a constant load of 12 N and different sliding velocities. The results show that the friction coefficient and wear rate increase with increasing sliding velocity from 0.2 to 0.4 m/s due to the adhesion between the sliding bodies and tearing of the graphene layer. The friction coefficient and wear rate tend to decrease at a sliding velocity of 0.6 m/s as a result of severe plastic deformation and grain refinement of the worn surface. However, at 0.8 m/s the friction coefficient reaches a minimum value and the wear rate increases and changes the wear mechanism to fatigue wear. It can be concluded that various wear mechanisms lead to different tribological performance of NiAl–1.5 wt% graphene composite.

Tribological behavior of a TiAl matrix composite containing 10 wt% Ag investigated at four wear stages

The useful longevity of mechanical components, such as gears and sliding bearings, were related with their tribological behaviors. The tribological behavior of a TiAl matrix composite containing 10 wt% Ag (TiAl–10 wt% Ag) was investigated at the four different wear stages. Wear stages, which were identified by the obtained friction coefficient and wear rate, were divided into the initial wear stage (INITIAL), fast wear stage (FAST), stable wear stage (STABLE) and severe wear stage (SEVERE). The results showed that tribological behavior at INITIAL was improved for work hardening. The friction coefficient and wear rate at FAST were small for the formation of mixed layers containing a solid lubricant Ag. Excellent tribological behavior at STABLE was attributed to the existence of lubricant films containing massive amounts of solid lubricant Ag. Poor tribological behavior of TiAl–10 wt% Ag at SEVERE was obtained for the lubricant film destroyed by the propagation of fatigue cracks. It was found that TiAl–10 wt% Ag, because of the excellent tribological behavior at STABLE, could be chosen as a promising structural material for mechanical components.

Effect of multiwalled carbon nanotubes on the lubricating properties of TiAl–Ag composites based on the changes in applied loads and testing temperatures

The rapid development of self-lubricating materials has been driven by the urgent demands of aerospace and automobile industries. In this paper, the effect of multiwalled carbon nanotubes (MWCNTs) on the lubricating properties of TiAl–Ag self-lubricating composites is studied based on the changes in applied loads and testing temperatures. The results show that the TiAl substrate composite containing 4.0 wt% Ag and 1.7 wt% MWCNTs (TAC) obtains a small mean friction coefficient of 0.21 and a low mean wear rate of 2.14 × 10−4 mm3 N−1 m−1 at 13 N–450 °C. It could be concluded that the lubricating film formed at 13 N–450 °C contains massive Ag and MWCNTs with 50–200 GPa in tensile strength, leading to the improvement of the tensile strength of the lubricating film. The improvement of the tensile strength of the lubricating film is beneficial for acquiring the excellent friction and wear behavior of TAC at 13 N–450 °C. Because of its excellent tribological performance, TAC can be chosen as the promising structural material for mechanical components.

Effects of frictional heat on the tribological properties of Ni3Al matrix self-lubricating composite containing graphene nanoplatelets under different loads

In order to analyze the effects of frictional heat on the tribological performance of Ni3Al matrix self-lubricating composite containing 6.2 vol.% graphene nanoplatelets (NB), the dry sliding friction tests of Ni3Al-based alloy and NB against GCr15 steel ball are undertaken under different loads from 3 to 18 N. The effects of different amount of frictional heat on the friction and wear mechanism of NB are also studied. The results show that tribological performance of NB is better than that of Ni3Al-based alloy under same working conditions. The addition of graphene nanoplatelets promotes the formation of stable glaze layer on worn surface. In addition, graphene nanoplatelets enhance the thermal conductivity of NB, which makes the surface temperature of wear scar of NB in a proper range (about 413 ℃) at 13 N and avoids the serious friction and wear caused by the accumulation of frictional heat. At 13 N, NB shows the lower friction coefficient (0.32) and wear rate (3.6 × 10−5 mm3·N−1·m−1). It is attributed to the appropriate local temperature (about 413 ℃) of worn surface, resulting in the formation of stable glaze layer with good friction reducing and wear resistance on worn surface. This study was meaningful for optimizing applied loads to realize the appropriate frictional heat and good tribological behavior of NB.