Qiufeng Wang

Oil-Lubricated Fretting Behaviors of 304 Stainless Steels under Different Fretting Strokes and Normal Loads

ABSTRACT The influence of oil lubrication on the fretting wear behaviors of 304 stainless steel flat specimens under different fretting strokes and normal loads has been investigated. The results proved that fretting regimes and fretting wear behaviors of 304 stainless steels were closely related to the fretting conditions. In general, the increase in normal load could increase wear damage during sliding wear. However, according to the results, a significant reduction in wear volume and increase in friction coefficient was observed when the normal load was increased to critical values of 40 and 50 N at a fretting stroke of 50 μm due to the transformation of the fretting regime from a gross slip regime to partial slip regime. Only when the fretting stroke further increased to a higher value of 70 μm at 50 N, fretting could enter the gross slip regime. There was low wear volume and a high friction coefficient when fretting was in the partial slip regime, because oil penetration was poor. The wear mechanisms were fatigue damage and plastic deformation. There was high wear volume and low friction coefficient when fretting was in the gross slip regime, because the oil could penetrate into the contact surfaces. Unlike the wear mechanisms in the partial slip regime, fretting damage of 304 stainless steels was mainly caused by abrasive wear in the gross slip regime.

Fretting Wear Behavior of UHMWPE—Influence of Load and Stroke

ABSTRACT In this study, the tribological behavior of ultra-high-molecular-weight polyethylene (UHMWPE) against a GCr 15 steel ball during fretting wear conditions was investigated using an oscillating reciprocating tribometer. The aim of this study was to characterize the critical value of normal load and stroke corresponding to this transition in UHMWPE worn surface at room temperature. Results showed that there existed a critical value of load or stroke at fixed condition. The friction coefficient and wear volume loss of UHMWPE at or near the critical values of load and stroke exhibited extreme changes. Based on observation of the worn surface by scanning electron microscopy (SEM) and 3D surface profiler measurements, it can be found that damage to the worn surface can be linked to the contact load and stroke. In addition, results showed that during the process of fretting wear under different load or stroke conditions, the gross slip regime dominated throughout the whole test period.

Investigation of Transfer Behaviors of Embedded Polytetrafluoroethylene in Different Metal Substrates

ABSTRACT Transfer behaviors of molded polytetrafluoroethylene (PTFE) blocks embedded in metal substrates were studied using a DFPM reciprocating tribometer under designed conditions. The substrate properties markedly affected the embedded PTFE transfer behaviors. For instance, the surface friction coefficient when embedded in AISI-1045 steel had evident fluctuations even after 1000 cycles although the friction coefficient decreased with the increase of the sliding cycles. On the other hand, the friction coefficient when the PTFE was embedded in 2024Al was remarkably reduced during the first 200 cycles, reaching a low and stable state. The loads played different roles in the transfer process; a higher load was advantageous for the steel-PTFE embedded composites, but it resulted in the opposite result for the Al-PTFE embedded composites. The motion direction of the GCr15 tribometer steel ball had no remarkable effect on the transfer behaviors. The worn surface of the substrates and the steel ball were observed and analyzed using scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The results indicate that the efficiency of second transfer film formation on the 2024Al substrate was better than for the AISI-1045 steel. The adhesion properties of Al enhanced the mechanical transfer of PTFE during the friction process.

Fretting Wear Behavior of UHMWPE Under Different Temperature Conditions

ABSTRACT The fretting wear behavior of ultra-high molecular weight polyethylene (UHMWPE) against a GCr15 steel ball was investigated using an Optimal SRV-IV oscillating reciprocating friction and wear tester (Optimal Corp., Germany). The influence of temperature, stroke size and frequency was studied in detail under a normal load of 10 N. The results showed that the friction coefficients initially decreased and then increased afterward with the increasing of temperature, having the lowest value at 0°C. The wear loss of UHMWPE at a stroke of 100 µm showed a similar tendency as the friction coefficients, but monotonously increased with increasing of temperature for a stroke of 200 µm. According to an analysis of the worn surface, it was concluded that abrasive wear accompanied with local plastic deformation dominated the wear mechanism in the process of the fretting test at −30°C. The plastic deformation was slightly less at 0°C than that at −30°C. With the increasing of temperature, the hardness of UHMWPE decreased significantly, plastic deformation and adhesive wear became more severe. In addition, a lubricating transfer film was formed on the steel ball.