Zhou Zhongrong

Effect of surface topography on formation of squeal under reciprocating sliding

Abstract Under reciprocating sliding there are at least four states available to distinguish whether squeal occurs or not and how squeal evolves if it is present: (1) no squeal is emitted in the whole reciprocating sliding as many as 3800 cycles or more; (2) squeal is not emitted when the friction coefficient is smaller in the beginning stage of reciprocating sliding; (3) squeal is emitted when the friction coefficient arrives at a larger (critical) value; (4) sometimes squeal disappears after more cycles. These four states are found to be to some extent in correlation with the topography characteristics of the wear scars. Acoustic and dynamic measuring techniques were applied to ascertain the area where squeal was present on a wear scar. By means of SEM observations of wear scars, a comparative investigation into the characteristics of scar surfaces was carried out under both silent and squealing conditions. The result shows that for flat–flat contact the area associated with squeal on a wear scar is characterized by uneven serious pit-like detachment of the specimen material. For flat–ball contact it is found that the area related to squeal is characterized by adhesively joined asperities. Moreover, the effect of a negative friction–velocity slope on squeal formation is examined. The result seems to demonstrate that not all negative friction–velocity slopes can cause squeal. A possible alternative mechanism of squeal formation is proposed and dependence of squeal generation on the friction coefficient are also discussed based on the detachment of the material or formation of adhesively joined asperities.

The fretting wear-resistant properties of steel with ion-sulphuration+shop-peening and shot-peening+ion-sulphuration duplex treatments

The fretting wear-resistant properties of ion-sulphuration+shot-peening and shot-peening+ion-sulphuration duplex-treated coatings on 1045 steel substrate were investigated. The results show that the fretting wear-resistance of shot-peening+ion-sulphuration coating was better than that of the ion-sulphuration+shot-peening coating. The fretting wear process of the duplex-treated coatings in the gross slip regime could be described as the sulphuration coatings playing an important lubricating role in the incubation period. Then a series of changes took place continuously and alternatively on the contact surfaces, including adhesion, material transfer, oxidation, delamination of the oxide layer and degradation. In the last stage, the trapping, pulverization and elimination of debris restrained the adhesion between the contact surfaces and led to a decrease in the friction coefficient.

The deformation behavior of TiNi shape memory alloy under axial dynamic compression

The deformation behavior of Ti-50.9 at % Ni shape memory alloy under axial compression dynamic loads was investigated by an MTS 858 Mini Bionix test machine. The alloy were aged at 500°C for an hour before being machined into specimens. The compression experiments were conducted at 20°C and the variety of dynamic loads were controlled by the strain rate, which was 3 mm/min, 15 mm/min, 30mm/min and 50 mm/min, respectively. The experimental results indicate that in the case of 3 mm/min, stress-induced martensitic transformation occurs at about 350 MPa when loading and reverse transformation at about 200 MPa when unloading, during which the aged Ti-50.9 at % Ni alloy shows the recoverable nonlinear pseudoelastic strain of 4.3% with the residual strain of 1.2% reserved. With the strain rate increasing, the area encloses by loading-curve and unloading-curve, i.e stress (strain) hysteresis becomes smaller and smaller and the residual strain also decreases, while critical stress for inducing martensitic transformation rises. At a higher strain rate the alloy exhibits linear-like pseudoelasticity, which is up to 4.5%.

Effect of Stress State of Different Tin Films on Their Tribological Behavior

Titanium nitride films were deposited by the methods of ion beam enhanced deposition (IBED), plasma chemical vapor deposition (PCVD) and ion plating (IP). X-ray diffraction analysis was employed to determine the internal stress state of TiN film and 52100 steel substrate at both sides of the interface. The effect of stress state on their bonding strength and tribological behavior was analyzed systematically, their wear and failure mechanisms were discussed in detail as well.