Dong Guangneng

Effects of phosphorus-free antioxidants on oxidation stability and high-temperature tribological properties of lubricants

Oxidation stability plays an important role on the engine oil service performance. In this paper, the phosphorus-free antioxidants of diphenylamine, hindered phenol and dibutyldithiocarbamate, combined with zinc dialkyldithiophosphate were added as antioxidants in the base oil and the fully formulated 5W-30 oil, and the oxidation stabilities were evaluated by pressurized differential scanning calorimetry and Romaszewski oil bench oxidation standard tests. Meanwhile, the tribological properties of the fresh and aged oils were evaluated by a SRV tribo-meter. The results indicated that (i) an optimal ternary complex antioxidant of dibutyldithiocarbamate: diphenylamine: hindered phenol (ratio of 2:1:2) displayed good antioxidation property, and (ii) the fully formulated 5W-30 oil containing optimized ratio phosphorus-free antioxidants had better tribological properties than the commercial SN 5W-30 oil.

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%.