Limin Zhang

In the present study, Mo was added to Cu–15Ni–8Sn alloy as the fourth element to solve the limitation of service performance of the alloy by composition design. The phase composition, microstructure transformation and mechanical properties of Cu–15Ni–8Sn–xMo (x = 0.3, 0.9, 1.5 wt.%) alloy were systematically studied by simulation calculation and experimental characterization. The results show that the addition of Mo can improve the as-cast structure of Cu–15Ni–8Sn alloy and reduce segregation and Cu–Mo phase precipitates on the surface with the increase in Mo contents. During solution treatment, Mo can partially dissolve into the matrix, which may be the key to improving the properties of the alloy. Furthermore, the discontinuous precipitation of Sn can be effectively inhibited by adding the appropriate amount of Mo to Cu–15Ni–8Sn alloy, and the hardness of alloy does not decrease greatly after a long-time aging treatment. When Mo content is 0.9 wt.%, the alloy reaches the peak hardness of 384 HV at 4 h of aging. These results provide new ideas for composition optimization of Cu–15Ni–8Sn alloy.

The microstructure evolution of Cu-Sn-P alloy subjected to hot deformation was researched through electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) in the present study. The results indicated that after hot deformation, grains perpendicular to the force direction were elongated, and mostly became deformed grains, and then exhibited an obvious hardening effect. The Cu-Sn-P alloy could be strain hardened during hot deformation, but, with recrystallization, a softening effect occurred. Changes in dislocation density, textures, and grain sizes play different roles in flow stress behaviors of Cu-Sn-P alloy, and the dislocation density has a more evident effect at low temperature. However, with increase in temperature, recrystallization softening gradually dominates. Low-angle grain boundaries (LABs) account for the majority of hot deformed microstructures of Cu-Sn-P alloy. High dislocation densities in these zones make it easy to initiate the dislocation slipping systems. Deformation is realized through dislocation slipping and the slipping of edge dislocation pairs. The dislocation pile-up zones have high distortion energies, and, thus, elements of diffusion and recrystallization nucleation can occur easily. At different temperatures, the maximum polar density of textures gradually increases, and there are preferred orientations of grains. At 500 °C, stacking faults accumulate and promote the growth of twins. The twin growth direction is mainly determined by the migration of high-angle grain boundaries (HABs) and the clustering of high-stress zones.

More detailed and accurate modeling is very important for analyzing and optimizing the tribological performance of the piston-ring-cylinder liner system. However, due to the difficulty of modeling and solving, theoretical studies on the three-dimensional (3D) tribodynamics of piston rings are limited. The tribodynamic model which couples the dynamics, mixed lubrication, and blow-by of piston-ring pack assemblies has not been found yet. Therefore, in this study, a 3D tribodynamic model of the piston-ring pack is developed considering the influence of piston secondary motion and the interaction forces and moments between piston ring and cylinder liner as well as between piston ring and ring groove. In addition to the ring end gaps, the influence of ring dynamics is also contained in the blow-by model. Coupled with gas flows and piston rotation, ring motions in the ring groove are investigated. It is found that ring dynamics has significant effects on the tribological performance, the axial reversing movement of piston ring is the main cause of gas pressure oscillation, piston motion has an obvious influence on the ring dynamics, the interaction forces and moments between piston and rings increase the secondary motion amplitude of piston, especially near the fire top dead center.