Mechanical, tribological, and electrochemical behavior of Cr1−xAlxN coatings deposited by r.f. reactive magnetron co-sputtering method

Chromium aluminum nitride (Cr_1−xAl_xN) coatings were deposited onto AISI H13 steel and silicon substrates by r.f. reactive magnetron co-sputtering in (Ar/N₂) gas mixture from chromium and aluminum targets. Properties of deposited Cr_1−xAl_xN coatings such as compositional, structural, morphological, electrochemical, mechanical and tribological, were investigated as functions of aluminum content. X-ray diffraction patterns of Cr_1−xAl_xN coatings with different atomic concentrations of aluminum (0.51 < x < 0.69) showed the presence and evolution of (1 1 1), (2 0 0), and (1 0 2) crystallographic orientations associated to the Cr_1−xAl_xN cubic and w-AlN phases, respectively. The rate of corrosion of the steel coated with Cr_1−xAl_xN varied with the applied power; however, always being clearly lower when compared to the uncoated substrate. The behavior of the protective effect of the Cr_1−xAl_xN coatings is based on the substitution of Cr for Al, when the power applied to the aluminum target increases. The mechanical properties were also sensitive to the power applied, leading to a maximum in hardness and a reduced elastic modulus of 30 and 303 GPa at 350 W and a monotonic decrease to 11 and 212 GPa at 450 W, respectively. Finally, the friction coefficient measured by pin-on disk revealed values between 0.45 and 0.70 in humid atmosphere.     

Can non-propagating hydrodynamic solitons be forced to move?

Development of technologies based on localized states depends on our ability to manipulate and control these nonlinear structures. In order to achieve this, the interactions between localized states and control tools should be well modelled and understood. We present a theoretical and experimental study for handling non-propagating hydrodynamic solitons in a vertically driven rectangular water basin, based on the inclination of the system. Experiments show that tilting the basin induces non-propagating solitons to drift towards an equilibrium position through a relaxation process. Our theoretical approach is derived from the parametrically driven damped nonlinear Schr?dinger equationwhich models the system. The basin tilting effect is modelled by promoting the parameters that characterize the system, e.g. dissipation, forcing and frequency detuning, as space dependent functions. A motion law for these hydrodynamic solitons can be deduced from these assumptions. The model equation, which includes a constant speed and a linear relaxation term, nicely reproduces the motion observed experimentally.     

Robust location of new housing developments using a choice model

We consider the issue of choosing a subset of locations to construct new housing developments maximizing the satisfaction of potential buyers, which has not been previously studied in the literature. The allocation of demands to the selected locations is modeled by a choice model, based on the distance to the location, real-estate prices and incomes. We study two robust counterparts of the optimal location problem, where uncertainty lies on demand volumes for the first one, and on customer preferences for the second one. In both cases, the parameters subject to uncertainty appear both in the objective function and constraints. The second robust model combines a scenario-based approach with nominal, price-centric and distance-centric scenarios on customers preferences, and an uncertainty budget approach that limits the number of customers that can deviate from the nominal scenario. We show that the subproblem of finding the worst-case deviation of parameters subject to uncertainty is tractable and leads to linear formulations of the robust problem. Computational experiments conducted on instances of the Paris region show that the average loss of value of the robust solution is reasonably low when compared to the optimal solution of deviated instances. We also derive insights for the new housing development issue.     

铸造铝青铜合金Cu-14Al-4Fe-Mn的摩擦磨损性能

用往复式摩擦磨损试验机考察了新型高强度、高耐磨性铸造铝青铜合金Cu-14Al-4Fe-Mn(代号HSWAB)的摩擦磨损性能,利用形貌扫描电子显微镜观察分析了合金磨损表面形貌,探讨了其磨损机理.结果表明,HSWAB合金在干摩擦和油润滑条件下的摩擦磨损性能及磨损机理存在明显差异.在干摩擦条件下,合金中脱落的硬质点及氧化物等磨粒导致较为严重的磨粒磨损,摩擦系数高、磨损率大,主要磨损机理为磨粒磨损、粘着磨损、氧化磨损及疲劳磨损.在油润滑条件下,摩擦系数和磨损率均显著降低,疲劳磨损和氧化磨损受到抑制,主要磨损机理为磨粒磨损和粘着磨损.Cu-14Al-4Fe-Mn合金在油润滑条件下的摩擦系数低达0.08,磨损率低达3.7×10-6g/m,是一种优良的耐磨材料.