Dependence of the lattice parameter of {\gamma '} iron nitride,Fe4N1−x,on nitrogen content; Accuracy of the nitrogen absorption datairon nitride,Fe4N1−x,on nitrogen content; Accuracy of the nitrogen absorption data

Pure iron foils were converted into { \(\gamma ' - Fe_4 N_{1 - x} \) } foils of various compositions by means of nitriding in selected NH₃/H₂ gas mixtures at 803 and 843 K. The lattice parameter and the linear thermal expansion coefficient of { \(\gamma ' - Fe_4 N_{1 - x} \) } nitride and the surrounding gas atmosphere.     

The role of the substrate on the mechanical and thermal stability of Pd thin films during hydrogen (de)sorption

In this work, we studied the mechanical and thermal stability of ~100 nm Pd thin films magnetron sputter deposited on a bare oxidized Si(100) wafer, a sputtered Titanium (Ti) intermediate layer, and a spin-coated Polyimide (PI) intermediate layer. The dependence of the film stability on the film morphology and the film-substrate interaction was investigated. It was shown that a columnar morphology with elongated voids at part of the grain boundaries is resistant to embrittlement induced by the hydride formation (α?β phase transitions). For compact film morphology, depending on the rigidity of the intermediate layer and the adherence to the substrate, complete transformation (Pd-PI-SiO₂/Si) or partly suppression (Pd-Ti-SiO₂/Si) of the α to β-phase was observed. In the case of Pd without intermediate layer (Pd-SiO₂/Si), buckling delamination occurred. The damage and deformation mechanisms could be understood by the analysis of the stresses and dislocation (defects) behavior near grain boundaries and the film-substrate interface. From diffraction line-broadening combined with microscopy analysis, we showed that in Pd thin films, stresses relax at critical stress values via different relaxation pathways depending on film-microstructure and film-substrate interaction. On the basis of the in-situ hydriding experiments, it was concluded that a Pd film on a flexible PI intermediate layer exhibits free-standing film-like behavior besides being strongly clamped on a stiff SiO₂/Si substrate.     

Structural inhomogeneities of AlSi alloys rapidly quenched from the melt

Hypo- and hyper-eutectic AlSi alloys were rapidly quenched from the melt using the melt-spinning technique with two spinning velocities. Structural differences between the wheel (chill) and upper sides of the melt-spun ribbons were investigated by optical and scanning electron microscopy and X-ray diffraction methods (texture- and size-strain analyses). The Al-rich phase of the hypo-eutectic alloys was textured. The textures observed from both sides of the ribbons were different; in neither case was it of fibre type. For the larger spinning velocity applied, the structural imperfection of the wheel side was larger than that of the upper side for both the Al-rich and the Si-rich phases.     

Electrochemical behavior and performances of Ni-BaZr0·1Ce0·7Y0.1Yb0.1O3−δ cermet anodes for protonic ceramic fuel cell

High performance Ni-BCZYYb cermet anode were prepared at 1300 °C using electrolyte powders prepared by combustion and commercial NiO. The cermets are porous (39 vol% of porosity), show a high electronic conductivity (1097 S cm^?1) and sufficient mechanical properties. The electrochemical behavior of the Ni-BCZYYb/BZCYYb-ZnO/Ni-BCZYYb symmetrical cell elaborated by co-pressing and co-sintering was investigated using electrochemical impedance spectroscopy. The impedance spectroscopy study show that the electrode reaction involves three steps. The total polarization Area Specific Resistance decreases by about one order of magnitude when increasing the temperature from 450 to 600 °C or the H₂ concentration from 5 to 100 vol% to reach 0.049 Ω cm² at 600 °C under pure hydrogen.     

Relation between microstructure and adhesion of hot dip galvanized zinc coatings on dual phase steel

The microstructure of hot dip galvanized zinc coatings on dual phase steel was investigated by electron microscopy and the coating adhesion characterized by tensile testing. The zinc coating consists of a zinc layer and columnar ζ-FeZn₁₃ particles on top of a thin inhibition layer adjacent to the steel substrate. The inhibition layer is a thin compact and continuous layer that consists of η-Fe₂Al_5–xZn_x fine and coarse particles. The coarse faceted particles are on top and fine faceted particles are at the bottom. The steel surface is covered with small fraction manganese oxides, which may impair adhesion of the zinc coating. The adhesion at various interfaces that exist in zinc-coated steel was quantitatively estimated using a so-called “macroscopic atom” model. In addition, the adhesion at the interfaces in zinc-coated steel was qualitatively assessed by examining the fracture and delamination behavior upon tensile testing. In accordance with this model, fracture along zinc grain boundaries preceded fracture along the zinc layer/inhibition layer and ζ-FeZn₁₃ particle/inhibition layer interfaces.     

On the use of conformal mapping for the computation of hydrodynamic forces acting on bodies of arbitrary shape in viscous flow. Part 2: multi-body configuration

Two-dimensional viscous flows around obstacles are considered in an unbounded liquid. The basic idea developed in Part 1 is further extended from a single body to multi-body configurations. This idea follows from the formulation by Quartapelle and Napolitano (AIAA J. 21:991–913, 1983) who proposed computation of the force and moment in incompressible viscous flow without explicitly calculating the pressure. The principle is the projection of Navier–Stokes equations on a set of functions. Surprisingly, these functions have a precise meaning in potential theory. They are the solutions which lead to the added masses and added moment of inertia for the potential flow around the studied arrangement of obstacles. By revisiting this problem, a general identity of the full coupled matrix of added masses and added moment of inertia is formulated. To this end conformal mappings for multi-body configurations are used. Robustness of the proposed algorithms is tested and illustrated. The obtained potential solution is merely a mathematical solution and it does not allow to describe the actual potential flow since the circulation is not accounted for. However, its interest is crucial for implementing the projection technique developed by Quartapelle and Napolitano. The interest of such a method is two-fold. Firstly, it provides a way of computing the force without explicitly calculating the pressure. Consequently and secondly, it offers an alternate way to validate the computation of the loads. In effect, these loads are always available from a direct integration of the Cauchy stress tensor (pressure plus friction). It is worth mentioning that the present technique allows an a posteriori computation of the pressure.     

On the use of conformal mapping for the computation of hydrodynamic forces acting on bodies of arbitrary shape in viscous flow. Part 1: simply connected body

Some aspects of the force and moment computations in incompressible and viscous flows are revisited. The basic idea was developed in Quartapelle and Napolitano (AIAA J. 21:991–913, 1983). They formulated the way to compute the force and moment without explicitly calculating the pressure. The principle is to project Navier–Stokes equations on a set of functions. Surprisingly these functions have a meaning in potential theory. They are precisely the solutions which give the added masses and added moment of inertia for potential flow. By revisiting this problem for two-dimensional flows in unbounded liquid, a general identity giving the added masses and added moment of inertia is formulated. To this end a conformal-mapping technique is used to transform the fluid domain. Once the potential solution has been obtained, the projection method by Quartapelle and Napolitano is implemented. In addition an a posteriori computation of the pressure is described. Applications illustrate the present study.