Instituto Tecnológico de Saltillo

Abstract: Pulsed plasma nitriding and post-oxidizing process have been applied to hot work H13 tool steel to enhance the tribological properties (friction coefficient and wear rate). Nitriding was accomplished under specific conditions to generate a free white layer surface in order to avoid an abrasive wear mechanism. Post-oxidizing treatment was carried out in the same reactor after finishing the nitriding treatment; processing time was varied for 30 and 60 min. The morphology, phase’s composition and wear performance of duplex-treated samples were evaluated by scanning electron microscopy, x-ray diffraction analysis and pin-on-ball wear technique. The results show that the duplex treatment produces a bilayer arrangement constituted by an 80 μm diffusion zone with expanded martensite as the main phase underneath a 2–4 μm hematite–magnetite-oxidized layer. The duplex treatment modified the main wear mechanism of the nitrided sample from abrasive to plastic yielding. The changes in wear mechanisms resulted in a noticeable decrease, about 40%, in friction coefficient for oxidized samples in comparison with the nitrided-only sample. It was also established that the lowest friction coefficient values can be obtained when hematite is the main phase in the oxidized layer.

Abstract: The aim of this work is to achieve a meshfree implementation for the numerical prediction of 3D flows during mould filling processes in metal casting using a generalized finite difference method. The free surface incompressible flow problem is numerically solved using a semi-implicit Chorin–Uzawa’s projection scheme where the normal vectors needed for the free surface computations are computed with a simple and efficient idea. Further, the boundary conditions incorporation involved in this industrial problem is done in a simple and direct manner. The main characteristics in this meshfree formulation together with details of its computational implementation are given. The numerical results of a benchmark example using this formulation are reported and compared with published numerical and experimental results, and finally, the numerical solution of some three-dimensional test problems is reported which show that this formulation is promising for predicting three-dimensional complex free surface flows in mould filling processes in casting.

Abstract: A new technique to prepare porous materials has been developed for recycling of used glasses. Porous materials were produced from used glass powders by hydrothermal reaction of glass powders with water at low temperatures followed by calcination at high temperatures for expansion. The new technique does not require additional vesicants such as calcium carbonate, silicon carbide, and organic polymers that have been used in the ordinary method. In this process, the water incorporated into the glass structure by hydrothermal treatment acts as a vesicant. When the hydrothermally treated glass was heated at high temperatures around 700 °C, water was released as vapor from the softened glass to form pores. The obtained porous materials had different pore structures that were determined by the sizes of raw glass particles. Crystallization occurred during the calcination of the hydrothermally treated glass powder.