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Selective laser melting (SLM) technology has the advantage of quickly producing complex-shaped parts. To achieve good mechanical properties, it's vital to minimize defects that can occur because of high residual porosity if incorrect processing techniques are used. One effective way to prevent defects is by using computer simulations of underlying processes before printing in the industry. This paper presents a reduced-order numerical model of SLM processing that accurately predicts material porosity by focusing on the key mechanisms that affect the melting and consolidation processes. The focus is on the formation of defects and the expected time that is required until the consolidation of a powder bed is completed. Then the elasticity of the SLM processed materials near defects is analyzed. The modeling results for powder consolidation are shown for comparison with experimental data on stainless steel 316L powder during SLM. This information can be further used for proper selection of SLM parameters such as the scanning speed and the power of the laser source. [ABSTRACT FROM AUTHOR]

Recent capillary flow experiments, conducted on a combined wetting/non-wetting assemble, consistently feature an anomalous flow over the non-wetting substrate: (i) apparent abrupt or gradual recession stages in the motion of the contact line, (ii) non-monotonic abrupt changes in the receding contact angle, and (iii) contact angle overshoot above the nominal equilibrium contact angle. We find that such behavior of a liquid metal alloy cannot be explained by the standard capillary flow models. However, a model that includes the ageing of the equilibrium contact angle predicts all the observed features qualitatively. We use the phase field formulation for capillary flows with a diffusive motion of the triple line to accommodate the novel diffusive boundary condition with the time-evolving quasi-equilibrium contact angle. We discover that the observed anomalies in capillary flow are qualitatively explained by two factors: (1) time evolution (ageing) of the quasi-equilibrium contact angle and (2) high viscosity of the partially molten braze. We also discover that for the given flow geometry, the transition from the initial to the final configuration may follow two distinct topological paths: one is characterized by a coalescence of liquid–solid contact domains, the other by a contact separation. The selection of the two paths in the configurational space is dependent on both contact ageing parameters and viscosity. [ABSTRACT FROM AUTHOR]

The problem of surface processing and microstructure refinement in stainless steels in laser surface processing in the presence of an external magnetic field has been studied experimentally and theoretically. The effect of both alternating and permanent magnetic fields is discussed. The experimental part includes microstructure assessment of a thin stainless plate annealed by a quasi-continuous laser in the presence of an electromagnetic acoustic transducer. Complementary analytical calculus and numerical simulations of complex transport phenomena in the melting zone are performed. Based on the received data, the effect of the electromagnetic field on the molten zone under laser melting conditions is evaluated and quantified. The obtained results are relevant to laser surface hardening and additive manufacturing. [ABSTRACT FROM AUTHOR]

The importance of the problem of hole-filling by a molten metal lies in the application of brazing for repairs in space, under microgravity conditions. The negligible effects of gravity and dominance of capillary forces can be approximated under terrestrial conditions, provided that the hole and the quantity of liquid are small, as quantified by the Bond number. In this paper, we report experimental results, modeling, and analysis of the hole-filling problem using the liquid aluminum brazing alloy on aluminum substrate. Depending on the hole size, the capillary driven flow may result in the hole being either filled or not filled. The equilibrium problem (energy minimization) has multiple solutions in some regions of the parameter space. Therefore, the experimental outcomes may depend on the availability of sufficiently strong perturbation, required to dislodge the system from a metastable equilibrium. We report good agreement between experimental results and theoretical/computational predictions. In general, a deeper and narrower hole favors the filled outcome. [ABSTRACT FROM AUTHOR]

A superhard boron-based ceramic coating was deposited on a cylindrical surface of a steel disk by high-energy short-pulse laser melting. During severe sliding friction, the coating can act as a solid lubricant with an ultralow coefficient of friction (COF). In combination with different counterface materials, the coating was subjected to sliding wear tests under boundary lubrication conditions. The obtained results show that resistance to severe adhesive wear and associated surface damage (galling) correlate with chemical inertness of tested materials with respect to boron carbide, which is the main component of the superhard coating. Chemically inert materials such as bronzes and babbitt alloys, while sliding against the boron-based coating, exhibit a transition to low friction behaviour at high normal loads and high sliding rates. In this case, the low COF was attributed to the formation of the B–O bonds. The bond appearance was confirmed by the X-ray photoelectron spectroscopy. On the other side, sliding of aluminium alloys against the boron-based superhard coatings leads to galling due to the reaction of B 4 C with aluminium at the interface and, associating with this, the extent of Al–B junction growth that occurs on further sliding, so this combination of materials is incompatible. • Ceramic coatings based on B 4 C and h-BN were deposited on steel disks. • Wear tests show good compatibility of the coatings with bronzes and babbitt alloys. • Appearance of B–O bonds in the coatings explains a transition to ultralow friction. • Combination of the coatings with aluminium alloys is incompatible. • The incompatibility is explained by chemical adhesion of components. [ABSTRACT FROM AUTHOR]