Papers by Keyword: Build-Up

Abstract: “Art is everywhere” to quote Ben, a renowned French contemporary artist. However, there are some areas in which art is more prevalent. Thermal spray is one of them, as this presentation seeks to demonstrate. For this, each of the arts (according to their official classification) is shown to correspond to a specific key point of the thermal spray process for coating: e.g., coating build-up, additive manufacturing, deposition onto brittle and/or temperature sensitive materials (glass, wood, fabrics, polymers), powder optimization, and adhesion. Both modeling and experimental aspects are discussed, focusing on the study of particle-to-particle or particle-to-substrate interfaces, shock phenomena and advanced investigation techniques such as X-ray microtomography or high-speed instrumentation. Plasma spray and cold spray provide the relevant examples that this contribution elaborates. They relate to different industrial sectors such as aircraft-aerospace, luxury, biomedical and the automotive industry. Beyond anecdotal evidence, the discussion aims to show that an artistic approach to thermal spray does help to understand better this powerful coating process.

Abstract: When SSM material is subjected to a sudden transient the rate of buildup (aging) is negligible compared to the rate of breakdown (shear rejuvenation). While this is generally true, due to prolonged processing or the geometry the local shear rate in some regions may become equal or lower than the critical value, where aging becomes as important as shear rejuvenation. In this work we simulate in detail shear rejuvenation and aging in semisolid slurries. Using a standard thixotropic model used widely for modeling SSM suspensions but a novel computational method we reveal and confirm numerically for the first time shear banding. The phenomenon is found to be time dependent where the material first yields fully and then, after a certain time the yielded front retreats to form two distinct bands -one yielded and one unyielded. This phenomenon must be accounted for in the evaluation of the material constants since the time scale of the process is similar to the time scale of the phenomenon.

Abstract: Due to the distinct rheology of semisolid slurries the process has well established advantages over competing near-net-shape manufacturing technologies. Despite the obvious advantages of the process its adoption by the casting industry, however, has been slow. This is primarily due to lack of confidence of how these slurries flow in die cavities. The added cost associated with the specially prepared slurry has also affected the process commercial success. Nevertheless despite these problems attention to the semi-solid metal process has indeed increased over the years. The main focus of this review is the modeling of semisolid slurries. The objective here is to present an overview of relevant aspects of modeling by focusing on the physics of the slurry and by stressing consistent mathematical and analysis methods to determine the material constants.

Abstract: In metal forming processes in the tool-workpiece contact area occur high pressure, surface expansion and elevated temperature. It makes ideal circumstances for braking of the lubricant film that causes a direct contact between metallic surfaces. Such a contact usually leads to buildups creation on the tool surface. These phenomena mainly result product surface damage. Damages can also refer to tool surface since the hardness of buildups can be comparable with the tool hardness. The cause of this investigation was finding the answer of the question what was the reason of extreme hardness of buildups created during bulk metal forming processes of 1H18N9T austenitic stainless steel. The studies were conducted using transmission electron microscopy (TEM). On the basis of analysis structural and electron diffraction pattern it was suggested that simultaneously to very well known strengthening mechanism like grain refinement, the additional mechanism can not be excluded. Based mostly on the electron diffraction pattern (appearance of forbidden reflexes for FCC) it is suggested that this additional mechanism could be the marthensitic transformation caused by very high plastic deformation.

Abstract: The use of electron beam technology for freeforming 321 SS was investigated using 347 SS solid wire and BNi-2 brazing paste as filler materials. The electron beam freeforming (EBFF) studies involved examining the effect of processing parameters on the characteristics of the line build-ups. Specifically, the effective growth rate and the dimensional features (height-to-width ratio) of the build-ups were found to be dependent on the beam energy and the filler material conditions (e.g. wire feed rate and the number of re-melting passes). The EBFF work indicated that build-ups with either filler material could be deposited on 321 SS using an optimized processing window that resulted in properties comparable to technical data available for 347 SS and BNi-2.