Results 1 - 10 of 2764
Results 1 - 10 of 2764. Search took: 0.027 seconds
|Sort by: date | relevance|
[en] Additive Manufacturing (AM), the layer-by layer build-up of parts, has lately become an option for serial production. Today, several metallic materials including the important engineering materials steel, aluminium and titanium may be processed to full dense parts with outstanding properties. In this context, the present overview article describes the complex relationship between AM processes, microstructure and resulting properties for metals. It explains the fundamentals of Laser Beam Melting, Electron Beam Melting and Laser Metal Deposition, and introduces the commercially available materials for the different processes. Thereafter, typical microstructures for additively manufactured steel, aluminium and titanium are presented. Special attention is paid to AM specific grain structures, resulting from the complex thermal cycle and high cooling rates. The properties evolving as a consequence of the microstructure are elaborated under static and dynamic loading. According to these properties, typical applications are presented for the materials and methods for conclusion.
[en] Electron beam melting (EBM) is one of the powder bed fusion technologies, which utilizes a high-energy electron beam, as a moving heat source, in order to melt (by rapid self-cooling) metal powder and produce parts in a layer-building fashion. Anyway, many technical aspects concerning the quality of EBM-produced components are still industrial open items and studies need to be carried out. In accordance with the industrial needs, in this work researchers have studied the influence of two process parameters, i.e., samples orientation and height in the build chamber. The experiments have consisted in rectangular parallelepiped (50 × 10 × 10 mm) samples Ti6Al4V produced by EBM following a two-factor DOE. A tomographic investigation of all the samples produced by EBM has been carried out in order to get a complete set of data on porosity defects that have been analyzed showing the influence of process parameters on the porosity generation and pointing out typical features of defect distributions. The results obtained from this work have given precious information to designers and EBM technologists in order to: optimize the components’ design and the building setup obtaining a manufacturing process with the minimal level of porosity defects (best growth orientation).provide information for mechanical post-processing (metal removal).
[en] Objectives are (1) to develop a model of Internal Centrifugal Zone Growth (ICZG) and (2) to use this model to improve present ICZG systems. During the present year, models were developed for finite samples heated by finite induction coils. These models enable calculation of two-dimensional temperature profiles in solid samples. Molten zone shapes can be calculated provided that simplified boundary conditions for the rf field are employed. Experiments to test these models were conducted here and at ORNL. The heating instability phenomenon was possibly observed but not quantified
[en] The patented heater element for the manufacture of monocrystals by zone melting of layers consists of a heated pipe on which short pipes or rings are slipped. A heater element of this design allows high volume capacity of expanded melt. (Ha)
[en] The well-known glass-forming alloy Fe40Ni40P14B6 was surface melted by an electron beam traversing its surface at various velocities in an identical manner for both the crystalline and the amorphous state of the alloy. Cross-sectional optical metallography and numerical heat-flow analysis were used to show that (1) crystallization of the amorphous state does not occur during treatment around or in the regrown layer at the highest processing speeds, a behavior consistent with an extrapolation of isothermal nucleation and growth measurements; (2) initial resolidification of the molten layer is always crystalline when the melt pool contacts underlying crystalline material where nucleation is immediate; and (3) solidification front velocities greater than 5 +- 0.5 cm/s exceed the maximum kinetic limit for growth of the crystalline phase and amorphous layers are formed, a result consistent with the eutectic nature of the alloy. Inconsistencies with the work of previous investigators of this system are discussed