AM deposition of components for the biomedical applications increases gradually its applications. There has been done a lot of work on AM deposition of Ti alloys such as commercially pure alloys Ti Gr.2, Ti Gr.4 and mainly Ti-6Al-4V alloy. However, there are some drawbacks such a slow strength values for both Ti Gr. 2 and 4 and relatively high elastic modulus for all mentioned Ti alloys (1-3). Moreover, Ti-6Al-4V exhibits potentially negative aspect related to alloying elements dissolution in the body and absorption by human organs. Therefore, other alloys are being There are currently certified two beta-titanium alloys for the biomedical applications: Ti-13Nb-13Zr (ASTM F1713) and Ti-12Mo-6Zr-2Fe (ASTM F1813), that are investigated in this work. These materials are in the presented study deposited by Laser Powder Bed Fusions process (LPBF) and by Directed energy Deposition system (DED). Microstructures investigations are accompanied by mechanical properties assessment in terms of quasi-static and cyclic test, that are presented here together with dynamic elastic modulus measurements. The elastic modulus values achieved here are significantly closer to behavior of human bone, than standardly used Ti 6Al-4V. Assessment of behavior for both consider alloys deposited by two AM deposition processes is performed based on the results achieved here and compared with previously obtained results for Ti 6Al-4V.
Keywords:Narrow fine grain layers of material are often generated in the vicinity of frictional interfaces in manufacturing processes as a result of severe shear deformation. These layers change some surface properties of machine parts. The latter affects the performance of structures and machine parts under service conditions. Therefore, it is of importance to develop a method to connect parameters of manufacturing processes and parameters that characterize properties of fine grain layers generated by these processes. The strain rate intensity factor is the coefficient of the leading singular term in a series expansion of the equivalent strain rate in the vicinity of maximum friction surfaces. Such expansions are available for several material models that are often adopted to describe the response of material in metal forming processes. The objective of the present paper is to develop a general approach to use the strain rate intensity factor for predicting the evolution of material properties within the fine grain layers. The present paper includes a conceptual approach, experimental results on upsetting and drawing and a special numerical method for calculating the strain rate intensity factor. The latter is necessary since the strain rate intensity factor appears in singular solutions and conventional finite element methods are not capable of calculating this factor. The method proposed is based on the method of characteristics. Two criteria for the thickness of the fine grain layer are considered.
Keywords:In the manufacturing processes of red-green-blue (RGB)-type organic light emitting diode (OLED) displays, Invar (Fe-36 wt.% Ni alloy) is used as a material for the fine metal mask (FMM), which guides the evaporated diode materials through its small holes onto the correct positions of the substrate glass. Because the hole size of the FMM should not change during the evaporation process, Invar, whose thermal expansivity approaches zero[1], must be used for the FMM material. For high-quality color images in the display, the thickness of the FMM needs to be thinner [2]. Contrary to the conventional top-down method of producing Invar, a bottom-up approach of electroforming is a promising technology for producing very thin FMMs. The present authors have recently presented that the electroformed Invar via sophisticated heat treatment exhibits the coefficient of thermal expansion (CTE) lower than that of the conventional Invar [3]. The current work has been aimed at investigating the effect of the microstructure evolution on the CTE during heat treatment in electroformed Invar. Finally, we propose optimal process conditions to manufacture the Invar FMM applied for an ultra high definition (UHD) grade of the OLED display.
Keywords:This article addresses modeling of the solidifying material structure during 3D welding/printing of fully dense Mg alloy products by fused deposition of molten droplets from a uniform droplet spray source on a motorized X-Y table substrate [1]. The resulting crystallite size distribution is simulated by a solidification model consisting of nucleation/fragmentation and constrained growth description, calibrated via structural data from a single droplet splat [2]. This is enabled by a semi-analytical thermal modeling framework, based on superposition of moving Green's and Rosenthal functions for the temperature field from a Gaussian source distribution [3], in which the deposit solid geometry and heat transfer boundary conditions are accounted for by mirror source images of modulated efficiency [4]. The simulation model is implemented for layered ellipsoidal deposit sections on planar substrates by multi-pass spraying, and its predictions are validated against measured crystal size by image analysis of experimental micrographs of a Mg97ZnY2 alloy, to an error margin of +15%. The computationally efficient simulation provides insight to the deposit microstructure, and is intended as a process observer in a closed-loop, adaptive control scheme based on infrared temperature measurements.
Keywords:[1] Fukuda H, "Droplet-Based Processing of Magnesium Alloys for the Production of High-Performance Bulk Materials", PhD Thesis, MIE Dept, Northeastern University, Boston, MA (2009). [2] Ioannou Y, Fukuda H, Rebholz C, Liao Y, Ando T. Doumanidis C.C, "Constrained crystal growth during solidification of particles and splats in uniform droplet sprays", Int J Adv Manuf Technol 107, 1205–1221 (2020). [3] Rosenthal, D., "Mathematical Theory of Heat Distribution During Welding and Cutting", Welding Journal 20 (5), (1941), pp. 220s - 234s [4] Carslaw, H.S., Jaeger, J.C., Conduction of Heat in Solids, 2nd Ed, Oxford Science Publ. (1951)
As the additive manufacturing (AM) processes are developing and expanding their capabilities and subsequently also application fields, new alloys are being implemented in order to fulfil specific requirements for highly demanding applications. In the current paper, beta-titanium alloy Ti-13Zr13Nb is investigated. This materials is special due to low elastic modulus and its certification for bio applications. The experimental material is deposited by powder blown directed energy deposition process. Microstructure and local mechanical properties at room temperature under quasi-static loading conditions are investigated here. Optical and electron microscopy investigations including EBSD analyses are carried out here in order to provide detailed information on the microstructure of the AM deposited material. Mechanical properties in terms of tensile properties are investigated using miniaturized tensile test specimens excised in various orientations regarding the deposition process. Microstructure and mechanical properties homogeneity together with imperfections observations are investigated for the material of interest. Obtained results are compared with properties of the other Ti-alloys produced in conventional way and by AM processes.
