3RD INTL. SYMP.ON ADVANCED MANUFACTURING FOR SUSTAINABLE DEVELOPMENT

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.

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.

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.

The, results of variations of structure in oxidizing atmosphere at high temperatures (after heating and thermocycling up to 600 – 1400 ^oC), and electrical conductivity (after long time heating at 600 ^oC) of MAX Ti₂AlC-, Ti₃AlC₂- and (Ti,Nb)₃AlC₂-based bulk materials with different porosity (prepared by synthesis in vacuum and/or by hot pressing) and coatings (vacuum-arc deposited) are presented. The characteristics of highly dense Ti-Al-C composite bulks and vacuum-arc deposited 6 m thick coatings before and after heating at 600 ^°C in air for 1000 h were compared. High electrical conductivity ((The, results of variations of structure in oxidizing atmosphere at high temperatures (after heating and thermocycling up to 600 – 1400 ^oC), and electrical conductivity (after long time heating at 600 ^oC) of MAX Ti₂AlC-, Ti₃AlC₂- and (Ti,Nb)₃AlC₂-based bulk materials with different porosity (prepared by synthesis in vacuum and/or by hot pressing) and coatings (vacuum-arc deposited) are presented. The characteristics of highly dense Ti-Al-C composite bulks and vacuum-arc deposited 6 &#181;m thick coatings before and after heating at 600 °C in air for 1000 h were compared. High electrical conductivity (delta m/S =1.3•10⁶ S/m) of the highly resistant toward oxidation (delta m/S=0.07 mg/cm²) Ti-Al-C coating was preserved after long-term heating in air. It was found that the specimen surface layers of MAX-phases Ti₃AlC₂ and Ti₂AlC based bulks and chromium-containing Crofer 22APU steel became semiconductors because of high-temperature long-term oxidation (at 600 ^°C). The vacuum-arc deposited Ti-Al-C coating revealed high oxidation resistance and electrical conductivity along with good mechanical characteristics, namely nanohardness H (10 mN)= 9.5±1.5 GPa, and Young’s modulus E=190±10 GPa, which make it very promising for interconnects of solid oxide fuel cells (SOFCs).
Acknowledgements
The investigations were performed in the frames of the project NATO SPS G5773 “Advanced Material Engineering to Address Emerging Security Challenges” for 2020-2023, the project 03-03-20 of Ukrainian-Belorussian cooperation for 2020-2021, and the projects III-3-20 (0779), III-5-19 (0778), and II-5-19 (ІНМ-29/20) supported by the National Academy of Sciences of Ukraine.

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.

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