Materials Science Forum Vol. 879

Abstract: Spherical powders via gas atomization etc. are recommended for use in SLM, however, the spherical powders are expensive and able to make in limited types of metal materials. Using non-spherical powder in SLM are capable of applying SLM to cheap part production and diversify powder materials for SLM. In this paper, to study the feasibility of using Ti6Al4V milled powder via hydride-dehydride method for SLM, characteristics of powders, powder bed performances, and SLM fabricated samples made from gas atomization powder and milled powder were analyzed and compared. The milled powder which added a fumed silica as a lubricant were also analyzed. In the results, flow and packing characteristics of the milled powder are lower than the gas atomized one. The characteristics of the milled powder are improved by adding fumed silica as lubricant, and had comparable characteristics to the gas atomized one. Microstructure of the SLM fabricated samples has a comparable size and morphology regardless of powders. Hardness of the SLM fabricated sample made from milled powder are larger than that of it made from gas atomized powder, owing to solid solution hardening by oxygen.

Abstract: Gallium nitride (GaN) transparent and semiconducting thin films were prepared on an amorphous glass substrate by a reactive sputtering method using Ar-N₂ radio-frequency plasmas. In addition, GaN thin films were prepared on amorphous silicon-dioxide (SiO₂) layer-deposited Si (111) single-crystalline substrates by a reactive evaporation method. Optical transmission properties, electrical properties, and crystallinities of the films prepared on the glass substrate were investigated as a function of the mixing ratio of the reactive sputtering gases. On the other hand, variations in the crystallinities of the films prepared on the amorphous SiO₂ layer-deposited Si (111) substrates were investigated as a function of the thickness of the amorphous SiO₂ layers.

Abstract: In addition to conventionally casting, dental metallic framework can be manufactured using different CAD/CAM technologies (selective laser melting, milling). The milling of porous CoCr blanks followed by sintering under protective gas is a new 2012 introduced dental technology called Ceramill Sintron. For this new material so far, there exist few studies on the corrosion behavior. The aim of this study was to investigate the influence of different pH values as well as fluoride additions on the corrosion behavior of the sintered CoCr alloy compared to the cast condition by electrochemical corrosion measurements according to ISO 10271.

Abstract: Liquid Composite Molding techniques are widely used technologies in order to manufacture fiber reinforced plastic composites using near-net-shaped preforms consisting of single reinforcements, e.g. woven textiles or multiaxial fabrics. All LCM process variants have in common to impregnate and saturate dry reinforcing structures with a liquid thermoset resin system. The challenge during LCM process development and mold designing is the prevention of potential error sources for safe in-spec FRPC production. Race tracking zones and air inclusions are two major issues which need to be avoided in order to ensure an excellent FRPC quality. The knowledge about preform transmissibility, i.e. permeability, of the dry reinforcing structure to the liquid flow during the saturation phase is of major importance. The knowledge about the filling and flow behavior during FRPC processing is responsible for the process efficiency and process success. In-plane and out-of-plane permeability characterization is of great interest. Especially industry is interested in precise permeability values for numerical mold filling simulations in order to support the process development and the mold design. Industrial work is also carried out for filling strategies and textile development as well as textile improvement. The paper presents different LCM processing techniques and discusses the advantages and disadvantages as well as the linked challenges during FRPC processing. Furthermore, the in-plane permeability characterization of reinforcing structures and moreover influencing factors on the filling behavior are presented. Finally the significance of accurate and reliable permeability values according to numerical filling simulations and their validity are discussed.

Abstract: This work presents a photolithographic rapid prototyping process for producing thin films ("Rapid Phototyping"). This process allows a quick and cost-effective generation of scalable thermopile microstructures using commercial equipment and materials. Structural widths of 100x250μm can be produced reproducible in a lift-off process with an accuracy of 5 microns vertically and 30 microns horizontally.

Abstract: In this paper, the influence of corrosive conditions on the mechanical performance of Flow Drill Screw (FDS) joints is investigated in greater detail. Different combinations of light metals such as aluminium or magnesium alloys and high strength/stainless steel served as the test material. The joint strength of FDS joints, under quasi-static and cyclic loading, was measured before and after six weeks’ of corrosion climate change testing. Furthermore metallographic sections of the samples were compared in order to evaluate the stage of surface, galvanic and crevice corrosion. To classify the effect of progressing corrosion on the mechanical properties of FDS joints, the following factors are taken into account: corrosion resistance of the materials, joining parameters and the geometry of the joint. For all material combinations there is an apparent change in both the fatigue strength and the failure behaviour after corrosion testing.

Abstract: During the early stages of the plastic deformation of a polycrystal, dislocations can pile-up against grain boundaries. Experimental results on large-grained materials have provided excellent verification of this phenomenon. Such a pile-up may activate dislocation slip in the neighbouring grain. Whether this occurs depends on the misorientation between the grains and the resolved shear stresses in the affected grain. Several approximate criteria have been proposed to predict the occurrence of this mechanism. Here, the problem will be assessed directly by calculating the Peach-Köhler force produced by a single dislocation pile-up in one grain on all the possible slip systems in the neighbouring grain, in combination with the effect of the applied external stress as obtained through calculation of the Schmid factor. It will be seen that the problem is significantly more complex than what is generally assumed in basic explanations of the Hall-Petch effect: highly localised stress concentrations are generated for certain misorientations, which are capable of punching out small dislocation loops which may then propagate into the neighbouring grain.

Abstract: We have developed a manufacturing system by combination of high-pressure synthesis method using a multi-anvil press, and spark plasma sintering (SPS) method. By means of the system, we have succeeded in synthesizing new filled skutterudite-type thermoelectric materials Mm_xCo₄Sb₁₂ (Mm=mischmetal). The thermoelectric properties of partially filled skutterudite compounds Mm_xCo₄Sb₁₂ synthesized under high pressure have been investigated. The Seebeck coefficient of Mm_xCo₄Sb₁₂ shows negative value, which means n-type conductivity. The highest dimensionless figure of merit ZT value is 0.25 for Mm_0.6Co₄Sb₁₂ at 700 K.

Abstract: Silicon carbide fiber reinforced silicon carbide composite (SiC/SiC composite) is expected as a potential replacement of the current Zircaloy fuel cladding in the light-water reactor because of its many superiorities, where it is necessary to develop the end-cap seal of SiC/SiC composite cladding. In this research, the applicability of diode laser irradiation for joining between Zircaloy and SiC/SiC composite tubes was examined based on the caulking method. As the method for fitting two tubes, the screw cutting was conducted for the inner face of Zircaloy tube and the outer surface of SiC/SiC composite. In addition, as a method to improve the joinability of Zircaloy and SiC/SiC composite, titanium nanopowder was inserted into a gap between two tubes. The laser beam irradiation was circumferentially applied to the outer surface of Zircaloy tube. Although the mechanical caulking joint was successfully produced, the airtightness was insufficient for the end-caps of SiC/SiC composite cladding. However, the good adhesion between Zircaloy and SiC/SiC composite was partially produced as the result of the generation of all proportional solid solution between titanium and zirconium. Namely, it can be concluded that the circumferential diode laser irradiation with inserting titanium nanopowder between Zircaloy and SiC/SiC composite tubes would have a good potential for producing the caulking joint of two tubes.

Abstract: The grain refinement and kinetics of submicrocrystalline structure formation in a Cu-0.3%Cr - 0.5%Zr alloy during large plastic deformation were investigated. The fraction of high-angle boundaries and the fraction of ultrafine grains were used to estimate the kinetics of grain refinement and submicrocrystalline structure evolution during large plastic deformation. The multidirectional forging (MDF), equal channel angular pressing (ECAP), and high pressure torsion (HPT) were used as methods of large plastic deformation. Comparative analysis showed that the grain refinement process occurred faster during HPT and MDF in comparison with ECAP. The fraction of ultrafine grains achieved almost 1 after 3 HPT turns and after MDF to the total strain of 4; while the one reached only 0.29 after 4 ECAP passes. The modified Johnson-Mehl-Avrami-Kolmogorov equation could be applied to determine the kinetics of grain refinement in copper alloy during large plastic deformation as a function of true strain.