Materials Science Forum Vol. 1016

Abstract: Conventionally, brass has toughness more than other metals, so there is a concern about its poor machinability. Therefore, improvement of machinability was attempted by adding lead to brass. This brass called free cutting brass, typified by JIS C3771. This free-cutting brass is used for piping components and machine parts. There is a concern about elution of the lead into drinking water. Hence, Drinking Water Quality Standards Law has been amended and it restricts lead content in the free cutting brass. Therefore, lead-free free-cutting brass with no lead or minimized content of lead is required.Consequently, a lead-free free-cutting brass had been developed to improve in machinability such as JIS C6931 and JIS C6803 that are added Si and Bi instead of lead respectively. Lead was also used for the solder for joining among pure copper pipes and brass valves. That causes elution of lead from the solder into drinking water. For this reason, Lead-free solder such as Sn-Sb and Sn-Ag-Cu have been used.A fire torch technology often was used for soldering of brass. The purpose of this study is investigating soldering-ability and wettability of lead-free solder on lead-free free-cutting brass. Hence, we investigated the soldering ability of lead-free solders, Sn-5%Sb and Sn-3%Ag-0.5%Cu, for pure Cu and brass joints with nonuniform heating by hot plate.

Abstract: The influence of different thickness combinations was investigated on the strength of the lap joint of dissimilar steels. In this study, lap joints of dissimilar steels were welded by laser welding. The tensile shear test was conducted for the lap joints. Rotational deformation process around the weld bead of the lap joint was observed by a digital video camera during the test. Motion analysis from the video of the tensile shear test indicated that the rotation angle around the weld bead was reduced by overlapping higher strength grade steel. Three-dimensional elastic-plastic finite element analysis was performed for the tensile shear test of the lap joint. The numerically calculated deformation behavior of the lap joint subjected to tensile shear loading showed reasonable agreement with the experimental record. It was found that the rotation angle was reduced and tensile shear strength of the lap joint increase by overlapping higher strength grade steel sheet.

Abstract: Friction stir processing is a solid-state welding technology capable of joining metal parts without the melting. The microstructure of the material evolved during the process vary from columnar grain along the thermal gradient in the melt pool to fine equiaxed grains. Evaluation on its mechanical properties in terms of micro-hardness was performed. A significant decrease in microhardness was observed in the processed region. The decrease in the microhardness is mainly attributed to the dissolution of hardening precipitates in the aluminium matrix.

Abstract: In this study, the effect of surface treatment of Al with alkaline (pH 10.5 and pH 12.4) and acidic (pH 3.7) electrolyzed water was investigated on bonding strength of solid phase diffusion bonded Al. Aluminum hydroxide and hydroxyl groups were appeared on the surface of Al which was treated with alkaline electrolyzed water of pH 12.4 at 323 K for 2700 s. It was found that such treatment is similar to the one with NaOH aqueous solution at 323 K for 30 s. For bonding strength, shear strength of the bonded Al specimens treated with electrolyzed water of pH 12.4 at 293 K for 3 s and 30 s were higher than that of the untreated specimen.

Abstract: Rina Consulting Centro Sviluppo Materiali (CSM) has been involved in the study and development of powder metallurgy for different applications, thanks to its participation in many research industrial and funded projects. The entire metal powder production chain takes place within the company's own researcher and facilities. This allows to produce high quality powders starting from alloy design, VIGA atomization and chemical, rheological and particle size analysis. In recent years, the development has mainly concerned manufacturing processes. Currently only a limited number of metal alloys can be processed by AM. For that reason, the alloy design becomes a really important topic to enlarge AM capabilities to other materials and applications. Starting from commercial Thermodynamic and Kinetic codes and proprietary models on solidification and micro-segregation, the alloy chemical composition can be fine-tuned to optimize the microstructure, considering the target properties of the material and the relevant AM processing windows, taking into account also the post process treatment conditions. Moreover, the knowledge of the production plants allows CSM to have a wide vision on the realization and the characterization of the metal powders focusing to achieve the best powder quality suitable for AM applications. Finally, AM is a relatively “new” process, standardization is still an ongoing activity involving several communities and organizations like ASTM, AWS and ISO; in this contest CSM has already designed the guidelines for qualification and certification processes and has created a dedicated laboratory to qualify powders of AM players.

Abstract: The element of zirconium (Zr) belongs to the same group 4 as Ti in the periodic table. Therefore it possesses similar chemical properties. The Ti-Zr binary system forms a continuous solid solution for both high temperature β phase with the body centered cubic (BCC) structure and low temperature α phase with the hexagonal close-packed (HCP) structure throughout the entire range of composition. As is well known, on the other hand, the element of iron (Fe) is not only inevitable but also effective element in Ti.By incorporating Fe at the stage of alloy design, off-grade sponge titanium can be employed. Both elements seem to be effective in strengthening the titanium alloys. The purpose of this work was to prepare Ti-Zr-Fe alloys and then mechanical property and heat treatment behaviours were investigated as a fundamental research. Ti-x mass% Zr-1mass% Fe alloys (x=0, 5, 10) were melted in a laboratory-scale arc furnace under a high purity argon atmosphere from the sponge Ti, the sponge Zr and the Fe wire. The resulting ingots were hot forged and rolled at approximately 1120 K to obtain plates of approximately 2 mm in thickness. Well-mixed and homogeneous samples could be obtained, oxygen contaminations were less than 0.09 %. Solid solution of Zr into Ti was confirmed by the XRD peak shift in α phase. Vickers hardness and proof stress increased with Zr content. No remarkable changes could be observed in the microstructures after the solution treatment at 1173 K. However, Young’s modulus increased at x=10 by the treatment.

Abstract: Additive manufacturing of Al alloys can represent an interesting solution for high-performance components in various industrial fields, as for instance the automotive and aerospace industry. Often, for these applications, the alloys are required to withstand exposure to high temperatures. Therefore, the investigation of the evolution of material properties with increasing temperature is of utmost importance in order to assess their suitability for this kind of applications. In the present study, tensile properties at high temperature were investigated for an AlSi10Mg alloy. Samples were manufactured by laser-based powder bed fusion in horizontal and vertical direction in order to examine the influence of building direction on material behavior. The samples were tested in as-built condition and after exposure to high temperature. Tensile tests were performed up to 150 °C and the effect of holding time at the test temperature was evaluated. Furthermore, the alloy was characterized by mechanical spectroscopy in order to evaluate the behavior of dynamic modulus with temperature and, thus, to provide a comprehensive characterization of the material behavior. It was found that the peculiar microstructure of the alloy produced by additive manufacturing is responsible for good high-temperature strength of the material up to 150 °C. The material also exhibits a good thermal stability even after holding at test temperature for 10 h.

Abstract: We demonstrate an automatic materials design method using continuous representation of molecule and its atomic arrangement via a neural network algorithm. This method is applied to optimizing and predicting the HOMO-LUMO gap within the molecules composed of carbon, oxygen, nitrogen, fluorine, and hydrogen. Adopting the Quantum Machine 9 (QM9) dataset as a training dataset for the molecules, we first established a continuous representation of molecules in a latent space, then predicted molecules that have target values of the HOMO-LUMO gap. In the gap maximization calculation, the CF₄ with the largest gap value in the QM9 dataset was automatically found despite there is no a priori data for the gap. In the case of a target gap value of 0.10 hartree, we found a new molecule whose gap value is closer to 0.10 hartree than any other molecules in the QM9 dataset.

Abstract: Estimated 30 percent or more of coral reefs are now in danger of extinction by coastal construction increases and global temperatures rise. Several restoration techniques such as fragmentation, forming, Biorock have been developed in the past few years. In vertebrates such as mammals, osteoblast is known to form the bones composed of hydroxyapatite. Therefore, bone substitutional devices are generally surface modified to improve the adhesion of osteoblasts on the surfaces. Titanium dioxide film is often employed as the surface material for hard tissue substitutes made of titanium and its alloys. In hard corals, on the other hand, the soft tissue covered on the skeletons made of calcium carbonate has osteoblasts as well. The purpose of this work was to investigate the potential of titanium (Ti) and titanium dioxide (TiO₂) as scaffolds for proliferating coral reefs by analysing the several interfacial reactions. The rods of pure Ti were anodised in aqueous phosphoric acid at a constant voltage of 80 V. The surfaces were confirmed to be anatase type TiO₂. The coral fragments were kept in contact with the rods in a lab-scale aquarium with artificial seawater for several days. The colony of polyps vigorously expanded on the surfaces. Fragments of coral were placed on pure Ti, TiO₂ coated pure Ti in Petri dishes and were reared in artificial seawater. Fine spherical precipitates of calcium carbonate with aragonite structure, which is the same inorganic substance as corals, were observed radially and regularly on the surfaces of TiO₂. In addition, the adherence of planula larva to the sputtered TiO₂ film was observed by using a QCM (Quartz Crystal Microbalance) method. The approach and adhesion of planula larva to the surface could be detected by monitoring the resonance frequency and resistance. The surfaces might have a great potential in coral reef regenerations.

Abstract: The Co-20Cr-15W-10Ni (CCWN, mass%) alloy has excellent corrosion resistance and strength-ductility balance and is applied in almost all balloon-expandable stent platforms. To further reduce the invasiveness of stent placement, it is necessary to reduce the diameter of the stent. That is, both high strength and high ductility should be achieved while maintaining a low yield stress. In our previous studies, it was discovered that low-temperature heat-treatment (LTHT) at 873 K improves the elongation of the CCWN alloy. In this study, we focused on the grain refinement by swaging and static recrystallization to improve the strength of the alloy. The as-swaged alloy was recrystallized at 1373–1473 K for 100–300 s, followed by LTHT. A fine grain structure with an average grain size of 3–17 μm was obtained by static recrystallization. The η-phase (M₁₂X-M₆X type precipitates, M: metallic elements, X: C and/or N) formed during the recrystallization at 1373–1448 K. The alloys recrystallized at 1448 and 1473 K had a homogeneous structure with a small variation in the grain size. On the other hand, the alloys recrystallized at 1373 and 1423 K had an inhomogeneous structure in which fine and coarse grains were mixed. Both the strength and ductility of the CCWN alloy were improved by combining high-temperature short-time recrystallization and LTHT.