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Generally, molds are fabricated by the machining of massive billets of tool steels, such as AISI4140 or H13, but it has drawbacks, such as a large material loss and long-delivery time. The Wire-Arc Additive Manufacturing (WAAM) process could be an alternative fabrication method. It has the advantages of less material loss, short-delivery time, and the chance to make a reinforced mold using dissimilar materials. 5 Cr – 4 Mo steel wire has high potential to produce molds via the WAAM process. This is a commercial tool steel solid wire initially designed for the repair and modification of tools and molds that has superior hot wear resistance and toughness. However, no study has examined the WAAM of tool steels, even though it has high potential and advantages. Shielding gas has a significant effect on the performance of the WAAM process, which is based on gas metal arc welding (GMAW). Argon (an inert gas) and carbon dioxide (a reactive gas) are generally used for the GMAW of steel alloys, and they are frequently used as mixed gases at various ratios. Shielding gases have a significant influence on the arc stability, weld quality, and formation of weld defects. Therefore, using a proper shielding gas for the material and process is important to sound WAAM performance. This paper discusses the effect of the shielding gas on the additive manufacturability of tool steel, as a first step for the WAAM of die casting molds. The experiments were conducted with two different shielding gases, M21 (Ar + 18% CO2) and C1 (100% CO2). The use of C1 showed neither surface contamination nor internal defects, and resulted in a larger amount of deposition than the M21.

The analog memristive switching of iron oxide (γ-Fe2O3) nanoparticle assembly was investigated. The γ-Fe2O3 nanoparticles were chemically synthesized with ∼10 nm in diameter and assembled to be a continuous layer as a switching element in Pt/nanoparticles/Pt structure. It exhibited the analog switching that the resistance decreased sequentially as repeating −V sweeps and pulses while increased as applying +V. The capacitance-voltage curves presenting hysteresis with flatband voltage shift and distortion of their shapes with respect to the applied voltage supported the redistribution of space charges in nanoparticle assembly that might induce resistive switching. The polarity-dependent analog resistance change proportional to pulse voltage, time, and number of pulses was analogy to potentiation and depression of adaptive synaptic motion.

This study observed the effect of filler metal type on mechanical properties of NAB (NiAl-bronze) material fabricated using wire arc additive manufacturing (WAAM) technology. The selection of filler metal type is must consider the field condition, mechanical properties required by customers, and economics. This study analyzed the bead shape for representative two kind of filler metal types use to maintenance and fabricated a two-dimensional bulk NAB material. The cold metal transfer (CMT) mode of gas metal arc welding (GMAW) was used. For a comparison of mechanical properties, the study obtained three specimens per welding direction from the fabricated bulk NAB material. In the tensile test, the NAB material deposited using filler metal wire A showed higher tensile strength and lower elongation (approx. +71 MPa yield strength, +107.1 MPa ultimate tensile strength, −12.4% elongation) than that deposited with filler metal wire B. The reason is that, a mixture of tangled fine α platelets and dense lamellar eutectoid α + κIII structure with β´ phases was observed in the wall made with filler metal wire A. On the other hand, the wall made with filler metal wire B was dominated by coarse α phases and lamellar eutectoid α + κIII structure in between.

The aim of this work was to perform thermal characterization of commercially pure titanium in dry air to determine its oxidation kinetics and the structure of the oxide. The oxidation kinetics were determined thermogravimetrically under isothermal conditions in the temperature range 300 to 750 o C for 48 hours and the structure of the oxides was determined by differential thermal analyses and X-ray diffraction in the temperature range room temperature -1000 o C. The oxidation rate of titanium increased with increase in temperature. It was high in the initial stages of oxidation and then decreased rapidly with time, especially up to 600 o C. The kinetic laws varied between inverse logarithmic at the lower temperatures (300 and 400 o C) and parabolic at the higher temperatures (650, 700 and 750 o C). Evidences from X-ray diffraction and differential thermal analyses data revealed that the passive oxide film formed at room temperature crystallized into anatase at about 276 o C. The crystallized oxide formed in the range 276 -457 o C consisted of anatase, in the range 457 -718 o C consisted of anatase and rutile sublayers, and at temperatures beyond 718 o C consisted of a layer of pure rutile. Scanning electron microscopy observations reveled that the oxidized surfaces were crack-free and the surface roughness increased steadily with oxidation temperature.Keywords: Titanium, oxidation kinetics, oxide film, structure. Cinética de oxidação de um titânio puro comercial RESUMOO objetivo deste trabalho foi de realizar uma caracterização térmica de um titânio puro comercial para estudar sua cinética de oxidação e seus produtos de corrosão formados em atmosfera de ar seco em função da temperatura. A cinética de oxidação foi determinada por termogravimetria em condições isotérmicas entre 300 e 750 o C por 48 horas e os óxidos formados foram caracterizados por análise térmica diferencial e difração de raios-X entre a temperatura ambiente até 1000 o C. A cinética de oxidação aumenta com a temperatura e é muito rápida nos primeiros instantes, diminuindo rapidamente com o tempo, especialmente até 600 o C. As leis cinéticas variaram entre a logarítmica inversa nas temperaturas mais baixas (300 e 400 o C) e a parabólica nas temperaturas mais altas (650, 700 e 750 o C). As análises por difração de raios-X e análise térmica diferencial mostraram que a cristalização do filme passivo de óxido, formado naturalmente à temperatura ambiente, ocorre aproximadamente a 276 o C. A estrutura do óxido é composta de anatásia cristalina entre 276 e 457 o C, anatásia e rutilo entre 457 e 718 o C, e somente rutilo acima de 718 o C. Observações por microscopia eletrônica de varredura revelaram que as superfícies oxidadas não apresentam fissuras e que suas rugosidades aumentam uniformemente com a temperatura de oxidação.Palavras-chave: Titânio, cinética de oxidação, filme de óxido, estrutura.