Key Engineering Materials Vol. 658

Abstract: The objective of this research is to develop the welding procedure for multilayer hardfacing of 3.5 %chromium cast steel and study wear behavior of hardfacing deposits. Austenitic stainless steel and martensitic hardfacing electrodes were selected as buffer and hardfacing, respectively. Four types of welding procedures were investigated, using shielded metal arc welding (SMAW) process. Three different preheatings were applied in this study. Characteristic of the macro, microstructure and worn surface deposits was investigated by optical microscope. The hardfacing deposits were also determined by the dry sand rubber wheel machine according to procedure A of the ASTM G65 standard. The results indicated that the multilayer hardfacing with and without preheating revealed no crack or defect in the Heat Affected Zone (HAZ) and other regions. The wear resistance of hardfacing presented a little difference. The best abrasive wear resistance was obtained from sample without preheating. This was due to the full martensitic microstructure of the hardfacing.

Abstract: The objective of this research was to develop the welding procedure for multilayer hardfacing of 13% Mn cast steel and study behavior of hardfacing deposits after impact applied. Austenitic stainless steel and martensitic hardfacing electrode were selected as buffer and hardfacing, respectively. Two different atmospheric conditions were compared which the first was controlling cooling rate on specimen by water during welding and another was un-controlling (by air), using shielded metal arc welding (SMAW) process. Macrostructure and microstructure were investigated by optical microscope. The hardfacing deposits were also determined by the dry sand rubber wheel machine according to procedure A of the ASTM G65 standard. The results indicated that the hardfacing layers revealed martensitic type microstructure in both controlled and uncontrolled cooling rate but their grain shapes were a little difference. For buffer layer showed austenitic type microstructure. And base metal layer presented amount of carbide in controlled cooling rate is less than in another one. The best wear resistance was obtained from controlled cooling rate condition.

Abstract: To produce the forming limited diagram for predicting and studying material behavior in sheet metal forming, grid etching or grid marking on blank surface are applied before forming. But in single point incremental forming process, sheet metal blanks are subjected to highly strain or highly deformation which the conventional gridding is no longer to be occurred on the surface of formed part. And some material such as titanium, nickel based alloy etc are difficulty to etch the grid marks on its surface. So this paper is proposed the drilling hole technique to substitute with the grid etching technique in single point incremental forming process. The holes 2 mm. diameter were drilled on the SUS 304 stainless steel blank before forming. The deformed holes are calculated as true major strain and true minor strain and plot into a forming limited diagram. The results are compared with the conventional etching techniques which show an according trend. The drilling hole technique could be used in study the material behavior in single point incremental forming, it a low cost convenient and easy than grid etching technique.

Abstract: Titanium dioxide has attracted worldwide attention due to its prominent photocatalytic activity. It is generally accepted that nanoparticulate titanium dioxide with pure anatase structure exhibits high reactivity. Sol-gel is a simple and cost-effective technique capable of synthesizing anatase-phase titanium dioxide with particle sizes in nanometer range. This research aimed at examining effects of ageing periods on compositions and sizes of titanium dioxide synthesized by sol-gel technique. Experimental results revealed that prolonged ageing period demoted formation of anatase phase. Pure anatase phase was observed at ageing period of 1 day, while both anatase and rutile phases were observed at ageing periods of 4 and 7 days. The results also indicated that particle sizes decreased as the ageing periods increased. Nanoparticulate titanium dioxides with average sizes of 71.5, 50.4, and 29.7 nanometer were observed at ageing periods of 1, 4, and 7 days, respectively.

Abstract: PdCoNi nanocomposites supported on graphene (PdCoNi/G) have been obtained from chemical reduction of metal catalysts and graphite oxide (GO) with a strong reducing agent, followed by calcination at high temperature under N₂ condition, and used for electrooxidation of methanol in direct methanol fuel cell. The morphologies and structural properties of electrocatalysts were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). X-ray spectroscopy techniques (X-ray photoelectron spectroscopy XPS) was used to investigate the chemical state of the synthesized catalysts. The results of Pd XPS spectra showed the metallic Pd and PdO phases for precalcined and calcined PdCoNi/G nanocomposite, respectively. The X-ray measurement of Co and Ni displayed the various metallic oxides in synthesized electrocatalysts. For electrochemical analysis, cyclic voltammetry (CV) and chronoamperometry (CA) indicated that the PdCoNi/G nanocomposites enhanced the methanol oxidation, compared to the lower activity in the calcined electrocatalysts.

Abstract: The advanced high strength (AHS) steels, for example, dual phase (DP) steels, transformation induced plasticity (TRIP) steels and complex (CP) steels principally exhibit multiphase microstructure features. Thus, mechanical behavior of the constituent phases significantly affects the resulting overall properties of such AHS steels. Novel material characterization techniques on micro- and nano-scale have become greatly more important. In this work, stress-strain response of the DP steel grade 1000 was determined by using the Nanoindentation testing. The DP steel showed the microstructure containing finely distributed martensite islands of about 50% phase fraction in the ferritic matrix. The nano-hardness measurements were firstly performed on each individual phase of the examined steel. In parallel, finite element (FE) simulations of the corresponding nano-indentation tests were carried out. Flow curves of the single ferritic and martensitic phases were defined according to a dislocation based theory. Afterwards, the load and penetration depth curves resulted from the experiments and simulations were compared. By this manner, the proper stress-strain responses of both phases were identified and verified. Finally, the effective stress-strain curve of the investigated DP steel could be determined by using 2D representative volume element (RVE) model.