Abstract: AISI 441 ferritic stainless steel is a good candidate for metallic interconnects in solid oxide fuel cells (SOFCs). The minor elements Ti and Nb are used to stabilize the ferritic matrix and also to reduce creep by a combination of solid solution strengthening and precipitation of intermetallic Laves phase particles along the grain boundaries. However their influence on the oxidation behavior is not well understood. This study focuses on the early stages oxidation (from 4 to 24 h) at 800 °C of AISI 441 under 5% H2O in O2. A relatively smooth micro-crystallized oxide scale and Ti, Nb containing nodules are observed. The internal microstructure of these objects is studied by FIB tomography which allows computing cross sectional views in any direction of interest. FIB study reveals a complex microstructure and a development strongly linked to the presence of niobium and/or titanium in the substrate.
Abstract: In present study, Sn–9Zn, Sn–9Zn–xCu and Sn–9Zn–xNi solders (x = 1.0, 2.0 and 3.0 wt%) were prepared via melting process. Effects of Cu and Ni addition on microstructure, thermal behavior, wettability and corrosion resistance of Sn–9Zn solders were investigated. The experimental result showed that microstructure of the Sn–9Zn was composed of β–Sn and Zn–rich phases. Addition of Cu to the Sn–9Zn solders, Cu6Sn5 and Cu5Zn8 IMCs were observed. While addition of Ni to the Sn–9Zn solders, Ni3Sn4 and Ni5Zn21 IMCs were observed. It was also found that, amount of those IMCs obviously increased with increasing of Cu and Ni contents. The results obtained from thermal analysis showed that melting temperature of the Sn–9Zn solder was 199.6°C. While melting temperatures of the Sn–9Zn–1.0Cu and Sn–9Zn–1.0Ni solders were 199.9°C and 204.2°C, respectively. The Cu and Ni contents had little effect on both spread rate and wetting angle of the Sn–9Zn–xCu and Sn–9Zn–xNi solders. However, increasing of Cu and Ni contents significantly increased the corrosion potentials of the Sn–9Zn–xCu and Sn–9Zn–xNi solders.
Abstract: Aluminum alloy is well-known as a sacrificial anode material which can provide higher-electrochemical capacities than other types of sacrificial anodes. Al-Zn-In-Si alloys are primarily used to protect steel structures for marine application. The electrochemical behaviors of aluminum sacrificial anodes were investigated using experimental set-up conformed to NACE standard TM0190-2012. The electrochemical capacity of Al-5 wt% Zn-0.015 wt% In-0.1 wt% Si alloy is about 2,600 Ah/kg. The results indicate that the electrochemical capacities of Al-Zn-In-Si based alloys are improved by addition of Ti. Al-5 wt% Zn-0.015 wt% In-0.1 wt% Si alloy with Ti addition can provide higher-electrochemical capacities up to 2,747 Ah/kg.
Abstract: High Strength Low Alloy (HSLA) steels or microalloyed steels are developed in order toimprove the strength and toughness compared with conventional carbon steels. During the reheatingprocess at 1250-1300 °C for a few hours, the furnace consumes large amount of energy, and the slabsuffers from thick oxide scale. This results in significant mass loss. The long reheating time ensuresmaximum dissolution of the microalloying elements, which must be kept to precipitate duringcooling at the end of the hot rolling process. To minimise the reheating time and save the energyconsumption, this research studied the dissolution kinetics of vanadium in HSLA steel. Vanadium isa main microalloying element added to provide higher strength mainly by precipitation hardening. Itis supposed to be dissolved readily according to the solubility limit. The samples were reheated to1200 °C and 1250 °C for 0, 10, 30, and 60 s. After that the fraction of vanadium dissolved in the solidsolution and the remaining undissolved phases of VC, CN, and V(C,N) were measured bysynchrotron XAS. As soon as the sample reaches as low temperature as 1200 °C, a large atomicfraction of 0.878 of vanadium can be dissolved in the solid solution.
Abstract: The tensile test has been developed to assess scale adhesion of hot-rolled steel. The tensile testing machine was equipped with the CCD camera to follow the failure of scale during straining. The hot-rolled steel with different silicon content was used to investigate the scale adhesion behavior. The result is shown the mechanical adhesion energy of scale formed on the hot-rolled steel with higher Si contain was 115 J.m-2, higher than the hot-rolled steel with lower Si contain which was 56 J.m-2. This might be due to the presence of oxide containing Si at interface which promoted adhesion, implying that longer time for descaling would be required.
Abstract: This research aimed to investigate the microstructure and hardness properties of hardfacing surface on SCM440 alloy steel by using metal active gas and flux cored arc welding processes. Due to the difficulty of welding the high strength steel, the changes in base metals’ microstructures were found after welding. Preheating the specimens at 350°C and post weld heat treatment the specimens at 550°C were performed for 1 hour, to reduce the residual stresses and avoid the undesired formation of microstructures. The weld metals’ microstructures that were found from both welding processes are acicular ferrite, polygonal ferrite and side plate ferrite. The hardness value of weld metal resulted from flux cored arc welding process is higher than that of the metal active gas welding process. Each welding process produced different quantities of weld metals’ microstructures, causing the difference in hardness values. The data will be used for investigating and improving parameters of shaft repairing, in order to use it more effectively.
Abstract: In hot forging process, the common failure modes of forging die are wear, fatigue fracture and plastic deformation. Normally die wear is occurred the most frequently and it influents directly to shape, dimension and surface quality of product. For this research, the hot forging process of idle gear was studied to focus on die wear. This product is forged in three steps. There are preform step, rougher step and finisher step. Height of preform shape in preform step was a parameter to study effect on die wear. Archard’s wear model in finite element modeling was used to predict die wear. The finite element modeling was verified by real hot forging process for reliable model and then it was used to determine the optimum preform height to reduce die wear. Finally the result showed that the maximum wear depth on the forging die was reduced 41.2% from original industry process.
Abstract: Electric Upsetting Process (EUP) is a process combining the forming process with the electric heating system. It is commonly used to manufacture a preform of a bar with high upsetting ratio, such as an axial shaft. The reliable forming process requires the understanding the effect of process and electrical parameters. Currently, the designer develops this process by trail-and-error. To successfully develop this process, the relationship between the electric heating and the forming parameters needs to be clearly understood. In this study, three parameters are investigated; namely anvil speed, upsetting load and heating voltage. Finite Element Modeling (FEM) is used as a tool for evaluating these parameters. The FEM results indicate that those parameters play significant roles on the material flow as well as the heating characteristics (i.e. temperature distributions and heat flow).
Abstract: This paper presents a new method to calculate the feed scallop height for a toroidal cutter during a free-form surface machining in multi-axis milling. The proposed method is an extended analytical boundary method to define the cut geometry during a free-form surface milling. The algorithm was developed by taken into account the existence of inclination angle. The proposed method was successfully implemented to calculate the scallop for two model parts with different surface profiles. The accuracy was verified by comparing the scallop height calculated using the proposed method with those measured using Siemens-NX. The results proved that the proposed method was accurate