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In this study, the effect of α and β those stabilizers on the microstructure and phase transformation of cast Ti-6wt%Al-4wt%V alloy at various solution treatment temperatures was investigated. The dependence of the transformation behavior of the β phase during the solution treatment and its dependence was determined by the partitioning of α and β stabilizing elements. Solution treatments were conducted at 850 ~ 1050 ℃ for 0.5 h and, followed by water quenching. Aging treatments at 550 ℃ for 24 h were then performed. The α` martensite was transformed from the β phase when the concentration of vanadium in the β phase was less than 4.27 at%, while the metastable β phase did not transform to α` martensite when the concentration of vanadium in the β phase was over 5.14 at%. (Received May 24, 2016; Accepted September 8, 2016)

keyword : metals, annealing, microstructure, hardness test, stabilizer

A composite having 60 vol% of TiC particles was successfully fabricated by the infiltration of molten SKD11 tool steel into a TiC preform. The density of this composite was achieved to be 25% lighter than conventional steels. The penetration of the liquid metal reached geometrically complex regions without any interfacial flaws. The interface between the TiC and steel was semi-coherent nature and had a specific orientation relationship, i.e., [111]_α-Fe//[001]_TiC, (112)_α-Fe//(220) _TiCㆍTensile tests were conducted at 25, 700, 750 and 800 ℃. The composite exhibited the enhanced strength compared with the unreinforced SKD11, and its reinforcement was most effective at 800 ℃. The TiC particles were fractured preferentially along the {100} cleavage plane, which was responsible for the main fracture of the composite. However, at and above 750 ℃ debonding of the TiC interface began to occur. The tensile fracture and strengthening mechanisms are discussed in terms of the TiC/ matrix interface and dislocations. (Received June 10, 2016; Accepted August 30, 2016)

keyword : composites, infiltration, interfaces, transmission electron microscopy (TEM), tensile test

Intermetallic compounds (IMCs) developed on the interface between a solder alloy and its bonding pads are an important factor in the failure of electronic circuits. In this study, the mechanical behaviors of the IMCs formed in the Cu-Ni-Sn ternary alloy system are investigated. Presumably, Ni can act as a diffusion barrier to Cu and Sn to form the IMCs. Detailed analysis of the microstructure is conducted using an electron probe micro-analyzer (EPMA). The addition of Ni softened the IMCs, which is determined based on the fracture toughness increasing (from 0.71 to 1.55 MPa√m) with the Ni layer thickness. However, above a critical amount of Ni involved in the Cu-Sn IMCs, the softening effect is diminished, and this could result from the segregation of Ni inside the IMCs. Therefore, the optimized condition must be determined in order to obtain a positive Ni effect on enhancing the reliability of the electronic circuits. (Received July 22, 2016; Accepted December 13, 2016)

keyword : Pb-free solder; Intermetallic compound; mechanical properties, nanoindentation

High-purity and good sinterable mullite powder (3Al₂O₃·2SiO₂) was synthesized by a sol-gel process to prepare a high-purity mullite crucible. The densified mullite crucible was fabricated by slip casting with the powder followed by sintering at 1600 ℃. Solar salt was put into the mullite crucible and then fired at the temperature of 1000 ℃ and 1250 ℃ with 4~24 h holding time. The inside surface of the crucible which was in contacted with the melted salt was analyzed using XRD, SEM and EDS. Corrosion of the crucible by the melted solar salt was insignificant. The reacted surface area displayed mullite, spinel and forsterite crystal phases, with a very thin reactant layer of 10~20 μm. The EDAX result of the very thin surface layer showed a relatively higher Na and Mg contents in the sample heat-treated at 1250 ℃ for 4 h compared to the sample heat-treated at 1000 ℃ for 24 h. EDS mapping showed that the reactant layer are mainly consisted of MgO, SiO₂ and Al₂O₃. From these results, it can be speculated that mullite is attacked by the Mg component in the solar salt, rather than Na and S. Finally, the very thin reactant layer of the mullite surface at high temperature means that a pure mullite crucible can be used as a commercial ceramic container for the firing of solar salt. (Received June 28, 2016; Accepted September 21, 2016)

keyword : mullite, sol-gel process, solar salt, reaction behavior, crystal phase

Despite of many attractive properties of TiN, the current concern about the TiN focuses on its low fracture toughness below the ductile-brittle transition temperature. To improve its mechanical properties, the approach generally utilized has been the addition of a second phase to form composites and to make nanostructured materials. In this respect, highly dense nanostructured TiN and TiN-graphene composites were obtained within two min at 1250 ℃. The grain size of TiN was reduced remarkably by the addition of graphene. The addition of graphene to TiN simultaneously improved the fracture toughness and hardness of TiN-graphene composite due to refinement of TiN and deterring crack propagation by graphene. This study demonstrates that the graphene can be an effective reinforcing agent for improved hardness and fracture toughness of TiN composites. (Received June 13, 2016; Accepted August 24, 2016)

keyword : sintering, composite materials, nanomaterials, mechanical properties

In case of the uranium (U) and zirconium (Zr) powders which have been utilized for the production of a metallic fuel in the various nuclear applications, the homogenous distribution of U powders in the Zr-U pellet has influenced significantly on the nuclear fuel performance. The inhomogeneity in a powder process was changed by various intricate factors, e.g. powder size, shape, distribution and so on. Particularly, the U inhomogeneity in the Zr-U pellets occurs by segregation derived from the great gaps of densities between Zr and U during compaction of the mixed powders. In this study, the relationship between powder size and homogeneity was investigated by using the different-sized U powders. The microstructure in Zr-U pellets reveals more homogeneity when the weight ration of Zr and U powders are close to 1. In addition, homogeneous pellets which were produced by fine U powders have higher density because the homogeneity affects the alloying reaction during sintering and the densification behavior of pore induced by powder size. (Received August 18, 2016; Accepted September 22, 2016)

keyword : powder size, powder processing, segregation, homogeneity, Zr-U

The effects of nitrogen content on the HAZ softening of Ti-containing high strength steels manufactured by accelerating cooling were investigated and interpreted in terms of the microstructures in the softening zone. Regardless of their content, all of the steels investigated showed a softened zone 9-10 mm wide. The minimum hardness in the zone, however, was different, with lower hardness in the higher nitrogen content steel. Microstructural observations of the steel showed that the amount of soft ferrite was increased in the zone with an increase of nitrogen content of the steel, suggesting that microstructural evolution in the HAZ is influenced by the nitrogen content. Measurements of TiN particles showed that the degree of particles coarsening in the HAZ was lower in the higher nitrogen content steel. Therefore, it is believed that finer TiN particles in the HAZ inhibit austenite grain growth more effectively, and lead to an accelerated ferrite transformation in higher nitrogen content steel, resulting in a higher amount of soft ferrite microstructure in the softened zone. (Received August 4, 2016; Accepted August 31, 2016)

keyword : alloys, welding, microstructure, hardness test, HAZ softening

The shadowing effect is one of the most urgent issues yet to be solved in high-volume manufacturing using extreme ultraviolet lithography (EUVL). Many studies have been conducted to mitigate the unexpected results caused by shadowing effects. The simplest way to mitigate the shadowing effect is to reduce the thickness of the absorber. Since nickel has high extinction coefficients in the EUV wavelengths, it is one of more promising absorber material candidates. A Ni based absorber exhibited imaging performance comparable to a Tantalum nitride absorber. However, the Ni-based absorber showed a dramatic reduction in horizontal-vertical critical dimension (H-V CD) bias. Therefore, limitations in fabricating a EUV mask can be mitigated by using the Ni based absorber. (Received August 24, 2016; Accepted August 26, 2016)

keyword : extreme ultraviolet lithography, semiconductor, thin film, optical properties, computer simulation

Computational fluid dynamic modeling of a continuous rheo-casting technology was conducted, consistent with the manufacturing of 3 mm-thin plates made of aluminum alloy A356. The A numerical simulation on of the stabilizing time of the material crystallization was carried out using the ANSYS FLUENT code. Solidification and melting models were simulated with heat transfer and solid-liquid phase transformation involving the latent heat of crystallization were simulated. The calculated temperature distribution and the evolution of cooling rate through the material were examined and used to clarify their influence on microstructure, and further investigated with hardness testing. The thickness of the mushy zone was determined for the steady conduction solution of the continuous rheo-casting process. (Received December 29, 2015; Accepted August 9, 2016)

keyword : semisolid processing, solidification, solid - liquid phase transition, computer simulation

Sn-doped ZnO (ZTO)/Ag/ZTO tri-layer films were deposited on glass substrates by radio frequency (RF) and direct current (DC) magnetron sputtering and then vacuum annealed at 100, 200 and 300 ℃ for 30 min with a proportions of H₂/N₂ gas flow of 6/6 sccm, to investigate the effects of annealing temperature on their electrical, and optical properties. After annealing at a temperature of 300 ℃, the optical transmittance in the visible wavelength region increased from 82.0 to 83.8% and their electrical resistivity decreased to as low as 5.38×10-⁵ Ω cm at an annealing temperature of 300 ℃. The figure of merit revealed that ZTO/Ag/ZTO films annealed at 300 ℃ have higher optical and electrical performance than the other TCO films prepared under different conditions. (Received June 7, 2016; Accepted August 30, 2016)

keyword : thin films, sputtering, optical properties, AFM, figure of merit.