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In order to study the effect of microstructural change on the tensile properties of discontinuous precipitated Al-Zn binary alloy, four different Al-Zn alloys(25, 30, 35, 45 wt% Zn) were aged at 160 ℃ for different aging times(0, 5, 15, 30, 60, 120, 360 min) after being solution treated at 400 ℃, and successively drawn at room and cryogenic temperatures(-197 ℃). Discontinuous precipitation was formed during aging in the Al matrix(which contained more than 30 wt% Zn) in Al alloys containing more than 30 wt% Zn. The tensile strength of continuous precipitated Al-35Zn alloy decreased with increasing drawing ratio, however, the tensile strength of discontinuous precipitated Al-35Zn alloy increased with further drawing. The strength and ductility combination, 350 MPa-36% was achieved by drawning discontinuous precipitated Al-Zn alloy at room temperature. The discontinuous precipitated Al-Zn alloy drawn at cryogenic temperature showed a higher value of tensile strength, over 500 MPa, although ductility decreased. †(Received July 22, 2016; Accepted August 16, 2016)

keyword : Al-Zn alloys, continuous precipitation, mechanical property, microstructure, discontinuous precipitation

Reverse cyclic loading introduces alternatinf tensile and compressive loads to a structure. Several researchers have reported that a reverse cyclic load decreases the fracture resistance curve of carbon steel. In this paper, the fracture toughness of SA312 TP304 stainless steel, which is a nuclear piping material, was investigated under a reverse cyclic load with various incremental plastic displacements. From the test results, the incremental plastic displacement effect on the fracture toughness curves was analyzed. The test results were also normalized and compared with SA516 Gr.70. It was found that the fracture toughness curves were degraded with small incremental displacement regardless of the kind of material. The normalized fracture toughness data showed that the small incremental plastic displacement induces a similar trend in lower fracture toughness in both materials. It seemed that the normalized fracture toughness curves are limited by the elongation of the materials. †(Received May 04, 2016; Accepted August 30, 2016)

keyword : seismic load, reverse cyclic load, fracture resistance curve, fracture toughness

Fe-(20, 45 wt%) Gd intermetallics were vacuum arc melted as the mother alloy of a neutron shielding and absorbing material. The structure of the cast Fe-20 wt% Gd intermetallics had primary dendrites with a short width of about 2 μm, which became coarse with increasing Gd content. The final compositions of the Fe-20 wt% Gd and Fe-45 wt% Gd intermetallics determined by Rietveld refinement were mainly Fe3Gd with 26.6 at% Fe2Gd, and Fe3Gd with various intermetallics like 13.9 at% Fe2Gd, 7.3 at% Fe9Gd and 3.9 at% Fe17Gd2, respectively. The micro-hardnesses, yield strength, ultimate compressive strength and elongation of the Fe-20 wt% Gd intermetallics were 629±12 Hv, 753 MPa, 785 MPa and 4%, respectively, and those of the Fe-45 wt% Gd intermetallics were 741±13 Hv, 772 MPa, 823 MPa and 3%. Passivity was not present in artificial sea water at room temperature. The corrosion potentials and the corrosion rates of the Fe-20 wt% Gd and Fe-45 wt% Gd intermetallics were -624 mVSHE, 2.771 mA/cm2, and -804 mVSHE, 3.397 mA/cm2, respectively. The corroded surface of the Fe-Gd intermetallics contained corrosion products like gadolinium with iron, which detached to leave a trail of pits. †(Received April 11, 2016; Accepted August 29, 2016)

keyword : gadolinium, gd intermetallics, rietveld refinement, mechanical properties, corrosion behaviors

The aim of this study is to establish an optimized hot-press sintering condition for aluminum matrix composites (AMCs) by analyzing their sintered microstructure and mechanical properties. The fabricated AMCs in this study consisted of a blend of commercial Ecka Alumix 431 powder, and Al-Si/SiCp powder manufactured by gas atomizer (Al-Si/SiCp). The Al-Si/SiCp powder was added to the Alumix 431 powder as a binder. The blended powder was hot-pressed and sintered and its properties were analyzed based on three variables: the blending ratio of each powder, sintering time and sintering temperature. The MgZn2 phases in the Alumix 431 powder were finely and homogeneously distributed when the sintering temperature was increased. The liquid phase of the Al-Si alloy facilitated densification of the Alumix 431 particles and promoted a reduction in pores in the sintered body. Dispersion of the MgZn2 phases, degree of porosity and densification of the fabricated AMCs affected the ultimate tensile strength (UTS) of the sintered body at room temperature (RT). The highest UTS of the fabricated AMCs was 242MPa at RT. The optimum sintering conditions were: a mixing ratio of Al-Si/SiCp to Alumix 431 powders of 5 to 95 wt%, a sintering time of 30 min and a sintering temperature of 610 ℃. Wear behavior of the specimens prepared with the optimized sintering conditions included stick-slip, abrasive, adhesive and delamination phenomena for each test condition, under correlated vertical load and linear speed. †(Received April 25, 2016; Accepted August 16, 2016)

keyword : composites, sintering, mechanical properties, wear, scanning electron microscopy (SEM)

Despite of the many attractive properties of TiO2, its low fracture toughness limits many industrial applications. To improve its fracture toughness, the approach commonly utilized has been the addition of a second phase, to form composites, and to make nanostructured composites. In this regard, highly dense nanostructured TiO2 and TiO2-graphene composites were consolidated within one min at 1000 ℃. The effect of graphene on the microstructure and the mechanical properties (hardness and fracture toughness) of TiO2-graphene composites was investigated. †(Received July 18, 2016; Accepted August 18, 2016)

keyword : sintering, composite materials, nanomaterials, mechanical properties

The effect of post-bond heat treatment (PBHT) on diffusion-bonded polycrystalline Ni-base alloy Hastelloy X (Ni-22Cr-18Fe-8Mo) was evaluated in this study. Diffusion bonding was conducted under a compressive pressure of 14 MPa in the temperature range of 1100-1200 ℃. While (Cr,Mo)-rich and (Mo,Si)-rich precipitates were developed along the interface at 1100 ℃, the precipitates were dissolved and grain boundary migration across the interface occurred above 1150 ℃. As the dissolution of precipitates is related to the temperature rather than compressive pressure, a modified diffusion bonding condition (1120 ℃/10 MPa) was applied. Brittle fracture with low tensile ductility was observed at the testing temperature of 700 ℃, but substantial recovery of ductility was achieved up to a testing temperature of 900 ℃ through PBHT (1180 ℃/1 h). The reduction of discontinuity at the interface was found to bring about the ductile behavior at high temperature. †(Received April 18, 2016; Accepted August 23, 2016)

keyword : metals, diffusion bonding, grain boundary, tensile test, hastelloy X

The deformation and failure behaviors of dissimilar metal joints between SS400 steel and STS316L steel were investigated. The dissimilar metal joints were fabricated using the tungsten inert gas (TIG) welding process with STS309 steel as a filler metal. The microstructures of the dissimilar metal joints were investigated using an optical microscope and EBSD technique. The mechanical properties of the base metal (BM), heat affected zone (HAZ) and weld metal (WM) were measured using a micro-hardness and micro-tension tester combined with the digital image correlation (DIC) technique. The HAZ of the STS316L steel exhibited the highest micro-hardness value, and yield/tensile strengths, while the BM of the SS440 steel exhibited the lowest micro-hardness value and yield /tensile strengths. The grain size refinement in the HAZ of SS400 steel induced an enhancement of micro-hardness value and yield/tensile strengths compared to the BM of the SS400 steel. The WM, which consists of primary δ-ferrite and a matrix of austenite phase, exhibited relatively a high micro-hardness value, yield /tensile strengths and elongation compared to the BM and HAZ of the SS400 steel. †(Received May 31, 2016; Accepted September 7, 2016)

keyword : metals, arc welding, fracture, electron backscattering diffraction(EBSD), digital image correlation(DIC)

Investment casting for the thin (4 mm thick) rectangular tube (40 mm wide, 80 mm high and 200 mm long) was carried out numerically and experimentally for Alloy 738, which is a precipitation-hardened Ni-base superalloy. Two types of rectangular tubes, one with a regular array (10 mm by 10 mm square array) of protruded rods (3 mm in diameter and 3mm in height) embedded on the outer surface and the other with just smooth surface, were investment-cast at the same time through the side feeding mold design. The investment casting simulation predicted the presence of cavities, particularly in the area away from the gate for both types of rectangular tubes. In particular, for the rectangular tube with embedded protruded rods cavities were found mainly in the areas between the protruded rods. This simulation result was qualitatively consistent with the experimental observation from the X-ray analysis. Also, both prediction and experiment showed that the dimensional shrinkage (particularly in the longitudinal direction) of the investment-cast rectangular tube is reduced by having protruded rods embedded on the outer surface. Additional numerical attempts were made to check how the amount of cavities and dimensional shrinkage change by varying the preheating temperature and the thickness of the mold. The results predicted that the amount of cavities and the dimensional shrinkage are significantly reduced by increasing the preheating temperature of the mold by 200 ℃. However, an increase in mold thickness from 10 mm to 12 mm showed almost no difference in cavity population and a slight decrease in dimensional shrinkage. †(Received September 7, 2016; Accepted November 12, 2016)

keyword : Alloy 738, Ni-base superalloy, investment casting, shrinkage, cavity, simulation

The missing hole phenomenon in a wafer pattern is a critical issue in extreme ultraviolet lithography. It occurs randomly, even when the process conditions are consistent. The main reason for this phenomenon is thought to be the photon shot noise effect, which is a random reaction between photons and photoresist particles. We speculate that side lobe intensity can be another reason, since the missing hole is affected by the light distribution of the main hole pattern. To confirm the effect of side lobe intensity and photon shot noise on the missing hole phenomenon, we used an attenuated phase shift mask (PSM), whose reflectivity can be changed without varying the total absorber stack thickness. The results show that the photon shot noise effect and the side lobe intensity are both affected by the reflectivity of the PSM and are the critical factors for the missing holes. (Received August 24, 2016; Accepted August 25, 2016)

keyword : EUV phase shift mask, lithography simulation, missing hole, photon shot noise effect, side lobe intensity

As with any solvent, stabilizing a multivalent element at a given oxidation level in the glass depends on the thermodynamic conditions. The effects of temperature in the oxidation-reduction equilibrium have been previously noted with higher temperatures being conductive to reduced states. 30Ce2O-70P2O5 binary system glasses were prepared. The effects of melting temperature and time on Ce4+ and Ce3+ ion concentration were studied with X-ray photoelectron spectroscopy (XPS). Different melting conditions were investigated at temperatures ranging from 1300 to 1500 ℃ for 60 min, and 1400 ℃ for from 30 min to 90 min. Changes in the catalytic properties of the glasses as a function of Ce4+ and Ce3+ ion concentration were confirmed based on the changes in decomposition starting temperatures using thermogravimetric analysis (TGA). The main changes in the valence states in relation to melting conditions are discussed in terms of the catalytic properties on cerium phosphate glasses. (Received June 10, 2016; Accepted August 23, 2016)

keyword : glasses, melting condition, Ce oxidation state, catalytic property