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Morphology and microstructure of Sr aluminate:Eu/Dy phosphor storage particles fabricated by a plasma spray method and a usual sintering method have been investigated by means of X-ray diffraction, Xray energy dispersive spectroscopy, and scanning and transmission electron microscopy. It has been confirmed that the phases and the morphologies of Sr aluminate:Eu/Dy phosphor storage particles were quite different in accordance with fabrication methods of phosphor storage particles. The morphology of phosphor storage particles was spherical in the plasma spray method, but that of phosphor storage particles was multi-plane type in the sintering method. Large amounts of Sr(Dy·EU)2O4 particles, which formed probably during sintering at high temperature and reduce the properties of phosphor storage material owing to the decrease of Eu/Dy solubility in the matrix phase, were distributed within phosphor storage particles prepared by the sintering method. On the contrary, only a few Sr(Dy·EU)2O4 particles were observed within phosphor storage particles prepared by the plasma spray method, leading to the increase of the properties of phosphor storage material. This is probably due to the fact that the nucleation of Sr(Dy·Eu)2O4 particles are suppressed by the rapid quenching from high temperature into room temperature. Crystal defects such as twins were observed within α-SrAl2O4 phosphor storage particles, resulting in the change of crystal fields.

keyword : Strontium aluminate, Storage phosphor material, Plasma spray method, Morphology; Microstructure

This study is concerned with the effects of V and Mo on tensile and Charpy impact properties of API X70 linepipe steels. Twelve kinds of steel specimens were fabricated by varying V and Mo additions and hot-rolling conditions. The addition of V and Mo promoted to form acicular ferrite, bainitic ferrite, and martensite-austenite constituents, resulting in an increase in tensile strength. The results of CVN impact tests show that the microstructures composed of acicular ferrites and fine polygonal have high upper shelf energy and low energy transition temperature. According to EBSD analysis data, the effective grain size of acicular ferrite was determined by crystallographic packets composed of a few fine grains having similar orientations. Thus, the decreased ETT in the specimens with acicular ferrite structure could be explained by the decrease in the overall effective grain size due to the presence of acicular ferrite having smaller effective grain size.

keyword : API X70 Linepipe steel, Charpy impact test, Upper shelfenergy, Energy transition temperature, Acicular ferrite

The present study aims at analyzing fracture toughness in the transition temperature region of API X70 linepipe steels according to ASTM E1921 standard test method. Three kinds of steels were fabricated by varying finish cooling temperatures after rolling in the two-phase region, and their microstructures, tensile and Charpy impact properties, and fracture toughness were examined. Elastic-plastic cleavage fracture toughness, Kjc was determined by 3-point bend tests, using precracked Charpy V-notch (PCVN) specimens, and then the measured Kjc values were interpreted by the 3-parameter Weibull distribution. Relationship between reference temperature and plane strain fracture toughness in the transition region was discussed on the basis of the cleavage fracture behavior. The steel cooled at 500℃ showed the highest plane strain fracture toughness and the lowest reference temperature because it contained a small amount of bainite instead of martensite and had a small effective grain size.

keyword : API X70 Linepipe steel, ASTM E1921 standard test method, Elastic-plastic cleavage fracture toughness, Weibull distribution

The present study is concerned with the improvement of hardness and wear resistance in (Cr3C2,CrB)/carbon steel surface composites fabricated by high-energy electron beam irradiation. Two kinds of powder mixtures, i.e., 50Cr3C2-50STS304, 50CrB-50STS304 (wt.%), were placed on a plain carbon steel substrate, which was then irradiated with electron beam without using flux. The surface composite layer of 1.0~1.3 mm in thickness was successfully formed without defects, and contained a large amount (up to 58 vol.%) of Cr7C3 or Cr1.65Fe0.35B0.9 in the austenite or martensite matrix. The hardness and wear resistance of the surface composites layer were directly influenced by hard carbides or borides, and thus were about 2~3 times greater than those of the steel substrate. Particularly in the surface composite fabricated with CrB powders, selective wear of the matrix was considerably reduced as a number of fine borides were homogeneously distributed in the hard martensite matrix, thereby leading to the excellent wear resistance. These findings suggested that the high-energy electron beam irradiation was useful for the development of surface composites with improved hardness and wear resistance.

keyword : Surface composite, High-energy electron beam irradiation, Plain carbon steel, Wear Resistance, Self-fluxing

A numerical and experimental study on the coating process was executed in order to know how to tailor process conditions to produce fully-amorphic metal coating by plasma spraying. As a calculation result, the cooling rate during deposition stage of plasma spraying after collision of in-flight molten powders onto substrate was higher by 5000 times than that of gas atomization. For this reason, it could be understood that nearly full amorphous coatings of Fe based alloys were formed via plasma spraying even though when partially crystallized powders were used. However crystallization of plasma-sprayed Ni-Zr alloy in air surrounding was unavoidable, which has been coated using fully-amorphic powder. This is because amorphization of Ni-Zr alloy is highly dependent on oxygen contents of process surrounding, that was certificated by producing nearly fully-amorphous coating by reducing oxygen contents in surrounding during plasma spraying.

keyword : Plasma spray coating Numerical analysis, Smorphous metallic coating, Gas atomization, Controlled atmosphere

This work focused on the monitoring of open circuit potential(ocp), cathodic protection potential, and potential shift and the effects of salt and cathodic protection on rebar corrosion in concrete. Open circuit potential of salt added sand concrete was more base than that of river sand concrete, and the ocp of both samples is gradually increased to noble direction but the former was still base. Salt water exposure to concrete made the ocp more base and resulted in severe rebar corrosion. On the base of destruction of concrete samples, rebar in salt added sand concrete was severely corroded than that of river sand concrete, and salt water exposure facilitated the corrosion of rebar. However, the rebar corrosion in concrete by salt and salt water was inhibited using cathodic protection, and the protection situation could be monitored by the measurements of protection potential and potential shift.

keyword : Rebar corrosion, Salt, Cathodic protection, Concrete, Anode

Flow accelerated corrosion behavior of carbon steel piping material in the temperature range of 150℃ to 270℃ was studied using high temperature rotating cylinder electrode (HTRCE). Electrochemical corrosion potential (ECP) and current density were measured as a function of temperature and rotating speed using potentiodynamic method. ECP values dropped at the rate of -1.51 mV/℃, which is attributed to the formation of magnetite on steel surface. The ECP shifted upward in all temperature ranges with increasing rotating speed of the RCE. This shift may be attributed to the diffusion enhancement of oxidizing agent. From the velocity exponent of the cathodic half-cell current density on the steel surface, it was evident that a mass transfer process first dominated the corrosion reaction at 150℃, and then an activation process controlled the corrosion kinetics with increasing temperature.

keyword : Flow Accelerated Corrosion, High Temperature Rotating Cylinder Electrode, Carbon Steel, High Temperature Corrosion

Effects of the photocurrent and photocatalytic activity of the plasma sprayed TiO2 coatings by rapid cooling heat treatment were examined. Thermal deformation of the plasma sprayed plastic polymer substrate was investigated, and the effect of additives for prevent thermal deformation was examined. Fine 20% BiSO4 additive particles, acting as inhibition of the polymer`s movement, were prevent thermal deformation of plastic polymer substrate during rapid cooling after plasma spray. Adhesion area was increased to the partial melt of plastic polymer by plasma spray TiO2 particles. The maximum phocurrent of plasma sprayed TiO2 coatings by rapid cooling was about 20 mA/cm2 and the result of photocatalytic experiments were showed that bacterial ability(elimination rate) was 99.8% by rapid cooling after plasma spray. This phenomenon was caused to formation of n-type semiconductor in large quantifies TiO2 by rapid cooling after plasma spray.

keyword : Plasma Spray, Photocatalytic, N-type semiconductor TiO2, Rapid cooling heat treatment

The mechanism of electrolytic pickling in a neutral sodium sulfate solution as well as the correlation between oxide scale and the pickling has not been clearly understood in spite of the vast use of the pickling method. Hence, AES, thin film x-ray diffraction (TFXD) and calculation of phase equilibria for scale analysis, and the electrochemical tests such as galvanostatic test and potentiodynamic test for electrochemical analysis were employed finally to propose the mechanisms of pickling two types of stainless steels(type 430 and type 304).The electrolytic pickling of the stainless steels in a neutral sulfate solution begins with the preferential dissolution of the oxide consisting chromium and manganese placed in the outer layer of the scale. However, the differences in the characteristics of oxide scale between type 430 and type 304 such as thickness and constitution make next pickling step depend on type of stainless steel. Mter the preferential dissolution, the residual scale on type 430 being as thin as 30 nm and mainly consisting of iron oxide is proposed to separate by accumulation of vacancy at the interface between the scale and the matrix, according to point defect model and surface charge approach. On the other hand, the residual scale on type 304 being as thin as 600 nm and consisting of iron and chromium oxide and silicon oxide is proposed to be separate by the dissolution of chromium metal and iron metal at the matrix/scale interface.

keyword : Oxide scale, Thin film X-ray diffraction, Selective oxidation, Galvanostatic test, Auger electron spectroscopy, Surface charge approach, Point defect model