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The fracture resistance and tensile properties of Y2O3 oxide dispersion strengthened steel containing 9 wt% Cr (9Cr-ODS) were measured at various temperatures up to 700oC. The fracture characteristics were compared with those of commercial E911 ferritic/martensitic steel. The strength of 9Cr-ODS was at least 30% higher than that of E911 steel at the test temperatures below 500oC. The strength difference between the two materials was almost diminished at 700oC. 9Cr-ODS showed cleavage fracture behavior at room temperature and unstable crack growth behaviors at 300oC and 500oC. The J-R fracture resistance of 9Cr-ODS was much lower than that of E911 steel at all temperatures. It was deduced that the coarse Cr2O3 particles that were formed during the alloying process provided the crack initiation sites of cleavage fracture in 9Cr-ODS.

keyword : nanostructured materials, mechanical alloying, fracture, mechanical properties, strength, microstructure, toughness

This study aims to analyze the formability property of surface texturing processed automotive steel sheet for improving the sheet forming property. In the paper, the effect of cavities fabricated using the laser surface texturing technique on automotive high strength steel sheets was studied. The frictional behavior of the sheet drawing is a function of interface parameters such as sheet surface roughness, holding force, contact pressure, etc. For these reasons, automotive steel researchers want to optimize the surface topography of automotive steel sheets in order to enhance the formability. Therefore, this study presents the behavior of deformation of a laser surface texturing steel sheet by considering the frictional operation during the deep drawing process.

keyword : metals, drawing, mechanical properties, computer simulition, Laser surface texturing

Forged and flat-bar rolled STD11 tool steel shows anisotropic dimensional change during heat treatment. The dimensional change in the rolling direction is larger than that in the transverse direction. The cause of the anisotropic dimensional change is that the steel is anisotropic in composition, microstructure and other properties. The decrease of anisotropic distortion in tool steel is important for making better precision cold working dies. In this study, the effect of ingot weight and hot rolling reduction ratio on the anisotropic dimensional change of STD11 during heat treatment has been studied. Dimensional change was evaluated by simulating a real heat treatment process, including gas quenching and tempering. Experimental results showed that all the rolled flat-bar products had anisotropic distortion to some degree, but the anisotropic distortion was reduced as hot rolling ratio increased. Ingot weight had a little effect on anisotropic distortion. Microstructural observation showed that the anisotropic dimensional change of STD11 tool steel was closely related to the amount, shape and distribution of coarse carbides.

keyword : anisotropy, STD11, tool steel, heat treatment

The color of a natural diamond that contains nitrogen impurities can be enhanced by a high pressure high temperature (HPHT) treatment. Type IaAB diamond samples containing nitrogen impurities were executed by HPHT process of 5.6 Gpa, 10 min by varying the annealing temperature at 1600, 1650, and 1700℃. Property characterization was carried out using an optical microscope, FT-IR spectrometer, lowtemperature PL spectrometer, and micro Raman spectrometer. By observing optical micrographs, it can be seen that diamond sample began to alter its color to vivid yellow at 1700℃. In the FT-IR spectrum, there were no Type changes of the diamond samples. However, amber centers leading to brown colors lessened after 1700℃ annealing. In the PL spectrum, all the H4 centers became extinct, while there were no changes of yellow color center H3 before or after treatment. In the Raman spectrum, no graphite spots were detected. Consequently, diamond color enhancement can be done by higher than 1700℃ HPHT annealing at 5.6 GPa- 10 min.

keyword : diamond, HPHT, optical properties, raman spectroscopy, PL

Ball-milled Ni-Al powder compacts have been synthesized by the heat of molten cast iron and have been coated on cast iron. The effects of the ball-milling time on the microstructure of the intermetallic coatings have been investigated. The experimental results showed that the ball-milled Ni-Al powder compacts were completely reacted and were successfully coated on the cast iron without re-melting the substrate. Densification of the coating layers was enhanced by increasing the ball-milling time. This might be attributed to the fact that the heat released during the intermetallic reaction was dispersed over a prolonged reaction time by the ball-milling of the elemental powders.

keyword : intermetallics, coating, microstructure, ball-milling, thermal analysis

Titanium has good deformability, high hardness, high biocompatibility, excellent corrosion resistance and low density. Due to these attractive properties, it has been used in many industrial applications. Dense nanostructured Ti was sintered from mechanically activated Ti and TiH2 powders by high frequency induction heating under pressure of 80 MPa. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. TiH2 powder was decomposed to Ti during sintering. The hardness of Ti increased and the average grain size of Ti decreased with increasing milling time. The average grain sizes of Ti samples sintered from Ti and TiH2 powder milled for 5 hrs were about 26 nm, 44 nm, respectively. The hardness of Ti sintered from Ti and TiH2 powder milled for 5 h was 504 kg/mm2 and 567 kg/mm2, respectively.

keyword : sintering, nanomaterials, mechanical properties, Ti, high frequency induction heating

Nanopowders of TiCo were synthesized from Ti and Co by high energy ball milling. Highly dense nanostructured TiCo compounds were consolidated at low temperature by pulsed current activated sintering within 3 minutes from the mechanical synthesis of the powders (TiCo) and horizontal milled Ti+Co powders under 100 Mpa pressure. This process allows very quick densification to near theoretical density and prohibits grain growth in nanostructured materials. The grain sizes of the TiCo compounds were calculated. Finally, the average hardness values of the nanostructured TiCo compounds were investigated.

keyword : TiCo, nanostructure, sintering, mechanical properties

Thermodynamics of carbon in manganese alloy melts is important in manufacturing low carbon ferromanganese and silico-manganese alloys. In order to predict the carbon solubility in liquid Mn-Si-Fe-Csat alloys as a function of melt composition and temperature, thermodynamic interactions among carbon, silicon and iron in carbon saturated liquid manganese should be known. In the present study, the effects of silicon and iron on the carbon solubility in Mn-Si, Mn-Fe and Mn-Si-Fe melts were measured in the temperature range from 1673 to 1773 K. The carbon solubility decreases significantly as silicon and iron contents increase in liquid manganese alloy. The interaction parameters among carbon, silicon and iron in carbon saturated liquid manganese were determined from the carbon solubility data and the Lupis` relation for the interaction coefficient at constant activity.

keyword : manganese alloys, carbon solubility, thermodynamic properties, activity coefficient, interaction parameter

Hydrogen-delayed fracture (HDF) was analyzed from the deposited weld metals of 600-MPa and 800-MPa flux-cored arc (FCA) welding wires, and then from the diffusible hydrogen behavior of the weld zone. Two types of deposited weld metal, that is, rutile weld metal and alkali weld metal, were used for each strength level. Constant loading test (CLT) and thermal desorption spectrometry (TDS) analysis were conducted on the hydrogen pre-charged specimens electrochemically for 72 h. The effects of microstructures such as acicular ferrite, grain-boundary ferrite, and low-temperature-transformation phase on the time-tofailure and amount of diffusible hydrogen were analyzed. The fracture time for hydrogen-purged specimens in the constant loading tests decreased as the grain size of acicular ferrite decreased. The major trapping site for diffusible hydrogen was the grain boundary, as determined by calculating the activation energies for hydrogen detrapping. As the strength was increased and alkali weld metal was used, the resistance to HDF decreased.

keyword : ferrous alloys, welding, microstructure, thermal desorption spectrometry, hydrogen delayed fracture

Studying the long-range ordering of nanopores on the anodic aluminum oxide (AAO) membranes under a hard anodization (HA) approach is crucial in producing well-aligned nanopores on the AAO membranes. Electro-polishing in a mixture of ethanol and perchloric acid for 5 min removed marks formed by rolling and produced flat surfaces on aluminum substrates. The AAO was formed by the first HA process, providing seeds for the subsequent production of uniform AAO nanopores. The second HA process carried out on the seeds produced well-aligned, uniform AAO nanopores. The AAO nanopores, varying in size and shape, were observed with voltages applied for HA. This study provides a route for controlling the size and shape of AAO nanopores by changing the applied voltages.

keyword : nanostructured materials, anodization, microstructure, image analysis, anodic aluminum oxide