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This paper presents a correlation study between microstructural parameters and fracture properties in heat affected zones of high-strength low alloy (HSLA) steels, i,e., a normalized steel and four TMCP steels. This allowed a comparison between microstructures such as grain size and the amount of martensite island. The influence of the local brittle zone (LBZ) on toughness was investigated by means of simulated HAZ tests as well as welded joint tests. The LBZ in the HAZ is the intercritically reheated coarse grained HAZ, whose impact energy values decrease monotonically with increasing the amount of martensite islands. Thus, the martensite island is the main metallurgical factor which contributes to local embrittlement in microstructures containing larger volume fractions of martensite island, thereby leading to the reduction of toughness.

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This study is concerned with a correlation between microstructure and plane strain fracture toughness in heat affected zones of high-strength low alloy (HSLA) steels, i.e., a normalized steel and a TMCP steel. The micromechanism of fracture processes involved in void and microcrack formation is identified and quantified. The fracture toughness results were also interpreted using simple fracture initiation models based on the basic assumption that crack initiates at a certain critical strain or stress developed over some microstructurally significant distance. The calculated K_IC values are found to scale roughly with the square root of the spacing of the stringer type martensite islands, confirming that martensite islands play an important role in reducing the toughness of the coarse grained HAZ. These foundings suggest that the LBZ in the HSLA steels studied can be explained quantitatively using different fracture models.

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Diamond film was deposited on silicon (100) wafer by R F plasma CVD method, using the methane and hydrogen gas mixture. The relationship between the diamond morphologies and the process variables was investigated with SEM, XRD, and Raman Spectroscopy. Gas mixture(CH₄,: 0.5∼2% of total gas volume) was fed at the flow rate of 50 sccm and the system pressure was in the range of 5∼20 torr. Substrate was heated by the inductive heating and the temperature was controlled by the setup of angle in the plasma. The RF power was 1 KW and its frequency was 13.56MHz. Diamond film having a clear crystal habit was deposited when the substrate temperature was about 900℃ and the methane concentration was low. With increasing methane concentration and lowering substrate temperature, films tend to contain amorphous phase as well as graphitic carbon phase.

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The chief roadblock to the application of titanium is melting and casting. During the last several years, a great deal of efforts has been made to improve the melting and casting processes of titanium. In this study, melting and casting of TiAl intermetallic compounds were conducted by the VIM(vacuum induction melting) process. In the VIM process, various crucibles were applied in order to investigate the condition of crucible reaction with titanium melt. The effects of A1 content on the microstructures and mechanical properties of TiAI intermetallic compounds were also studied. Melting crucible made from CaO + 5% CaF₂ was available for titanium melting. The volume fraction of lamellar structure in TiAl intermetallic compounds was found to be maximum at Ti-44at%A1 ingot.

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Low pressure gas plasma for TiN ion plating was analyzed by differentially pumped Plasma Mass Spectrometer. Identification of chemical species and the relative intensities of reactant gases were traced as varying discharge conditions;anode voltage, electron energy, electron density in order to obtain optimum discharge conditions. There exists optimal ionizing electron current which gives maximum substrate current. Ion current ratio of Ar^(+2) and Ar^+ showed a maximum at anode voltage 80V, electron energy 75eV, but N₂^+/N^+ increases with anode voltage, which gives maximum substrate current. Under those conditions, the product mass spectrum TiN^+ was obtained successfully first in the reference

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Amorphous Fe_(80-x)Co_xSi_6B_(14)(10≤X≤70) alloys were annealed below their Curie temperatures in AC magnetic field in order to improve soft magnetic properties. Magnetization measurements were made as a function of applied AC magnetic field and annealing temperature and time. Magnetic measurement results clearly demonstrated that some beneficial effects can be provided by applying AC field during annealing, in improvement of the soft magnetic properties : a significant decrease both in coercive and in AC Power loss, and a tendency toward a square shape of hysteresis loop were observed in the our present study. The optimum experimental condition to obtain best magnetic properties for the amorphous Fe_(80-x)Co_xSi_6B_(14) alloys was determined to be AC field annealing treatment at 380℃ for 30 min with H_a≥30 Oe.

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Laves phases of NdFe₂, Nd(Fe_(0.5)Co_(0.5))₂ stoichiometry were prepared using a rapid solidification technology. Low temperature magnetic properties show ferromagnetic behaviors for the Nd(Fe_(0.5)Co_(0.5))₂, SmCo₂ and Sm(Fe_(0.5)Co_(0.5))₂Laves compounds while a sort of antiferromagnetism has been suggested for the supposed composition of NdFe₂ alloy. This rapidly solidified NdFe₂ alloy is believed to consist of metastable rhombohedral NdFe_7 phase plus fine particles of Nd-rich phase. Some evidence of phase transition from the mixture of unstable NdFe_7 compound plus Nd-rich to Nd₂Fe_(17) plus Fe-Nd-O phase was obtained after annealing the NdFe₂ alloy. The pseudo-binary Laves compound, Sm(Fe_(0.5)Co_(0.5))₂, exhibits a high coercivity 4 k0e at room temperature with Curie temperature of 400℃ while the Nd(Fe_(0.5)Co_(0.5))₂ compound shows a magnetic moment 3.0∼3.5μB/f.u.

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Crystal structures and magnetic properties of annealed and rapidly solidified Fe-(Al-Fe) alloys have been investigated and compared with each other. In annealed alloys, it was found that paramagnetism appeared at the alloys with x≤0.25, superparamagnetism for x=0.30 and ferromagnetism for x=0.35, 0.40. Rapidly solidified alloys showed paramagnetism at x≤0.15, superparamagnetism at x=0.20, 0.25 and ferromagnetism at≥0.30. Magnetization increased as x increased. The rapidly solidified specimens showed magnetic behaviors than the annealed ones. X-ray diffraction data revealed that specimens both annealed and rapidly solidified, were single-phased in B2 (CsCl)structure with constant lattice parameter, 2.19Å. However, rapidly solidified alloys exhibited some extent of disorder in the site occupancies of Al atoms. The experimental results were analized on the point of view of the local environmental effect of magnetic atoms.

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An analysis of clad-wire drawing has been made by the elasto-plastic finite element method. The results are in reasonable agreement with experimental ones. The effects of half die angle, friction and sheath metal are predicted. The softer sheath metal reduces internal cracking and the smaller half die angle makes the more homogeneous deformation in both the core and sheath layer. The maximum effective strain develops near surface because of smaller shear at the surface.

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The effect of tempering temperature on the tensile properties of dual phase steels, obtained from different microstrctures, were studied. The starting microstructures of the studied dual phase steels were three kinds ; ferrite+coarse pearlite(F+P₁), ferrite+fine pearlite(F+P₂) and martensite(M). By increasing the tempering temperature, tensile strength was decreased, independently of the starting microstructures. Yield strength of the F+P starting structures was increased at the tempering temperature around 200 C and then decreased with the increased tempering temperature. However, the DP steel of M-starting structure has shown progressive decrease in yield strength with increased tempering temperature. The tempering effect on the elongation was similar, independently of the starting structures. At the early stage of tempering, tensile properties were influenced predominantly by the segregation of carbon at dislocation sites. At the later stage of the tempering, softening effect by the decomposition of martensite is more effective.

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