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We investigated the effect of additional laser irradiation on the energy state of a laser-ablated plume from a graphite target. Optical emissions from the plume were observed by a spectrometer equipped with an intensified charged couple device (ICCD) immediately after additional laser irradiation at various time delays relative to the ablation. The emission intensity from atomic carbon, ionic carbon, C2 and C3 increased when an ArF excimer laser irradiated the carbon plume. The atomic carbon absorbed the ArF excimer laser resonantly and was ionized. Using the fourth harmonic output of an Nd:YAG laser or a KrF excimer laser, the emission intensity from C2 and C3 only increased. However, no emission spectra change was observed with additional irradiation fundamental output of an Nd:YAG laser. The emission intensity from the atomic and ionic carbon and carbon clusters (C2 and C3) following ArF excimer laser irradiation of the plume was stronger than that using any other lasers.

Carbon nitride films with high nitrogen content were prepared by reactive pulsed-laser deposition at nitrogen partial pressures varying from 0.1 to 20.0 Torr. It was found that the nitrogen content in the films first increases with increase of the nitrogen pressure, reaches a maximum of 46 at. % at 5.0 Torr, and then decreases to 37 at. % at 20.0 Torr. The almost pure carbon nitride films were systematically characterized by using X-ray photoelectron spectroscopy (XPS) concerning the core-level and valence-band structures. Some fingerprint information, which shows the role of nitrogen in controlling the electronic structure of carbon nitride films, was found based on the XPS studies. With enhancing the nitrogen incorporation, both the binding energy and the peak intensity of the core-level and the valence-band spectra vary systematically as a function of nitrogen content in the films.

Growth of nano-crystalline diamond by pulsed laser deposition (PLD) in an oxygen atmosphere on a sapphire (0 0 0 1) substrate is reported. The experiments were performed at a substrate temperature of ∼550°C and in an oxygen pressure of 0.11–0.15 Torr. Field-emission scanning electron microscope, X-ray diffraction and micro-Raman spectroscopy were used to characterize the products. Results indicated that hexagonal and cubic diamond crystals with an average size of ∼30 nm were formed. The crystal nucleation and growth were non-uniform and discontinuous. The possible diamond growth mechanism by PLD in an oxygen environment is discussed. Compared with diamond growth in a chemical-vapor-deposition process, the conditions for diamond nucleation and growth by PLD in an oxygen atmosphere are quite critical.

In the first report, stabilizing effects of a CO2 laser on a TIG arc were discussed from the arc voltage. It was made evident that the unstable arc which formed discontinuous weld beads was stabilized and good beads were made with the laser beam. In such a case, the laser plume played the role as a path of electrons, and the anode spots of the arc were formed around the hot spot by the laser beam.In this report, the effect of Ar gas flow rate on shapes of weld bead sections will be investigated. In the case of the conditions that the TIG arc current, the quasi-single mode laser output, the traveling speed of a base metal and the distance between a SUS304 base metal and a tungsten electrode were 100 A (DCEN), 2 kW, 150 mm/s and 15 mm, respectively, the beads width increased with the Ar shielding gas whose flow rate was from 0.67 × 10-3 to 1.33 × 10-3 m3/s. When the gas flow rate was 1.33 × 10-3 m3/s, the value of the ratio of beads width by the arc with the laser to ones by the laser only was 2.15. On the other hand, the penetration depth increased 22% under the same conditions. The arc voltage became high when the gas flow rate was large. The same phenomena were recognized under the multi mode laser.When the base metal-electrode distance and the gas flow rate was large, the arc path became long and the arc column was bent easily. Therefore, the anode spot rolled from side to side of the laser spot and the bead width was increased by the arc. In such a case, the penetration depth was scarcely increased compared with the one by the laser only. When the gas flow rate was large, the absorption coefficient of the laser increased, because the melted surface was irradiated with the laser beam.As the result, it would be considered that the role of the arc in this surface treatment process is extension of the beads width, and the penetration depth is increased by the laser.

Carbon nitride thin films were deposited by pulsed laser deposition with nitrogen ion beam assistance at a substrate temperature varying from room temperature to 800 °C. The effect of the substrate temperature on the nitrogen content, surface morphology, structure, and electrical property of the carbon nitride films was investigated. The deposited films were characterized by atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and four-probe resistance. The nitrogen content of the deposited films reached its maximum value of 25% at a substrate temperature of 400 °C. AFM images revealed that an island structure occurred and developed on the surface of the films deposited at the high substrate temperature. FTIR and XPS spectra showed the existence of sp3C–N and sp2C=N bonds in the deposited films. The deposited carbon nitride films had an amorphous structure with two carbon nitride phases inclusions, which had a stoichiome...

Visible Raman spectroscopy excited at 532 nm was used to characterize the carbon bonding in tetrahedral amorphous carbon (ta-C) films. The vibrational modes of the sp3 bonding in ta-C films were revealed directly. An additional Raman band occurring below 1350 cm−1 was observed. It consisted of two features centered on ∼1270 and ∼1170 cm−1, which were associated with sp3 bond stretching. The observed sp3 related Raman spectrum approached the vibrational density of states of amorphous diamond.

This article describes the measurement of the fractional ionization in an ablated plume produced by excimer laser, and the application of the plume as an ion source. Laser ablation of iron, aluminum, and tantalum with a KrF excimer laser was performed in a vacuum chamber. The ablated plume was caught by a cup type electrode used to measure the amount of charged particles as current wave forms. Applying electrostatic potential larger than 40 V, the current wave forms were separated into electropositive and electronegative peaks. Each peak indicates ions and electrons, respectively. The amount of ions, 6×1013 ions/pulse, was estimated by integrating the electropositive peak. The ionization degree of 1.7% was also estimated by a series of analyses. For an aluminum target, the ion current reached 2 A at the peak and 1 mA on average at 60 kJ/m2, 500 mJ, and 50 Hz.

In the first report, stabilizing effects of a CO2 laser on a TIG arc behavior were discussed from the point of the arc voltage and of the interaction between the arc and the laser plume.In this report, the CO2 laser beam was scanned by a beam oscillator, and the shapes of melted parts of the base metal were investigated. Furthermore, the behavior of a TIG arc with a scanning CO2 laser beam was investigated by high speed video-pictures. The main experimental conditions were as follows. The TIG arc current, the laser output, the scanning frequency and the scanning width of a laser beam, the traveling speed of a SUS304 base metal and the distance between the base metal and a tungsten electrode were 100 A (DCEN), 2 kw, 25 Hz, 8 mm, 20 mm/s and 15 mm, respectively.As a result, the arc could be controlled by the scanning laser beam, and wide and shallow beads were made using this method under the suitable conditions. Therefore, it was found that the arc with scanning laser beam is excellent as heat source for surface treatment.On the other hand, the arc voltage and the range of its change decreased according as the scanning frequency increased from 5 Hz to 20 Hz. According to the observation using high speed video-pictures, the arc went straight forwards from the electrode and bent toward the scanning laser plume, and the bending point of the arc became increasingly far from the tip of the electrode when the scanning frequency increased. It would be considered that the arc voltage was affected by the bending point of the arc column because of the arc stiffness.

In order to develop a fast surface treatment method or a fast welding method using an electric arc with a laser beam, stabilizing effects of a CO2 laser on a TIG arc were investigated. A TIG arc makes discontinuous molten pools even when the travelling speed of a base metal is high and the distance between a base metal and a tungsten electrode is large. In such a case, the behavior of an arc usually becomes unstable and the arc voltage changes in the range of 5-8 V. Whereas, the arc behavior became stable by using a CO2 laser beam simultaneously, and good continuous weld beads were made on conditions that the TIG arc current, the laser output, the distance between a SUS304 base metal and a tungsten electrode, and the travelling speed of a base metal were 100 A (DCEN), 2 kW, 15 mm and 200 mm/s, respectively.It was found that the anode spot was fixed on the molten pool formed by the laser beam, and, the molten pool, the laser plume and the metallic vapor affected the stabilization of the path of a TIG arc and its voltage. Therefore, it is effective to controle a long arc by a laser that the beam irradiates near the tip of the arc where the arc stiffness becomes weak.

The effect of ion beam irradiation on the adhesion strength of Mo films was examined using an ion beam assisted excimer laser PVD apparatus. We also examined the effect of energy density, target-substrate distances, and target rotation on the surface morphology. Spectroscopic diagnosis for a Mo plume was performed. The adhesion of the Mo film was improved by ion beam irradiation which removes a thin surface layer of the substrate. Smooth surface Mo films without droplets were successfully formed under laser fluence conditions of less than 0.25MJ/m2, a target-substrate distance greater than 40mm, and with target rotation. Mo films with a b.c.c. structure show the (110) preferred orientation of . The Mo plume generated by laser ablation is in an excited state containing Mo+.The effect of ion beam irradiation on the adhesion strength of Mo films was examined using an ion beam assisted excimer laser PVD apparatus. We also examined the effect of energy density, target-substrate distances, and target rotation on the surface morphology. Spectroscopic diagnosis for a Mo plume was performed. The adhesion of the Mo film was improved by ion beam irradiation which removes a thin surface layer of the substrate. Smooth surface Mo films without droplets were successfully formed under laser fluence conditions of less than 0.25MJ/m2, a target-substrate distance greater than 40mm, and with target rotation. Mo films with a b.c.c. structure show the (110) preferred orientation of . The Mo plume generated by laser ablation is in an excited state containing Mo+.

A new method of Zn-Ni alloy coating has been developed in which Zn/Ni double coated films were electroplated onto steel substrates, and then irradiated by a high-power CO2-laser to alloy the Zn/Ni.Alloying conditions of the laser-irradiated films were then examined. X-ray diffraction analysis revealed that the irradiated films were of the Ni5Zn21 (γ-phase) structure. EPMA line analysis showed that the surface of the irradiated films was produced by diffusion from the Ni in the underlying film to the surface of the Zn overlying film.This demonstrated the utility of alloying Zn/Ni double coated films by CO2-laser irradiation.

Metallic materials with thermal barrier coatings are available under high temperatures (about 2000K). However, it is unknown whether or not the coating materials can resist repeated thermal shock. The authors have been developing laser spraying methods which can easily form metallic or ceramic coatings. In order to examine the characterestics of the coatings produced by the laser spraying methods, a new testing apparatus for repeated thermal shock was needed. Therefore, the testing apparatus was made on an experimental basis. The heat source of the apparatus was a carbon dioxide laser beam (maximum power supply: 5kW) and the tested materials were titanium nitride layers which were coated on mild steel plates by means of laser spraying methods. As a result of testing, the surface temperature reached 2000K in 4 seconds in the case of 290 W/cm2 (power supply: 4kW; beam diameter: 42mm), and it was possible to repeat thermal shocks between room temperature and 2000K (at the surface) or 1000K (at the bottom of the coating; thickness: 1mm) at the rate of 3 times a minute.

A new spray gun for laser spraying has been developed. The gun consists of a center outlet for a wire as a spraying material and two coaxial ring nozzles (inner and outer one) for assist gases. The wire was fed into a carbon dioxide laser beam with a high energy density and melted. The assist gas made the molten wire into fine particles and carried them to a substrate, where they formed a coating as a sprayed layer. In this report, a pure titanium wire was melted and blown in the form of titanium particles by argon, or titanium nitride ones by nitrogen. It has been found that gas flows are important in bringing about stable spraying and a small divergence of the particles, and influence the spraying efficiency and surface roughness.

TIG arc welding has been used to date as a method for clad welding of white metal as bearing material. We propose a new clad welding process that combines a CO 2 laser and a TIG arc, as a method for cladding at high speed. We hypothesized that this method would permit appropriate control of the melted quantity of base metal by varying the laser power. We carried out cladding while varying the laser power, and investigated the structure near the boundary between the clad layer and the base metal. Using the laser-TIG combined cladding, we found we were able to control appropriately the degree of dilution with the base metal. By applying this result to subsequent cladding, we were able to obtain a clad layer of high quality, which was slightly diluted with the base metal.

The optical emission spectra of the plasma produced by infrared and ultraviolet laser ablation of graphite in a vacuum were observed. The fundamental output of an Nd: YAG laser was used as the infrared laser. The fourth harmonic output of an Nd: YAG laser and a KrF excimer laser were used as the ultraviolet lasers. The emission intensity of the ionic carbon as well as C2 and C3 from the plasma produced by the infrared laser were stronger than that produced by the UV lasers at the same fluences. The C2 and C3 emission intensities decreased rapidly with increasing the distance from the target. The emission intensity of atomic carbon at 247.8 nm from the plasma produced by the KrF excimer laser was much stronger than that produced by the other lasers at the same laser fluence, due to the wavelenght of the KrF laser being so close to that of atomic carbon's emission line as to raise its electrical state.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We formed tin- doped Indium oxide (ITO) films at room temperature (R.T.) by using the excimer laser assisted electron- beam(EB) deposition method. The effect of laser irradiation on crystallization of EB-deposited ITO films was investigated. We made crystallographic analysis for ITO films deposited on glass and single crystal plates.By using the excimer laser assisted EB- deposition method ITO film is hetero-epitaxially grown on an YSZ single crystal substrate at R.T.. The value of misfit strain between substrates and films is suggested to intensely influence the growth orientation of films.The best resistivity and transparency were obtained for ITO films deposited at R.T. at the laser fluence of 22mJ/cm2, resistivity, ρ, mobility, μ, and free-carrier density, n, being ρ = 9×10−4 Ω cm, μ = 12cm2/ Vs and n= 5.5×1020cm−3, respectively. The film formed without laser assist is black and opaque, whereas the film formed with laser assist is transparent in the visible region of the spectrum, 400 ∼ 800nm, where the transparency is higher than 80%.We formed tin- doped Indium oxide (ITO) films at room temperature (R.T.) by using the excimer laser assisted electron- beam(EB) deposition method. The effect of laser irradiation on crystallization of EB-deposited ITO films was investigated. We made crystallographic analysis for ITO films deposited on glass and single crystal plates.By using the excimer laser assisted EB- deposition method ITO film is hetero-epitaxially grown on an YSZ single crystal substrate at R.T.. The value of misfit strain between substrates and films is suggested to intensely influence the growth orientation of films.The best resistivity and transparency were obtained for ITO films deposited at R.T. at the laser fluence of 22mJ/cm2, resistivity, ρ, mobility, μ, and free-carrier density, n, being ρ = 9×10−4 Ω cm, μ = 12cm2/ Vs and n= 5.5×1020cm−3, respectively. The film formed without laser assist is black and opaque, whereas the film formed with laser assist is transparent in the visible region of the spectrum, 400 ∼ 800nm, where t...

This paper describes both the velocity distribution of laser-ablated tantalum atoms in a plume and the plume temperature in order to discuss the behavior of particles inpulsed laser deposition (PLD). Optical time-of-flight (TOF) was used for the analysis. The velocity distributions of tantalum atoms ablated at the laser fluence in a range of 4-20J/cm2 agreed well with the Maxwell-Boltzmann distribution with center-of-mass velocity. This agreement enabled us to estimate the atom density distribution in the plume.Based on the analysis of atom density distribution in the plume, a simple particle filter for PLD using a pair of thin plates with parallel slits was designed to reduce the number of large particles, such as splashed liquid, which often deposit on the film surface causing to deterioration in film properties; i.e., in transparency, uniformity and corrosion resistance.With the particle filter, tantalum films with a smooth and particle-free surface were obtained in a vacuum over a range of 10−3-10Pa.This paper describes both the velocity distribution of laser-ablated tantalum atoms in a plume and the plume temperature in order to discuss the behavior of particles inpulsed laser deposition (PLD). Optical time-of-flight (TOF) was used for the analysis. The velocity distributions of tantalum atoms ablated at the laser fluence in a range of 4-20J/cm2 agreed well with the Maxwell-Boltzmann distribution with center-of-mass velocity. This agreement enabled us to estimate the atom density distribution in the plume.Based on the analysis of atom density distribution in the plume, a simple particle filter for PLD using a pair of thin plates with parallel slits was designed to reduce the number of large particles, such as splashed liquid, which often deposit on the film surface causing to deterioration in film properties; i.e., in transparency, uniformity and corrosion resistance.With the particle filter, tantalum films with a smooth and particle-free surface were obtained in a vacuum over a range of 10−3-10Pa.

Ta-O films were formed using KrF excimer laser ablation of a Ta target in 5 mass% O3-O2 gas. The formation process of Ta-O films was discussed with respect to the oxidization of ablated Ta particles on the deposited film surface and during the flight from the target to the substrate. The optical transparency and corrosion resistance of the Ta-O films were examined.Dense films with a smooth surface were obtained by a PLD method in 5 mass% O3-O2gas. The O/Ta ratio of the films was much improved by using 5 mass % O3-O2gas. The Ta-O films possessed high optical transparency of 80% at 400nm, and the stainless steel coated by the Ta-O film indicated the good corrosion resistance as well as Ta.Ta-O films were formed using KrF excimer laser ablation of a Ta target in 5 mass% O3-O2 gas. The formation process of Ta-O films was discussed with respect to the oxidization of ablated Ta particles on the deposited film surface and during the flight from the target to the substrate. The optical transparency and corrosion resistance of the Ta-O films were examined.Dense films with a smooth surface were obtained by a PLD method in 5 mass% O3-O2gas. The O/Ta ratio of the films was much improved by using 5 mass % O3-O2gas. The Ta-O films possessed high optical transparency of 80% at 400nm, and the stainless steel coated by the Ta-O film indicated the good corrosion resistance as well as Ta.

The L-PVD of tantalum-oxide using tantalum target and KrF excimer laser was investigated experimentally in the formation of a high performance corrosion-resisting film.This report describes the effects of oxygen pressure during ablation on chemical composition, surface morphology and crystal structure of formed films. An EMPA was used to determine the chemical composition of the deposited films.Both the deposition rate of films and the oxygen content of deposited films increased gradually with increasing oxygen pressure up to 10Pa. The SEM images showed a smooth film surface in this pressure region. At 5Pa the oxygen/tantalum ratio of films measured was 2.5, which is equal to the ratio of Ta2O5. According to the XRD results, the films were amorphous. A crystallized Ta2O5 film, however, was obtained after annealing at 973K in vacuum.Both the deposition rate of films and the oxygen ratio in deposited films indicated obvious saturation around 100Pa. At oxygen pressures higher than 50Pa, the surface of deposited films abruptly became porous.The L-PVD of tantalum-oxide using tantalum target and KrF excimer laser was investigated experimentally in the formation of a high performance corrosion-resisting film.This report describes the effects of oxygen pressure during ablation on chemical composition, surface morphology and crystal structure of formed films. An EMPA was used to determine the chemical composition of the deposited films.Both the deposition rate of films and the oxygen content of deposited films increased gradually with increasing oxygen pressure up to 10Pa. The SEM images showed a smooth film surface in this pressure region. At 5Pa the oxygen/tantalum ratio of films measured was 2.5, which is equal to the ratio of Ta2O5. According to the XRD results, the films were amorphous. A crystallized Ta2O5 film, however, was obtained after annealing at 973K in vacuum.Both the deposition rate of films and the oxygen ratio in deposited films indicated obvious saturation around 100Pa. At oxygen pressures higher than 50Pa, the surface of deposi...

Pulsed laser deposition method (PLD) is known to have high deposition rate per pulse which gives high cooling rate during film formation. PLD is therefore suitable for forming amorphous alloy films. In this research we examined the formation of Ta-Ni amorphous alloy films by PLD from Ta-Ni sintered targets. Ta-Ni amorphous alloys have the extremely high corrosion-resistance in both acid and alkaline solution and promising characteristics as catalyst carrier.Amorphous films in a wide composition range of Ta-40-80mass% Ni were obtained by PLD. At a laser energy density of 20J/cm2, Ni having a lower boiling point than Ta, was ablated preferentially. On the other hand, at the laser energy density of 28J/cm2, we got the films having the same composition as the targets. The grain size of the films was smaller than that of Ta-Ni amorphous flakes prepared by a splash-quenching method. It was suggested that PLD gave larger cooling rate than a splash-quenching method.Pulsed laser deposition method (PLD) is known to have high deposition rate per pulse which gives high cooling rate during film formation. PLD is therefore suitable for forming amorphous alloy films. In this research we examined the formation of Ta-Ni amorphous alloy films by PLD from Ta-Ni sintered targets. Ta-Ni amorphous alloys have the extremely high corrosion-resistance in both acid and alkaline solution and promising characteristics as catalyst carrier.Amorphous films in a wide composition range of Ta-40-80mass% Ni were obtained by PLD. At a laser energy density of 20J/cm2, Ni having a lower boiling point than Ta, was ablated preferentially. On the other hand, at the laser energy density of 28J/cm2, we got the films having the same composition as the targets. The grain size of the films was smaller than that of Ta-Ni amorphous flakes prepared by a splash-quenching method. It was suggested that PLD gave larger cooling rate than a splash-quenching method.

A new application of excimer laser, surface modification of ceramics for bonding a metals to ceramics is demonstrated in this paper.Excimer laser irradiation of Si3N4and AIN gave an Si and AI rich layer on the surface of Si3N4 and AIN, respectively. These layers were the by-products of the decomposition of ceramics. Although they often cause deterioration of qualities in processing such as cutting and ablation, we found them effective as the binder for bonding ceramics to metals such as Cu and AI. The strength of the bonding interface between the laser irradiated Si3N4 and the ion sputtered surface of the Cu, for example, exceeds the strength obtained by conventional bonding methods. The tensile strength of 100-200MPa were obtained even at low bonding temperature, 560K.A new application of excimer laser, surface modification of ceramics for bonding a metals to ceramics is demonstrated in this paper.Excimer laser irradiation of Si3N4and AIN gave an Si and AI rich layer on the surface of Si3N4 and AIN, respectively. These layers were the by-products of the decomposition of ceramics. Although they often cause deterioration of qualities in processing such as cutting and ablation, we found them effective as the binder for bonding ceramics to metals such as Cu and AI. The strength of the bonding interface between the laser irradiated Si3N4 and the ion sputtered surface of the Cu, for example, exceeds the strength obtained by conventional bonding methods. The tensile strength of 100-200MPa were obtained even at low bonding temperature, 560K.

Carbon–nitride thin films were deposited by pulsed laser ablation of graphite with assistance of low energy nitrogen-ion-beam irradiation. The nitrogen to carbon (N/C) atomic ratio, bonding state, microstructure, surface morphology, and electrical property of the deposited carbon–nitride films were characterized by x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, micro-Raman spectroscopy, x-ray diffraction (XRD), atomic force microscopy, and four-probe resistance. The irradiation effect of low energy nitrogen-ion beam on the synthesis of carbon–nitride films was investigated. The N/C atomic ratio of the carbon–nitride films reached the maximum at the ion energy of ∼200 eV. The energy of ∼200 eV was proposed to promote the desired sp3-hybridized carbon and the C3N4 phase. Electrical resistivity of the deposited films was also influenced by the low energy nitrogen-ion-beam irradiation. However, the low energy irradiation had little effect on the surface morphology of the films. XRD...

Carbon nitride films were deposited by pulsed Nd:yttrium–aluminum–garnet laser ablation of graphite with assistance of low energy nitrogen-ion-beam bombardment. The nitrogen to carbon (N/C) atomic ratio, surface morphology, bonding state, and microstructure of the deposited carbon nitride films were characterized by x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, micro-Raman spectroscopy, atomic force microscopy (AFM), and x-ray diffraction. The influence of laser fluence on the synthesis of carbon nitride films was investigated. The N/C atomic ratio of the carbon nitride films can reach the maximum at the highest laser fluence. XPS and FTIR analyses indicated that the bonding state between the carbon and nitrogen in the deposited films was significantly influenced by the laser fluence during deposition. The carbon–nitrogen bonding of C–N and C=N were observed in the films. In addition, α and β C3N4 phases were found to coexist in the carbon nitride films with relat...

Graphite was ablated by three lasers and the resultant carbon plumes were investigated by time- and spatially-resolved spectroscopy. A KrF excimer laser (248 nm) and an Nd:YAG laser (1064 and 266 nm) were used. Near the target surface, C2 (Swan band) and ionic emissions from the plume produced by the 1064-nm laser at a fluence of 6 J/cm2 were stronger than those produced by the 248-nm and 266-nm lasers. The C emission lines (247.9 and 193.1 nm) produced by the KrF excimer laser were stronger than those produced by the other lasers. The most probable velocity of C+ was highly dependent upon the laser wavelength. The dependence of the most probable velocity on the fluence was small. The velocity of C+ ablated by the 248-nm laser was twice as fast as that ablated by the 1064-nm laser, when the fluence of the 1064-nm laser was six times as large as that of the 248-nm laser.

Thin films from six kinds of nonlinear optical nonpolymeric organic compounds were prepared by pulsed laser deposition (PLD) using a KrF excimer laser (248 nm) at various fluences up to 50 mJ/cm2. Changes in the chemical structure of the films with changes in fluence were studied. The experimental results show that for every compound at least minor decomposition has already started at the threshold fluence for deposition. More serious degradation occurs with increasing fluences, and little of the original chemical structure remains in films prepared by PLD at a fluence of 50 mJ/cm2.

The effect of hardness and grain size of steels and their welds on fracture stress and sensitivity of Liquid Metal Embrittlement Cracking in molten Zinc (LMEC) was investigated. The experiment was conducted using commercial weldable structural steels and Sustained Load Test (SLT) was conducted in molten Zinc with heating range of 430°C-470°C.The results obtained are as follows.(1) The LMEC behavior of steels and welds in molten Zinc is of thermal activated process, and fractures are intergranular (IG) type which corresponds to actual LMEC in hot dip galvanizing.(2) Estimation of fracture stress of steels and welds in molten Zinc is obtained by measuring Vicker's hardness and grain size, and these estimation values are correspond with test results.(3) The sensitivity of LMEC is affected by hardness of steels and welds.

Fracture behavior of the weld zone of 80kg/mm2 class HSLA steel has been investigated by means of tensile test, Charpy impact test and three point bending test. The results obtained gave convincible evidences that showed the following important role played by the martensite-austenite (M-A) constituent on the initiation and propagation processes of cracks.For ductile fracture, cracks were initiated by cracking flaky M-A constituent or debonding blocky M-A constituent from ferrite matrix. Then cracks expanded to voids and developed to deep holes. The main crack was formed by coalescence of deep holes by internal necking and led to fracture of specimen with a ductile deep dimple fracture surface.On the other hand, for brittle fracture, cracks nucleated at the interface of blocky M-A constituent and ferrite matrix. Then the crack propagated into the specimen, resulting in catastrophic fracture with a brittle river pattern surface.

By tensile tests on polished and etched small flat specimens the micro-mechanisms of fractures induced by M-A constituent have been identified at room temperature and at the temperature of liquid nitrogen. At room temperature, due to the heavy strain of ferrite, the stress concentrated on the interfaces between M-A constituent and ferrite and made the former cracked or debonded from the latter. Then cracks grew to voids and by coalescence of the latter the main crack occurred and developed and finally led to rupture of the specimen. At the temperature of liquid nitrogen, the M-A constituent gave rise to the concentration and triaxiality of stress near the interface on the side of ferrite and induced it to cleavage crack. By COD test and Charpy impact test this fracture mechanism was furthvr identified and it was found that the factor controlling the cleavage cracking was the size of the M-A constituent.

After simulation of microcrackings by three point bending test, effect of some parameters on the microcrackings are studied. Results are as follows.1) Without hydrogen charge, microcrackings were not detected by M.T.. In this case, those were observed by microcsope, and crack distribution was submitted to logarithmic normal distribution. Mean crack propagation rate in the observation area was 7.1×10-3 mm/hr.2) With hydrogen charge, crack susceptibility by M.T. increased as current density increased, or as deflection increased. Crack number and crack ratio increased with current density. Test coupon with grinder finish contained more microcrackings than that of as welded.3) With hydrogen charge in sea water, microcrackings initiated on the surface of test coupon.

The weld construction using heavy section steel and/or high strength low alloy steel is made by multipass welding. In that case, weld metal is reheated to various temperatures by welding heat of the subsequent pass. This result will lead to both microstructural change and through thickness toughness variation in weld metal.In this work, an investigation was carried out about the reheated zone toughness in weld metal.It is found by this work that, for simple Si-Mn system weld metal, the reheated zone toughness is improved as compared with as-welded touhgness, and increases with the ratio of reheated structure to aswelded structure. This improvement is caused by both the disappearance of columnar structure and the refinement of microstructure.While, for high strength low alloy system weld metal, the reheating shows the complex effect. The reheated zone toughness in this system deteriorates at peak temperature range between 750°C and 950°C, although the remarkable optical microstructural change is not observed.The reheating effect to the toughness of high strength low alloy system weld metal shows the inverse phenomenon as compared with that to the toughness of simple Si-Mn system weld metal.

The liquid metal embrittlement cracking (LMEC) of heat affected zone (HAZ) of steel in hot dip galvanizing was investigated. The experiment was conducted using synthetic HAZ of JIS G 3444 STK55 and Sustained Load Test (SLT) at 370°C-470°C heating range in liquid (molten) and solid Zinc.The results obtained are as follows.(1) LMEC behavior is of thermal activated process and LMEC sensitivity is affected by hardness of HAZ.(2) The coarse grain region in HAZ showed the highest LMEC sensitivity.(3) The interfacial energy of steel is reduced by the existence of Zinc.(4) The reaction rate process of LMEC of steel is controlled by grain boundary diffusion of Zinc.(5) The nucleation and the propagation of LMEC in steel are likely to have a close relation to the reduction of interfacial energy due to the grain boundary diffusion of Zinc.