Yoshiaki Arata

Electrical conductivity of plasma-sprayed titanium oxide (rutile) coatings

Abstract Plasma spraying has been used to prepare n-type polycrystalline TiO2 coatings on SUS304 steel substrates. The influence of plasma spray process on the phases (corundum type Ti2O3, monoclinic Ti3O5, triclinic magneli phases, and tetragonal rutile) formed and the relation between deoxidation and the electrical conductivity of plasma-sprayed TiO2 coatings have been studied. The amount of oxygen loss in the plasma-sprayed TiO2 coatings is influenced greatly by the addition of hydrogen in the plasma gas. Accordingly, the electrical conductivity of TiO2 coatings increases with decreasing oxygen during plasma spraying. The amount of reduced TiO2 coating increases with a drop in pressure of the plasma spray atmosphere and an increase in the quantity of hydrogen. The amounte of Ti2O3 and Ti3O5 phases formed by plasma spraying increase with the deoxidation of TiO2 coatings.

Beam hole behaviour during laser beam welding

Fundamental phenomena during laser beam welding in steel and glass, including beam hole shape, molten metal flow and peculiar plasma behaviour, were observed dynamically using a transmission X-ray system and high speed camera. The effect of altering the flow rate of helium assist gas were also studied. It was found that the gas flow rate had a strong effect on the beam hole shape, molten metal flow and plasma production. In order to avoid the interference effect of laser plasma, a new laser welding process, which we have named “Laser Spike Seam Welding”, was developed. This process allows considerably deeper penetration than conventional continuous welding. The reasons for this superiority were analyzed by the above high-speed film method.Fundamental phenomena during laser beam welding in steel and glass, including beam hole shape, molten metal flow and peculiar plasma behaviour, were observed dynamically using a transmission X-ray system and high speed camera. The effect of altering the flow rate of helium assist gas were also studied. It was found that the gas flow rate had a strong effect on the beam hole shape, molten metal flow and plasma production. In order to avoid the interference effect of laser plasma, a new laser welding process, which we have named “Laser Spike Seam Welding”, was developed. This process allows considerably deeper penetration than conventional continuous welding. The reasons for this superiority were analyzed by the above high-speed film method.

Weld bead and joint strength characteristics during laser welding of 87% AI2O3 ceramics ‐ High‐power CO2 laser welding of 87% Al2O3 ceramics (1st report)

Summary To develop a joining technology for thick ceramics, the fundamental characteristics of high‐power CO2 laser welding of 87% A12O3 ceramics have been investigated. The results suggest that a penetration depth of 20 mm is possible at a welding speed of 6.5 mm/sec and laser power of 10 kW. The porosity ratio is lower at lower input powers, also tending to decrease with a decreasing welding speed at the same input power. The bending strength decreases with an increasing porosity ratio. Porosities, especially large sink mark porosities at the bead centre, strongly affect the bending strength of welded joints in alumina ceramics. The root bending strength of 4 mm thick butt‐welded plate has the same value as the base material.

Study on prevention of welding defects for thick plates with high power CO2 laser

The authors have examined proper welding condition which enclosed good weld beads in terms of welding appearance for full penetration welding. For CO2 laser welding of large output, it is generally known that porosity may occur in the weld bead when a deep penetration welding in single pass is performed in the ambient atmosphere. Welding defects mainly including porosity also occur more frequently with increase of plate thickness even though in the case of using proper welding condition.In order to spread laser welding generally, porosity is one of the most important problems to be solved. It is thought that formation mechanism of porosity is expressed as follows. Bubbles are generated mainly at the bottom of keyhole, which are trapped in molten metal during floating up and remain as porosity in metal.In this context, to reduce welding defects in welded bead, the authors paid attention to the following two conceptions; the first is that long heat input time would enable to delay beginning of molten metal solidification; the second is that molten metal could be fluidified smoothly by changing direction of recoil pressure. The authors adopted use of twin spot condensing system and improvement for the radiation angle of laser to test piece to accomplish these conception. Twin spot welding was the method of welding with two spot lasers which were condensed two laser beams which were divided from an uncondensed laser beam so that heat input increased in spite of decrease of penetration depth. Forehand welding was performed using a method of inclined laser radiation so that molten metal could be fluidified smoothly by changing direction of recoil pressure.In this report, the authors discuss in detail the prevention of welding defects which are generated by mainly porosity for thick plates.The authors have examined proper welding condition which enclosed good weld beads in terms of welding appearance for full penetration welding. For CO2 laser welding of large output, it is generally known that porosity may occur in the weld bead when a deep penetration welding in single pass is performed in the ambient atmosphere. Welding defects mainly including porosity also occur more frequently with increase of plate thickness even though in the case of using proper welding condition.In order to spread laser welding generally, porosity is one of the most important problems to be solved. It is thought that formation mechanism of porosity is expressed as follows. Bubbles are generated mainly at the bottom of keyhole, which are trapped in molten metal during floating up and remain as porosity in metal.In this context, to reduce welding defects in welded bead, the authors paid attention to the following two conceptions; the first is that long heat input time would enable to delay beginning of molten metal ...

Generation of an ultra‐high energy density electron beam and its application for deep penetration welding: Characteristics of a 500 kV electron beam heat source (1st report)

Summary This paper describes the development of an ultra‐high voltage electron beam heat source with an electron gun incorporating a stacked array of 11 electromagnetic acceleration units. The characteristics of the electron beam are studied, and a strongly focused electron beam with an ultra‐high average beam power density of 160 ∼ 170 kW/mm2 using a beam power of 140 ∼ 180 kW is successfully generated. Its applicability to flat‐position single‐pass welding of ultra‐thick stainless steel plates is investigated. This beam allows a penetration depth of max. 240 mm in flat‐position welding at a beam power of 180 kW and a welding speed of 6.7 mm/sec to be achieved while enabling a narrow weld bead to be produced with high efficiency.

Electric-field-assisted treatment of plasma-sprayed ZrO2 coatings

Abstract A systematic experimental investigation was carried out to clarify the phenomena which occur during the electric-field-assisted treatment of ZrO 2 (8% Y 2 O 3 ) coatings sprayed on copper and SS41 steel substrates, and the possibility of improving the adhesive strength between substrate and coating by the electric field assisted treatment was examined. It was found that the occurence of a Zr-Cu-O layer was clearly recognized at the interface between the ceramic coating and the copper substrate, which was arranged as the cathode in the experiment. It was revealed that the adhesive strength of a coating can be raised by the electric-field-assisted treatment to over three times that of a sprayed coating. The electric-field-assisted treatment was also applied to ZrO 2 sprayed onto mild steel but no improvement in adhesive strength resulted. However, when the coated steel was heated in air to form an iron oxide at the coating-substrate interface, the adhesive strength was nearly doubled by a subsequent electric-field-assisted treatment.

Condition setting method utilizing data base system in CO2 laser surface hardening

The effective method to investigate the interaction model in the heat processing is discussed. The computer processing system in this method consists of the data base and several peripheral modules.The hardness estimation of CO2 laser surface hardening is carried out as the concrete application of this system. The automatic evaluation of the hardness estimation models is discussed. These models are implemented by composing and utilizing small and simple program modules which are evaluated automatically and improved by steps. This process is very effectively executed in the whole system. The most suitable model that has been evaluated by the above method can be applied to the hardness estimation within the wide range of condition.For the verification, the automatic condition setting is done. The estimated results of the set condition closely correspond to the experimental surface hardened results.The effective method to investigate the interaction model in the heat processing is discussed. The computer processing system in this method consists of the data base and several peripheral modules.The hardness estimation of CO2 laser surface hardening is carried out as the concrete application of this system. The automatic evaluation of the hardness estimation models is discussed. These models are implemented by composing and utilizing small and simple program modules which are evaluated automatically and improved by steps. This process is very effectively executed in the whole system. The most suitable model that has been evaluated by the above method can be applied to the hardness estimation within the wide range of condition.For the verification, the automatic condition setting is done. The estimated results of the set condition closely correspond to the experimental surface hardened results.