Katsuya Akamatsu

Compositional structure of dual TiNO layers deposited on SUS 304 by an IBAD technique

Abstract Surfaces of stainless steel SUS 304 were coated with dual titanium oxynitride (TiNO) layers using a nitrogen ion beam-assisted deposition technique. The N ions were accelerated at energy of 0.5–2.0 keV with an intensity of 0.1 mA/cm 2 on the substrate surface. First, a TiNO film was deposited on substrates at 700 °C, and subsequently, another TiN film was deposited on the previous TiNO film surface at 400 °C. Hydrogen carbon nitride, CrFe, and metal carbide M 23 C 6 were produced in the near-surface region of stainless steel during the TiNO deposition at 700 °C, and three characteristic layers consisting of iron nitride, chromium nitride and nickel nitride were formed between the TiNO films deposited and the stainless steel. These characteristic layers disappeared during deposition of the TiNO layer at a temperature of 400 °C.

Plasma nitriding behavior of low carbon binary alloy steels

Abstract Effect of alloying elements, Cr, Ta, Ti and V with the content of 0.5, 1.0 and 1.5 mass% on plasma nitriding behavior at 823 K of nitriding temperature was examined in low carbon binary alloy steels. Deep diffusion layer with high hardness up to HV900 below the surface thin compound (γ′-Fe 4 N) layer was formed in these alloys. The hardness increased with increasing alloying content. Optical microscope and X-ray diffraction (XRD) analyses did not reveal the formation of any nitride of these alloying elements in the diffusion layer. Transmission electron microscope revealed the evidence of coherent pre-precipitation phase. In XRD analysis, broadening and shift of diffraction peak of α-Fe as a matrix of the diffusion layer were observed. The peak broadening and the peak shift had a good correlation with the hardness and the nitrogen content in the diffusion layer, respectively. Accordingly, these results suggested that the hardening in the diffusion layer was caused by the microstrain in the matrix induced by the formation of coherent pre-precipitation phase.

Relationship between hardness and lattice parameter for TiN films deposited on SUS 304 by an IBAD technique

Abstract Titanium nitride films were deposited on SUS 304 stainless steel using an ion beam-assisted deposition technique. The N ions were accelerated at energy of 0.5–2.0 keV with an intensity of 0.1 mA/cm 2 on the substrate. Substrates were held at temperatures of 400–770 °C during deposition. For the TiN films, hardness was in the range from 350 to 550 GPa, depending on the N ion-beam energy, while the lattice parameter was dependent on the N ion-beam energy and substrate temperature. The lattice parameter dependence of hardness for the TiN films deposited at temperatures lower than 600 °C differed from that for films deposited at temperatures above 700 °C.

Pulsed Electric Current Bonding of Tungsten to Copper with Intermediate Layer

Pulsed electric current sintering (PECS) was applied to the bonding of W (tungsten) to Cu (copper) using Nb or Ni powder as an intermediate layer. The influence of the intermediate layer on the bond strength of the joint was investigated by observation of the microstructure. The bonding process was carried out at carbon-die temperatures of 1073 and 1173 K for 1.8 ks at a bonding pressure of 130 MPa. The bond strength of the joint with an intermediate layer of Ni powder was 250 MPa. This joint fractured in the Cu base during the tensile test. SEM observations of the joint with an intermediate layer of Ni revealed that a diffusion layer formed at the joint interface.

Microstructure of SiC/Cu Interface by Pulsed Electric-Current Bonding

Pulsed electric-current sintering (PECS) was applied to the bonding of SiC (pressureless-sintered silicon carbide) to Cu (oxygen-free copper) using a mixture of Cu and Ti powders as an intermediate layer. The influences of the intermediate powders on the bond strength of the joint were investigated by observation of the microstructure. The bonding was carried out at carbon-die temperatures from 973 to 1173 K at a bonding pressure of 10 MPa for 3.6 ks. The application of intermediate layers of 100% Ti, 95% Ti + 5% Cu, and 5% Ti + 95% Cu remarkably improved the bond strength as compared with direct bonding without an intermediate powder. SEM observations of the joint with the intermediate powders revealed that a Cu solid-solution layer, a TiC layer, and a Ti5Si3 layer had covered most of the interface, similar to those observed in the friction-bonded and pulsed-electric current bonded joints of SiC to Cu in which the application of a Ti foil as an intermediate layer remarkably improved the bond strength.

Dependence of film thickness on nitrogen ion energy and substrate temperature for titanium nitride films on stainless steel using an ion beam assisted deposition technique

Abstract Stainless steel (SUS-304) was coated with titanium nitride (TiN) using a ion beam assisted deposition (IBAD) technique. The deposited TiN films were polycrystals oriented in the 〈1 1 1〉 〈2 0 0〉 and 〈2 2 0〉 directions. The thickness of the deposited TiN films was measured using Rutherford backscattering spectrometry with He ions. The thickness of the films decreased with increasing N ion energy, and they were not dependent on substrate temperature but significantly decreased with substrate temperature above a specific temperature for SUS-304 because the sticking coefficient of Ti to SUS-304 was less than unity.

Preparation of Homogeneous Nb-Al Intermetallic Compound Sheet by Multi-Layered Rolling and Subsequent Heat Treatment

The intermetallic compound Nb3Al is widely investigated because of its high temperature strength, superior superconductivity and relatively small density. As Nb3Al has an extremely high melting point and lack of deformability, it is impossible to prepare it by using the conventional metallurgy. In this study, a Nb-Al intermetallic compound was prepared by multi-layered roll-bonding of elemental Nb and Al foils. The process consisted of the accumulative roll-bonding (ARB) for making a laminated Nb/Al sheet and the subsequent heat treatment promoting a solid-phase reaction in the laminated Nb/Al sheet. Accumulated foils were roll-bonded at 573 K. The rolling reduction at 1 pass was ~50%, and the final rolling reduction at 4 passes was ~94%. A pulsed electric current sintering (PECS) process was used for the subsequent heat treatment. The microstructures produced at each processing stage were characterized by X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). A homogeneous intermetallic compound of Nb3Al could be obtained after the subsequent heat treatment for 1.8 ks at 873 K and for 0.9 ks at 1673 K.

Titanium oxy-nitride films deposited on stainless steel by an ion beam assisted deposition technique

Surfaces of stainless steel SUS304 were coated with titanium oxy-nitride (TiON) films at temperatures of 400–770°C using an ion-beam assisted deposition technique constructed from an electron beam evaporator for Ti evaporation and a microwave ion source for ionizing nitrogen gas. The N ions were accelerated at energies of 0.5–2.0 keV. Most of the deposited TiON films consisted of (60–80)% TiN and (40–20)% TiO2, and the fraction of TiO2 increased with increasing substrate temperature. Hardness of the TiNO films varied in the range from 160 GPa to 260 GPa with increasing substrate temperature. The titanium oxy-nitride film could be deposited on stainless steel without a significant deterioration surface layer at 600°C. However, when TiNO films were deposited at temperatures higher than 700°C, the thickness of the TiNO films were significantly thinner and a thick layer containing nitride such as Cr2N, CrFe, Fe2N and Fe4N was formed in a near surface region of stainless steel because more nitrogen diffused into stainless steel.

Fiber Laser Welding of Noncombustible Magnesium Alloy

Noncombustible magnesium alloy AMC602 (Mg-6mass%Al-2mass%Ca) extruded sheet of 2.0mm thickness was successfully welded using a fiber laser welding process at welding speed of 10m/min at 3kW laser power. Tensile strength of the welded joint was about 82 to 88% of that of the base metal. Vickers hardness, tensile strength and micro structural properties are also discussed.

Effect of Pre-Deforming on Plasma Nitriding Response of 304 Stainless Steel

The effect of a modified layer caused by pre-deforming on the low temperature plasma nitriding of AISI 304 austenitic stainless steel was investigated. The aim of using the deformed layer is to produce a thicker nitrided layer and to decrease the nitriding temperature due to the much faster diffusion of nitrogen. The pre-deformed sample was prepared by the rolling in 0, 1, 2, 3, and 4% ratios. Plasma nitriding was carried out at 673 and 723 K for 18 ks under 600 Pa pressures in presence of N2/H2 in 50:50 ratio. The microhardness, thickness and phase composition of nitrided layers formed on the surface of pre-deformed and non-deformed samples were investigated using Vickers microhardness tester, optical microscope and X-ray diffraction techniques, respectively. After nitriding, maximum hardness ~1150 HV was achieved on the pre-deformed sample. XRD pattern showed that most dominant phase of the nitrided layer consisted of the expanded austenite (S phase). In addition, the pre-deforming by rolling had a significant influence on the hardness and thickness of the S phase. That is, the hardness and thickness of the S phase were increased by applying the pre-deformation.