Masayuki Mizumoto

Development of new additive for grain refinement of austenitic stainless steel

Abstract Recently, a new additive for grain refinement of Ni based superalloys has been developed. In those studies, it was considered that niobium carbide in Ni–Nb–C alloy additives would act as nuclei on the solidification of Ni based superalloys. It is known that the crystallographic characteristics of iron are quite similar to those of nickel. Thus, it was expected that niobium carbide would act as a grain refiner for iron base alloys, especially for austenitic steels. In this study, the effect of the additives on the microstructure of SUS316 steel was examined in various experimental conditions. The grain size of SUS316 specimens without inoculation was ∼2700 μm. On the other hand, when NbC containing alloy additives were added into the SUS316 melt, fine equiaxed grains were observed and the grain size of the specimen was significantly reduced to ∼200 μm.

Electrochemical Fabrication of Metallic Nanowires and Metal Oxide Nanopores

A nuclear track etched polycarbonate membrane filter with numerous cylindrical nanopores was applied as a nanoporous template for growing metallic nanowires. Nickel, cobalt, and iron nanowires were electrodeposited into the cylindrical nanopores. Cathodic polarization curves were measured to determine an optimum condition for growing nanowires. The shape of nanowires was observed using scanning electron microscope (SEM) and the crystal structure was analyzed using transmission electron microscopy (TEM). Diameter and length of nanowires corresponded to those of nanopores and each nanowire was composed of a single crystal. Anodized aluminum oxide films were also fabricated as a novel nanoporous template. The pore length and diameter was controlled changing anodizing conditions. Ordering behavior of nanopores array in an anodized aluminum oxide film was also investigated to make a novel nanoporous template with a highly ordered honeycomb array of nanopores.

Microstructure Control of Particle Reinforced Metal Matrix Composites Fabricated by Low Pressure Infiltration Process

Process parameters to control the microstructure of particle reinforced MMC in the low pressure infiltration process (LPI process), have been investigated. The mixed powder of reinforcement particle and pure aluminum particle in various volume fraction was employed to control the volume fraction of the reinforcement particles in PRMMC. The Al–12 mass%Cu alloy melt was forced to infiltrate into the mixed powder layer by applying a certain pressure of argon gas on the melt surface. The pressure required to infiltrate remarkably increased from 0.05 to 0.5 MPa with a decrease in the particle size from 100 to 20 μm, indicating that the pressure at the advancing melt surface decreased due to the resistance based on a capillary force and a friction force between melt and particle. In the microstructure of PRMMC obtained, the reinforcement particles were homogeneously distributed and a linear relationship was obtained between the volume fraction of reinforcement particle in the mixed powder and the observed area fraction. It was found that a homogeneous particle distribution and accurate control of the volume fraction of reinforcement particles could be attained in the LPI process.

Novel Separation Technique of Particle Reinforced Metal Matrix Composites by Fused Deposition Method

To develop a novel separation technique of matrix alloys from metal matrix composite, separation experiments for various kinds of particle reinforced metal matrix composites (PRMMCs) were carried out. The Al-4mass%Cu alloy, Al-7mass%Si alloy and cast iron were used as matrix. The SiC particles (particle size: 75μm) and Al2O3 particles (particle size: 120μm) were used as reinforcement. The PRMMC specimen was placed in a silica tube container with a small nozzle (nozzle size: 0.75mm) at the bottom and was melted by H.F. induction heating. Then the molten PRMMC specimen was forced to flow out through the nozzle by applying a certain pressure of Ar gas. Most of the molten matrix alloy flowed out through the nozzle and the remainder in the container consisted of the reinforcements and a part of the matrix alloy. The amount of separated matrix alloy increased with decreasing the volume fraction of reinforcement particles in PRMMC specimens. With decreasing the fabrication temperature from 1273K to 1073K, the amount of matrix alloy separated from SiCP/Al-7mass%Si alloy composites increased. It is considered that a reaction layer formed on the surface of SiC particles at 1273K improves the wettability between the molten matrix alloy and SiC particle, which prevents the separation of molten matrix alloy from reinforcements. On the other hand, the amount of separated matrix alloy from 20vol% Al2O3P/cast iron composites was very high due to no reaction layer formed at interface between Al2O3 particle and cast iron.

Solid Free-Form Fabrication of Metallic Components

The influence of process parameters on shape stability and surface smoothness of cylindrical and rectangular castings produced by fused spinning deposition (FSD) method was investigated. The optimum conditions to control the shape and smoothness of side surface of the castings produced by the FSD method without water-cooling were limited to a narrow range of process parameters. The casting with a stable shape and a smooth side surface was obtained with the aid of water-cooling. The tensile strength of the castings produced by the FSD method was 1.4 times higher than those of the specimens cast into metal-mold and sand-mold, due to a finer equiaxed grain structure of the FSD castings. Employing the combination of the deposition patterns for tube and solid castings, some practical metallic components were fabricated by the FSD method.

Development of Actuator Utilizing Hydrogen Storage Alloys

The actuators utilizing hydrogen storage alloys (HSAs) have been developed. In order to convert a volume expansion of HSA accompanied by hydrogen absorption into a bending motion, the actuators have a bimorph structure which consists of sheet-shape HSA and non-HSA. Pd-Ni and V-Ti based HSAs, which have high pulverization resistance on hydrogen absorption - desorption cycles and enough ductility to form into sheet, are used for the actuators. The shape change behavior of the V-Ti alloy actuators was improved by the sputtered Pd layer which would act as a catalyst and a protective layer against oxidization. Pd-Ni alloy actuators exhibited cyclic bending motion accompanied by hydrogen absorption- desorption cycles. The shape change behavior of the actuators could be controlled by controlling the hydrogen pressure. By forming the sample shape into the “L” shape, the rotational motion could be achieved without modifying the basic bimorph structure of the actuator.

Electrodeposition of Ferromagnetic Metal Nanowires

Ni-Fe alloy films and nanowires were fabricated using electrodeposition technique. The cylindrical shape of nanowires was precisely transferred from the nanochannels of membrane filters and the aspect ratio reached to around 60. Coercive force in in-plan direction of Ni-Fe alloy films decreased to ca. 1 Oe with increasing Fe content in deposits while, in perpendicular direction, the films were hardly magnetized. Magnetic hysteresis loops revealed that the nanowires were spontaneously magnetized to the long axis direction and the coercive force reached to ca. 200 Oe.

Effect of Alumina Fibers on Fabrication Process and Characteristics of Alumina Fiber Reinforced Aluminum Alloy Composites

In order to develop the alumina fiber reinforcements optimized to FRMMCs, the effect of characteristics of alumina fibers on the fabrication process and the characteristics of the alumina fiber reinforced Al alloy composites was investigated. Alumina fibers which have different alumina content were prepared. Alumina content in the fibers was varied from 80% to 100%. Al-4mass%Cu alloy, Al-12mass%Si alloy and Al-10masss%Mg alloy were used as matrix. The FRMMC specimens were fabricated by a low-pressure infiltration process (LPI process). The formability of the preform was improved with increasing alumina content in the fibers. However, broken fibers were observed in the preform when alumina fibers with high alumina content were used. The number of the broken fibers seemed to be increased with increasing alumina content in the fibers. This result could be attributable to a change of fiber strength resulting from a change of alumina content in the fiber. The FRMMC specimens were characterized by using Vickers hardness test. The Vickers hardness of FRMMC specimens depended on the elasticity or the hardness of the fibers. The results obtained suggest that the characteristics of the FRMMCs largely depend on the intrinsic characteristics of the reinforcement fibers.

Electrodeposition of metallic nanowires in nanoporous polycarbonate films

A polycarbonate membrane filter with numerous cylindrical nanopores was used as a template for growing metallic nanowires such as Ni, Co and Fe. The nanoporous template with pore-diameter of 150 nm, pore-length of 6000 nm, and pore-density of 108 pore•cm-2 was modified as a cathode with sputter-deposited gold layer. Inside the nano-pores, the metallic nanowires were electrochemically deposited from an acidic sulfate solution containing metal ions. The growth rate of metallic nanowires depended on the cathode potential during electrodeposition. The diameter of electrodeposited nanowires corresponded to that of nanopores in the template. TEM diffraction pattern suggested that each metallic nanowire composed of a single crystalline structure.