Papers by Author: Kazuhiro Matsugi

Abstract: The improvement of thermal conductivity of tool steel is extremely important for order to achieve life prolongation of metal die used in die-casting. In order to improve the thermal conductivity without the degradation of mechanical properties, VGCF (vapor grown carbon fiber) and TiB₂ particles added in tool steel (SKD61) and to obtain the composites. Composites was fabricated by spark plasma sintering (SPS). Before sintering, SKD61 powders with 70μm in diameter and 1.9-3.8 vol. % VGCF with 0.15-0.2μm in diameter and 10-20μm in length or 4-8 vol. % TiB₂ particles with 2.62μm in average diameter was mixed by V shape type ball milling or planetary ball milling. Composites were sintered at 1273K with 50 MPa. The relative density of all composites is higher than 97%. The thermal conductivity improved from 20W/mK to 36W/mK by adding 8 vol. % TiB₂ particles, and to 25W/mK by adding 1.9 vol. % VGCF. On the other hand, the tensile strength of 1.9 vol. % VGCF/ SKD61 composites prepared under the condition of V shape type ball milling has 2200MPa. Composites with addition of 4vol. % TiB2 particles with V shape type ball milling and 1.9 vol. % VGCF with planetary ball milling is almost equal to the monolithic alloy. Good mechanical properties of the composites are caused by the grain refinement or interfacial strengthening by adding dispersants. But as increasing the contents of dispersants, the aggregation of the dispersants degrade the mechanical properties.

Abstract: Pure aluminum (Al) has been used as high performance heat sink, electrical line and power supply line because of its light-weight, good thermal and electrical conductivities and high cost performance. On the other hand, the higher performance heat sink and eletrtorical line at room and high tempertture are reqired because of the increment of the power density and higher integration of semiconductor and LED. The use of Al matrix composites is one of suilable solution, because these parts needs multi functional propertes. In this study, titanium die-broide (TiB₂) particles was selected as the dispersant in Al matrix composites because of its good thermal and electrical conductivity, and good mechanical propertes. At first, the mixed power of Al and TiB₂ particles was obtained from six kinds of mixing process, which parameters are conventional boll milling, ultrasonic vibration after conventinal milling, planetary ball milling, which milling process was performed in wet process with ethanol and dry process. 20 vol. % TiB₂/ Al composites was obtained from spark plasma sintering. The dence comopsites with over 98% in relative density with highly dispersed TiB₂ particles was obtained from wet mixing process. But the tensile strength of the composites prepared from dry mixing process is higher than that of wet mixing process. The thermal conductivity of the composites is about 120 W/mK, and the obvious diferrence between the wet process and dry process was not observed.

Abstract: In order to obtain the high performance materials with high thermal conductivity, high electrical conductivity, low thermal expansion, good mechanical properties and low density, TiB₂ particle dispersed aluminum (Al) composites was developed by spark plasma sintering. As these properties are affected by the dispersibility of the particles, the relationship among the dispersibility of dispersant and the thermal conductivity and mechanical properties was investigated, 20 vol. % TiB₂ dispersed Al composites with different dispersibility were fabricated by spark plasma sintering (SPS). The dispersibility was estimated quantitatively by using the definition method of local number of particles (LN2DR method), and two composites having 6.884 and 4.839 for number of LN2DR was obtained. Thermal conductivity of the composites with homogeneous distribution of TiB₂ particles was lower than that with heterogeneous distribution and clustering. On the other hand, the tensile strength of the composites improved as increasing temperature compared with Al block. Furthermore, strength of the composites with homogeneous distribution of TiB₂ particles at 200°C and more was higher than that of the composites with heterogeneous distribution and clustering.

Abstract: In this study, the fabrication of carbon containing aluminum composites was attempted by using low-pressure infiltration method. At first, porous preform containing vapor grown nano-fiber (VGCF) and pure aluminum powder was fabricated by spark plasma sintering (SPS) method. Porosity in preform was controlled by changing the applied pressure during plasma sintering. Consequently, the porous preform with 40-50vol％ in porosity was obtained, which has enough compression strength for low-pressure infiltration (<1MPa). Then, the molten pure aluminum infiltrated to porous preform with 0.4MPa in applied pressure at 1023K, and consequently we can obtain the composite with 62-86% in density. The electrical and thermal conductivity of composites was affected by the porosity, strongly.

Abstract: Vapor grown carbon fiber (VGCF) was sleaved in acetone with ultrasonic vibration. Then pure aluminum powders with 3 μm in average diameter was poured into VGCF containing acetone and mixed with ultrasonic vibration. The composites were fabricated by electro spark sintering. The strength, rigidity, electrical conductivity and microstructure of the composites was investigated. VGCF was distributed uniformly and no pores was observed in composite. As increasing the volume fraction of VGCF in composites, the strength of composites increased gradually but the elongation decreased. The electrical resistivity of the composites increased as increasing VGCF content, constantly. The theoretical resistivity of composites without residual stress is lower than that of experimental results. It seems that is caused by the high dislocation density and strain introduced by big difference of thermal expansion between VGCF and pure aluminum.

Abstract: In order to fabricate the metal matrix composites by low-pressure infiltration by gravity casting machine, the preform made from FeCrSi fiber with 40μm and matrix of A336.0 aluminum alloy was used. The volume fraction of fiber in preform was about 20%. The temperatures of die, preform and molten alloy were 200 oC, 400 oC and 750 oC, respectively. By controlling the infiltration of molten aluminum alloy to one direction by using barrier plate, the quantity of pores caused by curling of air degrades dramatically. Molten aluminum alloy was able to infiltrate at low pressure of 0.2MPa. As increasing the pressure, porosity in composites decreased. The composite with no pores was obtained by barrier plate and 0.8 MPa of molten alloy pressure. This composite had high strength at high temperature of 200-400oC.

Abstract: MgAl2O4 layer with several decade nano-meter in thickness was coated uniformly on Al18B4O33 whisker by vapor-deposition of pure magnesium in vacuum and then heat-treated in atmosphere in order to prevent to the direct reaction between Al18B4O33 whisker and molten ZK60 (Mg-(4.8-6.2)%Zn-(0.45-0.8)%Zr) alloy in preparing the composites. By the coating, the composite have no interfacial reaction in whisker and matrix. As the consumption of Zn at the interface was not observed during preparation of the composites, the composites have good aging behavior, but showed the shortening of the time to reach the peak hardness. As the cooling speed of the composite after solution treatment is slow because of low thermal conductivity of the composites, some precipitation (MgZn2) was observed in the composites. Furthermore, the precipitation grew around the interface between whisker and matrix preferentially because of thermal stress around the interface. It seems these phenomena affect to the shortening of the time to reach the peak hardness.

Abstract: In order to infiltrate the molten aluminum alloy to the reinforcement preform by low pressure in casting process and acquire the high performance composites with high density, the effect of the ultrasonic vibration on the infiltration was investigated by model experiments using clear solution and glass or aluminum borate preform, which is correspond to a molten matrix and reinforcement, respectively. Ultrasonic vibration improves the wettability of liquid polyester resin on glass plate, dramatically. The final infiltration height and infiltration speed of liquid polyester resin in glass capillary were improved by the ultrasonic vibration. Furthermore, the infiltration speed of water to aluminum borate preform accelerated by ultrasonic vibration. This effect was more remarkable, when the infiltration height is lower or infiltration time is shorter. In actual, the molten aluminum alloy infiltrate to SiC preform using ultrasonic vibration easily and acquire the high dense composites without pores.