Ceramic materials are the most suitable materials for cutting tools because they have excellent properties in heat resistance, thermal shock resistance and wear resistance. Since an alumina material was developed for cutting tool in the 1938, various ceramic materials such as silicon nitride, sialon, whisker composites et al. have been developed for the cutting tool. The range of the material application has been greatly expanded by improving its performance, and it is expected that it will be developed to difficult-to-cut materials in the near future.
In this paper, development methods for each material would be discussed and application examples would also described. In addition, the material concept and the properties of new grade: Bidemics are shown. Finally, we will discuss future directions of ceramic cutting tools.
This study investigated hydrogen formation by reaction of commercially available AZ magnesium alloys and methanol. AZ31 alloy with 3 mass% Al and 1 mass% Zn showed a high hydrogen generation performance. 2 g of its alloy chips completely reacted within 10 min to produce 2000 cm3 of hydrogen, which is almost a conversion yield of 100%. The heat caused by the exothermic reaction accelerated the formation of hydrogen. The reaction became slower with an increase in Al content of Mg alloy and needed 100 min to complete for AZ91 alloy with 9 mass% Al because of an increase in corrosion resistance. However, the hydrogen formation of AZ91 alloy chip was improved by mixing with AZ31 alloy chips, and completed by 20 min. The by-product of the reaction was Mg(OCH3)2, and then converted to MgO by heating to 500°C. A hydrolysis reaction changed Mg(OCH3)2 to Mg(OH)2, which is environmentally friend and safe material. Therefore, it is said that the commercial AZ alloys are useful for hydrogen generation by reaction with methanol.
Fe-Al alloy powder was mixed with Fe2O3, NiO and SiO2 powders, and the mixed powders were cold-pressed and annealed at 800°C. Nano-sized Al-oxides were precipitated within the α-Fe matrix of the Fe-Al alloy powder mixed with Fe2O3 and NiO. On the other hand, oxide precipitation was not confirmed within the α-Fe matrix of the SiO2 doped alloy. This difference is caused by the thermodynamic stability of the oxides, where Fe2O3 and NiO are not in equilibrium with α-Fe so that they are dissolved in the α-Fe matrix to form more stable Al-oxides, while SiO2 is in equilibrium with α-Fe thus the chemical driving force for the Al-oxide precipitation was small.
We investigated the possibility of atomizing molten magnesium (Mg) alloy by air instead of argon gas in order to manufacture the powder at low cost. As a result, we obtained the powder from molten Mg alloy containing yttrium (Y), calcium (Ca) or aluminium (Al) by air atomization without combustion. Each powder had approximately 100 nm thick oxide film with condensed Y, Ca or Al, which could make the oxide film dense enough to isolate the molten Mg alloy droplet surface from air. In the case of Al, 6 mass% Al or more was required to prevent combustion. Al was also condensed in the matrix near the interface with oxide film, which could reduce the Mg vapor pressure on the matrix surface under the oxide film. High cooling rate of droplet is also effective to prevent combustion. As air atomized AZX912 powder has the same matrix structures as argon gas atomized one, we expect that the sintered parts of air atomized Mg alloy powder can be obtained by breaking the oxide film in the forming process.