PURPOSE: To obtain a material which is provided with a coefficient of thermal expansion at 145×10-7/°C or higher, which has a characteristic at a Vickers hardness of 600 or higher and which does not cause a chemical erosion reaction excessively between other head constituent materials by a method wherein TiO2 is contained in a specific amount and the residual part is composed of NiO.
CONSTITUTION: TiO2 is contained at 0.1 to 2wt.% and the residual part is composed of NiO. For example, TiO2 is added in a desired amount to an NiO raw-material powder which is obtainable at a market; they are mixed by using a ball mill and dried; after that, this mixture is molded by using a CIP; it is baked temporarily at 850 to 1100°C in Ar; and then, it is crushed by using a coarse crusher and crushed powders are sieved by using a sieve of 100 to 200μm. the temporarily baked powders are treated for 20 to 72 hours by using a wet ball mill in ethanol and crushed to fine powders of 1μm or less. They are changed to particles, molded by using a CIP and sintered at 1230 to 1400°C in O2; after that, they are treated by using an HIP. The following are desirable as conditions of this HIP treatment: 800 to 1200kg/cm2; 1200 to 1350°C; and 1 to 2 hours. Thereby, it is possible to obtain a sintered substance which is dense, which has a rock-salt structure and whose characteristics are nearly the same as those of a magnetic-film structure substance in its coefficient of thermal expansion and its hardness as well.
HOSAKA KOJI
NAGASE RYUICHI
