Abstract: In a material for a ceramic ball according to an embodiment, a sphericity is 2% or less, and an arithmetic mean roughness Ra is 0.2 ?m or more and 2 ?m or less. In the material for the ceramic ball, a total height of profile Rt is preferably 4 ?m or more and 20 ?m or less. In the material for the ceramic ball, when a surface roughness Ra in a circumferential direction of a belt-like portion mark is defined as Ra1, and a surface roughness Ra of a circumference in a direction perpendicular to the belt-like portion mark is defined as Ra2, Ra1/Ra2 is preferably 0.2 or more and 2 or less.

Abstract: A ceramic ball storage tray includes a storage portion that stores a ceramic ball. The storage portion of the ceramic ball storage tray has a protruding portion formed such that a center of a bottom surface portion of the storage portion is hollow. A height of an outer circumferential surface of the protruding portion relative to a diameter of the ceramic ball is within a range of 0.05 or more and 0.30 or less. A height of the storage portion relative to the diameter of the ceramic ball is preferably within a range of 1.05 or more and 2.00 or less. A height of an inner circumferential surface of the protruding portion relative to the diameter of the ceramic ball is preferably within a range of 0.01 or more and 0.10 or less.

Abstract: The sliding member according to the embodiment includes a silicon nitride sintered body that includes silicon nitride crystal grains and a grain boundary phase, in which a percentage of a number of the silicon nitride crystal grains including dislocation defect portions inside the silicon nitride crystal grains among any 50 of the silicon nitride crystal grains having completely visible contours in a 50 ?m×50 ?m observation region of any cross section or surface of the silicon nitride sintered body is not less than 0% and not more than 10%. The percentage is more preferably not less than 0% and not more than 3%.

Abstract: The present invention provides a silicon nitride wear resistant member comprising a silicon nitride sintered compact containing ?-Si3N4 crystal grains as a main component, 2 to 4% by mass of a rare earth element in terms of oxide, 2 to 6% by mass of Al in terms of oxide, and 0.1 to 5% by mass of Hf in terms of oxide, wherein the silicon nitride sintered compact has rare earth-Hf—O compound crystals; in an arbitrary section, an area ratio of the rare earth-Hf—O compound crystals in a grain boundary phase per unit area of 30 ?m×30 ?m is 5 to 50%; and variation of the area ratios of the rare earth-Hf—O compound crystals between the unit areas is 10% or less. Due to above structure, there can be provided a wear resistant member comprising the silicon nitride sintered compact having an excellent wear resistance and processability.

Abstract: The present invention provides a silicon nitride sintered body comprising a silicon nitride crystalline particle and a grain boundary phase, the silicon nitride sintered body having an area ratio of the grain boundary phase per 100 ?m×100 ?m unit area of 15 to 35% when an arbitrary cross section thereof is photographed. Further, it is preferable that the area ratio of the grain boundary phase per 100 ?m×100 ?m unit area is 15 to 25%. Furthermore, the silicon nitride sintered body is suitable for a wear resistant member. Due to above structure, there can be provided a silicon nitride sintered body and a wear resistant member having a high processability (workability) and an excellent sliding property.

Abstract: The present invention provides a silicon nitride wear resistant member comprising a silicon nitride sintered compact containing ?-Si3N4 crystal grains as a main component, 2 to 4% by mass of a rare earth element in terms of oxide, 2 to 6% by mass of Al in terms of oxide, and 0.1 to 5% by mass of Hf in terms of oxide, wherein the silicon nitride sintered compact has rare earth-Hf—O compound crystals; in an arbitrary section, an area ratio of the rare earth-Hf—O compound crystals in a grain boundary phase per unit area of 30 ?m×30 ?m is 5 to 50%; and variation of the area ratios of the rare earth-Hf—O compound crystals between the unit areas is 10% or less. Due to above structure, there can be provided a wear resistant member comprising the silicon nitride sintered compact having an excellent wear resistance and processability.

Abstract: The present invention provides a silicon nitride sintered body comprising a silicon nitride crystalline particle and a grain boundary phase, the silicon nitride sintered body having an area ratio of the grain boundary phase per 100 ?m×100 ?m unit area of 15 to 35% when an arbitrary cross section thereof is photographed. Further, it is preferable that the area ratio of the grain boundary phase per 100 ?m×100 ?m unit area is 15 to 25%. Furthermore, the silicon nitride sintered body is suitable for a wear resistant member. Due to above structure, there can be provided a silicon nitride sintered body and a wear resistant member having a high processability (workability) and an excellent sliding property.