JP-WO2025041805-A5 - Silicon nitride sintered body and wear-resistant member using the same

Dates

Publication Date

20260507

Application Date

20240821

Description

The embodiments described later relate to silicon nitride sintered bodies and wear- resistant members using the same. Silicon nitride sintered bodies possess excellent mechanical properties (hardness, toughness, strength, etc.). Taking advantage of these properties, silicon nitride sintered bodies are used in wear-resistant components and substrates for semiconductor devices. Wear- resistant components include bearing balls, friction stir welding tool components, and engine parts. In recent years, silicon nitride sintered bodies have been used in bearing balls for electric vehicle motors, and demand for them is increasing. As shown in Non-Patent Document 1, a change in rotational speed leads to a change in torque. Torque, in mechanics, is the moment of force acting around a fixed axis of rotation. A change in rotational speed is a change in the number of rotations per unit time. When the rotational speed changes, the torque (i.e., stress) on the bearing balls also changes. In the bearing balls described in Patent Document 1 or Patent Document 2, durability sometimes decreased when used in environments where torque changes. If necessary, it is preferable to perform a hot isostatic pressing (HIP) treatment at 30 MPa or higher in a non-oxidizing atmosphere after the sintering process. The non-oxidizing atmosphere is, for example, a nitrogen atmosphere or an argon atmosphere. The temperature of the HIP treatment is preferably in the range of 1500°C to 1900°C. By performing the HIP treatment, it is possible to reduce (e.g., eliminate) pores in the silicon nitride sintered body. If the pressure of the HIP treatment is less than 30 MPa, such an effect cannot be fully obtained. For this reason , the pressure is preferably 30 MPa or higher. There is no particular upper limit to the pressure of the HIP treatment, but it is preferably 200 MPa or lower. If it is higher than 200 MPa, the load on the equipment may increase. In the embodiments, the rate of increase in the sliding noise of the bearing balls was suppressed. In embodiments 10 and 14-16, the rate of increase in sliding noise after 800 hours was slightly larger than in the other embodiments. This is thought to be due to the larger area ratio of the white region. In addition, in many embodiments, the occurrence of electrolytic corrosion of the bearing balls was suppressed. From these results, it was found that according to the embodiments, even silicon nitride sintered bodies manufactured from silicon nitride powder with a high amount of impurities can have their properties improved. In embodiments 14-16, although the wear resistance was good, the occurrence of electrolytic corrosion was confirmed. This is because the amount of impurities (amount of Fe, Cr, or Ca) was higher compared to the other embodiments. In contrast, in the comparative examples, the rate of increase in sliding noise after 800 hours was large. The occurrence of electrolytic corrosion was also confirmed.