Silicon nitride wear resistant member and method of manufacturing the member

• US 6,784,131 B2
• Filed: 01/11/2002
• Issued: 08/31/2004
• Est. Priority Date: 01/12/2001
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Komorita, Hiroshi, Tonai, Hiroki, Komatsu, Michiyasu
• Primary Examiner(s): GROUP, KARL E
• Application Number:
  US10/042,254
• Publication Number:
  US 20020136908A1
• Time in Patent Office: 963 Days
• Field of Search: 501/97.1, 501/97.2, 501/97.3, 501/97.4, 384/492, 384/907.1
• US Class Current: 501/97.1
• CPC Class Codes: C04B 2235/3206 Magnesium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3217 Aluminum oxide or oxide forming salts thereof, e.g. bauxite, alpha-alumina
• CPC Class Codes: C04B 2235/3224 Rare earth oxide or oxide forming salts thereof, e.g. scandium oxide
• CPC Class Codes: C04B 2235/3225 Yttrium oxide or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3232 Titanium oxides or titanates, e.g. rutile or anatase
• CPC Class Codes: C04B 2235/3241 Chromium oxides, chromates, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3244 Zirconium oxides, zirconates, hafnium oxides, hafnates, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3251 Niobium oxides, niobates, tantalum oxides, tantalates, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3256 Molybdenum oxides, molybdates or oxide forming salts thereof, e.g. cadmium molybdate
• CPC Class Codes: C04B 2235/3258 Tungsten oxides, tungstates, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3865 Aluminium nitrides
• CPC Class Codes: C04B 2235/3878 Alpha silicon nitrides
• CPC Class Codes: C04B 2235/3895 Non-oxides with a defined oxygen content, e.g. SiOC, TiON
• CPC Class Codes: C04B 2235/5445 submicron sized, i.e. from 0,1 to 1 micron
• CPC Class Codes: C04B 2235/604 Pressing at temperatures other than sintering temperatures
• CPC Class Codes: C04B 2235/6565 Cooling rate
• CPC Class Codes: C04B 2235/658 Atmosphere during thermal treatment
• CPC Class Codes: C04B 2235/6581 Total pressure below 1 atmosphere, e.g. vacuum
• CPC Class Codes: C04B 2235/661 Multi-step sintering
• CPC Class Codes: C04B 2235/723 Oxygen content
• CPC Class Codes: C04B 2235/75 : Products with a concentration gradient
• CPC Class Codes: C04B 2235/77 : Density
• CPC Class Codes: C04B 2235/94 : Products characterised by their shape
• CPC Class Codes: C04B 2235/95 : Products characterised by their size, e.g. microceramics
• CPC Class Codes: C04B 2235/96 : Properties of ceramic products, e.g. mechanical properties such as strength, toughness, wear resistance
• CPC Class Codes: C04B 2235/963 : Surface properties, e.g. surface roughness
• CPC Class Codes: C04B 35/5935 : obtained by gas pressure sintering
• CPC Class Codes: F16C 33/32 : Balls

Abstract

The present invention provides a silicon nitride wear resistant member composed of silicon nitride sintered body containing 1-10 mass % of rare earth element in terms of oxide thereof as sintering agent, wherein a total oxygen content of the silicon nitride sintered body is 6 mass % or less, a porosity of the silicon nitride sintered body is 0.5 vol. % or less, and a maximum size of pore existing in grain boundary phase of the silicon nitride sintered body is 0.3 μm or less. According to the above structure of the present invention, there can be provided a silicon nitride wear resistant member and a method of manufacturing the member having a high strength and a toughness property, and particularly excellent in sliding characteristics.

Claims

1. A rolling bearing member comprising a silicon nitride sintered body comprising 1-10 mass % of rare earth element in terms of oxide thereof as sintering agent, wherein a total oxygen content of said silicon nitride sintered body is 6 mass % or less, a porosity of said silicon nitride sintered body is 0.5 vol. % or less, and a maximum size of pore existing in grain boundary phase of the silicon nitride sintered body is 0.3 μ

m or less.

2. The rolling bearing member according to claim 1, wherein said silicon nitride sintered body has a three point bending strength of 900 MPa or more and a fracture toughness of 6.5 MPa·

m^1/2 or more, and a rolling life defined as a rotation number of steel balls rolling along a circular track formed on the rolling bearing member formed of said silicon nitride sintered body until a surface of said silicon nitride rolling bearing member peels off is 1×

10⁸ or more, when said rolling life is measured in such a manner that a circular track having a diameter of 40 mm is set on the rolling bearing member, three rolling balls each having a diameter of 9.525 mm and composed of SUJ2 are provided on said circular track, and the rolling balls are rotated on the track at a rotation speed of 1200 rpm under a condition of being applied with a pressing load of 400 Kg.

3. The rolling bearing member according to claim 1, wherein said silicon nitride sintered body has a crash strength of 200 MPa or more and a fracture toughness of 6.5 MPa·

m^1/2 or more, and a rolling fatigue life defined as a time until a surface of rolling balls composed of said silicon nitride rolling bearing member rolling along a circular track formed on a steel plate peels off is 400 hours or more, when said rolling fatigue life is measured in such a manner that three rolling balls each having a diameter of 9.525 mm are formed from said silicon nitride rolling bearing member, said three rolling balls are provided on the circular track having a diameter of 40 mm set on the steel plate formed of SUJ2, and the rolling balls are rotated at a rotation speed of 1200 rpm on the track under a condition of being applied with a pressing load so as to impart a maximum contact stress of 5.9 GPa to the balls.

4. The rolling bearing member according to any one of claim 1 to 3, wherein said silicon nitride sintered body comprises at most 5 mass % of at least one of aluminum and magnesium in terms of the amount of oxide thereof.

5. The rolling bearing member according to claim 1, wherein said silicon nitride sintered body comprises at most 5 mass % of aluminum nitride.

6. The rolling bearing member according to claim 1, wherein said silicon nitride sintered body comprises at most 5 mass % of at least one element selected from the group consisting of Ti, Hf, Zr, W, Mo, Ta, Nb and Cr in terms of oxide thereof.

7. The rolling bearing member according to claim 1, wherein said silicon nitride sintered body comprises an outer peripheral portion having an oxygen content lower than that of a center portion, and a difference of the oxygen contents between the outer peripheral portion and the center portion is within a range of 0.2-2 mass %.

8. The rolling bearing member according to claim 1, wherein said silicon nitride sintered body has a Vickers'"'"' hardness of 1200 or more.

9. The rolling bearing member according to claim 7, wherein said rare earth element comprises a metal, and a difference in content of the metal contained in sintering agent in the outer peripheral portion and the center portion is 0.2 mass % or less.

10. The rolling bearing member according to claim 7, wherein said silicon nitride sintered body comprises an intermediate portion of which oxygen content is at most 1 mass % lower than that of the center portion.

11. The rolling bearing member according to claim 7, wherein said rolling bearing member comprising the silicon nitride sintered body is a bearing ball.

12. The rolling bearing member according to claim 11, wherein said bearing ball has a diameter of 9 mm or more.

13. A method of manufacturing a rolling bearing member according to claim 1, comprising:

preparing a material mixture by adding 1 to 10 mass % of a rare earth element in terms of the amount of an oxide thereof to a silicon nitride powder containing at most 1.5 mass % of oxygen and 75-97 mass % of α

-phase type silicon nitride and having an average grain size of 1.0 μ

m or less;

molding said material mixture to form a compact;

degreasing said compact;

heating and holding said compact at a temperature of 1,250-1,600°

C. for a predetermined period of time on the way to a sintering step; and

conducting a main sintering for the compact at a temperature of 1,650-1,850°

C. thereby to form a rolling bearing member composed of silicon nitride sintered body.

14. The method claim 13, wherein said method further comprises moderately cooling the sintered body at a cooling rate of at most 100°

C. per hour until the sintering temperature is reduced to a point at which a liquid phase formed by the rare earth element during the sintering step solidifies.

15. The method of claim 13, wherein at most 5 mass % of at least one of aluminum and magnesium in terms of the amount of oxide thereof is added to said silicon nitride powder.

16. The method of claim 13, wherein at most 5 mass % of aluminum nitride is added to said silicon nitride powder.

17. The method of claim 13, wherein at most 5 mass % of at least one element selected from the group consisting of Ti, Hf, Zr, W, Mo, Ta, Nb and Cr in terms of oxide is added to said silicon nitride powder.

18. The method of claim 13, wherein said method further comprises conducting a hot isostatic pressing treatment (HIP) on said silicon nitride sintered body in a non-oxidizing atmosphere of 300 atm or more at a temperature of 1,600-1,850°

C. after completion of the sintering step.