ASTM F2094/F2094M-18a

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: F2094/F2094M − 18 F2094/F2094M − 18a
Standard Specification for
Silicon Nitride Bearing Balls
This standard is issued under the fixed designation F2094/F2094M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This specification covers the establishment of the basic quality, physical/mechanical property, and test requirements for
silicon nitride balls Classes I, II, and III to be used for ball bearings and specialty ball applications.
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard.
1.3 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 Order of Precedence:
2.1.1 In the event of a conflict between the text of this document and the references herein, the text of this document takes
precedence. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been
obtained.
2.2 ASTM Standards:
C1161 Test Method for Flexural Strength of Advanced Ceramics at Ambient Temperature
C1421 Test Methods for Determination of Fracture Toughness of Advanced Ceramics at Ambient Temperature
2.3 ANSI Standard:
ANSI/ASQC Z1.4 Sampling Procedures and Tables for Inspection by Attributes
2.4 ABMA Standards:
STD 10 Metal Balls
2.5 ASME Standard:
B 46.1 Surface Texture (Surface Roughness, Waviness, and Lay)
2.6 ISO Standards:
4505 Hardmetals—Metallographic Determination of Porosity and Uncombined Carbon
2.7 JIS Standards:
R 1601 Testing Method for Flexural Strength (Modulus of Rupture) of High Performance Ceramics
R 1607 Testing Method for Fracture Toughness of High Performance Ceramics
This specification is under the jurisdiction of ASTM Committee F34 on Rolling Element Bearings and is the direct responsibility of Subcommittee F34.01 on Rolling
Element.
Current edition approved April 1, 2018May 1, 2018. Published July 2018. Originally approved in 2001. Last previous edition approved in 20142018 as
ɛ1
F2094/F2094M–14–18. . DOI: 10.1520/F2094_F2094M-18.10.1520/F2094_F2094M-18A.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Application for copies should be addressed to the American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Application for copies should be addressed to the American Bearing Manufacturer’s Association, 1200 19th Street NW, Suite 300, Washington, DC 20036-2401.
Application for copies should be addressed to the American Society of Mechanical Engineers (ASME), ASME International Headquarters, Three Park Ave., New York,
NY 10016-5990, http://www.asme.org.
Application for copies should be addressed to the Available from International Organization for Standardization (ISO), ISO Central Secretariat, BIBC II, Chemin de
Blandonnet 8, CP 401, 1214 Vernier, Geneva, Switzerland, http://www.iso.org.
Application for copies should be addressed to the Japanese Standards Organization (JSA), 4-1-24 Akasaka Minato-Ku, Tokyo, 107-8440, Japan, http://www.jsa.or.jp.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2094/F2094M − 18a
2.8 CEN Standards:
EN 843-1 Advanced Technical Ceramics—Monolithic Ceramics—Mechanical Properties at Room Temperature, Part 1.
Determination of Flexural Strength
ENV 843-5 Advanced Technical Ceramics—Monolithic Ceramics—Mechanical Properties at Room Temperature, Part 5,
Statistical Analysis
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 ball diameter variation, Vdws, n—ball diameter variation is the difference between the largest and smallest diameter
measured on the same ball.
3.1.2 ball gauge, S, n—prescribed small amount by which the lot mean diameter should differ from nominal diameter, this
amount being one of an established series of amounts. A ball gauge, in combination with the ball grade and nominal ball diameter,
should be considered as the most exact ball size specification to be used by a customer for ordering purposes.
3.1.3 ball gauge deviation, ΔS, n—difference between the lot mean diameter and the sum of the nominal diameter and the ball
gauge.
3.1.4 ball grade, G, n—specific combination of dimensional form and surface roughness tolerances. A ball grade is designated
by a grade number followed by the letter “C” indicating Silicon Nitride Ceramic.
3.1.5 blank lot, n—single group of same-sized ball blanks processed together from one material lot through densification.
3.1.6 ceramic second phase, n—sintering additive based phases, for example, yttria and alumina, which appear darker or lighter
than the silicon nitride matrix, but are not highly reflective in nature when viewed under reflected light microscopy and bright field
illumination.
3.1.7 color variation, n—an area that appears lighter or darker than the surrounding area under reflected light microscopy but
with no discernible physical discontinuity associated with it.
3.1.7.1 Discussion—
Color variation is often not visible under scanning electron microscopy (SEM) examination.
3.1.8 c-cracks, n—curved, constant radius cracks, the result of ball-to-ball impact during finishing or subsequent handling. In
extreme cases, the cracks can form a complete circle and multiple concentric cracks can form.
3.1.9 cracks, n—irregular, narrow breaks in the surface of the ball typically having a visible width of less than 0.002 mm
[0.00008 in.]
3.1.9.1 Discussion—
Most cracks are formed after densification but occasionally may be present as material faults. Some cracks may not be visible with
normal white light microscopy and may only show up under ultraviolet light after processing with a suitable fluorescent penetrant.
3.1.10 cuts, n—Mechanically induced random, short, linear depressions in the surface.
3.1.11 deviation from spherical form, ΔRw, n—greatest radial distance in any radial plane between a sphere circumscribed
around the ball surface and any point on the ball surface.
3.1.12 finish lot, n—single group of same-sized balls (which may be derived from multiple blank lots of the same material lot)
processed together through finishing.
3.1.13 inclusion, n—any discrete imhomogeneity in the microstructure that is not intended to be included in the material.
3.1.13.1 Discussion—
Inclusions typically consist of foreign material as a result of unintended external powder contamination and resulting reaction
product after sintering.
3.1.14 lot diameter variation, Vdwl, n—difference between the mean diameter of the largest ball and that of the smallest ball
in the lot.
3.1.15 lot mean diameter, Dwml, n—arithmetic mean of the mean diameter of the largest ball and that of the smallest ball in
the lot.
Application for copies should be addressed to the British Standards Institute (BSI), 389 Chiswick High Rd., London W4 4AL, U.K., http://www.bsi-global.com.
F2094/F2094M − 18a
3.1.16 material lot, n—single process lot of a blended powder (blended with additives), produced from a single lot of silicon
nitride or silicon metal raw powder received from a material supplier.
3.1.16.1 Discussion—
What constitutes a “single process lot” of blended powder can vary depending on the standard practices of the vendor and the
requirements of the customer and application. For example, for many customers/applications, combining multiple mill charges
from one raw material lot into a single material lot is acceptable while for others, each mill charge would be considered a separate
material lot. It is difficult, if not impossible, for a single definition of material lot to apply to all applications. The material lot should
be defined such that application-appropriate traceability is maintained and adequate testing appropriate for the intended application
is performed to ensure that the chemistry and material properties of densified parts meet specifications. The material lot
requirements should be discussed and agreed between the vendor and customer.
3.1.17 mean diameter of a ball, Dwm, n—arithmetic mean of the largest and the smallest actual single diameters of the ball.
3.1.18 metallic phase, n—material phase that is highly reflective when viewed by reflected light microscopy and bright field
illumination.
3.1.19 metallic smears, n—metallic material from lapping or measuring equipment transferred onto the ball surface.
3.1.20 nominal diameter, Dw, n—size ordered that is the basis to which the nominal diameter tolerances apply. The nominal
diameter is specified in inches or millimeters (decimal form).
3.1.21 nominal diameter tolerance, n—maximum allowable deviation from true specified nominal diameter for the indicated
grade.
3.1.22 pits, n—voids or cavities in the ball surface.
3.1.22.1 Discussion—
Pits can be formed by severe material pullout during ball finishing. Pits can also be a result of breakout of inclusions during
finishing.
3.1.23 porosity, n—small, closely spaced voids permeating a region of the ball surface or the whole ball.
3.1.24 pressing defects, n—the result of cracks in the ball blanks prior to densification.
3.1.24.1 Discussion—
Some pressing defects heal more or less completely on densification resulting in a region of material with slightly different
composition and optical characteristics than the rest of the ball. These are known as healed or partially healed pressing defects.
Unhealed or open pressing defects can have the appearance of cracks or fissures.
3.1.25 raw material lot, n—single process lot of raw silicon nitride or raw silicon metal powder received from a material
supplier.
3.1.26 scratches, n—narrow, linear, shallow abrasions on the surface.
3.1.27 scuffs, n—a dense concentration of small, parallel superficial scratches.
3.1.28 single diameter of a ball, Dws, n—the distance between two parallel planes tangent to the surface of the ball.
3.1.29 snowflakes, n—regions of microporosity in the grain boundary phase that often display a dendritic appearance.
3.1.29.1 Discussion—
Snowflakes show up as white dendritic features when viewed with oblique illumination or with ultraviolet light after processing
with a fluorescent penetrant. The individual micropores are often submicron in size and the snowflakes can range in size from less
than 10 μm [.00039 in.] to over 1,000 μm [.039 in.] in extreme cases.
3.1.30 surface roughness Ra, n—surface irregularities with relative small spacings, which usually include irregularities resulting
from the method of manufacture being used or other influences, or both.
3.1.31 unit container, n—container identified as containing balls from the same manufacture lot of the same composition, grade,
and nominal diameter, and within the allowable diameter variation per unit container for the specified grade.
4. Classification
4.1 Silicon nitride materials for bearing and specialty ball applications are specified according to the following material classes
(see Appendix X1 for typical current applications):
F2094/F2094M − 18a
4.1.1 Class I—Highest grade of material in terms of properties and microstructure. Suitable for use in the most demanding
applications. This group adds high reliability and durability for extreme performance requirements.
4.1.2 Class II—General class of material for most bearing and specialty ball applications. This group addresses the concerns of
ball defects as is relative to fatigue life, levels of torque, and noise.
4.1.3 Class III—Lower grade of material for low duty applications only. This group of applications primarily takes advantage
of silicon nitride material properties. For example: Light weight, chemical inertness, lubricant life extension due to dissimilarity
with race materials, and so forth.
5. Ordering Information
5.1 Acquisition documents should specify the following:
5.1.1 Title, number, and date of this specification.
5.1.2 Class, grade, and size (see 4.1, 8.6, and 8.7).
6. Material
6.1 Unless otherwise specified, physical and mechanical property requirements will apply to all material classes.
6.2 To be classified as Class I, silicon nitride balls shall be produced from either silicon nitride powder having the compositional
limits listed in Table 1 or from silicon metal powder, which after nitridation complies with the compositional limits listed in Table
1.
6.3 Composition is measured in weight percent. Testing shall be carried out by a facility qualified and approved by the supplier.
Specific equipment, tests, and/or methods are subject to agreement between suppliers and their customers.
6.4 Compounds may be added to promote densification and enhance product performance and quality.
6.5 Iron oxides may be added to promote densification with the total iron content for the final product not to exceed 1.0 weight
%.
6.6 Precautions should be taken to minimize contamination by foreign materials during all stages of processing up to and
including densification.
6.7 A residual content of up to 2 % tungsten carbide from powder processing is allowable.
6.8 Final composition shall meet and be reported according to the specification of the individual supplier.
6.9 Notification will be made upon process changes.
6.10 Specific requirements such as specific material grade designation, physical/mechanical property requirements (for
example, density) or quality or testing requirements shall be established by specific application. The special requirements shall be
in addition to the general requirements established in this specification.
6.11 Typical mechanical properties will fall within the range listed in Table 2. Individual requirements may have tighter ranges.
The vendor shall certify that the silicon nitride material supplied has physical and mechanical properties within the range given
in Table 2. In the case of properties indicated by (+), the provision of the data is not mandatory.
7. Physical Properties
7.1 The following physical properties shall be measured, at a minimum, on each material lot.
7.1.1 Average values for room temperature rupture strength (bend strength/modulus of rupture) for a minimum of 20 individual
determinations shall exceed the minimum values given in Table 3. Either 3-point or 4-point test methods may be used for flexural
strength, which should be measured in accordance with Test Method C1161 (size B), CEN 843-5, or JIS R 1601. Weibull modulus
for each test series shall also exceed the minimum permitted values given in Table 3. If a sample set of specimens for a material
lot does not meet the Weibull modulus requirement in Table 3, then a second sample set may be tested to establish conformance.
TABLE 1 Compositional Limits for Starting Silicon Nitride
Powders or Silicon Powder Converted to Silicon Nitride for
A
Class I Materials
Constituents Limits (wt %)
Silicon nitride 97.0 min.
Free silicon 0.3 max.
Carbon 0.3 max
Iron 0.5 max.
A
Other impurities or elements such as sodium, potassium, chlorine, etc. individu-
ally shall not exceed 0.02 wt % max.
F2094/F2094M − 18a
A
TABLE 2 Typical Mechanical Properties
Properties Minimum Maximum
Density, g/cc [lb/ft ] 3.0 [187] 3.4 [212]
Elastic modulus, GPa [ksi] 270 [39 150] 330 [47 850]
Poisson’s ratio 0.23 0.29
Coefficient of thermal expansion, ×10 2.3 3.4
-6/°C
(room temp. to 500 °C)
10 16
+ Resistivity, Ohm-m 10 10
+ Compressive strength, MPa [ksi] 3000 [435]
A
Special material data should be obtained from individual suppliers.
TABLE 3 Minimum Values for Mean Flexural Strength and
Weibull Modulus
Material Class
Unit I II III
Transverse-
rupture
A
strength
3 point σ MPa 900 [920] 800 [825] 600 [625]
3,40
(σ )
3,30
Weibull 12 9 7
modulus
Transverse-
rupture
A
strength
4-point σ MPa 765 [805] 660 [705] 485 [530]
4,40
(σ )
4,30
Weibull 12 9 7
modulus
A
The Flexural strength equivalents are based on Weibull volume or surface
scaling using the value o
...