ASTM B578-21

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Designation: B578 − 87 (Reapproved 2015) B578 − 21
Standard Test Method for
Microhardness Microindentation Hardness of Electroplated
Coatings
This standard is issued under the fixed designation B578; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 This test method covers the determination of the hardness of metallic coatings upon various substrates. The measurements are
made with the Knoop indenter under a test load of 0.245 N (25 gf) or 0.981 N (100 gf).
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
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 ASTM Standards:
E92 Test Methods for Vickers Hardness and Knoop Hardness of Metallic Materials
E384 Test Method for Microindentation Hardness of Materials
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Special Requirements
3.1 In addition to the requirements listed herein, the test method shall be performed in accordance with Test Method E384.
3.1.1 The measurement shall be made on the cross section with the long diagonal of the indentation parallel to the substrate using
a Knoop indenter.
NOTE 1—When a nondestructive test is necessary, the measurement may be made normal to the surface provided that the whole of the indentation is
clearly delineated in the field of the microscope at the magnification specified in Test Method E384, and the coating thickness is at least 0.7 that of the
long diagonal. The outlines of the indentation must be sharp and undistorted by any mechanical effects resulting from the thinness of the coating such
as “butterfly” fractures, etc. Values obtained from measurements made normal to the electroplated surface may not be equivalent to those obtained on
microsections and are not, therefore, reportable according to Section 6.
This test method is under the jurisdiction of ASTM Committee B08 on Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on Test
Methods.
Current edition approved March 1, 2015Oct. 1, 2021. Published April 2015October 2021. Originally approved in 1973. Last previous edition approved in 20092015 as
B578 – 87 (2009).(2015). DOI: 10.1520/B0578-87R15.10.1520/B0578-21.
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.
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B578 − 21
3.1.2 The thickness of the coating shall be at least 38 μm for soft coatings such as gold, copper, and silver, and 25 μm for hard
coatings such as nickel, cobalt, iron, and hard gold. This is approximately equivalent to 0.6 times the length of the long Knoop
diagonal.
3.1.3 Make the indentation near the center of the cross section of the coating.
3.2 No single test load is applicable to all coatings. Use a load of 0.245 N for soft coatings (from 50 to 300 HK) and a load of
0.981 N for hard coatings (greater than 300 HK).
3.2.1 A load of less than 0.245 N is not recommended. However, when the length of the diagonal is great enough at a load of 0.245
N, which may occur for very soft coatings such as tin and indium, a lighter load or a lower magnification shall be specified
provided the requirements of 3.3 are met. When testing extremely hard coatings, a load greater than 0.981 N may be used provided
this is specified in the purchase order. The Knoop hardness number decreases appreciably with loads from 0.245 N to 0.981 N
especially for the higher hardness numbers.
3.3 Measure the length of the long diagonal to within 0.25 μm or 0.4 %, whichever is larger, at the magnification specified in Test
MethodMethods E384E92.
3.4 When readings are taken in a direction parallel to the substrate, space them from each other by at least the length of the long
diagonal. When two readings are taken in the direction of the short axis, separate them by at least one and a half the length of the
diagonal perpendicular to the substrate (short diagonal). In such cases, the distance from the substrate and from the outer surface
of the coating to an edge of the indentation shall be at least twice the width of the short diagonal.
3.5 If the electroplated coating is cracked, or if cracks or “butterfly” markings (see 7.2 of Test Method E384) appear when the
indentation load is applied or removed, the hardness measurement is invalid.
4. Preparation of Test Specimen
4.1 Overplate the specimen to a thickness of at least 12 μm with a metal of a contrasting color whose hardness approximates that
of the coat
...