Standard Test Method for Hardness of Electrical Contact Materials

Abstract

3.1 The Rockwell hardness and Rockwell superficial tests are useful when the test specimens are sufficiently thick (in relation to the indentor load) to ensure that the results are not affected by the flow of metal on the surface of the anvil. On a solid piece the flow of metal on the under surface may be detected by a bulge or marking. On composite pieces where the contact materials are attached to backings of a different material, the thickness limitations imposed for a solid piece shall apply to the contact material portion of such composite pieces. Note 1: As a matter of information, it may be stated that tests on fine silver showed that on annealed samples having a Rockwell 15T hardness of 27, the readings were not affected on thicknesses 1/16 in. (1.6 mm) or over. On thicknesses of 1/32 in. (0.8 mm) Rockwell 15T scale readings of 72 and higher were not affected. 3.2 The microindentation hardness test is of questionable significance when the metallic phases in a material are so large that the indentation does not represent an accurate average hardness. Sintered contact materials usually contain segregates differing greatly in hardness from the matrix hardness and may destroy the validity of microindentation hardness readings. 3.3 Other aspects of significance and use shall be as described in the particular ASTM test method used, as listed in Section 2.