Surface Hardness Test Method of Thermal Spray Coating

When the thickness of thermal spray coating is thin, such as the thickness of spray coating is less than 0.15 mm, the Vickers and Knoop microhardness test of metal coating and other related coatings (GB 9790-88) can be referred to.

When the thickness of thermal spray coating is above 0.15 mm, the surface Rockwell hardness N and T scales are used for hardness test according to the hardness of the spray coating. The N scale should be used when the hardness of the sample is equivalent to 20 HRC ~ 65 HRC; the T scale should be used when the hardness of the sample is equivalent to 99 HRB ~ 32 HRB.

Minimum thickness of spray coating with N and T scales

According to the difference in hardness of the sample, the minimum thickness of the spray coating required by the N scale and T scale is shown in Table 1 and Table 2.

Table 1 Minimum thickness of spray coating tested by Rockwell N scale

Table 2 Minimum thickness of spray coating tested by Rockwell T scale

The spray coating surface of the sample should be finely polished and not be affected by deformation caused by temperature and sample preparation process.

The recommended holding time of the total test force F is: for the sample that does not continue to deform with time after the test force is applied, the holding time is not less than 2 s. For specimens that continue to deform over time after the test force is applied, the holding time is 6 to 8 seconds. For specimens that are significantly deformed after the test force is applied, the holding time should be 20 to 25 seconds.

The distance between the centers of the two indentations or the distance between the center of the indentation and the edge of the specimen should not be less than 3 mm.

The hardness value is accurate to 0.5 hardness units. Each specimen should give the hardness value of 5 consecutive points. At the same time, the arithmetic mean of these 5 consecutive points should be given, and the lowest and highest values should also be given.