ISO 23458:2020 pdf free download – Fine ceramics (advanced ceramics, advanced technical ceramics)一Test method for determining thermal expansion coefficient and residual stress of CVD ceramic coatings.
5.5 Data recording system
A system capable of measuring displacements to an accuracy better than 0,0 00 1 mm. The system shall allow recording of the test piece temperature and the displacement simultaneously.
An analogue chart recorder or digital data collection system should be used. The error of the recording system shall be 1 % or lower. The minimum data collection frequency shall be 15 Hz and a response frequency of 50 Hz is deemed adequate.
5.6 Dimensional measuring devices
The dimensions of the test piece shall be measured using a Vernier calliper conforming with Iso 3611 and with precision of 0,02 mm or better, or other calibrated measuring device providing the same or better measurement accuracy.
Coating thickness shall be measured by using a calibrated optical microscope with magnification of 1 000 times or better. Sample displacement shall be measured using a calibrated electronic micrometer with a precision of at least 0,001 mm and resolution of 0,000 5 mm or better, or other measuring device providing the same or better measurement accuracy. All calibrations shall be traceable to national standards.
6 Specimens
6.1 Test piece
In order to simplify the preparation of test pieces, three different symmetrical structures of coating configurations are considered:
a) coating on upper and lower surfaces of the test pieces only (two-face coating, Figure 2 a);
b) coating on four surfaces of the test pieces (four-face coating, Figure 2 b);
c) coating on cylinder surface of the test pieces (around coating, Figure 2 c). Any of the three coating configurations may be used for evaluating the properties of the coating layer.
7.4 Calculation of the residual stress in CVD coatings
Residual stress in coating is not a material constant and varies with the cross-sectional area ratio of the substrate to coating. For a coated component, the residual stress can be calculated from elastic modulus, expansion coefficient, cross-sectional area ratio of the coating and substrate, and preparation temperature. Both the residual stress of the test pieces and the residual stress of any component with the same coating but different area ratios can be calculated.
For the real structural CVD coatings, the cross-sectional area ratio of the substrate to coating is obtained by using an optical microscope and then the residual stress in coatings is calculated.
9 Test report
The test report shall contain at least the following information:
a) the name and address of the testing establishment;
b) the date of the test and customer name, address and signature;
c) a reference to this document, i.e. ISO 23458:2020;
d) the test piece shape, size and coating thickness;
e) a description of the test material (material type, manufacturing code);
f) the maximum testing temperature;
g) the testing atmosphere;
h) the minimum, mean and maximum values of residual stress;
i) the minimum, mean and maximum values of linear thermal expansion coefficient;
j) the temperature and humidity of the laboratory.