The automatic testers in microhardness measurement and ISE effect

Abstract

The measurement of micro-hardness with the applied loads 0.09807 N, 0.24518 N, 0.49035 N and 0.9807 N has been carried out by three automatic and one manually-operated micro-hardness testers. The certified reference material (CRM) was the tested sample. Each operator obtained the readings of the tester, which she/he normally operates. The measurement was repeated after thirty months. The influence of the testers and their stability, as well as applied load on the measured values of the micro-hardness and the indentation size phenomenon (ISE), were evaluated. The parametric and non-parametric tests, Analysis of Variance (ANOVA), Z-score and Total Dispersion Zone were used for the evaluation of the statistical significance of obtained factors. The ISE was evaluated using Meyer’s and Proportional Specimen Resistance model and also by Hays – Kendall approach. The variability of measured values of the micro-hardness and parameters of ISE is high despite the use of automatic hardness testers with practically excluding the impact of the operator. The results are affected by operators, used testers and by applied loads. The measurement system can’t be considered to be stable.