The non-uniformity of the hardness reference block is one of the important factors, which influence the hardness measurement. For calibration of hardness reference block, the elementary idea to reduce the error from this factor is to make the indentations at the distributed location as though covering the entire test surface with limited number of indentations. The principle to decide the appropriate numbers and locations of the measurement is to consider the trend and frequency of hardness distribution. “Stratified sampling” was introduced to the study on the assumption that the confidence of average hardness estimation would be increase with an appropriate test location. Six Vickers hardness reference blocks of 200, 600, 900 HV from 2 different manufacturers were selected for the experiment. The numbers of indentations were made on the entire surface of all blocks with three different levels of the test force. The analysis of hardness distributions was carried out with their measurement data with several aspects of the study. The possible trends of hardness distribution of the blocks, which, considered in the study i.e., circumferential divisions and radial divisions were selected to view the difference in hardness variation. The effect of stratified conditions to the measurement result was judged by using the analysis of variance (ANOVA). In most case of the experimental results, both stratifying conditions had significant influences on the reference blocks from both manufacturers with the different trends. Therefore, for higher confidence of hardness number estimation, the idea of test location specification should be taken into account by a considering of both stratifying conditions. Basically, the minimum numbers of indentations that give the reproducible hardness value upon the repeated measurement is desirable. By varying the stratifying conditions, the observed variations in hardness tended to decrease with the increasing number of strata. From the experiment, more than 6 to 12 strata were recommended for reliable hardness reference block measurement whereas 5 indentations were required as the minimum number in ISO 6507 part 3 [1].

Thermal barrier coatings (TBCs) have been applied to vanes / blades of gas turbines for recent electric power stations and these contribute to the efficiency of gas turbines. Measurement of Young’s modulus of the top-coat of TBCs with high accuracy is important since it is a dominant factor for determining the magnitude of thermal stress. However, until now, evaluation method for Young’s modulus of the top-coat has not been established, due to difficulty of material testing in its coated form. Furthermore, a porosity of the top-coat is changed by progress of sintering phenomenon caused by long-term high temperature exposure in air, consequently Young’s modulus of the topcoat is also influenced. In this study, various trials to evaluate Young’s modulus of the top-coat for application of the indentation test were conducted. Firstly, both dependency of the testing load and anisotropy on calculated Young’s modulus of the top-coat were discussed. Next, measurement of Young’s modulus of the top-coat after long-term high temperature exposure was carried out. Obtained results were verified by comparing with other method to measure Young’s modulus of the top-coat.

A new calibration machine according to the requirements given by ISO 14577-3 [1] was described in [2]. The results of the verification are reported in this paper. It is shown that the calibration machine can be used as a national standard for the materials parameter of the instrumented indentation test.

Hardness standard of tungsten single crystal were utilized in order to check stability and reproducibility of nanoindentation testers. The pop-in load and maximum penetration depth were measured and monitored during several hundreds of repeated experiments. One of the tested instruments showed gradual increase of pop-in load and decrease of maximum depth, which indicate the indenter tip was damaged by repeated tests. The both parameters, the pop-in load and the maximum depth, can be used to detect the change of the area function; the pop-in force is more sensitive and should be easy for general users. Other applications of tungsten single crystal are also discussed.

Among the various methods for characterizing the mechanical properties of small volume of materials, nano-indentation testing has gained more and more interests, due to its simple principle, the easy realization and application for various specimen, etc. However, nano-indentation instruments often fail to measure the mechanical properties of materials which demonstrate heavy creep, plasticity, etc. To overcome the disadvantages of nano-indentation instruments, here a new approach to develop the next generation of nano-indentation systems is proposed, in which the well-developed MEMS technique is employed. As one of the key components in the to be developed system, the loading component is now realized by an electrostatic comb-drive actuator, which can generate the required indentation force with high resolution. This microminiature indentation system will feature the advantages of small size, low power consumption, high precision in manufacture, the potential for low cost through batch fabrication, the ability for on-site applications, etc. In this paper the design of the MEMS system is detailed, including the simulation of the mechanical system and the system performance.