The Rockwell hardness test is commonly used and accepted by many industrial users, but the hardness value requires conversion between scales because the geometry of the indenters and the load ranges are different. On the other hand, hardness calculation using pyramidal indenters is quite simple and can be applied to any load range, though it is much more complicated to calibrate the frame compliance and the truncation of indenters in nanoindentation measurement. For this reason, nanoindentation measurement is not yet fully industrially friendly. In order to improve the above situation, newly developed industrial hardness test methods and a new concept of “Equivalent indentation depth (or indentation depth index)” were proposed and investigated in this paper. These methods are based on the principle of “similarity” of Vickers and other pyramidal indenters, and take advantage of the industrial and practical usability of the Rockwell hardness test. Experimental results that covered macroscopic through nanoscopic ranges show that the methods can be applied to a wide range of test loads. One of the expected advantages of the methods of performing nanoindentation and other instrumented indentation tests (ISO 14577) is that the hardness is not significantly influenced by the frame compliance or the truncation of indenters. Other advantages over conventional hardness tests are also discussed in this paper. More experimental work is necessary to confirm and establish the new methods.

Brinell hardness measurements are widely used at industrial level. For the calculation of Brinell hardness values, the measurement of the diameter of indentations is necessary. In practice, the measurement of the image created by the optical systems used for the magnification of the indentation is usually carried out. The dimension of the indentation image depends by the optical system that, in practice, transform the real indentation in image using properties of light reflection. The paper describe the effect of this influence parameter in Brinell hardness measurements in experiments carried out at hardness laboratory of Istituto Nazionale di Ricerca Metrologica (INRIM) (formerly Istituto di Metrologia “G. Colonnetti” – IMGC) with application to the data obtained at international comparison at the National Metrology Institutes level. Moreover, some methods for its evaluation and possible correction will be proposed.

Significant measurement differences have been continually observed worldwide in Brinell hardness tests, even in the secondary calibration laboratories that calibrate test block reference standards. The main cause of this problem is the edge of the indentation is not a distinct boundary, but is instead a curved surface from either material piling up (pile-up) or sinking in (sink-in) caused by plastic flow of the material surrounding the ball indenter. This makes it difficult to clearly resolve the edge of the indentation and thus determine the indentation diameter. In this research, Brinell hardness indentations were made using various indentation forces and ball indenter sizes. Using a confocal microscope, the indentations were measured in three dimensions from which the indentation profiles were determined. Additionally, finite element analysis (FEA) models were developed for studying the location of contact points at indentation pile-up edges. From both microscope measurements and FEA simulations, the difference between the measured indentation diameter and the actual contact diameter was determined for each indentation.

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.