Metrological characteristics of newly developed reference Vickers hardness blocks for the high hardness range

Abstract

The paper describes the development and characterisation of metrological characteristics of reference Vickers hardness blocks for the high hardness range, development of the system for indentation analysis and interlaboratory comparison. The primary goal of the research was to develop the reference Vickers hardness block from nanostructured hardmetal with a hardness value of approximately 2000 HV1. Based on long-term and extensive research, reference Vickers hardness blocks with optimal metrological characteristics were selected and presented in the paper. Two blocks were consolidated using different powder metallurgy processes; sintering in a hydrogen atmosphere and a sinter hot isostatic pressing (sinter-HIP) process were described. The surfaces of the blocks were researched in terms of material and metrological characteristics and prepared to maintain the requirements according to EN ISO 6507-3:2005, concerning flatness, parallelism and surface roughness. In order to achieve more accurate and precise measurements of the indentations, the lengths of diagonals were measured using the 1D optical measurement system (1D OMS) developed by the National Laboratory for Length HMI/FSB-LPMD for high accuracy line scale calibration. Custom software was developed in Visual Studio 2012. To confirm the reliability of the hardness values determined by the 1D OMS and newly developed software for indentation analysis, the interlaboratory comparison was performed on the primary micro-hardness machine installed in the Physikalische-Technische Bundesanstalt (PTB), Germany. From the conducted research it was concluded that preliminary Vickers hardness blocks were developed successfully from nanostructured hardmetals. Higher hardness and lower non-uniformities over the test surface were achieved for fully dense blocks consolidated by a sinter-HIP process. The intercomparison confirmed the reliability of the measured results determined on the reference hardness standard and 1D OMS with newly developed software.