Microform Calibration Uncertainties of Rockwell Diamond Indenters

Abstract

National and international comparisons in Rockwell hardness tests show significant differences. Uncertainties in the geometry of the Rockwell diamond indenters are largely responsible for these differences. By using a stylus instrument, with a series of calibration and check standards, and calibration and uncertainty calculation procedures, we have calibrated the microform geometric parameters of Rockwell diamond indenters. These calibrations are traceable to fundamental standards. The expanded uncertainties (95 % level of confidence) are ±0.3 μm for the least-squares radius; ±0.01° for the cone angle; and ±0.025° for the holder axis alignment calibrations. Under ISO and NIST guidelines for expressing measurement uncertainties, the calibration and uncertainty calculation procedure, error sources, and uncertainty components are described, and the expanded uncertainties are calculated. The instrumentation and calibration procedure also allows the measurement of profile deviation from the least-squares radius and cone flank straightness. The surface roughness and the shape of the spherical tip of the diamond indenter can also be explored and quantified. Our calibration approach makes it possible to quantify the uncertainty, uniformity, and reproducibility of Rockwell diamond indenter microform geometry, as well as to unify the Rockwell hardness standards, through fundamental measurements rather than by performance comparisons.

Establishing a world-wide unified Rockwell hardness scale with metrological traceability

“…The form er is mainly a standardization issue; the solution would be an international agreement on a standardized common testin g cycle for world-w ide uni® ed scales. The latter is a m etrological issue; the solution is based on precision metrology to establish high-quality standard Rockwell indenters [12,13]. Ideally, these standard indenters should be characterized by high geometric uniformity, high hardness performance uniformity, interchangeability and reproducibility [13].…”

“…The latter is a m etrological issue; the solution is based on precision metrology to establish high-quality standard Rockwell indenters [12,13]. Ideally, these standard indenters should be characterized by high geometric uniformity, high hardness performance uniformity, interchangeability and reproducibility [13].…”

“…Both geometric and nongeometric properties affect the hardness perform ance of the indenters. We discuss these properties below [13].…”

A method for measuring the geometrical topography of a Rockwell diamond indenter

“…It is necessary to identify the geometrical topography of the indenter in advance. Several pieces of apparatus [7][8][9] have been developed to measure the geometrical topography of the Rockwell diamond indenter with the contact stylus method. Although they have good results, they are time consuming for three-dimensional (3D) measurement.…”

CCM pilot study overview: geometrical measurement of the Rockwell diamond indenter

“…Illustration of the measurement sections of the Rockwell diamond indenter. The figure on the left is oriented with diamond tip pointing towards to the operator[3] …”