Influential factors on hardness uniformity of Vickers hardness blocks for high hardness range

• Vickers hardness blocks were developed by two processes of powder metallurgy.
• The emphasis of research was placed on hardness uniformity which was tested by ANOVA.
• The surface of the blocks was divided into radial and circumferential divisions.
• Hardness distribution has a trend according to the manufacturing process and wt.% Co.
• The best properties were obtained on 9 wt.% Co block consolidated by sinter-HIP.

Reference Vickers hardness blocks for high hardness range were developed from WC 9–Co and WC 6–Co mixtures by two different processes of powder metallurgy, conventional liquid phase sintering in hydrogen and vacuum-sintering with subsequent hot isostatic pressing in one cycle, sinter-HIP, in order to analyse the appropriateness of the manufacturing process and the influence of starting characteristics of the mixtures on hardness uniformity and overall metrological characteristics. WC powder of 150 nm grain size and 2.5 m2/g specific surface area with the addition of grain grow inhibitors was used as starting material. The emphasis of the research was placed on hardness uniformity of the test surface as it is the most important property placed on hardness blocks. For that purpose the surface of the blocks was divided into radial and circumferential divisions, forming different sections on the block surface. Hardness measurements were performed in each section with HV1 measuring method. A total of 40 indentations were performed, based on which the conclusions about hardness uniformity of Vickers hardness blocks were drawn. Hardness measurements and uniformity were tested by analysis of variance, ANOVA, for single factor in order to determine if significant hardness variations across the block surface were present. From the research conducted it was concluded that hardness distribution across test surfaces of Vickers hardness blocks had a trend according to a process of manufacturing and the amount of binder in the WC–Co mixture. The best material and metrological characteristics were obtained on the block manufactured by sinter-HIP with 9 wt.% Co.