Vickers Hardness Test VHT

The 136° angle between the opposite faces of the indenter was chosen because of the similarity between the Brinell hardness number (henceforth BHN) and the DPN. Due to this similarity, the DPN is on the same hardness scale as the BHN and their values are about the same up to 300 BHN. Only beyond this BHN value do the two curves shown in Fig. 1.54 deviate one from the other. Significant deviation between these two types of measurement occurs at high hardness values, particularly above 600 BHN, due to the deformation of the indenter. The DPH 

In Fig. 1.56, graphs show the Vickers hardness variations for several refractory carbides under loads. These experiments were performed for a wide range of test forces, between 0.49 N and 196 N. All three graphs below show the same pattern 

There is no preferential orientation and the grain sizes are 0.43 mm for (a), 1.4 mm for (b) and 2.5 mm for (c). Furthermore, as expected, an indentation size effect with hardness values should be observed for all carbides tested, because the size of the impressions are related to the load applied, being smaller for smaller loads or for harder materials. This, indeed, is the case, as shown in Rg. 1.58. The shapes of the cmves in the illustrated materials are similar to those given by Li [34] and associates as  

In the above relations, d is the indentation size and a2 are constants, which can be determined from the lines in Fig. 1.58. Thus, ai and aa are represented by the slope and the intercept, respectively. Recalling the definition of hardness in Eq. (1.126) and combining it with Eq. (1.128a), one obtains  

A few more examples of the versatility of the VHT may be cited that were performed on polycrystalline ceramics, as shown in the following graphs. Note 

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