*High Entropy Alloys for Medical Applications DOI: http://dx.doi.org/10.5772/intechopen.89318*


#### **Table 3.**

*Microhardness values for biomedical HEA samples.*

#### **Figure 11.**

the formation of a homogenized alloy band, with a dendritic microstructure,

*The interface with undissolved Ta particle (a) and semi-quantitative composition spectrum (b) of the*

the oxidation and diffusion effects. An image of the boundary between an

The heat treatment effects on mechanical hardness characteristics are highlighted by the different microhardness values determined with the help of the

Shimadzu HMV 2 T microhardness tester, presented in **Table 3**.

The effects of the heat treatment are also highlighted by means of an EDS analysis performed with an AMETEC Z2e analyzer on micro-zones located both at the center of the CrFeMoTaTiZr samples as well as at the edges, in order to quantify

*The oxidized layer of CrFeMoTaTiZr alloy after heat treatment at 800°C/24 hours/slow cooling in the furnace*

undissolved Ta particle and the embedding metal matrix is illustrated in **Figure 10**.

The analysis of the microhardness values resulted from applying a homogenization treatment showed that hardness increases in the highly alloyed metal matrix up to the average value of 1290 HV0.2 in case of the CrFeMoTaTiZr alloy. The diffusion of the chemical elements during the treatment determined a reduced hardness in the marginal zone adjacent to the surface (located at a distance of approx. 200

located immediately below the complex oxide layer (**Figure 9**).

**3. Microhardness**

**192**

**Figure 9.**

**Figure 10.**

*with fractures (a) and peeling (b).*

*Engineering Steels and High Entropy-Alloys*

*heat-treated CrFeMoTaTiZr alloy.*

*Evolution of microhardness for experimental biocompatible HEA.*

microns), where the average hardness value was 882 HV0.2, that is, approx. 66 HRC, as well as the formation of a homogenization band of approx. 45 microns, where the hardness increased to 1337 HV0.2. The microstructural aspects are in accordance with the microhardness values.

As can be seen from the data presented in **Table 3** and **Figure 11**, HEAB 1–HEAB 5 have very close values of microhardness, with the average being around 750 HV0.2. A notable difference was obtained with the HEAB 6 alloy, which had the lowest hardness value (544 HV0.2) before heat treatment. Also, for the HEAB 7 alloy, the microhardness was between the minimum and maximum values of the other materials (655 HV 0.2).

After heat treatment, the HEAB 6 alloy recorded a considerable increase in hardness in some areas (under the oxidized layer), which came to about 1337 HV0.2. This development, which represents an increase of over 150%, can be exploited in terms of obtaining high-wear-resistant surfaces for medical instruments.
