**3.6 Microhardenss**

390 Sintering of Ceramics – New Emerging Techniques

cemented carbide doped with rare-earth elements were obtained for the samples containing 1 % of La2O3 (1055 MPa) and 1 % of CeO2 (943 MPa). In addition, the complex variation observed for the mechanical strength may be associated with the fact that some samples did

The axial compressive elasticity modulus of the cemented carbides obtained from the

**0.0 0.5 1.0 1.5 2.0**

**Rare-earth content (%)**

The cemented carbides are characterized by a high modulus of elasticity. In a way similar to the axial compressive strength, it is observed that the axial compressive elasticity modulus increased with the incorporation of rare-earth oxides. This is mainly due to higher

Fig. 11. Axial elasticity modulus of the cemented carbides sintered under HPHT.

densification of the cemented carbide doped with these additives.

tension-deformation curve resulting from axial compression tests is shown in Fig. 11.

Fig. 10. Appearance of the pellets of WC10wt.%Co obtained via HPHT.

**La2O5 CeO2**

not show regular cylinder geometry (Fig. 10).

**3.5 Axial compressive elasticity modulus** 

**0**

**2000**

**4000**

**Axial elasticity modulus (MPa)**

**6000**

**8000**

**10000**

Figure 12 shows the values of microhardness for the pellets of WC10wt.%Co doped with rare-earth elements. The results show that the microhardness increases with the addition of rare-earth elements. This increase may be due to increased densification with the rare earth added. On the other hand, the complex variation in microhardness values may have been influenced by the geometric irregularity at the top and bottom of the samples caused by the sintering process as previously described.

Fig. 12. Microhardness of the cemented carbides sintered under HPHT.

It can be seen in Fig. 12 an increase in microhardness when 0.5 % of La2O3 is added. A decrease in microhardness occurs with the addition of 1 % of La2O3. With the addition of 1.5 % of La2O3, the microhardness increases again and back to decrease with 2 % of La2O3. For cemented carbide containing cerium oxide, there is an increase with the addition of 0.5 % and a subsequent decrease between 1 to 1.5 %. An increase occurs again with the addition of 2 % of CeO2. It can also be observed that the highest values of microhardness of the cemented carbide doped with rare-earth elements were obtained for the samples containing 0.5 % of La2O3 (2609 HV) and 0.5 % of CeO2 (1979 HV).

#### **3.7 Wear resistance**

Table 3 presents the values of wear resistance for the pellets of cemented carbide doped with rare-earth elements obtained under HPHT conditions. The results indicated that all samples of cemented carbide containing rare-earth elements showed less mass loss compared to the reference sample (WC10wt.%Co). This was expected, since the decrease in grain size caused by the rare-earth elements and also the positive influence of high pressure leads to increased microhardness and, consequently, to reduce the wear.

High Pressure Sintering of WC-10Co Doped with Rare-Earth Elements 393

Fig. 14. Optical micrograph of the AL5 sample sintered under HPHT.

Fig. 15. Optical micrograph of the AL6 sample sintered under HPHT.

Fig. 16. Fracture surface of the of the AL1 sample sintered under HPHT.


Table 3. Wear resistance of the cemented carbides sintered under HPHT.

The results in Table 3 also show that the best samples in terms of wear resistance are those with 1.0 to 2.0 % of La2O3 and 0.5, 1.5 and 2.0 % of CeO2.
