**3.8 Microstructural analysis**

Optical micrograph of the sample of WC10wt.%Co free of rare-earth sintered under HPHT is shown in Fig. 13. One can observe a non-homogeneous distribution of WC by the structure, indicating a possible change of the sintering conditions. On the other hand, there is a good distribution of cobalt for samples containing rare-earth elements (Figs. 14 e 15). This means better mixing or influence of the rare-earth about the process.

SEM micrographs of the fractured surfaces of the samples of WC10wt.%Co with and without rare-earth additives are presented in Figs. 16 - 18. It may be noted that the appearance of the fractured surface is typical of brittle fracture for all samples.

Fig. 13. Optical micrograph of the AL1 sample sintered under HPHT.

The results in Table 3 also show that the best samples in terms of wear resistance are those

Optical micrograph of the sample of WC10wt.%Co free of rare-earth sintered under HPHT is shown in Fig. 13. One can observe a non-homogeneous distribution of WC by the structure, indicating a possible change of the sintering conditions. On the other hand, there is a good distribution of cobalt for samples containing rare-earth elements (Figs. 14 e 15).

SEM micrographs of the fractured surfaces of the samples of WC10wt.%Co with and without rare-earth additives are presented in Figs. 16 - 18. It may be noted that the

Samples Wear resistance (%)

AL1 7.7 AL2 3.7 AL3 0.2 AL4 0.1 AL5 0.1 AL6 0.1 AL7 1.7 AL8 0.2 AL9 0.3

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

This means better mixing or influence of the rare-earth about the process.

Fig. 13. Optical micrograph of the AL1 sample sintered under HPHT.

appearance of the fractured surface is typical of brittle fracture for all samples.

with 1.0 to 2.0 % of La2O3 and 0.5, 1.5 and 2.0 % of CeO2.

**3.8 Microstructural analysis** 

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.

High Pressure Sintering of WC-10Co Doped with Rare-Earth Elements 395

Fig. 19. EDS spectrum for the AL1 sample sintered under HPHT.

Fig. 20. EDS spectrum for the AL2 sample sintered under HPHT.

Fig. 21. EDS spectrum for the AL7 sample sintered under HPHT.

Fig. 17. Fracture surface of the of the AL5 sample sintered under HPHT.

Fig. 18. Fracture surface of the of the AL7 sample sintered under HPHT.

Line spectrums for the samples of cemented carbides determined using EDS are shown in Figs. 19-21. The following constituent elements of the cemented carbides sintered under HPHT were detected: W, C, Co, La, and Ce.

The sintered microstructures of the AL5 (2 % La2O3) and AL7 (1 % CeO2) samples obtained via SEI/SEM are shown in Figs. 22-23, respectively. One can clearly observe the formation of cobalt lakes surrounding the tungsten carbide grains and pore possible. This may be related to different factors: i) mixing process inefficient; and ii) HPHT processing. According to North et al. (1992), high pressure applied continuously during the heating cycle can provide in some regions the formation of cobalt lakes, which persist at high temperatures even with some structural rearrangement of the WC.

Fig. 17. Fracture surface of the of the AL5 sample sintered under HPHT.

Fig. 18. Fracture surface of the of the AL7 sample sintered under HPHT.

HPHT were detected: W, C, Co, La, and Ce.

some structural rearrangement of the WC.

Line spectrums for the samples of cemented carbides determined using EDS are shown in Figs. 19-21. The following constituent elements of the cemented carbides sintered under

The sintered microstructures of the AL5 (2 % La2O3) and AL7 (1 % CeO2) samples obtained via SEI/SEM are shown in Figs. 22-23, respectively. One can clearly observe the formation of cobalt lakes surrounding the tungsten carbide grains and pore possible. This may be related to different factors: i) mixing process inefficient; and ii) HPHT processing. According to North et al. (1992), high pressure applied continuously during the heating cycle can provide in some regions the formation of cobalt lakes, which persist at high temperatures even with

Fig. 19. EDS spectrum for the AL1 sample sintered under HPHT.

Fig. 20. EDS spectrum for the AL2 sample sintered under HPHT.

Fig. 21. EDS spectrum for the AL7 sample sintered under HPHT.

High Pressure Sintering of WC-10Co Doped with Rare-Earth Elements 397

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**6. References** 

Fig. 22. SEM micrograph of the AL5 sample sintered under HPHT.

Fig. 23. SEM micrograph of the AL7 sample sintered under HPHT.
