**2.3 Characterization of the cemented carbide pellets**

After high pressure sintering, the cylindrical pellets (6 mm in diameter and 4 mm in height) were removed from the capsule. The surface in contact with the graphite was clean and was later made a grinding surface resulting in parallel tops and cylindrical side.

For metallographic analysis, the sample was embedded in thermosetting polymer resin and then was made polishing in diamond paste. The metallographic analysis was made using an optical microscope (Zeiss, model Neophot-32) that contains an image capture system with CCD camera attached.

Scanning electron microscopy operating at 10 kV (model SSX 550, Shimadzu) was used to examine the gold-coated fracture surfaces of the sintered cemented carbide pellets via secondary electron images (SEI). EDS also was used to identify the constituent elements of the sintered samples.

The crystalline phases after sintering were investigated between 2θ = 20º and 2θ = 90º via Xray diffraction analysis (Shimadzu, model XRD 7000) with Cu-Kα radiation (40 kV, 40 mA). The phases were identified from peak positions and intensities using reference data from the JCPDS handbook.

The following properties have been determined: apparent density, relative density, coercive force, mechanical strength, elasticity modulus, microhardness, and wear resistance. Archimedes method of immersion in water was used to determine the apparent density. For this purpose, the cemented carbide pellets were weighed at dry state (M1), then boiled in water for 2 h, cooled, and weighed again a second time in water (M2). The pellets were weighed again at the saturated wet state (M3). The apparent density (ρa) of pellets was determined according to:

Fig. 1. Anvil type high pressure device with toroidal concavity for press of 630 tonnes: a) the high pressure device without applying pressure; and b) the high pressure device with application of pressure. 1) Anvil of WC; 2) multi-rings; 3) deformable capsule; 4) sample of

After high pressure sintering, the cylindrical pellets (6 mm in diameter and 4 mm in height) were removed from the capsule. The surface in contact with the graphite was clean and was

For metallographic analysis, the sample was embedded in thermosetting polymer resin and then was made polishing in diamond paste. The metallographic analysis was made using an optical microscope (Zeiss, model Neophot-32) that contains an image capture system with

Scanning electron microscopy operating at 10 kV (model SSX 550, Shimadzu) was used to examine the gold-coated fracture surfaces of the sintered cemented carbide pellets via secondary electron images (SEI). EDS also was used to identify the constituent elements of

The crystalline phases after sintering were investigated between 2θ = 20º and 2θ = 90º via Xray diffraction analysis (Shimadzu, model XRD 7000) with Cu-Kα radiation (40 kV, 40 mA). The phases were identified from peak positions and intensities using reference data from the

The following properties have been determined: apparent density, relative density, coercive force, mechanical strength, elasticity modulus, microhardness, and wear resistance. Archimedes method of immersion in water was used to determine the apparent density. For this purpose, the cemented carbide pellets were weighed at dry state (M1), then boiled in water for 2 h, cooled, and weighed again a second time in water (M2). The pellets were weighed again at the saturated wet state (M3). The apparent density (ρa) of pellets was

WC10wt.%Co; 5) disk of protection; and 6) gasket (Ramalho, 1998).

later made a grinding surface resulting in parallel tops and cylindrical side.

**2.3 Characterization of the cemented carbide pellets** 

CCD camera attached.

the sintered samples.

JCPDS handbook.

determined according to:

$$
\rho\_{\text{a}} = \text{M1/M3 - M2} \tag{1}
$$

The relative density (ρr) was determined according to the following expression:

$$
\mathfrak{p}\_{\mathbf{r}} = \mathfrak{p}\_{\mathbf{a}} / \mathfrak{p}\_{\mathbf{t}} \tag{2}
$$

in which ρa is the apparent density (g/cm3) and ρt is the theoretical density of the WC10wt.%Co (14.53 g/cm3).

The coercive force of the pellets was determined using a coercive force meter, which create a magnetic field. The test of coercive force was performed as follow. Initially, the coercive force meter was reset. The pellets were placed in the polarized magnetization devices. It was then made to read the display of the coercive force.

In this work the mechanical strength of the pellets was evaluated through axial compression strength due to the size of the pellets obtained. This means that the values of mechanical strength of the samples obtained in this work are for comparison only among themselves. The axial compressive strength (σc) was determined using an universal testing machine (EMIC, model DL – 10000) at a loading rate of 0.5 mm/min according to

$$\mathfrak{G}\_{\mathfrak{c}} = 4\mathcal{P} \;/\ \,\pi\mathcal{D}^2 \tag{3}$$

in which P is the load at rupture and D the specimen diameter.

The axial compressive elasticity modulus (ECA) was determined using the stress-strain curve according to

$$\mathbf{E\_{CA}} = \mathbf{σ\_{AC}} / \,\mathrm{\mathbf{e}}\tag{4}$$

in which σAC is the axial compressive tension and ε is the relative deformation.

The Vickers microhardness tests were performed using a microhardness apparatus coupled to an optical microscope according to

$$\text{HV} = 0.189 \text{ P} / \text{ d}^2 \tag{5}$$

in which P is the applied load (kgf) and d is the average length of the impression diagonal (mm).

The abrasion wear tests were performed using an abrasion meter (AROTEC, model AROPOL E) with maximum speed of 620 rpm and disk of carborundun. The following procedure was adopted: i) the sample is weighed before the wear test; ii) the sample was fixed in a chuck property for the test; iii) the disk is rotated and applied a vertical load on the sample fixed; iv) the sample was kept fixed in a straight line for 10 min; and v) the sample is weighed after the test for determining the mass loss. Thus, the wear resistance of the sintered pellets was determined according to

$$
\Delta \mathbf{M} = \mathbf{m}\_i - \mathbf{m}\_\ell \;/\; \mathbf{m}\_i \times 100\tag{6}
$$

in which mi is the initial mass (g) of the pellets and mf is the final mass (g) obtained after the wear test.

High Pressure Sintering of WC-10Co Doped with Rare-Earth Elements 385

following factors: i) sensitivity of the WC to the loss of carbon as consequence of their low formation energy; ii) sintering atmosphere with characteristic oxidant; and iii) the presence in the starting powders of compounds that react with the carbide, consumining the carbon. Another important aspect that must be considered is that the HPHT sintering process is very fast. This can take the carbon to react with the adsorbed oxygen also quickly, resulting in decrease or loss of carbon of the WC. The consequence is not having a good dissolution of

Figures 3 and 4 show the X-ray diffraction patterns of the cemented carbide samples doped

**WC**

γ

**20 30 40 50 60 70 80 90**

**2**θ **(Degree)**

**20 30 40 50 60 70 80 90**

**2**θ **(Degree)**

As can be observed, the samples doped with rare-earth elements (La2O3 (Fig. 3) and CeO2 (Fig. 4)) had a phase composition very similar to that of the rare-earth free samples. It is noticed that only small differences in the peak intensities occurred. This means that the

Fig. 4. XRD pattern of the WC10wt.%Co doped with 2 % of CeO2 sintered under HPHT.

**Co3W3**

**C**

γ

Fig. 3. XRD pattern of the WC10wt.%Co doped with 2 % of La2O3 sintered under HPHT.

**WC**

γ

**Co3W3C**

γ

**WC WC**

**WCWC WC WC**

> **WC**

**WC WC WC**

**WC WC**

free carbon in the liquid phase, so new phases can occur by diffusion.

**WC**

**WC**

**Co3W3C**

**WC**

**WC**

**Co**

**Co3W3C**

**Intensity (a.u.)**

**3W3C**

**Co3W3C**

**Intensity (a.u.)**

com rare-earth elements.
