**2.2 High pressure sintering of the cemented carbide**

The mixed powders initially were submitted to a single action die-compaction step using a hydraulic press (Danpresse, model DC 20) in a cylindrical 7 mm diameter steel die without lubrificants at 800 MPa. The compact dimensions were 7 mm in diameter and 7 mm in height. After uniaxial compaction, the consolidated samples were pressed under high pressure and high temperature (HPHT).

The high pressure compaction needs an apparatus that can stably generate a pressure of more than 1 GPa. A toroidal type high-pressure device was used in the experiments. Fig. 1 shows a typical drawing of the high-pressure device (Ramalho, 1998). This device allows the compaction tests in cylindrical powder samples until 7 mm of diameter and 9 mm of height. The high-pressure tests were carried out in a special hydraulic press (Ryazantyashpressmash, DO 138B model). The tests were carried out as follows: the precompacted mixed powder sample was placed without slackness into central aperture of the deformable capsule (Fig. 1). The deformable capsule is made of a calcite based powder compact (95 % CaCO3 + 5 % (SiO2, Al2O3, Fe2O3)). The calcite based material is a solid pressure medium well known in the field of ultrahigh pressure technology (Vianna et al., 2001). For effective heat conduction in the sample, the capsule was covered with two caps composed of 50 % of graphite and 50 % of calcite. A high pressure anvil made of hard metal was used as mould, where the capsule was fixed in its concavity, and then sealed with the outer side of the mould. Finally, the complete device was axially placed in the mobile table of the press. When the force is applied, the capsule is deformed with concomitant formation of a gasket and the generation of a high pressure. A high pressure of 5.5 GPa was applied to the samples. The high pressure into the compression chamber was transmitted to the cemented carbide powder samples by the capsule. The high pressure level reached was maintained for 30 s, and then the temperature was raised to 1400 ºC. These conditions of high pressure and high temperature were maintained for a time of 40 s.

High Pressure Sintering of WC-10Co Doped with Rare-Earth Elements 383

in which ρa is the apparent density (g/cm3) and ρt is the theoretical density of the

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

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

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

ECA = σAC / ε (4)

The Vickers microhardness tests were performed using a microhardness apparatus coupled

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

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

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

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

(EMIC, model DL – 10000) at a loading rate of 0.5 mm/min according to

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

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

WC10wt.%Co (14.53 g/cm3).

according to

(mm).

wear test.

to an optical microscope according to

the sintered pellets was determined according to

then made to read the display of the coercive force.

ρa = M1/M3 - M2 (1)

ρr = ρa / ρt (2)

σc = 4P / πD2 (3)

HV = 0.189 P / d2 (5)

ΔM = mi – mf / mi x 100 (6)

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