Estudo da síntese de pós compósitos e sinterização do sistema W-Ni

Abstract

In this work, it was studied the obtaining of W-Ni composite powders, through high energy grinding, at different times (2h, 5h and 10h), of the precursor powders of ammonium paratungstate (APT) with nickel (20% p.Ni ) and tungsten with nickel (20% p.Ni). It started with ammonium paratungstate (APT) mixed with nickel, in the proportion of 20% p.Ni, reducing it with hydrogen gas (H2), at a temperature of 850 °C and with a reaction isotherm time of 60 minutes, compaction and then the sintering of the reduced green compacts, with a heating rate of 10 °C/min. The precursor and reduced powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and particulometry. The effects of different grinding times (2h, 5h and 10h), compaction loads (500 MPa and 600 MPa) and sintering temperatures (1450 °C and 1550 °C) on the properties of hardness, microstructure and density of the obtained W-Ni. At the same time, samples were obtained from tungsten and nickel metals under the same experimental conditions for comparison purposes. From the results it was possible to conclude that the SEM images of the W-Ni mixtures revealed that the powders presented morphology with particles of varying sizes and shapes and quite agglomerated. In the case of the W-Ni mixture from the reduction of APT-20% p.Ni, the powders showed particles of smaller size and with good dispersion and homogenization of the phases. The analysis via XRD showed the W and Ni4W phases, with a reduction in ammonium paratungstate. We can conclude that the samples with grinding carried out in the time of 10h, compacted with pressure 500 MPa and sintering temperature of 1450 °C presented, greater microstructural homogeneity, presenting greater value of hardness (400.9 HV).