Estudo da substituição do cobalto pela liga Invar no metal duro com base em carbeto de tungstênio

Abstract

Cobalt is the most widely used binder in tungsten carbide (WC) -based hard metals due to its properties, mainly wettability. However, this metal can cause toxicity problems, and, in addition, it has a high production cost. In addition to cobalt, iron and nickel are already widely used in hard metals as binders. Therefore, this research aims to analyze the Invar alloy (Fe-36% Ni) as an alternative binder in the WC via the pulsed current sintering technique (“Spark Plasma Sintering - SPS”). The samples were sintered with isothermal levels of 1100, 1200 and 1300 ºC. WC-Co samples were sintered at 1200 ºC for comparison. The results show that the microstructure presents a good distribution of WC and a decrease in porosity with the increase of temperature. In addition, the η phase was not found in the WC-Invar and WC-Co samples. EDS analysis point revealed regions of element dissolution in both WC-Invar and WC-Co. The dilatometry tests showed that the WC-Invar showed a coefficient of thermal expansion of 6.01 x10-6 ° C-1, while the WC-Co showed 6.23 x10-6 ° C-1. The highest densification achieved at WC-Invar is 98.9%. The increase in the isothermal level provided an increase in densification, hardness, resistance to diametrical compression and modulus of elasticity. The Invar WC sintered at 1100 ° C showed a hardness of 1777 HV, surpassing WC-Co hard metals found in the literature, and fracture toughness of 15.6 MPa m1 / 2. The WC-Invar sintered at 1300 ° C showed the highest resistance to diametrical compression, 376 MPa, greater modulus of elasticity, 990 GPa, and greater hardness, 1992 HV. In view of these results, the Invar alloy, produced in this research, provided the carbide WC-Invar in comparison with WC-Co of this research with good microstructural characteristics, low thermal expansion, high hardness combined with fracture toughness and higher compressive strength.