| Abstract:Conventional homogeneous cemented carbide with homogeneous composition and microstructure in bulk has sharp contradiction between hardness and toughness, which has restricts further application areas. It is difficult to meet the development of modem social Oil the double high require, namely high hardness and high toughness. The micron grained WC has the high hardness and high wearing resistance, while the ultrafine WC has the high micro-hardness and fracture toughness. In this paper, the WC-Co cemented carbide with coarse grained WC was produced through low pressure sintering processes using WC with different grain size and Co powders as raw materials. The microstructure, phase composition, hardness, fracture toughness, transverse rupture strength and electrochemical corrosion properties of WC-Co cemented carbide were investigated. The main results are as follows:(1)The WC with different grain size and Co powders are raw materials, the mixtures were prepared through the ball milling in anhydrous alcohol for24h at the milling speed of300r/min and the ball-to-powder is2:1. Every powder got fully mixing, did not produced other chemical reaction and have no the impurity composition in the raw powder.(2) When the size of coarse grained WC is1μum, the hardness of alloy decreases from1930HV to1800HV, while the fracture toughness increases from12.85MPa·m1/2to15.05MPa·m1/2, the comprehensive mechanical properties of the cemented carbide achieve the best balance. There is an obvious crack deflection in the crack extension process by addition of coarse grained WC, the trans-granular fracture phenomenon increases obviously. It can resistance the crack propagation, and improves the toughness of cemented carbide.(3)By the contents of1μm WC powder from0to30wt.%, the relative density of alloy is gradually lower, the fracture toughness increases from12.85MPa·m1/2to15.05MPa·m1/2, and the transverse rupture strength increases from1750MPa to2100MPa, while the hardness of alloy decreases from1930HV to1800HV, the alloys with10wt.%1μm WC powder addition show the best combination of mechanical property, the transverse rupture strength is1850MPa, the hardness is1700HV, and the fracture toughness is13.82MPa·m1/2.(4) The alloys have different size of coarse grain WC for as electrochemical experiment materials.(The1alloy have no coarse grain WC,2alloy include1μm grain size of WC,3alloy include2μm grain size of WC,4alloy include3μm grain size of WC). The results of electrochemical experiments show that:In lmol/L HC1solution, the corrosion rate of2#alloy is biggest, and the corrosion rate of1#alloy is the smallest, but when the3#alloy has anode polarization, other alloys are still in cathodic polarization, the anode polarization of1#alloy is finally appeared, so1alloy is most corrosion resistant. In1mol/L NaOH solution, the corrosion rate of1alloy is smallest, and2#alloy is most corrosion resistant, followed by1#alloy. Comprehensive, the1#alloy (no coarse grain WC) has the best corrosion resistant performance, In the ultrafine grained WC cemented carbide, add the different size of coarse grain WC powder to reduces the electrochemical corrosion properties of materials. |
