Ultrafine High-Cobalt VK40 Hard Alloy. I. Structure and Properties

    

I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Krzhizhanovsky str., 3, Kyiv, 03142, Ukraine
Powder Metallurgy - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2008, #03/04
http://www.materials.kiev.ua/article/707

Abstract

Ultrafine WC-41 wt.% Co powders (VK40) are densified under 1000-1200 MPa at 950-1250 °C and in 0.13 Pa vacuum. It is examined how the pressing temperature and annealing at 1190 °C influences the density, structure, physical and mechanical properties of VK40 alloy. It is shown that high-pressure sintering produces dense samples with ultrafine structure (Lwc = 0.35-0.45 ?m) and low degree of contact for carbide particles (contiguity Cwc = 0.08-0.1) in solid phase. The highest mechanical properties are exhibited by samples densified at 1150-1250 °C or by samples annealed after preliminary pressing at 1050-1150 °C. The alloy has the following properties: transverse rupture strength (TRS) of 3200-3400 MPa, fracture toughness of 25-33 MPamІ/2, Vickers hardness of 7.5-7.7 GPa under 300 N, compressive strength of 2600-2800 MPa, compressive offset yield stress σ0,2 of 2200-2400 MPa, compressive plastic strain of 6.5-7.0%, and fracture energy of 180-200 MJ/m3. These mechanical properties of ultrafine VK40 alloy differ from those of standard shockproof coarse-grained hard metals in higher TRS, fracture toughness, and yield stress.


MECHANICAL PROPERTIES, SOLID-PHASE DENSIFICATION, TUNGSTEN CARBIDE, ULTRAFINE GRAIN STRUCTURE