Influence of pulse-plasma modification of VK10KS solid alloy surface by titanium and boron on its structure and properties

Abstract

Modification of the surface of VK10KS solid alloy with titanium alongside with boron by the method of pulse-plasma exposure (electro-explosive alloying) is considered. In this case, a superhard (27,500 MPa nanohardness) layer is formed with a thickness of 2.0 – 2.5 μm and a low (μ = 0.10) friction coefficient compared to the friction coefficient of a hard alloy in the sintered state (μ = 0.41). This layer consists of finely dispersed high-hard phases TiB2, (Ti, W)C, W2C (according to scanning, transmission electron microscopy and X-ray phase analysis). Below is a hardened (with a nanohardness of 17,000 MPa) surface layer (heat affected zone) 10 – 15 μm thick, identified by W2C and WC carbides and alloyed with a cobalt binder. This layer smoothly passes into the base. By profilometric studies it was established that after electroexplosive alloying with titanium and boron, the roughness increases (Ra = 2.00 μm) compared to the initial one (Ra = 1.32 μm), but remains within the specifications (Ra = 2.50 μm). The authors have revealed changes that occur in the surface carbide and near-surface cobalt phases during electroexplosive alloying. In the carbide phase, accumulations of dislocations were indicated. In the cobalt binder, deformation bands (slip bands), single dislocations, and also finely dispersed tungsten carbide precipitates were found. This change can be explained by stabilization of the cubic modification of cobalt, the crystal lattice of which has a large number of slip planes during deformation and a greater ability to harden compared to the hexagonal modification of cobalt. Additional alloying with a cobalt binder will positively affect the operational stability of tungsten carbide alloys as a whole due to their stabilization.