Liquid-phase boriding of high-chromium steel

Using the methods of modern physical materials science, structuralphase states and tribological properties of 12Kh18N10T steel, subjected to electroexplosive alloying with titanium and boron and subsequent electron-beam processing in various modes depending on electron beam energy density, exposure pulse duration and their quantity have been analyzed. It has been established that electroexplosive alloying of steel with titanium and boron leads to formation of surface layer with multiphase submicro-nanocrystalline structure, characterized by presence of micropores, microcracks, and microcraters. Complex processing, combining electroexplosive alloying and subsequent irradiation with high-intensity pulsed electron beam, leads to formation of 60 μm thick multiphase submicro-nanocrystalline surface layer. It is shown that phase composition of surface layer of steel is determined by mass ratio of titanium and boron during electroexplosive alloying. Microhardness of modified layer is defined by relative mass fraction of titanium borides in surface layer and can be more than 18 times higher than microhardness of steel in its initial state (before electroexplosive alloying). Modes of complex processing have been determined at which surface layer containing exclusively titanium borides and intermetallic compounds based on titanium and iron is formed. The maximum (approximately 82 % by weight) titanium boride content is observed when steel is processed at regime with the highest mass of boron powder in the sample (mB = 87.5 mg; mTi /mB = 5.202). With decrease in mass of boron powder, relative content of borides in surface layer of steel decreases. It was found that integrated processing of steel is accompanied by sevenfold increase in microhardness of surface layer, wear resistance of steel increases by more than nine times.

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

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.

Ti-Y Surface Alloy Formed by High-Energy Methods

The alloying of the titanium layer by yttrium is carried out with the combined method of electroexplosive alloying and the subsequent radiation by a high-intensity electron beam. The research of structure, element and phase composition, mechanical and tribological properties of the alloyed layer is executed. The saturation of the titanium layer by atoms of yttrium, oxygen and carbon that leads to formation of oxides and carbides of the titanium and yttrium is revealed. The formation of two types of an eutectic is established. It is shown that the eutectic enriched with the titanium has a globular form when the eutectic enriched with yttrium has a plated one. The multiple increasing of microhardness, decreasing of friction coefficient and the wear rate of the alloyed layer is revealed.