Hot Sliding Wear of 88 wt.% TiB–Ti Composite from SHS Produced Powders

Titanium alloys and composites are of great interest for a wide variety of industrial applications; however, most of them suffer from poor tribological performance, especially at elevated temperatures. In this study, spark plasma sintering was utilized to produce a fully dense and thermodynamically stable TiB–Ti composite with a high content of ceramic phase (88 wt.%) from self-propagating high temperature synthesized (SHS) powders of commercially available Ti and B. Microstructural examination, thermodynamic assessments, and XRD analysis revealed the in situ formation of titanium borides with a relatively broad grain size distribution and elongated shapes of different aspect ratio. The composite exhibits a considerable hardness of 1550 HV30 combined with a good indentation fracture toughness of 8.2 MPa·m1/2. Dry sliding wear tests were performed at room and elevated temperature (800 °C) under 5 and 20 N sliding loads with the sliding speed of 0.1 m·s−1 and the sliding distance of 1000 m. A considerable decline in the coefficient of friction and wear rate was demonstrated at elevated temperature sliding. Apart from the protective nature of generated tribo-oxide layer, the development of lubricious boric acid on the surface of the composite was wholly responsible for this phenomenon. A high load bearing capacity of tribo-layer was demonstrated at 800 °C test.

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.

Researching of the Structure and Properties of Wear-resistant Coatings Obtained by Surfacing With Powder Electrodes Based on the Fe-Ti-B-C System

In this study the main purpose was to provide “in situ” synthesis while flux cored arc welding (FCAW) for obtaining hardfacing with fine structure with uniformly distributed titanium borides and carbides in the Fe-Ti-B-C system. Also, Fe-Ti-Mo-B-C with equimolar content of Me/B4C was researched. Powders electrodes was manufactured with using of pure metal powders to provide “in situ” synthesis. Initial components were powders of Ti, Mo and B4C. It was investigated that the offered harfacings are characterized by high hardness and fine-grained structure. Addition of Ti to Fe-Mo-B-C system leads to elimination of the ferrite-boride eutectics, that exist in Fe-Mo-B-C. Also, the structure of hardfacing of Fe-Ti-Mo-B-C is characterized with absence of defects and pores that exist in case of using Fe-Ti-B-C hardfacing. Analysis was carried out using scanning electron microscopy (SEM) and electron backscatter diffraction (BSD). Hardness was measured by Rockwell method. According to the analysis of literature and experimental researches, a systems of powder electrode materials was manufactured by FCAW method with high content of hard borides and carbides. The obtained value of the hardness of Fe-Ti-B-C system is 67 HRC and for Fe-Ti-Mo-B-C system is 69 HRC.

In Situ Formation of TiB2 in Fe-B System with Titanium Addition and Its Influence on Phase Composition, Sintering Process and Mechanical Properties

Interaction of iron and boron at elevated temperatures results in the formation of an E (Fe + Fe2B) eutectic phase that plays a great role in enhancing mass transport phenomena during thermal annealing and therefore in the densification of sintered compacts. When cooled down, this phase solidifies as interconnected hard and brittle material consisting of a continuous network of Fe2B borides formed at the grain boundaries. To increase ductile behaviour, a change in precipitates’ stoichiometry was investigated by partially replacing iron borides by titanium borides. The powder of elemental titanium was introduced to blend of iron and boron powders in order to induce TiB2 in situ formation. Titanium addition influence on microstructure, phase composition, density and mechanical properties was investigated. The observations were supported with thermodynamic calculations. The change in phase composition was analysed by means of dilatometry and X-ray diffraction (XRD) coupled with thermodynamic calculations.

Complex Saturation of Titanium Alloys with Boron, Chromium and Titanium

This work described the technology of boronizing of titanium Grade2 from the generation of the gas phase directly in a sealed container during the decomposition reactions of the powder saturating medium. With such an implementation of the process in a closed volume, waste gas neutralization devices are not required, since the generation and decomposition of active saturating gases occurs in a closed volume. At saturation of titanium from the gas mixture, titanium borides, titanium nitrides, as well as titanium and chromium carbides can be produced in the coating. The microhardness of the coating is 2800–3200 HV0.1. The thickness of the diffusion coatings in this case can be up to75 microns. It is indicated that diffusion coatings on titanium by this technology should not exceed a thickness of more than 100 microns, and if the thickness of the diffusion coating exceeds 100 microns, the risk of chipping will increase.

Structural features of layered composite materials based on titanium borides by free SHS compression

The work shows the structural features layered composite materials based on titanium boride on titanium alloy VT6 (Ti6Al4V) by the method of free SHS compression, which implements the combination of combustion processes and high-temperature shear deformation. The layered structure of the produced materials was established, the feature of the structure of the transition zone at the boundary of the ceramic composite - titanium alloy was studied in details.

Structural and phase states of titanium borides produced by the self-propagating high-temperature synthesis method in the field of ultrasound oscillations

The effect of ultrasound oscillations (USO) on the velocity and temperature of combustion during self-propagating high-temperature synthesis (SHS) in the Ti-B system and structural and phase states of the produced titanium borides is studied using the earlier developed experimental setup. The effect of USO on SHS is subdivided into thermal and physical (non-thermal). The thermal influence is connected with cooling of the specimen surface because of the occurrence of forced convection of the ambient gas, and the physical effect is due to the action of USO on complex interaction processes in the SHS wave such as melt spreading, heterogeneous reactions and mass transfer in the liquid phase. Imposition of USO on the SHS process brings about changes in the phase composition of the synthesis products. For charge composition Ti–1.0В the content of orthorhombic modification of phase TiB increases from 78.2 % without USO to 82.9 % at the USO amplitude ξ = 10 mm, while the content of the cubic modification of this phase decreases from 9.2 % at ξ= 0 to 6.8 % at ξ = 10 mm. For all the examined compositions, the amount of residual titanium and Ti3B4decreases and the content of TiB2increases. It is determined that carrying out SHS in the field of USO results in a change of the specific heat capacity of the target synthesis products: with raising the USO amplitude it increases by 4–5 %. Thereby it is shown that imposition of USO on SHS is an efficient physical method for purposeful regulation of structural and phase states and therefore properties of the synthesis products and can be used as a means for controlling the synthesis process.

Self-Propagating High-Temperature Synthesis of Boron-Containing MAX-Phase

An attempt was made to obtain boron-containing MAX-phase by the process of self-propagating high-temperature synthesis (SHS) of Ti3AlC2, replacing some carbon atoms by boron atoms. This was conducted by burning powder mixtures (charges) of the composition 3Ti+2Al+2((1-x)C+xB), where x is the fraction of boron atoms (0.10, 0.15, 0.25, 0.50, 0.75, 0.90), replacing the carbon atoms. X-ray diffraction analysis of the products of combustion have shown that the replacement of carbon with boron to half of the content of carbon atoms in the charge (x=0.10-0.50), does not change the phase composition of the products, including Ti3AlC2 and TiC, but leads to a shift of the peaks of these phases in the diffraction pattern in the direction of smaller angles. When replacing more than half of the carbon atoms with the boron (x=0.75 and 0.90), the peaks of titanium carbide and MAX-phase are not observed, and the XRD peaks appear of the titanium borides TiB and TiB2, and intermetallic compound Al3Ti. Photomicrographs obtained with an electron microscope show that the SHS products synthesized from the charge with replacing up to half of the carbon atoms with the boron represent plates with a thickness of about 1 μm typical for MAX-phases, but rounded particles of borides and intermetallic compound of titanium appear at a higher boron content. Based on these results, it is concluded that replacement of a part (up to 50%) of the carbon atoms with boron atoms in the SHS charge 3Ti+2Al+2C leads to the synthesis of boron-containing MAX-phase based on the crystal lattice of Ti3AlC2.

Vibrational Spectroscopy of Binary Titanium Borides: First-Principles and Experimental Studies

Vibrational dynamics of binary titanium borides is studied from first-principles. Polarized and unpolarized Raman spectra of TiB, TiB2, and Ti3B4 are reported along with the experimental spectra of commercial powder and bulk TiB2 containing less than 1 wt.% of impurity phases. The X-ray diffraction spectroscopy, applied for phase composition examination of both bulk and powder materials, identifies only the TiB2 phase. The simulated Raman spectra together with literature data support interpretation and refinement of experimental spectra which reveal components arising from titanium dioxide (TiO2) and amorphous boron carbide (B4C) impurity phases as well as graphitic carbon. These contaminations are the by-products of synthesis, consolidation, and sintering aids employed to fabricate powder and bulk titanium diboride.