Microstructure, mechanical properties and machining performance of hot-pressed Al[2]O[3]-ZrO[2]-TiC composites

The effect of adding nanocrystalline ZrO[2] and submicron TiC to ultrafine Al[2]O[3] on mechanical properties and the microstructure of the composites developed by hot pressing was investigated. It was shown that by means of hot pressing in an argon atmosphere at a sintering temperature of 1500 °С one can obtain the composites Al[2]O[3] - ZrO[2] - TiC with a fine structure and minimal porosity. It has been shown that in material a multi-scale hierarchical structure is formed, which possesses high physical and mechanical properties: the hardness and fracture toughness was 21.5 GPa and 5.2 MPa*m{1/2} respectively, the modulus of elasticity was 500 GPa and bending strength was 390 MPa. Tests on composites' cutting properties were carried out on interrupted cutting of hardened steel. All samples had wear of the cutting edge in the form of chips of the grain rear working surface of the tool, but the cutting tool which was made by Al2O3 - 10% ZrO2 - 10% TiC had a minimum width of wear

Wear Mechanism and Failure of Carbide Cutting Tools with Nanostructured Multilayered Composite Coatings

The aim of this work is to study physical and chemical properties of nanostructured multi-layered composite coating based on three-layered architecture, deposited to a carbide substrate, as well as to study the mechanism of wear and failure of coated carbide tools under the conditions of stationary cutting. The coating were obtained by the method of filtered cathodic vacuum arc deposition (FCVAD). Here, the microstructure of coating as well as its hardness, strength of the adhesive bond to the substrate, chemical composition and phase composition were investigated on a transverse cross-section of experimental samples. The studies of cutting properties of the carbide inserts with developed coatings was conducted on a lathe in longitudinal turning of steel C45 (HB 200). The analysis of mechanisms of wear and failure of coated tool was carried out, including the processes of diffusion and oxidation in the surface layers of the coated substrate. Tools with harder and less ductile coatings showed less steady kinetics of wear, characterized by sharp intensification of wear and failure in transition from “steady” to drastic wear, i.e., at the end of the tool life. The X-ray microanalysis showed a considerable increase in oxygen content in the transverse cracks in the coating

Composite materials based on high-modulus compounds for additive technology

The effect of adding nanocrystalline ZrO[2] and submicron TiC to ultrafine Al[2]O[3] on mechanical properties and the microstructure of the composites developed by hot pressing was investigated. It was shown that by means of hot pressing in argon atmosphere at the sintering temperature of 1500 °C one can obtain the composites of Al[2]O[3]-ZrO[2]-TiC with a fine structure and minimal porosity. It was shown that in the material a multi-scale hierarchical structure is formed, which possesses high physical and mechanical properties: the hardness and fracture toughness was 22 GPa and 5.2 MPa*m1/2, respectively. It has been shown that mechanical properties of the composite are better than those of commercial composites based on aluminum oxide (Al[2]O[3], ZTA, Al[2]O[3]-TiC) and are comparable to those of silicon nitride

Diagnostic Systems as Basis for Technological Improvement

AbstractHereunder the ways of technical diagnostics in metal manufacturing and peculiarities of challenges which are faced in technical diagnostics are given. The matters of the ways of technical diagnostics, which are required to be solved in near future, are described in the article. Solutions of problems concerning diagnostics of condition of an edge tool, using real-time vibration analysis, are provided. The article says about affect of bearings of spindle units on three-dimensional distribution of vibration parameters. An example concerning a spindle unit that induces auto vibration, which produce a false diagnosis regarding the condition of the edge tool, is given

Recent changes in shelf hydrography in the Siberian Arctic : potential for subsea permafrost instability

Summer hydrographic data (1920–2009) show a dramatic warming of the bottom water layer over the eastern Siberian shelf coastal zone (<10 m depth), since the mid-1980s, by 2.1°C. We attribute this warming to changes in the Arctic atmosphere. The enhanced summer cyclonicity results in warmer air temperatures and a reduction in ice extent, mainly through thermodynamic melting. This leads to a lengthening of the summer open-water season and to more solar heating of the water column. The permafrost modeling indicates, however, that a significant change in the permafrost depth lags behind the imposed changes in surface temperature, and after 25 years of summer seafloor warming (as observed from 1985 to 2009), the upper boundary of permafrost deepens only by ∼1 m. Thus, the observed increase in temperature does not lead to a destabilization of methane-bearing subsea permafrost or to an increase in methane emission. The CH4 supersaturation, recently reported from the eastern Siberian shelf, is believed to be the result of the degradation of subsea permafrost that is due to the long-lasting warming initiated by permafrost submergence about 8000 years ago rather than from those triggered by recent Arctic climate changes. A significant degradation of subsea permafrost is expected to be detectable at the beginning of the next millennium. Until that time, the simulated permafrost table shows a deepening down to ∼70 m below the seafloor that is considered to be important for the stability of the subsea permafrost and the permafrost-related gas hydrate stability zone

Development of bioceramic material for spinal surgery implants

Highly porous zirconia-based ceramics were prepared. The ceramic samples sintered at 1600°C had porosities from 40% to 43%, with pore size ranges as follows: "big pore" 100-220 pm and "small pore" 0.8-8 pm. This makes the ceramic structure to be very similar to the structure of the natural spinal bone. The level of mechanical properties of the synthesized zirconia-based ceramics is determined by the pore sizes. The values of the compressive strength and the effective Young's modulus are very similar to those characteristics of the natural spinal bone

Dinamika beregov vostochnykh arkticheskikh morej Rossii: osnovnye faktory, zakonomernosti i tendentsii (Dynamics of the Russian east Arctic sea coast: Major factors, regularities and tendencies)

Climatic, geocryological, geological and hydrodynamic conditions and available data on Arctic coast dynamics are analyzed. The basic laws of ice-rich coast development in varied geocryological and climatic conditions are investigated. Functional connections of coastal destructive cryogenic processes activity with summer air temperature and storms recurrence are revealed. The forecast of ice-rich coast rate retreat for the Laptev Sea and East-Siberian Sea is executed in connection with prospective changes of climate in XXI century