In the present work there are given the results of experimental investigations of contact fatigue and the wear of deformable high strength ADI (DADI) class aluminum cast iron depending on the phase ratio in metallic matrix. It is shown that: Modification of cast iron melt with the magnesium vapor gives the opportunity the low silica (0.5-0.7% Si) high strength cast iron to be received, in which the concentration of sulfur will not exceed 0.002%. Besides, the type and degree of austenite transformation of the received cast iron can easily be varied so that required ratio of phase components such as upper bainite, lower bainite, martensite, carbide and the retained austenite could be provided in the metallic matrix and therefore the hardness in the range of 30-57HRC can be given. The wear rolling and rolling with creep tests carried out on the specimens tempered till different levels of hardness showed strong dependence of contact fatigue and the wear on the amount of retained austenite in the samples with optimal ratio, required for keeping the high wear resistance of wearing surfaces, of bainite and martensite phase components in the matrix structure. The stated parameters of the contact fatigue and the wear gives us reason to treat the high strength DADI class aluminum cast iron as an efficient substitute for the expensive steel as a constructional material for manufacturing the critical parts for high pressure multistep gas pumping compressors.
The present work is dealing with the study of a nano-compositional material which was obtained on the basis of PTFE with 2.5÷10wt% of core-shell type Fe-doped carbon nano-tubes and carbon nano-particles as fillers. The PTFE samples without the fillers were prepared too. Weight wear, friction coefficient and temperature were measured after passing some velocity steps, and afterwards the linear wear was calculated. The obtained results have shown that the incorporation of about 2,5÷5wt% of Fe-doped CNTs into PTFE matrix drastically improves the antifrictional properties in comparison to the unfilled PTFE. Namely, the wear resistance of these nanocompositions increased by the factor of 500-150 in the range of friction velocities 0.25÷1.25 m/sec. Increase of the filler portion up to 10wt% transforms the obtained nanocomposite from antifrictional to friction material with the enhanced coefficient of friction up to 0.32, but with the unexpectedly ultra-low wear. SEM-EDX analyses of the worn surfaces of the tested nanocomposites and the cast iron samples after working as a tribological pair, revealed some favorable effects of the Fe-doped CNTs filler on the formation mechanism of a transfer film and its role in promoting very low wear of the obtained new nanocomposites.
The results of investigation of physical-mechanical and tribological properties of polytetrafluorethylene (PTFE), composites filled with small (5-10 wt. %) amounts of nanoceramic and nano metallic powders are presented. BN, B 4 C and Co were used as nanopowder fillers. At compression by 30 MPa pressure they are subjected to 10 mass % filled composites on the base of B 4 C and Co is equal correspondingly to deformation of 3.20 and 2.46 % that 6.5 and 8.5 times exceeds the index of unfilled polymer. Developed composites have 2-4 times better wear-resistance than that of the commercial “Superfluvis” on the base of PTFE.
Using the methods of scanning electron microscopy (SEM), Auger electron spectrometry (AES), fast electron diffraction (FED) in the “on reflection” regime and wavelength dispersive spectrometry (WDS) a complex investigation of the hierarchical sequence of amorphous Beilby layer formation has been studied due to the self-organizing dissipative processes, associated with extensive cold work, on the surface of an Fe-Cr-Ni-Al-La alloy, with high (>40%) chromium content. It was established that, the surface layer (≤1μm thickness) of the mechanically polished specimen of Fe-44%Cr-1%Ni-4%Al-0.3%La alloy consists of the amorphous Beilby layer and that its adjacent matrix layer, crushed due to the plastic deformation, formed an entropy “excited” functional system, which at the temperature of 1200°C in laboratory atmosphere permits the formation of an oxide surface layer with a micro-wrinkles modulated structure of uniform thickness, in the form of mixture of nanocrystallites (100÷500nm) made of oxides of atoms constituting the basic metallic matrix. Beneath this layer a thin alumina scale is observed to form. Increasing the oxidation temperature causes the regrowth of nanocrystallites and also the recrystallization processes, accompanied by solid-phase reactions between oxide nano-particles. This leads to scale delamination at the superficial oxide thin uniform alumina layer interface. The Al2O3 layer is characterized by high adherence with metallic substrate and provides protective features against both high temperature (1200°C) oxidation of the matrix and resistance to abrasion. By the pretreatment at 1200°C of the investigated alloy’s surface modified specimens, there forms a low thickness (several microns) scale which has ultra fine graininess (~1μ) with no porosity and blocked grain boundaries short-circuit diffusion paths. This gives to the scale the ability to protect the metallic matrix against high temperature gas (and other aggressive environment) corrosion.
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