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Frictional and fretting wear behaviors of Inconel X-750 alloy against GCr15 steel ball were investigated in dry contact condition with ∼60% air humidity. Fretting tests were run at the high frequency tribosystem SRV 4 in room temperature and ball-on-flat contact configuration were adopted with the relative oscillatory motion of small displacement amplitude (40 μm). Sliding regimes, wear volumes, frictional properties, and material damage mechanisms were studied with regard to different normal loading and test durations. After the tests, the worn surface morphologies were analyzed by three-dimensional (3D) optical surface profiler, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) to distinguish fretting running conditions and material responses for different test cases. It was found that the material removals by abrasive and adhesive wear, debris formation and oxidization, and wear delamination were the main damage mechanisms under the lower normal load where the full slide or gross slip regime (GSR) was dominant between the contact surfaces. On the other hand, fretting regime was found to be a stick-slip or a partial slip at greater loads where damage mechanisms were correlated with deformed asperities, fatigue cracks, and thick layer removal due to highly concentrated cyclic stresses. Time dependence was crucial during GSR where the wear volume increased substantially; however, the wear volumes and scars sizes were consistent over time because of stick-slip effects under the higher normal load.

A substantiated choice of an optimum regime of heat treatment of titanium alloys is possible only on the basis of a complex investigation of the regular features of the structural and phase transformations and their relation with the mechanical properties after annealing conducted for different times and in a wide temperature range. The present work concerns low-temperature transformations in double-phase titanium alloys and their effect on the processes of embrittlement in a temperature range of 300 -800~ with holds lasting from 0.25 to 500 h.Structural and phase transformations and their relation with the properties of titanium alloys have been described in many monographs [1][2][3][4][5], which shows the complexity of these problems. Primarily, this is due to the great number of metastabte phases formed in titanium alloys in the processes of mechanical and heat treamaent. In accordance with the growth of the content of alloying 13-stabilizing elements, these phases can be arranged into the following series: a m , ct', a", co, 13m" Many questions related with the mechanism and kinetics of the ct ~ 13 transformation and the formation and decomposition of metastable phases, especially in titanium alloys after plastic deformation, are still being discussed.We studied flat deformed preforms up to 150 mm thick from an industrial titanium alloy containing Ti-6% A1-2% V-6% Zr. The preforms were fabricated by the method of hot deformation in the 13-(Gt + 13) region. The temperatures of the transition of the alloy into (cL + 13)-and 13-regions corresponded to 850 and 1010~Metallographic and electron microscopic studies have shown that the structure of deformed preforms over the thickness is represented by macrostrips flattened and extended in the direction of the rolling. Each strip consists of several colonies of plates of an a-phase (with a hexagonal closepacked lattice) separated by interphase layers sometimes of a composite "sandwich" structure but based on the crystal structure of a 13-phase (with a body-centered cubic lattice) (Fig. la). The mean width of a-plates is 3.0 ~-n, the thickness of the interphase layers is 0.3 gm. The initial hot-deformed state of the alloy is characterized by the presence of a 310great number of bending extinction contours in its structure, which indicates that the substructure is in a stress state (Fig. la ).By the data of x-ray diffraction analysis, we see that the structure of the alloy in the initial state consists of ct(ct')-, 13-, and ct"-phases.The results of an x-ray spectral analysis (Fig. 2a ) show that the hot deformed alloy is characterized by a considerable concentration inhomogeneity in the distribution of the alloying elements both within a-colonies and in individual a-plates and 13-layers. When scanning the surface of polished specimens by an electron probe, we identified 13-layers with the help of the profiles of the currents of absorbed electrons. It has been established that the interphase layers (13r~t) contain an elevated amount of not only 13-stabilizing elements...