Papers by Author: Vener Valitov

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Authors: Vener Valitov, Rustam Kaibyshev, N. Gajnutdinova
Authors: R. DiDomizio, M.F.X. Gigliotti, J.S. Marte, P.R. Subramanian, Vener Valitov
Abstract: This paper discusses the development of a novel processing route to produce ultra finegrain bulk alloy forgings; the microstructural response of these forgings to thermal exposure; and the comparison of mechanical properties to those from conventionally processed material. A Ni- 20Cr [wt%] alloy was processed by near-isothermal multi-axis forging to a grain size of approximately 1 μm. A heat-treatment study over the range 900 to 1200°C was conducted to determine the resultant grain size as a function of time and temperature. Tensile properties were measured at room temperature, 500°C, and 930°C. High-cycle fatigue properties were measured at room temperature. The room-temperature tensile strength was approximately 2.5 times greater than that of conventionally processed Ni-20Cr. Fatigue data showed that the room-temperature highcycle fatigue run-out stress was greater than 100% of the yield stress.
Authors: Vener Valitov, F.Z. Utyashev, Shamil Kh. Mukhtarov
Authors: Shamil Kh. Mukhtarov, Vener Valitov, M.F.X. Gigliotti, P.R. Subramanian, J.S. Marte, Nadya Dudova
Abstract: The influence of severe thermomechanical treatment via multiple forging on the formation of a nanocrystalline (NC) structure in bulk samples of Alloy 718 and ATI 718Plus has been investigated. It was observed that a step-wise decrease of processing temperature from 950 down to 575°C allowed the refinement of the initial coarse grain structure to a NC state. Investigations of structural changes in the deformed samples have shown that extending the temperature interval of dynamic recrystallization to low homologous temperatures resulted in the formation of a fine-grained recrystallized structure. The temperature of NC structure formation in ATI Alloy 718Plus was 50-100°С higher than that required for alloy 718. This was due to the presence of the additional γ′-phase, which increased the recrystallization temperature. This decreased the total strain required to produce NC structure, as compared with Alloy 718. It was observed that increasing the total strain and decreasing temperatures step-wise during deformation via multiple forging resulted in a uniform structure across the cross-section of the samples. The room temperature mechanical properties of the investigated alloys with various grain sizes are also compared.
Authors: Vener Valitov, Oscar A. Kaibyshev, Shamil Kh. Mukhtarov, B.P. Bewlay, M.F.X. Gigliotti
Authors: Vener Valitov, Shamil Kh. Mukhtarov, Ramil Ya. Lutfullin, Rinat V. Safiullin, Minnaul Mukhametrakhimov
Abstract: Nickel-iron Alloy 718 is widely used for fabricating parts by superplastic deformation. Refinement of grains down to a nanostructure (NS) size improves the alloy’s processing properties. Thermomechanical treatment has been carried out to form a NS state in bulk alloy by multiple isothermal forging (MIF) at gradually decreasing temperatures. Investigation of superplastic properties and processing behavior of Alloy 718 has been performed. The alloy with a grain size of 80 nm displays superplasticity (SP) at a temperature which is lower than for a conventional fine grained alloy by about 350°C. The values of the relative elongation  and the strain rate sensitivity coefficient m are 350% and 0.37, respectively. The experimental data on the influence of grain size on solid-state weldability in the range of SP have been obtained. The application of the effect of low temperature SP yields lower temperatures of superplastic forming (SPF) and pressure welding (PW) as compared with conventional SP of fine-grained material. The experiment of the combined process of SPF and PW by counter-forming of two polished sheets, demonstrates its low temperature processing feasibility using NS specimens. The SPF processing of NS sheets in a cylindrical die has been investigated. It has revealed that macro-deformation is uniform in cross and longitudinal sections. Mechanical properties of Alloy 718 in NS condition and after strengthening heat treatment have been discussed.
Authors: Gennady A. Salishchev, Oleg R. Valiakhmetov, Vener Valitov, S.K. Mukhtarov
Authors: Vener Valitov, Gennady A. Salishchev, Shamil Kh. Mukhtarov
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