SEVERE THERMOMECHANICAL PROCESSING AS AN EFFECTIVE METHOD FOR THE PREPARATION OF BULK AND SHEET NANOSTRUCTURED SEMIFINISHED PRODUCTS FROM NICKEL ALLOYS 718 AND 718PLUS

The paper considers the scientific basis of a new methodological approach for processing bulk and sheet nanostructured semi-finished products from nickel base alloys 718 and 718Plus. This approach involves carrying out severe thermo-mechanical processing (STMP) using primarily schemes of multiple isothermal forging (or forging followed by rolling) at temperatures decreasing gradually from (0.9-0.8)Tm to (0.6-0.5)T m. Such processing results in a step-by-step structure refinement: a coarse-grained macroduplex type structure transforms to a microduplex one (d=1-3μm) and then to a nanoduplex structure (d=0.5–0.05μm). The paper considers examples of production of complex profile turbine engines components from materials with a microduplex type structure and shows the possibility for applying semi-finished products with a nanoduplex type structure in advanced manufacturing procedures of pneumatic forming and pressure welding under low temperature superplasticity (LT SP) conditions.