Formation of a set of requirements for methods of evaluating the workability of welded joints "base-welded metal" of nickel heat-resistant alloys of ZhS6 and ZhS32 type, simulating the repairing of the edges of blades of Aircraft Gas Turbine Engine in industrial conditions

During the microplasma powdered overlaying welding process (МPOW), the special type of overlay metal structure difficult-to-weld Ni-based superalloys ZhS6- and ZhS32-type is formed, which differs from similar cast by dendritic structure grinding, reduction of carbide particle size and more uniform distribution. Numerous metallographic studies conducted by Paton EWI, SE ‘Ivchenko-Progress’, JSC ‘Motor-Sich’ for the corresponding welded joints of alloy ZhS32 with a volume of overlay metal up to 2–5 cm3 showed no tendency to crack at all stages of repair technology. The operability of such welded joints of the alloy ZhS32 in the conditions of long operation of the restored working blades at 950–1100°C is repeatedly checked in practice. An important component at the stage of pre-production preparation of repair technology based on the МPOW process is to perform comparative certification tests of mechanical properties (short-term and long-term strengths) of the respective welded joints in volumes equivalent to the requirements of technical conditions for cast superalloys. Suitable welded preparations for the subsequent cutting of samples for mechanical tests are made by multilayer overlaying. However, an increase in its volume of more than 2–5 cm3 for nickel-based superalloys of ZhS6 and ZhS32 type is accompanied by a significant increase in the tendency to crack. To find out the reasons for their formation, a comprehensive study of the microstructure of these welded joints ‘base–overlay metal’ (by means of the scanning electron microscopy) and evaluation of their short-term and long-term strengths at T = 1000°C is made. Results of study of the microstructure and mechanical properties of welded joints ‘base–overlay metal’ nickel-based superalloy ZhS32 obtained by МPOW process are compared with similar published data on the overlay metal ZhS32 obtained by the method selective laser sintering (SLS). For interpretation of results of the tendency to cracking formation during multilayer overlay of nickel-based superalloys with a content of strengthening g¢-phase with 60 vol.%, the results of metallographic studies of ZhS32 overlay metal obtained by electro-spark process are also used. The results of the performed research testify to the prospects of including in the complex of certification tests the mechanical properties of welded joints of nickel-based superalloys with the content of strengthening g¢-phase more than 50 vol.% of high-temperature tests for static strength of the overlay metal. This will allow detecting violations of technological strength or low plasticity of their local areas before more expensive and complex tests (long-term strength, low- and high-cycle fatigue, fatigue crack growth rate) and further more adequately interpret their results. © 2022 G. V. Kurdyumov Institute for Metal Physics, National Academy of Sciences of Ukraine