Microstructural refinement and tribological response of Cryo-Thermal treated Incoloy 925 using WEDM process

Cryogenic treatment improves the machinability of a material and Incoloy 925 is one of the hard-to-machine materials. In the current work, Incoloy 925 is processed using deep cryogenic treatment at −185 ºC with 12 h of soaking time to relieve the residual stresses and to improve the machinability of the material. Tempering was carried out at 300 ºC for 3 h and cooled under two different conditions, viz., in ambient conditions and the furnace environment individually. The processed Incoloy 925 samples were characterized using X-ray diffraction analysis (XRD). Energy dispersive X-ray Spectroscopic analysis (EDAX) and Scanning Electron Microscopic analysis (SEM) for microstructural changes. The Specimens were then subjected to microhardness measurements and wire electrical discharge machining (WEDM) to assess the effect of cryogenic treatment and tempering on the material's machinability using material removal rate, surface roughness, and kerf width. The process parameters of WEDM were optimized using Entropy-EDAS methods. It was understood from the results that the cryo-treated and tempered Incoloy 925 exhibited refined crystal size and surface morphology. The cryo-treated and tempered Incoloy 925 with furnace cooling exhibited a high microhardness value and machinability owing to more refinement in microstructure during the treatment and tempering process. From the optimization results, a minimum surface roughness, maximum materials removal rate and kerf width were obtained for a pulse on time of 25 µs, a pulse off time of 48 µs and an input current of 4 A. These alloys find their applications in gas turbine shafts and pump shafts.