Microstructural studies on nanocrystalline oxide dispersion strengthened austenitic (Fe-18Cr-8Ni-2W-0.25Y2O3) alloy synthesized by high energy ball milling and vacuum hot pressing

In the present work, nanostructured (Fe-18Cr-8Ni-2W) austenitic base and oxide dispersion strengthened (ODS) alloy powders were produced through mechanical alloying and these nano powders were consolidated by vacuum hot pressing. The results showed that initially bcc solid solution formed in both the alloys and this transformed to fcc with continued milling. The bcc solid solution formation and the subsequent transformation to fcc were significantly faster in the ODS alloys when compared to the base alloy. In the ODS alloy, a grain size of similar to 25 nm is achieved within 5 h of milling. Study of variation of microhardness of mechanically alloyed powder particles with grain size showed linear Hall-Petch kind of behavior. Following vacuum hot pressing of mechanically alloyed powders, nearly fully dense (> 99% of theoretical density) compacts were obtained with a grain size of similar to 80 nm. The bulk hardness of base and ODS alloys are similar to 530 and similar to 900 HV, respectively. These are significantly higher than the values reported in the literature so far. The enhanced strength the ODS alloy is due to increased dislocation density and presence of fine dispersoids along with the nanocrystalline grains.