Effect of hot working on room temperature mechanical properties and stress-rupture behaviour of ESR processed Fe-16wt%Al intermetallic alloys

Abstract

The effect of hot working (forging) on structure and mechanical properties of electroslag remelted (ESR) Fe3Al based intermetallic alloys containing approximately 16 wt% (28 at%) aluminium and 0.013 to 0.50 wt% carbon are reported. The ESR alloys having low (0.013 to 0.06 wt%) carbon content were severely cracked during forging probably due to the presence of pre-existing microcracks. ESR ingots with high (0.14 to 0.50 wt%) carbon content were successfully forged at 1000 degrees C. At high (60% or more) forging reductions the cast columnar structute of ESR alloys was transformed into recrystallized grain structure. The room temperature mechanical properties did not improve significantly after forging. During creep and stress-rupture tests carried out at 600 degrees C and 140 MPa, the cast ESR ingot with columnar structure exhibited lower minimum creep rate and higher creep life than those exhibited by the corresponding forged ingots with recrystallized grain structure. There is only a marginal improvement in creep life with increase in carbon content from 0.14 to 0.50 wt%. The stress-ruptured specimens exhibited predominantly ductile dimple failure with elongations in excess of 50%. The creep and stress-rupture properties of the alloys with high (0.14 to 0.50 wt%) carbon contents are better than those reported for wrought Fe-16 wt%Al alloys with low (< 0.01 wt%) carbon contents. This may be attributed to the presence of uniformly distributed Fe3AlC precipitates as well as the interstitial carbon present in the alloys.