Effects of Al and Cr on microhardness and phase separation of Fe-Cr-Al alloys

The effects of Al and Cr on the microhardness and phase separation of the α' phase in Fe-Cr-Al alloys aged at 750 K are studied by using the hardness measurement and phase-field (PF) simulation, and the correlations between the mechanical properties and morphology kinetics are clarified. The separation of α' phase shows the substantial effect on the hardness increment, by addition of Al, the increment of hardness is suppressed in the low Cr content Fe-25Cr at.% alloy, while the increment of hardness is intensified in the high Cr content alloys. The Cr depletion and Al enrichment at the interface of α/α' phases is showed in Fe-25Cr-10Al at.% alloy rather than in the high Cr content alloys. With the Cr content changing from 25 to 35 at.%, the early stage variation rate of volume fraction and later stage coarsening rate are quickened, correspondingly, the average particle distance goes through a descent of early stage and ascent of growth and coarsening stage. Large volume fraction and small particle distance of α' phase explains the high hardness of the high Cr content alloys. In addition, the time exponents of average particle radius are close to 0.3 at the growth and coarsening stage, while less than 0.3 at the later coarsening stage, a dependence of the time exponent on the phase separation stage is revealed.