Quaternary chromium-based alloys strengthened by Heusler phase precipitation

Five quaternary chromium-based alloys have been designed in order to precipitate β′-Ni2AlTi Heusler phase strengthening particles while forming a protective alumina scale. These alloys were prepared by arc or induction melting as small polycrystalline ingots. β′-Ni2AlTi Heusler phase was observed as massive particles in the interdendritic areas of the cast alloys and as fine precipitates within the dendrites. The level of aluminium added in these alloys was however not enough to promote the formation of a continuous alumina protective scale before or during cyclic oxidation tests at 1100°C. Surface aluminium enrichment of cyclic oxidation samples was carried out by vapour-phase aluminization to promote formation of a protective alumina scale at 1100°C. That resulted in a dramatic improvement of the cyclic oxidation resistance of the Cr-based alloys. Compressive creep test performed at 850°C and 1100°C demonstrated the significant strengthening effect of the β′-Ni2AlTi Heusler phase precipitates when compared with pure chromium.