High-temperature strengthening mechanism and thermal stability of Laves in ferritic matrix

The high-temperature creep strengthening mechanism and thermal stability of Laves phase are the key factors that affect its strengthening property in ferritic matrix. Therefore, in this study, two types of C14 Laves phase alloys, namely, Fe2Nb Laves phase Alloy S1 (Fe-9Cr-4Al-2Nb) (wt.%) and Fe2W Laves phase Alloy S2 (Fe-9Cr-4Al-2W) (wt.%) were prepared to investigate the strengthening mechanism and strengthening effect of Laves phase with different compositions in ferritic matrix. The creep properties and microstructure character-istics of the two alloys, in particular, the interfacial structure characteristics between Laves phases (Fe2Nb and Fe2W) and ferritic matrix were analyzed. The true stress exponent n for both Alloys S1 and S2 is 5, and the true activation energies Q of Alloys S1 and S2 are 372.47 and 365.82 kJ mol 1, respectively. The creep mechanisms of Alloys S1 and Alloy S2 are both dislocation climbing-dominated processes reinforced with precipitated phases. Alloy S1 exhibits higher high-temperature creep resistance than that of Alloy S2. The grain size of Alloy S1 is smaller than that of Alloy S2. Both the precipitates Fe2Nb in Alloy S1 and Fe2W in Alloy S2 are mostly located at the grain boundary. The density of dislocation in Alloy S1 is higher than that in Alloy S2, and the bending degree of dislocation lines caused by precipitate hindrance is also higher than that in Alloy S2. The orientation re-lationships between the Laves phase Fe2Nb and ferritic matrix in Alloy S1 are [011]alpha-Fe//[5 194]Fe2Nb, (011)alpha-Fe//(03 3 1)Fe2Nb, with the atomic interface mismatch of 1.6%; the orientation relationships between the Laves phase Fe2W and ferritic matrix in Alloy S2 are [001]alpha-Fe//[01 1 2]Fe2W, (1 1 0)alpha-Fe//(01 11) Fe2W, with the atomic interface mismatch of 1.9%. The results indicate that the Fe2Nb-type Laves phase may be more suitable to candidate for the strengthener in the ferritic matrix compared with Fe2W-type.