Laves Phase Precipitation Behavior and the Orientation Relationship with BCC in Cr–Mo–Nb System

Abstract

The isothermal sections of the Cr–Mo–Nb ternary phase diagram have been studied. The C15 NbCr₂ Laves precipitation behavior in three different alloys has been investigated in the Cr–Mo–Nb ternary system. The orientation relationship (OR) of NbCr₂ in BCC matrix among BCC/Laves two-phase alloys and Cr-rich BCC₁/Mo-rich BCC₂/Laves three-phase alloy is different at 1473 K; OR 1: (011)_BCC // (111)_C15], [011]_BCC] // [110]_C15] and OR 2: (411)_BCC] // (111)_C15, [011]_BCC] // [110]_C15] with low lattice mismatch are both observed in Cr-rich alloys #3 (74Cr–16Mo–10Nb) and #2 (50Cr–30Mo–20Nb). OR 3: (011)_BCC // (111)_C15, [111]_BCC] // [011]_C15] with a lattice mismatch relatively larger than that of OR 1 and OR 2 is only observed in alloy #2, which may be due to the presence of BCC₁ and BCC₂ interphases formed after BCC decomposition. Only discontinuous precipitation is observed at grain boundaries in Cr-lean alloy #1 (42Cr–31Mo–27Nb) without obvious OR between the BCC matrix and Laves phase.

Fig. 17 Atomic matching at three BCC/C15 interfaces.