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

摘要

The isothermal sections of the Cr-Mo-Nb ternary phase diagram have been studied. The C15 NbCr_2 Laves precipitation behavior in three different alloys has been investigated in the Cr-Mo-Nb ternary system. The orientation relationship (OR) of NbCr_2 in BCC matrix among BCC/ Laves two-phase alloys and Cr-rich BCCi/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 BCQ and BCC_2 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.