Laves phase precipitation behavior and the orientation relationship with BCC in CrMoNb system

Abstract

The isothermal sections of the CrMoNb ternary phase diagram have been studied. The C15 NbCr2 Laves precipitation behavior in three different alloys has been investigated in the CrMoNb 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 1473K; OR 1: (011)BCC // -111+C15, =011BCC // =110C15 and OR 2: -411 +BCC // (111)C15, =011BCC // =110C15 with low lattice mismatch are both observed in Cr-rich alloys #3 (74Cr16Mo10Nb) and #2 (50Cr30Mo20Nb). OR 3: (011)BCC //(111)C15, =11 1BCC // =011C15 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 (42Cr31Mo27Nb) without obvious OR between the BCC matrix and Laves phase.