Order-induced strengthening in Ni4Mo

The mechanism of order-induced intrinsic embrittlement in a stoichiometric Ni4Mo alloy by TEM and 3DAP characterization

“…In addition, they thought that the ordering reaction proceeded homogeneously first, and late a heterogeneous reaction was initiated along the grain boundaries. However, to a stoichiometric Ni 4 Mo alloy, the molybdenumdepleted zones formed alongside grain boundaries are some difficult to be understood because the statistical short-range order mode implied homogeneous ordering below the critical temperature T c , and after nuclei, ordering proceeds by atomic rearrangement within the domains [5]. Further, though the final microstructure seems two-phase, which was analogous to the classical ␥/␥ system in terms of precipitate shape, spatial distribution and a minimum distance of separation between ␥ precipitates as dictated by the interplay between strain and interfacial energies [9], the two-phase composition was still not evinced because the determination of exact composition of precipitates from EDS data would necessarily involve correction for the matrix overlap.…”

“…Some researchers [5][6][7][8] have investigated the mechanism of order-induced embrittlement in Ni-Ni 4 Mo alloys earlier. They showed that homogeneous matrix ordering only caused a moderate loss of ductility and the fracture mode remained to be transgranular.…”

The metastable phase Ni2Mo and the initial stages of ordering in NiMo alloys

“…On prolonged aging these are· sub~equently replaced by the equilibrium Ni3Mo phase. In the studies [4][5][6][7][8] on the developm~t of lro in Ni 4 Mo, on the other hand, the for I11 .ation of metastable NiZMo phase has nev~r been repor ted. by Richards [ 14], by Richards and Calm.…”

Crystal Structure of and Chemical Bonding in MoNi4

“…Based on the current phase diagram information [28] and additional reports, [11,14–19] preparation of single‐phase material of MoNi 4 cannot be done straight forward, because of the peritectoid formation of this phase from the Ni(Mo) solid solution and MoNi 3 – at for this system – relatively low temperature 867 °C (cf. melting temperatures of 2623 °C (Mo), 1425 °C (Ni) and the lowest eutectic temperature of 1309 °C).…”

“…The presence of a fully ordered structure may be however questionable, as the phase is forming as a result of a solid‐solid peritectoid reaction from disordered fcc solid solution of molybdenum in nickel with MoNi 3 at 867 °C [19,28] . The fastest ordering process can be achieved when annealing at approximately 775 °C [16] …”