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

To illustrate the mechanism of order-induced intrinsic embrittlement in a stoichiometric Ni4Mo alloy, TEM and 3DAP were employed to investigate the phase separation during ordering in this paper. It showed that the atomic ordering initiated homogeneously, but some oriented ordered domains can grow preferentially later. Therefore, with atomic ordering, the average ordered domain size continues to increase, which improves the yield strength and ultimate strength due to increasing the critical shear stresses. However, except the growth of ordered phase, different phases with enriched molybdenum and depleted molybdenum were formed after ordering. The depleted molybdenum phase gradually reduces the Mo composition, which deteriorates the ultimate strength, and meantime the strength of grain boundary does not enhance, or even weakens. Hence, the atomic ordering induces embrittlement.