Age hardening of Ni–P–Mo electroless deposit

A Ni–P–Mo autocatalytic coating was developed in order to study the structural changes according with the molybdenum codeposition and the effects of aging treatment. Results show that heat treatment induces structural changes that allow for total crystallisation of amorphous regions and the reordering of crystalline phases, to produce a Ni–Mo solid solution with precipitation of Ni₃P and MoNi₄ particles. Hardness of the as plated condition is similar to high phosphorous Ni–P deposits as mentioned in the literature, however the present work revealed that subsequent heat treatment was beneficial in enhancing the hardness of the metallic coating with a maximum of 1450 HV(100 g) being measured for coatings treated at 500°C for 2 h. This hardening can be interpreted as a consequence of amorphous to crystalline phase transformation and the aging processes of Ni–P–Mo ternary alloy. This enhancement is further reinforced by the precipitation of MoNi₄ intermetallic particles.