Thermal stability of electrodeposited Ni–P alloys

Abstract

Ni–P alloys were electrodeposited from phosphorous acid solutions in order to study their thermostructural stability, thermal desorption, and dimensional modifications during heat treatments. The quantity of phosphorus codeposited is not a linear function of the bath phosphorous acid content. X-ray diffraction shows that three characteristic composition ranges can be defined. In the first, corresponding to a Ni–P solid solution containing up to 9at% of phosphorus, the microstructural refining is attended by a disappearance of the (100) preferential orientation. Simultaneously with this textural change, a slight adsorption of hydrogen is observed. Beyond 9at% of phosphorus, the microcrystallized alloys are preferentially oriented in the [111] direction, and the gradual amorphization of Ni–P alloys is attended by adsorption of a very high volume of hydrogen. Beyond 17at% of phosphorus, the alloys are amorphous and the amount of hydrogen included during the electrocrystallization is at its maximum. A large part of the hydrogen is desorbed before the crystallization temperature and less of it is desorbed during the crystallization.