Study of nickel-plated iron powder for powder metallurgical applications.

The use of coated iron-nickel powders in the production of sintered components of low-alloy steels has certain advantages over blended mixtures of the elemental powders. In particular, the former produce a more homogeneous material after a specific sintering treatment.There is a limited amount of evidence that the improvement in the degree of homogeniety produces an improvement in the tensile strength of quenched and tempered sintered compacts.The present investigation has aimed to develop a technique by which nickel coated iron powder may be produced and to determine the modulus of rupture of various sintered iron-nickel alloys produced from such powders. The coated powder was produced in a three phase fluidised bed, which contained iron powder, nickel plating solution and a fluidising gas. Coating of nickel on the iron powder particle was achieved by electro-deposition, using cathode rods suspended in a fluidised bed. The central anode consisted of nickel shot contained inside an anode bag. The apparent deposition efficiencies frequently exceeded 100%, which indicated that a process other than electro-deposition was also involved.The second process was shown to be due to a cementation reaction, in which the iron was replaced by nickel. An examination was made of the effect of temperature, anode bag fabric and type of anode material on both types of deposition process. It appears that a nickel coating may be readily prepared by the use of the electroless process alone. 'The modulus of rupture of compacts prepared from both plated and blended materials was strongly dependent on porosity while the degree of homogeneity had a significant effect at the higher nickel contents only. An increase in nickel content improved the modulus of rupture after a specified sintering and hardening treatment, although the magnitude of this effect became smaller as the porosity of the compacts was increased. A comparison of the results obtained from plated and blended powder compacts showed that the former possessed higher values of modulus of rupture, although once again the magnitude of this effect was diminished as the porosity of the compacts increased.