The Evolution of Texture During Annealing of Nanocrystalline Electroless Nickel Alloy Deposits

Abstract

The electroless Ni–Co–P alloy films containing up to 13.4% Co and 7.6% P were deposited on a 5086 aluminum alloy sheet using baths consisting of NiSO₄, CoSO₄, (NH₄)₂SO₄, NaH₂PO₂, sodium citrate and thiourea. The deposits were solid solutions having a grain size of 6–7 nm and strong 〈111〉 texture. When the deposits were annealed for 2 h, Ni₅P₂ was precipitated at 325°C and transformed into the stable Ni₃P phase at higher temperatures. During annealing the texture of deposit changed from 〈111〉 to 〈100〉. The texture change was attributed to preferential growth of 〈100〉 grains at the expense of 〈111〉 grains to decrease the thermal strain energy of the deposits. On the other hand, the electroless Ni–Cu–P alloy films containing Cu and P deposited on 5086 aluminum alloy sheet had the microstructures and textures which are similar to these of the Ni–Co–P alloy films. However, their initial 〈111〉 texture remained relatively stable even after annealing. The differences in annealing textures of Ni–Co–P and Ni–Cu–P alloy films have been discussed.