Electrodeposition with intermittent addition of trimethylamine borane to produce ductile bulk nanocrystalline Ni-B alloys

We developed a technique to dope electrodeposited Ni with B to produce ductile bulk electrodeposits of Ni-B alloys. The conventional method, in which TMAB is added as a source for B-doping to the deposition bath before electrodeposition, affected only the first layer, producing two layers of Ni-B alloys and pure Ni in the bulk electrodeposits. These inhomogeneous specimens showed poor tensile properties, because of processing-defects presented in the layer of Ni-B alloys. These defects were produced because TMAB immediately decomposes during electrodeposition, generating hydrogen gas. In contrast, the developed technique for B-doping, in which TMAB is added intermittently during electrodeposition, produced a more-uniform B content of 0.04 at.% in the growth direction. This B distribution resulted in a uniform nanocrystalline structure with a grain size of ~28 nm. The sample of bulk nanocrystalline Ni-B alloys exhibited a good tensile elongation of 7.6% with a high tensile strength of 1.45 GPa. The developed B-doping technique avoids the harmful effects of the hydrolysis of boron compounds, and it can produce electrodeposited bulk nanocrystalline Ni-B alloys with good ductility.