The unique aspects of twinning found in electrodeposited Ni–Mn alloys were identified. Previous reports had concluded that the twin boundaries effectively refined the grain size, and enhanced mechanical strength. Quantitative measurements of transmission electron microscopic images showed that the relative boundary length in the as-plated microstructure comprised mainly twin interfaces. Detailed transmission electron microscopic characterization revealed a range of length-scales that was associated with twinning; beginning with colonies (1000nm) and going down to the width of individual twins; which was typically less than 50nm. Also considered was the connection between the crystallographic texture of the electrodeposit and the orientation of the twin planes with respect to the plating direction. The Ni–Mn alloy deposited here possessed a {110}-fiber texture. Twinning could occur on {111} planes either perpendicularly or obliquely to the plating direction in {110}-oriented grains, but plan-view transmission electron microscopic images showed that twins formed mainly on planes parallel to the plating direction. Therefore, grains enclosed by twins and multiply-twinned particles were produced. Another consequence of a high twin-density was the formation of large numbers of twin-related junctions. An area density of twin junctions was measured that was comparable to the density of dislocations in a heavily cold-worked metal.

Characterization of Twinning in Electrodeposited Ni–Mn Alloys. G.Lucadamo, D.L.Medlin, N.Y.C.Yang, J.J.Kelly, A.A.Talin: Philosophical Magazine, 2005, 85[22], 2549-60