On the Selective Oxidation of Novel Electrodeposited Nanocomposites Distributing Cr or/and Al Nanoparticles

Using an electrochemical deposition method,nanoparticles of Cr or/and Al were assembled into a nanocrystalline metal template to fabricate novel metal-matrix nanocomposites.The nanocomposites would be easier to develop protective scales of chromia or alumina during high temperature exposure, based on a selective oxidation model proposed for these types of nanocomposites.That is,the nanoparticles in the near-surface zone of the nanocomposites would convert into chromia or alumina islands at the onset of oxidation.Then,the nano length scale distribution of the nanoparticles,together with the nanograined metal-matrix structure,would favor a rapid linkage of the oxide islands to form a continuous layer of chromia or alumina.Using the oxidation model,we can explain the oxidation behavior of various nanocomposite systems such as Ni-Cr,Ni-Al,Ni-Cr-Al,Cu-Ni-Cr,etc.,by comparing to those of conventionally coarse-grained alloys of similar composition and the electrodeposited composites dispersing conventional micron-sized particles instead of equivalent weight of nanoparticles.

Using an electrochemical deposition method, nanoparticles of Cr or/and Al were assembled into a nanocrystalline metal template to fabricate novel metal-matrix nanocomposites. The nanocomposites would be easier to develop protective scales of chromia or alumina during high temperature exposure, based on a selective oxidation model proposed for these types of uanocomposites. That is, the nanoparticles in the near-surface zone of the nanocomposites would convert into chromia or alumina islands at the onset of oxidation. Then, the nano length scale distribution of the nanoparticles, together with the nanograined metal-matrix structure, would favor a rapid linkage of the oxide islands to form a continu- ous layer of chromia or alumina. Using the oxidation model, we can explain the oxidation behavior of various nanocomposite systems such as Ni-Cr, Ni-Al, Ni-Cr-Al, Cu-Ni-Cr, etc., by comparing to those of conventionally coarse-grained alloys of similar composition and the electrodeposited composites dispersing conventional micron-sized particles instead of equivalent weight of nanoparticles.