Articles incorporating nickel tungsten alloy deposits having controlled, varying, nanostructure
Bipolar wave current, is used to electrodeposit a nanocrystalline grain size. Polarity Ratio is the ratio of absolute value of time integrated amplitude of negative and positive polarity current. Grain size can be controlled in alloys of two or more components, at least one of which is a metal, and at least one of which is most electro-active, such as nickel and tungsten and molybdenum. Typically, the more electro-active material is preferentially lessened during negative current. Coatings can be layered, each having an average grain size, which can vary layer to layer and also graded through a region. Deposits can be substantially free of either cracks or voids.
1. An article of manufacture of a deposit comprising an alloy selected from the group consisting of cobalt tungsten alloy and cobalt molybdenum alloy, wherein the deposit comprises a coating on a substrate, the deposit comprising:
a. a first layer region having a nanocrystalline structure with a first average grain size;
b. adjacent said first layer region, and in contact therewith, a second layer region having a nanocrystalline structure with a second average grain size, which second size differs from the first size, wherein the difference between the first average grain size and the second average grain size is at least 50 nm; and
further wherein the deposit is substantially free of either voids or cracks, and
further wherein, one of the layer regions comprises a region having a nanocrystalline structure with a graded variation in average grain size, such that the graded variation region has a first average grain size at a first location and spaced therefrom, at a second location, the graded variation region has a second, different average grain size, with varying average grain sizes between the first and second locations.
2. The article of claim 1 , wherein the first layer region has a first composition and the second layer region has a second composition different than the first composition.
3. The article of claim 1 , wherein the first layer region is formed on the second layer region.
4. The article of claim 1 , wherein the deposit comprises a cobalt tungsten alloy.