Strategy to Improve the High-Temperature Mechanical Properties of Cr-Alloy Coatings

Abstract

Electroplated Cr-C alloy coatings exhibit significant increases in hardness and strength when exposed to elevated temperatures up to about 600°C, owing to the evolution of their nanostructure. In this article, we describe a strategy by which this evolution can be shifted to even higher temperatures (approaching 850°C), through a ternary addition of phosphorus. The resulting Cr-C-P coatings may be suitable for applications at higher service temperatures, where more conventional Cr-based coatings soften rapidly.

Characterization of as-deposited and annealed Cr–C alloy coatings produced from a trivalent chromium bath

“…Since the maximum solubility of carbon in Cr is about 0.02 at.% [12], it is concluded that the Cr-C alloy coating deposited is supersaturated by carbon. It should be noted that the carbon is usually incorporated into the coating from decomposed organic compounds produced in bath, by the reduction of organic constituents under the extremely high electrical field [13]. Thus, higher current density applied at pH 0.5 would cause more reduction of formic acid as an organic Table 2 The EDS analyses and hardness values of Cr-C alloy coatings before and after annealing at 300 • C and 600 • C.…”

“…2) and increased the hardness of coating up to 1670 HV. Gines et al [13] have investigated the effect of annealing temperature in the range of 400-900 • C on the hardness of electrodeposited Cr-C alloy coatings. As reported by these researchers, the maximum hardness of 13.7 GPa has been obtained after annealing at 600 • C. Similar trend was also reported by Kwon et al [16], who examined the annealing temperature in the range of 200-800 • C. The results show an ideal behaviour of passivation for as-deposited Cr-C coatings, identified by the presence of a region of nearly constant current density.…”

Codeposition of Particles: Role of Adsorption of the Electroactive Species

“…The main advantage of this technique is that it provides an effective method to obtain deposits with unique properties, resulting of the combination of the particles' characteristics (ceramic, metallic, organic) with those of the electrodeposited metal. As a consequence composite coatings have several applications, among which the development of wear and corrosion resistant deposits, 1,2 self-lubricating coatings 3,4 and dispersion strengthened coatings 5 are the most important, as has been already stated by Celis et al 6 However, these are just some uses of the codeposition technique that have been reported so far; several new applications have been envisaged in the last decade 7 and many others are still to be developed. 8,9 Although the incorporation of particles during electrodeposition has been known since the advent of the electroplating industry 10,11 the first attempt to produce a technological coating using this method dates from 1928.…”

Thermal and Dry Sliding Wear Behavior of Plasma Sprayed Red Mud-Fly Ash Coatings on Mild Steel

“…Interfaces that are usually exposed to elevated temperatures are of various moving assemblies in the aerospace industry, power generation and metal working processes [5]. Metallic or metallic alloy coatings when exposed to above 200 °C; most of them lose their initial properties and soften appreciably [6]. So such coatings are limited to low temperature applications.…”