TWI Industrial Member Report Summary 844/2006
By M A Riley
The aim of this work was to undertake a further evaluation of high velocity oxyfuel coatings prepared from amorphous and nanocrystalline materials in order to improve the corrosion properties whilst retaining the wear resistance, following the previous work on this subject (1).
Hard chromium plating has been used for many years in applications that require hard, abrasive or sliding wear resistant coatings, such as hydraulic cylinders, rotating shafts, landing gears, pistons, valves, etc. Although hard chromium plating is still used in industry, it is expected that its use will be restricted or even banned in the next ten years. This is due to changes in environmental legislation which aims to reduce the use of plating operations due the toxicity of some of the processes.
High velocity oxyfuel (HVOF) sprayed WC-Co-Cr is a candidate material for hard chromium plating replacement and is used where combined wear and corrosion resistance are required. It is already approved for aerospace applications, but is an expensive coating system, which limits its wider use in industry. Therefore, there is a need for the development and evaluation of affordable coatings with the combined properties of wear and corrosion resistance as alternative coating materials to hard chromium plate.
In the previous work (1), LMC-C+TM, LMC-MTM and SHS-717, which were marketed as nanocrystalline or amorphous materials, were investigated as alternative coatings. Some of these coatings were found to have limited corrosion resistance. In this report further work is described which aims to improve the corrosion properties of the coatings prepared from amorphous and nanocrystalline powders, whilst retaining wear resistance. The coatings investigated in this work were LMC-MTM, sprayed using revised parameters compared to the previous work, and SHS-7574, which is claimed by the manufacturer to offer improved corrosion resistance compared to the SHS-717 powder. The structure and corrosion and wear performance of the deposited coatings are compared with a conventional WC-Co-Cr HVOF sprayed coating, hard chromium plating and the results of the previous work.
- To deposit good quality coatings on steel and stainless steel substrates using amorphous and nanocrystalline powders and the JP5000 HVOF system.
- To determine the microstructure, bond strength, corrosion resistance, wear performance, deposit efficiency and deposition cost of these coatings and compare them against electrolytic hard chromium plating and WC-Co-Cr HVOFcoating.