Corrosion Properties of Ni-P-B Dispersion Coating for Industrial Knives and Blades (2022)

Industrial blades, particularly the one used in food processing, requires not only a high hardness and a good wear protection but also an adequate corrosion protection. Currently, there is a wide variety of materials being used for this purpose that satisfy the above requirements. However, they come at a cost. Typically, steel with a high number of alloyed elements is chosen because the alloyed elements improved the steel quality. For example, incorporation of nickel, chromium, phosphorus and molybdenum in the steel improves amongst others the corrosion protection. However, the thermal processing of such steel, that is quenching, repeated tempering and followed by nitriding or boriding, is lengthy and complicated which drive the cost to produce knives using such steel up. Besides steel cutting tools, there is also cutting tools made from ceramic and carbide. Compared to steel knives, carbide knives have a longer lifespan and provide a higher temperature tolerance, which results in the application of the carbide cutting tools at higher speed and for longer periods without experiencing tool failure. Admittedly, due to carbides high hardness and thus the increase in difficulty to machine carbide, the production cost of carbide cutting tools is much higher compared to their steel counterparts. For ceramics, while the material is corrosion free and can maintain hardness and wear properties at a very high temperature, it is also more brittle than steel and carbide cutting tools. This results in premature chipping of the cutting edge and a shorter lifespan of the blade. To further reducing the production cost of industrial knives, the alternative of using a low alloyed steel which is coated with a hard coating and adjacently thermally treated for 1 h is investigated. This method is chosen because the tempering process of the low alloyed steel is not as lengthy as for high alloyed steel. The homogenously incorporated boron particles in the nickel phosphorus coating reduce the subsequent thermal treatment duration due to a shorter diffusion path compared to the conventional boriding. Previous study by the author [1] shows this approach to produce a high hardness at approx. 900 HV. Electroless nickel phosphorus coating is applied due to its good anti-corrosive properties. The presence of boron as particles in the coating or as boride after thermal treatment could change the corrosion behaviour of the coating. To date, no studies have yet been done to determine its corrosion properties and benchmarking this Ni-P-B dispersion coating with the other coating systems. In this study, the corrosion behaviour of the dispersion layer as coated and after thermal treatments at different temperatures is investigated. The corrosion resistance in NaCl 3.5 % is characterized though potentiodynamic polarisation and electrochemical impedance spectrometry. The results will be evaluated and compared to the other established coating systems. [1] The previous study will be presented at 241 st ECS Meeting in Vancouver, Canada and has not yet been published at the time this abstract is submitted for the 242 nd ECS Meeting in Atlanta.