It is forecast that nano-materials will revolutionise surface engineering because remarkable combinations of properties, such as strength, hardness, toughness, impact and corrosion resistance, will be achievable simultaneously due to nano-scale grain refinement.
At present, nano-structured coatings are mostly produced by vapour phase deposition, ion or sol-gel processes and are limited to high value components.
To introduce nano-structured coating benefits to a wider market more processes such as HVOF spraying and low cost materials such as steel will be needed. To date, nano-structured thermal spray powders have been produced by expensive processes such as the agglomeration and sintering of mechanically milled nano-sized particles to form macro-powders.
TWI, however, has recently completed the preliminary evaluation of HVOF coatings prepared from powder containing a mixture of crystalline and amorphous structures. Initial trials show these coatings are characterised by very low porosity (0.2%), high hardness (960HV0.2) and low oxygen content (0.2%).
Work continues in the Core Research Programme comparing the wear and corrosion behaviour of coatings produced from amorphous and nano-structured powders with HVOF carbide coatings and hard chrome plating.
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