Hi all,
As per the literature available, HVAF (high velocity air fuel) spray coatings (WC based) resulted into superior quality coatings as compared to HVOF (high velocity oxy fuel) coatings. HVAF have many advantages over HVOF as reported by some researchers like as lower temperature flame, strong pinning effect of blasting particles (high compressive residual stresses), Air cooled (no water cooling required), 3-4 times high spray rate (time and cost saving), High hardness and ductility, Axially powder feeding (less decarburization).
With the having above advantages, Why HVAF spray process did not get any attention for commercialization in industries?
Hi Nitesh,
It is not so clear as you describe. HVAF technology has certain advantages over HVOF, but there are enough disadvantages. These disadvantages are often "forgotten" by HVAF manufacturers.
The real advantages of the modern HVAF systems from Kermetico and Uniquecoat over modern HVOF systems ( for example CJS from Thermico ) include only the following:
The principal disadvantages of HVAF are:
A statement that quality of HVAF layers is always better than of HVOF layers is a fiction. As well as at HVAF and at HVOF there are layers with very different qualities, from "very bad" to "good". In terms of quality, there are no principal differences between HVOF and HVAF: both types of layers consist of unmelted particles and are therefore permeable to gases and liquids.
Also the statement that the HVAF layers are hard and ductile at the same time is ridiculous. These properties are the functions of modulus of elasticity of the layer, which under no circumstances can be simultaneously low (ductility) and high (high hardness and stiffness).
By the way, I personally do not like these two technologies, because the layers, although low in porosity, are always permeable. In order to be able to produce really good, gas-tight layers, molten particles must be used, and this is only possible by means of plasma spraying:
Article Coatings of carbide-metal systems (Cr3C2-NiCr and WC-Co-Cr) ...
I think that as well as HVOF and HVAF are totally overvalued today.
To my knowledge, HVAF is very popular in China but not as popular as HVOF in the US and Europe. That's because thermal spraying industries are quite developed in European companies, most of which already have various kinds of HVOF equipments. Though the quality of HVAF coatings can be a little bit better than those of HVOF coatings under strictly controlled conditions, it is difficult to persuade the European companies to change their spraying systems from a consideration of cost performance. As I know, a lot of newly founded Chinese companies prefer to choose HVAF system. But I don’t think HVAF will replace HVOF in near further.
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