Abstract
A new, cost-efficient and on-site-applicable thermal spraying process for depositing NiAl metallic overlay or bond-coat coatings for high temperature applications by synthesizing the desired intermetallic phases in-flight during oxy-acetylene flame spraying is presented. Base-metal powders were used for spraying and, by adjusting the spraying conditions, excellent NiAl-based coatings were achieved on various substrates, including mild steel, stainless steel and aluminium alloys. Expensive, pre-alloyed or agglomerated powders are avoided and the method is very promising for in-situ work and repairs. We call the new method “Combustion-Assisted Flame Spraying” (CAFSY) and its viability has been demonstrated at a pre-industrial level for coating metallic substrates. The NiAl-based coatings produced by CAFSY exhibit very high integrity with good adhesion, very low porosity, high surface hardness and high erosion resistance at a substantially lower cost than equivalent coatings using pre-prepared alloy powders.
Highlights
State of the ArtProtective coatings can impart superior properties on a substrate and are used in a large number of engineering applications
A new, cost-efficient and on-site-applicable thermal spraying process for depositing NiAl metallic overlay or bond-coat coatings for high temperature applications by synthesizing the desired intermetallic phases in-flight during oxy-acetylene flame spraying is presented
The performance and applicability of flame spraying has been enhanced in this work by the development of In-Flight Combustion Synthesis which allows the use of simple metal powders instead of pre-alloyed powders
Summary
Protective coatings can impart superior properties on a substrate and are used in a large number of engineering applications. Not all processes are suitable for all coating materials and not all coating thicknesses are attainable with all methods. Sprayed hard coatings are extremely effective at increasing a metallic component’s life and value, decreasing machinery down time and improving performance in a wide variety of applications, by imparting improved hardness, wear and corrosion resistance, lowering friction etc. Thermal spraying is applicable to a large range of coating materials, coating thicknesses and coating characteristics. Thermal spraying methods are grouped into three main categories: flame spraying, electric arc spraying and plasma arc spraying, referring to the energy sources producing the flame to heat the coating material to a molten or semi-molten state. Droplet size and injection velocity [3] are the most important parameters, whereas the injection angle is of lesser importance
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