TWI Industrial Member Report Summary 737/2002
R D Halldearn and A J Sturgeon
While traditional applications of thermal sprayed coatings have addressed issues of surface protection, there is growing interest in the use of the technology to produce engineered microstructures for multi-functional surfaces or devices. Thermal spraying now offers the capability to construct coatings with predefined and well-controlled variations in both material types and microstructure features such as porosity. As a result, thermal spray technology is increasingly being considered as an innovative and unique means of processing and synthesizing high performance coating structures and materials.
An example is the possibility of rapidly forming multi-layer or laminate coating structures that consist of alternating layers of ceramic and metal alloy. Such a multi-layer structure could consist of many micron sized (mesoscale) layers of predetermined thickness in a coating or free standing structure of 0.2 to several millimetres in total thickness. The HVOF spraying process uses a high velocity gas jet to heat and propel a powder consumable at high velocity towards a substrate surface. On impact with the surface these particles deform to build up dense, well-bonded deposits. Compared to most other thermal spraying processes, HVOF spraying may be more suited for the preparation of multi-layer coatings. This is because the process can produce high quality deposits of metal, cermet and ceramic materials that have large differences in melting temperatures using a similar set of spraying conditions.
- Demonstrate the feasibility of preparing a multi-layer coating consisting of alternating 40mm layers of alumina and nickel alloy using the HVOF spraying process.
- Show that the multi-layer coating can provide both wear and corrosion resistance.