Thermal Barrier Coating | Carbide Coatings
HVOF Thermal Spraying
A thermal barrier coating is a layer of special material that insulates the components of machinery that are normally exposed to very high temperatures. Examples of components that are protected using thermal barrier coatings are the parts of aircraft engines as
well as the parts of gas turbines. In these two engines, the blades of the turbine, the vanes that guide the nozzles as well as the ducts of the combustor can are all covered in thermal barrier coating. The main purpose of applying the Thermal Barrier Coating (TBC) on these parts is so as to allow the parts to function even in increased operating temperature. Thermal Barrier Coating (TBC) has extremely low thermal conductivity. As a result, the coating exhibits a large temperature gradient whenever it is used in areas with high operating temperature. This means that the TBC can maintain its insulating properties in a wide range of high temperatures. One of the materials that is applied on machinery parts so as to form a TBC on them is yttria stabilized zirconia (YSZ). This material can resist thermal shocks and fatigue up to a temperature of 1150º C. This material is applied on the machinery parts by processes such as plasma spraying and Electron Beam Physical Vapor Deposition (EBPVD). Other materials that can be used to perform TBC are metal alloys, alumina compounds, stainless steel and refractory metals too.
A standard TBC comprises a metallic layer and a ceramic layer. These two layers have different thermal coefficients. This property can cause problems when the metallic layer is bonding with the ceramic one. As such, a bond coat is applied in between them. It assists these layers to adhere to each other. Moreover, when the bond coat is exposed to high temperatures, it reacts and forms a new layer known as the thermally grown ceramic oxide layer. As such, after exposure to heat, the TBC eventually comprises 4 layers. These are the metal layer, the bond coat layer, the ceramic oxide and the ceramic substrate layer. These layers work together to protect machinery parts from the degrading effects of very high temperatures.
How TBC is done
The process of Thermal Barrier Coating (TBC) has a number of characteristics. One of the main characteristics is the purpose of the bond coat layer. Also known as the bonding layer, this part of the TBC adds many positive qualities to the coating. As a result of including the bond coat, the coating becomes hard and durable. Thus, it can withstand the wear and tear of daily use. Moreover, the bond coat absorbs any thermal stress that may be experienced by the top coat. It also absorbs thermal shocks experienced by the metallic layer. As a result, the coating lasts for a long time.
The coating can be applied on the machinery parts using various methods. In the case where plasma spraying is used, the parts being coated are placed in a protective enclosure. This is so that the fumes produced do not escape the enclosure and interfere with the health of technicians. The process of plasma spraying is fully automatic. In some special cases where the parts being sprayed are few and limited in number, the coating is done manually. Both the automatic and manual methods of applying this coating have some elements in common. These are light, noise, dust or fumes, electricity and heat.
The process of thermal spraying is very noisy. This is because the tools used to perform this task make use of compressed gas. As such, the plasma spraying is done in an enclosure that isolates the noise. In a process where the TBC is sprayed on the machinery parts, flames or an electric arc can be implemented. If the flame is used, it is very bright and very hot as well. On the other hand, when an electric arc is used, a byproduct of the process is ultraviolet (UV) light. This type of light is very harmful to the eyes. As such, special UV absorbent glass is used to prevent this light from shining out of the enclosure. Also, if the technicians are handling the nozzle of the electric arc manually, they should wear protective glasses that block the nozzle from view. This is to protect their eyes from the harmful effects of UV light.
During the process of spraying the TBC, dust and fumes are produced in substantial amounts. To prevent them from getting absorbed into the coating, the dust can be sucked right out of the enclosure using an air filtering machine. Also, if the technicians are applying the TBC manually, they must wear masks which have breathing filters to protect themselves. Also, they should wear protective overalls due to the effects of the chemical components in the coating. It is important that all technicians involved in the process follow the required instructions of various methods of TBC
In a case where a flame is used to coat the machinery parts, heat is produced. The spray gun is fueled by a mixture of oxygen and acetylene. These collaborate to produce the force, heat and pressure that are necessary to perform the coating. The technicians involved must ensure that there is no leakage of any of these gases to prevent other materials in the area getting ignited. If the technician is using an electric arc nozzle, they must carefully monitor the current produced by the tools. This is so that they protect themselves from electrocution.
Get all your TBC supplies with National Alloy Solutions
There are many companies out there that have a small facet of the TBC needs. Here at NAS, we have everything you’ll need to get your job done right! You may need to have the parts on your machinery coated to ensure they last for a long time. The Thermal Barrier Coating (TBC) process requires specialized equipment and expertise. Our friendly staff are very qualified to get you set up with exactly what your company need to fulfill your needs. We are open Monday through Saturday from 9 a.m.-7 p.m. CST. You can get in touch with us to book an appointment. A company representative will promptly answer your call and assist you. For high quality TBC, National Alloy Solutions in Houston, TX is the industry leader!