Some of our customers will ask us about the impact of the Heat Affected Zone (HAZ) on their components, and for good reason. The HAZ can weaken the component and potentially lead to failure. But rather than crossing laser cladding off your list of preferred processes, there are ways to mitigate the HAZ.
First, a brief explanation of the HAZ. Laser cladding an alloy onto a substrate or base material creates a region just below the weld/base material interface in which the base material was not melted, but the localized temperature was raised to the point that its microstructure and therefore material properties were changed. This region is known as the “Heat Affected Zone”. The depth of the HAZ can vary depending on process variables such as base metal type, thermal contact time, geometry of the component and the amount of energy applied.
These changes to the material properties are usually less than desirable, and may compromise a component’s function or lifespan. If the original material properties are critical to the design or performance criteria of the component, the HAZ must be considered. This microstructure change can result in reduced strength, increased brittleness or lower corrosion resistance. The HAZ can definitely be an issue for more demanding applications, especially for the aerospace industry, industrial gas turbines, and for downhole applications in the oil & gas industries. However, designers will often take the HAZ into account when designing their components.
A question we are frequently asked is how small a HAZ we can achieve. Unfortunately, the answer is not always straightforward. We have used the laser metal deposition (LMD) technique for our aerospace clients that resulted in a HAZ so small we were unable to measure it. However, the process techniques used to accomplish this may not always be economical for some of our other customers. A more general value for HAZ in most applications is around 0.003” – 0.008”.
Another solution for dealing with the HAZ is to perform a post-weld heat treatment (PWHT). However, depending on the components, this can sometimes be too costly or impractical if there is concern about the PWHT initiating distortion into the other regions of the part.
Here’s where laser cladding offers an advantage – we can control the heat input of the laser very precisely and reduce the heat affected zone compared to other process such as PTA, GTAW or TIG welding. This ability to control the heat improves the manufacturability of the component, and may eliminate the need for a post-weld heat treatment.
This blog post just scratches the surface of this topic, so talk to your laser cladding specialist to discuss the specifics of the HAZ for your application and learn how you can beat the heat.