The Heat Affected Zone: how to beat the heat

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.

A look at our latest feasibility study

Feasibility studies are an important part of our work at American Cladding Technologies. We recently conducted a project involving side plates for a rock crushing machine for a quarry, which you can see in the video and photos below.

The customer is looking to improve the lifespan of these plates for a couple of reasons: not only are the plates expensive to replace when they wear through, but the installation time is a day’s worth of work.

Left picture: Showing current wear pattern for rock crushing side plate.
Right picture: A new side plate with the laser applied coating which will be installed for testing.

In our development trial with the quarry, we used laser metal deposition (also known as laser cladding) to coat one side plate in a tungsten carbide alloy. Take a look at the video to see the cladding process:

The other side plate is the control and was left untreated. The quarry will test them in the field and compare the performance.

We’re always interested in experimenting with different processes to help customers advance their products. Learn more about our feasibility studies and applications lab here.

Dilution: keep it to a minimum

Many of our customers interested in laser metal deposition (LMD) are concerned about the dilution of the coating applied to their part – and with good reason. Just like dilution can ruin a perfectly good martini, resulting in a watered-down, disappointing cocktail, it can also be an issue with metal coatings. Here’s why.

 

First, a quick definition. “Dilution” is a term used when welding two dissimilar alloys together – a base alloy and a dissimilar clad alloy. To achieve a metallurgical bond, some mixing or stirring at the interface of the clad and the base material is required. The stirring results in a dilution zone, meaning the base material has been raised into the clad layer. The hotter the weld pool and the longer it takes to solidify, the bigger this dilution zone becomes.

If dilution is excessive, it can compromise the material properties of the clad and reduce the wear or corrosion performance of the clad layer.

As an example, it’s common for the valve manufacturing/repair industry to apply Cobalt 6 (commonly called Stellite 6) to their valve seating surfaces. Due to concerns about dilution, their typical cladding thickness can be ¼ inch to 3/8 inch thick. This thickness is required to ensure that the full material properties of the clad are achieved and are not compromised by the base material. However, the more material added to the component, the greater the weight and distortion and the higher the filler material cost.

Here’s where Laser Metal Deposition offers a big advantage. LMD can minimize dilution so that the full material properties of the clad can be achieved within 0.010” to 0.035” of the weld interface. This reduced clad thickness not only results in less stress and distortion to the customer’s component, but also significantly reduces filler material cost and post-processing.

Here’s another example.

One customer came to us with a ductile cast iron component that showed premature wear failures in the field after the product was released. The component couldn’t be redesigned – not only would it be too costly but the redesign would take too much time. A more traditional hardfacing application was not an option.

We used laser metal deposition to apply a thin enough wear-resistant coating that achieved full material properties after final machining and still met the overall design thickness requirement of the wear surface. Per customer requirements, our challenge was staying at or below 3% iron, with raw powder starting at 2.6% iron. Thanks to the laser metal deposition process, we were able to meet these requirements.

The takeaway: in many cases, laser metal deposition can achieve full material properties at half the thickness of conventional coatings. This means less machining afterwards and, since less metal powder is needed, less cost for the customer. Just one reason why LMD has become the preferred method of application by many industries.

So, whether it’s mixing the perfect martini or mixing a corrosion/wear-resistant coating — keep the dilution to a minimum. Cheers!

What is laser cladding, anyway?

Not exactly sure what laser cladding is? It’s OK – we hear that a lot. So we thought we’d kick off our blog with a short video explaining laser cladding – also known as laser metal deposition – and showing how it works.

Very briefly, laser cladding uses a laser to deposit powdered metals on the surfaces of components to mitigate corrosion or erosion. Laser cladding helps protect and extend the life of valuable equipment by adding a protective coating.

Scott Poeppel explains more here:

Laser cladding is used in many industries, including aerospace, power generation including waste-to-energy, valve manufacturing, oil and gas exploration, and locomotive transportation.

In future blogs, we’ll discuss the pros and cons of laser cladding, and also explore some of the advances we’ve been working on to push the technology even further.

Stay tuned for more blog posts, and subscribe to the blog for email notifications whenever a new post is published.

Join us for our grand opening on May 17!

We’re growing, and it’s time to celebrate! American Cladding Technologies has just moved into a brand-new home, and we’re hosting a grand opening on Wednesday, May 17.

If you’re in Connecticut or Western Massachusetts, please stop by from 5:30 – 8:00 p.m. to check out our new space and enjoy some hors d’oeuvres, wine and beer. Our new location is 15 International Drive in East Granby, CT with easy access to I-91. If you’re attending the Eastec show in West Springfield, MA, we’re only 20 minutes away, so come over after the show and check us out!

If you register for the grand opening in advance, you’ll be entered in a drawing for a chance to win one of three iPad Minis. Registration is currently closed. Guests attending the grand opening can also win a full-day session at our applications laboratory, valued at $3,000. The applications lab day will enable the winner to consult with our experts while on site, and assist in the development of the laser metal deposition process for their specific applications. Learn more about our applications lab here.

Our new 20,000-square foot facility will enable us to expand our laser cladding services and increase our capacity and staff. At the grand opening, you’ll be able to see our equipment and chat with our experts about our solutions for hardfacing overlays, corrosion and erosion-resistant overlays, original material restoration and more. We look forward to seeing you!

Event Details

• Ribbon cutting ceremony
• Tour our facility and chat with experts
• Opportunity to win a full “Applications Lab” day (est. value $3000)
• Hors d’oeuvres, beer and wine

DATE: Wednesday, May 17, 2017

TIME: 5:30 pm – 8:00 pm | 6:00 pm – Ribbon cutting ceremony

WHERE: 15 International Drive, East Granby, CT 06026