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!


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