Opting for the incorrect metal can have serious consequences. Do you go too lightweight and risk catastrophic failure? Do you go for something too heavy and pay hundreds of thousands in excess fuel costs over the lifetime of the application? The choice isn’t always clear.
Start With the Thermal Profile, Not the Material Catalog
Most selection mistakes are not due to “bad” materials, but because selecting the right material necessarily requires selecting the right threshold specifications for that material based on the operational environment of that specific component.
That’s why most engineers working on new components begin the search process “backwards”: not by looking at material options, but by creating a detailed map of the application environment and the service requirements they need the material to meet.
When Standard Grades Stop Being Enough
Although stainless steel is suitable for many applications, it cannot be used for applications where permanent set can occur. This type of material does not allow significant elastic deformation and full recovery without causing any effect.
Typical austenitic stainless steel grades start to deform plastically at less than 0.5% strain; this is why it’s not suitable for springy components, flexible connectors, or any application that requires repeated flexing with no permanent deformation.
In situations like this, engineers must select specific alloys, and the material choice actually starts to drive the mechanical design instead of simply enabling it.
Shape memory and Superelastic Alloys as Design Tools
The deformability of titanium-nickel alloy Nitinol is considered beyond typical industry benchmarks for most medical devices and other product applications. This allows for the physiochemical deformation of part geometries when manufacturing a device, rather than being constrained to purely elastic deformation as with most traditional synthetic materials. One common example is the ability to create compressed springs that are grossly over-deformed during the loading process.
In certain designs, it allows for increased manufacturing capability (especially for existing manufacturing lines). Larger deformations often require less accurate loading manufacturing equipment (e.g. mandrel winding for catheters). Additionally, most tubing is deformed past its requested percentage strain to ensure that end-product does meet minimum strain requirements.
However, overall, it would be wrong to suggest that the relative deformability advantages of Nitinol over other materials might be insignificant for developing a new product. It all ultimately depends on the device design specifications and what the device needs to do. The elastic strain limit of stainless steel does not always force complex articular joint/complex designs. It just means the stainless is typically not the material you would use in such a design.
Workability and The Supply Chain Reality
Choosing the right high-performance alloy for the stress and strain your part will see is just the beginning of your material journey. Material selection is limited by the alloy compositions proven in clinical trials, yet a supplier with a stock of more exotic materials can be your competitive differentiator if you hit on an innovation in your product. Who can reliably provide those materials within your tolerances and quantity needs are questions 2 and 3.
Treating Material Selection as Competitive Advantage
When you rigorously apply material science, the things you can build change. Engineers consider alloy selection as a design decision, and not as a sourcing task. They will invariably get smaller, lighter, more reliable components compared to teams that reactively select material. This advantage multiplies with every subsequent cycle of optimization. Products that are designed with the right material lead to lesser redesigns, as the goal is to reduce complex assemblies and push the product to meet its performance objective in the fewest development cycles. The design is not constrained by the material but the material defines how far the design can go.
