It is clear that there are many materials available for AM, but in the larger world of engineered materials used in final applications, only a few dozen materials are regularly deployed for long-use AM components. This gap provides a tremendous opportunity for innovation in customizing material feedstocks for AM as well as exploring AM processes to bring new materials into the AM space. Polymers, metals, ceramics, and many different types of composite materials are being pursued for commercial deployment in AM and research is continuing at the intersection of AM processes and materials. The characteristics of thermoplastic and thermosetting polymers and the thermal and photo energy sources needed to process and shape these materials drive the AM technology choice for obtaining the desired polymeric part. Thermoplastics are most often encountered in ME using filaments or pellets. While the availability of high-quality filaments poses a barrier to bringing new thermoplastic materials into AM, the use of pellet extrusion AM is highly desirable as this feedstock is widely used in the plastics industry for molding. Photopolymer thermosets are the feedstock that enables both vat photopolymerization and photo material jetting, as in PolyJet systems. While other thermosets are beginning to be explored for industrialized AM, like liquid silicone rubbers and epoxies, these types of direct ink writing processes are usually confined to the research and exploratory domains.
While the total number of alloys available to AM are significantly less than those for conventional technologies, the full range of alloy systems are now available, and often for multiple different processes. As a result, having a suitable metallic material no longer limits a product team. As AM processes become more widespread in industry, niche’ alloys that either deliver improved performance or lower cost for a given application will become available. The most likely candidates being more temperature and corrosion resistant alloys for heat exchangers, jet engines, and fluid systems, many of which will be designed to take advantage of either rapid solidification or solid-state processing to achieve properties previously unattainable via ingot metallurgy. Other candidate materials are metal-matrix composites for applications requiring higher temperatures or wear resistance. Finally, the wide range of solid-state metal AM processes means that fusion weldability is no longer a prerequisite for an alloy to be used for AM.
Ceramics is the least developed of the engineered materials. This is due in part to a number of factors, such as:
- Relatively simple shapes of many ceramic applications and limitations on complexity due to the brittle nature of ceramics
- Existing low-cost methods to fabricate shapes
- Typical challenges of sintering of ceramics are the same for AM, so the lead time savings is minimal
That said, the existence of a large range of available powder feedstocks combined with final processing likely being the same as for conventional products (sintering), mean that as AM equipment and expertise become more available to the ceramics industry that the range of material systems will become as widespread as there are for metallics.
Finally, there are a wide range of composite feedstocks available for AM, even though the composite nature of materials presents processing challenges. Many vat photopolymerization resins are in fact composites to introduce reinforcement into the generally brittle acrylate crosslinked material. Additionally, the available ceramic resins for vat photopolymerization are composites of photopolymers and ceramic particles that provide adequate, if not high-performance consolidation upon sintering. Composite material AM is challenging because there are many variables in formulating the composite material and usually composite fillers increase the melt viscosity of thermoplastics or flow viscosity of photopolymer resins. Regardless of difficulties in processing, many materials, especially plastics, are deployed as composites and there are some commercial thermal ME resins on the market from major manufacturers, such as SABIC, in order to meet the demands of applications in structural, automotive, and aerospace applications.