March_2022_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A R C H 2 0 2 2 2 7 allow for more efficient thermal cycles in engine applications. Parts made from the nickel-based alloys also exhibit high strength, as well as corrosion, oxida- tion, and creep resistance. As operating temperatures rise, especially above 1100°F, it is import- ant to consider the stresses experi- enced by the individual parts as well as the duration of those stresses. For pre- cipitation-hardened alloys, over-aging can occur at high temperatures over time, and material properties can de- grade. Long term temperature expo- sure can also lead to embrittlement as the phases that once strengthened the alloy breakdown with exposure at eval- uated temperatures. Additionally, cor- rosion and oxidation also become more of a concern at higher temperatures even for nickel-based alloys. GOING BEYOND ‘WORKHORSE’ ALLOY 718 There has been good reason for Alloy 718’s reputation as a workhorse. It offers superior strength at low- to-intermediate temperatures, with its strength primarily coming from pre- cipitation hardening via the γ " (Nb) & γ ' (Ti & Al) phases during the aging cycle of post printing heat treatment. Of Alloy 718, IN625, Hast-X, and HS282, Alloy 718 offers the highest strength in operating ranges of 1200° to 1300°F. However, with significant time at temperatures above 1200°F, Alloy 718 becomes over-aged as the precipitates decompose. Embrittlement can occur as well as microstructural damage from corrosion and oxidation. Therefore, for higher temp/high strength applications, Amperprint 0233 Haynes 282 (HS282) has been devel- oped (Fig. 5). This precipitation-hard- ened alloy is γ ' strengthened (Ti & Al) and can be used with operating tem- peratures up to 1700°F. Above 1200°F, HS282 offers higher strength and higher creep-resistance than Alloy 718. The duration of exposure to high temperatures must also be taken un- der consideration when choosing a su- peralloy for AM. Solution-strengthened alloys such as IN625 and Hast-X are cho- sen for applications with prolonged ex- posure to high temperatures because they avoid over-aging, since they do not have γ ' precipitates that will degrade with time. Bothmaintain good strength, ductility, and creep after thousands of hours at high operating temperatures, but these alloys lack the strength of the HS282 and Alloy 718 discussed above. IN625 and Hast-X both exhibit ex- ceptionally high ductility, which is ad- vantageous in operating environments with high thermal stresses such as heat exchangers. When comparing the two, IN625 provides higher strength and creep resistance below 1400°F, where Hast-X provides superior creep resis- tance in the 1400° to 1600°F range. Hast-X also provides additional cor- rosion resistance at higher tempera- tures—especially above 1600°F. Velo3D is actively developing the nicked-based alloys discussed above for specific ap- plications with their partners in the jet engine and space industries. SEEDING THE GROUND FOR THE NEXT NEW AM MATERIAL The development of new materi- al capabilities for L-PBF applications is providing aerospace design engineers with unprecedented opportunities to realize much greater design freedom than they’ve experienced with tradi- tional manufacturing methodologies. The ground is now seeded for even more impressive material-plus-appli- cation synergies moving forward. The challenges of a lack of specifications, and not having MMPDS allowables, are actively being addressed by the indus- try. As the groundwork is laid, these will become stepping stones in the progress to flight certification. Robust material specifications are just the starting point. Tight additive manufacturing process control is key to ensuring that the latest high-perfor- mance alloys live up to their potential to produce flight-critical 3D-printed parts. More robust, consistent AM processes are allowing engineers to fully realize the advantages of these new materials. The most advanced AM systems that are now available are meeting and exceed- ing the industry’s high expectations— and producing parts that have already achieved liftoff. ~AM&P For more information: Will Hasting, di- rector of solutions engineering, Velo3D, 511 Division St., Campbell, CA 95008, 408.610.3915, info@velo3d.com, www. velo3d.com . Fig. 5 — Cut view of a test ramjet engine, additively manufactured with laser powder bed fusion (L-PBF) using Haynes 282 superalloy, a material that can survive the temperature extremes of hypersonic flight.