Digital Metal Adds Low Alloy Steel and Superalloy to BJT Material Line

Nickel-Chromium Precipitation Hardening Superalloy DM 718 Components (Courtesy Digital Metal)

Digital Metal, part of the Swedish group Höganäs, has added low alloy steel DM 4140 and nickel-chromium superalloy DM 718 to the range of materials that can be processed on its Binder Jetting System (BJT). Other materials in the range already include pure copper DM Cu, stainless steel 316L and 17-4PH, tool steel DM D2, superalloys DM 625 (equivalent to Inconel 625) and DM 247 (equivalent to MAR M247 ), and Titanium Ti6Al4V.

DM 4140, a low alloy steel powder, was developed within Hyundai Motors to manufacture gearbox control fingers using BJT. By adding carbon steel to its BJT technology, Digital Metal would have broadened its offering of tool-less design freedom, shortened delivery times and potential weight savings.

Control finger for automotive gearboxes, binder sprayed with DM 4140 and shown here in a green condition (courtesy of Digital Metal)

The material is additively made with ink commonly used for other steel and nickel-based alloys, although the process has been modified to achieve properties in accordance with MIM standards (ISO22068). By alternately applying quenching and post-tempering treatment in the as-sintered state, the tensile properties can be matched to the requirements of the application.

Low alloy steel components, made by metal injection molding (MIM), have been used in general engineering and automotive manufacturing since the early 1980s. Its strength, toughness and resistance to deformation during quenching would have made DM 4140 a popular shade.

The DM 4140 is well suited for the production of components exposed to high loads, such as sprockets, connecting rods, fasteners, couplings, gears, belt pulleys and shafts. With adaptation to hardening conditions, the DM 4140 is also available as a turnkey solution for customers who already have Digital Metal systems processing other steels and superalloys.

DM 718 is a precipitation hardening nickel-chromium based superalloy, which would be equivalent to UNS N07718 (Inconel® alloy 718). It is said to offer high strength, along with creep and corrosion resistance, at cryogenic and elevated temperatures (up to about 650 ° C). This alloy composition is considered to be the most widely used nickel-chromium superalloy in AM metals, in addition to being one of the most commonly used superalloys overall.

The material properties of DM 718 are considered satisfactory in the as-sintered state; however, post-sintering heat treatments are necessary to take full advantage of its composition. The alloy can be strengthened using industry standard treatments, consisting of annealing and solution quenching, followed by aging steps

Compared to other superalloys which have similar high temperature strength characteristics, one of the main advantages of Alloy 718 would be its weld behavior, especially its resistance to post weld cracking. The alloy has a slow response to aging and is mainly enhanced by double prime gamma precipitates (γ ”).

This combination is said to provide better weldability compared to high gamma prime (γ ‘) alloys, such as DM 247. However, the γ’ ‘phase begins to dissolve at temperatures above 650 ° C, resulting in means that the material then loses part of its strength. During this time, the phase would remain stable and continue to provide strength at slightly higher temperatures. However, in general, alloys with high levels of ‘cannot be welded.

Digital Metal will begin offering printing services for DM 718 components in the as-sintered state, as well as working with external partners to offer components in various other heat-treated states, in the fourth quarter of 2021. This Alloy is also available as a turnkey solution (including consumables and process parameters), for customers who already use Digital Metal systems to process other steels and superalloys.

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