A defect-resistant Co–Ni superalloy for 3D printing

Abstract

Additive manufacturing promises a major transformation of the production of high economic value metallic materials, enabling innovative, geometrically complex designs with minimal material waste. The overarching challenge is to design alloys that are compatible with the unique additive processing conditions while maintaining material properties sufficient for the challenging environments encountered in energy, space, and nuclear applications. Here we describe a class of high strength, defect-resistant 3D printable superalloys containing approximately equal parts of Co and Ni along with Al, Cr, Ta and W that possess strengths in excess of 1.1 GPa in as-printed and post-processed forms and tensile ductilities of greater than 13% at room temperature. These alloys are amenable to crack-free 3D printing via electron beam melting (EBM) with preheat as well as selective laser melting (SLM) with limited preheat. Alloy design principles are described along with the structure and properties of EBM and SLM CoNi-base materials.

Design and Tailoring of Alloys for Additive Manufacturing

“…[122][123][124][125][126][127] The emergence of this new class of alloys was coincident with the thrust to develop new ICME tools, creating the opportunity for the design of alloys matched to PBF additive processes. [128,129] In this case study, the primary goals for alloy design were good high-temperature strength up to 1000°C (achieved by precipitation of a high volume fraction of the L1 2 phase), L1 2 solvus between 1100°C to 1250°C, high solidus and liquidus temperatures, high resistance to oxidation via alumina formation, and favorable printability. Nickel-base alloys strengthened with high volume fractions of L1 2 are well known for their tendency to crack during PBF printing.…”

“…Additional details are given elsewhere. [129] Figure 9 shows a cross section normal to the [001] single crystal growth direction of the SB-CoNi-10 alloy and the associated analysis of distribution coefficients extracted from electron microprobe scans of the dendritic structure; details of this analysis are given elsewhere. [128,129] Significantly, the degree of segregation of the alloying elements as a function of fraction solid is less severe compared to nickel-base alloys, which also have wider freezing ranges compared to the CoNi alloys.…”

“…[129] Figure 9 shows a cross section normal to the [001] single crystal growth direction of the SB-CoNi-10 alloy and the associated analysis of distribution coefficients extracted from electron microprobe scans of the dendritic structure; details of this analysis are given elsewhere. [128,129] Significantly, the degree of segregation of the alloying elements as a function of fraction solid is less severe compared to nickel-base alloys, which also have wider freezing ranges compared to the CoNi alloys. [141] The combined effect of lower solidification segregation, lower freezing ranges, and the 125°C solidus to solvus gap likely suppresses the tendency for liquid-mediated cracking during printing and subsequent cooling below the solidus temperature.…”

“…Nevertheless, the design tools have been able to identify a promising composition from the ''printable'' point of view, with only one batch of powder being produced and standard ranges of printing parameters being employed in both L-PBF and E-PBF. [129] Given the combination of a high dimensional alloy design space and the complexity of the physics of PBF printing, suites of predictive tools will greatly enhance our ability to design ''printable'' alloys. [142] 4.…”

Effects of Post Heat Treatments on Microstructures and Mechanical Properties of Selective Laser Melted Ti6Al4V Alloy

“…Compared to Direct Energy Deposition (DED), selective laser melting (SLM), which is laser-based powder bed fusion [6], is more suitable to fabricate small-scale components with complex geometries and high precision [7]. A wide variety of alloys have been utilized in SLM, ranging from superalloy [8,9], steel alloys [10,11], aluminum alloys [12,13], and titanium alloys [14,15]. Ti-6Al-4V (Ti-64) is the most extensively used titanium alloy due to its high specific strength, excellent corrosion resistance, and good mechanical performance [16].…”