Page 65 - MSAM-1-3

Materials Science in Additive Manufacturing Inconel 718-CoCrMo bimetallic structures

Finally, for increased bioactivity, AM-processed titanium dental crowns [19-21] . However, this alloy’s high hardness
(Ti)-tantalum (Ta) bimetallic structure has shown a and wear resistance make it very difficult to machine .
[22]
significant improvement in biocompatibility similar to pure As a result, many studies look at the cutting force and
[5]
Ta . A recent review documents many such performance anisotropic effects to explain how to properly machine
enhancements through AM-processed bimetallic and these alloys without compromising the alloy surface or
multi-material structures that highlight the innovation the milling tools [23,24] . The strengthening mechanism in
opportunities using AM with the next-generation metallic CoCrMo alloy comes from the various carbides, such as
[25]
[6]
materials . The interface between the coating and the Co C and Cr C . Therefore, the properties of CoCrMo
23
6
6
bulk material can form various intermetallic compounds, alloys can be altered using different heat treatments, which
which have been shown to increase the strength of some results in various carbide formations [26,27] . The oxidation
bimetallic systems, such as Ti6Al4V/Al12Si and Ti/Ni [7,8] . resistance of CoCrMo at high temperatures is not well
However, this interfacial behavior can be detrimental in reported; however, the alloy’s carbide forming abilities and
some cases, which has prompted studies to understand the chromium oxide layer offer good oxidation resistance.
better and model the behavior of these bimetallic systems . Since CoCrMo is wear- and corrosion-resistant and
[9]
In addition, research has been conducted to manufacture Inconel 718 is high-temperature oxidation-resistant, a
multi-material and bimetallic systems more efficiently to coating of one of these materials may prove effective in
be better suited for industry . increasing the bulk and surface properties of the bimetallic
[10]
Inconel 718 is a nickel-based superalloy consisting of structures. In cases where a strong bulk structure is needed
about 55% nickel (Ni), 18% chromium (Cr), 18% iron (Fe), with high oxidation resistance, Inconel 718 coating on
5% niobium (Nb), and 3% molybdenum (Mo). This alloy CoCrMo would be preferred. A CoCrMo coating on
is used extensively in aerospace applications due to its Inconel 718 could be preferred in cases where superior
excellent high-temperature strength, along with corrosion corrosion resistance is needed. A recent study using laser
and oxidation resistance . Inconel 718 is a standard alloy powder bed fusion (L-PBF) of Inconel 718 and CoCrMo
[11]
used in AM due to its excellent weldability . This alloy is functionally graded structure exhibited low porosity and
[12]
[28]
particularly strong for the formation of the γ’ (Ni Ti and smooth composition transitions ; however, there is
3
Ni Al), the γ” (cubic Ni Nb), and the δ (orthorhombic still a knowledge gap on processing-structure-properties
3
3
Ni Nb) phases, all of which have been observed in heat- relationships of DED-manufactured bimetallic structures
3
treated Inconel 718 samples that were printed by selective of Inconel 718 and CoCrMo. Addressing this gap is the
[13]
laser melting (SLM) . Different heat treatments can primary focus of this research. Inconel 718 and CoCrMo
control the amount of these phases formed in Inconel bimetallic structures were manufactured by DED-based
718 [14-16] . This allows manufacturers to tailor the properties AM and were subjected to various tests for microstructure
of Inconel 718 depending on the application and further and phase analysis, hardness, compression testing, and
demonstrates the versatility of this alloy. The corrosion measuring high-temperature oxidation resistance. Figure 1
resistance of Inconel 718 comes from the Cr and Mo, outlines the processing strategies for the Inconel 718 and
which forms a surface passivation layer limiting oxygen CoCrMo bimetallic structures using DED.
flow into the bulk structure. Because of microstructural
and phase evolutions, corrosion resistance for Inconel 718 2. Materials and methods
also depends on the manufacturing and post-processing 2.1. Directed energy deposition (DED) of bimetallic
methods used. It has been reported that excessive carbide structures
formation during solution treatment caused Cr and Mo Inconel 718 and CoCrMo bimetallic structures were
[17]
depletion throughout the bulk Inconel 718 . Oxidation manufactured using a powder-based DED printer
resistance is typically attributed to the Cr O film, which (FormAlloy, CA). The computer uses a G-code input
3
2
prevents oxygen diffusion into the bulk structure; however, file derived from a computer-aided design (CAD) file
a NbO film also forms at temperatures higher than 800°C containing the shape information. This G-code input
to further aid oxidation resistance .
[18]
file dictates the machine parameters while printing,
Cobalt-chromium molybdenum (CoCrMo) alloy including speed, layer thickness, laser power, powder flow
consists of around 60% cobalt, 30% Cr, and 5% Mo, with 5% rate, and shield gas flow rate, which prevents powders
being other elements such as Ti. Due to its excellent wear from melting onto the nozzle and clogging it. These
and corrosion resistance, this alloy is used in cutting tools alloys were printed onto 316L stainless steel substrate.
and other applications requiring better wear resistance, Inconel 718 powder (Powder Alloy Corporation, Ohio)
such as articulating surfaces of biomedical implants and was used with a particle size of 50–150 μm. CoCrMo

Volume 1 Issue 3 (2022) 2 https://doi.org/10.18063/msam.v1i3.18