Comparison of Microstructures and Mechanical Properties for Solid and Mesh Cobalt-Base Alloy Prototypes Fabricated by Electron Beam Melting

Abstract

The microstructures and mechanical behavior of simple, as-fabricated, solid geometries (with a density of 8.4 g/cm 3 ), as-fabricated and fabricated and annealed femoral (knee) prototypes, and reticulated mesh components (with a density of 1.5 g/cm 3 ) all produced by additive manufacturing (AM) using electron beam melting (EBM) of Co-26Cr-6Mo-0.2C powder are examined and compared in this study. Microstructures and microstructural issues are examined by optical metallography (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDS), and X-ray diffraction (XRD), while mechanical properties included selective specimen tensile testing and Vickers microindentation hardness (HV) and Rockwell C-scale hardness (HRC) measurements. Orthogonal (X-Y) melt scanning of the electron beam during AM produced unique, orthogonal and related Cr 23 C 6 carbide (precipitate) arrays (a controlled microstructural architecture) with dimensions of 2 lm in the build plane perpendicular to the build direction, while connected carbide columns were formed in the vertical plane, parallel to the build direction, with microindentation hardnesses ranging from 4.4 to 5.9 GPa, corresponding to a yield stress and ultimate tensile strength (UTS) of 0.51 and 1.45 GPa with elongations ranging from 1.9 to 5.3 pct. Annealing produced an equiaxed fcc grain structure with some grain boundary carbides, frequent annealing twins, and often a high density of intrinsic {111} stacking faults within the grains. The reticulated mesh strut microstructure consisted of dense carbide arrays producing an average microindentation hardness of 6.2 GPa or roughly 25 pct higher than the fully dense components.

Microstructural Architecture, Microstructures, and Mechanical Properties for a Nickel-Base Superalloy Fabricated by Electron Beam Melting

“…In contrast to conventional directional solidification processing, [3,10,11] a relatively new process, electron beam melting (EBM), builds components by the additive layer-by-layer melting of metal or alloy powder layers. [15][16][17] In this process, illustrated schematically in Figure 1, precursor powder in cassettes is gravity fed onto a build table, where it is sequentially raked into a layer~50-to 100-lm thick (depending on the powder size and size distribution), which is preheated by multiple-pass electron beam scanning, and then selectively melted with a melt scan directed by a CAD program. Recent fabrication of Co-base alloy components by EBM from atomized powder produced a novel, discontinuous columnar architecture composed of Cr 23 C 6 (cubic, fcc) precipitates forming columnar arrays spaced~2 lm.…”

Advancements in three-dimensional titanium alloy mesh scaffolds fabricated by electron beam melting for biomedical devices: mechanical and biological aspects

“…The selective melting of powder is based on CAD design. The powder bed is initially heated tõ 750°C, for instance, in the case of titanium alloy powder [1,27,[62][63][64]. In general, powders are heated to 0.5-0.6T m (T m : melting temperature of powder).…”

“…Titanium alloy components processed by EBM were characterized by a columnar structure and~50-60 nm thick lamellar plates with indentation hardness of~2.5 GPa, which was similar to the hardness of~2.3 GPa obtained for SLM processed component. Co-Cr alloy (Co-26Cr-6Mo-0.2C) was processed by EBM to fabricate femoral (knee) prototypes as a reticulated mesh structure (density of 1.5 g cm ) [1,64] characterized by array of orthogonal Cr 23 C 6 carbides. The microstructure of the Co-Cr alloy was~2 µm in the build plane, perpendicular to the build direction, and the carbide columns were present in the vertical plane, parallel to the build direction.…”

On the Growth Rate of Tribomaterial in Bovine Serum Lubricated Sliding Contacts

“…The reader should keep in mind that the term "affected area" describes the fraction of the nominal contact area at which the local contact pressure is bigger than zero. Since abrasion and its submechanisms bring about a mainly monotonic stress-strain loading the cutoff pressure for plastic flow was chosen on the basis of monotonically measured properties, e.g., from hardness-in a first and rough approximation-following the cavity model of [53] and the relations found by [54] for solution annealed solid CoCrMo-alloy samples. Thus, it would be about 1/3 of the hardness of the metal matrix, which would be 1500 MPa.…”