Effect of Building Position on Phase Distribution in Co-Cr-Mo Alloy Additive Manufactured by Electron-Beam Melting

Abstract

Cobalt-chromium-molybdenum (Co-Cr-Mo) alloys are used for biomedical implants such as arti cial joints because they have excellent wear and corrosion resistance and biocompatibility. Electron-beam melting (EBM) is a type of additive manufacturing technique for metals. We used EBM to fabricate 20 rods of a Co-Cr-Mo alloy with height of 160 mm arranged in a 4 × 5 matrix and observed the phase constitution in the middle part (at a height of 80 mm) of the rods by scanning electron microscopy-electron backscatter diffraction. We found that the rods in the center part of the matrix consisted of more of the face-centered cubic (γ) phase and less of the hexagonal close-packed (ε) phase than rods in the outer part. This happened because even though each rod was fabricated under the same beam condition, the rods at the center had been exposed to higher temperature than those in the outer part, and less thermal dissipation took place because the neighboring rods were also heated by the electron beam. This difference in the thermal histories should be taken into consideration when many objects are fabricated simultaneously.

Nano-Mechanical Properties and Creep Behavior of Ti6Al4V Fabricated by Powder Bed Fusion Electron Beam Additive Manufacturing

“…Curiously, the calculated creep stress exponents decrease with increasing maximum loads (10–100 mN), which is opposite to the results of CoCrFeMnNi HEAs obtained by He et al [ 23 ]. Lee et al investigated nanoindentation creep behavior of CoCrFeMnNi high-entropy alloys and obtained creep stress exponent n = 14.34 for Pmax = 10 mN and n = 18.34 for Pmax = 50 mN [ 41 ].…”

“…For sample B, both the Al and V concentration in α phase and β ribs is very similar. Since the conditions of heat accumulation and conduction are tightly linked to scanning strategies and relative position of the sample [4,34,41], the X-Y cross-section plane, 2 mm away from the base, was chosen for EBSD observation. Grain morphology and corresponding inverse pole figure (IPF) are shown in Figure 5a,b, respectively.…”

“…To analyze the effects of scanning strategy on phase constitution of the PBF-EB AM Ti6Al4V alloy, a region with high magnification and a smaller step size (0.01 µm) was selected. The corresponding results are shown in Figure 5c,d Since the conditions of heat accumulation and conduction are tightly linked to scanning strategies and relative position of the sample [4,34,41], the X-Y cross-section plane, 2 mm away from the base, was chosen for EBSD observation. Grain morphology and corresponding inverse pole figure (IPF) are shown in Figure 5a,b, respectively.…”

Development of Diffraction Research Methodologies for Mediloy S-CO Alloy Speciments Made Using LPBF Additive Manufacturing

“…Further confirmation of the existence of two phases (γ-fcc and ε-hcp) in the material of Co-Cr-Mo alloy parts using incremental methods can be found in Takashima et al (2016). The authors concluded that their specimens positioned in the central part of the matrix consisted more of the γ-fcc phase and less of the ε-hcp phase than those in the matrix's outer part.…”

Dislocation Density of Electron Beam Powder Bed Fusion Ti–6Al–4V Alloys Determined via Time-Of-Flight Neutron Diffraction Line-Profile Analysis

“…Moreover, a wide range of process parameters, such as the power and scanning speed of the electron beam, and a unique preheating procedure [7,8], are beneficial for minimizing building defects. Therefore, EB-PBF has been applied to a variety of metals and alloys, such as titanium [9][10][11][12][13][14][15][16], biomedical Co-Cr-Mo alloys [17][18][19], Ni-based superalloys [20][21][22][23][24][25], steels [26][27][28][29], copper [30,31], and high-entropy alloys [32][33][34][35][36]. In the EB-PBF process, a high-energy electron beam scans a metal powder bed, creating a highly localized melt pool that enables rapid heating and cooling [4,5].…”