The limitations of investment casting of cobalt-based alloys are claimed to be less problematic with significant improvements in metal additive manufacturing by selective laser melting (SLM). Despite these advantages, the metallic devices are likely to display mechanical anisotropy in relation to build orientations, which could consequently affect their performance “in vivo.” In addition, there is inconclusive evidence concerning the requisite composition and postprocessing steps (e.g., heat treatment to relieve stress) that must be completed prior to using the devices. In the current paper, we evaluate the microstructure of ternary cobalt-chromium-molybdenum (Co-Cr-Mo) and cobalt-chromium-tungsten (Co-Cr-W) alloys built with direct metal printing and LaserCUSING SLM systems, respectively, at 0°, 30°, 60°, and 90° inclinations (Φ) in as-built (AB) and heat-treated (HT) conditions. The study also examines the tensile properties (Young’s modulus, E; yield strength, RP0.2; elongation at failure, At; and ultimate tensile strength, Rm), relative density (RD), and microhardness (HV5) and macrohardness (HV20) as relevant physicomechanical properties of the alloys. Data obtained indicate improved tensile properties and HV values after a short and cost-effective heat-treatment cycle of Co-Cr-Mo alloys; however, the process did not homogenize the microstructure of the alloy. Annealing heat treatment of Co-Cr-W led to significant isotropic characteristics with increased E and At (except for Φ = 90°) in contrast to decreased RP0.2, Rm, and HV values, compared to the AB form. Similarly, the interlaced weld-bead structures in AB Co-Cr-W were removed during heat treatment, which led to a complete recrystallization of the microstructure. Both alloys exhibited defect-free microstructures with RD exceeding 99.5%.

The limitations of investment casting of cobalt-based alloys are claimed to be less problematic with significant improvements in metal additive manufacturing by selective laser melting (SLM). Despite these advantages, the metallic devices are likely to display mechanical anisotropy in relation to build orientations, which could consequently affect their performance ‘in vivo’. In addition, there are inconclusive evidence concerning the requisite composition and post-processing steps (e.g. heat-treatment to relieve stress) that must be completed prior to the devices being used. In the current paper, we evaluate the microstructure of ternary cobalt-chromium-molybdenum (Co-Cr-Mo) and cobalt-chromium-tungsten (Co-Cr-W) alloys built with Direct Metal Printing and LaserCUSING SLM systems respectively at 0°, 30°, 60° and 90° inclinations (Φ) in as-built (AB) and heat-treated (HT) conditions. The study also examines the tensile properties (Young's modulus, E; yield strength, RP0.2; elongation at failure, At and ultimate tensile strength, Rm), relative density (RD), and micro-hardness (HV5) and macro-hardness (HV20) as relevant physico-mechanical properties of the alloys. Data obtained indicate improved tensile properties and HV values after short and cost-effective heat-treatment cycle of Co-Cr-Mo alloy; however, the process did not homogenize the microstructure of the alloy. Annealing heat-treatment of Co-Cr-W led to significant isotropic characteristics with increased E and At (except for Φ = 90º) in contrast to decreased RP0.2, Rm and HV values, compared to the AB form. Similarly, the interlaced weld-bead structures in AB Co-Cr-W were removed during heat-treatment, which led to a complete recrystallization in the microstructure. Both alloys exhibited defect-free microstructures with RD exceeding 99.5%.

Powder-bed based additive manufacturing techniques are of high interest for the medical sector and recent trial studies have shown their feasibility. Due to the rapid improvements made in the machinery and the related changes in the type and characteristics of the utilized power source, optimizations regarding the fabrication parameters tend to differ amongst various machines. In this study, a parameter optimization was undertaken for a biocompatible dental CoCrMo alloy on a SLM 280HL machine, featuring a 400 W fibre laser. It was shown that the availability of higher laser powers enables a more energy efficient fabrication. Moreover, parameter sets for fast and economic fabrication, as well as for high density and fine-grained microstructure, were defined.

SynopsisThe acid-base titration curves of solid nylon 6 resins and nylon 66 fibers have been measured, and isoionic points and endgroups determined. Five nylon 6 polymers of different molecular weights and two commercial nylon 66 yarns have been studied. Titration curves of these materials with hydrochloric acid and sodium hydroxide in the absence of added salt, and of nylon 66 in the presence of added salt, at three different temperatures, and with benzenesulfonic, trichloroacetic, and naphthalene-2-sulfonic acid, allowed the effect of polymer molecular weight, salt, temperature, and anion affinity on the titration curves to be determined. All the results are consistent with the view that nylon possesses a zwitterion structure at neutral pH, carboxyl groups being protonated on acid titration. A proportion of the endgroups is not available to titration in the solid polymers. Existing theories of the acid-base combination of solid polymers fail to explain all the results. The titration curves and elastic properties of the following modified nylon 66 yarns have also been determined and interpreted: nylon deaminated by nitrous acid, dinitrophenylated, acetylated, carboxymethylated, hydrolyzed, and dihydrophenylated nylons, and nylon treated with alkaline hypochlorite, boiling water, and boiling benzene. In all cases the increase in the work to stretch the filament is independent of pH.

Frorr, the load and displacement data, a "flow curve" (stress vs strain) is derived and several mechanical properties are determined.