Journal List > J Korean Acad Prosthodont > v.52(2) > 1034809

Choi, Koak, Heo, Kim, Ahn, and Park: Comparison of the mechanical properties and microstructures of fractured surface for Co-Cr alloy fabricated by conventional cast, 3-D printing laser-sintered and CAD/CAM milled techniques

Abstract

Purpose

The purpose of present study is to compare mechanical properties and microstructural characteristics of fractured surface for cast, 3-D printing laser sintered and CAD/CAM milled cobalt-chromium (Co-Cr) alloy specimens and to investigate whether laser sintered technique is adequate for dental applications.

Materials and methods

Thirty six flat disc shape Co-Cr alloy specimens were fabricated for surface hardness test and divided into three groups according to the manufacturing methods; 12 specimens for casting (n=12), 12 specimens for laser sintered technology (n=12) and 12 specimens for milled technology (n=12). Twelve dumbbell shape specimens for each group were also fabricated for a tensile test. Statistical comparisons of the mechanical properties for the alloys were performed by Kruskal-Wallis test followed by Mann-Whitney and Bonferroni test. The microstructural characteristics of fractured surfaces were examined using SEM.

Results

There were significant differences in the mean Vickers hardness values between all groups and the cast specimen showed the highest (455.88 Hv) while the CAD/CAM milled specimen showed the lowest (243.40 Hv). Significant differences were found among the three groups for ultimate tensile strength, 0.2% yield stress, elongation, and elastic modulus. The highest ultimate tensile strength value (1442.94 MPa) was shown in the milled group and the highest 0.2% yield strength (1136.15 MPa) was shown in the laser sintered group.

Conclusion

Different manufacturing methods influence the mechanical properties and microstructure of the fractured surfaces in Co-Cr alloys. The cast Co-Cr alloy specimens showed the highest Vickers hardness, and the CAD/CAM milled specimens revealed the highest tensile strength value. All alloys represent adequate mechanical properties satisfying the ISO standards of dental alloy. (J Korean Acad Prosthodont 2014;52:67-73)

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Fig. 1.
Test specimen with radial shoulders for tensile strength test.11
jkap-52-67f1.tif
Fig. 2.
Scanning Electron microscopy images of fractured surfaces for alloys. The characteristics of the cast specimen; unique loose pattern and typical casting porosity, A (×1000, ×2500 original magnification), the laser sintered specimen; coarse granular structure with flat facets like characteristic features, B (×1000, ×2500 original magnification), and the CAD/CAM milled specimen; homogenous and regularly dense microstructure, C (×1000, ×2500 original magnification) are represented.
jkap-52-67f2.tif
Table 1.
Chemical composition of cast, laser sintered, and milled Co-Cr alloys as a percentage according to the manufacturer's instructions (wt %)
Alloys Co Cr Mo W Si Fe Mn
JEWOOS02 (Cast) 63 28 5.5 etc. max. 3.5      
EOS CobaltChrome SP2 granule (laser sintered) 63.8 24.7 5.1 5.4 1 max. 0.50 max. 0.10
Starbond CoS (milled) 59 25 3.5 9.5 1 max. 1.5
Table 2.
Means and standard deviations of Vickers hardness test
Group N Mean (Hv) SD
Cast 12 455.88 37.08
Laser sintered 12 413.10 8.77
CAD/CAM milled 12 243.40 8.97
Total 36 370.79 95.61
Table 3.
Means and standard deviations of tensile strength test for the cast, laser sintered, and CAD/CAM milled specimens
Group   Ultimate tensile strength (MPa) 0.2% Yield strength (MPa) Elongation (mm) Elastic modulus (GPa)
Cast (n=12) Mean 831.51 620.67 0.59 59.0
  SD 41.10 20.06 0.11 .
Laser sintered (n=12) Mean 1411.12 1136.15 0.87 67.0
  SD 17.00 49.10 0.14 .
CAD/CAM milled (n=12) Mean 1442.39 1014.94 1.87 61.0
  SD 13.25 48.29 0.24 .
Total (n=36) Mean 1228.34 923.92 1.11 62.33
  SD 286.06 226.78 0.59 .

0.2% yield strength ≥ 250 MPa will comply with the requirement of ISO specification.

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