Microstructures and Mechanical Properties of Laser-Sintered Commercially Pure Ti and Ti-6Al-4V Alloy for Dental Applications

Abstract

To apply laser-sintered titanium (Ti) materials to dental prostheses with a three-dimensional structure such as partial dentures, we examined the microstructures and mechanical properties of commercially pure (CP) Ti grade (G) 2 annealed after laser sintering and laser-sintered (as-built) Ti-6Al-4V alloy. The tensile and fatigue properties of CP Ti G 2 annealed at 700 °C for 2 h after laser sintering were close to those of wrought CP Ti G 2 annealed at the same temperature after hot forging. The ultimate tensile strengths (σ_UTS) of 90°- and 0°-direction-built CP Ti G 2 rods after laser sintering 10 times were 553 and 576 MPa and the total elongations (TE) of these rods were 26% and 28%, respectively. The fatigue strengths (σ_FS) at 10⁷ cycles of the 90°- and 0°-direction-built CP Ti G 2 rods after laser sintering 10 times were ~320 and ~365 MPa, respectively. The ratio σ_FS/σ_UTS was in the range of 0.5-0.7. The changes in the chemical composition and mechanical properties after laser sintering 10 times were negligible. The fatigue strength of the laser-sintered Ti-6Al-4V alloy was ~600 MPa, which was close to that of wrought Ti-6Al-4V alloy. These findings indicate that the laser-sintered CP Ti and Ti-6Al-4V alloy can also be applied in dental prostheses similarly to laser-sintered Co-Cr-Mo alloy. In particular, it was clarified that laser sintering using CP Ti G 4 powder is useful for dental prostheses.

Keywords: dental prostheses; fatigue property; laser sintering; microstructure; physical property; tensile property; titanium materials.

Figure 1

(a) Building directions of cylindrical specimens in laser sintering; (b) laser-sintered cylindrical specimens.

Figure 2

(a) Particle size distributions of 10-times-sintered EOS (EOS 10) and once-sintered (TILOP 0) and 10-times-sintered TILOP (TILOP 10) commercially pure (CP) Ti G 2 powders; SEM images of (b) 10-times-sintered EOS and (c) TILOP CP Ti G 2 powders.

Figure 3

Effect of repeated laser sintering on oxygen concentration in Ti powders and laser-sintered Ti materials.

Figure 4

Optical microscopy images of (a,b) 10-times-laser-sintered EOS CP Ti G 2 and (c,d) once-sintered TILOP CP Ti G 2 built in (a–c) 90° and (d) 0° directions; (a,c,d) transverse (T) sections to the building direction and (b) longitudinal (L) section perpendicular to the building direction; (e,f) optical microscopy images of wrought and dental-cast (center part) CP Ti G 2 rods, respectively.

Figure 5

TEM images of transverse sections of (a,b) once-sintered TILOP CP Ti G 2 built in 90° direction; (c,d) electron beam diffraction patterns obtained at the location indicated by p (precipitation) and m (matrix) in (b), respectively; (e,f) EDS patterns of precipitate indicated by p and m in (b).

Figure 6

Optical microscopy images of once-sintered Ti-6Al-4V alloys built in 90° direction; (a,b) transverse (T) sections to the building direction and (c,d) longitudinal (L) sections perpendicular to the building direction; (e,f) TEM images of transverse section of once-sintered Ti-6Al-4V alloys built in 90° direction.

Figure 7

Optical microscopy and SEM images of Ti-6Al-4V alloy annealed at (a,b) 840, (c,d) 900, and (e,f) 920 °C for 2 h after laser sintering.

Figure 8

Effects of repeated laser sintering on mechanical properties (σ_{0.2% PS}, σ _UTS, TE, and RA) of laser-sintered EOS CP Ti G 2 rods.

Figure 9

SEM images of fracture surfaces of the tensile-tested TILOP CP Ti G 2 (10-times-sintered); (b) magnification of rectangular area in (a), and (c) magnification of rectangular area in (b).

Figure 10

S–N curves of laser-sintered (a) EOS (once- and 10-times-sintered) and (b) TILOP (once-sintered) CP Ti G 2 rods; dental-cast CP Ti G 2 in (a) and wrought CP Ti G 2 in (b).

Figure 11

S–N curves of once-sintered Ti-6Al-4V alloy built in 90° direction and wrought Ti-6Al-4V alloy.

Figure 12

SEM images of fracture surfaces of fatigue-tested TILOP CP Ti G 2 (once-sintered 0°); (b) magnification of upper rectangular area in (a), (c) magnification of rectangular area in (b), (d) magnification of lower rectangular area in (a), (e) magnification of rectangular area in (d), and (f) magnification of rectangular area in (e).

Figure 13

Partial dentures manufactured by laser sintering with CP Ti G 2 powder. (a) laser-sintered metal frame; (b) polished metal frame; (c) partial denture.