IADR Abstract Archives
Thickness of Hardened Layer Formed on Cast Titanium Surfaces
Objective: This study examined the effect of the size of titanium castings on the thickness of their contaminated surface layers (the a-case). Methods: Commercially pure Ti (CP Ti: ASTM grade 2) and Ti-6Al-4V (ASTM grade 5) (n=2) specimens (10 mm x 5 mm; 0.5, 0.75, 1.0, 1.5 or 2.0 mm thick) were cast in a MgO-based mold (Selevest CB, Selec, Japan) using a centrifugal casting machine (Ticast Super R, Selec) and then bench cooled. The Vickers hardness of the cast surface was determined starting at 25 µm (HS) and continuing to 500 µm below the surface using a microhardness tester. The microhardness of four randomly chosen areas at each depth was determined on two cast specimens for each metal. The thickness of the a-case for each alloy was evaluated based on the hardness profiles. The microhardness (n=8) and the a-case thickness (n=4) were statistically analyzed using one-way ANOVA (a=0.05). Results: The results are as follows: [Means (SD): Identical letters indicate no statistical differences (p>0.05)]
|
Specimen thickness (mm) |
0.50 |
0.75 |
1.00 |
1.50 |
2.00 |
|
|
HS |
CP |
400.6(24.1)a |
444.8(49.5)b |
459.3(27.1)ab |
516.6(55.6)bc |
517.9(49.0)bc |
|
64 |
519.7(20.3)bc |
544.3 (39.4)c |
540.6 (51.7)c |
552.3 (50.8)cd |
612.4 (27.7)d |
|
|
a-case (µm) |
CP |
73.8 (15.4)ab |
119.0 (21.7)bcd |
136.5 (23.7)cd |
160.3 (30.6)de |
186.3 (20.2)e |
|
64 |
73.5 (6.0)a |
84.3 (18.9)ab |
91.3 (13.0)abc |
132.3 (15.1)cd |
130.5 (11.2)cd |
|
The surface hardness (HS) and a-case thickness tended to increase with the increase in the thickness of the castings for both CP Ti and Ti-6Al-4V. Conclusions: The microhardness and the thickness of the hardened layer formed on the cast titanium surface increased with the specimen thickness since more oxygen (a main contaminant) diffused into the thicker specimens, which cooled at a slower rate. Supported by NIH/NIDCR grant DE11787.