Titanium casting: the surface reaction layer of castings obtained using ultra-low-temperature molds

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1 27 Journal of Oral Science, Vol. 43, No. 1, 27-33, 2001 Titanium casting: the surface reaction layer of castings obtained using ultra-low- s Hisaji Kikuchi, Makoto Onouchi, Hsueh-Chuan Hsu, Tomoko Kurotani Minoru Nishiyama Department of Dental Materials, Nihon University School of Dentistry, Tokyo of Dental Laboratory Technology, Chung Tai Institute of Health Sciences Technology, Taichung, Taiwan, R.O.C. (Received 12 September 2000 accepted 1 February 2001) Abstract: To examine whether the surface reaction layer of titanium castings can be reduced by lowering the during casting, we cast titanium at three s, including an ultra-low produced by cooling the liquid nitrogen, then measured the elongation of the castings. The titanium was cast using a centrifugal casting machine, the s were incinerated according to the manufacturers' instructions. Castings were then made the s at the ultra-low was good. The Vickers hardness near the surface layer of castings decreased as the decreased. (J. Oral Sci. 43, 27-33, 2001) Key word: titanium; casting; reaction layer. Correspondence to Dr. Hisaji Kikuchi, Department of Dental Materials, Nihon University School of Dentistry, Ka- Surugadai, Chiyoda-ku, Tokyo , Japan. Address for Huseh-Chuan Hsu: Department of Dental Laboratory Technology, Ohung Tai Institute of Health Sciences Technology, 11, Po-Tze Lane, Takun, Taichung, Taiwan R.O.C.

2 28 Table 1 Investments used in this study Results Castability Figure 1 is a representative photo radiograph of castings obtained using Selevest CB in the ultra-low. No casting porosity was observed, either directly or via X-ray photograph, the casting shape was good at all three s. Good castings were also obtained using T-Invest C&B Titavest CB. Photograph of titanium castings X-ray transparent image of titanium castings Fig. 1 Photograph X-ray transparent image of titanium castings (Selevest CB, ultra-low ).

3 29 Fig. 2 Vickers hardness of titanium casting (Selevest CB). Fig. 3 Vickers hardness of titanium casting (T-Invest C & B). Ultra-low Fig. 4 Vickers hardness of titanium castings (Titavest CB). Fig. 5 Optical micrographs of the surface reaction layer (Selevest CB).

4 Ultra-low Ultra-low Fig. 6 Optical micrographs of the surface reaction layer (Tinvest C & B). Fig. 7 Optical micrographs became thicker 80, 100 differences were not significant. The highest elongation observed was Titavest CB at the ultra-low. 600, Figure 8 shows range of (about, 200 increasing differences in of. 325 T-Invest &B,the differences(t-test, three ultra-low elongation the at each in the at the castings With increasing to 400 MPa P<0.05)were The elongation for, s castings each no observed. were either investment. decreased but slightly significant No observed Selevest of significant among CB the or Titavest CB. Elongation layer respectively). Tensile was 120μm of the surface reaction (Titavest CB). increased each slightly investment decreasing material, but the Discussion Castability Kuroiwa et al. (11) evaluated the association between castability in titanium casting using plate patterns observed good castability even using s at room. In this study, to reduce the thickness of the reaction layer in titanium castings, s were cooled in liquid nitrogen to an ultra-low-. The more marked difference between ultra-low- s molten titanium was than the difference in Co-Cr casting was expected to affects castability; however, as Kuroiwa et al. (11) reported, we observed no such effects.

5 31 The casting machine used in this study is well-known in titanium casting (13,14), the castability was 100 % using patterns a thickness of 0.46 mm or more in our previous study on the morphology of casting plates (15).Therefore, the fact that reducing the does not affect the castability of titanium is due to the high pressure in the casting machine. The effects of the that are observed for Co-Cr alloys were not observed for titanium casting, even using ultra-low s. Reaction layer The reaction layer formed on the casting surface was evaluated comprehensively in terms of Vickers hardness, metal structure,, elongation. 1) Vickers hardness The Vickers hardness of the near surface was low for each investment material at the ultra-low ; a significant difference was observed between the ultra- Fig. 8 Tensile elongation of titanium castings.

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