PubMed · 4872249
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E Wagner. 1967. [A contribution to the precision casting technic].. https://pubmed.ncbi.nlm.nih.gov/4872249/
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Several investigations have examined magnesia-based investments for pure titanium casting. However, the thermal expansion value was insufficient at low casting temperatures and high interfacial reactivity occurred at high casting temperatures. The purpose of this investigation was to modify a magnesia-based investment by adding a heat-resistant mold material, zirconia, in different ratios to produce a more accurate titanium casting. The thermal expansion value was measured using a new precise automatic laser recording machine and pure titanium was cast using an argon casting machine. The marginal accuracy was measured using a stereomicroscope and the interfacial reactivity of the titanium was evaluated using X-ray diffraction analysis. The results indicate that adding different amounts of zirconia to a magnesia-based investment can increase its thermal expansion value and decrease the interfacial reactivity of the titanium. Maximal thermal expansion in the zirconia-modified investments significantly increased by 5-6 weight % (wt%) and peaked at 1.62% expansion. Selevest with 5 wt% zirconia had the smallest mean marginal discrepancy, 21.70 microm at 750 degrees C. Analysis of variance indicates significant differences in marginal discrepancy between zirconia-modified investments (p < 0.001). Adding zirconia can also decrease the interfacial reactivity of the titanium. The data indicated that proper amounts of zirconia (5-6 wt%) added to a magnesia-based investment can produce a more accurate and less interfacial reactive pure titanium casting.
OBJECTIVE: Reaction layer structure of the titanium castings surface was investigated when a new centrifuge-vacuum-pressure cast titanium machine and a zirconite inner investment was used. METHODS: The micro-hardness of titanium castings was measured using a Knoop's hardness tester. The structure of reaction layers and the distribution of elements on the surfaces of titanium castings were analysed by SEM and EDS, respectively, when zirconite was used as the inner investment for cast titanium. RESULTS: Knoop's micro-hardness at distances of 50 and 75 microm from the titanium casting surfaces made directly in phosphate investment molds had significantly harder surfaces than those made in zirconite coating molds. The thickness of the reaction layer on the surface of titanium castings was <35 microm with zirconite coating and was >50 microm without zirconite coating. The structure of reaction layer was divided into four layers from the outer surface to the inner including: sintering layer, alpha-Case, Si-rich layer, acicular crystal structure. The distribution of elements was different on each layer. SIGNIFICANCE: The thickness of the cast titanium reaction layer was reduced when the wax patterns were coated with zirconite. The surface of the titanium castings was smooth and without cracks, and the investment on the surface of titanium castings was easily removed.
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