Effect of Casting Force on Castability of Titanium Alloys

Objective: This study examined the effect of casting force on mold filling of an experimental 5mass%Cu titanium alloy. Methods: A Ti-5%Cu alloy (Ti-5Cu) was prepared in an argon-arc melting furnace (IVI Mark 3, Pembroke). Wedge-shaped patterns (10mm long right angle, 4mm thick) were prepared with either 15° or 30° angles and invested with a MgO based investment material (Selevest CB, Selec Co., Japan). The molds were cast using a centrifugal casting machine (Selecast Super R, Selec) at rotational speeds of 600, 1250, 1500 or 3000rpm. The castings (n=6) were sliced into four specimens parallel to the triangular surface. Mold filling (µm) was determined as the missing length between the edge of the cast wedge and the theoretical acute tip of the triangle (n=18). Commercially pure titanium (CP-Ti: ASTM grade 2) was used as a control. Results were statistically analyzed by ANOVA/Tukey's tests (a=0.05).

Results: The determined mold fillings [mean (SD): µm] are listed in the following (means with identical letters are not significantly different) (p>0.05):

		600	1250	1500	3000	Rpm
Ti-5Cu	30°	-	129(65)a	152(98)a	215(81)b
	15°	-	231(91)d	251(114)d	332(137)d
CP-Ti	30	268(55)c	159(76)a	161(48)a	112(45)a
	15°	-	298(168)d	254(98)d	223(153)d

For 30° at 3000rpm, mold filling of Ti-5Cu showed significantly higher than that of CP-Ti (p<0.05). There was significant difference in mold filing between 30° and 15° in each corresponding speed (p<0.05). For 15°, there was no significant difference in mold filling among metals, regardless of the rotational speeds (p<0.05). At 600rpm, all castings except one of CP-Ti were incomplete. Conclusion: Mold filling of the 5%Cu titanium alloy, which is difficult to cast due to “pasty freezing”, was found to be similar to CP-Ti even for 15° when cast at rotational speeds greater than 1250rpm. Partially funded by NIH/NIDCR grant DE011787 and the Baylor Oral Health Foundation.