Abstract:

BACKGROUND: So far, comparative studies about the application of magnesium oxide and zirconium oxide-bonded materials in pure titanium casting have not been reported in detail, but phosphate-bonded investment has an obvious stratification on the casting surface reaction layers, and can be used as the control.
OBJECTIVE: To study the effects of different investments on the surface reaction layer of cast titanium.
METHODS: Phosphate, zirconium oxide and magnesium oxide investments were embedded for pure titanium casting with specification of embedded 10 mm x 10 mm x 1 mm respectively, and the casting surface reaction layers were tested by scanning electron microscope, energy dispersive spectrometer, X-ray diffraction, micro-hardness and metallographic methods.
RESULTS AND CONCLUSION: The surface reaction layer thickness of the castings which cast by phosphate, zirconium oxide and magnesium oxide investments in metallographic photos was 70, 45, and 12 μm, respectively. The hardness value of these three species castings was obviously reduced 100, 60 and 40 μm from the surface respectively; from this place to the internal titanium cast, their hardness value changed stably. Major element Al, Si, O content in reaction layer was decreased gradually as the depth of reaction layer increased. Compared with zirconium oxide and phosphate investments, the reaction between magnesium oxide investment and titanium casting was slighter, and reaction layers were less, moreover, there was less pollution in pure titanium casting. These findings suggest that magnesium oxide investment is the most ideal investment for pure titanium casting.