[Effect of mold temperature on mechanical properties of Ti-Zr alloy castings].

Objective: To investigate the influence of mold temperature on the mechanical properties of Ti-Zr alloy castings.

Methods: Ti-Zr alloy was cast into a mold which was made of a zircon (ZrO2.SiO2) investment with a casting machine (China) designed as vacuum, pressure and centrifuge. At three mold temperatures (room temperature, 300 degrees C, 600 degrees C) the Ti-Zr alloy was cast separately. The ultimate tensile strength (sigmab), 0.2% offset yield point strength (sigma0.2), and elongation to fracture (delta) were determined by a universal testing machine with 15 mm pre-marked gauge interval. The surface micro-structures of Ti-Zr alloy castings at three mold temperatures were observed by optical microscope.

Results: At a higher mold temperature during casting, the tensile strength and yield strength of Ti-Zr alloy were significantly increased, while the elongations were significantly decreased. The micro-structure of the surface was different from the inner part. There was a reacted layer in the outermost surface. The thickness of reacted layers at the three mold temperatures was about 35.5 man (room temperature), 55.0 microm (300 degrees C) and 65.5 microm (600 degrees C), respectively. The inner part of microstructure composed of main a phases within the prior alpha grain boundaries.

Conclusion: The mold temperature is one of the major factors influencing Ti-Zr alloy mechanical properties. Comparing with Ti6Al4V alloy and Co-Cr alloy castings, Ti-Zr alloy is more suitable for denture frame.