Experimental Analyses On Solidified Structures And Mechanical Properties Of Centrifugal Precision Titanium Castings

Titanium and titanium alloys have some excellent properties, such as low density, high specific strength, high specific rigidity, high melting point, low coefficient of thermal expansion, as well as high corrosion resistance. Titanium alloys are used more and more extensively in aviation and astronavigation industry. Titanium alloys can be made into parts in many ways: machining, forging, casting, welding, powder metallurgy and so on, but they are quite expensive. In order to reducing the costs, the interesting in the net shape and near net shape technologies becomes more and more increased, especially, the precision casting has become the most successful and extensively used method as near net shape technique for manufacturing titanium alloy parts with thin-walls and complicated shapes.In this thesis, we completed the work mainly in experiment researches, at the same time with simulation of the computer as an auxiliary analysis method. We cast Ti-6Al-4V alloy using the methods of centrifugal precision casting, and also vacuum gravity casting. We observed the casting alloy structures, analyzed the formation mechanism of the casting/solidification defects, and measured the mechanical properties. So we could determine the quantitative relationship among the cooling parameters in the solidification processes, the structures and the mechanical properties.The macro- and micro-structures, as well as the corresponding mechanical properties, of the solidified parts of the titanium alloy at different positions of the centrifugal precision casting and the gating system were observed and analyzed. AnyCasting software is used to simulate and compute the cooling curves of the centrifugal precision casting system. By computing and analyzing the cooling curves, we got the relationships among the grain size, the model parameters and the cooling velocities of the cast parts, we also got the relationships among the slice thickness ofα/β, the model parameters and the cooling velocities of the parts. Using a designed steel mold for cylindrical step-castings, Ti-6Al-4V alloy was gravity cast in an ISM furnace. The macro- and micro-structures of the solidified casting were observed and analysed.