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Effect of Titanium Casting Structure and Temperature

Effect of Titanium Casting Structure and Temperature

Influencing the performance of the mold is mainly the thermal conductivity, strength and yield of the mold and the stability to molten titanium. The use of high thermal conductivity, that is, large heat storage capacity, high strength, poor yield, such as machined graphite cast titanium and titanium alloy castings, usually have surface cracks. Surface cracks are the most common defects in titanium and titanium alloy castings and are generally cold cracks. In order to eliminate surface cracks, it is best to use molds with low thermal conductivity, moderate strength, and good concession, such as tamping and melting model shells. Secondly, the stability of the mold to molten titanium also has a great influence on the surface cracks of titanium and titanium alloy castings. Ti-5Al alloy castings are poured into molten lead shells such as ordinary lead dioxide, fused corundum, magnesia, etc., because the surface of the casting is contaminated by gap elements H, C, O, N, etc., the C, N, H content on the surface of the casting It is not much different from the inside, but the O content of the surface layer is about an order of magnitude greater than that of the center, so that a brittle layer is formed on the surface of the casting, and it is easy to produce surface cracks under the action of thermal stress. Therefore, the surface condition of the casting is one of the main factors affecting the formation of cold cracks.
Preheating the mold properly can remove part of the adsorbed gas on the surface of the mold, reduce the harm of gap elements, and reduce the cooling rate of the casting in the mold. Under the condition that the casting is full, reduce the temperature of pouring titanium liquid, reduce the mutual reaction between the titanium liquid and the mold, and avoid the serious a surface embrittlement layer. These all help prevent cracks on the casting surface.
Castings with complex structure and large wall thickness have relatively poor crack resistance, and castings with relatively uniform wall thickness are better. Therefore, when designing and producing castings with complex structures and large wall thickness differences, more attention should be paid to the casting structure and process design, as well as the use of a reasonable pouring system to strictly control the parameters of the process.

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