Spalling Behavior of Ti-2Al-9.2Mo-2Fe Alloy under Impact Loading

Lightweight is one of the development trends of weapon systems. Titanium alloys are widely used in fields such as armor protection due to their low density and high specific strength. To explore the spalling behavior of titanium alloys under impact loading, the equiaxed β phase Ti-2Al-9.2Mo-2Fe alloys with different grain sizes are obtained through heat treatment. The pre-impact loading with small residual deformation and spalling strength of the alloy are tested by a light gas gun device. The variation law of spalling strength and the microstructure evolution behavior of the alloy were analyzed through microscopic observation. The results show that the spalling strength of the alloy increases with the increase in grain size. Under the condition of non-pre-impact loading and the spalling strength of the alloy increases with the pre-impact loading amplitude when the grain sizes are 67 µm and 126 µm. The spalling process of the alloy exhibits a quasi-ductile fracture mode, and the microcracks are formed by the nucleation, growth and connection of micropores. With the increase in grain size, the nucleation position of the spalling micropores are formed by the transformation from the nucleation at dense acicular phase within the grains to the nucleation within the grains and at the grain boundaries. Pre-impact loading causes the accumulation of dislocations and other defects at the grain boundary, and the tendency of spalling micropores to nucleate at the grain boundary increases. The microcrack propagation path is more tortuous, the ductile fracture characteristics of the spalling fracture morphology are more prominent, and the spalling strength of the alloy is also improved. However, when the grain size is too large, the grain boundaries become longer and straighter, making the microcracks easier propagate, which leads to a decrease in the spalling strength.