The effects of the formation of a multi-scale reinforcing phase on the microstructure evolution and mechanical properties of a TiAlC/TiAl alloy.

In order to acquire TiAl composites with a multi-scale reinforcing phase, and to improve the microstructure and tensile properties at elevated temperatures, TiAl alloys have been prepared with different added carbon content levels via vacuum arc melting. The results show that when the carbon content is greater than or equal to 1.0 at%, then TiAlC forms and the microstructure changes from having a dendrite morphology to an equiaxed crystal morphology. The B2 phase disappears in the TiAlC-containing alloys. As the carbon content increases from 0 to 3.0 at%, the lamellar colony size decreases from 148.4 to 32.8 μm and the lamellar width decreases from 441.2 to 117.6 nm. More nanoscale TiAlC particles form in the α lamellae at a higher carbon content, and there are a lot of dislocations around them. As the carbon content, the TiAlC content increases from 0 to 16.8 vol% and the length-diameter ratio decreases from 9.2 to 1.8. The reason for the microstructure refinement is that carbon and carbide act as heterogeneous particles during solidification, and carbide dissolves some alloy elements, improving the microstructure uniformity. Compressive testing shows that the maximum compressive strength is 2324.3 MPa at a carbon content of 1.5%. At a carbon content of 2.5%, the compression strain is higher (28.1%). Tensile testing at elevated temperatures shows that upon increasing the temperature from 750 to 850 °C, the tensile strength increases from 398 to 541 MPa, and the strain increases from 6.1 to 12.2% with a temperature increase from 750 to 950 °C. The increase in the mechanical properties is attributed to the refined lamellar colonies and lamellar width, the solid solution of elements, and the formation of nanoprecipitates.