Effect of cooling rate on solidification microstructure and mechanical properties of TiB2-containing TiAl alloy
(1. College of Mechanical and Vehicle Engineering, Taiyuan University of Technology, Taiyuan 030024, China;
2. Advanced Metal Composite Forming Technology and Equipment Engineering Research Center of Ministry of Education, Taiyuan University of Technology, Taiyuan 030024, China;
3. TYUT-UOW Joint Research Centre, Taiyuan University of Technology, Taiyuan 030024, China;
4. National Key Laboratory for Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin 150001, China)
2. Advanced Metal Composite Forming Technology and Equipment Engineering Research Center of Ministry of Education, Taiyuan University of Technology, Taiyuan 030024, China;
3. TYUT-UOW Joint Research Centre, Taiyuan University of Technology, Taiyuan 030024, China;
4. National Key Laboratory for Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin 150001, China)
Abstract: Effects of cooling rate and 0.25 at.% TiB2 addition on solidification microstructure and mechanical properties of Ti-48Al-2Cr-2Nb alloys fabricated by the investment casting with different thicknesses were studied. The results show that with the cooling rate increasing from 37 to 2×102 K/s, the solidification path of the studied alloys is unchanged. The grain size of the matrix alloy is refined from 650 to 300 μm, while the grain size of Ti-48Al- 2Cr-2Nb-TiB2 is reduced from 550 to 80 μm. The lamellar spacing of matrix alloy is reduced from 360 to 30 nm with increasing the cooling rate from 37 to 2×102 K/s, while TiB2 addition shows little refinement effect on the lamellar spacing. Ti-48Al-2Cr-2Nb-TiB2 sample under medium cooling rate (69 K/s) exhibits superior microhardness (HV 550) and ultimate tensile strength (570 MPa) among the studied alloys. The refined grain size, lamellar spacing and fine TiB2 particles could account for the favorable mechanical properties of the studied TiB2-containing alloy. The microstructure evolution was discussed in light of cooling rate, constitutional supercooling and borides addition.
Key words: titanium aluminides; TiB2; cooling rate; microstructure evolution; mechanical properties