Effect of Pulsed Current on Microstructure Evolution in Solidification of Ti-44.5Al-3Nb-0.8Si Alloy for Internal Combustion Engine

The influence of current-density and frequency on the microstructures in Ti-44.5 Al-3 Nb-0.8 Si alloy,an internal combustion engine material solidified in pulsed current method,was investigated.The results show that the current-density and frequency had a major impact.For instance,solidified at large current-density and high frequency,the primary and secondary dendrite,BCC-phased and β-structured domains,perpendicular to each other,dominated.Solidified at 80 Hz,as the current-density increased to 96 mA/mm²,the primary dendrite distance changed in a decrease-increase manner,minimizing at 64 mA/mm².The primary dendrite distance decreased with an increasing frequency.An increase of current-density resulted in formation of lamellar texture; as the current-density increased,α2/γ phased inter-laminar spacing varied in a decrease-increase mode.A higher frequency also reduced the inter-laminar spacing.We suggest that the pulse current may promote formation of finer domains and more uniform lamellas in solidified TiAl alloy.