Transient creep in titanium alloys: Effect of stress, temperature and trace element concentration

The influence of stress, temperature and trace element concentration viz. Fe, Ni on the transient creep behavior of Ti-834 alloy, i.e. Ti–5.8Al–4.0Sn–3.5Zr–0.7Nb–0.5Mo–0.35Si–0.06C (in wt%) was studied. Two Ti-834 alloys, DMR Ti834 and TIMETAL 834 with higher and lower contents of (Fe, Ni) respectively were chosen for this study. Both alloys were given controlled heat treatments to develop microstructures containing 15 vol% primary α in a matrix of transformed β. The creep behavior of both alloys was studied in the temperature range 873–1023 K and stress range 80–350 MPa. Subsequent analysis showed that the limiting transient creep strain reduced with increasing stress and temperature. Also it was observed that DMR Ti834 yields a smaller transient creep strain value in comparison to TIMETAL 834. The creep activation energy (Q) in the transient creep region was also determined and again found to be smaller in DMR Ti834 (Q=284 kJ/mol) in comparison to TIMETAL 834 (Q=399 kJ/mol). The difference in transient creep strain and Q values was rationalized vis-a-vis the (Fe, Ni) content. The stress and temperature dependence of the transient creep strain and transient time were studied to understand the rate controlling mechanism of transient creep.