Effect of Ti and Ta content on the oxidation resistance of Co-Ni-based superalloys

Co-Ni-based superalloys are known for their capability to function at elevated temperatures and superior hot corrosion and thermal fatigue resistance.Therefore,these alloys show potential as crucial high-temperature structural materials for aeroengine and gas turbine hot-end components.Our previous work elucidated the influence of Ti and Ta on the high-temperature mechanical properties of alloys.However,the intricate interaction among elements considerably affects the oxidation resistance of alloys.In this paper,Co-35Ni-10Al-2W-5Cr-2Mo-1Nb-xTi-(5−x)Ta alloys(x=1,2,3,4)with varying Ti and Ta contents were designed and compounded,and their oxidation resistance was investigated at the temperature range from 800 to 1000℃.After oxidation at three test conditions,namely,800℃for 200 h,900℃for 200 h,and 1000℃for 50 h,the main structure of the oxide layer of the alloy consisted of spinel,Cr_(2)O_(3),and Al_(2)O_(3)from outside to inside.Oxides consisting of Ta,W,and Mo formed below the Cr_(2)O_(3)layer.The interaction of Ti and Ta imparted the highest oxidation resistance to 3Ti2Ta alloy.Conversely,an excessive amount of Ti or Ta resulted in an adverse effect on the oxidation resistance of the alloys.This study reports the volatilization of W and Mo oxides during the oxidation process of Co-Ni-based cast superalloys with a high Al content for the first time and explains the formation mechanism of holes in the oxide layer.The results provide a basis for gaining insights into the effects of the interaction of alloying elements on the oxidation resistance of the alloys they form.

Effect of Ti addition on high-temperature oxidation behavior of Co-Ni-based superalloy

The oxidation behavior of a newly designed Co-Ni-based alloy with varied addition of Ti(1.4 and 2.1 wt.%,hereafterreferred as 1.4Ti and 2.1Ti alloys)was explored in air at 900℃.It is found that an outer oxide layer composed of CoO,anintermediate oxide layer composed of intermittent TiO,plus continuous Cr,W-rich oxides,and an inner oxidized regioncomposed of Al2O3 were formed on the surface of 1.4Ti alloy,whereas the oxide structure of 2.1Ti alloy was composed of Co0 as the outer oxide layer,continuous TiO2,Cr2O3 and WO3 as intermediate oxide layer,and Al2O3 as the inner oxidizedregion.With increasing Ti content.continuous TiO2 films formed in the intermediate oxide layer,which would lead to theformation of compact Cr2O3 and improved oxidation resistancc after 100 h oxidation at 900℃.These observations indicatedthat Ti addition can improve the high-temperature oxidation resistance of Co-Ni-based aloys.