| The isothermal oxidation behaviors of Co-Re-Cr,Co-Re-Cr-Al and Co-Re-Cr-Si model alloys at 1000-1300? were investigated in this work.The research results will further develop the theory of high temperature oxidation of multicomponent superalloys,provide a theoretical basis for the design and preparation of commercial superalloys,and meet the increasing demand of high performance of high temperature materials in the turbine industry,which has important guiding significance for developing new superalloys.?1?The high temperature oxidation behaviors of Co-20Re-20Cr,Co-20Re-25Cr and Co-20Re-30Cr alloys have been investigated at 1000-1300? under 3.04×10-5 Pa O2?low oxygen pressure?.It was observed that the three alloys all showed oxidative weight loss.Meantime,these alloys displayed the smaller oxidative weight loss and the better high temperature oxidation resistance under the higher Cr content and the lower oxidation temperature.Additionally,the scales formed on these three alloys after oxidation at 1000-1300? were very thick.Proceeding from the scale/gas towards the interior there was first an outermost CoO layer.The following second layer was C?r2O4 spinel.The innermost layer in contact with the alloy substrate was a extremely thin Cr2O3 layer.Due to the high oxidation temperature,the outer three oxide scales were cracked or even peeled off.Compared t?o-20Re-20Cr and Co-20Re-25Cr,Co-20Re-30Cr alloy shown the best temperature oxidation resistance.?2?The high temperature oxidation behaviors of Co-20Re-25Cr-5Al,Co-20Re-25Cr-7Al and Co-20Re-25Cr-10Al alloys have been studied at1000-1300? under high and low oxygen pressure.Under the condition of 0.1 MPa pure O2?high oxygen pressure?,the above three alloys all showed oxidative weight loss.Additionally,the scales formed on these three alloys after oxidation at1000-1300? were very thick.Proceeding from the scale/gas towards the interior there was first an outermost CoO layer.The following second layer was?Co,Cr,Al?mixed oxide.A transverse crack was generated between the oxide scales and the substrate,causing the oxide scales to peel off.Under the above conditions,the oxidation resistance of the three alloys was not ideal,and the oxidation under the conditions of 3.04×10-5 Pa O2?low oxygen pressure?was further studied.Under the condition of 3.04×10-5 Pa O2,the opposite oxidation behavior appeared.All the alloys were in the state of oxidative weight gain,and the oxidation of most alloys were accorded with the parabolic law.All three alloys formed a protective Cr2O3oxide scale,and internal oxidation of Al element occurred in the Cr-depleted region.Due to the synergy between the Cr and Al elements,the high temperature oxidation resistance of the alloy was greatly improved under low oxygen pressure.?3?The high temperature oxidation behaviors of Co-20Re-25Cr-1Si,Co-20Re-25Cr-2Si and Co-20Re-25Cr-3Si alloys have been investigated at1000-1300? under high and low oxygen pressure.Under the condition of 0.1 MPa pure O2?high oxygen pressure?,it was observed that the three alloys exhibited oxidative weight loss,but the overall oxidation was better than that of the Co-Re-Cr-Al alloy.Additionally,proceeding from the scale/gas towards the interior there was first an outermost CoO layer.The following second layer was?Co,Cr?mixed oxide.The innermost layer in contact with the alloy substrate is a thin and discontinuous Cr2O3 layer.The internal oxidation of Si element occurred below Cr2O3.Under the above conditions,the oxidation resistance of the three alloys was not ideal,and the oxidation under the conditions of 3.04×10-5 Pa O2?low oxygen pressure?was further studied.Under the condition of 3.04×10-5 Pa O2,all three alloys followed the parabolic law well.Unlike under high oxygen pressure,the oxide scales formed on the surfaces of the alloys were very thin.Most of these three alloys formed a continuous and dense Cr2O3 oxide scale,which hindered the evaporation of Re oxide.The Si element underwent internal oxidation in the Cr-depleted region and exhibited a semi-continuous growth state near the alloy substrate under the Cr2O3layer.Due to the synergistic effect between Cr and Si,the high temperature oxidation resistance of the alloy was greatly improved under low oxygen pressure. |
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