Study On High Temperature Oxidation Resistance Of Fe-Cu-Ni-Al

The development of advanced high-temperature materials tends to use multi-alloys to obtain comprehensive properties such as high temperature strength,room temperature toughness and chemical stability that meet the requirements of service conditions.Superalloys usually include Co-based,Fe-based and Ni-based superalloys.Fe-based superalloys are relatively inexpensive among them,which have good high-temperature mechanical properties and outstanding oxidation resistance.They are widely used in aerospace,shipbuilding,thermal energy and petrochemical industries.Six quaternary Fe-45Cu-15Ni-5Al,Fe-65Cu-15Ni-5Al,Fe-45Cu-15Ni-7Al,Fe-65Cu-15Ni-7Al,Fe-45Cu-15Ni-10Al and Fe-65Cu-15Ni-10Al alloys were selected in this paper to investigate the constant temperature and cyclic oxidation behavior at 700�C-1000�C.The study helps to clarify the oxidation mechanism of the multi-element model superalloy.Explore the effect of different Al content on the oxidation resistance of the alloy and the differences in the two different oxidation conditions of isothermal oxidation and cyclic oxidation.At the same time,it has guiding significance for the design,preparation and application of new materials.The isothermal oxidation behavior in pure oxygen and the cyclic oxidation behavior in air at 700-1000�C of Fe-45Cu-15Ni-5Al and Fe-65Cu-15Ni-5Al quaternary alloys were investigated.Except that Fe-65Cu-15Ni-5Al alloy is mainly Cu₂O in the outermost layer at 1000�C.Under the other conditions,the outermost layers are formed mainly of CuO.The intermediate layer is composed of oxides of Fe,Ni and Al and composite oxides formed between them.The innermost layer is Al₂O₃ layer.In addition to Fe-65Cu-15Ni-5Al alloy under constant temperature oxidation conditions at 700-900�C,it is easier to form continuous Al₂O₃.The alloy do not have internal oxidation.It has better oxidation resistance.In other cases,discontinuous Al₂O₃ layers were formed in the inner layer,and Al internal oxidation occurred below the Al₂O₃ layer.Due to the repeated rupture of the Al₂O₃ layer at 900-1000�C,the internal oxidation of the alloy cannot be prevented.Therefore,the copper-rich Fe-65Cu-15Ni-5Al alloy have a higher corrosion rate than the Fe-45Cu-15Ni-5Al alloy.Especially under cyclic oxidation conditions at 1000?,the alloy peels off in large areas due to stress during cooling.The alloy fresh substrate is exposed to air and continues to be oxidized.Thus,alloy corrosion rate accelerated.The isothermal oxidation behavior in pure oxygen and the cyclic oxidation behavior in air at 700-1000�C of Fe-45Cu-15Ni-7Al and Fe-65Cu-15Ni-7Al quaternary alloys were investigated.After the initial stage of oxidation,the Al₂O₃ layer formed at the interface between the oxide film and the matrix of the two alloys is more continuous than the Fe-Cu-Ni-5 at.%Al alloy.Corrosion rate is lower under the same conditions.Oxide film structure similar to Fe-Cu-Ni-5 at.%Al.Fe-45Cu-15Ni-7Al alloy is not continuous enough in the?-phase region due to the low content of Al in the iron-rich?-phase region.Some internal oxidation zones have appeared.Fe-65Cu-15Ni-7Al alloy forms a very continuous layer of Al₂O₃ at four temperatures of isothermal oxidation.There is essentially no presence of an internally oxidized region.The anti-oxidation performance of the alloy is better than Fe-45Cu-15Ni-7Al alloy at constant temperature.Under cyclic oxidation conditions,the Al₂O₃ layer of the alloy cracked while continuously regenerating at 900�C.The corrosion rate of Fe-65Cu-15Ni-7Al alloy under cyclic oxidation at 900�C is still lower than that of Fe-45Cu-15Ni-7Al,which is in accordance with the isothermal oxidation law.However,this result was changed at1000�C under cyclic oxidation conditions.The isothermal oxidation behavior in pure oxygen and the cyclic oxidation behavior in air at 700-1000�C of Fe-45Cu-15Ni-10Al and Fe-65Cu-15Ni-10Al quaternary alloys were investigated.When Al content increases to 10 at.%,in the early stage of oxidation,the surface of the alloy can rapidly generate a continuous Al₂O₃ layer,which can earlier suppress the oxidation of Cu and Fe.Fe-65Cu-15Ni-10Al quaternary alloy is more likely to produce a continuous dense Al₂O₃ layer,and the outer oxides are basically Al₂O₃.It has excellent oxidation resistance at constant temperature.Under cyclic oxidation conditions at 1000�C,although both alloys produced a continuous Al₂O₃ layer in the early stage,due to the different coefficients of expansion of the different oxides and the stress acting on the cooling process,the alloy oxides spalled very seriously.The oxidation behavior of the two alloys are similar and the corrosion rate are very fast.