Effect Of Al/Cr/Re Elements On Oxidation Properties At High Temperature For Cu-Based Alloy

The Cu-Ni-Fe based alloy were prepared by vacuum melting in this paper as thesubstrate alloy. Aluminum element and other alloyed elements were added tosubstrated alloy. Optical metallography, microhardness, and the differential thermalanalysis （DTA） were used to detecte the physical properties for the tested alloy. Theoxidation kinetic curves and the oxidated film were analysised. The results revealed:In order to improve oxidation resistance for experimental alloy further,14wt.%,18wt.%,22wt.%mass percentage Cr element or1.5wt.%La+0.5wt.%Y,1wt.%La+1wt.%Y,0.5wt.%La+1.5wt.%Y mass percentage rare earth （RE） elementswere added to based alloy with8wt.%Al element. The effect of Al/Cr/RE elements onoxidation resistance was investigated for Cu-based alloy at high temperature. Thecomposition and morphology of the oxide film were analysised by X-ray diffraction（XRD）, scanning electron microscope（SEM）, energy dispersive spectroscopy（EDS）.The results revealed that Al/Cr/RE elements could improve the oxidation resistance athigh temperature through the role of refined grain and riveting for tested alloy.The microstructure of Cu-Ni-Fe alloy contained rich-Fe phase and α-Cu phase.CuO and Fe2O3was formed on the surface of tested alloy. When the Al-doping contentwas greater than8wt.%, the NiAl phase was formed in the microstructure ofCu-Ni-Fe-Al alloy. At the same time, the rich-Fe phase was dispered. With theincreasing Al content, the volum peretage of NiAl phase was increased. Because ofthe exist of NiAl phase, the continous and density α-Al₂O₃was formed on thesurface of tested alloy at high temperature oxidation. The oxidation kinetic curve wasthe straight-line law for Cu-Ni-Fe alloy, and based the national criterion, the oxidationproperties were deteriorated. The oxidation kinetics curves for Cu-Ni-Fe-Al alloyswere the parabolic law. The optimal content was doped8wt.%Al element for massgain. The oixidation properties was improved and weight gain was decreased to100times for the alloy. The Al element was not only changed the alloy microstructure, butalso changed the oxidation mechanism because of the daformation of continous anddensity α-Al₂O₃on the surface for the tested alloy.The microstructure contained α-Cu phase, NiAl phase, and some of the rich Cr phase. The oxidation kinetics curves were the parabolic law for tested alloy. Withthe improving of Cr-doping content, the oxidation weight gained was slightly betterthan that of tested alloys without Cr-doping element alloy for Cu-Ni-Fe substratedalloyDoped a small amount of RE elements La and Y in Cu-Ni-Fe-Al alloy, theoriginal microstructure were refined, and the oxidation type was parabolic law. Acontinuous and density layer of α-Al₂O₃oxidation film was formed on the surface ofalloy. The RE oxides played a role of riveting effect to α-Al₂O₃oxidation film. Theadhesive strength between the oxidation film and the substrated alloy was improved.So the oxidation properties was improved by the α-Al₂O₃oxidation film to protect thematrix alloy.