| Ferro based supperalloys have broad prospect in the application fields of aircraft, spacecraft, energy resource, metallurgical and petrochemistry industrys. The zooming morden industry calls for critical high temperature oxidation ressitance of materials. By research of composite oxide scale on high temperature oxidation resistane, it is of great significance to understand the oxidation resistance mechanism, find new method and technology for oxidation resistance in higher temperature, and develop new unique properties ferro based supperalloys.Based on Ferro based supperalloy K273 and heat resistant steel ZG40Cr24, test alloys were cast by intermediate frequency induction furnace with non-oxidation method by alloying of Al and Si. The oxidation reistance at 1100℃for 500 hours of test alloys was carried out according to oxidation weight gain method by Chinese standard. By Scan Electricle Microscope, Energy Dispersive Spectroscope, X-ray Diffractor, Direct Current Resistance Meter, and Laser Thermal Conductivity, the effects of scale morphology and compositions on oxidation resistance were analyzed, the thermodynamic forming, oxidation resistance mechanism, oxidation kinetics, thermal stability and exfoliaton resistance of composite scale were studied systematically. A kind of dual phase ferro based supperalloy was developed on the experiment and theory analysis, and the high temperature oxidation resistance, high temperature and room temperature mechanical properties were examined.By alloy planting of 2wt.%Si and 4wt.%Al, the oxidation resistance of supperalloy K273 and heat rsistant steel ZG40Cr24 at 1100℃were both elevated remarkablely, the oxidation weight gain rate decreased from 12.2557g.m-2.h-1 and 3.5319g.m-2.h-1 to 0.3542g.m-2.h-1 and 0.0633g.m-2.h-1 respectively, the properties changed from none oxidation resistance to strong oxidation resistance for K273, and from the poor to the complete for ZG40Cr24.The growing modle of composite scale was established, by thermodynamics calculation of alloying elements. According to the Gibbs energy, Fe, Cr, Ni, Mn, Al, Si compete to be oxidated or deoxidated, so the composite scale made up of Cr2O3,α-Al2O3, SiO2 and spinel Fe(Ni,Mn)Cr2O4 came into being. Plane and compact structure, fine and even oxide grains endowed the composte scale with excellent high temperature oxidation resistance.By tests and analysis of oxides morphology, phase composition, elements distribution, electrical resistance, and thermal diffusion, the essence of composite scale oxidation resistance was fond to be that, the P type and N type semiconductor oxides in composite scale compose to be PN junctions, every PN junction is unilateral electrical conductivity, and numerous PN junctions arrange out of order in space, so the composite scale comes to be isolated on the whole, the transferring of ions and electrons in scale are hold back greatly, thus the further oxidation rate of base metal falls greatly, and the oxidation resistance of composite scale goes up markedly.With the adding of Al and Si, the scale exfoliation resistance of K273 and ZG40Cr24 was reinforced greatly, the scale exfoliation weight gain rate at at 1100℃descend from 1.2681g.m-2.h-1 to zero, reaching complete exfoliation reistance for ZG40Cr24 test alloy. Beacause of 1.5< PBRα-AlO3 Fe<2 and the growning of SiO2 from the out side of scale- scale/oxyzen interface, the composite scale grows whole and compact without accumulation of growing stress. At the same time, the even and fine oxides grains strengthen the scale intension by Hall-Petch theory. So the composite scale thermal stability of the boost up.According to the oxidation weight gains, the oxidation kinetics curves were plotted, and the equations were regressed by least squear method and none-linear curve fitting. The oxidation kinetics curves of composite scale strictly follow the power function of y=axb (a>0,0 |
PDF Full Text Request