Oxidation Resistance Mechanism OfβPhase Porous Ni-Al-Cr Intermetallics Synthesized Via Rapid Thermal Explosion Reaction

Porous Ni-Al based intermetallic compounds contain both covalent bond and metallic bond,and they have the common advantages of high temperature resistance and corrosion resistance of porous ceramic materials and good ductility and conductivity of porous metal materials.They are functional materials with excellent performance and have potential applications in high-temperature dust removal,filtration adsorption,wastewater purification and other fields.The thermal explosion（TE）method is an important preparation process for porous Al-based intermetallic compounds.TE reaction utilizes the instantaneous heat released by the reaction of raw materials during the heating process to complete the reaction and achieve energy supply without the need for additional energy from the outside,thus possessing the characteristics of time-saving and energy-saving.A stable heating mode enables the sintered products to maintain good macroscopic morphology and form a structure with high porosity and uniform pore distribution.This article prepared porous Ni-Al based intermetallic compounds through TE technology,and mainly investigated the effects of heating rate,Cr element doping amount,and Ni/Al atomic ratio during the preparation process on the TE reaction,phase composition,microstructure,and high-temperature oxidation resistance of porous Ni-Al-Cr products.The pore source and high-temperature oxidation resistance mechanism of porous products were elucidated.Firstly,this thesis investigates the effects of heating rate（2,5,10,20℃/min）on the macroscopic morphology,microstructure,diffusion behavior,high-temperature oxidation resistance,and mechanical properties of sintered products.When the heating rate is 2℃/min,the diffusion reaction is significant,and the sintered products have good macroscopic morphology.However,the multiphase composition（Ni₂Al₃,Ni Al,Ni）complicates its oxidation process and reduces its antioxidant performance.When the heating rate is 20℃/min,the TE reaction is significant,and the product is a uniform Ni Al phase,which also exhibits excellent stability in oxidation resistance experiments.However,at high heating rates,intense reactions can lead to melting deformation in the products.Using three-dimensional tomography technology,we found that at a heating rate of 10℃/min,the product phase composition is uniform,the morphology is good,and its porosity is as high as 57.31%,which is the most suitable process parameter for preparing porous Ni-Al based intermetallic compounds.In response to the problem of slow formation rate of protective oxide layer in porous Ni Al intermetallic compounds during oxidation process,in subsequent experiments,0,5,10,and 20 wt.%Cr elements were added to Ni-50Al at.%,respectively.Porous Ni-Al-Cr intermetallic compounds were prepared by TE method,and the mechanism of Cr element on TE reaction and high-temperature oxidation resistance was explored.The results indicate that Cr element avoids the risk of product melting and deformation by reducing the release of the heat in the system.In addition,Cr promotes the diffusion reaction between elements,resulting in a large number of Kirkendall pores,the maximum porosity can reach 62.6%.In the oxidation experiment,compared with porous Ni Al materials,the porous Ni-Al-Cr materials（5～10 wt.%Cr）in theβphase region can promote the formation rate ofα-Al₂O₃,enhance the high-temperature oxidation resistance through the oxygen absorption effect.Subsequently,further explore the TE behavior and high-temperature oxidation resistance mechanism ofβphase porous Ni-Al-Cr intermetallic compounds.Based on the atomic ratio of Ni/Al,theβphase samples can be divided into the Al-rich and the Al-poor sample,and focused on studying the TE behavior and oxidation resistance mechanism of Al-rich and Al-poor samples.The results indicate that the TE reaction of Al-rich sample is more intense,with uniform phase composition and higher porosity.However,the high porosity structure limits the improvement of its high-temperature oxidation resistance.The Al-poor sample has weak TE effect and low porosity,which can easily form obvious sintering necks in the products.The low porosity structure inhibits the erosion of air to the internal matrix,and enhances its high-temperature oxidation resistance.There are 70 figures,9 tables and 136 references in this thesis...