| The development of hot gas filtration and cleaning technologies are widely concerned as modern industry growing and environmental advantages.And number of countries are researching and developing hot gas filtration and cleaning technologies and key materials.Although porous ceramic and FeAl filtration have excellent high-temperature corrosion resistance,they are limited development owing to difficult of machining and serious brittleness.In recent years,the porous Ni-Cr-Al material have widely been concerned as they have excellent high temperature corrosion resistance,weld and mechanical properties.The porous Ni-Cr-Al material were firstly fabricated by pressureless sintering of Ni,Cr and Al elemental powders.The pore-forming mechanism and high-temperature oxidation resistance of Ni-Cr-Al porous materials were also studied.The research work mainly achieved the following results:The research results showed that the sintering specimen of Ni-Cr-Al porous material was best formed when the final sintering temperature was 1200-1250 ?.The high temperature oxidation resistance of the porous material with 9 wt.%Al was better than that of the mass fraction of 4.5 and 12.5.The expansion rate,pore structure and phase composition of porous Ni-16Cr-9A1 alloys in the process of reaction synthesis were characterized to research the pore forming process and explore the mechanism of pore.The research results showed that the porosity and radial expansion of Ni-16Cr-9Al porous materials were first increased and then decreased slowly,with the increase of temperature.When the sintering temperature was less than 920 ?,the diffusion coefficient of Al in Ni was considerably greater than Cr in Ni and the entire diffusion process was determined by the Al-Ni diffusion couple.By contrast,when sintering temperatures exceeded 920?,Al has fully spread into Ni and the diffusion coefficient of Cr has improved significantly.So the entire diffusion process was determined by the Cr-Ni and Cr-NiAl diffusion couples at sintering temperatures above 920 ?.The main pore formation mechanisms were the Kirkendall effect,high temperatura phase change and the development of interparticle pores.The oxidation behavior and mechanism of porous Ni-16Cr-9Al alloys at 800 ?and 1000 ? in air were studied using isothermal temperature oxidation method.The differences of surface morphology,phase and pore structure paraments between material oxidized and non-oxidized were characterized by SEM,XRD and mercury intrusion.The results showed that the open porosity and the permeability of porous Ni-16Cr-9Al alloys decreased with the oxidation time extended.What's more,the higher the oxidation temperature increased,the more these parameters decreased.The oxidation rate of the porous Ni-16Cr-9Al based samples which oxidized 420 h at 800 ? was 0.012%2/h and the oxidation products were Al2O3 and Cr2O3.The oxidation rate of the porous Ni-16Cr-9Al based samples which oxidized 390h at 1000? was 0.415%2/h and the oxidation products were Al2O3,Cr2O3,Ni(Cr?Al)2O4.The oxidation kinetics curves of the porous Ni-16Cr-9A1 based samples at 800 ? and 1000 ? all obeyed the parabolic law.The oxidation products of Ni-16Cr-9Al porous were closely attached to the substrate,so as to prevent the further oxidation,showing excellent high temperature oxidation resistance.Analyzed experiment result of this paper,the porous Ni-16Cr-9Al alloys were prepared by reactive powder synthesis method,which combining high filter fineness and high-temperature stability.The mentioned fabricated method has the special characteristics of simplicity,controllability and low cost,which show great significance of the development of other systems of porous materials and the corresponding industry applications.After sintered at 1200 ?,the porous Ni-16Cr-9A1 materials has the porosity of 35.02%,maximun pore size of 9.82 ?m and gas permeability of 296.09 m3m-2h-1Kpa-1. |
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