Study On Composition Design And Structural Characteristics And Performances Of Porous Ti-Si-Mo(-Al)

Porous intermetallic compounds,with the advantages of lightweight,large specific surface area,have excellent energy absorption performance,high-temperature oxidation and corrosion resistance,so that they could be widely applied to high-temperature functional materials.In this paper,a variety of porous Ti-Si-Mo?-Al?with different Mo contents of 12 wt.%,14 wt.%,16 wt.%and 18 wt.%,and different NH₄HCO₃ addition amount of 10 wt.%,20 wt.%,30 wt.%and 40 wt.%in Ti-8Si-18Mo?wt.%?,and different Al contents of 0 wt.%,5 wt.%,10 wt.%and 15 wt.%in Ti-8Si-18Mo+40wt.%NH₄HCO₃?wt.%?,were prepared by the powder metallurgy process of"high-energy ball milling-pressure forming-vacuum sintering".The effects of Mo?NH₄HCO₃ and Al contents on the microscopic morphology,phase composition,structural characteristics and performances of sound absorption,oxidation resistance and acid corrosion resistance were examined and investigatived.The current works and innovative achievements are as follows:?1?The microcosmic organization structure and phase composition were investigatived.Powder mixtures with Ti,Si,Mo and Al elements emerged significant refinement and homogenization after high energy milling.The microstructure of sintered porous Ti-Si-Mo?-Al?composed of skeletons of Ti-Si?Mo-Si and Ti-Al intermetallic compounds and pores.Porous Ti-Si-Mo-Al consisted of Mo₅Si₃,TiSi,Ti₅Si₄,Ti₅Si₃ and TiO phases and Al₂Ti₃ and Al₂O₃ phases were detected after adding Al element.?2?The porosity,pore size distribution and fractal dimension were investigatived.The porosity of sintered porous Ti-Si-Mo?-Al?reached 40.58%⁶3.82%.The porosity and pore size gradually increased as the NH₄HCO₃addition amount and Al contentincreased.The pore size was mainly distributed less than 1?m ranging from200 nm to 400 nm most.However,pores with the size from 400nm to 800nm and from 1?m to 30?m gradually increased after adding the NH₄HCO₃ and Al.The fractal dimension of the sintered porous Ti-Si-Mo?-Al?was very large,about 2.9,indicating that pores have excellent complexity and connectivity.?3?The sound absorption performance,including sound absorption coefficient and airflow resistivity,was investigatived.The sound absorption coefficient of porous Ti-Si-Mo with a porosity from 40.58%to 57.40%was around 0.2⁰.3.The equivalent damping of porous Ti-Si-Mo increased wth the porosities,and the sound absorption coefficient increasedup to 0.308 at the NH₄HCO₃ content of 30wt.%consequently.In addition,the resonance frequency increased with the porosity.The sound absorption coefficient reached the maximum,then gradually decreased and tended to be stable at the higher sound frequency as the porosity increased.The viscosity and heat conduction effectsgradually increased with the porosity and the number of micron-sized pores.As a result,the airflow resistance increased up to1.10×10⁸Pa·S/m² at the NH₄HCO₃ content of 40wt.%.As the airflow resistance of porous Ti-Si-Mo increased,the sound absorption coefficient gradually increased and then decreased,and there was the best airflow resistance.?4?The high-temperature oxidation resistanceperformanceat 1473K,including the morphology,phase composition and oxidation kinetics curve,was investigatived.The surface of the oxidized samples was a dense oxide film composed of TiO₂ oxide layer and a little SiO₂ particles.The surface oxidation products were composed of anatase or rutile TiO₂ phase,quartz SiO₂ phaseandAl₂O₃ phase.After adding Al,the Al₂O₃phase peaksappeared.The mass gain gradually decreased with the Mo contentand increased with the porosity.The high-temperature oxidation resistance performance was the best when the Mo content was 18wt.%and the mass gain after oxidation for100h was 0.094g/m².However,appropriate Al₂O₃ particles as a reinforcement enhanced the high-temperature oxidation resistance,while excessive Al₂O₃ particles reducing the density declinedhigh-temperature oxidation resistance.When the Al content was 5wt.%,its high-temperature oxidation resistance was optimal and the mass gain after oxidation for 100h was 0.047g/m².?5?The corrosionresistanceperformanceof immersion corrosionin 1 mol/L HCl solution,including the morphology and corrosion kinetic curve,were investigatived.The intermetallic compounds peeled off slightly in the pores.The mass loss increased with the Mo content on the whole and the corrosionresistanceperformance decreased.The acid corrosion resistance was the best when the Mo content was 12wt.%and the mass loss after corrosion for 100h was 0.044g/m².However,the mass loss of the samples with the Mo content of 16.wt%was more serious because there was no oxides in the sintered sample,which could not form the protective layer.The mass loss gradually increased because the porosity increased wth the NH₄HCO₃ addition amount.However,appropriate Al improved the corrosion resistance due to the oxides of Al₂O₃ while excessive Al reduced the corrosion resistance because of the primary battery formedon the surface.When the Al content was within 5wt.%,the acid corrosion resistance had little effect,but when the Al content exceeded 5wt.%,the acid corrosion resistance significantly decreased.In summary,porous Ti-Si-Mo?-Al?with a hierarchical porestructure dominated by submicron pores were innovatively prepared in this paper.They possess light weight,excellent high-temperature oxidation resistance and acid corrosion resistance.In addition,their sound absorption performance conformed to the law of traditional porous sound-absorbing materials.This paper provided scientific basis and technology foundation for the composition design and preparation of porous materials used in the fields of sound absorption,heat transfer and filtration in harsh environments.