Preparation Of Al₂O₃Particles Reinforced Fe-based Composite Materials Via In-situ Synthesis

The non-ferrous metal matix composite reinforced by Al₂O₃particles has madegreat progress in recent years, but the poor wettability between Al₂O₃particles andiron matrix limits the research on the iron matrix composites reinforced by Al₂O₃particles. There exist some preparation processes to improve the wettability betweenAl₂O₃particles and iron matix at present, such as the chemical coating process for theAl₂O₃particles surface treating, and self-propagating high-temperature synthesis（SHS）. Both of the two methods could achieve a better Al₂O₃particulate reinforcediron matrix composites, but the former method limited the particle size of Al₂O₃, whilethe latter has a big exotherm of thermite reaction and poor controllability. A newcontrollable technology in-situ synthesis for iron matrix composites reinforced byAl₂O₃particles in order to improve the wettability and interfacial combination betweenAl₂O₃particles and iron matrix was developed in this paper.The alumina sol precursor was prepared by the sol-gel and Al₂O₃/Fe mixedpowders was got by adding iron powder to the liquid-solid doping with hydrogenreduction in situ synthesis. Then iron matrix composite reinforced by Al₂O₃particleswas prepared by adding alloying elements of C and Mo in ratio to the Al₂O₃/Fe mixedpowders before mixing cold press and sintering. And the study of influence factors onalumina sol as precursor and alumina powders was carried out. Characterization to themicrostructure morphology and the hardness of the composites before and afterquenching was also carried out. A new controllable technology in-situ synthesis foriron matrix composites reinforced by Al₂O₃particles in order to improve thewettability and interfacial combination between Al₂O₃particles and iron matrix wasdeveloped in this paper.The alumina sol precursor was prepared by the sol-gel and Al₂O₃/Fe mixedpowder was achieved by adding iron powder to the liquid-solid doping with hydrogen reduction in situ synthesis. Then the iron matrix composite reinforced by Al₂O₃particles was prepared by adding alloying elements of C or other alloying elementsbefore mixing cold press and sintering. XRD, SEM and TEM were employed toobserve and analysis the alumina sol as precursor, alumina powders and sintered,quenched Al₂O₃/Fe based composite materials. And also the hardness of the materialwas characterized.The results are shown as follows.（1） The alumina sol with stable performance could be prepared by the sol-gelmethod using aluminum nitrate and citric acid with molar ratio of1:3, initial pH valueof1at80℃. The dry gel transfers to no fixed shape, with γ-Al₂O₃, α-Al₂O₃+γ-Al₂O₃and α-Al₂O₃singly at600℃,800℃,950℃and1100℃, respectively. And Al₂O₃powder achieved at1100℃has a diameter of about20-30nm, with a sphericalmorphology and good distribution.（2） The iron matrix composites reinforced by Al₂O₃particles prepared by in situsynthesis has a dense structure, and the Al₂O₃particles combine better with iron matrixcomposites. The matrix structure is pearlite with singling adding C, while the othergroups are ferrite. And the reinforcement with Mo or without Mo is α-Al₂O₃phase orFeAl₂O₄.（3） The microstructure and properties of iron matrix composites reinforced byAl₂O₃particles are significantly affected by quenching. The matrix structure of thespecimen adding C element singly after quenching is martensite, while the matrixstructure of other groups has no change after quenching. And the hardness ofspecimens added with C element after quenching increased more than twice incomparison with that of before quenching. However, the hardness of specimens addedwith Mo element after quenching has a little improvement. And the hardness ofspecimens without C and Mo elements after quenching is less.