Research On Iron Matrix Composites Reinforced By In-situ Al₂O₃ Particles

In recent years, copper matrix, aluminum matrix, magnesium matrix and zinc matrix composites reinforced by Al₂O₃ particles have made great progress, while the progress of iron matrix composites reinforced by Al₂O₃ particles was relatively slow. The focus of current research also focuses on improving wettability between iron and Al₂O₃ particles.In this paper, self-made Al(OH)3 powder, as precursor, was mixed with Fe powder to research and develop a kind of iron matrix composites reinforced by Al₂O₃ particles.Ethanol, which is much smaller surface tension than water, can effectively reduce agglomerating force and prevent from agglomerating when aluminum hydroxide is dried. It is, in this paper, ethanol that was used as reaction media. Aluminum nitrate was dissolved in ethanol (absolute ethyl alcohol) to form the solution with a certain concentration, then the ammonia was slowly dropped, constantly stirring, into it to neutralize and form white precipitate, after washing with ethanol, filtering and drying, some aluminum hydroxide, a kind of white ultra-fine powder, is obtained. Aluminum hydroxide, by calcining at 1200℃about 3 hours, become intoα- Al₂O₃. Compared with the original method that neutralization reaction was reacted in water, then Al(OH)3 was repeatedly washed with ethanol, a large number of ethanol can be save to achieve the same effect.Aluminum hydroxide powder and iron powder, in a certain proportion, fully are mixed, and by pressing and sintering, iron matrix composites reinforced with in-situ Al₂O₃ particles was made. The effect of carbon content on microstructure of sintered compacts has been studied in this paper. The experimental results demonstrated as follows: When the content of carbon was 1.2%, there were no particles of Al₂O₃ in the sintered compacts, in contrast, a great number of hercynite was found, which aluminum hydroxide reacted with iron to form at high temperature. The research results above provide a new method for the sintering synthesis of hercynite that is a kind of new-type high-performance refractory materials. When content of carbon was above 4% and reducing atmosphere became strong to restrain formation of hercynite, aluminum hydroxide formedα- Al₂O₃ particles after dehydration. A lot of Al₂O₃ particles can be seen in iron base when volume fraction of Al₂O₃ particles was 10%, while many holes which Al₂O₃ particles dropped off to leave can be found when volume fraction was 20%. In addition, another tester by directly adding 10%(Vol)Al₂O₃ particles into iron powder was made to contrast with one by in-situ autogenous. The results showed that the combination between Al₂O₃ particles and iron base by in-situ autogenous was better than by directly adding.Finally,The effect of sintering temperature on structure and properties were studied. With the decreasing of sintering temperature, the bond between Al₂O₃ particles and iron base became better and better. When the sintering temperature was 1050℃, sintering of iron base wasn't enough, hardness of the tester was low and abrasive resistance was the worst; When the temperature was between 1100℃and 1150℃, hardness of the tester was higher and abrasive resistance was the best, because the bond between Al₂O₃ particles and iron base was good, thus Al₂O₃ particles can effectively resistant cutting and scratches by Al₂O₃ sand paper; When the temperature reached and exceeded 1200℃, although hardness was high, the bond between Al₂O₃ particles and iron base was worse, Al₂O₃ particles easily dropped off, the abrasive resistance had fallen. Therefore, the best sintering temperature is 1100-1150℃under this experiment condition.