Preparation Of Nanocrystalline Al-Fe In-situ Composites By Mechanical Alloying And Spark Plasma Sintering

Al-Fe composites are characterized by light weight, high specific strength, abundant raw materials and low price, which can be partly substituted for titanium alloy, conventional heat resistant Al alloy, steel and other materials, having wide application prospects in automobile, aerospace, military industry and other fields. In this work, nano-crystalline Al-Fe composites were in-situ synthesized by mechanical alloying and spark plasma sintering(MA-SPS) methods. The phase constitution, microstructure and element distribution were characterized by using analytical means of X-ray diffraction(XRD), scanning electron microscope(SEM), transmission electron microscope(TEM), energy dispersive spectrometer(EDS) and so on. The mechanical properties such as micro hardness, compressive and tensile properties were also tested. The effects of MA key parameter- ball gradation and Fe content on the microstructure and mechanical properties were systematically investigated. The main research results are as following.In-situ Al13Fe4/Al composites with nearly full dense were fabricated by MA-SPS, whose microstructure were composed of ?-Al and Al13Fe4 phases. Reinforced phase Al13Fe4 existed in three morphologies: large particles(1~2 ? m), short-clavite ultrafine particles(0.1~1.0 ?m) and nano particles(~20 nm). The former two kinds of Al13Fe4 phase formed by the reaction of undissolved Fe particles and the Al melt whilst the last one originated from the precipitation of supersaturated Al(Fe) solid solutions.Using ball gradation during MA optimized the structure and property of Al13Fe4/Al composites. Compared with no ball gradation, gradation of grinding balls could effectively enhance the MA effect, the grain size was smaller(9.75nm) and the solid solubility was higher(3.7 at.%), which was far beyond the limit equilibrium solid solubility(0.03 %); after SPS, the sintered sample with ball gradation showed improved ductility with 13.6% in plastic deformation, which was mainly due to the combination of large quantities of coarse ?-Al particles and ultrafine Al13Fe4 particles.Special attention was paid to the effects of Fe content on microstructure and properties of the composites. Three compositions(Al-2Fe, A-10 Fe, Al-12.5Fe, at.%) were prepared by MA for 80 h. After MA, the grain size reduced from 15.65 nm to 9.35 nm and the solid solubility increased from 15.65 nm to 9.35 nm, while the powder size decreased first and then increased for the Al-10 Fe with the minimum size(~10 ?m). After SPS, with the increase of Fe content, the strength raised while the ductility reduced: the hardness increased from 127 to 326 HV, and the compressive strength also added from 615.5 to 873.4 MPa, with the plastic deformation dropping from 43.4 down to 6.5% in contrast. In summary, Al-10 at.%Fe alloy showed the most excellent compressive performance: hardness was up to 227 HV(1.2 GPa), and its compressive s trength was 845.8 MPa with 13.6% plastic strain at room temperature. Among the three samples, Al-2Fesamples shows the best tensile properties with tensile strength 263.03 MPa and 17.62% in elongation.