Microstructures And Properties Of The Carbon/Al-based Amorphous Composites

In recent years, Al-based amorphous alloys have attracted more and more attention because of their excellent properties, such as their high specific strength and low density,however, the low glass forming ability and poor plasticity at room temperature of Al-based amorphous alloys hinder their usages in practical engineering fields. In this paper, Al85Fe15 amorphous alloys have been successfully synthesized by mechanical alloying(MA). The Carbon(graphene Gr, carbon nanotubes CNTs and graphite C)/Al85Fe15 amorphous matrix composites have been fabricated by using mechanical mixing. The thermal stability of Carbon/Al85Fe15 amorphous matrix composites and the interface combination between different carbon materials and amorphous matrix alloy have been investigated. Bulk Al-based amorphous composite materials were prepared by using spark plasma sintering(SPS) and conventional powder metallurgy methods and the microstructure and mechanical properties of bulk alloys were analyzed. The results are as follows:(1) Al85Fe15 amorphous alloy was prepared by using MA. The results show that after 200 h of MA, Al85Fe15 alloy powder forms amorphous alloy with a small amount of face-centered cubic(fcc) Al under the certain MA condition. Prolonging the milling time from to 290 h, the alloy still keeps amorphous structure. The onset crystallization temperature(Tx) increase gradually with the increasing of milling time. The grain size decrease firstly and then are stable.(2) The Carbon(Gr, CNTs and C)/Al85Fe15 amorphous matrix composites were fabricated by using mechanical mixing. The results show that after 4, 6 and 8 h of mechanical mixing, the powder still contains amorphous phase, the values of Tx decrease with the increasing of milling time. 0.3 wt.% CNTs can be well dispersed in the matrix and produce mechanical bond with the matrix alloy after the mixing time of 8 h, moreover, much broken CNTs can be avoided. Based on the study of CNTs/Al85Fe15 amorphous matrix composite powder, 0.3 wt.% Gr and Gra can also be well dispersed and produce mechanical bond with the matrix alloy after the mixing time of 10 h. The values of Tx for containing 0.3 wt.% Gr and C alloy are 1300 and 1303 K, indicating that Gr and C addition decrease that of Al85Fe15 amorphous alloy. The crystallization activation energy(Ex) of the alloys with 0.3 wt.% CNTsaddition are largest than that of other alloys(3) Bulk Al-based amorphous composite materials were prepared by using SPS. The results show that the sintered bulk samples are fully crystallized, the Vickers hardness of adding different carbon materials obviously decrease and the relative density distinctly increase. In addition, particle surface melting, the part fusion between particles and stoma can be observed from the SEM images of the sintered samples.(4) Bulk Al-based amorphous composite materials were prepared by using conventional powder metallurgy method. The results show that the sintering samples with same pre-pressure are partially amorphous composite when the temperature is below 1273 K, the samples are fully crystallized when increasing the temperature. The density of the sintered samples increase with the increasing of temperature, moreover, the microhardness of samples are the largest which are sintered at 1173 K. The sintered samples are also amorphous composite under different pre-pressure and same temperature and the density and microhardness for the samples increase with the increasing of pre-pressure. Carbon/Al-based amorphous composite are sccessfully prepared under a pre-pressure of 1.875 GPa and 1173 K,the microhardness of sintered sample is obviously improved due to CNTs, Gr and Gra addition.