Microstructural evaluation and mechanical properties of Al-CNT nanocomposites produced by different processing methods

Abstract

In this research, the semi-wet (SW) and slurry based (SB) methods were applied to synthesize Al-1.5 wt.%CNT nanocomposites powder. The initial 30 mm diameter compacted billets were produced through cold pressing and pressure-less sintering at 550 °C for 2 h for both types of nanocomposites. The billets were hot extruded at 400 °C to produce 10 mm diameter rods. The synthesis parameters of composites were investigated through experiments of tension, compression, FTIR, XRD, STA and Raman. The dispersion of CNTs within Al powder and fracture surface analysis was studied through FE-SEM.The yield and tensile strength of pure Al sample were measured as 90 and 136 MPa, respectively. These values were increased to 110 and 170 MPa for SW sample and improved to 152 and 203 MPa for SB product, by adding 1.5 wt.% CNT to pure Al. The strengthening effect of fibers was investigated using load transfer mechanism with fiber length less than critical value (l < lc) for SW and long fiber issue (l > lc) for SB samples. According to the fracture surface analysis, the bridging and CNTs fracture phenomena were observed in SB specimen and CNTs pull out was detected for SW sample. These results showed good agreement with strengthening efficiency of fibers (R) versus shear stress diagram including R = 25.6 in CNTs fracture and R = 13 in pull out regions. The Al4C3 interphase formation was characterized by XRD and Raman spectroscopies whereas end-contact and side-contact of carbides around CNTs were suggested as preferred sites for SB and SW products, sequentially.