Study on defects of 2D-Cf/Al composite prepared by liquid-solid extrusion following vacuum infiltration technique

Abstract

Two-dimensional Cf/Al composites were fabricated by liquid-solid extrusion following vacuum infiltration technique (LSEVI), and defects were studied and analyzed through optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope(TEM), and the tests of ultimate tensile strength (UTS). Through research, it was found that gas impurities were the main factors to generate hole defects within the 2D-Cf/Al composites, so vacuum level of the test system should be higher than 0.09 MPa. The infiltration of composites would not be sufficient and uniform under the low squeeze pressure of 50 MPa and low squeeze temperature of 590 °C. However, when squeeze pressure was larger than 90 MPa, fiber damage appeared, and macro internal cracks even occurred if it was over 100 MPa. Poor tensile behavior of composites between carbon fibers and matrix might arise because of the inappropriate process parameters. Brittle tensile fracture of composites was observed under the higher preform preheating temperature of 640 °C, and Al4C3 was found. Separated fibers and aluminum alloy of tensile fracture might occur under the lower preheating temperature of 580 °C. These defects hindered the improvement of property of Cf/Al composites greatly, and they should be avoided. Through contrast of UTS, internal cracks and poor tensile behavior were the most detrimental factors. Their UTSs were 45 and 117 MPa, respectively, which were less than 120 MPa of matrix. Improved process parameters were used to prepare the 2D-Cf/Al composite, and its defects were seldom found, so UTS of composite was improved 93.3 % than that of matrix.