Experimental determination of threshold pressure and permeability based on equation-solving method for liquid metal infiltration processes

A new method for determining two key parameters(threshold pressure and permeability)for fabricating metal matrix composites was proposed based on the equation-solving method.An infiltration experimental device was devised to measure the infiltration behavior precisely with controllable infiltration velocity.Two experiments with alloy Pb-Sn infiltrating into Al2O3 preform were conducted independently under two different pressures so as to get two different infiltration curves.Two sets of coefficients which are functions of threshold pressure and permeability can be obtained through curve fitting method.By solving the two-variable equation set,two unknown variables were determined.It is shown that the determined threshold pressure and permeability are very close to the calculated ones and are also verified by another independent infiltration experiment.The proposed method is also feasible to determine the key infiltration parameters for other metal matrix composite systems.

Effect of Growth Temperature on Carbon Nanotube Grafting Morphology and Mechanical Behavior of Carbon Fibers and Carbon] Carbon Composites

High-purity carbon nanotubes （CNTs） with different orientation and lengths were grafted on carbon fibers （CFs） in woven fabrics by using double injection chemical vapor deposition and adjusting the growth temperature. Scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and Raman investigations reveal that the grafted CNTs change from being predominantly aligned and uniform in di- ameter to absolutely disordered and variable in diameter, whilst they show significantly increased crystallinity, as the growth temperature is increased from 730 ~C to 870 ~C. In tensile tests of fiber bundles, much more strength degradation of CFs was observed after the growth process at higher temperature than that at lower temperature. These hybrid preforms produced at different growth temperatures were used to reinforce carbon/carbon （C/C） composites. An increment of 34.4% in out-of-plane compressive strength （OCS） was obtained for the composites containing CNTs grown at 730℃, while the OCS increment exhibits an obvious decrease with increasing the growth temperature. Compared with the higher growth temperature, the lower temperature contributes to the decrease in the strength loss of reinforcing fibers and meanwhile the growth of large extending length of CNTs, which can provide long reinforcement to the pyrocarbon matrix, and thus increase the compressive strength better.