UC San Diego

A aluminum matrix-W rod/wire structural material in support of DARPA initiative BAA 08-23 was developed and its density and mechanical strength ascertained, both being part of the DARPA matrices. Aluminum tubes and four 90 degree cross-ply tungsten fiber layers were arranged such that under extreme static pressure conditions the aluminum would viscoplastically flow into the tungsten arrangement to create a metal matrix composite. It was found that a cold isostatic process induced "Brazilian" fracture in the tungsten fibers and that the pressurization rate affected the onset of buckling of the tungsten fibers coiled in the hoop direction. The best results were obtained with two treatments using a hot isostatic pressing process at 500 Celsius and 200 MPa, one treatment for each pair of tungsten fiber layers. No noticeable reaction between aluminum and tungsten was detected. No "Brazilian" fracture and reduced buckling of the tungsten wire in the axial and radial directions were achieved with this manufacturing process. The resulting samples in this successful approach had approximately the desired density of steel, 7.8 g/cc, and an average mechanical strength of 453 MPa, exceeding the DARPA phase 1 matrix of 345 MPa