Selective Etching and Laser Melting Studies of Monotectic Composite Structures

Abstract

Thin slices of directionally solidified, fibrous composite, monotectic alloy samples have been selectively etched to remove the fibrous phase, so to produce fine sieves of filters having pore diameters ≲10μm. Alloys in systems Al-In, Al-Bi and CuAl-Pb have been examined using as etchants aqueous nitric acid (Al-In, Al-Bi) and aqueous citric acid (CuAl-Pb) without applied anode voltages. These alloys and etchants illustrate examples in which fiber and matrix are attacked to different extents (Al-In), the phase interface is selectively attacked (Al-Bi) or only the fibers are attacked (CuAl-Pb). Hole sizes and perfection are compared for etching times, concentrations and anode voltage.Laser melting of the surface of CuAl-Pb samples has been used to screen or frame areas of the composite microstructure and also shows how local melting of the fibrous Pb phase can be used to assess the heat affected zone.