Structure and mechanical properties of Al/Al xO y vacuum- deposited laminates

Abstract

High yield strength materials can be fabricated by many techniques. A method proposed by Koehler is to alternate thin layers of a high shear modulus material with thin layers of a low shear modulus material. The layers must be less than one hundred atomic layers in thickness and must be single crystals of similar lattice spacing epitaxially grown on top of each other. The mechanical effect is to inhibit dislocation formation and the mobility of dislocations through the solid. The stress required to move a dislocation through the laminate can be of the order of 1% of the lower modulus material. A novel technique has been developed to produce a laminate of Al/Al x O y by a pulsed gas process in an electron beam gun system. Samples of 25 μm and thicker have been readily produced. The surface finish of the growing deposit appears to remain as smooth as the glass substrate. The tensile testing data for layer spacings of 50–1200 nm show that the material obeys a Hall-Petch relation for yield strength. The friction stress was measured directly on a pure vapor-deposited sample at 27 MPa. The K value was found to be 0.086 MN m - 3 2 .