Nanoscale/Multilayer Gradient Materials for Application in the Electromagnetic Gun Systems
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*US Army Armament Research, Development and Engineering Center, Picatinny Arsenal, NJ "**LawrenceBerkeley Laboratory, University of California Berkeley, CA
ABSTRACT Analysis of fired rails from electromagnetic railguns indicates severe surface damage occurs due to high current arcing and tribological mismatch. We have explored the behavior of several nanoscale multilayered materials as possible routes to improve the thermomechanical properties of the rail and armature materials. Structures investigated include (i) Ti-Co alloy on Ta-Cu alloy on dlc (diamond-like carbon) on stainless steel; (ii)Ti-Co alloy on Ta-Cu alloy on dlc on Cu, (iii) Ti-Co alloy on Ta-Cu on Cu; and (iv) Ti-Co on Ta-Cu alloy on Al. The alloys were all 50:50 at% and film thicknesses were in the range 400-1000 A. The films were formed using a repetitively pulsed vacuum arc plasma deposition method with substrate biasing- and ]BAD-like techniques. The surfaces were characterized by scanning electron microscopy, transmission electron microscopy, Rutherford backscattering spectroscopy, optical microscopy, microhardness measurements, arc erosion resistance and scratch resistance tests. Preliminary results show improvement in the microhardness, arc erosion resistance and scratch resistance, most especially for the dlc-coated surfaces. This kind of multilayered approach to the fabrication of electromagnetic railgun and armature surfaces could be important for future advanced Electromagnetic EM Gun systems. INTRODUCTION Copper and aluminum have been used in the design of the electromagnetic (EM) rails and armatures. The primary reasons for selecting these materials are based on the high electrical and high heat conductivities of both metals. Recent data indicate that in addition to these two important properties, the creep behavior also plays an important role. This is particularly so when the EM gun is designed to function in the hypervelocity regime with repeated firing capability. Research on the materials behavior of copper railguns and aluminum armatures was initiated in the early 1980s by several universities and centers where most ofthe EM gun research thus far has been conducted. Based on these efforts, the thermomechanical behavior of most elements and alloys materials used in EM system, such as Cu, Mo, W, and A] alloys, has been known for some time. Thermoionic and thermoelectric properties have also been investigated. In addition, extensive data on the behavior ofthese materials have now become available through simulation, structural design studies, laboratory studies of materials commonly employed in various phases of the EM gun, theoretical results derived from application of the imposed electrodynamic conditions, fluid dynamics, and the characteristics of field tested launch package materials. These investigations have shown that the electromagnetic and electrodynamic properties of the railgun vary with time and space throughout the length of the gun barrel. From a structural design standpoint these variations, if true, give rise to seve
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