Mechanical Properties of Sputter-Deposited Nb 5 Si 3 Film and Nb 5 Si 3 /Nb Microlaminates
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layers). Of these designs, multilayer composites potentially offer an architecture tailored to combine desired high-temperature properties by optimizing layer thickness for various materials. Metal/intermetallic (or ceramic) microlaminates have been processed using vacuum hotpressing of foils, physical vapor deposition, and casting and solid-state reaction. For example, Nb 5 SWINb laminates have been fabricated by vacuum hot-pressing Nb5 Si3 compacts with Nb have beenmagnetron producedsputtenng. by a casdin ' foils, Iwo-phase Nb5 Si 3-Nb alloys or in-situ composites by planar process, and Mo/A120 3 and Nb/MoSi 2 have been processed Vacuum hot-pressing and casting yield microlaminates with thick (> 50 ltm) alternating layers, whereas sputtering is generally used to deposit extremely thin-layered (10 nm) microlaminates. Vacuum hot-pressed Nb5 Si3/Nb laminates exhibited significant toughness increases over that of monolithic Nb 5 Si3. In-situ fracture monitoring of the laminate revealed crack blunting by the Nb layer. Also, the two-phase Nb 5 Si 3/Nb alloys produced by casting and subsequent extrusion processing exhibited balanced mechanical properties, having significant strength up to 1500"C and high fracture toughness at room temperature. This toughening has been primarily attributed to ductile particle crack bridging in the presence of Nb-rich particles. Although these composite architectures provide structural material that potentially offers high-temperature strength and low-temperature toughness, mechanical properties are influenced significantly by processing methods and associated microstructures. To effectively produce contamination-free material with a controlled microstructure, an in-situ processing technique must be developed to fabricate the NbsSi 3/Nb microlaminate system. Our investigation is focused on whether a sputter deposition technique can produce in-situ Nb 5SiJ/Nb microlaminates and Nb5 Si3 films with high purity and a controlled microstructure. A sputtering technique also provides unique flexibility to process Nb 5 Si3/Nb microlaminates with 397 Mat. Res. Soc. Symp. Proc. Vol. 356 ©1995 Materials Research Society
optimum ratios and thicknesses of alternating layers (Nb 5 Si 3 and Nb) to obtain the best combination of strength and toughness for high-temperature structural components. This paper discusses the processing conditions, microstructure, and mechanical properties of as-deposited Nb 5 Si3/Nb microlaminates constructed from alternating layers of equal thickness of crystalline Nb 5Si 3 and Nb with modulation wavelengths, X,of 40 and 200 nm and monolithic Nb5 Si3 films. EXPERIMENTAL PROCEDURE MaterialProcessing: Materials were deposited in a three-cathode RF/DC magnetron sputtering system with a sputter-down cathode configuration. Deposition rates were determined by sputtering the Nb and Si separately, using high-purity Ar onto optically flat sapphire substrates at several power settings with substrate temperatures ranging from 20-800"C. Nb and Si were sputtered using DC potentials, with
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