On nanostructured molybdenum–copper composites produced by high-pressure torsion

Abstract

Nanostructured molybdenum-copper composites have been produced through severe plastic deformation of liquid-metal infiltrated Cu30Mo70 and Cu50Mo50 (wt%) starting materials. Processing was carried out using highpressure torsion at room temperature with no subsequent sintering treatment, producing a porosity-free, ultrafine-grained composite. Extensive deformation of the Cu50Mo50 composite via two-step high-pressure torsion produced equiaxed nanoscale grains of Mo and Cu with a grain size of 10-15 nm. Identical treatment of Cu30Mo70 produced a ultrafine, lamellar structure, comprised of Cu and Mo layers with thicknesses of $ 5 and $ 10À20 nm, respectively, and an interlamellar spacing of 9 nm. This microstructure differs substantially from that of HPT-deformed Cu-Cr and Cu-W composites, in which the lamellar microstructure breaks down at high strains. The ultrafinegrained structure and absence of porosity resulted in composites with Vickers hardness values of 600 for Cu30Mo70 and 475 for Cu50Mo50. The ability to produce Cu30Mo70 nanocomposites with a combination of high-strength, and a fine, oriented microstructure should be of interest for thermoelectric applications.

Microstructure and Failure Characteristics of Nanostructured Molybdenum–Copper Composites

“…The grain size of the Mo‐phase is not determinable by SEM; however, from Figure f, it can be inferred that it is smaller than the one to be expected for the equilibrium or saturation grain size of the pure elements, which is rather in the range of a couple hundreds of nanometers . A more comprehensive investigation of the microstructural evolution of the present alloy can be found elsewhere …”

“…[31] A more comprehensive investigation of the microstructural evolution of the present alloy can be found elsewhere. [25] Along with the microstructural refinement, the hardness and tensile behavior was investigated (Figure 4). The hardness as a function of applied strain (Figure 4a) was obtained by converting the radial positions of the hardness measurements into γ (Equation ( 1)).…”

“…[19][20][21][22][23][24] Molybdenum is ideally suited for microelectronic packaging because its thermal expansion coefficient is close to the one of Si. [21] In a former study where Cu 30 Mo 70 was subjected to high pressure torsion (HPT), it could be already shown that a nanostructured, oriented microstructure with hardness levels up to 600 HV is achievable, [25] which would be also well suited for thermoelectric applications. The idea for a continuation of the studies on this alloy is twofold: on the one hand, UFG copper has shown to have good damage tolerance [26] whereas Mo is known to become severely brittle in the SPD state.…”

In situ atomic-scale observation of oxidation and decomposition processes in nanocrystalline alloys

“…Nanostructuring and alloying are strategies to obtain enhanced properties for bulk metals 1 – 5 . Severe plastic deformation (SPD) can effectively generate novel metallic nanocrystalline materials by drastically refining and mechanically alloying normally immiscible composites 6 – 10 . Now combined with powders processing technique, SPD is extended to produce nanocrystalline alloys with desirable compositions directly from blended powders without any precasting 11 , which is a convenient low-cost route in manufacturing applicable bulk materials.…”