Processing of Copper Based Foil Hardened with Zirconia by Non-Deformation Method

© 2017 Materials Research. 2017; 20(3): 835-842 DOI: http://dx.doi.org/10.1590/1980-5373-MR-2016-0574 Processing of Copper Based Foil Hardened with Zirconia by Non-Deformation Method Luiz Eloi Vieira Juniora,b*, Tatiana Bendoa, Maria Izabel Nietoc, Aloísio Nelmo Kleina, Dachamir Hotzaa, Rodrigo Morenoc, João Batista Rodrigues Netoa a Programa de Pós-graduação em Ciência e Engenharia de Materiais - PGMAT, Universidade Federal de Santa Catarina - UFSC, 88040-970, Florianópolis, SC, Brazil b Fundação Universidade Regional de Blumenau, 89030-000, Blumenau, SC, Brazil c Instituto de Cerámica y Vidrio - ICV, Consejo Superior de Investigaciones Científicas CSIC, 28049, Madrid, Spain Received: August 2, 2016; Revised: March 6, 2017; Accepted: April 5, 2017 Flat sintered copper and copper-zirconia substrates, with zirconia nanoparticles contents of 1 and 3 vol%, were produced by aqueous tape casting and controlled sintering. Aqueous suspensions were prepared to a solid content of 58 vol% using 3 wt% commercial binder emulsion. The green tapes were treated at 350 ºC in air to remove organics and sintered at temperatures ranging from 800 to 1000 ºC in atmosphere of Ar/5%H2. Copper tapes reached almost full densification at 900 ºC. Composite with 1 vol% zirconia, sintered at 800 ºC, maintained high density and provided a noticeable increase of the mechanical strength, whereas further additions up to 3 vol% reduced the densification and the resulting mechanical performance became poorer. Keywords: Tape casting, Copper-zirconia, Metal-matrix composites, Particle-reinforcement, Mechanical testing 1. Background Copper is one of the most important non-ferrous metals used at large scale in industry. Its main property is the electrical conductivity, which is just below that of silver. Copper is generally used as bronze alloys with additions of Ni, Sn, Pb and C (graphite bronze). Copper alloys are used in environments requiring high corrosion resistance, ductility and thermal and electrical conductivities1. According to the literature, the values obtained from mechanical strength for copper commercially vary considerably depending on the manufacturing techniques products, such as molten copper and thermally treated or forged with severe deformations that require time and energy to achieve the final mechanical properties and which are correlated with the final grain size. In case of sintered components required properties is related mainly its porosity, in this case, an inversely proportional relationship. These values include tens (<50 MPa) to a few hundred (<400 MPa)2-4. Another useful tool for increasing the mechanical strength and wear of copper components can be the introduction of ceramic particles which are homogeneously dispersed. Table 1 shows some examples of ceramic materials used as reinforcement in copper matrix. As can be seen, there are a variety of ways to increase the mechanical strength of copper. Note that adding micrometer particles can increase their concentration within the metal matrix. Moreover, by adding up submicron or nanoscale particles, the concentrations are * e-mail: reduced because of the greater amount of ceramic composite particles per volume, leading to the reduction of their required mechanical and electrical properties. Conventional routes for the production of metal alloys and composite sintered with dispersion of nanoscale particles, such as high energy milling require high processing times for mixing, milling and dispersion of the second phase, and the thermal annealing treatment17,18. The colloidal route provides an alternative way to produce nanostructured composites with excellent microstructural homogeneity. Using knowledge dispersion of particles consolidated in the production of ceramic materials, the mixing process and homogenization phase in liquid medium is far more efficient than dry. Finally is obtained a different microstructure, controlled and reproducible beyond much less processing time than conventional processes. Among those applications, the potential use as a component in solid oxide fuel cells (SOFCs) is receiving current attention. There is an increasing interest to reduce the operating temperatures of SOFCs below 800 ºC without a remarkable loss in efficiency. The configuration using Ni/ YSZ as the anode, however, presents some disadvantages. When hydrocarbons are used as fuel, carbon deposition in the form of whiskers can occur decreasing the operational performance19. To solve this problem, copper anodes have been tested. Copper does not present the inconvenience of carbon deposition, it is reasonably tolerant to the presence of sulfur and is cheaper than nickel. Copper-based composites 836 Vieira Junior et al. Materials Research Table 1. Examples of ceramic materials used to produce copper matrix composites. Size (µm) Vol.% Processing Mechanical strength (MPa) Ref. 45 2.3 - 9.4 HP 280 - 600 [5] C-nanotube 0,02 0 - 2.0 CP x [6] Ni coated C 0.2 - 0.3 1.9 HP x [7] SiC 75 5.0 - 20 HP 150 - 97 [8] TiB2 3.0 - 5.0 15 - 60 HP 150 - 650 [9] 25 5.0 - 25 CP 180 - 350 [10] Reinforcement Ti3AlC2 Zr2Al3C4 Diamond 40 - 50 0 - 14 HP x [11] C-nanotube 0.01 - 0.02 0.1 - 0.4 HP 100 - 300 [12] Al2O3 < 0.1 1.3 - 3.8 CP < 40 [13] C-Fiber > 0.2 33 HP 150 - 270 [14] TiB2 - 0.77 Infiltration 300 - 510 [15] Ti2SnC 0.5 5.0 - 30 Legend: HP: Hot pressing; CP: Cold pressing. CP 164 - 326 [16] like Cu/YSZ and Cu/CeO2 have been proposed as anodes to work at intermediate temperatures20,21. However, a major limitation for those applications is to find suitable processing routes capable to produce homogeneous mixtures of metal powders with small amounts of ceramic particles. The scenario is much more complicated when one of the phases lies within the nanometric range. To obtain such nanostructured composites, the use of colloidal processing routes has demonstrated to be a powerful route. One of the most popular colloidal methods for shaping ceramics is tape casting, which is a low-cost technique for the production of thin substrates through a deposition/ evaporation mechanism. Tape casting is widely used to produce capacitors, sensors, piezoelectrics, heat sinks, and electrodes for SOFC22-24. As in any colloidal processing route, a major concern is the preparation of a well-dispersed suspension with the highest solids content, thus requiring the suitable selection of a deflocculant25-30. Other processing additives such as binders and plasticizers are also needed to provide the desired strength and flexibility. In order to produce suitable substrates, the slurries should behave as pseudoplastic fluids to have adequate flowability during casting and high viscosity at rest. This research aims to produce thick films of Cu-ZrO2 composites by an aqueous tape casting route for obtaining homogeneous mixtures of metallic copper with zirconia nanoparticles. Tape casting performance wi (...truncated)