Mechanical and Thermal Properties of Pulsed Electric Current Sintered (PECS) Cu-Diamond Compacts
- PDF / 679,212 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 54 Downloads / 222 Views
CTION
COPPER is widely used because of its high electrical and thermal conductivity, albeit it has low strength and quite high coefficient of thermal expansion (CTE).[1–3] To circumvent this, copper has been strengthened by several different ways, one being dispersion strengthening (DS) with dispersions possessing thermodynamic and chemical stability, low diffusivity, and low solubility in the copper matrix.[2,3] Diamonds are well known for high strength and good thermal properties,[4–8] so it can be expected that a Cu-diamond composite may have improved thermal properties, e.g., small CTE,[4–7] enhanced mechanical properties, and thermal stability.[6,9–11] These composites may be suitable for many applications, i.e., in electronic components,[4,8,12] heat-spreading substrates,[4] and heat sinks.[5,7–9,13] Improvements in mechanical properties of the products can be achieved by limiting the grain growth during processing.[2,3,14] This is possible by applying nonconventional consolidation methods that exploit high sintering speed, short sintering time, and low temperature like pulsed electric current sintering (PECS; also known as spark plasma sintering, SPS). This method utilizes pulsed direct current (DC) and uniaxial pressure RIINA RITASALO, Doctoral Student, YANLING GE, Researcher, and SIMO-PEKKA HANNULA, Professor, are with the Aalto University School of Chemical Technology, P.O. Box 16200, 00076, Aalto, Espoo, Finland. Contact e-mail: riina.ritasalo@aalto.fi ULLA KANERVA, Research Scientist, is with the VTT Technical Research Center of Finland, P.O. Box 1300, 33101, Tampere, Finland. Manuscript submitted January 29, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
for compacting powders.[14] Studies on PECS-processed Cu with nanodiamonds,[10,13] submicron- or micron[11,15,16]-sized diamonds are quite limited. Hanada et al.[10] studied mechanically milled nanocomposites containing 0 to 30 at. pct (i.e., about 0 to 8 wt pct) nanodiamonds after consolidation. The PECS resulted in high density, but agglomeration and low hardness of 0.57 to 0.69 GPa (58 to 70 HV), whereas a homogeneous microstructure and higher hardness of 0.78 GPa (80 HV) were achieved by hot pressing and subsequent hot extrusion (HP + HE). One of the biggest challenges in processing of Cu-diamond composites is the poor wettability between copper and diamond, which leads to weak interfacial bonding[7,8,10,11,15] and thus high CTE and low hardness. This issue has been tackled also by PECS using carbide-forming alloying elements, e.g., Cr, B, Si, or Ti,[11,13,15,16] to facilitate interfacial reactions. For example, Nunes et al.[13] prepared a Cu-Cr-nanodiamond powder mixture by ball milling and subsequent annealing to promote carbide precipitation before consolidation by PECS. After PECS, a homogeneous dispersion of diamonds was found even if bonding was good; no difference to the non-doped sample was found. Also, Chu et al.[15] reported good interfacial bonding between Cu- and Cr-coated micron-sized diamonds after PECS, similar to the finding of Zhang et
Data Loading...
