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Production of in Situ Cu/NbC Nanocomposites Powders via Mechanical Alloying and Investigation the Mechanical (Wear Resistance) and Physical (Electrical Conductivity) Properties

Gholami Shiri, Sajjad | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43818 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Abachi, Parvin; Purazarang, Kazem
  7. Abstract:
  8. For application such as electrical contacts and spot welding electrodes, both high electrical conductivity and wear resistance are required. Additionally, such parts should have structural stability at evaluated temperature. Copper based composites containing carbides or oxides reinforcement can be the good choice for production of such parts. In present work, in-situ Cu/NbC composite via mechanical alloying with homogenous distribution of nano reinforcement particle has been produced. For this purpose, in first stage, copper powder was milled with 5, 8, 10 and 12 wt. % of niobium powder in two types of mills, i. e. vibratory dicky mill and planetary ball mill for 5 and 32 h respectively. At second stage, stoichiometric amount of graphite powder for formation of final composition of Cu-6.36, 10.11, 12.57 and 15vol. % NbC were added to the Cu-Nb alloyed powder. At this stage, duration was selected as 2 and 32 h for vibratory dicky mill and planetary ball mill, respectively. Milled powders with vibratory dicky mill were consolidated via two-step-press plus spark plasma sintering (SPS) processes. The milled powders using planetary ball mill were used to production of functionally graded parts. Densification route was two- step press. A side of FG consists of 100% pure copper and the other side, composite with percent of NbC. Afterward, sintering at 900 0C for 1h under 10-3 torr vacuum performed on specimens for farther consolidation. Specimen's microstructure was investigated using field emission scanning electron microscopy (FESEM) and XRD. Physical properties such as density and electrical resistivity were determined. The hardness and wear tests were performed on specimens. XRD peaks showed complete dissolution of Nb in Cu after 5 h and partial formation of NbC after 7 h of milling with vibratory dicky mill. Complete formation of NbC was occurred after sintering. Production of Cu/NbC with crystallite size between 20- 40 nm and NbC particle size of 35 nm were confirm with XRD test and FE- SEM images. Comparing the FE-SEM image, no great grain growth was observed after sintering which confirms structural stability of produced composite at high temperature. Results of electrical resistivity measurements test showed a reduction of electrical conductivity by increasing reinforcement. In Cu/NbC (15 vol.%) electrical conductivity was reduced to 31.12 % IACS. Electrical conductivity of FG parts were high and an electrical conductivity of 82 %IASC was achieved in specimen of Cu/NbC (6.36 vol. %). Increasing of hardness and wear resistance were gained in composite specimens in comparison to pure copper. Wear resistance of FG parts were considered similar to composite specimens which show high wear resistivity in comparison to that of the pure copper sample. So, composite sample with good mechanical properties and structural stability in high temperature as well as good electrical conductivity can be used in industrial application. Although, FG parts with both high electrical and mechanical properties can be the best candidate for electrical contact and spot welding electrode applications
  9. Keywords:
  10. Nanocomposite ; Mechanical Alloying ; Specific Electrical Resistivity ; Wear Resistance ; In-Situ Reaction ; Copper/Niobium Carbide (cu/Nbc)Nanocomposite

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