Dobijanje nanostrukturnih prahova u cilju proizvodnje novih disperzno ojačanih sinterovanih materijala u sistemu Cu-Al2O3

Abstract

U doktorskoj disertaciji je ispitivana mogućnost sinteze nanostrukturnih kompozitnih materijala na bazi bakra i glinice novom metodom, koja predstavlja kombinaciju termo-hemijskog postupka sinteze i mehaničkog legiranja. Termohemijska sinteza se odvija kroz tri faze i to: sušenje raspršivanjem rastvora nitrata, oksidaciono žarenje i redukcija. Metoda sinteze je razvijena sa ciljem dobijanja materijala sa superiornijim osobinama u odnosu na konvencionalne. U toku rada određeni su optimalni parametri procesa za svaku od faza sinteze, kao i karkaterizacija praha prekursora dobijenog hemijskim putem i finalnog praha dobijenog mehaničkim legiranjem različitim instrumentalnim metodama (SEM, XRD i AEM). Prahovi sa 1; 1,5 i 2% Al2O3 su sinterovani na različitim temperaturama u opsegu od 725-925°C u toku 15-120 min sa ciljem optimizacije parametara procesa sinterovanja dobijenih prahova. Određena je optimalna temperatura od 875°C i vreme od 1h. U cilju potvrđivanja upotrebnih osobina materijala, sinterovani uzorci su dalje mehanički i termički tretirani. Dokazano je da termo-mehanički tretman ima pozitivan uticaj na karakteristike materijala i kombinaciju električnih i mehaničkih svojstava koja se zahteva od ove vrste materijala. Vrednosti električne provodljivosti nakon termomehaničkog tretmana su na nivou od 61%IACS, a tvrdoće od 57HRF. Na osnovu mikrostrukturnih analiza i merenja električne provodljivosti i tvrdoće materijala, ojačavanje do kog dolazi u ispitivanom sistemu može biti objašenjeno mehanizmom koji čine disperzno, deformaciono i ojačavanje granicama zrna. Ojačavanje granicom zrna se postiže ne samo disperzoidom već i novoformiranom trećom fazom koja je detektovana u strukturi, čime se sprečava proces rasta zrna i povećava stabilnost materijala na povišenim temperaturama. Prednost predložene metode dobijanja se ogleda u velikom potencijalu za industrijsku proizvodnju i dobijanja značajnih količina prahova po relativno niskoj ceni, zbog jednostavnosti procesa sinteze i korišćenja sirovina sa niskom cenom za dobijanje materijala sa unapređenim osobinama. Ova doktorska disertacija je urađena u okviru realizacije projekta tehnološkog razvoja koje je finansiralo Ministarstvo za nauku i tehnološki razvoj Republike Srbije evidencioni broj 19032 ”Dobijanje nanostrukturnih prahova u cilju proizvodnje novih disperzno ojačanih sinterovanih materijala u sistemu Cu-Al2O3” (2008-2010).

This PhD thesis presents the possibility of nanostructured composite materials based on copper and alumina synthesis trough a new method, which is a combination of thermo-chemical synthesis and mechanical alloying. Thermochemical synthesis is carried out through three stages: spray drying of nitrate solutions, oxidation and reduction. Synthesis method was developed with the aim of obtaining materials with superior properties compared to conventional ones. For each phase of synthesis process parameters were optimized. Characterization of powder precursors obtained by chemical means and the final powder obtained by mechanical alloying was carried out by different instrumental methods (SEM, XRD and AEM). Powders with 1, 1.5 and 2% Al2O3 were sintered at different temperatures in the range of 725-925°C during 15-120min in order to optimize sintering process parameters obtained. Optimal sintering temperature at 875°C was determined and sintering time of 1h. In order to confirm utility properties, sintered samples were further mechanically and thermally treated. It is proven that the thermo-mechanical treatment has a positive influence on the properties of materials and a combination of electrical and mechanical properties that is required for this type of material. The values of electrical conductivity after thermo-mechanical treatment on the level of 61% IACS, and the hardness of 57HRF. Based on microstructural analysis and measurements of electrical conductivity and hardness of materials, reinforcement that appears in the examined system can be explained by complex mechanism involving dispersive, deformation and grain boundary strengthening. Grain boundary strengthening is achieved not only by dispersoide, but by the newly formed third phase detected in the structure, which prevents the process of grain growth and increases the stability of the material at elevated temperatures. The advantage of the proposed method is in it’s the great potential for industrial production and production of significant amounts of powders at relatively low cost because of the simplicity of the synthesis process and use of low cost raw materials for production of materials with improved properties. This PhD thesis is part of the technological development project funded by the Ministry of Science and Technological Development of Serbia, No. 19032 ”Obtaining of nanostructured powders for production of new dispersion strengthened sintered material in the system Cu-Al2O3” (2008-2010).