Characterization of dispersion strengthened copper with 3wt%Al2O3 by mechanical alloying

Abstract

The copper matrix has been dispersion strengthened with 3wt.%Al2O3 by mechanical alloying. Commercial alumina powder with an average particle size of 0.75mm was used for alloying. The mechanical alloying process was performed in a planetary ball mill up to 20h in air. After milling all powders were treated in H2 at 4000C for 1h, and finally hot pressing was used for compaction (800oC, 3h, Ar). Structure observations revealed a lamellar structure (Al2O3 particles largely restricted to interlamellar planes between adjacent copper lamellae) accompanied also by structure refinement. These structural changes were mostly completed in the early stage of milling, and retained after compaction. Micro hardness was found to progressively increase with milling time. So, after 5h of milling the micro hardness of the Cu+3twt%Al2O3 compact was 1540MPa, i.e. 2.5 times greater than for the as-received electrolytic copper powder (638MPa) compacted under identical conditions, while after 20h of milling it was 2370 MPa. However after exposing the tested compact at 800oC up to 5h, the achieved hardening effect vanished.

Osnova bakra disperzno je ojačana mehaničkim legiranjem sa 3tež.,%Al2O3. Za ojačavanje je korišćen komercijalni prah Al2O3 prosečne veličine čestica 0,75mm. Mehaničko legiranje izvršeno je u planetarnom mlinu sa čeličnim kuglama u trajanju do 20h. Posle redukcije (4000C/1h, H2), prahovi su kompaktirani toplim presovanjem (8000C/3h, Ar, 34MPa). Već na početku mlevenja prahova došlo je do usitnjavanja zrna i stvaranja lamelarne strukture, sa česticama Al2O3 raspoređenim po površinama susednih lamela. Ova struktura čestica praha zadržala se i posle kompaktiranja. Sa vremenom mlevenja mikrotvrdoća kompakata raste do 2370MPa. Posle 5h mlevenja mikrotvrdoća kompakata Cu+3tež.%Al2O3 (1540MPa) je 2,5 puta veća u odnosu na mikrotvrdoću kompakta od praha elektrolitičkog bakra komapktiranog pod istim uslovima (638HV). Međutim, efekat ojačavanja gubi se nakon žarenja na 800oC.