EFFECT OF COLD DEFORMATION ON HIGH TEMPERATURE OXIDATION OF COPPER

Abstract

The oxidation of Cu and its alloys at higher temperatures lead to considerable loss due to sealing. This necessiated the study, on behaviour of Cu and its alloys at high temperature in the oxidizing environment. The addition of alloying elements have found to improve the oxidation resistance such as Al, Si, Sn, Mn, Be etc. Cu is also used in form of strips which are formed by cold rolling operation. Cold rolling will lead to deformation. The extent of reduction will effect the morphology of crystals and extent of residual stresses in the rolled material.. In the present work an attempt has been made to investigate the effect of degree of reduction by cold rolling on the oxidation behaviour of pure Cu in lower as well as higher temperature ranges i.e. 400 ,500°Cand 800, 900°C respectively. The Cu sheet has been given deformation of the order of 20/, 30/ and 50/. The oxidation runs have been conducted in a thermogravimetric set up using Quartz helical spring. The data has been examined for determining the rate law governing the oxidation. The oxidation products have been examined by optical metallography, scanning electron microscopy and X—ray diffractometry. iv For both undeformed and deformed specimens the increasing temperature of oxidation leads to increase in the rate of oxidation, parabolic rate constants at lower temperature are of the order of (.83 — 2.49) x 10-8 gm2/cm4 sec. and for higher temperature (4.98 — 17.015) x 10-8 gm2/cm4 sec. The extent of weight change is manifold at higher temperatures i.e. 800,900°C as compared to 400 and 500°C. The weight gain increases with the extent of deformation. The scale formed at lower temperature is very fragile for deformed and undeformed samples, whereas at higher temperatures scale is much more adherent and continuous. From the X—ray diffractograms, it's clear that both phases i.e. CuO and Cu20 are present. At lower temperatures concentration of CuC is more while at higher temperatures concentration of Cu20 is more than CuO.