Oxidation Behavior of Ag-20Cu-30Cr Alloy Prepared by Powder Metallurgy Method in 0.1 MPa Pure O2 at 700 and 800 °C

Abstract

The oxidation behavior of Ag-20Cu-30Cr alloy prepared by powder metallurgy method was investigated in 0.1 MPa pure O 2 at 700 and 800 °C. The alloy oxidation kinetics deviates from the parabolic rate law and consists of several quasi-parabolic stages with different rate constants. The alloy oxidation rate at 800 °C is bigger in the initial 4 h and afterward smaller than that at 700 °C up to 24 h. Ag-20Cu-30Cr alloy produces complex oxide scales. At 700 °C, the outer region consists of CuO layer partly covered by metal Ag, while the inner mixed oxidation region consists of alloys and oxides. With the increase of time, an irregular continuous and protective thin layer of Cr 2 O 3 is produced at the base of oxide scales. At 800 °C, the outer region consists of CuO layer, the middle region consists of a metal Ag layer plus a mixed layer of Cu, Ag and Cr oxides or their double oxides, while the inner region consists of a regular continuous and protective thin layer of Cr 2 O 3 , which avoids the further oxidation of the alloy.

Oxidation Behaviour of Microstructurally Highly Metastable Ag-La Alloy

“…In practice, nearly all metallic materials are thermodynamically unstable, and convert to oxides in most high-temperature environments. The proceeding of the oxidation process depends on the materials’ composition and on the environmental conditions (temperature and oxygen partial pressure) [ 1 , 2 , 3 ]. Basically, the high-temperature oxidation of alloys can be divided into two limiting cases: (i) oxidation processes where only external oxide phases are formed; (ii) oxidation processes with internal oxide formation, which can be terminated by transition to the external oxidation.…”