© Microstructure Evolution during Internal Oxidation of Copper-Rare Earth 
Alloys 
i Ivan Anzel*, Albert C. Kneissl** 
hat this 
*Faculty of Mechanical Engineering, University of Maribor, Slovenia 
a **[nstitute of Physical Metallurgy and Materials Testing, University of Leoben, Austria 
Versaturation 
he Sermination, 
119.) pia Abstract 
A Combination of rapid solidification and internal oxidation was used for producing a fine dispersion 
: of rare earth oxide particles in the copper matrix. An overall microstructural analysis has shown that 
the internal oxidation temperature, the rapidly solidified microstructure and its changing before the 
internal oxidation front strongly influence the mechanism of the internal oxidation process and the 
resulted microstructure. Internal oxidation in the solid state (at temperatures below the eutectic 
temperature-Tg) took place mainly by direct oxidation of the intermetallic particles and partly by 
dissolution of these particles ahead of the internal oxidation front and oxidation of the alloying 
element from the solid solution. In the semisolid state (ac.tL) the internal oxidation process 
occurred by precipitation of the rare earth oxides from the liquid phase and continued with 
solidification of the nearest surrounding melt. In the former case, the internal oxidation proceeding 
was unsuccessful in producing suitable oxide particles through the whole ribbon, while the internal 
Negra oxidation in the semisolid state leads to uniformly distributed, fine oxide particles in the Cu matrix. 
Introduction 
With the development of various composite materials the internal oxidation of heterogeneous alloys 
becomes again interesting (1,2). It is a well-known phenomenon which involves selective reaction 
of a second phase particles with oxygen diffusing in from the surface. The process can be used also 
for oxide dispersion strengthening (ODS) of copper. The strength in these alloys is increased by a 
fine dispersion of oxide particles, which act as barriers to dislocation motion (3). The strengthening 
effect depends on the size of the particles and on the nature of the particle-matrix interface. 
Rare earth oxides are also attractive candidates for dispersion strengthening of copper (2,4), but 
pose significant processing challenges owing to the low solubility of the oxide-forming elements in 
Cu. These elements occur in the cast structure as coarse intermetallic segregates that prevent a fine 
dispersion of oxide particles by direct internal oxidation process. The problem may be circumvented 
by a synthesis approach coupling rapid solidification (RS) and internal oxidation (10), followed by 
powder metallurgy consolidation. With the rapid solidification, nonequilibrium supersaturated solid 
solution of potential dispersoid-forming elements and a refined microstructure can be obtained. 
These supersaturated solid solutions decompose upon subsequent annealing at suitable temperatures 
to form fine intermetallic particles that can be internally oxidised to the corresponding oxides. 
The purpose of our investigation was to study the influence of the starting microstructure of Cu-RE 
(RE = Yb, Er) alloys and internal oxidation conditions on the mechanism of the internal oxidation 
process and on the resulting internal oxidation microstructure. The objectives were to identify 
optimal starting microstructure and internal oxidation conditions that will lead to uniformly 
distributed. fine. incoherent oxide particles in the Cu matrix. 
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