The water-cooled designs with Cu-alloys as heat sinks are being considered for the cooling system of ITER. Pure copper has a very high thermal conductivity but its strength is relatively low. Furthermore, the lifetime of pure copper is limited by its high creep, swelling rate and irradiation hardening. Pure copper can be strengthened by different ways, such as cold working, grain refinement, solid solution, precipitation hardening or dispersion of hard particles. Dispersion strengthened Cu-0.8wt%Y has been produced by a powder metallurgy route that includes the consolidation by hot isostatic pressing at 1123 K and 172 MPa. Cu-0.8wt%Y microstructure is characterized by equiaxial grains with sizes ranging from 0.5 to 30 mm. Yttrium-rich particles with an average size of 0.92 mm have been observed inside the grains and also in the grain boundaries. The tensile curves performed from room temperature to 773 K have revealed that both the YS and the UTS decrease on increasing the temperature. The mechanical measurements have shown that the presence of yttrium-rich particles in the copper matrix yields to a strengthening of Cu-0.8wt%Y.

Abstract

Mechanical Behaviour

Name Address e-mail

Gabriel Carro Departamento de Física, Universidad Carlos III de Madrid

Avd. Universidad 30, 28911-Leganés, Madrid (SPAIN) gcarro@fis.uc3m.es

Conclusions A fully dense Cu-0.8wt%Y alloy has been produced by HIP. The microstructure consists of a Cu matrix of equiaxed grains with sizes ranging from 0.5 to 30 mm and Y-rich particles uniformly distributed inside the grains and along the grain boundaries. The mean size of the Y-rich particles is 0.92 mm. They are related to Cu-Y intermetallic compounds compatible with the Cu-Y phase diagram. The microhardness and tensile properties of Cu-0.8wt%Y are superior to the ones of annealed OFHC Cu.

Production Route

Initial Ingot: • Cu at 99.9 % of purity. • Y at 99 % of purity.

Atomize Process: Melted in a induction furnace and subsequent argon gas atomization.

Canning and Degassing: Degassed at 573 K for 24 hours into a steel can.

HIP Process: Hot Isostatic Pressing at 1123 K under 179 MPa for 2 hours.

Target Composition • Cu 99.2 wt% • Y 0.8 wt%

Microstructural and mechanical characterization of Cu-0.8wt%Y

G. Carro, A. Muñoz, M.A. Monge, B. Savoini and R. Pareja Universidad Carlos III de Madrid, Departamento de física, Avda. de la Universidad 30, 28911-Leganés, Madrid, (Spain)

Temperature

(K)

YS

(MPa)

UTS

(MPa) UTS/YS

True strain necking

(eUTS) (%)

Final True strain

(ef) (%)

293 99 355 3.6 25.9 29.1

373 92 318 3.4 24.5 29.3

573 82 213 2.6 18.5 29.6

773 51 109 2.1 23.0 37.4

Yield strength and Ultimate Tensile strength. Thermal evolution

Microstructure

Material

Theoretical

Density

(g/cm3)

Experimental

Density

(g/cm3)

Densification

(%)

Cu 0.8wt%Y 8.889 8.895(15) 100 %

Microhardness (Vickers Method) of sintered material compared to pure copper values.

Density measured with a helium ultrapycnometer

SEM-BSE Images of the Fracture : Cross (a) and lateral view (b) at room temperature and cross (c) and lateral view (d) at 373 K.

a) b)

c) d)

20 mm 20 mm

20 mm 20 mm

100 mm

100 mm 100 mm

100 mm

Initial Powder Particles Final Sintered material

Size Distribution of the Y-rich precipitates

Grain Size distribution of the sintered material measured and recalculated by the Schwartz-Saltykov method.

Particle Size distribution of the initial powder measured by laser diffraction.

Average Grain sizes of powder particles have been measured in particles with different diameters.

Experimental XRD patterns from powder and sintered material.

Initial powder: Optical Microscope (a) and SEM-BSE (b) images. The powder particles are meanly spherical. The grain size decreases on decreasing the particle size. The grain boundaries present an eutectic internal structure formed by pure copper and some Cu-Y intermetallic compound.

30 mm

a)

2 mm

b)

#

* *

*

#

#

Sintered Material: Optical Microscope (a) and SEM-BSE (b) images of the sintered material. The microstructure consists of equiaxed grains ranging from 0.5 to 30 mm. The primitive powder particles can be identified. Y-rich precipitates are homogeneously distributed in the copper matrix.

10 mm

b)

a)

60 mm

#

*

#

#

#

Tensile curves of the sintered material. Strain rate 1.11·10-4 s-1.

Material Microhardness

(GPa)

Pure Copper 0.369

Annealed Copper 0.530

Worked Copper 1.079

Cu-0.8wt%Y 0.660(20)

Tensile Test Initial Test Fractography