Microstructure and Thermo-mechanical Properties of Self Formed Cu-W Graded Materials

D. Jankovic Ilic (Sp), J. Fiscina, Saarland University, Saarbrücken (Germany); C.J.R. González-Oliver, CONICET, S.C. de Bariloche (Argentina); F. Mücklich, Saarland University, Saarbrücken (Germany) 
 
Concept of graded materials is well accepted nowadays, primarily due to stress reduction at critical interface allowing application of these materials in extreme conditions; such as high temperature flux. The aim of this work is to understand the relationship between microstructure, electrical, and mechanical properties of Cu-W graded materials produced by segregation and infiltration.

Self formed W graded preform has been produced by segregation induced by vertical vibration. Porosity gradient in W is created by segregation of different W particle-agglomerate sizes. Two different W particle size powders have been vibrated for different time, in order to study a microstructual development after sintering. The skeleton type microstructure has been obtained for vibration time shorter than 2 h, while after 2 h of vibration the graded type microstructure was obtained. The final graded material with the W phase content in the range between 60 and 100 volume % has been obtained by infiltration of molten Cu into sintered W graded perform.

Sintering behavior as well as thermoelastical properties are strongly influenced by W microstructural evolution. Experimental results of electrical resistivity showed that the optimal microstructure for electrical properties consists of a highly 3-D interconnected Cu phase, i.e. of skeleton type of microstructure. The higher W-W contiguity and stronger W-W sintering bonds are detrimental for current flow.

The position dependant Young’s modulus was also determined via ultrasound B-Scan imaging methods. Higher values of Young’s modulus obtained in graded type of microstructure are related to the increase in W-W contiguity. These results are discussed through consideration of W-W contiguity as the microstructural parameter, residual porosity and the phase content.

Keywords: C-W functionally graded material; Segregation; Electrical resistivity; Young’s modulus.