The field of possible applications of W/Cu-composites varies over a wide range, which includes components in military, space and fusion technologies as well as parts in electronic devices (heatsinks) and energy systems (e.g. contact material of power switches). Due to the mismatch of thermal expansion and Young's moduli, the joining of these two materials can result in high residual and thermal stresses at the interface, ultimately reducing component lifetime. Therefore, the present study focuses on Low Pressure Plasma Spraying (LPPS, 120 mbar) and Water Stabilized Plasma Spraying (WSPS). For both the influence of different powders and the W:Cu ratio has been investigated. LPPS has turned out to be a good method to produce W/Cu-composites and gradients which exhibit homogeneous distributions of W and Cu in the composite, no oxidation, sufficiently high density and good thermal conductivity, especially at higher temperatures. Variations within the whole composition range are possible and due to a very small step size every desired gradient function and almost continuous gradients are achieved. Advantages of Water Stabilized Plasma Spraying (WSPS) are (i) the reduced heat transfer to the substrate, which offers the possibility to spray a full composite up to 100% W at the top surface and therefore saves one joining step, and (ii) higher deposition rates due to the use of bigger particles, which at the same time reduce the ability of change compositions within few microns. Studies in this field will be continued and have to take into account that the fabricated composites will have a higher oxide content and porosity. Oxide particles can be removed completely by a heat treatment in H3-atmosphere but this results in losses in strength and density. The Young's modulus of pure W and Cu sprayed by WSPS is only 50% of the LPPS- layers, the thermal conductivity is even reduced by 60 to 70%.
Microstructural and mechanical properties of plasma sprayed W/Cu-graded composites for extreme thermal conditions
2003
12 Seiten, 14 Bilder, 1 Tabelle, 15 Quellen
Aufsatz (Konferenz)
Englisch
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