Papers by Author: Karol Iždinský

Abstract: Abstract: Reactions during compaction of Mo/Mo silicide wires with Ni interlayers are qualitatively assessed in this work. It appeared that due to extreme high temperature strength of MoSi₂ hot pressing even at 1800°C/60 min/30 MPa in vacuum had not been sufficient to compact the Mo/Mo silicide wires in the absence of any additional interfacial layer. Therefore Ni had been chemically coated on the surface of Mo/Mo silicide wires that were subsequently compacted by hot pressing. Structural analysis revealed the reaction between Ni and MoSi₂ resulting in the formation of ternary (MoNiSi) compounds. These established an interfacial bonding with minimal porosity.

Abstract: Copper matrix composite with pure copper matrix reinforced with high modulus carbon fibres Thornel K 1100 was prepared by gas pressure infiltration technique. As-received composite was subjected to thermal expansion and thermal conductivity measurements in longitudinal and transversal directions. Large anisotropy of properties as well as surprisingly good structural stability has been observed. The mean coefficients of thermal expansion as low as 0.8 x 10-6 K-1 in longitudinal and as high as 23.5 x 10-6 K-1 in transversal directions were determined, the thermal conductivities as high as 650 Wm-1K-1 in longitudinal direction and as low as 60.7 Wm-1K-1in transversal directions were measured.

Abstract: In Plasma Facing Components (PFCs) for nuclear fusion reactors, the protective material, carbon based or tungsten, has to be joined to the copper alloy heat sink for optimum heat transfer. High temperature vacuum brazing is a possible joining process as long as a proper interlayer is introduced to mitigate the residual stresses due to the mismatch of thermal expansion coefficient (CTE). Pure copper can act as plastic compliant layer, however for carbon based materials a proper structuring of the joining surface is necessary to meet the thermal fatigue lifetime requirements. In this work pure molybdenum and tungsten/copper Metal Matrix Composites (W-wires in Cu-matrix) interlayers have been studied as alternative to pure copper for carbon based protective materials in flat tile configuration. Finite element simulations of the brazing process have been performed to evaluate the expected residual stress reduction near the metal-carbon interface. In fact it has been demonstrated that stiff low CTE interlayers can shift the peak stresses from the weak carbon-metal interface to the strongest metal-metal one. Relevant samples have been manufactured and subjected to preliminary metallographic and thermal shock tests. Results obtained so far are encouraging and active cooled mock-ups are being prepared for high heat flux testing. Research work is in progress as regards monoblock configuration with both Wf/Cu MMC and graded Cu/W plasma sprayed and HIPped layers.

Abstract: Tungsten is the main candidate material for the armor of plasma facing components for ITER and future fusion devices [1]. Plasma spraying is an alternative method for manufacturing tungsten-based coatings, including composites and graded layers, having a number of advantageous features [2]. On the other hand, the main limitation to application of these coatings on high heat flux components, is their low thermal conductivity, originating in the layered structure [3]. This paper is focused on four methods of improving the coatings’ thermal conductivity. First method consists in modification of the basic spraying parameters, which have a direct influence on the coating structure and therefore properties. The other three methods involve post-processing of the coatings: molten copper infiltration, laser remelting and densification by HIPping. The latter encompasses also tungsten-copper composites of various compositions. Experimental results, including structural and thermal characterization, are presented for each method. Finally, the applicability of these methods, from the point of view of manufacturing the plasma facing components, is discussed.