Fabrication And Properties Of W-Cu Functionally Graded Material As First Wall Material

W-Cu functionally graded material (FGM) is different from the traditionalW-Cu composite. It can solve the connecting problem between W and Cu wellfor their great difference of melting point and decrease the thermal-inducedstress effectively due to their large gap of other properties. Thus, based on suchbackground, W-Cu FGM as ideal first wall material has attracted much attentionduring recent years. This paper is aimed at investigating the feasibility of thefabrication of W-25Cu/W-50Cu/W-75Cu three layers FGM with good propertiesvia powder metallurgy method.Firstly，in this paper the three different composite powder including W-25Cu,W-50Cu and W-75Cu was prepared by mechanical alloying method. Then theW-25Cu composite powder with different ball milling time was characterized byXRD, SEM and other analysis methods. The obtained results show that duringthe ball milling process, Cu dissolved into W lattice partly and the W (Cu) solidsolution was formed. Additionally, the morphology of W-25Cu compositepowder changed with the increment of ball milling time. What’s more, after30hball milling the uniformity of W-25Cu composite powder was relatively ideal.Thus,30h was chosen as final ball milling time.In this paper, the three composite powder after stacking layer by layer wasfabricated by spark plasma sintering (SPS) method at different temperature(960℃,990℃,1020℃and1050℃), which hasn’t been reported ever as far aswe know. Then with assistance of XRD， SEM and EDX technology, weinvestigated the influences of different sintering processes on the structure andsome mechanical and physical properties of the prepared materials. Theobtained results are as following. The W-Cu FGM sample sintered at1050℃has better microstructure and properties. In the sample sintered at1050℃, it canbe observed that W particles were enwrapped by continuous net-like Cu and thegraded structure similar to the original design was maintained. In addition, therelative density of the specimen sintered at1050℃reached96.53%and theVickers hardness and whole flexure strength of it were largest. This sampleshows high thermal conductivity of140W/m·K at room temperature and151W/m·K at800℃. The thermal shock test showed that at the temperature of800℃, no cracks were occurred at the interface of the sample sintered at1050℃, which indicated that the sample has good thermal shock resistance. Apart fromthis, in this paper we also used traditional hot-pressing method to fabricationthe W-Cu FGM with the same composition. The result showed that the structureof net-like Cu still existed in the sample sintered at1250℃,while the net-likeCu seemed to be uncontinuous. The composition of graded structure has a bigdeviation with original design. The relative density of the sample sintered at1250℃was closed to91.85%. What’s more, the thermal conductivity of thesample was126W/m·K at800℃. The thermal shock test showed that at thetemperature of800℃, there existed obvious cracks at the interface of W-richand middle layers. All of these indicated that the SPS method was superior tothe HP method in fabricating the W-Cu FGM.What’s more, in this paper we also used electroless plating method tosynthetize the W-Cu composite powder and got the best plating process. Theresults indicated that the synthesis of W-Cu composite powder via electrolessplating method was feasible, which provided a novel way to synthetize theW-Cu composite powder.