Controlling the carbide formation and chromium depletion in W-Cr alloy during field assisted sintering

Abstract

Tungsten is a refractory metal, suitable for a broad range of high-temperature applications, due to its high melting point and high-temperature strength. Recently, tungsten alloys became of great interest in thermonuclear fusion research. The alloys maintain low sputtering yield and high melting point, but greatly improve some drawback properties comparing to pure tungsten. These alloys are commonly prepared by mechanical alloying and compacted using Spark Plasma Sintering/Field Assisted Sintering. Powder in a graphite die is consolidated by applying pulsed electric current and pressure. Graphite foil is commonly placed between the die and the powder, to prevent adhesion. However, for number of applications it is necessary to avoid carbon contamination. In the present study we have examined carbon contamination mechanism of W - 10 wt.%Cr - 1 wt.%Hf alloy during Field Assisted Sintering along with the alloy's properties. The experiments have shown that the graphite foil leads to significant dealloying via mechanism of liquid phase sintering. As a result, tailored properties of the material are deteriorated after several minutes of the consolidation process. Therefore, application of carbon diffusion barrier was proposed, examined and compared with the alloy sintered with graphite foil.