Mechanical and microstructural investigations of tungsten and doped tungsten materials produced via powder injection molding

Abstract

The physical properties of tungsten such as the high melting point of 3420°C, the high strength and thermal conductivity, the low thermal expansion and low erosion rate make this material attractive as a plasma facing material. However, the manufacturing of such tungsten parts by mechanical machining such as milling and turning is extremely costly and time intensive because this material is very hard and brittle. Powder Injection Molding (PIM) as special process allows the mass production of components, the joining of different materials without brazing and the creation of composite and prototype materials, and is an ideal tool for scientific investigations. This contribution describes the characterization and analyses of prototype materials produced via PIM. The investigation of the pure tungsten and oxide or carbide doped tungsten materials comprises the microstructure examination, element allocation, texture analyses, and mechanical testing via four-point bend (4-PB). Furthermore, the different materials were characterized by high heat flux (HHF) tests applying transient thermal loads at different base temperatures to address thermal shock and thermal fatigue performance. Additionally, HHF investigations provide information about the thermo-mechanical behavior to extreme steady state thermal loading and measurements of the thermal conductivity as well as oxidation tests were done. Post mortem analyses are performed quantifying and qualifying the occurring damage with respect to reference tungsten grades by metallographic and microscopical means

Refractory Materials for Energy Applications

“…Therefore, this technique is an ideal tool for R&D, as well as for materials science. Isotropic materials, equiaxed grain orientation (see Figure ), good thermal shock resistance, shape complexity and high final density are several typical properties of tungsten produced by PIM …”

Tungsten-Based Composites for Nuclear Fusion Applications

“…W has unique characteristics, which have increased its value relative to other materials. The properties which confer this valuable status in nuclear engineering include its refractoriness, high melting point, high thermal conductivity, low thermal expansion coefficient, good chemical stability, high heat resistance, high sputtering threshold energy, low sputtering rate, low erosion rate at edge plasma temperatures of less than 40-50 eV, low deuterium/tritium retention rate, low tritium permeability, high moduli of elasticity, good thermal shock resistance, lack of hydride formation and adequate corrosion resistance [12,15,[18][19][20][21][22][23][24][25][26][27][28][29][30]. The use of W is associated with other advantages as well.…”

“…Due to its high hardness, high brittleness, and poor machinability, the manufacturing of W parts is very costly and time-consuming [20]. The joining of W to a Cu-based (CuCrZr) heat sink is troublesome, owing to the large difference in the CTEs of these two materials [18].…”

“…Like oxides, carbides are also drawing much attention as a candidate dopant to produce dispersion-strengthened W composites [5]. Many types of carbide are being investigated, including TiC, TaC [20], WC [23], ZrC [59] and SiC [11]. WC/W composites, when sintered at 1800°C after an addition of 5 and 10%vol WC, are converted into 8.9vol%W 2 C/W and 17.8vol%W 2 C/W by the aW+bWC→(a−b)W+bW 2 C reaction.…”

“…The green compacts of W-TaC composites, produced by injection molding, were sintered in an H 2 atmosphere after removing the binder, the impurities and the residual stress by debinding. High agglomeration of TaC particles and brittleness in the resultant composites were observed [20]. In addition to powder injection molding, attempts to produce TaC/W composites with enhanced properties using SPS, hot rolling followed by annealing [60] and mechanical alloying with subsequent hot isostatic pressing have been used [61].…”