Microstructural Transitions during Powder Metallurgical Processing of Solute Stabilized Nanostructured Tungsten Alloys

Abstract

Exploiting grain boundary engineering in the design of alloys for extreme environments provides a promising pathway for enhancing performance relative to coarse-grained counterparts. Due to its attractive properties as a plasma facing material for fusion devices, tungsten presents an opportunity to exploit this approach in addressing the significant materials challenges imposed by the fusion environment. Here, we employ a ternary alloy design approach for stabilizing W against recrystallization and grain growth while simultaneously enhancing its manufacturability through powder metallurgical processing. Mechanical alloying and grain refinement in W-10 at.% Ti-(10,20) at.% Cr alloys are accomplished through high-energy ball milling with transitions in the microstructure mapped as a function of milling time. We demonstrate the multi-modal nature of the resulting nanocrystalline grain structure and its stability up to 1300 °C with the coarser grain size population correlated to transitions in crystallographic texture that result from the preferred slip systems in BCC W. Field-assisted sintering is employed to consolidate the alloy powders into bulk samples, which, due to the deliberately designed compositional features, are shown to retain ultrafine grain structures despite the presence of minor carbides formed during sintering due to carbon impurities in the ball-milled powders.

Influence of Pre-Milling on the Mn Solid Solubility in the Al-Mn-Cu Alloy during Mechanical Alloying

“…An anomalous increase in solid solubility is observed after mechanical alloying due to severe plastic deformation and the resulting high density of crystalline defects, e.g., vacancies, dislocations, and grain boundaries [29,[32][33][34][35][36][37][38][39][40]. The solute content of the low-soluble elements in aluminum, Nb [41,42], Co [43], V [44,45], Zr [46,47], and Ti [26], increases, and a strong extension of the Mn [4,48] and Mg [49] solubility is observed.…”

Unraveling Thermodynamic and Kinetic Contributions to the Stability of Doped Nanocrystalline Alloys using Nanometallic Multilayers

“…Furthermore, Ta‐doped nanocrystalline Cu has been shown to exhibit a similar transition, where the driving force for grain growth was initially reduced due to the saturation of grain boundaries with Ta and subsequently followed by the formation of Ta dispersoids kinetically stabilizing the microstructure at higher temperatures due to the increased volume fraction of pinning particles. [ 45 ] A similar explanation applies to nanocrystalline metals containing impurities [ 46 ] where segregation and second‐phase formation at grain boundaries will ultimately shift the mechanism governing stability as demonstrated in Ni‐based [ 38,47 ] and W‐based [ 48 ] alloys. As understanding both the contributions of, and transition between, stabilization mechanisms is central to realizing stable nanocrystalline alloys, new material architectures are sought to assess different solute distributions and their implications for thermal stability.…”