In this study we present a series of light-weight (6.24 to 6.42 g/cm3), Ti-rich Mo-Si-Ti alloys (≥40 at.% nominal Ti content) with the hitherto best combination of pesting and creep resistance at 800 ...and 1200 °C, respectively. This has been achieved by fine-scaled eutectic-eutectoid microstructures with substantial fractions of primarily solidified (Mo,Ti)5Si3. (Mo,Ti)5Si3 was found to be oxidation-resistant in these alloys and also beneficial for the creep resistance. The enhanced solidus temperature is of specific relevance with respect to the latter point. The creep resistance is competitive to the non-pesting resistant, but most creep-resistant (among the Mo-Si-Ti alloys) eutectoid alloy Mo-21Si-34Ti developed by Schliephake et al. Schliephake et al., in Intermetallics 104 (2019) pp. 133–142. Moreover, it is favourably superior to the commercially applied Ni-based single crystal alloy CMSX-4 for the applied compressive loading conditions under vacuum.
The quality and properties of metal powders are essential for powder metallurgical (PM) processes in general and for additive manufacturing (AM) processing routes in particular. Thus, a variety of ...atomization technologies were established meeting the multiple needs of the different processing technologies. However, the production of refractory metal alloy powder remains challenging due to their high liquidus temperatures (>2000 °C), the formation of brittle intermetallic phases, as well as the reactivity with and sensitivity to interstitials of the constituting elements. In this contribution, powders made of Mo-20Si-52.8-Ti (at.%) were produced by a novel ultrasonic atomization (UA) process at laboratory-scale using an industrial electrode induction gas atomization (EIGA) process with a modified electrode concept for the first time. UA allows flexibility in alloy composition due to the arc melting-based principle, while the EIGA electrode is PM manufactured from elemental powders to provide similar flexibility on a larger scale. The powders resulting from these two processes were compared with respect to size distribution, sphericity, microstructure and phase constitution, chemical composition, and interstitial impurity content. In addition, several powder batches were produced with the UA process in order to assess the process reliability and stability. The properties, quality, and quantities of UA powders perfectly meet the requests for alloy development for powder bed fusion AM, while the modified EIGA process allows the upscaling of the alloy powder quantities.
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The present work is an extension of the studies conducted by Kellner et al. M. Kellner et al., Acta Materialia, vol. 182, pp 267–277, 2020., to show the transferability of their ...concentration-driven nucleation mechanism to other systems. The implementation of this method improves the adjustment process of directionally solidifying eutectic structures in two-dimensional phase-field simulations. To quantitatively evaluate the nucleation mechanism, the velocity-spacing relationships of different eutectic and off-eutectic melt compositions are investigated for AlCu-5Ag. A good agreement between simulations with and without the nucleation mechanism is found for all studied compositions.
Cr-13.5Si-32.2Mo (at%) solidifies as metastable σ-phase with a dendritic microstructure during arc melting. Heat treatment leads to a decomposition into a fine-lamellar microstructure of (Cr,Mo)ss ...and (Cr,Mo)3Si. A protective Cr2O3 layer with low growth rates was formed upon cyclic oxidation at 800, 1100 and 1200 °C for up to 100 h. In addition to the Cr2O3 layer, the formation of an internal silicon oxide layer is found for 1200 °C. Oxide scales show parabolic growth rates at 1100 and 1200 °C. Up to 100 h, the oxidation occurred remarkably free of nitridation, spallation or pesting.
•Pesting resistance is obtained at 800 °C for Cr-13.5Si-32.2Mo (at%).•Monolithic σ phase in Cr-Si-Mo system decomposes into A2 solid solution and A15 intermetallic.•Outstanding oxidation at 800 °C and reasonable oxidation resistance up to 1200 °C is obtained for 100 h.•Protective Cr2O3 scales form, no nitridation or spallation occurs at 800–1200 °C up to 100 h.
Mo–Si–Ti alloys, like eutectic Mo–20Si–52.8Ti (at%), have previously been intensely investigated, owing to their excellent oxidation and creep resistance. To better understand high‐temperature ...mechanical behavior, a holistic assessment of microstructural features is necessary. Correspondingly, 3D‐focused ion beam tomography is carried out in Mo–20Si–52.8Ti. The results indicate a severely interconnected network of Mo solid solution (MoSS) and intermetallic (Ti,Mo)5Si3. Both phases retain similar network connectivity, lamellar sizes, etc. The brittle to ductile transition temperature (BDTT) is then determined through a series of bending tests and interpreted using the microstructural information. The BDTT is found to be ≈1100–1150 °C, different from Mo–9Si–8B with a continuous MoSS network. The BDTT is an immediate consequence of the continuous network of both MoSS and (Ti,Mo)5Si3. The MoSS network is instrumental in crack trapping and bridging, indicating that the present phase distribution maximized the mechanical performance over (Ti,Mo)5Si3. Having determined the network microstructure and BDTT, tensile creep behavior is evaluated and compared to previously published compressive creep results. The results show consistency in terms of strain rate, stress exponent, and microstructural features indicating a reliably good creep resistance for the network microstructure of Mo–20Si–52.8Ti regardless of loading direction.
Some Mo–Si–Ti alloys exhibit exceptional oxidation and creep resistance in conjunction with low density. To highlight their engineering potential, brittle to ductile transition temperature (BDTT) and tensile creep behavior are analyzed and set in relation to the material's 3D microstructure.
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