Vellios Nikos, Tsakiropoulos Panos
Department of Materials Science and Engineering, Sir Robert Hadfield Building, The University of Sheffield, Mappin Street, Sheffield S1 3JD, UK.
Materials (Basel). 2022 Aug 23;15(17):5815. doi: 10.3390/ma15175815.
In this work, the RM(Nb)IC alloy Nb−30Ti−10Si−5Cr−5Sn−3Fe−2Al−2Hf (NV2) was studied in the as-cast and heat-treated conditions; its isothermal oxidation at 700, 800 and 900 °C and its room temperature hardness and specific strength were compared with other Sn-containing RM(Nb)ICs—in particular, the alloy Nb−24Ti−18Si−5Cr−5Fe−5Sn (NV5)—and with RCCAs and RHEAs. The addition of Fe (a) stabilised Nbss; A15−Nb3X (X = Al, Si and Sn) and Nb3Si; metastable Nb3Si-m’ and Nb5Si3 silicides; (b) supported the formation of eutectic Nbss + Nb5Si3; (c) suppressed pest oxidation at all three temperatures and (d) stabilised a Cr- and Fe-rich phase instead of a C14−Nb(Cr,Fe)2 Laves phase. Complex concentrated (or compositionally complex) and/or high entropy phases co-existed with “conventional” phases in all conditions and after oxidation at 800 °C. In NV2, the macrosegregation of Si decreased but liquation occurred at T >1200 °C. A solid solution free of Si and rich in Cr and Ti was stable after the heat treatments. The relationships between solutes in the various phases, between solutes and alloy parameters and between alloy hardness or specific strength and the alloy parameters were established (parameters δ, Δχ and VEC). The oxidation of NV2 at 700 °C was better than the other Sn-containing RM(Nb)ICs with/without Fe addition, even better than RM(Nb)IC alloys with lower vol.% Nbss. At 800 °C, the mass change of NV2 was slightly higher than that of NV5, and at 900 °C, both alloys showed scale spallation. At 800 °C, both alloys formed a more or less continuous layer of A15−Nb3X below the oxide scale, but in NV5, this compound was Sn-rich and severely oxidised. At 800 °C, in the diffusion zone (DZ) and the bulk of NV2, Nbss was more severely contaminated with oxygen than Nb5Si3, and the contamination of A15−Nb3X was in-between these phases. The contamination of all three phases was more severe in the DZ. The contamination of all three phases in the bulk of NV5 was more severe compared with NV2. The specific strength of NV2 was comparable with that of RCCAs and RHEAs, and its oxidation at all three temperatures was significantly better than RHEAs and RCCAs.
在本研究中，对RM(Nb)IC合金Nb−30Ti−10Si−5Cr−5Sn−3Fe−2Al−2Hf（NV2）在铸态和热处理条件下进行了研究；将其在700、800和900℃下的等温氧化以及室温硬度和比强度与其他含锡RM(Nb)IC合金——特别是合金Nb−24Ti−18Si−5Cr−5Fe−5Sn（NV5）——以及RCCA和RHEA进行了比较。添加Fe（a）稳定了Nbss；A15−Nb3X（X = Al、Si和Sn）和Nb3Si；亚稳Nb3Si-m’和Nb5Si3硅化物；（b）促进了共晶Nbss + Nb5Si3的形成；（c）在所有三个温度下抑制了晶间腐蚀氧化；（d）稳定了富含Cr和Fe的相，而不是C14−Nb(Cr,Fe)2拉夫斯相。在所有条件下以及在800℃氧化后，复杂浓缩（或成分复杂）和/或高熵相与“传统”相共存。在NV2中，Si的宏观偏析减少，但在T >1200℃时发生了液化。热处理后，不含Si且富含Cr和Ti的固溶体是稳定的。建立了各相中溶质之间、溶质与合金参数之间以及合金硬度或比强度与合金参数之间的关系（参数δ、Δχ和VEC）。NV2在700℃下的氧化性能优于其他添加或未添加Fe的含锡RM(Nb)IC合金，甚至优于Nbss体积分数较低的RM(Nb)IC合金。在800℃时，NV2的质量变化略高于NV5，在900℃时，两种合金均出现了氧化皮剥落。在800℃时，两种合金在氧化皮下方或多或少形成了连续的A15−Nb3X层，但在NV5中，该化合物富含Sn且严重氧化。在800℃时，在NV2的扩散区（DZ）和基体中，Nbss比Nb5Si3受到的氧污染更严重，A15−Nb3X的污染介于这两个相之间。在DZ中，所有三个相的污染都更严重。与NV2相比，NV5基体中所有三个相的污染都更严重。NV2的比强度与RCCA和RHEA相当，并且其在所有三个温度下的氧化性能明显优于RHEA和RCCA。
