On the Microstructure and Properties of Nb-12Ti-18Si-6Ta-5Al-5Cr-2.5W-1Hf (at.%) Silicide-Based Alloys with Ge and Sn Additions

Abstract

The microstructures and properties of the alloys JZ3 (Nb-12.4Ti-17.7Si-6Ta-2.7W-3.7Sn-4.8Ge-1Hf-4.7Al-5.2Cr) and JZ3+(Nb-12.4Ti-19.7Si-5.7Ta-2.3W-5.7Sn-4.9Ge-0.8Hf-4.6Al-5.2Cr) were studied. The densities of both alloys were lower than the densities of Ni-based superalloys and many of the refractory metal complex concentrated alloys (RCCAs) studied to date. Both alloys had Si macrosegregation and the same phases in their as cast and heat treated microstructures, namely βNb5Si3, αNb5Si3, A15-Nb3X (X = Al, Ge, Si, Sn), C14-Cr2Nb and solid solution. W-rich solid solutions were stable in both alloys. At 800 °C only the alloy JZ3 did not show pest oxidation, and at 1200 °C a thin and well adhering scale formed only on JZ3+. The alloy JZ3+ followed parabolic oxidation with rate constant one order of magnitude higher than the single crystal Ni-superalloy CMSX-4 for the first 14 h of oxidation. The oxidation of both alloys was superior to that of RCCAs. Both alloys were predicted to have better creep at the creep goal condition compared with the superalloy CMSX-4. Calculated Si macrosegregation, solid solution volume fractions, chemical compositions of solid solution and Nb5Si3, weight changes in isothermal oxidation at 800 and 1200 °C using the alloy design methodology NICE agreed well with the experimental results.

Refractory Metal (Nb) Intermetallic Composites, High Entropy Alloys, Complex Concentrated Alloys and the Alloy Design Methodology NICE—Mise-en-scène † Patterns of Thought and Progress

“…Remarkably, in (a) and (c), where B is included in the data, the B always belongs in specific groups with/without the elements Al, Cr, Ge, Hf, Si, Sn, Ti and with/without RMs [ 7 , 8 ]. The elements Al, B, Cr, Ge, Hf, Si, Sn, Ti are key additions for improving the oxidation resistance of RM(Nb)ICs, meaning suppressing pest oxidation and improving oxidation resistance at high temperatures [ 1 , 3 ], and suppressing scale spallation [ 1 , 3 , 19 , 20 , 21 , 25 , 26 ]. To the author’s knowledge, additions of B, Ge or Sn have not been reported in RHEAs, and RCCAs studied to date and were not reported for the RCCAs reviewed in [ 13 ], but they have been used only in RM(Nb)ICs some of which are also RHEAs or RCCAs, e.g., [ 3 , 19 , 20 , 21 , 25 ].…”

“…Unfortunately, there is no data about the creep of RHEAs and RCCAs and about the properties of the M 5 Si 3 and Laves phase(s) that are observed in these UHTMs. No RHEAs and RCCAs with A15-Nb 3 X compounds have been studied to date outside our research group [ 19 , 25 , 26 ].…”

“…The brown and pink arrows show the shift towards the Hf-free alloy OHS1 [ 26 ], where Ge and Sn were in synergy with Al and Cr. The blue arrow shows the change owing to having Ge and Sn in synergy with Al, Cr, Hf and Ta (JZ3+ [ 25 ]) or Mo (JZ5 [ 19 ]). The purple arrow shows the effect of adding to OHS1 the elements Hf and Ta (JZ3 [ 25 ]) or Hf and Mo (JZ4 [ 19 ]), and the green arrow shows the effect of increasing the Ti concentration (JZ5).…”

“…The alloy design methodology NICE [ 1 ] (Niobium Intermetallic Composite Elaboration) has made it possible to construct such visual forms, namely maps based on the aforementioned parameters. Indeed, RM(Nb)ICs, RHEAs and RCCAs not only share common alloying elements, but they also share “common ground in parameter maps” [ 3 , 24 , 25 ]. Maps of aforementioned parameters, for example δ versus ΔH mix or ΔS mix , have been produced in studies of phase stability in HEAs and to compare the latter with bulk metallic glasses (BMGs).…”

“…In this paper, my approach to the subject matter is to provide a brief coverage/review of the alloying of RM(Nb)ICs (discussed in the refs [ 7 , 8 , 9 , 10 , 11 ] that dealt closely with issues that pertain to the alloys and their phases) and to show how my ideas that were instigated from these studies, despite their having been conceived and organized separately over many years, converged and were unified in NICE [ 1 ] to give a perspicuous and straightforward account of a new alloy design methodology that is useful both for RM(Nb)ICs and for RHEAs and RCCAs [ 1 , 3 , 19 , 20 , 21 , 24 , 25 ]. I use this opportunity to draw attention to RM(Nb)ICs and RCCAs with B, Ge or Sn additions and expand on the data presented in [ 1 , 3 , 7 , 8 , 9 , 10 , 11 ] and, most recently, in [ 19 , 26 ].…”