Materials Technology Presently Available for Advanced Rankine Systems

Aging effects on microstructural and mechanical properties of select refractory metal alloys for space-reactor applications

“…Lessmann and Gold [5] reported an increase in the bend test ductile-to-brittle transition temperatures (DBTT) for FS-85 aged at 1255 K for 1000 h or greater, while aging at 1088 K produced no increase. Their study also demonstrated an increase in DBTT on aging at 1422 K, but for times greater than 5000 h. Similar effects were also observed in weldments, where embrittlement occurred upon aging at 1255 K for over 100 h, but could be alleviated by annealing at 1588 K for as little as 1 h [5,20]. Embrittlement was not observed in tensile tests of FS-85 aged 1000 h between 1089 and 1589 K by Frank [21].…”

Influence of thermal and radiation effects on microstructural and mechanical properties of Nb–1Zr

“…The appearance of intergranular fracture and the low measured values of uniform elongation in the aged Nb-1Zr suggests a potential embrittlement created by the presence of grain boundary precipitation. Reduction in ductility and an accompanied loss of tensile strength associated with failure prior to or just after yielding has been observed following aging for Cb-752 (Nb-10W-2.5Zr) at 1173 K [45], FS-85 near 1248 K [15,46,47], and Ta-base T-111 (Ta-8W-2Hf) at 1398 K [48]. In all cases the drop in ductility appears around 1000 h at temperatures in a narrow range between 0.4 and 0.44T melt .…”