The Cr-Ni-Hf (Chromium-Nickel-Hafnium) System

Abstract

The Cr-Ni-Hf system was reviewed by [2001Gup]. For development of high temperature resistant brazing alloys, the Cr-Ni-Hf system was studied at the Ni-corner. The results are reported here. In order to discuss the results it is necessary to recapitulate the binary systems. The Cr-Hf system [Massalski2] (Fig. 1) has only one intermediate phase Cr2Hf which exists in two polymorphic forms in high temperature Cr2Hf (Y) phase and a low temperature Cr2Hf (Y1) phase. The Y phase melts congruently at 1825 C and the polymorphic transformation temperature for the Cr2Hf phase is 1335 C. Two eutectics, LM a + Y and LM Y + a1, occur at 1665 and 1500 C, respectively. The a and a1 phases are the two body centered cubic (bcc) terminal solid solutions (Cr) and (bHf), respectively. A eutectoid reaction a1MY + x occurs at 1370 C; x is the close packed hexagonal (cph) terminal solid solution (aHf). The Cr-Ni system [1991Nas] (Fig. 2) is a simple eutectic system. The eutectic reaction LM c + a occurs at 1345 C, where c is the face centered cubic (fcc) terminal solid solution (Ni). The c phase extends to 50 at.% Cr and the bcc a phase extends to 32 at.% Ni. An ordered CrNi2 phase forms from the c phase at T < 600 C. The Hf-Ni system [1991Nas] (Fig. 3) has nine intermediate phases: HfNi5 (e), Hf2Ni7 (p), high temperature HfNi3 (k1) and a low temperature HfNi3 (k), Hf8Ni21 (h), Hf3Ni7 (w), Hf7Ni10 (b), Hf9Ni11 (m), HfNi (/1) phase at high temperature and HfNi (/) at low temperature, and Hf2Ni (n). The polymorphic transformation temperatures for the HfNi3 and HfNi phases are 1200 and 1175 C, respectively. The p and /1 phases melt congruently at 1460 and 1530 C, respectively. All other phases form through peritectic reactions: L + pM e at 1240 C, L + pM k1 at 1340 C, L + k1M h at 1300 C, L + hM w at 1350 C, L + /1 M m at 1340 C, L + m M b at 1290 C, and L + /1 M n at 1200 C. Three eutectic reactions LM c + e, LMw + b, and LM n + x occur at 1190, 1190, and 1150 C, respectively. The h and w phases exist at high temperature and transforms through eutectoid reactions hM k + w at 1177 C and wM k + b at 1020 C. The binary phases and their structure data are given in the review by [2001Gup]. No ternary phase exists in the Cr-Hf-Ni system. The Cr-Hf-Ni system has been reinvestigated at the Ni-Corner of the Cr-Hf-Ni system by [1999Kho]. Twenty two alloys were prepared using 99.98 mass% Cr, 99.9 mass% Hf, and 99.95 mass% Ni. The alloys were arc melted