Alloys With Chromium

Abstract

The diagram in Fig. 108 is due to [1]. It is based on the work of [2]. This diagram was compiled from data obtained over the whole composition range by metallographic, X-ray diffraction and electron microprobe investigations. The two intermediate phases, the E close-packed hexagonal (hcp) phase and the β Cr₃Si (A15) phase have composition ranges of ~20 at% at 900 °C to 68 at% at 1475 °C and 77 to 78 at% below ~ 1200 °C, respectively. The γ(Rh) ε-phase boundary slopes strongly with temperature. Peritectic and eutectic reactions were found at 1700±10 and 1475±10 °C; a peritectoid reaction takes place at 1265±12 °C [2]. Earlier work of an exploratory nature using X-ray diffraction, and metallographic methods had been carried out by [3, 4]. The former investigation showed the existence of the hcp ε-phase but not of the βA15 phase; the maximum solid solubility of chromium in rhodium was reported to be only ~8 at%. The latter paper, which carried out limited work on 29 other binary systems as well, looked at six alloys between 25 and 75 at% chromium; the alloys were arc-melted under helium, the operation being carried out twice to obtain adequate homogeneity. After annealing for up to 120 h at 1200 °C the hcp ε-phase was found between 50 and 65 at% chromium and the A15 RhCr₃ β phase at 75 at% chromium [4].