EFFECT OF CHROMIUM ON HEAT-RESISTANCE OF NB-TI-AL-CR ALLOYS

X-Ray analysis, gravimetry and hardness measurements were used for stu dying the behavior of Nb-30Ti-5Al-5V-1Zr (approx. wt. %) alloy additio nally alloyed with 5, 10 and 15% Cr when annealed for 100 h in air in the temperature range 700 to 1100 degrees C. Two sections can be disti nguished in the plot of specific weight increment versus time of oxida tion in the range 700 to 900 degrees C: a power dependence (up to 25 h at 700 degrees C, 10 h at 800 degrees C, 5 h at 900 degrees C) transf ormed then into a linear dependence. The highest heat resistance in th is temperature range is exhibited by alloys with 5 to 10% Cr in which the maximum volume fraction of the solid solution is retained after ag ing in the course of oxidation. Hexagonal alpha(2)(Ti3Al) and orthorho mbic alpha(2) (Ti2NbAl type) phases precipitate on aging of alloys wi thout Cr and with 5% Cr. On aging of alloys containing 10 to 15% Cr th e precipitating phase is cubic gamma[(Nb,Ti)Cr-2].