Structural parameters of the low-temperature metastable form of the carbide W2C

A sufficiently complete spectrum of superstructure reflections was obtained by the x-ray diffraction analysis of a monocrystal to unequivocally determ ine, for the first time, the ordered structure of W2C annealed for a long t ime at a temperature below that of its eutectoidal decomposition. It was sh own that W2C of eutectoidal composition in a metastable state has a rhombic ordered structure with the lattice parameters a = 4.719 +/- +/- 0.003 nm x 10 = c(0), b = 6.017 +/- 0.003 nm x 10 approximate to 2a(0), c = 5.181 +/- 0.003 nm x 10 approximate to root 3a(0) (a(0), c(0) = a(HCP), c(HCP)). The specimens were obtained from tungsten alloys containing 30.5 and 35 at. % C, prepared by are melting followed by annealing at similar to 2700 degrees C (I h) and stepwise cooling to 850 degrees C (the total annealing time at temperatures below 1200 degrees C was 538 h).