The solid solubility of nitrogen in Nb and Nbrich NbHf, NbMo and NbW alloys: Part I: The binary system NbN

Abstract

Using a dynamic leak method, a Sieverts apparatus and a combination of X-ray diffraction and microscopical techniques, a study has been made of the interstitial solid-solubility of nitrogen in niobium as a function of pressure and temperature. It has been found that Nb can accommodate 9.48 at.% N interstitially at 2200°C and 3 × 10 −1torr N 2, but the amount which can be retained in solution at room temperature is very much smaller, being about 1.0 at.% depending on the quenching rate. The results are fully in accord with those of Gebhardt, Fromm and Jakob, and of Cost and Wert who obtain a relationship x = 6.2 × 10 −4 (p N 2 ) 1 2 exp( 46,000 RT ) for the amount x, in at.% of nitrogen in solid solution, p N 2 being the nitrogen pressure in torr, R the gas constant and T in degrees Kelvin. The lattice parameter of Nb is increased from a =3.2986 A ̊ to 3.3060 Å with 1.05 at.% N retained in the lattice.