PRESSURE DERIVATIVES OF THE ELASTIC-MODULI OF BCC TI-V-CR, NB-MO AND TA-W ALLOYS

The single-crystal elastic moduli Cij and their pressure derivatives dCij/dP have been measured ultrasonically at 25 degrees C for six Ti-V-Cr, eight Nb-Mo and seven Ta-W solid solutions. The rigid-band model for the alloy electronic structure is known to work fairly well for these BCC metals in predicting the density of states at the Fermi energy and related properties. The results of this study show that changes in the composition dependence of the Cij and dCij/dP appear to be related to specific topological changes in the Fermi surface which occur as the electron population varies in the rigid-band model. The relationship between the bandstructure and the Cij is discussed and a qualitative explanation is given for the correlations between the moduli and the Fermi surface and for some of the differences between the three alloy series.