MECHANICAL PROPERTIES OF GROUP V CARBIDES

The mechanical properties of Group V carbides are summarized in Table 5.6. The values are average values reported in the recent litera-(see Sec. 4.1 ofCh. 4). 

Compound Vickers Hardness (GPa) Young s Modulus of Elasticity (GPa) Shear Modulus (GPa) Transverse Rupture Strength (MPa) 

The fracture mechanism and the ductile-brittle transition are similar to those of the Group IV carbides (see Sec. 4, Ch. 4). 

Hardness. Table 5.6 shows that carbides are die hardest, followed by the borides and the nitrides. The Group V carbides have higher hardness than those of Group VI but are not quite as hard as those of Group IV (see Ch. 4, Sec. 4.4 and Ch. 6, Sec. 4.0). This reflects the intermediate strength of M-C bonds found in these carbides. 

Hardness varies with composition as shown in Fig. 4.5 of Ch. 4 (see comments in Ch. 4, Sec. 4.4). Maximum hardness occurs with a carbon to metal ratio of about 0.8. It decreases with temperature as shown in Fig. 4.6 (Ch.4). 

---