Dependences of the crack propagation rate (CPR) and fracture toughness Ksub(Ic) on ultimate strength σsub(B), relative reduction phi and impact strength asub(H) after different thermal treatment conditions have been cons1dered. Ksub(Ic) indexes decrease with σsub(B) increase, and a crack propagates with higher rate. With phi increase from 15 up to 60% (at σsub(B)=1200 MPa) values of Ksub(Ic) pass through a maximum and CPR values pass through a minimum The effect of phase composition on Ksub(Ic) and CPR has been studied. It has been shown that alloys with martensite type structure passess maximum CPR values and minimum Ksub(Ic) values, and alloys with (α+β) structure passess minimum CPR values and maximum Ksub(IC) values. It has been also shown that materials with nonrecrystalized structure, and, specifically, with polygonized one, differ by their optimum combination of Ksub(Ic), CPR, σsub (B), phi, asub(H) parameters
Grabovetskaya, G. P.; Ratochka, I. V.; Mishin, I. P.; Zabudchenko, O. V.; Lykova, O. N.
The effect of the initial phase composition of a Ti-Al-V-Mo alloy (VT16 according to Russian classification) on the evolution of its structural-phase state during the formation of ultrafine-grained structure and subsequent annealing is investigated by methods of optical and transmission electron microscopy and x-ray diffraction analysis. The structure is produced by cyclic pressing with a change of the deformation axis in each cycle combined with a gradual decrease of the pressing temperature from 1073 to 723 K. As this takes place, α″ → α + β and β → α phase transitions are found to develop in the test alloy. The phase state of the ultrafinegrained material thus produced depends for the most part on its elemental composition and severe plastic deformation regime. Annealing below the recrystallization temperature is shown to give rise to a β→α phase transition and alloying element redistribution. The foregoing processes allow for retaining a high level of the strength properties of the alloy.