MICROSTRUCTURE AND FATIGUE PROPERTIES OF THE BETA-TITANIUM ALLOY BETA-CEZ

The influence of the microstructure on the fatigue properties of the h igh-strength beta titanium alloy beta-CEZ was investigated by comparin g three distinctly different microstructures: a lamellar (beta anneale d). a bi-modal (alpha + beta processed), and a necklace microstructure (processed through the beta transus). Comparing the three microstruct ures at the same yield strength level of 1200 MPa, the bi-modal micros tructure showed the best HCF and LCF properties. Concerning fatigue cr ack propagation, small surface cracks (microcracks) exhibited the slow est propagation rate in the bi-modal microstructure whereas the propag ation rates of large cracks (macrocracks) were similar in the three mi crostructures, with the tendency that the lamellar microstructure had a slightly higher resistance against macrocrack propagation. The fatig ue properties can be explained firstly by differences in the beta grai n size. In addition, the crack propagation behavior of macrocracks is influenced by the dimension of the alpha plates as a second parameter.