Twinning Deformation And Plasticity And Toughness Of α-Titanium Alloys

Tensile tests were carried out with Ti-2Al, Ti-2Zr, Ti-2Sn, Ti-Mo and TiC particle-reinforced titanium matrix composite(TiC/Ti) at RT(293K) and cryogenics (77K), respectively. And symmetrical push-pull low-cycle fatigue tests were systematically conducted with Ti-2Zr, Ti-2Sn and TiC/Ti . Then impact tests were performed with the most valuable Ti-2Zr and Ti-2Sn as well TiC/Ti. By metallography, SEM and TEM together with maths analysis, mechanical properties and deformation mechanisms of five α -titanium alloys at 293K and 77K were summarized and discussed, especially twinning mechanism and twinning influence factors . The results are as follows:1)Al, Zr, Sn and Mo remarkably increase the strength of α -titanium alloys at 293K and 77K, but keep excellent plasticity, especially in Ti-2Zr and Ti-Mo; the plasticity of TiC/Ti decreases at 77K .Fatigue lifves of the three alloys are still high at 77K. From 293K to 77K, impact works of Ti-2Zr and Ti-Mo change little, and both show ductile characteristic. But TiC/Ti shows great decrease of impact work and changes to brittleness from 293K to 77K.2) At 293K,dislocation slip is the dominant deformation mechanism in four alloying α -titanium alloys; at 77K, twinning becomes livelier and even is the main deformation mode in Ti-2Zr and Ti-Mo. However, slipping predominates in TiC/Ti, nomatter at 293K and 77K. More twin types occur in low-cycle fatigue tests.3)The influence of alloying elements on twinning is related to primitive phase, element solubility, electrically negative property and atom size. Among the four alloying elements, Zr and Mo have little influence on twinning, Sn secondary. TiC particle suppresses twinning in matrix titanium, which is mainly relevant to lattice structure and particle arrangement style.4) In commercially pure titanium at 77K,twin fraction increases with the increase of total strain and different twin types may occur at different stages; the occurrence of deformation twins needs an incubation period and will be up to maximum plasticity.