The Effect Of Alloy Elements On The Damping Property Of Ti-Nb Alloys

The thermal-activated diffusion and the reditribution of the interstitial atoms inbody-centered cubic metals are caused by the applied stress, and always occurbetween different interstitial sites. The effect of energy loss accompanied by the aboveprocess is known as Snoek relaxation. Snoek-type high damping Ti-alloys, whosedamping capacities originate from the relaxation process of oxygen atoms atoctahedral interstice sites of the matrix （β-type Ti-Nb）, are based on the point defectrelaxation effect, resulting in an excellent damping and mechanical properties in thetemperature range of400-600K.In order to provide experimental and theoretical evidences for the design of highdamping Ti-alloys, we systematically investigated the effects of alloying elements Mo,Al, and B, in-situ reinforcement element B and C, and rare-earth element La on thephase stability, damping property, dynamic mechanical properties, and Snoekrelaxation parameters of Ti-25.0Nb-1.5O （at.%） alloys, respectively. The Ti-Nb-X-O（X=Mo, Al, B） alloys were prepared by arc smelting method.The relationships between the parameters including dipole shape factor, d-orbitalenergy level, and lattice parameter can be obtained by theoretical calculation. It isfound that the dipole shape factor linearly increased with the increasing d-orbitalenergy level, and increased with the increasing change of the lattice parameter as well.Accordingly, The dipole shape factor, d-orbital energy level, and lattice parameter arethree important parameters for analyzing the Snoek relaxation process, since thevariation of the dipole shape factor directly indicates the change of Snoek-dampingpeak value. Hence, enhancing the d-orbital energy as large as possible, together withintroducing more lattice distortion should be first considered, when determining thealloying elements for adding into the damping alloys.The composition of the matrices of all the Ti-Nb-X-O （X=Mo, Al, B） alloys wasfound to be single β phase. As far as the effects of alloying elements, the addition ofMo has positive effects on the elimination of composition segregation and thehomogenization of alloy composition, the addition of Al leads to the generation ofAl₂O₃impurity, and the addition of B brings benefit to the refinement of the grains. Alloys containing B exhibited favorable damping property, while alloys with Mo, orB possessed satisfactory mechanical properties.Although the addition of B brought about favored comprehensive performance, theexistence form of B in the alloys is still under consideration. The damping behavior ofTi-Nb-B indicates that B can participate in the Snoek relaxation process as aninterstitial atom due to its small diameter. Furthermore, large content of B elementwill lead to multiple peaks in the curves damping property.Aiming at improving the formability of Ti alloy, Ti-Nb-O alloys were prepared bypowder metallurgy method as well. The results showed that the as-prepared alloys hadbetter performance, especially the damping value, than the alloys fabricated by arcsmelting. Hence, it convinced that it is possible to prepare Ti alloys by powdermetallurgy.