Unraveling microstructure evolution induced mechanical and corrosion resistance responses in extruded titanium alloy subjected to varied Cu regulation

Abstract

The study investigated the influence of hot extrusion on the microstructure, mechanical properties, and corrosion resistance of powder metallurgy titanium alloys with different Cu contents (x=1,5,10%). The microstructure of these alloys predominantly consists of coarse layered α and β phases. A higher Cu content leads to the formation of a coarse blocky Ti₂Cu phase, exhibiting dimensions in the range of hundreds of microns, along with an increased volume fraction of both the β and Ti2Cu phases. After hot extrusion, the microstructure undergoes significant refinement, transitioning from a coarse layered structure to nano-equiaxed grains at a Cu content of 1%. However, this grain refinement effect diminishes at a Cu content of 5%, where the equiaxed grains increase to about 1 μm, and the size of the Ti₂Cu phase is reduced to the nanometer scale. Further increases in the Cu content result in a mixed microstructure comprising ultrafine layers and equiaxed grains. The mechanical properties of compression tests are enhanced, achieving a yield strength of about 1500 MPa. The strength increases by approximately 380 MPa with the 1% Cu content, attributed to grain boundary strengthening. At 5% Cu content the strength rises by about 290 MPa, with contributions of 136 MPa from grain boundary strengthening, 60 MPa from precipitation strengthening, and the remainder from solid solution strengthening. The mechanisms of strengthening remain consistent with further increases in Cu content. The extruded Ti6Al4VxCu alloys with 5% Cu content exhibit the most favorable corrosion performance. The sizes of the grains, as well as the proportion and dimensions of precipitated phases, play a critical role in the formation of the passive film and affect galvanic corrosion, thereby impacting overall corrosion performance.