Fabrication of ultrafine-grained Ti-15Zr-xCu alloys through martensite decompositions under thermomechanical coupling conditions

Grain refinement is a well-recognized method to simultaneously increase the strength and ductility of metallic materials.Fabrication of ultrafine-grained metals in bulk using a simple low-cost approach is a long-term goal for material scientists.In this work,based on the chemical composition of a biomedical Ti-15Zr alloy,a series of novel Ti-15Zr-xCu(x=0,3,5,7 wt.%)alloys were designed and fabricated.The alloys were quenched in the singleβphase region to obtain a martensitic microstructure and deformed in the temperature range of 710–750℃to obtain an ultrafine-grained microstructure through martensite decomposition under thermomechanical coupling conditions.Experimental results showed that Cu alloying could increase the dynamic recrystallization(DRX)nucleation rate due to its role in both refining martensitic lath width and increasing dislocation density.Cu alloying could also suppress grain growth due to the precipitated Ti_(2)Cu particles exerting pinning forces on the grain boundaries.The optimal Cu content in the Ti-15Zr-xCu alloy was determined to be 5 wt.%.After being subjected to a compression leading to a 70%height reduction at 730℃and 1 s^(–1),the grain size of the Ti-15Zr-5Cu alloy was only 180±70 nm.The tensile strength of the as-prepared alloy reached 975±10 MPa,which was 45%higher than that of the conventional Ti-15Zr alloy(673±16 MPa).This increase in strength was achieved without any reduction in ductility.The comprehensive mechanical properties of the ultrafinegrained Ti-15Zr-5Cu alloy are better than that of the Roxolid Ti–Zr alloy currently used for dental implants.