Preparation And Mechanical Properties Of Nanocrystalline W-Ti Alloy Bulks

As a potential plasma-facing material,nanocrystalline W exhibits excellent radiation tolerance.However,nanocrystalline W is unstable at high temperature since the grains grow quickly as the temperature increases.This paper aims to prepare a nanocrystalline W-Ti alloy with a high thermal stability and good mechanical properties at room temperature and high temperature by adding Ti element.Nanocrystalline W,W₉₀Ti₁₀,W₈₀Ti₂₀ and W₇₀Ti₃₀ alloy powders were prepared by mechanical alloying.All the four powders had a single-phase BCC structure and an average grain size of about 12 nm.The nanocrystalline W,W₉₀Ti₁₀,W₈₀Ti₂₀ and W₇₀Ti₃₀alloy powders after ball milling were sintered under the condition of 4 GPa and 700??1200?.As the sintering temperature increases,the relative density of the W-Ti alloys increases first and then remains unchanged.The Vickers hardness of W-Ti alloys is mainly determined by the relative density and the average grain size.The average grain size of pure W,W₉₀Ti₁₀,W₈₀Ti₂₀ and W₇₀Ti₃₀ alloys sintered under the condition of 4 GPa and 1100?is 564,75,42 and 82 nm,respectively.The Vickers hardness and the average grain size of the four alloys follow the Hall-Petch relation.Thus,the high hardness of W-Ti alloys is mainly attributed to grain boundary strengthening.The segregation energy and grain boundary energy of W₉₀Ti₁₀,W₈₀Ti₂₀ and W₇₀Ti₃₀ alloys are calculated.The results show that the grain boundary segregation behavior of Ti is an important factor for the stability of nanocrystals.The EDS analysis of the W₈₀Ti₂₀alloy confirmed the phenomenon of grain boundary segregation.The compressive strength of the W₈₀Ti₂₀ alloy at room temperature is about 4603 MPa.But the plasticity of the W₈₀Ti₂₀0 alloy is poor,which is mainly due to the high grain boundary density of nanocrystalline and the excessive hindrance of grain boundary to dislocation motion.Under the action of high temperature,the degree of Ti segregation to grain boundary becomes greater,which reduces the grain boundary energy and keeps the alloys still in nanocrystalline structure.Hence,W-Ti alloys exhibit high compressive yield strength even at high temperature.The compressive yield strength of the W₉₀Ti₁₀ alloy at 900?can reach a high value of 1144 MPa.In this paper,the grain boundary segregation principle of W-Ti binary alloy is used to prepare nanocrystalline W-Ti alloys with excellent mechanical properties at both room temperature and high temperature,which provides a theoretical and experimental basis for the application of nanocrystalline W-Ti alloys in the future.