Effects of Co dopping on structure and hydrogen-permeation properties of Nb95W5 solid solutions

Alloying is an effective method to solve hydrogen embrittlement of ⅤB metals（Nb,V,Ta）. Effect of Co dopping on structure and hydrogen-permeation properties of Nb95-xW5Cox（x=1, 2, 3, 5） have been investigated in this work. The results indicate that as-melted Nb95-xW5Cox samples are all solo Nb-bcc solid solutions. The degree of lattice shrinking-distortion of these samples is affected by dopping amount of Co. Co-rich NbCo soluton structure is precipitated at grain boundaries and intracrystalline defects of Nb solid solution based on the matrix（Co-poor region）. Co-dopping resultes in the decrease of hydrogen solution and the increase of hydride formation enthalpy, which benefit H-diffusion and the improvement of hydrogen-permeation properties of Nb95-xW5Cox alloys. Nb90W5Co5 alloy has lower absolute value of hydride formation ehthalpy（-22.3 kJ/mol）, higher hydrogen-diffusion coefficient(1.57×10-9 cm2/s), the maximum values of critical load（78.4 N） and larger displacement amount（0.9 mm）. The improvement of hydrogen embrittlement resistance of Nb95-xW5Cox samples can be attributed to solution strengthening caused by Co-dopping.