• Korean Journal of Materials Research
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• v.2 no.6
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• pp.468-476
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• 1992

Stress rupture properties and fracture behavior of Ni microalloyed W were studied using direct load creep tester at 100$0^{\circ}C$, 110$0^{\circ}C$ and 120$0^{\circ}C$ in $H_2$. At the same grain size, 15${\mu}$m, the 100hr. stress rupture strength of W-0.4wt% Ni was 23% higher than that of W-0.2wt%Ni due to the grain growth during test. The minimum creep rate of W-0.2wt%Ni was decreased with an increase in initial grain size. By increasing the Ni content of Ni microalloyed W, rupture time was increased owing to the smaller number and size of cavity. All the specimens showed intergranular fracture by grain boundary sliding and nucleation, growth and coalescence of cavities at grain boundary.

• Korean Journal of Materials Research
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• v.2 no.4
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• pp.270-278
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• 1992

The effect of Ni-rich phase on the stress-rupture properties of Ni mlcroalloyed W were studied using direct load creep tester at 100$0^{\circ}C$, 110$0^{\circ}C$, and 120$0^{\circ}C$ in $H_2.$ The stress rupture strength of 100hrs. of W-0.4wt% Ni was 43% higher at 100$0^{\circ}C$ and 35% higher at 110 $0^{\circ}C$than that of W-0.2wt% Ni due to the larger initial grain size, the higher relative density and the higher grain growth during test. That of W-0.8wt% Ni was 90% higher at 100$0^{\circ}C$ and 60% higher at 110$0^{\circ}C$ than that of W-0.2wt% Ni. The activation energy of W-0.4wt% Ni for creep was 81.3 Kcal/mole. It was considered that creep deformation was controlled by the diffusion of W in the Ni rich phase between the grains and the deformation of grains. All of the specimens showed intergranular fracture by grain boundary cavitation and growth of cavity throughout the entire spcimen cross-section.