The effects of surface conditions on the ductile-to-brittle transi¬tion temperature of specimens of commercially pure sintered tungsten were evaluated by tensile tests carried out in vacuum. Prior to testing, the specimens were vacuum-annealed at 3500° F for 1 hour, electropolished, and then given the desired surface treatment. Percent reduction in area was used as the basic criterion to establish the transition temperature.nPreliminary tests showed that removal of 0.010 inch from the 0.170-inch-diameter test specimen by electropolishing increased the ultimate tensile strength of the annealed specimen from 68,000 to 82,000 psi;therefore, all specimens were electropolished to avoid ambiguous results due to the initial grinding of the test specimen. Specimens having an electropolished or oxidized surface and hence free from intentional sur¬face cracks or notches exhibited the lowest transition temperature (415° F). Results from specimens that were chemically etched and those that were ground indicated that the transition temperature was independ¬ent of degree of roughness as measured by a surface analyzer, but was a function of type of roughness. The transition temperature of specimens having a ground surface was approximately 75° F higher than that of spec¬imens having an etched surface condition. Annealing of the ground spec-imens prior to testing failed to change the transition temperature from that of the unannealed specimens, indicating that the high transition temperature of the ground specimens (compared with the electropolished condition) was due to surface roughness rather than a residual-stress state. Peening the ground surface also failed to lower the transition temperature. Results of notched specimens (theoretical stress concen¬tration factor of 6) indicated that recrystallized tungsten is notch-strengthened at the higher test temperatures, and the presence of the notch increased the transition temperature 360 F above that of the un-notched specimens.
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