Abstract
The microstructural defects acting as fracture source in P30 alloy, prepared by the use of recycled starting powder, were studied. Special defects, that is, pores accompanied by the βt layer (A1 defect) and binder pools to which βt layer attached (A2 defect) were often observed in sintered alloy and HIP-treated alloy, respectively. The strength of HIP-treated alloy was sharply affected by the appearance of the A2 defect. It was confirmed that the formation of A1 defect was caused by the segregation of extremely fine particles of impurity oxides, etc., where the segregation took place inevitably in the mixed powder. The result of model experiments showed that impurity atoms dissolved in the binder phase at the periphery of pores and then decreased the solid-solubility of W. It was suggested that the concentration gradient of W, Ti and Ta solutes in the liquid binder was produced near the pore, leading to the formation of the βt layer as above mentioned.
