THE STATE OF SURFACE ZONE OF COARSE POROSITY IN SINTERED REFRACTORY-METALS

The data on nonuniform distribution of pores in sintered billets of W, Mo and Nb, are given. On the example of tungsten wire manufacture pro cess it is shown that the near-surface zone of coarse porosity can sub stantially affect the semiproduct properties and that the small bar de fects are inherited during the working process. The most likely reason for this zone to be formed may hc elastic interaction on the metal-to ol boundary which causes tensile stresses generated during disloading after biller compaction as well as residues of liquid binder and atmos pheric gas bubbles sealed up by it which are pushed to the near-surfac e zone. During the downstream sintering operations liquid and gas resi dues are removed, and coarse pores are left near the sintered biller s urface.