MATRIX PENETRATION OF W/W GRAIN-BOUNDARIES AND ITS EFFECT ON MECHANICAL-PROPERTIES OF 93W-5.6NI-1.4FE HEAVY ALLOY

The matrix phase of 93W-5.6Ni-1.4Fe heavy alloy has penetrated into W/W grain boundaries during a newly developed heat treatment which consists of repeated isothermal holdings at 1150-degrees-C and water quenching between them. With the matrix penetration, the impact energy increases from 57 to 170 J, whereas the ultimate tensile strength and elongation remain unchanged. The tensile fracture surface of specimens appears similar regardless of the matrix penetration: predominant cleavage of W grains and dimple fracture of matrix. The fracture surface by impact, on the other hand, reveals a change of W/W interface failure toward ductile failure of penetrated matrix with many dimples by increasing the matrix penetration. The increase in the fraction of ductile failure and observed crack blunting is attributed to the increase in impact energy with the matrix penetration.