The effect of manganese addition on the microstructure of W-Ni-Fe heavy alloy

The influence of Mn addition on the growth kinetics and morphology of W grains in W-Ni-Fe heavy alloy has been studied. The addition of Mn was performed by placing a compact of Mn powder on the sintered specimens containing constant Ni/Fe ratio of 8/2 but different W contents of 93 and 97 wt pet followed by resintering. The sintering and resintering treatments were carried out at a temperature of 1485 degrees C under a dry hydrogen atmosphere. The addition of Mn leads to the deviation of growth rate of W grains from the diffusion-controlled Ostwald ripening: the growth rate is initially enhanced and then decayed. The difference in the average grain radius between the alloys containing high and low W contents is decreased by the addition of Mn. The cause of the change in the growth rate of W particles with the addition of Mn is discussed in terms of the competitive soluble reactions of Mn and W atoms. The addition of Mn also results in the morphological change of W grains from roundish to angular shape. The addition of Mn into the matrix phase, which is artificially made, forms the dendritic W grains. From these results, it is found that the morphological change of W grains is closely related to the precipitation reaction of W atoms on the preferred orientation.