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 gra ins in W-Ni-Fe heavy alloy has been studied. The addition of Mn was perform ed by placing a compact of Mn powder on the sintered specimens containing c onstant Ni/Fe ratio of 8/2 but different W contents of 93 and 97 wt pet fol lowed by resintering. The sintering and resintering treatments were carried out at a temperature of 1485 degrees C under a dry hydrogen atmosphere. Th e addition of Mn leads to the deviation of growth rate of W grains from the diffusion-controlled Ostwald ripening: the growth rate is initially enhanc ed 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 addi tion 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 o f W grains from roundish to angular shape. The addition of Mn into the matr ix phase, which is artificially made, forms the dendritic W grains. From th ese results, it is found that the morphological change of W grains is close ly related to the precipitation reaction of W atoms on the preferred orient ation.