to inclusions to cause adsorption of them on the crucible wall (for VIM process), filter surface (for filtration process)or in the molten slag (for ESR process). If the inclusions in the original metal decompose in the liquid metal during the special melting processes,the inclusion removal will result from the interaction between the liquid metal and vacuum atmosphere (for VIM and VAR processes) or melten slag (for ESR process).Therefore,the techaique for removing inclu- sions or improving cleanliness will be different under the two conditions mentioned above. In this paper,the behavior of inclusions during the VIM,VAR and ESR processes of superalloys has been investigated.For most superalloys,the prime target for inclusion reduction is that of nitrides,since their content is usually an order of magnitude higher than that of the oxides.The study emphasized the behavior of nitride inclusions. 1 The Decomposition of Pure TiN Powder in the Liquid Metal during the VIM Process of Superalloys In work 2,it was supposed that TiN cannot be decomposed by vacuum induction melting at pressures realistic for superalloy processing (ie.,>1um)and some technique (e.g,filtration)for removing solid TiN from the liquid super- alloy must be proposed. For confirming this viewpoint,a special experiment was arranged. The experiment was carried out in a 10kg VIM furnace.The alloys tested were the commonly used forging superalloy GH169 (In-718)and GH132 (A- 286).During the experimental process,a piece of forging bar from 30kg VIM ingot remelted in a corundum crucible at pressure of higher than 1330Pa.When the temperature of liquid metal reached 1550C,the pure TiN powder weighing 0.2 wt%of charge was added into the melt.The melt remained in the crucible at 1550C for 2 min then poured into a cast iron mold.The ingot weight was about 1.7kg. The nitrogen contents of original forging bar and VIM ingot were analysed by TN-114.The size,morphology and composition of TiN powder and the character of inclusions in the ingot were investigated by JMS-35C SEM. The nitrogen content analysis results are shown in Table 1.It can be seen that 240ppm and 236ppm nitrogen have been added into GH169 and GH132, respectively. The size of TiN powder is more than 104m,predominately,within 20-30 um.The size and morphology of TiN powder are shown in Fig.1,a. The SEM wave spectrum and the energy spectrum observation results indicated 502， · ， ， 爪 几 ， ， · ， ， 。 声 ， · · ， ” ， ， · 一 一 五 ， · ， 。 “ 皿 一 · ， 一 · 。 ， 拼 ， ， 一 “ · 一 ， · 尸