| An investigation was made to establish the pre-treatment conditions for hot forging of aγ-TiAl alloy. The investigation was based on the fractional ratios of the phases formed under varying rates of heating during reaction. The chemical composition of the experimental alloy was Ti-46.6Al-1.4Mn-2Mo(at%) and elemental powders were used as raw materials to synthesize the alloy. Representative phases in reaction-sintered elemental powders consisted of TiAl, Ti₃Al and TiAl₃, and a fast heating rate increased the amount of Ti₃Al but decreased that of TiAl₃. From the EPMA and EDS analysis it was concluded that the retention of TiAl₃, a source of porosity, was governed by the extent of solid-solid reaction below the melting temperature of Al. With the effect of the heating rate on the TiAl₃confirmed, we then experimented high frequency induction heating as a means to substantially increase the heating rate. A heating rate of 300℃/min thus obtained essentially removed the TiAl₃ phase and reduced porosity in the final material. As a result, a sound γ-TiAl with a fully lamellar microstructure of 50 ㎛ in grain size was produced in heat-treated condition. |
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