In this work, a Tie48Al alloy was induction melted and allowed to cool and solidify in a ZrO 2 based crucible with an inner layer of Y 2 O 3 , and the effect of superheating parameters (time and temperature) on the metalecrucible interface, alloy chemical composition, microstructure and microhardness is evaluated. Microhardness variation and segregation profiles of residual elements, namely yttrium and oxygen, from the surface to the inside of samples are presented and compared, in order to establish a relationship between the processing parameters, alloy contamination and the ''alpha-case'' extent. The alloy microstructure at the metalecrucible interface is characterized for each superheating time and temperature. The Y 2 O 3 crucible layer was found to suffer some erosion and be slightly dissolved by the molten alloy and the extent of that dissolution, and consequent metal contamination with yttrium and oxygen, depend on both superheating temperature and holding time. A relationship was found between oxygen concentration profiles and microhardness profiles of the a 2 þ g microconstituent, from the surface to the inside of samples, which depends on the superheating temperature, but is not affected by the holding time.

a b s t r a c tIn this work a Ti-48Al alloy was induction melted in a CaO crucible using different superheating temperatures. In the first stage, samples were allowed to cool to room temperature inside the crucibles, in order to simulate a low cooling rate, and in the second stage samples were centrifugally poured into a steel mould, in order to study the effect of the melting operation on the alloy contamination with oxygen. The effect of superheating temperature on the metal-crucible interaction, alloy chemical composition, microstructure and microhardness is evaluated. The CaO crucible was found to be slightly dissolved by the molten alloy and the extent of that dissolution depends on the superheating temperature. A relationship was found between oxygen concentration and microhardness profiles of the a 2 þ g microconstituent, from the surface to the inside of samples, which depends on the superheating temperature and cooling rate.

These reactions could contaminate the castings, due to the absorption of some residual elements, and produce chemical heterogenities, inclusions and structural variations. This paper describes the work done with titanium aluminides prepared from pure aluminium and titanium melting stock. The main objectives were two fold: I st Evaluation of the behaviour of some refractory materials during the melting of TiAl; 2nd The relationship between micro-hardness, the concentration profile of residual elements in those phases present at room temperature, and the extent of the "alpha-case" (a surface layer with an higher microhardness than the average value found in the bulk of the casting). This paper describes the processing results of TiAI alloys melted in a controlled atmosphere induction furnace, using crucibles made of graphite, calcia and zirconia stabilized with yttria, calcia and magnesia. Samples were poured into graphite permanent moulds or solidified and cooled inside the crucible, in order to simulate the worst case scenario in a metaV refractory reaction using this process. This paper presents segregation profiles of residual elements and their influence on the micro hardness of different phases and the extent of the "alpha-case".

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This paper describes the evaluation of different refractory compounds -SiO 2 , ZrO 2 and Y 2 O 3 -as face coats of investment casting shells for c-TiAl.The effect of the different refractories on the metal-mould interaction is studied in different aspects. Experimental results include characterisation of the constituents present at the metal/ mould interface, the segregation profiles of residual elements, namely oxygen, from the interface to the inner part of the samples, the extension and microhardness of the samples external hard case and the samples surface finishing.