Smart Composite Biomaterials TiAIV/AI 2 O 3 /TiNi
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577 Mat. Res. Soc. Symp. Proc. Vol. 459 ©1997 Materials Research Society
RESULTS AND DISCUSSION The cross-sectional cut of specimen containing plasma-coated TiNi wire in Ti6AI4V alloy is shown in Fig. 1. From this Figure, it is visible that the A120 3 coat reacts with melt and gas bubbles give rise. The TiNi wire (bright) with A120 3 coat (dark layer) followed by transition layer inTi6AI4V alloy matrix can be clearly seen. Analogous situation was observed in TiAIVNb alloys. The sources for creation of bubbles are different. The bubbles can form as a consequence of inappropriate flow of Ti-alloy melt during casting
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Fig.1. General view on TiNi/ A1203 embedded in Ti6AI4V matrix.
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Fig.2. Dendritic structure of TiNi containing Ti 4(NixAly) 2(O,N)z-type particles (darker phase).
process, however, the plasma coats contain some quantity of gaseous phase in their pores, which can expand. Finally, the gaseous oxygen may originate during the reaction 12Ti + 2A120 3 -+ 4Ti3AI + 302. It is apparent from Fig. I that the reaction intensity between alumina and individual metallic compounds (Ti-alloy or TiNi) differs depending on heat flow intensity. The plasma coating (dark layer surrounding TiNi wire) is thinner indirection towards the center of ingots and its thickness increases to the maximum value in direction where the maximum heat flow occurs (maximum cooling rate). Almost all bubbles are concentrated in region of greatest reaction intensity. The typical structure of TiNi alloys is shown in Fig. 2. The casting process is connected with remelting of TiNi wire because the casting temperature is higher than the melting point of TiNi. The structure after this remelting consists of TiNi dendrites and the darker interdendritic phase. It was identified by EDX analysis that the content ratio Ti to Ni in this darker phase corresponds to the value 2:1. However, using WDX analysis, it has also been found that this phase contains more oxygen and nitrogen if compared to the matrix. Based on observed results we can conclude that the detected composition corresponds to Ti 4(NiXAlY) 2(O,N)z phase [12]. The Ti6AI4V matrix consists of prmary oa-phase and transformed P-phase as can be seen in Fig. 3. The content of pdmary oa-phase (darker phase in Fig. 3) ranges between 10 and 15%, and it has been found that this phase contains carbon. The source of carbon, found in ax-phase, is carbon crucible. It is well known that carbon stabilizes a-phase, and its quantity depends on the carbon content. The most important areas of interest are the boundaries between alumina ceramics and metal systems. The general view on the regularly observed good bonding between A120 3 and TiNi or Ti6AI4V is shown in Fig. 4. The high temperature enables the aluminum atoms to diffuse into both TiNi and Ti6AI4V(Nb) alloys if the cooling rate is small enough and the interphases occur in the vicinity of different materials. Interphase which forms between A120 3 and Ti6AI4V (Nb) contains approximately 75 at % of Ti, 22 at % of Al 2 to 3 at
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