Selected mechanical properties of IN SITU Al-TiC composites compared with an EX SITU DURALCAN-SiC composites
Edward Fraś, Andrzej Kolbus, Andrzej Janas Akademia Górniczo-Hutnicza, Wydział Odlewnictwa, ul. Reymonta 23, 30-059 Kraków
Annals 2 No. 4, 2002 pages 176-179
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abstract Aluminium - based composites reinforced with particles of alien phases (MMCs) are considered products of the advanced technology. The service properties of MMCs can be controlled through changes in the type, content and dimension of reinforcing particles. In the case of MMCs based on aluminium alloys, the reinforcing particles used are most often carbides TiC, SiC, ZrC, oxides Al2O3, TiO2, MgO, ZrO2, nitrides BN, TiN, Si3N3 and borides TiB2, ZrB2,SiB2. In conventional route MMCs are fabricated by the ex situ methods, where the reinforcing phases are introduced to the metal bath by e.g. vortex process. A new interesting method of making composites is in situ process, where the reinforcing phases are produced directly in liquid metal as a result of the chemical reaction proceeding therein. In the in situ process it is possible to create a reinforcing phase nucleating in the metal bath, which ensures an excellent contact between this phase and the matrix enhanced by the phenomenon of a wettability of that phase by liquid alloy. In this paper the SHSB method of fabrication of the in situ composites Al-TiC was applied. The investigation was carried out on powdered titanium, aluminium and carbon of which after making the blend homogeneous and squeezed, briquettes of stoichiometric composition ensuring proper condition for the synthesis of TiC were formed. The synthesis of the composites was performed in a Balzers vacuum furnace, under argon protective atmosphere. After the exothermic reaction had taken place in the briquette and a suspension of TiC in aluminium alloys had been formed, the material was cast into steel mould. From the obtained castings, samples were taken for metallographic, structural and mechanical tests. In the second part of the experiment the Duralcan-SiC alloys were preparated. The X-ray examinations have revealed the presence of carbides TiC and Al3Ti in the Al-TiC alloys (Fig. 1a), and carbides SiC and Al4C3 in the Duralcan-SiC alloys (Fig. 1b). The structures of these two alloys are presented in Figure 2. Finally, the mechanical tests based on the test of isothermal sgueezing at temperature 293 K were performed (Figs 3 and 4). The results of this tests showed the Al-TiC MMCs have higher strenght compared with the Duralcan-SiC composites (Fig. 5).