Investigation Of Preparation Of TiAl-Based Alloys By Mechanical Alloying And Hot Pressing Sintering

Intermetallic compounds possess many attractive properties for potential high temperature applications.Titanium aluminide-base alloys, in particular, have been potentially developed for use in thermal protection systems, engines and aircraft turbines. These alloy offer the combination of low density, attractive high-temperature properties and high-specific properties compared to the incumbent Ni-base superalloys. A major disadvantage of TiAl alloys, however, is there poor room-temperature ductility and workability. Such low RT ductility poses a major obstacle to the widespread use of these materials, and recent studies and developments have focused on overcoming this problem. Mechanical alloying (MA) is known as a powder metallurgy processing route for producing compacts with an ultrafine grain structure. Therefore, titanium aluminides produced by MA are expected to exhibit improved workability at a decreased temperature. The majour work of this study is The majour work of this study is preparation of TiAl - base alloys by mechanical alloying and hot-pressing sintering, and their microstructure and mechanical properties studied.At first, blended powder with the nominal composition Ti₅₂Al₄₈ was mechanically alloyed in a planetary ball milling. The structure evolution in the powder was characterized by scanning electron microscope, X-ray diffraction and differential thermal analysis techniques. It was found that with increased milling time, powders became equiaxed , the size of composite powders gradually became to magnitude of nanometer and the distribution of particle size became narrow. In the whole process, no Ti-Al Intermetallic compound was found to come into being.Moreover, the densification behavior during hot-pressing sintering of compacted Ti/Al composite powders prepared by high-energy ball milling was experimentally investigated, and the thermodynamics and kinetics aspects were theoretically analyzed. The results show that high-energy ball milling promotes the sintering densification promotes the sintering densification process more effectively than othermeans, such as increasing the applied pressure, enhancing the sintering temperature, or prolonging the sintering time. The longer the milling time is , the higher the relative density of the as-sintered specimen. The density of the TiAl alloy obtained by hot-pressing sintering at 1300°C from the powder milled for 40 h was as high as 3.971 g/cm3, and the relative density w^s as high as 99^55%.Finally, the microstructure and mechanical properties of TiAl - based alloys by mechanical alloying and hot-pressing sintering were studied. It was shown that homogeneous Ti-Al based alloys with fine microstructures can be obtained by means of this way. The mechanical properties of the P/M Ti-Al based alloys are related to their microstructures. The finer the microstructure, the higher the room temperature strength and ductility.