چكيده به لاتين
γ-TiAl based intermetallic alloys have been extensively studied as poten tial replacement for nickelbased superalloys in different applications such as turbine blades for air craft engines, stationary turbines, and space vehicles. These alloys have relatively high yield strength at elevated temperatures, good creep characteristics, and excellent oxidation/corrosion resistance. In combination with their low density (3.9–4.1 g⁄cm^3 ), these materials seem very attractive as high temperature structural materials for aerospace, automotive, and other applications.
Over the past years, a search for new approaches to synthesis of intermetallics (including titanium aluminide and related materials) has led, among others, also to the technique of selfpropagating hightemper ature synthesis (SHS). The SHS process is based on the principle of maximum utilization of chemical energy of reacting substances(exothermicity) for obtaining inorganic compounds, such as intermetallics. The SHS method was discovered in the 1970s and some useful technologies were developed on the basis of this method, several of them with the application of mechanical pressure during the reaction.
In this study, the effect of Mg additive on SHS process velocity was investigated. Additives can change the intensity of the SHS reaction. They can also help control the degree of porosity caused by sintering. In this experiment, three different percentages of Magnesium by weight of 3, 5, and 10wt% were used in the Ti-Al mixture, which was increased at a constant heating rate of 5℃⁄min. Subsequent samples were then subjected to heat treatment at critical temperatures. It should be noted that in order to increase the heating rate in the next stage, the oxyacetylene burner was used in the vacuum compartment for heating. The results show that at low heating rates, the addition of magnesium up to 5wt%, reduces the combustion reaction temperature and leads to the formation of TiAl compounds with low Ti₃Al values. Also, in thermal treatments, the results showed that we need more time to synthesize the product. On the other hand, in order to reactively sintering, we needed a high heating rate that optimum condition can be prepared by the oxyacetylene burner in a vacuum quartz shield.
