g-TiAl intermetallic alloy have a good potential for use as biomaterial, due to its good corrosion resistance. In this paper, two fundamental electrochemical techniques namely electrochemical impedance spectroscopy and potentiodynamic anodic polarization were used to evaluate the corrosion performance of g-TiAl in Ringer's solution. Surface modification treatments were employed with the purpose of improving corrosion resistance. The samples were oxidized at 550°C in air for 1 h. The results show that oxidized Ti-47Al-2Cr has much better corrosion resistant in Ringer’s solution. The presence of the oxide layer formed with the surface treatments increased their corrosion resistance. The low values of corrosion rate, and the high values for corrosion potential (Ecorr) and polarization resistance (Rp) obtained experimentally implies that g-TiAl can be competitively considered as an alternative metallic biomaterial.

Reactive sintering is a kind of combustion synthesis processes for synthesize of new materials. In this research, the mentioned process was used for production of Titanium aluminide/alumina composite from starting materials of Titanium dioxide and aluminum. According to the obtained results, composite particles including TiO2/Al with a size around 100 nm can be produced. Densification of produced powders via cold isostatic pressing machine following by reaction sintering lead to produce a composite body consisting Titanium aluminids and alumina.

In this work, kinetics of intermetallic compounds formation in Al-Ti system was studied by immersing Titanium sheets in pure molten aluminum at 750oC, 850oC and 950oC. According to Scanning Electron Microscopy and X-Ray Diffraction Analysis results, TiAl3 is the only phase can form at the interface. Observations revealed that intermetallic layer thickness increases slowly at primary stages. After that an enhanced growth rate occurs due to layer cracking and disruption. Presumably, reaction starts with solving Titanium into the molten aluminum causing in Titanium super saturation and TiAl3 formation. At this stage, growth may be controlled by aluminum diffusion through intermetallic layer which consequently leads to TiAl3 formation at the interface of Ti-TiAl3. Furthermore, activation energy of intermetallic layer formation and growth was developed by measuring Titanium thickness decreases.

In this article, an attempt was made to investigate the effect of the addition of silicon on the Titanium aluminide compound formation from TiO2 and Al raw materials. Silicon has a eutectic with aluminum and can reduce its melting temperature, which can have effective impact on the formation of Titanium aluminide compounds. On the other hand, due to the production of Ti5Si3 compound, it can be effective in increasing the oxidation resistance of compounds and composites containing Titanium aluminide. With this aim in mind, the present paper has strove to determine the impact of this element on the formation of Titanium aluminides and the type of Titanium silicide phases by adding different amounts of silicon to TiO2 and Al raw materials. The key findings emerged, showed that when silicon is added to the system in small amounts (0.1), it not only does not have a positive effect on the reactions, it also prevents the formation of Titanium aluminide compounds, but with an increase in its percentage (0.28), it also causes the formation of these Titanium aluminide compounds and leads to the formation of Ti5Si3 phase. This phase changes from a discrete morphology to a continuous state as the percentage of silicon increases (0.6). With a further increase in the amount of silicon (1), the TiSi2 phase is formed, which is dispersed throughout the sample with a string-like structure.

Production of Titanium aluminides in TiO2-Al-Casystem has been investigated. For this' purpose, different compositions of raw materials were studied in a special reaction vessel. In a special case, the non-completed reaction of TiO2 with Al and Ca resulted in the production of granulates of Titanium aluminides especially Ti3Al and other Ti - Al phases as the metallic product and Ca12Al14O33as the non-metallic product. Remolding of metallic granulates led to production of TiAl ingot.

Titanium aluminides have received much attention due to their suitable properties such as lightness, maintaining strength at high temperatures, and resistance to corrosion and oxidation. Therefore, Titanium aluminides and their composite play a key role in the industry, especially in urban transportation and aviation industries. The melting of aluminum is recognized as the first step of the Titanium aluminide formation process from elemental powders or raw materials of TiO2 and Al. Facilitating the aluminum smelting could be a contributing factor to accelerating the Titanium aluminide-generating procedure. Selecting copper as an agent to reduce the melting point of aluminum is based on the binary phase diagram of Al-Cu in which a eutectic transformation is obvious. Different molar ratios of copper were added to the raw materials of aluminum and titania. Then the resulting compressed powder samples were subjected to heat treatment. It was found that up to a certain molar ratio, copper could reduce aluminum's melting temperature and promote the formation of Titanium aluminide intermetallic compounds. The optimal amount of copper (0.2) has also greatly contributed to the uniformity and homogeneity of the composite structure. In general, in this research, the effect of copper on the production of Titanium aluminide has been discussed both theoretically and practically.

Titanium aluminide intermetallic compounds are a small group of materials that can be used at high temperature structures where the specific strength (strength to density ratio) and specific stiffness (elastic modulus to density ratio) are very important. In this study, some output characteristics of electrical discharge machining (EDM) process; including material removal rate (MRR), surface roughness and topography are investigated for this material. The DOE method of full factorial is used for planning the machining tests that two main input parameters of pulse current and pulse on time are changed in five and four different levels, respectively and other input machining parameters are kept constant during tests. The results show that in lower currents (3 and 6 A), despite the increase in pulse time, there is no significant change in MRR and the MRR for these two currents is negligible, indicating that finishing process of Titanium aluminide is difficult and time consuming, but there is no such situation in more currents (12, 24 and 64 A) and the roughing process of this material is optimally carried out. For the currents above the 24 A, the gradient of MRR increase, is decreased because of arc appearance. In the states of higher electrical currents, the lengths of cracks on the machined surface are increased and the widths of cracks are growing. While arc is occurred for the higher electrical discharge energy, the surface roughness and topography are intensively different from the other current and pulse on time conditions.

In this research, the Planetary mill was used for mechanical alloying (MA) of Ti and Al powder mixture with equal at% (Ti50Al50). The effect of various factors, such as process control agent(PCA), speed of rotation of vial and ball-to-powder weight ratio, on process were studied and the best condition to synthesis the alloy was determined. Study on X-ray diffraction (XRD) patterns showed that at primary hours of milling, the powder mixture transmitted to metastable solid solution phase and with increasing the alloying time, that phase transformed to an amorphous, ultra fine grain and homogenous phase. Changes in grain size, lattice strain and impurity content during alloying and various condition were studied and at last with annealing of the product, the TiAl ( g) phase with high purity and nanostructered form was produced.

In this study, three series of electrical discharge machining experiments were carried out on γ-TiAl intermetallic. In the first series, by changing pulse current and pulse on time in EDM process and in the second series by changing the size and concentration of aluminum powder particles mixed in dielectric fluid, output characteristics including material removal rate (MRR), tool wear rate (TWR) and surface roughness (SR) are evaluated. In the third series of machining experiments, after determination of the optimum size and concentration of aluminum particles, current and pulse on time, are changed at levels as exactly the same levels in powder-free tests and MRR is evaluated. Finally, MRR of the EDM and optimum PMEDM processes, are compared. By increasing the aluminum particles concentration, TWR and SR will be decreased to an optimal level and then will be increased. For particle size of 2 μ m and 20 μ m, by increasing the aluminum powder concentration, MRR increases at first and then decreases, while for particle size of 63μ m, by increasing powder concentration, MRR decreases. The minimum and maximum increment of MRR in optimum PMEDM condition compared with EDM mode was 32% and 88%, respectively. With increase of electrical discharge energy, the addition of aluminum powder has less effect on increase of sparking frequency and consequently the MRR.

Modern intermetallic compound of gamma Titanium aluminide (γ-TiAl) due to its low density, high elastic modulus, high resistance to oxidation, corrosion, and ignition has recently been considered in the aerospace and automotive industries. Traditional machining of this alloy is so difficult. In the current study, electrical discharge machining of γ-TiAl samples is investigated using different tool electrodes of graphite, copper, and aluminum. The results show that when using aluminum electrodes, tool wear rate is averagely 3. 2 times more than copper and 5. 8 times more than graphite tools. In addition, when using graphite electrodes, the average material removal rate is 4. 2 times more than copper and 7. 7 times more than aluminum. Machining by aluminum tool leads to formation of Al2O3 and TiO2 oxide compounds on the work surface but in machining by graphite electrode, TiC and Ti8C5 carbide phases are created on the work surface. In machining by graphite due to formation of hard carbide compounds in the recast layer, the microhardness is higher than the machined sample by the aluminum tool, where oxide compounds exist on the surface and the hardness of recast layer in the machined sample by copper electrode is less than the other two electrodes, because of existing phases such as copper oxide with less hardness. The highest electrochemical corrosion resistance belongs to the machined specimen using graphite tool and the lowest corrosion resistance is related to the machined sample by aluminum electrode. Reducing oxide and aluminum compounds and increasing carbide phases enhance the corrosion resistance of γ-TiAl machined samples.