TiAl Research Articles

Influence of Electron Beam Powder Bed Fusion Process Parameters at Constant Volumetric Energy Density on Surface Topography and Microstructural Homogeneity of a Titanium Aluminide Alloy

In powder bed fusion additive manufacturing, the volumetric energy density E V is a commonly used parameter to quantify process energy input. However, recent results question the suitability of E V as a design parameter, as varying the contributing parameters may yield different part properties. Herein, beam current, scan velocity, and line offset in electron beam powder bed fusion (PBF‐EB) of the titanium aluminide alloy TNM–B1 are systematically varied while maintaining an overall constant E V. The samples are evaluated regarding surface morphology, relative density, microstructure, hardness, and aluminum loss due to evaporation. Moreover, the specimens are subjected to two different heat treatments to obtain fully lamellar (FL) and nearly lamellar (NLγ) microstructures, respectively. With a combination of low beam currents, low‐to‐intermediate scan velocities, and low line offsets, parts with even surfaces, relative densities above 99.9%, and homogeneous microstructures are achieved. On the other hand, especially high beam currents promote the formation of surface bulges and pronounced aluminum evaporation, resulting in inhomogeneous banded microstructures after heat treatment. The results demonstrate the importance of considering the individual parameters instead of E V in process optimization for PBF‐EB.

A tribological characterisation of Ti-48Al-2Cr-2Nb and Ti-6Al-4V alloys with dry, flood, and MQL lubricants

The development of cutting tools requires the knowledge of tribological phenomena at the tool – workpiece contact area. This knowledge is in dearth particularly for difficult-to-cut alloys like gamma titanium aluminide (gamma – TiAl alloys). Therefore, this article is an attempt to plug the gap and aid the development of cutting tools for gamma – TiAl alloys. To this end, friction, adhesion, and coating wear between AlTiSiN coated cemented carbide tool and Ti-48Al-2Cr-2Nb (Near lamellar), Ti-48Al-2Cr-2Nb (Duplex), and the most used titanium alloy of Ti-6Al-4V (alpha – beta) were experimentally derived. A Pin-on-Cylinder (PoC) tribometer with contact conditions corresponding to commercial machining conditions was used with dry, flood(EML), and two MQL lubricants. Additionally, the heat generated and partitioned between the pin and workpiece was quantified to assess the thermal exposure to the coatings. The results showed that Ti-6Al-4V had approximately 50% higher apparent friction coefficient than the Ti-48Al-2Cr-2Nb alloys. Interestingly, the friction coefficients of Ti-48Al-2Cr-2Nb alloys were nearly consistent across the entire test matrix. Notably, the change in the microstructure from near lamellar to duplex did not elicit any qualitative or quantitative change in the friction profile of Ti-48Al-2Cr-2Nb alloys. The contact pressure proved to be the statistically significant property influencing friction evolution inversely for Ti-6Al-4V alloy and directly for Ti-48Al-2Cr-2Nb alloys. The results showed higher probability of coating wear in dry conditions as opposed to the flood and MQL lubricants.

Integrating HIP and homogenisation heat treatment and its effect on the workability of a conventional peritectic TiAl alloy

The aim of this study was to understand how consolidation and homogenisation, as well as the possibility of integrating the two processes, influences the pre-compression microstructure and subsequent compression behaviour of an industry accepted, peritectic solidifying titanium aluminide ingot alloy; 45XD.This study differs from existing work with its emphasis on understanding the effect of integrating consolidation and homogenisation on workability, as well as how these processes influence the pre-and post-compression microstructure individually. This was assessed by the material's strain rate sensitivity in primary and secondary compression. The target microstructure was identified from the literature as being capable of a strain rate sensitivity of ≥0.3.The results presented here show that it is possible to integrate the consolidation and homogenisation stages, and this proved beneficial, namely achieving a high lamellar content and elementally homogeneous microstructure presented prior to compression. Subsequent deformation generated high values of dynamic recrystallisation fraction and globularisation returned upon primary compression, and the highest strain rate sensitivity at secondary compression, in comparison to material processed by the traditional approach. This is thought to be due to pressure and temperature during the integrated process reducing both segregation, seen through casting, and so the B2/β0 content compared to consolidated material. The integrated consolidation and homogenisation approach also prevented the grain growth seen in the traditional route; this is anticipated to be due to the two slow cooling stages involved in the traditional process rather than the effect of isostatic pressure.

Intermolecular Interactions and Electrochemical Studies on Highly Concentrated Acetate-Based Water-in-Salt and Ionic Liquid Electrolytes

Water-in-salt electrolytes constitute a new class of materials that have distinct properties relative to lower-concentration solutions. A recent approach to further increase the salt concentration and decrease the water content includes the addition of an ionic liquid to a highly concentrated aqueous solution. However, the physicochemical and electrochemical properties of aqueous lithium acetate-1-ethyl-3-methylimidazolium acetate solutions as well as the molecular interactions between electrolyte species have not been characterized. Here, we investigate these properties by evaluation of the ionic conductivity, viscosity, and thermal properties as well as the electrochemical behavior of various electrodes in these electrolytes. The intermolecular interactions are probed by nuclear magnetic resonance and infrared spectroscopies. We find that the addition of the ionic liquid increases the solubility limit of lithium acetate and that with an increase in both acetate salt and ionic liquid concentration in the electrolyte and decrease in water concentration, a strong acetate-water network is formed. The electrochemical stability window increases upon addition of the ionic liquid and reaches a value larger than 5 V for a set of negative Al and positive Ti electrodes in the highest acetate salt/ionic liquid concentration. Preliminary electrochemical charge storage performance measurements of a symmetric device based on two porous carbon electrodes cycled at a current density of 25 mA g-1 delivered a specific capacitance of 20 F g-1 with a Coulombic efficiency higher than 99% using a 1.8 V voltage window.

The inhibitive action of 2-mercaptobenzothiazole on the porosity of corrosion film formed on aluminum and aluminum–titanium alloys in hydrochloric acid solution

2-Mercaptobenzothiazole (2-MBT) in a solution of 0.5 M HCl is an effective corrosion inhibitor for aluminum and aluminum–titanium alloys. Tafel polarization and electrochemical impedance spectroscopy (EIS) were employed to assess this heterocyclic compound’s anticorrosive potential and complementary by scanning electron microscope (SEM) and calculating porosity percentage in the absence and presence of various inhibitor concentrations. Inhibition efficiency (IE%) was strongly related to concentration (10–6–10–3 M). Temperature’s effect on corrosion behavior was investigated. The data exhibited that the IE% decreases as the temperature increases. An increase in activation energy (Ea) with increasing the inhibitor concentration and the decrease in the IE% value of the mentioned compound with raising the temperature indicates that the inhibitor molecules are adsorbed physically on the surface. Thermodynamic activation parameters for Al and Al–Ti alloy dissolution in both 0.5 M HCl and the inhibited solution were calculated and discussed. According to Langmuir’s adsorption isotherm, the inhibitor molecules were adsorbed. The evaluated standard values of the enthalpy (Delta {H}_{ads.}^{o}), entropy (Delta {S}_{ads.}^{o}) and free energy changes (Delta {G}_{ads.}^{o}) showed that Delta {H}_{ads.}^{o} and Delta {G}_{ads.}^{o} are negative, while Delta {S}_{ads.}^{o} was positive. The formation of a protective layer adsorbed on the surfaces of the substrates was confirmed with the surface analysis (SEM). The porosity percentage is significantly reduced in the inhibitor presence and gradually decreased with increasing concentration. Furthermore, the density functional theory (DFT) and Monte Carlo (MC) simulations were employed to explain the variance in protecting the Al surface from corrosion. Interestingly, the theoretical findings align with their experimental counterparts. The planarity of 2-MBT and the presence of heteroatoms are the playmakers in the adsorption process.

Effect of Al–5Ti–0.3C–0.2B Master Alloy on the Structure and Properties of Ti6Al4V by Laser Solid Forming

Titanium matrix composites (TMCs) with the addition of in situ ceramic reinforcing particulates have attracted extensive interest. Herein, additive‐manufactured Ti6Al4V/Al–5Ti–0.3C–0.2B alloys are fabricated from mixed powders by laser solid forming. The contents of Al–5Ti–0.3C–0.2B with 1.5, 2.5, and 5.0 wt% are considered. The results indicate the apparent microstructure transition from columnar grain to equiaxed grain with increasing content of Al–5Ti–0.3C–0.2B. The in situ reaction between the Ti6Al4V and Al–5Ti–0.3C–0.2B produces TiB, TiC, and Ti3AlC reinforcements. The increase of Al–5Ti–0.3C–0.2B content will refine grains and reduce α′ martensite phase, which is associated with the formation of TiB at the grain boundaries. As the content of Al–5Ti–0.3C–0.2B increases, the ultimate tensile strength of Ti6Al4V–x wt% (Al–5Ti–0.3C–0.2B) alloy increases from 993.8 MPa to 1233.6 MPa. The strength increases because of an increase of the solid phases TiB and Ti3AlC, which is ascribed to the presence of precipitation and grain refinement strengthening mechanisms. Meanwhile, the elongation of the alloy increases from 1.1% to 4.9% because the Ti3AlC phase is conducive to reducing thermal transfer and interfacial stress. These findings provide insights into the selection of reinforcement materials for optimizing mechanical properties of TMCs alloys.

Comparison of Tool Wear, Surface Morphology, Specific Cutting Energy and Cutting Temperature in Machining of Titanium Alloys Under Hybrid and Green Cooling Strategies

Cutting energy must be reduced in order to make machining processes more eco-friendly. More energy was expended for the same amount of material removed, hence a higher specific cutting energy (SCE) implies inefficient material removal. Usually, the type of coolants or lubricants affects the SCE, or the amount of energy needed to cut a given volume of material. Therefore, the present work deals with a study of SCE in the turning of Ti–3Al–2.5V alloy under green cooling strategies. In spite of this, the research effort is also focused on the mechanism of tool wear, surface roughness, and cutting temperature under hybrid cooling, i.e., minimum quantity lubrication (MQL) and cryogenic. The tool wear rate, were explored with tool mapping analysis, and the results were compared with dry, MQL, and liquid nitrogen (LN2) conditions. The tool wear rate analysis claims that the dry condition causes more built up edge (BUE) formation. In addition, the hybrid cooling conditions are helpful in reducing the SCE while machining titanium alloys.

Development of a Kinetic Model for Ti‐Bearing Steel‐Slag Reaction

A kinetic model based on the double‐film theory is developed to predict the composition‐change behavior of Ti‐bearing steel and slag during the slag‐liquid steel reaction process and validated by experimental results. The chemical reactions between the slag‐metal, slag‐crucible refractory, and metal‐crucible refractory are considered. Specifically, a coupled reaction model based on the CaO–MgO–CaF2–SiO2–Al2O3–TiO2–FeO–MnO and Fe–Si–Al–Ti–Ca–Mg–Mn–S–O systems is applied to describe the reaction between liquid steel and slag. Furthermore, the activity coefficients of slag components are calculated using the ion and molecular coexistence theory model. The reaction between the slag and refractory is described using an empirical equation. The reaction between the liquid steel and refractory is described using a coupled reaction model, wherein the reaction between [Al] and MgO is considered. Finally, the effect of (TiO2) on the [Ti] is discussed using this model. The results indicate that the [Ti] decreases, the [Si] increases, and the [Al] increases initially and subsequently decreases with reaction time. An increase in (TiO2) can decrease the oxidation of [Ti] by (SiO2) and (Al2O3). When the (TiO2) increases, the mass ratio of CaO to SiO2 should be further increased to decrease the oxidation of [Ti].

Special deformation mechanisms dominated by grain boundary sliding of extrusion–refined Ti–22Al–25Nb alloy during compression in single BCC phase field

The deformation behavior of Ti–22Al–25Nb alloys with refined initial grain size was investigated under isothermal uniaxial compression in the BCC (B2) single-phase field, where a high-temperature extrusion process was used to produce the test materials with finer initial grains. As compressed at low to moderate strain rates, the present material exhibits significant continuous flow softening. To study the deformation and softening mechanisms during the compression, the samples' microstructures were examined using EBSD. The analysis shows that this alloy has a considerable grain boundary sliding (GBS) mechanism in addition to the conventional mechanisms of dynamic recovery (DRV), dynamic recrystallization (DRX), and texture softening. For the first time, this study offers direct evidence of the presence of GBS in current alloys. And the dominant role of GBS in high-temperature deformation and softening of current alloys was identified by comparing the impacts of various mechanisms on the dislocation density distribution. Besides, the impact of GBS on texture evolution was also discussed.

Laser powder bed fusion (L-PBF) of Ti–6Al–4V/Ti–6Al–2Sn–4Zr–2Mo and Ti–6Al–4V/γ-TiAl bimetals: Processability, interface and mechanical properties

Titanium alloys of near-α Ti–6Al–2Sn–4Zr–2Mo (Ti-6242) and intermetallic γ-TiAl (Ti–48Al–2Cr–2Nb) are commonly served as turbine blade materials operating at elevated temperatures. This study investigated the feasibility of using laser powder bed fusion (L-PBF) to fabricate two Ti–6Al–4V-based bimetals, i.e., Ti–6Al–4V/γ-TiAl and Ti–6Al–4V/Ti-6242, which may have great potential for the future manufacturing of aerospace components. Results indicated that the bimetal of Ti–6Al–4V/γ-TiAl was unsuccessfully built despite a gradient interface (∼250 μm) achieved via L-PBF. This failure was attributed to the intrinsic cold cracking of γ-TiAl processed by L-PBF instead of the weak interfacial bonding between the two materials. In comparison, another pair of bimetal, Ti–6Al–4V/Ti-6242, was manufactured successfully by L-PBF, resulting in a solid and defect-free interface. Horizontal tensile tests were conducted, and the ultimate strength of the bimetal Ti–6Al–4V/Ti-6242 was 1314 ± 21 MPa. However, compared to single materials, the elongation of the bimetal was lowered to 2.8 ± 0.9% because of the mechanical incompatibility between Ti–6Al–4V and Ti-6242.

PHASE FORMATION DURING ALUMINOTHERMAL REDUCTION OF Ti, Nb, Gd (Y) FROM OXIDES

Alloys based on titanium and aluminum with additions of niobium and rare-earth metals have unique mechanical and heat-resistant properties, and also it likely that such alloys would have increased corrosion resistance. The method of thermodynamic modeling using the HSC program was used to study a system with aluminum consumption varying in the range from 0 to 100% of the mass of the initial charge. The features of phase formation in Al–[50TiO2–5Nb2O5–1Y2O3 (Gd2O3)] systems have been studied. The calculation of the heat balance of the process at 1600°C and 44% of Al was – 0.196 MJ per 1 kg of charge, which indicates the possibility of its occurrence with only the aluminothermic reactions. The reduction of titanium and niobium can proceed by reactions through the formation of their oxides of lower valency – TiO, NbO2, NbO. The aluminothermic reduction of gadolinium is thermodynamically possible only at temperatures below 1200°C. The reduction of yttrium through the interaction of Y2O3 with aluminum with the formation of AlY, Al2Y3 AlY2 compounds for the range of 1000–1800°C is thermodynamically impossible. The results of thermodynamic modeling of interactions correlated well with the data of differential thermal and X-ray phase analysis using STA 449 F3 Jupiter (NETZSCH) synchronous thermal analysis and XRD-7000 diffractometer (Shimadzu) with automatic program control, respectively. It was found that the process enters the active phase after the appearance of liquid aluminum and, apparently, is accompanied by exothermic effects with the formation of double and triple intermetallic compounds of aluminum with rare (Nb, Ti) and rare earth (Gd, Y) metals. Transformation of titanium dioxide and niobium pentoxide in the process of transformations is likely carried out through successive and parallel stages of formation of simple and complex oxides with low oxidation states. At the initial stages of the interaction of aluminum with oxides, niobium and titanium aluminides are mainly formed. At subsequent stages, the formation of more complex compounds is observed. At temperatures above 1300°C, ternary intermetallic compounds Al43Nb4Gd6, Ti4Al20Gd and Ti4Al3Y6, Al3Ti, Al0.23Nb0.07Ti0.7 are formed. Gadolinium and yttrium tend to form complex intermetallic compounds in such systems.

Synaptic Resistor Circuits Based on Al Oxide and Ti Silicide for Concurrent Learning and Signal Processing in Artificial Intelligence Systems.

Neurobiological circuits containing synapses can process signals while learning concurrently in real time. Before an artificial neural network (ANN) can execute a signal-processing program, it must first be programmed by humans or trained with respect to a large and defined data set during learning processes, resulting in significant latency, high power consumption, and poor adaptability to unpredictable changing environments. Inthiswork, a crossbar circuit of synaptic resistors (synstors) is reported, each synstor integrating a Si channel with an Al oxide memory layer and Ti silicide Schottky contacts. Individual synstors are characterized and analyzed to understand their concurrent signal-processing and learning abilities. Without any prior training, synstor circuits concurrently execute signal processing and learning in real time to fly drones toward a target position in an aerodynamically changing environment faster than human controllers, and with learning speed, performance, power consumption, and adaptability to the environment significantly superior to an ANN running on computers. The synstor circuit provides a path to establish power-efficient intelligent systems with real-time learning and adaptability in the capriciously mutable real world.

Simultaneous improvement of Z-coordinate and overcut in EDM of titanium grade 5 alloy using a carbon-coated micro-tool electrode

Depth of machining and dimensional accuracy are important parameters in assessing the quality of microelectrical discharge machining (EDM); therefore, enhancement of these two entities is highly essential. The optimal process parameters in microEDM are significantly influenced by the electrode material, which directly affects the machining quality. In this study, depth of machining ([Formula: see text] co-ordinate) and overcut (OVC) in microEDM with carbon-coated electrode were selected; and capacitance ([Formula: see text]), voltage ([Formula: see text]), and rotary tool (RT) were the process parameters. The experimental work was performed on a titanium alloy (Ti-6 Al-4 V) with a thin film-coated microtool electrode. The surface of the tungsten carbide microtool electrode was coated with carbon and the thickness of the coating was approximately five microns. The results show that the Taguchi–multi-objective optimization based on ratioanalysis (MOORA) — analytic hierarchy process (AHP) is the best combination for performing a simple and concise calculation in the machining process; and [Formula: see text] V results in higher machining efficiency with [Formula: see text] pF and [Formula: see text] rpm. Our results show that the quality of the machined surface and machining accuracy in microEDM using coated electrode at optimal parameters are good.

Nb modified Ti-5553 alloy: Effects of heating rate on mechanical properties, corrosion behavior, and crystallographic texture

Ti–5Al–5Mo–5V–3Cr (Ti-5553) is a metastable β-type Ti alloy with excellent hardenability and high mechanical strength designed for aerospace applications. Previous studies have shown that the replacement of V with Nb, resulting in a Ti–12Nb–5Al–5Mo–3Cr (Ti-12553) alloy, can enhance the mechanical strength and hardenability. This study focuses on exploring the effects of V replacement with Nb in this alloy, aiming to evaluate the effects of the aging heating rate during aging heat treatment on the microstructure and its effect on hardness, tensile and compression strengths, corrosion resistance, and crystallographic texture development. The Ti-5553 and Nb-modified Ti-5553 (Ti-12553) alloys aged at 600 °C for 2 h resulted in a microstructure formed by α precipitates in a β matrix, with larger precipitates at a faster heating rate. This effect was more pronounced for the Ti-5553 alloy. The coarsening microstructure affected the mechanical behavior by decreasing the mechanical strength (hardness, ultimate tensile strength, and yield strength) while improving ductility and intergranular fracture mode in combination with a smaller region containing dimples. A decrease in hardness was observed at a faster heating rate, but it was still superior to that of the solution heat-treated samples. The textures formed in both alloys were similar and lacked any strong components. The replacement of V with Nb and the microstructure produced after aging heat treatment did not affect the samples’ corrosion resistance in a 3.5% NaCl solution. A stable passive protective layer with noble corrosion potential and reduced corrosion current density was observed.

Evaluation of Short-Term Oxidation Mechanism of Laser Cladded Ni–Cr–C Coating on Titanium Aluminide Substrate

In the present investigation, a NiCr–Cr3C2 powder mixture was deposited on titanium aluminide substrate by laser cladding. The kinetics and mechanism of oxidation of the substrate and coating were studied at 800–1100 °C using XRD, SEM, ToF–SIMS and XPS characterization techniques. The results demonstrated that the Ni–Cr–C coating had improved oxidation resistance, as compared to the substrate. The oxidized surface of the coating was covered with Cr2O3 and NiCr2O4 phases at the early stages of the oxidation. The formation of NiCr2O4 could be attributed to the reaction of NiO (an oxidation product of the NiCr phase) and Cr2O3 (an oxidation product of the chromium carbide phase) during oxidation. Increasing the oxidation time at 900 °C led to the partial formation of CrO3 as a result of the oxidation of Cr2O3. It was also found that the parabolic rate constant ratio of $$\left( {K_{{\text{p}}}^{{{\text{substrate}}}} /K_{{\text{p}}}^{{{\text{coating}}}} } \right)$$ increased with the temperature, which showed, comparatively, the better oxidation resistance of the coating at higher temperatures.

Microstructure and mechanical properties of gamma titanium aluminide alloys fabricated by metal injection molding using non-spherical powder

Microstructure and mechanical properties of gamma titanium aluminide alloys fabricated by metal injection molding using non-spherical powder

A new model to predict the tool life in turning of titanium aluminides

Several tool wear models for machining operations have been reported in the literature. However, most of them are capable of modeling only a part of the wear curve, designed for quasi-linear curves or need to be fitted by means of differential equations. In this research, a new analytical easy-to-use wear model is proposed, taking into consideration the geometry of the cutting insert and the influence of the cutting speed and the tool-workpiece contact stress. In addition, the effect of the critical machining time, relative to the tool degradation, has also been introduced. The wear model describes completely the wear curve, from the initial rapid wear stage to the thermal-activated wear rate acceleration. The constants and parameters of the equation are determined by cutting experiments from the cutting forces and flank wear registers under a variety of technological parameters. This model has been validated for turning process on Ti48Al2Cr2Nb aluminide with uncoated carbide tool under different cutting conditions, varying the cutting speed and the geometrical position of the tool. It has been demonstrated its suitability to predict tool life, according to a defined wear criterion.

Microstructure and wear properties of powder-pack borided Ti–5Al–2.5Sn alloy

The boride layer was prepared on the surface of Ti–5Al–2.5Sn alloy by powder-pack borided at 975–1075 °C for 20 h with a temperature interval of 25 °C, and surface morphology, phase composition, microstructure, hardness, and wear properties of the borided Ti–5Al–2.5Sn alloy were investigated. The crystal parameters of TiB2 phase in the boride layer at different boriding conditions were obtained from the Rietveld structure refinement of Ti–5Al–2.5Sn samples, and the theoretical hardness values of TiB2 were calculated using the first-principles calculations. The results indicate that the boride layer comprises the outer TiB2 layer and the inner TiB whisker, and TiB2 layer thickens and TiB whiskers coarsen with the increase of temperature. The hardness of TiB2 layer is related to the boriding temperature, the greater hardness of TiB2 layer corresponds to the higher boriding temperature, which is in good agreement with the theoretically predicted results. Ti–5Al–2.5Sn alloy borided at 1075 °C–20 h has the highest hardness and excellent wear resistance. Finally, wear mechanisms were also discussed, which is a combination of abrasive and adhesive wear.

On the Microstructural Evolution and Cracking Behavior of a Titanium Aluminide Alloy During Selective Laser Melting.

Selective laser melting of Ti-48Al-2Cr-2Nb usually ends up with serious cracking. The cracking mechanism, however, remains elusive. In this study, both bulk samples and samples containing only several layers were prepared and investigated. It is shown that a freshly built layer is dominated by single α2 phase. γ started to form from α2 during subsequent thermal cycling due to reheating effects and its volume fraction increased continuously with increased thermal cycles. The γ phase contains higher geometrically necessary dislocation (GND) density than α2. This could be due to its relatively lower hardness and higher thermal expansion coefficient, which made it easier to deform under stresses. With higher GND and thus probably higher distortion energy, the γ experienced more extensive recrystallization than α2 during reheating. Cracks are more liable to initiate from the interior of α2 or the γ/α2 interfaces, which could be due to incompatible deformation between the two phases.

Investigation of the nucleation and growth behavior of Ti2AlC and Ti3AlC nano-precipitates in TiAl alloys

Abstract In this work, the nucleation and growth behavior of Ti2AlC and Ti3AlC nano-precipitates in Ti–44Al–1.2C alloys were systematically studied by observing their distribution, morphology, and interface atomic structure. The experiment results show that the needle-like C atom segregation zones in TiAl alloys are the nucleation site of Ti2AlC, and the long axis direction of segregation zones is parallel to the TiAl(111) plane. The rod-like Ti2AlC nano-precipitates mainly distribute at the TiAl/Ti3Al interface, and the orientation relationship between them is [ 1 ̅ 01 \bar{1}01 ]TiAl//[ 11 2 ̅ 0 11\bar{2}0 ]Ti2AlC//[ 11 2 ̅ 0 11\bar{2}0 ]Ti3Al, (111)TiAl//(0001)Ti2AlC//(0001)Ti3Al. The needle-like Ti3AlC nano-precipitates distribute in TiAl with the orientation relationship of [001]Ti3AlC//[001]TiAl, (100)Ti3AlC//(100)TiAl, (020)Ti3AlC//(020)TiAl, and (110)Ti3AlC//(110)TiAl during the nucleation stage. After growing into the rod-like, the orientation relationship between Ti3AlC precipitates and TiAl is [ 1 1 ̅ 0 1\bar{1}0 ]Ti3AlC//[ 1 1 ̅ 0 1\bar{1}0 ]TiAl, (001)Ti3AlC//(001)TiAl, (220)Ti3AlC//(220)TiAl, and (111)Ti3AlC//(111)TiAl. Both the needle- and rod-like Ti3AlC precipitates preferentially grow along the [001]TiAl direction. The crystal structure and lattice mismatch between Ti2AlC and Ti3AlC nano-precipitates and the TiAl matrix determine their distribution, morphology, and interface atomic structure.