TiAl3 Layer Research Articles

The effect of interface atomic structure on the deformation mechanisms of Ti2AlN/TiAl composite under nanoindentation using MD simulations

In this study, we conduct molecular dynamics simulations to investigate the effect of interface atomic structure on the deformation mechanisms of Ti2AlN/TiAl composite under nanoindentation. It is found that the interface atomic structure has a remarkable effect on the deformation behavior of Ti2AlN/TiAl composite due to significantly different interface-dislocation interactive mechanisms. For the Ti2AlN(0 0 0 1)/TiAl(1 1 1) coherent interface system, although plenty of dislocations nucleate and propagate through the TiAl layer during the indentation process, there are no dislocations transmitting across the coherent interface. The formation of stair-rod dislocation and dislocation tangle is the major mechanism for blocking the slip motion of dislocations by the coherent interface. Thus, the Ti2AlN(0 0 0 1)/TiAl(1 1 1) coherent interface is beneficial for the strengthening effect of Ti2AlN/TiAl composite. For the Ti2AlN(1 0 3)/TiAl(1 1 1) incoherent interface system, the incoherent interface has some ability to annihilate the dislocations nucleated from the TiAl during the indentation process, but it cannot simultaneously annihilate plenty of dislocations. These dislocations accumulate in the incoherent interface and cause the stress concentration, providing the driving force for dislocation nucleation in Ti2AlN from the poor matching regions in the Al atomic arrays at the incoherent interface. Therefore, the incoherent interface can provide the access of dislocation transmission from TiAl to Ti2AlN, which benefits the ductility of Ti2AlN/TiAl composite.

Microstructure and mechanical properties of Ti/Al dissimilar joints produced by laser-MIG welding–brazing

We butt-welded AA6061 aluminum alloy to Ti6Al4V titanium alloy, dissimilar light metals, by using laser-MIG hybrid welding–brazing without grooves. The parameters of the laser and arc were optimized to produce sound joints with good formation and mechanical properties. The microstructure of the layer of intermetallic compounds (IMCs) was investigated by scanning electron microscopy and energy dispersive spectroscopy. We also tested the tensile strength of the joints with and without reinforcement. The morphology and thickness of the IMCs varied throughout the joints. A continuous thin layer of TiAl3 appeared on the top surface of the Ti6Al4V, on which some rod-like IMCs grew toward the fusion zone. In the upper region of the butt plane, because more heat accumulated there from the high-power laser coupled with the MIG arc, double-layer IMCs with a thickness of [Formula: see text]10.0 [Formula: see text]m formed, composed of TiAl (near the Ti alloy) and TiAl3 (near the fusion zone). In the lower region of the butt plane, the double-layer IMCs became continuous and uniform, the serrated morphology disappeared, and the thickness of the IMC layer decreased to 4.0 [Formula: see text]m. On the backside of the joint, the thickness of the compound layer (TiAl3) was about 1.0 [Formula: see text]m. The average tensile strengths of the reinforced and unreinforced joints were 226 MPa and 210 MPa, respectively, which are up to 88% and 81% of the AA6061 tensile strength, respectively.

Failure of the laminate composites under impact loading

The paper represents the results of numerical simulation of fracture of laminate composites under impact loading. The behavior of a composite target that consists of a titanium alloy (Ti-6-4) and a titanium-titanium trialuminide intermetallide (Al3Ti) layers were studied. A special model is applied to describe the brittle-like fracture of intermetallide. The axisymmetric problem is solved using the finite element method. In the computations, the thickness of the layers was varied. The multilayered composites were compared with monolithic intermetallide and titanium targets.

Volume Fraction Dependent Wear Behavior of Titanium-Reinforced Aluminum Matrix Composites Manufactured by Melt Infiltration Casting

This study aims to investigate the effect of volume fraction of commercially pure titanium (CP-Ti) on microstructural, mechanical, and tribological features of A356 aluminum matrix composites. Vacuum-assisted melt infiltration casting was performed to produce composites with 50%, 65%, 75%, and 80% CP-Ti contents. CP-Ti sawdusts were assembled under mechanical pressure in order to attain porous one-piece CP-Ti preforms which were infiltrated by A356 melt at 730 °C under 10−5 Pa vacuum atmosphere. TiAl3 layer was formed at the interface between A356 and CP-Ti phases. Owing to increased diffusion time through decreased diffusion path length, both thickness and hardness of TiAl3 phase were increased with increasing CP-Ti ratio, whereas the best wear resistance was obtained at 65% CP-Ti ratio. The main reason for decrease in wear resistance of 75% and 80% CP-Ti reinforced composites was fragmentation of TiAl3 layer during wear process due to its excessively increased brittleness. Strongly bonded TiAl3 phase at the interface provided better wear resistance, while weakly bonded ones caused to multiply wear rate.

Study of the microstructure modulation and phase formation of Ti[sbnd]Al3Ti laminated composites

It is extremely difficult to eliminate the voids and prepare densely TiAl3Ti laminated composites by using existing techniques. In this work, the endothermic semi-solid reaction and the self-propagating synthesis are employed to fabricate TiAl3Ti laminated composites. The SEM, EDS and XRD techniques are used to investigate the microstructure and phase formation process of TiAl3Ti laminated composites in detail. Results show that the endothermic semi-solid reaction technique can well eliminate the Kirkendall voids, while numerous voids are distributed in composites obtained by the self-propagating synthesis. It demonstrates that the interface phase evolution is Al3Ti, AlTi, AlTi3 and Al2Ti in sequence. The microhardness of both Ti and Al3Ti layers in the composite is tested and presents distinct behaviors with respect to sintering time. This work would suggest an effective way to fabricate densely TiAl3Ti laminated composites.

Effect of TiAl3 Coating Thickness and Morphology, Formed Using the Immersion of Titanium Sheets in Molten Aluminum, on Titanium Oxidation Behavior

In this research, TiAl3 layers with different thicknesses were deposited on a titanium sheet by immersion of titanium in molten aluminum for different times. The oxidation behavior of the coated titanium at 850 °C was investigated and the comparison of the results was made with the oxidation behavior of the uncoated titanium sheet. The results showed that the produced TiAl3 layer could protect the titanium substrate against the oxidation if it contains an appropriate quality and morphology, otherwise not only it cannot withstand the oxidation, but also it accelerates the oxidation process of the titanium substrate. The protection mechanisms of the layers were probed into, performing the XRD analysis. It was found that the TiAl3 layer morphology affects oxidation mechanism and oxidation products.

A Comparative Study on Titanium-Reinforced Aluminium Matrix Composites Produced by Melt Infiltration Casting and Squeeze Infiltration

The unresolved production problems including wettability and undesired intermetallic phase formation at the interface of aluminium matrix composites (AMCs) with ceramic reinforcements require a different approach to the subject. Titanium as a reinforcement is a strong candidate to overcome the current problems, without sacrificing beneficial features of conventional AMCs. This study aims to compare microstructural, mechanical and wear properties of bimetal composites manufactured by two different techniques: melt infiltration casting (MIC) and squeeze infiltration (SI). The temperature was set to 730 °C for both production methods. MIC was carried out in an open die with vacuum assistance, while SI was performed in a closed die in an atmospheric environment. Optical microscope, SEM, XRD, EDS, nanoindentation test device and ball-on-disc type tribometer with 3-mm-diameter Al2O3 ball were used for composite characterization. Al, Ti, Si and TiAl3 phases were formed in composite structure for both techniques. Homogeneous and continuous TiAl3 layer was obtained at Al/Ti interfaces. The volume fraction of TiAl3 was 20 times higher in SI than that in MIC due to long interaction time between Al and Ti. The thickness and the hardness of TiAl3 obtained were higher in SI. Abrasive and adhesive wear mechanisms were observed in worn surface examinations. The composite produced by SI showed slightly better performance against wear under the same test conditions. It was exposed to less plastic deformation and abrasive wear than composite produced by MIC. Although initial investment cost was higher, SI appeared to be more advantageous than MIC, considering the applicability in the industry.

Elasto-Plastic Mechanical Properties and Failure Mechanism of Innovative Ti-(SiCf/Al₃Ti) Laminated Composites for Sphere-Plane Contact at the Early Stage of Penetration Process.

A novel silicon carbide (SiC) continuous ceramic fiber-reinforced (CCFR) Ti/Al3Ti Metal-Intermetallic-Laminate (MIL) composite was fabricated. A high-efficiency semi-analytical model was proposed based on the numerical equivalent inclusion method (NEIM) for analyzing the small-strain elasto-plastic contact in the early stage of the penetration process. The microstructure and interface features were characterized by the scanning electron microscopy (SEM). Quasi-static compression tests were performed to determine the contact response and validate the proposed model. A group of in-depth parametric studies were carried out to quantify the influence of the microstructure. The comparison between results under the sphere-plane and plane-plane contact load indicates that, under the first sphere-plane, the compressive strength and failure strain are both lower and the SiC reinforcement effect on strength is very clear while the effect on ductility is not clear. The maximum plastic strain concentration (MPSC) in the Al3Ti layer is closest to the upper boundary of the central SiC fiber and then extends along the depth direction as the load increases, which are also the locations where cracks may initiate and extend. Moreover, the CCFR-MIL composite shows better mechanical properties when the center distance between adjacent SiC fibers is four times the fiber diameter and the volume fraction of Ti is 40%.

Enhancing the interface bonding in carbon nanotubes reinforced Al matrix composites by the in situ formation of TiAl3 and TiC

Achieving effective load transfer at the interface between carbon nanotubes (CNTs) and aluminum (Al) is a crucial issue for fabricating high-performance CNTs reinforced Al matrix (CNT/Al) composites. In this work, CNT/Al composites with different Ti additions and the compared materials were prepared by powder metallurgy. Micro-sized Ti particles in which CNTs are well-dispersed firstly circumvent the difficulty of CNT dispersion, and subsequently act as nucleation site for sandwiched TiAl3 layers that lock the dispersed CNTs in place and improve the CNT-Al interface bonding. Additionally, Ti addition not only allows modification of the dispersed CNTs but also enhances the strength of the composites by enhancing the load-bearing capacity of the CNTs through in situ formation of nano-sized titanium carbide (TiC). This work provides a new approach to improve the load transfer efficiency of CNTs by strengthening the interface bonding for fabricating high strength CNT/Al composites.

Influence of Ni coating on interfacial reactions and mechanical properties in laser welding-brazing of Mg/Ti butt joint

Laser welding-brazing characteristics of AZ31 Mg to Ti-6Al-4V in butt configuration without and with Ni coating was comparatively investigated with varied laser power. The interfacial reaction and mechanical properties were studied and the microstructure evolution mechanism was clarified based on thermodynamic calculation. The interfacial microstructure evolved from an ultra-thin Ti3Al layer, to a layer of Ti2Ni mingled with Ti3Al, to Ti3Al layer with increasing laser power. In addition, Ti2Ni phase formed on Ti substrate at high laser power. The driving force of Al diffusing to Ti substrate was higher than that of Ni at low laser power while the diffusion time of Ni was longer, resulting in formation of Ti3Al phase or mingled structure of Ti3Al and Ti2Ni at the interface. The driving force of Ni to Ti was larger than that of Al to Ti at high laser power, producing Ti2Ni phase on Ti substrate. Mg-Al-Ni intermetallics formed in the fusion zone near the interface and became scattered with increasing laser power. The fracture load of Mg/Ni-coated Ti joint was approximately three times that of Mg/bare Ti joint. The Mg/Ni-coated Ti joint reached the maximum value of 3900 N at laser power of 1500 W. In this case, the joints failed at Mg base metal while others cracked from the fusion zone-Ti interface.

Influence of annealing on the microstructure and mechanical properties of Ti/Al and Ti/Al/Nb laminated composites

Ti/Al-based composites and intermetallic compounds attracted great attention due to their good mechanical properties combined with low density. In the present work, Ti/Al and Ti/Al/Nb laminated composites were fabricated by diffusion bonding and subsequent rolling. The fabricated samples were then annealed at different temperatures below and above the melting temperature of pure aluminum. The results indicate that by annealing of the samples at temperatures lower than the melting point of aluminum, a dense and continuous layer of TiAl3 and NbAl3 intermetallic are formed. But during annealing at temperatures higher than the melting point of aluminum a dense layer of TiAl3 particles is formed at Ti/Al interface and a layer of distributed (Ti,Nb)Al3 intermetallic phase is formed at the Al/Nb interface. The mechanical properties demonstrate that the samples annealed at 650 °C have the highest tensile strength. The investigation of the kinetics of phase formation shows that the growth of TiAl3 and NbAl3 layers are controlled by diffusion and reaction at 600–650 °C, respectively. Whereas, the growth of TiAl3 layer at 700 °C obeys reaction-controlled kinetics.

Effects of Ti Activity on Mechanical Properties and Microstructures of Al 2 O 3 /Ag-Cu-Ti/Fe-Ni-Co Brazed Joints

Abstract Al2O3 ceramic/Fe-Ni-Co joints were achieved using Ag-Cu-Ti filler alloy to investigate the dependence of the joint microstructure and mechanical properties on the Ti content. Scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD) and electronic universal testing machine were used to characterize the microstructure and mechanical properties of the joints. The results show that the increase of Ti content can obviously intensify the interaction between Al2O3 and Ag-Cu-Ti. A layer of Ti-Al and Ti-O products is observed at the interface of Al2O3/Ag-Cu-Ti. The tensile strength of Al2O3/Ag-Cu-Ti/Fe-Ni-Co joint increases as the Ti content increases from 2 wt% to 8 wt%, and the tensile strength of the brazing joint reaches the maximum value of 78 MPa. Good reaction layer is formed by metallurgical reaction at the interface of Al2O3/Ag-Cu-4Ti, and the typical microstructure is Al2O3/TiAl+Ti3O5/NiTi+Cu3Ti+Ag(s,s)/Ag(s,s)+Cu(s,s)+(Cu,Ni)/Fe-Ni-Co when brazed at 890 oC for 5 min. Compared with AgCu4Ti filler, the microstructure of the joints changes slightly when addition of the active element Ti to 8 wt% except for the increase of the thickness of reaction layer adjacent to Al2O3 ceramic, which is accompanied by the formation of TiO and Ti3Al in the Al2O3/Ag-Cu-Ti interface.

Interfacial microstructure characterization and mechanical behavior of NiTi fiber reinforced Al3Ti composite

To improve the ductility of Al3Ti alloy, the continuous shape memory alloy NiTi fiber (CSMAR) was introduced into intermetallic Al3Ti matrix for fabricating the novel CSMAR-Al3Ti composite in this work. Microstructure characterizations demonstrated that the CSMAR-Al3Ti composite mainly consists of Al3Ti layer, NiTi fiber, eutectic area and interfacial reaction layer. EBSD results indicated that the eutectic area is made up of Al3Ti and Al3Ni phases, the Al3Ti phase shows a strong [001] crystallographic oriented structure, while the Al3Ni phase has a non-textured structure. TEM results showed that the interfacial reaction layer between NiTi fiber and eutectic area is a multiple phase mixture, including various Ti-Al and Ni-Al intermetallics. Furthermore, TEM and HRTEM analyses revealed a newly formed Ti2Ni layer between NiTi fiber and interfacial reaction layer. Tensile test results confirmed that the CSMAR-Al3Ti composite could effectively improve the ductility of the Al3Ti alloy. Based on the systematic investigations of interfacial microstructure characterization, mechanical behavior and fracture morphology observation, it is found that the toughening mechanism of CSMAR-Al3Ti composite is related to the interfacial fine grain strengthening effect with the gradual distribution characteristic. In addition, the excellent metallurgical bonding between fiber reinforcement and matrix is also beneficial to the mechanical properties.

Special Features of the Structure of Laser-Welded Joints of Dissimilar Alloys Based on Titanium and Aluminum

The structure of laser-welded joints of parts having different thicknesses fabricated from alloys based on aluminum and titanium has been studied. Results of transmission and scanning electron microscopy measurements and x-ray diffraction analysis show that the diffusion interaction of microvolumes of two alloys in the weld leads to the formation of two interlayers: (i) a continuous intermetallic TiAl layer with thickness below 1 μm adjacent to the titanium alloy and (ii) a layer consisting of TiAl3 intermetallic dendrites with thickness of 2 – 6 μm adjacent to the TiAl layer. The average microhardness of the intermetallic layer is about 490 HV.

Interface-correlated bonding properties for a roll-bonded Ti/Al 2-ply sheet

We investigated the influence of annealing conditions on the interface-correlated microstructural evolution and subsequent bonding properties of a warm roll-bonded Ti/Al clad sheet. A TiAl3 intermetallic compound layer with a thickness of 160nm was initially generated at the joint interface between the Ti and Al alloys by warm rolling. When the annealing time and temperature were increased to a maximum of 6h and 650°C, respectively, the thickness of the TiAl3 layer increased to 320nm. The feasible annealing conditions for the optimum bonding strength were within 550°C-6h and 600°C-3h. An improvement in the bonding strength between Ti and Al is strongly correlated with the generation of considerable metallurgical bonding. This is manifested in the zipper-like failure mode that occurs at the TiAl3 joint interface for a layer thickness of less than 300nm.

The Kirkendall void formation in Al/Ti interface during solid-state reactive diffusion between Al and Ti

In the current study, the formation of Kirkendall voids in Al/Ti interface during solid-state reactive diffusion between Al and Ti was investigated. In this regards, pure Al wire (grade 1100) was deposited on commercially pure Ti surface by means of GTAW processing and the prepared samples were annealed at 625 °C for different periods of time. The achieved results indicated that, during cladding process, a continuous layer of Al3Ti intermetallic compound with average thickness of about 2 µm, can be formed in Al/Ti interface. During annealing process, both Ti and Al diffused into each other and the growth of the Al3Ti layer occurred mainly towards the Ti side. At this condition, Kirkendall voids are formed and accumulated near to Al/Al3Ti interface. These voids started to connect to one another, coalesce into large gaps and resembling a line crack at the interface. The formed crack acts as a barrier in Al/Ti diffusing couple and inhibits the growth of Al3Ti phase.

Bimodal laminated Ti3Al matrix composite achieved by in situ formed Ti5Si3 reinforcements

The low density and high-temperature mechanical properties of intermetallic Ti3Al based alloys are highly desirable for a wide range of critical applications. In this paper, we designed and prepared a novel laminated Ti5Si3/Ti3Al composite (LTTC) consisting of alternating Ti5Si3-lean/coarse-grained Ti3Al layers (TCLs) and Ti5Si3-rich/fine-grained Ti3Al layers (TFLs). The processing route involves hot pressing of a stack of alternating Ti foils and Al-6Si foils, followed by a two-step reaction annealing. The tensile properties of the LTTC have also been evaluated, and the LTTC exhibited a good strength-ductility combination when compared with monolithic Ti3Al. By in-depth mechanism discussion, we propose the possible approaches to further enhance the mechanical properties of such LTTC.

Reactive wetting of TA2 pure Ti and TC4 alloy by molten Al 4043 alloy at 873–973 K

Wetting of typical industrial grades of Ti by Al 4043 alloy was studied by the sessile drop method at 873–973 K under high vacuum. Al/Ti is a typical reactive wetting system, and the double phases in TC4 alloy but only one phase in pure Ti caused the different interfacial structure. The mass transport was enhanced at liquid/solid interface due to the loosened Al3Ti layer in Al/TC4, but the compact Ti7Al5Si12 layer would block the mass transport in Al/TA2 pure Ti, that further caused the different final wettability. The spreading dynamics of both TA2 and TC4 can be described by reaction product control model, and the activation energy is in the range of 10–47 kJ/mol, which is corresponding to the surface energy difference per molar area between Ti and TiO2.

TIG welding-brazing of Ti6Al4V and Al5052 in overlap configuration with assistance of zinc foil

Under tungsten inert gas heating, a sound Ti6Al4V/Al5052 lap joint was obtained with the addition of zinc, which enhanced the spreadability of Al-based filler on Ti6Al4V substrate. Under high heat input, a serrated TiAl3 layer, which was replaced by a TiZn16+TiAl3 dual sublayer under low heat input, was observed at the brazing interface. TiAl3, Si, and Al–Si eutectic compounds were found in the fusion zone. The microhardness of the fusion zone was higher than those of the heat-affected zone and the Al5052 substrate given the presence of intermetallic compounds. At the optimal welding current of 80A, the tensile-shear strength of the joint reached 180MPa, which was equivalent to 80% the tensile-shear strength of the base Al5052 alloy. Failure occurred at the welded seam. The fracture surface was characterized by quasi-cleavage patterns. The effect of zinc on the spreadability of liquid filler metal and the formation of the Ti6Al4V/Al5052 lap joint were discussed.

Study on the Mechanical Properties of TiAl Crystals Grown by a Floating Zone Method

Unidirectionally solidified TiAl alloys were prepared by optically-heated floating zone method at growth rates of 10 to 70 mm/h in flowing argon. The microstructures and tensile properties of these crystal bars were found to depend strongly on the growth rate and alloy composition. TiAl alloys with composition of 47 and 50 at.%Al grown under the condition of 10 mm/h showed Ti3Al(α2)/TiAl(γ) layer structures similar to single crystals. As the growth rate increased, the alloys with 47 and 50 at.%Al compositions showed columnar-grain structures. However, the alloys fabricated under the condition of 10 mm/ h had a layered structure, but the alloy with increased growth rate consisted of γ single phase grains. The alloy with a 53 at.%Al composition showed a γ single phase regardless of the growth rate. Room-temperature tensile tests of these alloys revealed that the columnar-grained material consisting of the layered structure showed a tensile ductility of larger than 4 % and relatively high strength. The high strength is caused by stress concentration at the grain boundaries; this enhances the secondary slip or deformation twinning across the layered structure in the vicinity of the grain boundaries, resulting in the appreciable ductility.