Intermetallic Compound TiFe Research Articles

Weld Formation Mechanism and Microstructural Evolution of TC4/304 Stainless Steel Joint with Cu-Based Filler Wire and Preheating.

Ti-Fe intermetallic compounds were effectively suppressed with Cu-based filler wire and weld formation was greatly improved with the preheating of substrates when joining TC4 titanium alloy and 304 stainless steel. A Ti/Cu transition zone consisting of complex TiCu, Ti2Cu3, TiFe, and TiFe2 phases was formed between Cu-weld/TC4 interface, while Cu-weld/304ss interface was mainly composed of α-Fe and ε-Cu solid solution. At lower heat input, the undercut defect in back surface had potential to cause crack initiation and joint fracture. Though increasing heat input would improve weld morphology, the formation of thick interfacial reaction layer and weld cracking led to low weld quality and joint strength. The preheating of substrates had an obvious effect on wetting ability of liquid filler metal and could achieve a better weld quality at lower heat input. The back formation of weld was improved to decrease the occurrence of weld defects. The highest tensile strength of 365 MPa occurred at welding heat input of 0.483 kJ/cm, increasing by 47% compared to the joint without preheating. The interfacial reaction mechanism was discussed to reveal the relationship between microstructural characteristics and fracture behavior of Ti/steel welded joints with Cu-based filler wire.

Thermodynamic Study on Self-propagating High Temperature Synthesis of TiB2/Fe Composites

Based on the experimental analysis and theoretical calculation, the self-propagating high temperature synthesis of TiB2/Fe composite was studied. The experimental results show that the interfacial between TiB2 and Fe was smooth and clear, and the composite bending strength increased with the addition of Fe, however, the hardness decreased accordingly. The thermodynamics of the composites preparation process was calculated. The calculation results show that the primary chemical reaction was the reaction between Ti and B. The extra B can react with Fe, producing the brittle phase Fe2B. By increasing Ti, the production of Fe2B will decrease and a few of Ti-Fe intermetallic compound will be produced by the reaction between Ti and Fe in the composites. Finally, according to the Merzhanov condition of the adiabatic system, it is concluded that the Fe content must be selected between 16.3% and 54.3% by the thermodynamics temperature of reaction calculation.

Investigation on Microstructure and Mechanical Properties of TA10–Q245R Composite Plate Formed by Explosive Welding

The titanium alloy TA10 and the carbon steel Q245R are welded by explosive welding, and post-weld heat treatment (PWHT) is carried out for the TA10–Q245R composite plate. Microstructure and mechanical properties of the composite plate are investigated both in as-welded (AW) condition and after PWHT, respectively. Results show that, in AW condition, the bonding interface of composite plate presents wavy morphology, and at both sides of the interface plastic deformation is generated to a certain degree. Near the interface interdiffusion zone of alloying elements exists, and no Fe-Ti intermetallic compound is produced at the interface. SEM images indicate that the tensile fracture of composite plate presents the characteristic of ductile fracture, and no defects such as gas pores or impurities are found on the surface of shear fracture. After PWHT, the interfacial microstructure of the composite plate is obviously changed. Compared with the mechanical properties of the composite plate in AW condition, both tensile strength and shear strength of the composite plate are decreased to a certain extent after PWHT. With various factors into consideration, the suitable heat treatment procedure of TA10–Q245R composite plate is determined as follows: 550 °C × 1.5 h.

Amorphization and mechano-crystallization of high-energy ball milled Fe[sbnd]Ti alloys

Solid-state amorphization during mechanical alloying of Fe-xTi alloys (x = 33.3 and 50 at.%) and the subsequent mechanically-induced crystallization by continued ball milling was studied. In the case of Fe50Ti, it was revealed that by milling of Fe and Ti powders, firstly the nanocrystalline FeTi intermetallic compound forms, and then, the amorphous phase appears. In the case of Fe-33.3Ti, the amorphous phase formed directly and at lower energies. Continued milling of the Fe-33.3Ti system resulted in the devitrification of the powder with the appearance of the diffraction peaks of nanocrystalline α-Fe. For unambiguous analysis of the amorphization, the quantitative XRD amorphization parameter was taken into account. Examination of the milled powders revealed that, despite the dominance of fracturing compared to cold welding, the size of powder particles refines tremendously due to the amorphization and the brittleness it brings in the system. Conclusively, this works revealed some of the unknown aspects of amorphization in this system.

Interfacial microstructures and mechanical properties of dissimilar titanium alloy and steel friction stir butt-welds

Dissimilar welding of titanium to steel has received significant attention because of its potential application in power generation and chemical industries. However, it is considered to be very challenging to use fusion-welding processes to join Ti to steel due to their dramatically different thermo-physical properties and chemical compositions. In this work, linear friction stir butt-welding was successfully used to join 2 mm thick sheets of titanium alloy, Ti6Al4 V to medium carbon steel, 30CrMnSiNi2A. Defect-free butt-welded joints were produced using travel speeds from 47.5–75 mm/min with a constant tool rotation speed of 750 RPM. With increasing travel speed, the thickness of the interfacial reaction layer gradually decreases. FeTi intermetallic compound was detected at the interface by micro-XRD testing. An optimal interfacial reaction layer approximately 1 μm thick was formed in the weld made at a travel speed of 75 mm/min. A reaction layer ranging from ∼5 to 60 μm thick was found at the interface with a travel speed of 47.5 mm/min. Such thick reaction layer is in contrast with the thinner layer formed in friction stir lap welds, which is believed to be related to the relatively higher welding temperature of friction stir butt welds. Welds formed at travel speeds ranging from 47.5–75 mm/min exhibit higher tensile strengths than the steel base material and were found to fracture from thermo-mechanically affected zone to heat affected zone on steel side or at the interfacial reaction layer on Ti-side.

Microstructural and Mechanical Properties of Binary Ti-Rich Fe–Ti, Al-Rich Fe–Al, and Ti–Al Alloys

Three series of binary, FeTi (Ti-rich), FeAl and TiAl (Al-rich) alloy samples were produced in an argon arc furnace. An annealing treatment of 72 h at 1000 °C was applied to the samples, giving rise to different equilibrium microstructures depending on chemical composition. Their mechanical properties were studied through the determination of elastic constants that measure the stiffness of the elaborated materials. Young’s modulus of the binary alloys was determined using Resonance Ultrasonic Vibration (RUV). The accuracy of this technique was demonstrated. A scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) made it possible to identify intermetallic compounds FeTi and Ti, FeAl and Fe, and TiAl and Ti in respective systems Fe–Ti, Fe–Al, and Ti–Al. The link between their composition, microstructure, and elastic properties was established.

Effects of Ni addition on removing Fe-Ti intermetallic compounds in cold metal transfer arc-brazed TC4/304L dissimilar joints

Dissimilar titanium alloy TC4/304 L stainless steel joints suffer from the brittle and inevitable FeTi and Fe2Ti intermetallic compounds. Cold metal transfer (CMT) arc-brazing method was used to join titanium alloy TC4 to 304 L stainless steel by using Cu, CuNi10, and CuNi30 wires. The effects of Ni addition on the microstructure and mechanical property were studied. With the addition of Ni, Fe-Ti intermetallic compounds was removed. TC4/seam interfaces containing TiNiCu, Ti2Cu, TiCu, TiCu4, and TiNi formed instead of those with Fe2Ti, FeTi, Ti2Cu, TiCu, TiCu2Al, and τ4 (Ti37Cu63-xFex). (Fe, Ni) dendritic grains and (Cu) solution formed instead of amount of Fe-Ti intermetallics in the seam and on the 304 L/seam interfaces. The reason is different intermetallic formation enthalpies and solution enthalpies calculated from Miedema model. Due to the thinner and less brittle TC4/seam interface layer, the highest tensile strength was 334 MPa when the CuNi10 wire was used. Excessive Ni content resulted in a reduction of strength due to the formation of an excessively thick and uneven TC4/seam interface. All joints fractured at the TC4/seam interface.

Study of the Interaction with Hydrogen and Ammonia of Titanium and Its Alloys with Iron

Results of hydrogenation of titanium, intermetallic compound TiFe, and titanium-enriched alloys with iron, Ti67Fe33 (Ti2Fe) and Ti80Fe20 (Ti4Fe), with hydrogen and ammonia were summarized and analyzed. The phase transformations in the temperature range 20–500°C were found, the temperatures at which hydride phase are formed were determined, the alloy dispersion conditions were optimized, and the reaction products were analyzed. Specific features of the interaction of the polymetallic systems with ammonia in the presence of ammonium chloride at various temperatures were revealed, and the conditions in which hydride, hydride-nitride, and nitride phases are formed were determined. Data were obtained about the possibility of using Ti-Fe alloys as the working material in reusable metal hydride hydrogen accumulators.

Aging Temperature Dependence of α″-Martensite Decomposition Mechanism in Ti-Al-Fe-Si Alloy

The mechanism by which α″-martensite decomposes in Ti-4Al-4Fe-0.25Si-0.1O alloy is found to change depending on the aging temperature, with Fe-rich α first transforming in twins of α″-martensite. As the aging temperature increases, Fe is segregated at the boundaries between α″ and α. At temperatures > 773 K, the Fe-segregated boundaries provide a nucleation site for B2-structured TiFe intermetallic compounds. This process of α″-martensite decomposition is described as follows: α″ + α″Twin → α″Fe-rich + αFe-rich,V1 → αFe-lean,V2 + αFe-lean,V1 + TiFe.

Liquid state property, structural evolution and mechanical behavior of Ti[sbnd]Fe alloy solidified under electrostatic levitation condition

The thermophysical properties of hypereutectic Ti63.64Fe36.36 alloy at both normal and undercooled states, including density, volume expansion coefficient, ratio of specific heat to emissivity were measured by electrostatic levitation (ESL) method combined with a high-speed photography technique. The enthalpy, specific heat, solute diffusion coefficient and surface tension were simultaneously calculated as functions of temperature by molecular dynamics simulation (MD), from which the emissivity was also derived. The rapid solidification kinetics in the undercooling range from 50 K to a maximum value of 270 K (0.18TL) during ESL experiments was quantitatively studied. As undercooling increases, primary TiFe intermetallic compound evolves from coarse dendrites to refined equiaxed grains, whose volume fraction rises significantly. The growth velocity of primary TiFe phase increases according to a power relation with undercooling to a maximum of 170 mm/s, which agrees well with the calculated results from LKT/BCT model on the basis of above determined thermophysical properties. The inter-correlations among “undercooling-microstructure-hardness” were derived subsequently through experiments. The hardness of both primary TiFe intermetallic compound and Ti63.64Fe36.36 alloy increases almost linearly with the increase of undercooling, and the former one relates to its grain size by Hall-Petch function.

Butt brazing of titanium alloys/stainless steel plates by MIG-TIG double-sided arc welding process with copper filler metal

Butt brazing of titanium alloys with stainless steel by MIG-TIG double-sided arc welding (DSAW) process with copper filler metal has been performed. The microstructures and mechanical properties of the joint were investigated. The results show that a butt brazing joint with sound double-sided appearance was achieved. With low heat input of brazing mode and rapid cooling rate of arc welding process, the joint is free of brittle Ti-Fe intermetallic compounds (IMCs). The phase compositions in the joint are TC4/Ti2Cu+TiCu/TiCu+Ti5Si3/Cu+(Ti5Si3+Cu+βTiCu4)/Fe5Si3+(Cu)+FeSi/Fe(s,s)/304ss orderly from Ti6Al4V to 304ss. The average tensile strength of the butt joint reaches 278MPa. Compared with the fusion welding joint, the tensile strength of the arc-brazing joint is significantly increased because of the elimination of Ti-Fe IMCs.

Dissimilar welding between Ti–6Al–4V and 17-4PH stainless steel using a vanadium interlayer

In this study, electron beam welding, continuous laser welding, and pulsed laser welding were used to join Ti–6Al–4V alloy and 17-4PH stainless steel with a 1 mm pure V sheet interlayer. In addition, the effect of V composition on the mechanical properties of the welded joint by shifting the laser towards the 17-4PH was examined. Vanadium bonded well with Ti, and the weld metal was characterized by a (βTi,V) solid solution. In the V–steel welded joint, similar phases ((Fe,V)ss) but with different compositions were found in the MZs, which affected the mechanical properties. The cracked region was visible at the V–steel interface of the pulsed-laser-welded joint and contributed to its low tensile strength. Electron beam welding showed a good intact joint with no defects, and failure occurred in the vanadium interlayer. A common MZ was created for the three metals in EB1, which formed Fe2Ti and FeTi intermetallic compounds that acted as crack initiation sites and led to the failure of the welded joint during machine processing. Variation in V composition had a significant impact on the mechanical properties of the welded joints. Hardness increased incrementally with the V concentration, and joints with a composition of less than 35 at% V, which corresponded to α-Fe + (Fe,V)σ and α-Fe phase formation ranges, had better tensile properties than those with more than 35 at% V, which corresponded to the single (Fe,V)σ phase. However, care should be taken in regulating the laser beam in order to avoid a very low V content, since this could lead to the formation of unfused regions.

Synthesis of TiFe Hydrogen Absorbing Alloys Prepared by Mechanical Alloying and SPS Treatment

This study aims to clarify the influence of the Spark Plasma Sintering (SPS) method on structural morphology, mechanical properties and also functional characteristics, such as hydrogen absorbing properties, for titanium-iron intermetallic compounds. We could synthesize B2-TiFe phase using mechanical alloying (MA) during 3 h and SPS treatment of 5 min at 500–1000 °C, which was confirmed by XRD and Electron Probe Microanalyzer (EPMA) measurements. In addition, the synthesized TiFe intermetallic compound has been found to absorb hydrogen with high kinetics in both high pressure Differential Scanning Calorimetry (DSC) and Pressure-Composition-Temperature (PCT) measurements. Therefore, we have successfully developed TiFe alloy in bulk form from initial raw powders by using a combination of short period mechanical alloying and SPS heat treatment. This combined route enhances the potential of the SPS method to synthesize new materials.

HYDROGENATION OF Ti80Fe20 ALLOY

We investigated the interaction of alloy of composition 80 at. % of Ti + 20 at. % of Fe (Ti 80 Fe 20 ) with ammonia under pressure of 0.6 ÷ 0.8 MPa at the temperatures 100 ÷ 500 ºC: the phase transformations in the Ti 80 Fe 20 –NH 3 system were defined; the composition of products was established; the formation conditions of the hydride and nitride phases were found; the formation temperatures of the hydride phases with the greatest possible content of hydrogen for use of alloy in the metal hydride accumulators of hydrogen were determined. The study shows the dependence of the reaction direction of alloy with ammonia, taking place in presence of NH 4 Cl (the 10 wt. % of alloy quantity) as activator, on temperature. One of the products of the reaction, which is carried out at 100 ºC, is the hydride phase of composition Ti 4 FeH 8.3 . With further a slight increase in temperature of reaction, this phase decomposes on hydride phases of the titanium and of the intermetallic compound TiFe. At interaction temperature of 200 ºC and above, insignificant amount of nitrogen is introduced into a metal lattice of hydride of an intermetallide of TiFeH -2 with formation of the phase TiFeH -2 N x . At temperature of 350 ºC and above, the titanium nitride TiN appears as a part of reaction product. The interaction of alloy and ammonia at 500 ºC leads to mixture of titanium nitride and metallic - Fe. The sharp increase in a specific surface area of reaction products at increase in process temperature from 250 ºC to 400 ºC (from 0.2 m 2 /g to 46.4 m 2 /g) is shown to demonstrate the formation of mixture of high-disperse powders. The metal hydride accumulator of hydrogen on the basis of the studied alloy can work in a temperature range of room temperature to 600 ºC and allocate up to 3 wt. % of hydrogen.

Mechanical activation of TiFe for hydrogen storage by cold rolling under inert atmosphere

TiFe is a very interesting material for hydrogen storage in the solid state, due to its hydrogen capacity of 1.9 wt % and to the fact it can be absorb/desorb hydrogen at room temperature. However, the TiFe produced by casting does not absorb hydrogen, unless a procedure called activation is applied, which is based on a repetition of several thermal cycles. This study evaluates the effects of a mechanical activation route for the TiFe intermetallic compound, namely, cold rolling (CR) under inert atmosphere. Stoichiometric TiFe was prepared from elementary powders by arc melting. Ingot was grinded and then cold rolled for 20 and 40 passes under argon inside a glove box, with moisture and oxygen contents below 0.1 ppm. Cold rolled samples consisted of two parts: powder particles and thin cracked flakes. The results showed that mechanically activated samples by CR exhibited rapid absorption of hydrogen at room temperature, without using a thermal activation process. In general, the average storage capacity of hydrogen was 1.4 wt% H2 for the first absorption, regardless of the number of passes for both flake and powder samples.

Evolution on Microstructure and Mechanical Property of Ti65Fe35 Hypereutectic Alloys by Adding Low Melting Temperature Elements

The microstructural evolution and modulation of mechanical properties were investigated for a Ti65Fe35 hypereutectic alloy by addition of Bi53In47 eutectic alloys. The microstructure of these alloys changed with the additional Bi-In elements from a typical dendrite-eutectic composite to a bimodal eutectic structure with primary dendrite phases. In particular, the primary dendrite phase changed from a TiFe intermetallic compound into a β-Ti solid solution despite their higher Fe content. Compressive tests at room temperature demonstrated that the yield strength slightly decreased but the plasticity evidently increased with an increasing Bi-In content, which led to the formation of a bimodal eutectic structure (β-Ti/TiFe + β-Ti/BiIn containing phase). Furthermore, the (Ti65Fe35)95(Bi53In47)5 alloy exhibited optimized mechanical properties with high strength (1319MPa) and reasonable plasticity (14.2%). The results of this study indicate that the transition of the eutectic structure, the type of primary phases and the supersaturation in the β-Ti phase are crucial factors for controlling the mechanical properties of the ultrafine dendrite-eutectic composites.

A New Approach for Using Interlayer and Analysis of the Friction Welding of Titanium to Stainless Steel

Dissimilar material joining is often more difficult than joining the similar material or alloys with minor differences in physical properties and composition. The formation of deleterious intermediate phases consisting of intermetallic compounds during welding of titanium and stainless steel is a challenge to the welding processes, for decades. Friction welding has been used in an attempt to reduce formation of intermetallic compounds through inserting an interlayer material. In recent years, a number of approaches have been developed to insert interlayer between the substrates to avoid the metallurgical incompatibility. In this research, dissimilar joint of titanium and stainless steel were welded effectively using a new technique of electrodeposited nickel coating on one of the substrate (stainless steel) as interlayer. The bonding interface of the joints was characterized using optical microscopy, scanning electron microscopy and energy dispersive spectroscopy. Tensile strength of the nickel interlayer joints was higher than the direct joints. The microstructural characterization in the interface of titanium and stainless steel showed the absence of brittle Fe–Ti intermetallic compounds, which was a condition attributed to the use of interlayer technique. Whereas, the characterization of interface were identified as the presence of Ti–Ni phases which were more plastic than Fe–Ti intermetallic compounds.

Microstructure and properties analysis of laser-welded Ni–Ti and 316l sheets using copper interlayer

Dissimilar pulsed laser welding of 1 mm-thick sheets was carried out on Nitinol/S.S joint. In order to modify the chemical composition of weld metal and to restrict the formation of Fe-Ti intermetallic compounds (IMCs) in the weld metal, Copper thin film with different thicknesses, 100 and 150μm, was used as an interlayer. The effects of interlayer thickness on microstructure, microhardness profile and chemical composition of weld-metal was investigated. Investigations showed that the interlayer thickness has a great influence on the chemical composition of the weld metal and, consequently, affects all of joint properties such as microstructure and ultimate tensile strength. According to X-Ray diffraction analysis, it was revealed that the increase of interlayer thickness decreases the concentration of Fe-Ti IMCs in weld metal and this makes weld metal softer to some extent. Moreover, since the Copper is a ductile metal of low melting temperature, added Copper into weld metal can compensate thermal stresses. Therefore, cracks originated from thermal stresses as well as brittleness of weld-metal were eliminated when the thickness of interlayer increased. However, there were some restricting factors as to the increase of the thickness of Copper interlayer, namely, the formation of Ti-Cu IMCs as well as the formation of Cu-rich globules which have relatively weak bonds with their surrounding matrix and this turns their boundaries to a suitable place for nucleation and propagation of a crack.

Preparation and hydrogen storage properties of nanocrystalline TiFe synthesized by mechanical alloying

In this research, the mechanism of mechanical alloying (MA) synthesis of TiFe intermetallic compound (IMC) from individual components Ti and Fe has been studied. The partition coefficient of the apparent diffusion and the reaction rate constant during MA solid-state synthesis of the TiFe intermetallic compound in a planetary ball mill have been estimated. The results indicate that the apparent diffusion coefficient is close to 10–11cm2/s that is approximately one order higher than the conventional high temperature diffusion coefficient. The reaction rate constant is close to 1.75·10−6. The relation between the structure and the hydrogen storage properties of MA synthesized IMC TiFe have been briefly discussed.

Narrow gap multi-pass laser butt welding of explosion welded CP-Ti/Q235B bimetallic sheet by using a copper interlayer

Butt welding of explosion welded Ti/steel bimetallic sheet is still a challenging task due to brittle Ti-Fe intermetallic compounds (IMCs) generated in the transition zone between Ti and steel. Laser butt welding of Ti/steel bimetallic sheet was performed in this work. Preliminary results showed that cracks usually observed in the transition zone of arc welded joint could be effectively avoided by using laser welding and a copper interlayer. The key point was the elaborate control of the remolten volume of copper interlayer. The laser butt welded joint achieved was evaluated by using SEM, EDS and micro-hardness test. Tensile tests, bending tests and V-notched Charpy impact tests were conducted to reveal the mechanical properties. The tensile strength and impact absorbing energy of the butt joint were about 73% and 77% that of the CP-Ti/Q235B bimetallic sheet, respectively. The initiation position and propagation path of the crack were observed by high-speed imaging in both face and root bending tests. Finally, improvements brought by the laser butt welding process were concluded and strategies for improving the processing scheme in the future were suggested.