Intermetallic Compound TiFe Research Articles

Effects of TiFe Intermetallic Compounds on the Tensile Behavior of Ti-4Al-4Fe-0.25Si Alloy

The effect of the B2 (ordered BCC) intermetallic compound TiFe on the tensile behavior of the Ti-4Al-4Fe-0.25Si alloy was investigated. The nucleation mechanism of TiFe was dependent on the solution temperature, and the solution treatment and aging temperatures were also important to the final alloy. The presence of intra-granular TiFe, which nucleated at α′ (HCP) sites during aging, resulted in alloy brittleness. Alternatively, the presence of inter-granular TiFe, which nucleated only at nano-sized α (HCP) sites during aging, resulted in an excellent combination of strength and ductility compared to the original microstructure.

Mechanical and microstructural characteristics of commercial purity titanium implants fabricated by electron-beam additive manufacturing

Electron-beam additive manufacturing (EBAM) is a layer-by-layer additive manufacturing technique. In this study, the mechanical and microstructural characteristics of commercial purity (CP) titanium implants with various porosities, fabricated by EBAM, were examined. The results show that the CP-titanium implants were composed of fine grains and Fe-Ti intermetallic compounds with a size of 40nm. In addition, they exhibit high yield strength and a low elastic modulus that are comparable to those of human bone.

Deposition of polymer coating on metallic powder through ball milling: Application to hydrogen storage intermetallics

Summary Ball milling technique was used for deposition of the polytetrafluoroethylene (PTFE) coating on the powder of TiFe intermetallic compound. Measurement of pressure–composition hydrogen absorption isotherms revealed that the polymer-coated TiFe intermetallic compound kept its hydrogen storage ability. The TiFe/PTFE material demonstrated resistance to surface poisoning even after a prolonged exposure to air and was not subjected to pulverization during multiple hydrogenation–dehydrogenation cycles. Copyright © 2015 John Wiley & Sons, Ltd.

Analysis and Characterization of the Role of Ni Interlayer in the Friction Welding of Titanium and 304 Austenitic Stainless Steel

Joining of commercially pure Ti to 304 stainless steel by fusion welding processes possesses problems due to the formation of brittle intermetallic compounds in the weld metal, which degrade the mechanical properties of the joints. Solid-state welding processes are contemplated to overcome these problems. However, intermetallic compounds are likely to form even in Ti-SS joints produced with solid-state welding processes such as friction welding process. Therefore, interlayers are employed to prevent the direct contact between two base metals and thereby mainly to suppress the formation of brittle Ti-Fe intermetallic compounds. In the present study, friction-welded joints between commercially pure titanium and 304 stainless steel were obtained using a thin nickel interlayer. Then, the joints were characterized by optical microscopy, scanning electron microscopy, energy dispersive spectrometry, and X-ray diffractometry. The mechanical properties of the joints were evaluated by microhardness survey and tensile tests. Although the results showed that the tensile strength of the joints is even lower than titanium base metal, it is higher than that of the joints which were produced without nickel interlayer. The highest hardness value was observed at the interface between titanium and nickel interlayers indicating the formation of Ni-Ti intermetallic compounds. Formation these compounds was validated by XRD patterns. Moreover, in tensile tests, fracture of the joints occurred along this interface which is related to its brittle nature.

Interface microstructural control by probe length adjustment in friction stir welding of titanium and steel lap joint

The dissimilar lap joining of commercially pure Ti (CP-Ti) plate of 1.0mm in thickness and structural steel (SPCC) plate of 3.2mm in thickness was conducted by friction stir welding using different tools with probe lengths from 0.8 to 1.2mm for the purpose of controlling the joint interface microstructure. The sound joints showing the base plate fracture of CP-Ti have been obtained by using the tools with the probe lengths of 0.9 and 1.0mm. The transmission electron microscope examination revealed the two types of the interface microstructure. One was a non-intermixed type interface with a single interlayer of about 50–100nm in thickness, composed of FeTi intermetallic compound and β-Ti phase at the joint with the probe length of 0.9mm. The other was an intermixed interface with lamellar structure in which a FeTi or FeTi+Fe2Ti intermetallic compound layer of about 100nm in thickness and a β-Ti layer of about 1μm in thickness were alternately formed at the joint with the probe length of 1.0mm.

Study of hydrogen storage materials by neutron powder diffraction

Metal hydrides are interesting materials from a fundamental as well as practical point of view. Hydrogen storage applications have been the main driving force of research on these materials but lately uses such as thermal storage are considered. In this presentation we will review the use of neutron diffraction for the development of new metal hydrides. Two systems will be presented: BCC solid solution alloys and FeTi alloy. Ti-based BCC solid solutions are promising material for hydrogen storage applications which need high volumetric capacity and room temperature operation. One system that has been considered is Ti-V-Cr. Using only X-ray diffraction for structural identification does not provide information about hydrogen localization. Therefore, neutron diffraction is essential for complete determination of this class of hydrides. We will present examples of Ti-V-Cr compounds doped with Zr-Ni alloy. The peculiarity of this type of alloy is that, for neutron diffraction, the scattering lengths of the elements almost cancel. Therefore, the neutron pattern of as-cast alloy shows very small Bragg peaks but the advantage is that the hydride for is very easy to see and analyze. Another good candidate for hydrogen storage applications is the intermetallic compound TiFe which operates at around room temperature (RT) under mild pressure conditions. However one disadvantage of TiFe alloy synthesized by conventional metallurgical method is its poor activation characteristics. The alloy reacts with hydrogen only after complicated activation procedure involving exposure to high temperature (~4000C) and high pressure for several days. Recently we found that by doping this alloy with Zr and Zr7Ni10 the activation could be easily done at room temperature. We present here a neutron diffraction study of these compounds that shows the structural difference between the activated compound and the one cycled under hydrogen.

Study of hydrogen storage of the TiFe alloy by neutron powderdiffraction

Metal hydrides are interesting materials from a fundamental as well as practical point of view. Hydrogen storage applications have been the main driving force of research on these materials but lately, uses such as thermal storage are considered. In this presentation, we will review the use of neutron diffraction for the development of new metal hydrides. A good candidate for hydrogen storage applications is the low cost intermetallic compound TiFe which operates near room temperature (RT) under mild pressure conditions. However, the biggest disadvantage of TiFe alloy synthesized by conventional metallurgical method is it poor activation characteristics [1]. The alloy reacts with hydrogen only after complicated activation procedure involving exposure to high temperature (~4000C) and high pressure for several days. In the '90, some researches showed that the change in the nanocristallinity can modify the sorption property of the TiFe[2]. Other research works found that palladium increase the contaminant resistance. However, addition of palladium is too expansive for practical applications [3]. Recently, we found that, when doping TiFe with Zr and Zr7Ni10, the activation could be easily done at room temperature. We present here a neutron diffraction study of these compounds that shows the structural difference between the activated compound and the one cycled under hydrogen.

Hydrogen sorption properties of mechanically alloyed Mg1−2xFexTix powder mixtures

We report an investigation on the hydrogen sorption properties of mechanically alloyed systems of nominal composition Mg1−2xFexTix (x=0.10, 0.15 and 0.20). The starting metallic powder mixtures were milled in H2 ambient, till a steady state with no further H2 absorption was attained. The resulting samples were then characterized and submitted to several H2 discharge–charge cycles in order to determine their hydrogen sorption properties. With the aim to investigate the dependence of these properties on the sample microstructure we also studied samples of nominal composition Mg80Fe10Ti10 obtained through different processing routes. In those samples the Fe and Ti additives were added as a fine powder mixture or as the intermetallic compound FeTi while their mechanical alloying with Mg was conducted under H2 or Ar atmosphere. All the samples were characterized by X-ray diffraction and Mössbauer spectroscopy on 57Fe, before and after their cycling in H2. The results are analyzed in the framework of possible mechanisms for the transition metals catalytic action on the H2 sorption processes and the influence of the sample microstructure.

Properties of Friction Welding Titanium-stainless Steel Joints with a Nickel Interlayer

The probability and appropriate processing parameters of friction welding method of commercially pure titanium to a 304L stainless steel with an electroplated nickel interlayer have been investigated. The microstructure of the welded joints has been observed by optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy, and the main factors affecting friction welding process were analysed. Metallographic analysis revealed that a good bonding was obtained at both the titanium/nickel and nickel/stainless steel interfaces, and the diffusion products were identified in the weld zone. The effect of friction time and forging pressure on metallurgical and mechanical properties were evaluated. The results showed that atom diffused well and no presence of Fe–Ti intermetallic compounds appeared at optimum parameters. With the increment of friction time, the thermal degradation region increasing hence the thickness of interlayer material is decreasing. Microhardness test across the joining interfaces demonstrated the effect of solid solution hardening in the weld zone. The tensile strength increased with increasing forging pressure at constant friction time. Tensile test showed that the maximum average tensile strength of ∼289MPa was obtained for the joint welded at forging pressure of 320MPa. The tensile fracture surfaces are indicating river patterns of brittle mode of failure of the joints. The tensile fracture of the welded joint occurred in titanium side near the interface.

Adding Sn on the Performance of Amorphous Brazing Fillers Applied to Brazing TA2 and Q235

Amorphous filler Ti-Zr-Cu-Ni with better performance and higher melting point than the α → β phase transition temperature 882.5d the melting point of fillers is reducing with the increase of the Sn content; the joint gap that formed during brazing TA2 and Q235 using Ti-Zr-Cu-Ni-Sn foils is fully filled with continuous compact surface and smooth uniform fillet; the shear strength of the joint is raising with the increase of Sn content in brazing fillers and the strength reaches to 112 MPa when Sn content is 3%; adding more Sn, more brittle intermetallic compounds TiFe and TiFe2 are gathering to form cluster and the shear strength of the joint is reducing; the shear fracture always occurs in the center of the seam.

Mechanical alloying of nanocrystalline intermetallic compound TiFe doped with sulfur and magnesium

A series of nanostructured alloys based on TiFe intermetallic compound were synthesized from the metallic elements in a planetary ball mill by solid state mechanical alloying. Mg and S were added as doping components to a Fe–50%(at.) Ti powder mixture. Phase and structure transformations during mechanical alloying and subsequent annealing as well as hydrogen interaction with the alloys prepared were studied. It was shown that reversible hydrogen sorption capacities of the nanostructured alloys based on TiFe intermetallic compound were of 0.6 and 0.7wt.% at room temperature for the alloys with S and Mg, respectively. The alloys studied demonstrated a simplified activation of hydrogenation, especially for the S-containing one.

Study on the Microstructure and Properties of Low Cost TiFeAl Alloy

The high strength and low cost Ti-Fe based alloy was produced by double vacuum induction melting method followed by hot deformation. The microstructure has been investigated by Optical Microscopy, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The microstructure of as-forged alloy is composed of α and β phase without the precipitation of TiFe intermetallic compound. The Ti-Fe-Al alloys show good comprehensive mechanical properties, demonstrating ultimate tensile strength of 1100MPa and elongation above10%. The results indicate the Fe is a good candidate for solution strengthening and simultaneously increasing ductility in titanium alloys. Effect of the Fe and Al elements on the microstructure and mechanical properties have been discussed.

Structures and Tribological Characteristics of TiFe–xC Triboengineering Materials Obtained by Self-Propagating High-Temperature Synthesis

We study the tribological properties and structures of materials of the TiFe–xC system obtained by selfpropagating high-temperature synthesis. It is shown that these triboengineering materials exhibit good operating characteristics under the conditions of dry and abrasive friction under temperate loads at room temperature. The structure of the obtained materials is formed by Ti2Fe and TiFe intermetallic compounds, which represent thermodynamically stable phases with a great heat of formation. The addition of boron to the TiFe–хС system significantly reduces the temperatures of the main critical points of these compounds and extends the temperature range of synthesis. We determine the friction coefficients for friction couples formed by a ball of ShKh15 steel–TiFe–20C and a ball of ShKh15 steel–45 steel, which are equal to 0.11 and 0.15, respectively, under the identical conditions. The high strength characteristics of specimens of the TiFe–20C, TiFe–30C, and 55Ti–20C–30Fe–0.31B systems enable us to use these materials for the protection of the surfaces of nozzle leaves of the jet engines operating at high temperatures and under high loads.

Mechanical alloying of nanocrystalline intermetallic compound TiFe doped by aluminum and chromium

Abstract A series of nanostructured alloys based on TiFe intermetallic compound were synthesized from the metallic elements in a planetary ball mill by solid state mechanical alloying. Al and Cr were added as doping components to a Fe-50% (at.) Ti powder mixture. Phase and structure transformations during mechanical alloying and subsequent annealing as well as hydrogen interaction with the alloys prepared were studied. It was shown that reversible hydrogen sorption capacity of the nanostructural alloys based on the TiFe intermetallic compound was of 0.7 wt.% at room temperature. The alloys studied demonstrated a simplified activation of hydrogenation. A correlation between the alloys behavior in their reactions with hydrogen and structure parameters of the hydrogenated samples has been discussed.

Research on Three Microcosmic Interface Defects of Titanium/Steel Laminates Manufactured by Explosive Welding

Optical metallographic examination, scanning electron microscope as well as energy dispersive X-ray spectrometry was operated to the interface of titanium/steel laminates manufactured by explosive welding. Three types of microcosmic defects as brittle Ti-Fe intermetallic compound, shearing crack, and brittle Ti-Fe-O layer were found at the interface of titanium/steel laminates. The reasons for above three microcosmic defects were analysed.

Mechanochemical synthesis of a TiFe nanocrystalline intermetallic compound and its mechanical alloying with third component

The method of solid-phase mechanochemical synthesis is used to obtain nanostructured ternary alloys based on a TiFe intermetallic compound with manganese, copper and zirconium as alloying components. The phase and structural transformations in the process of the synthesis are determined by x-ray diffraction analysis. The interaction between the resulting compounds and hydrogen is studied, isotherms of absorption and desorption of hydrogen are plotted, and the hydration products are subjected to x-ray phase analysis. It is shown that the use of mechanical activation and the presence of a third component permits activation under less rigid conditions as compared to TiFe obtained by metallurgical alloying.

Three Wave Interfaces of Titanium/Steel Laminates Manufactured by Explosive Welding

Optical metallographic examination, scanning electron microscope as well as energy dispersive X-ray spectrometry was operated to the interfaces of titanium/steel laminates manufactured by explosive welding. According to the variation of the thickness of brittle Ti-Fe intermetallic compound at the interfaces, typical wave interfaces of titanium-steel laminates are classified as over melted wave interface, tinyly melted wave interface and optimum wave interface. Furthermore, the features of three wave interfaces are brought forward.

Hydrogen storage nanocrystalline TiFe intermetallic compound: Synthesis by mechanical alloying and compacting

Abstract Equiatomic nanocrystalline TiFe intermetallic compound was synthesized from elementary metals by mechanical alloying in a planetary ball mill. Then the powder produced was compacted by cold pressing into bulk samples keeping the nanocrystalline structure. The hydrogen capacity of TiFe bulk samples was found to be of 1.4 wt.%. The absorption isotherm had a long plateau corresponding to pressures of 0.3–0.4 MPa at room temperature. The bulk samples demonstrated high durability after 20 absorption–desorption cycles.

시효처리에 따른 Ti-6Al-4Fe-0.25Si 합금의 미세조직 변화

The effect of aging heat treatment on microstructure evolution of the Ti-6Al-4Fe-0.25Si alloy with an initial microstructure of an elongated alpha was investigated. Aging treatments of the samples were carried out at 550°C for up to 100 hours. The microstructure of the 5 hours heat-treated sample consisted of alpha grains, beta matrix and some TiFe intermetallic compounds that were precipitated from the beta matrix. Increasing the aging time to 10 hours, most of the beta matrix was decomposed to very fine alpha grains (~ 0.5 μm) and TiFe, and thus the volume fraction of the beta matrix was significantly decreased. EBSD analysis revealed that newly formed tertiary-alpha-grains in the vicinity of TiFe had high angle boundaries with respect to the primary and secondary alpha grains. As a result of these phase transformations during aging, the fraction of the alpha/alpha grain boundary was increased while that of the alpha/beta phase boundary was decreased. (Received March 30, 2012)

A study on crystal structure, bonding and hydriding properties of Ti–Fe–Ni intermetallics – Behind substitution of iron by nickel

Intermetallic compound TiFe, known for its hydrogen storage applications, is modified by substituting iron by nickel and related changes of properties and applicability of the obtained compounds are studied. Samples TiFe1−xNix (x = 0.2–0.6) are synthesized by melt-spinning and their crystal structure, desorption characteristics and electronic structure are investigated by TPD, 1H NMR and Mossbauer spectroscopy. State-of-the-art DFT calculations give further insight into the changes in electronic structure and bonding related to the hydrogen absorption and substitution of iron by nickel. The increase of Ni/Fe ratio in the TiFe1−xNix is found to result in the increase of hydride cohesive energies and in the systematic shifting of Fermi energy (EF) to lower values, in both pure intermetallics and appropriate hydrides. Hydride formation was found to influence the Fermi energy lowering and the increase of number of states at EF.