TiFe Phase Research Articles

Investigation of Wear and Corrosion Behaviour of AISI 316 L Stainless Steel Coated By ESD Surface Modification

AISI 316 L austenitic stainless steel is widely used in various sectors of the industry (chemical, petro-chemical industry, paper industry, nuclear engineering, dairy equipment and medical field) because of its good corrosion resistance and biocompatibility. In contrast to these superior properties, it has a low hardness and poor wear performance, thus, limiting its use in some areas of industry. As a result of progress in science and technology, the expectation of superior properties from materials has increased and the surface modification has become an important part of this development. Amongst many coating processes, Electro-spark Deposition (ESD) is a micro-bonding process that is used to deposit a stronger, more robust and durable coating layer on a metallic substrate. This method can also be used to repair damaged parts, tools or equipment or to extend the tool and equipment life. In this study, the surface of AISI 316 L stainless steel was coated with WC and Ti6Al4V by ESD method. Morphology and microstructure of the deposited layers were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Surface hardness distributions were determined with a micro hardness tester. XRD analysis revealed that Fe–α, Fe–γ, W2C, Cr–Ti, Al–Fe–Ti phases exist on the deposited layers. The wear behavior of the coated surfaces was carried out by ball-on-disc wear method using WC-Co ball bearing with a diameter of 8 mm for a sliding distance of 250 meters at a sliding rate of 0.3 m/s under a dry condition using a load of 5 N. Corrosion behavior of coated surfaces i.e. Tafel extrapolation and linear polarization methods were investigated for the duration of 1 h in the SBF (Simule Body Fluid) solution. Morphology of layers formed on steel surface was examined by SEM microscope. Wear tests showed that AISI 316 L stainless steel has a low surface hardness but wear resistant coatings improved this property. The wear rate of coated AISI 316 L stainless steel decreased by 3–10 times with respect to the type of coating. The electrochemical experiments showed that the expected improvement was not achieved due to the high corrosion resistance of AISI 316 L stainless steel. However, the weakness of the surface hardness was partly replaced by an acceptable compromise from corrosion resistance.

Microstructure and Mechanical Properties of Rapidly Solidified β-Type Ti–Fe–Sn–Mo Alloys with High Specific Strength and Low Elastic Modulus

The microstructure and mechanical properties of rapidly solidified β-type Ti–Fe–Sn–Mo alloys with high specific strength and low elastic modulus were investigated. The results show that the phases of Ti–Fe–Sn–Mo alloys are composed of the β-Ti, α-Ti, and TiFe phases; the volume fraction of TiFe phase decreases with the increase of Mo content. The high Fe content results in the deposition of TiFe phase along the grain boundary of the Ti phase. The Ti75Fe19Sn5Mo1 alloy exhibits the high yield strength, maximum compressive strength, large plastic deformation, high specific strength, high Vickers hardness, and large toughness value, which is a superior new engineering material. The elastic modulus (42.1 GPa) of Ti75Fe15Sn5Mo5 alloy is very close to the elastic modulus of human bone (10–30 GPa), which indicating that the alloy can be used as a good biomedical alloy. In addition, the large H/Er and H3/Er2 values of Ti75Fe19Sn5Mo1 alloy indicate the good wear resistance and long service life as biomedical materials.

Effect of high zirconium content on hydrogenation properties and anti-poisoning ability of air-exposed TiFe alloy

In order to improve the anti-poisoning ability of air-exposed TiFe alloy, the TiFe+x wt.% Zr (x=8, 12 and 16) alloys were synthesized by arc melting and subsequently exposed in air for different time. The results show that all samples handled in air can absorb the hydrogen directly without any incubation time. In addition, their first hydrogenation kinetics increases with the proportion of zirconium. And for the samples exposed in air for 35h, all samples also can absorb the hydrogen without any heating and mechanical treatment, but x=8 sample needs a long incubation time. Further study, it can be found that each alloy exposed in air for 35h includes three phases: a TiFe main phase with very small amount of zirconium, a hcp secondary phase with high proportion of zirconium and very small titanium phase. Also, more hcp secondary phases are beneficial for the improvement of the first hydrogenation kinetics but also lead to higher loss of capacity after first absorption and desorption. Above results suggest that introducing high zirconium content can improve the anti-poisoning ability of TiFe alloy effectively. This may be because that the bright phase (hcp phase) probably can⿿t be oxidized as easily as the dark phase (TiFe phase).

Feasibility study of different filler metals on MIG-TIG double-sided arc brazing of titanium alloy-stainless steel

The feasibility of Cu, Cu-Si and Cu-Ni based filler metals on MIG-TIG double-sided arc brazing (DSAB) of TC4-304ss (Ti-SS) was studied. The microstructures and mechanical properties of the joints were investigated and compared. Defect-free Ti-SS brazing joints with double-sided sound forming were achieved using different filler metals. Thin reaction layers with the thickness of 75 μm and 50 μm were respectively formed at the Ti-side interfaces in the Cu filled joint and the Cu-Si filled joint, which mainly consisted of various Ti-Cu phases. The reaction layer with a width of 115 μm formed in the Cu-Ni filled joint showed complex phases of β-Ti, Ti2Cu, TiNi, Ti(Cu1-xNix)2 (x = 0.20–0.82), (Cu1-x Nix)1-y Tiy (x = 0–1; y = 0–0.14), TiCu4, Cu (s,s) phases. The Ti-Fe brittle phases formed at the SS side interface and weld zone in Cu-filled joint were replaced by the Ti-Si-containing phases in Cu-Si filled joint and Cu-Ni-containing phases in Cu-Ni filled joint. The tensile strength of the joints was 256 MPa, 273 MPa and 276 MPa, respectively. The Cu filled and Cu-Si filled joints fractured at the SS side interface due to the presence of the flat interface and the formation of brittle intermetallic compounds (IMCs). The Cu-Ni filled joint fractured at the thick Ti side interface, which induced by Ti(Cu1-xNix)2 phase with high brittleness.

Catalytic hydrolysis of HCN over Fe–Ti-O catalysts prepared by different calcination temperatures: Effect of Fe chemical valence and Ti phase

Abstract A series of Fe–Ti-Ox catalysts calcined at different temperatures (signed as Fe–Ti-x, and x symbolized the calcination temperature of 300, 400, 500, 600 and 700 °C, respectively) were prepared and studied for the catalytic hydrolysis of HCN in the presence of H2O. The results implied that Fe–Ti-4 (the calcination temperature was 400 °C) showed the best catalytic hydrolysis efficiency of HCN and the abundant productions (CO and NH3). With the calcination temperature increasing, the catalytic hydrolysis of HCN activity decreased dramatically, which was related to the reduction of specific surface areas and redox property, the formation of rutile TiO2 and decline in quantity of Fe2+ species. Besides, Fe–Ti-Ox catalysts with amorphous states of TiO2 could enhance catalytic hydrolysis of HCN, which depended on the effect of calcination temperature during the preparation process of Fe–Ti-Ox catalysts.

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.

Thermal decomposition of ThMn12-type phase and its optimum stabilizing elements in SmFe12-based alloys

We investigated the phase stability of SmFe12-based compounds by experimental and computational first-principles approaches. The effect of particle size and alloy composition on the thermal decomposition rate is addressed. We show that decomposition begins with Sm evaporation from particle surface, resulting in the formation of α-Fe and Fe2Ti phases. The decomposition rate scales inversely with particle size. A significant stabilizing effect can be realized by substituting Fe with phase stabilizing elements such as V or Ga. According to ab initio calculations, Ti, V, and Ga lower the formation energies. However, when the reduction in magnetic moment is considered, the most effective stabilizing element that can minimize the reduction of μ0M is Ga. These findings present a useful insight on the potential solutions for the development of bulk Sm(Fe0·8Co0.2)12-based magnets.

Interdiffusion behavior in 304L SS/Ti–5Ta–2Nb system

This paper presents the results of an experimental and computational study on interdiffusion and related structure-property changes in 304 L stainless steel/Ti–5Ta–2Nb system. Diffusion annealing treatments were carried out in the temperature range of 873–1173 K, above and below the β transus temperature of Ti. The formation of σ, FeTi and Fe2Ti phases at the interface as well as stabilization of α-Fe and β-Ti in 304 L SS and TiTaNb respectively has been unambiguously established in this study. Growth kinetics of the reaction zones has been determined and effective interdiffusion coefficients in various phases were calculated using Wagner's approach. Temperature dependant variations in the mechanical property of the base materials and diffusion couples have also been predicted using JMatPro® and compared with literature. Finally, the evolution of microstructure at the interface and diffusion path in the diffusion couples were compared with SS/Ti based diffusion bonded joints and explosive clads to understand the interdiffusion behavior under equilibrium and non-equilibrium conditions.

Effect of milling time on the microstructure and magnetic properties of amorphous Ti50Fe50 alloys prepared by mechanical alloying

The effect of milling time on the microstructural evolution and magnetic properties of Ti50Fe50 alloys prepared by mechanical alloying were investigated. The results showed that the powder size was decreased sharply and then stabilized. Correspondingly, the milled powders experienced a transition from the lamellar shape to the spherical shape due to severe plastic deformation as well as the competition of cold welding and fracturing when the milling time was increased. Compared with the detailed composition primary powder (composed of Ti and α-Fe phases), the nanocrystalline Ti and α-Fe phase gradually disappeared and the amorphous phase were formed in the Ti50Fe50 alloys after milling for 40 h. When the milling time was increased to 60–90 h, the nanocrystalline disappeared and the complete amorphization of the milled Ti50Fe50 alloys occurred. However, a small amount of the nanocrystalline TiFe was formed except for a large of amorphous phase in Ti50Fe50 alloys for 100 h. Meanwhile, the formation of paramagnetic amorphous/nanocrystalline Ti and TiFe phase resulted in the saturation magnetization and coercive of the milled Ti50Fe50 alloys were decreased. Therefore, they exhibited excellent soft magnetic (0–90 h) and paramagnetic properties (100 h).

Microstructure and mechanical properties of diffusion bonded W/MA956 steel joints with a titanium interlayer by SPS

Diffusion bonding is an effective technique for joining dissimilar metals. In this paper, tungsten and MA956 steel were diffusion-bonded by Spark Plasma Sintering (SPS) technique with titanium (Ti) foil as an interlayer. The bonded joints were evaluated by metallographic analysis and mechanical tests, and the results reveal that all W/Ti/MA956 joints were well bonded by efficient SPS technique. Microstructure analysis showed that W-Ti solid solution formed at W/Ti interface; reaction phases at Ti/MA956 steel interface varied with the joining temperature, e.g. intermetallics phases FeTi for 850 °C, FeTi, Fe2Ti and Cr2Ti for 900 °C and 950 °C joining temperature. The peak value of microhardness occurred at the interfaces of Ti/MA956 steel owing to the formation of intermetallic compound. All specimens of shear testing fractured at the Ti/MA956 steel interface close to MA956, and the average shear strength of joints was 182 MPa, 228 MPa and 164 MPa bonded at 850 °C, 900 °C and 950 °C respectively.

Microstructure and hydrogen storage properties of V48Fe12Ti15-xCr25Alx (x=0, 1) alloys

The microstructure and hydrogen storage characteristics of V48Fe12Ti15-xCr25Alx (x = 0, 1) alloys prepared by vacuum arc melting were studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and pressure–composition isotherm measurements. It was confirmed that all of the alloys comprise a BCC phase, a Ti-rich phase, and a TiFe phase. Al as a substitute for part of the Ti content caused an increase of lattice parameters of the BCC phase and of the equilibrium pressures of hydrogen desorption, but decrease of the hydrogen storage capacities. The kinetic mechanism of the hydrogenation and dehydrogenation of the alloys was investigated by the classical Johnson–Mehl–Avrami equation. The reaction enthalpies (ΔH) for the dehydrogenation of alloys without and with Al were calculated by the Van't Hoff equation based on the PCI measurement data, which are 30.12 ± 0.14 kJ/mol and 28.02 ± 0.46 kJ/mol, respectively. The thermal stability of the metal hydride was measured by differential scanning calorimetry. The hydrogen desorption activation energies were calculated using the Kissinger method as 79.41 kJ/mol and 83.56 kJ/mol for x = 0 and 1, respectively. The results suggest that the substitution of titanium with aluminum improves the thermodynamic properties of hydrogen storage and reduces the kinetic performance of hydrogen desorption.

Characterization of Microstructure and Interface Reactions in Friction Welded Bimetallic Joints of Titanium to 304 Stainless Steel Using Nickel Interlayer

Direct joining of 304 stainless steel to titanium poses many challenges because of a lack of metallurgical compatibility and the formation of FeTi and CrTi types of brittle intermetallic compounds. The use of a low thermal heat input process of friction welding allows to obtain good microstructure properties through the improvement of metallurgical compatibility between two metals. In the present investigation, a novel approach of nickel interlayer was applied to explore a new bimetallic structure of titanium to stainless steel. Microstructure characterization, interface formation and its reactions were analysed via scanning electron microscope, X-ray diffraction and electron probe microanalyser analyses. The results exhibited that the intermetallic phases were successfully avoided through the use of Ni interlayer. Microhardness values demonstrated the absence of brittle FeTi and CrTi phases in the weld interface. The weld interface was found to be within two intermetallic layers situated at Ti/Ni interface.

First Hydrogenation Enhancement in TiFe Alloys for Hydrogen Storage Doped with Yttrium

The aim of this investigation was to improve the first hydrogenation of TiFe by adding yttrium. The compositions studied were TiFe + x wt.% Y with x = 4, 6, and 8. From electron microscopy it was found that all alloys were multiphase with a matrix of TiFe phase containing less than 0.4 at.% of Y and a secondary phase rich in yttrium. When x increased, the chemical compositions of the matrix changed and the secondary phase changed. The sample with 8% of yttrium had the fastest kinetics. The hydrogen capacity increased with the amount of Y.

The rapidly solidified β-type Ti–Fe–Sn alloys with high specific strength and low elastic modulus

The β-type Ti–Fe–Sn alloys with high specific strength and low elastic modulus are prepared by rapidly solidified technology. The microstructure and mechanical properties of Ti–Fe–Sn alloys were investigated. The results show that the phases of Ti80Fe20 and Ti79Fe20Sn1 alloys are mainly composed of β-Ti phase, and of a small quantity of α-Ti and FCC TiFe phases. The phases of Ti77Fe20Sn3 and Ti75Fe20Sn5 alloys are composed of β-Ti, a large number of α-Ti, and a small quantity of TiFe phases. The contents of β-Ti phase reduce with increase of Sn content, and the corresponding contents of α-Ti phase increase with increase of Sn content. The Ti75Fe20Sn5 alloy that has high yield strength, high fracture strength, large plastic strain, and high specific strength can be considered as a new engineering alloy. The elastic modulus (33.6 GPa) of Ti75Fe20Sn5 alloy measured by using the nanoindentation technique is very close to that of human bone (10–30 GPa), and are the further smaller than the elastic modulus (120 GPa) of commercial Ti-6Al-4V biomedical alloy. The Ti75Fe20Sn5 alloy can be considered as a new biomedical alloy. The large H/Er and H3/Er2 of Ti77Fe20Sn3 and Ti75Fe20Sn5 alloys indicate the good wear resistance and anti-wear ability of materials, respectively.

Significant coercivity enhancement of Ti doping in Nd–Ce–Fe–B melt spun alloys

Abstract The influences of doping Ti on the phases, microstructures and magnetic properties are systematically investigated in (Nd0.8Ce0.2)12Fe82−xTixB6 melt spun alloys. It is found that Ti could promote the glass forming ability of the studied alloys and increase the stability of the amorphous phase. Significant coercivity enhancement due to Ti doping is observed. The coercivity increases from 9.5 kOe for Ti-free sample to 18.5 kOe with Ti addition of 5 at%, and further reaches to 19.5 kOe when Ti addition rises to 7 at%. The Fe2Ti phase is found to precipitate in the 2-14-1 phase grain boundaries investigated by transmission electron microscopy (TEM) and high angle annular dark field (HAADF). With the Ti contents increasing, the precipitated phase becomes larger and more continuous, which is responsible for the huge improvement of the coercivity.

Nanoindentation and microstructure analysis of Ti/Fe dissimilar joint

Ti/Fe bimetallic plate was joined by Cu20V filler. Ti/Fe interface was characterized by fine dendrite structures (β-Ti + FeTi) with hardness ranging from 11 to 16 GPa. These fine dendrites were transformed into coarse cellular structures (CuTi2) when approaching Cu20V weld metal (WM). Cu4Ti and V(s,s) phases were dominant in the central of Cu20V WM with hardness ranging from 4 to 11 GPa. Complex phase constitutions were observed at Cu20V/Fe WM interface consisted of Cu4Ti, V(s,s), Cu(s,s), σ-FeV and Fe2Ti phases with hardness ranging from 4 to 18 GPa. A simplified scenario describing how these phases evolution at Cu20V/Fe WM interface was proposed.

Deformation induced precipitation of MgZn2-type laves phase in Ti-Fe-Co alloy

Generally, the formation of Laves phase precipitates is induced by heat treatment, and deformation-induced precipitation of these phases has not been reported so far. In this work, we observed the precipitation of the compression-induced C14 laves phase particles along dislocation walls within B2 TiFe phase in a semi-solid sintered TiFeCo alloy. Interestingly, coherent interfaces were formed between the Laves phase and the TiFe parent phase, and the corresponding orientation relationships: (011¯1)C14//(1¯10)B2 and [21¯1¯0]C14//[001]B2. The present study indicates that the feasibility that Laves phases can be introduced into metallic materials by deformation processing.

Effects of adding over-stoichiometrical Ti and substituting Fe with Mn partly on structure and hydrogen storage performances of TiFe alloy

In this paper, over-stoichiometrical Ti was added into the TiFe alloy and Fe was further substituted partly by Mn for improving the hydrogen storage performances of the alloys. X-ray diffraction and scanning electron microscope results revealed that the as-cast TiFe and Ti1.1Fe alloys contain TiFe, TiFe2 and Ti1.3Fe phases. Adding over-stoichiometrical Ti leads to the reduction of TiFe2 and Ti1.3Fe phases to some extent, and TiFe phase becomes the main phase for the alloy. Further substituting Fe with Mn partly causes TiFe2 phase to reduce significantly and Ti1.3Fe phase to disappear completely. In addition, some new generated β-Ti phases also were observed in the backscatter electron images for the as-cast Ti1.1Fe0.8Mn0.2 alloy, which provides the initial driving force to the pulverization of the alloy powders in the hydrogen absorption process. Field emission transmission electron microscopy results show that all the alloys are nanocrystalline structure. Further substituting Fe with Mn partly makes the average grain size (D) decrease. It is also beneficial to the reduction of the gaseous activation condition and the improvement of the hydrogen storage capacity and kinetics, while results in a slight increase of the value of the dehydrogenation enthalpy (ΔHdes).

Gallium-assisted diffusion bonding of stainless steel to titanium; microstructural evolution and bond strength

Strong joints between stainless steel 304 L and pure titanium (grade-2) were made using the novel method of “gallium-assisted diffusion bonding”. The microstructural evolution and interfacial reactions were investigated in detail. The possible mechanisms of phase changes at the joint interface when bonding with and without a nickel interlayer were identified. Layers of FeTi and (Fe,Cr)2Ti intermetallic compounds were found at the reaction zone in the case of direct bonding, whereas (Fe,Ni)Ti and Fe2Ti phases were identified in the reaction zone of the samples bonded using nickel interlayers. A layer of αFe was observed on the steel side of the reaction zone in both the cases, probably due to the enrichment of Cr at the interface. The diffusion of gallium led to formation of a layer of αTi, while the diffusion of Fe and Ni assisted in the formation of a duplex (α + β)Ti phase in the inter-diffusion zone. The joints fractured along the intermetallic layers at the interface, during tensile testing, with limited ductility. The maximum tensile strengths of the bonded samples were 280 and 313 MPa with and without nickel interlayer, respectively. The latter equals 92% of the tensile strength of the pure grade-2 titanium used in this work (i.e. 340 MPa).

Structure and hydrogenation performances of as-cast Ti1.1-xRExFe0.8Mn0.2 (RE = Pr, Sm and Nd; x = 0, 0.01) alloys

The AB-type Ti1.1-xRExFe0.8Mn0.2 (RE = Pr, Sm and Nd; x = 0, 0.01) alloys in cast are fabricated. The relationships of phase composition, surface morphology and crystal structure to the hydrogenation performances of the alloys are studied. X-ray diffraction (XRD) results show that the as-cast Ti1.1Fe0.8Mn0.2 (TFM for short) alloy includes the base phase of TiFe phase and the second phases of TiFe2 phase and TiO phase. Backscatter electron (BES) images show that there is Ti segregation phase besides TiFe phase and TiFe2 phase in the TFM alloy. Substituting Ti with RE partly causes Ti phase to increase and RE phases to generate. The lowest activation temperature decreases from 573 K for the TiFe alloy to 423 K for the Ti1.1-xRExFe0.8Mn0.2 (RE = Pr, Sm and Nd; x = 0, 0.01) alloys. Substituting Ti with RE partly makes the incubation time reduce from 5900 s for the TFM alloy to 3850, 3900 and 4050 s for the Pr0.01, Sm0.01 and Nd0.01 alloys, respectively. And it also is able to weaken the stability of the hydrides, while causes variable degrees of the hydrogenation capacity decrease.