TiFe Phase Research Articles

Pressure-less joining SiCf/SiC tube and Kovar alloy with AgCuInTi filler: Interfacial reactions and mechanical properties

The brazing of tube-bar structures is more difficult than that of traditional plate-plate structures, owing to the absence of pressure on the interface. In this study, AgCuInTi filler was employed to join SiCf/SiC tube and Kovar alloy bar and the joining can be completed at a significantly lower temperature of 780 °C, benefiting from the addition of In. Moreover, the lower temperature not only hindered the formation of Fe2Si and Ni2Si at the ceramic interface, but also avoided the appearance of the Fe2Ti phase in the joint. The typical microstructure of the joint was SiCf/SiC-(TiC + Ti5Si3) layer + (Ag, In) (s, s) + Cu (s, s) + Cu7In3+ Ni3Ti-Kovar. The finite element analysis indicated that lower brazing temperature can also reduce the level of residual stress compared to that of AgCuTi filler, which contributes to the maximum shear strength of 86.1 MPa despite the press-less joining. The fracture path originated from the SiC fibers, then passed through the interfacial reaction layer, and finally extended into the brazing seam.

Effect of bell annealing on the interface microstructure and mechanical properties of titanium/steel composite plates prepared by hot rolling

This study investigates the effect of bell annealing (600 °C–750 °C/3 h–15 h) on the interfacial microstructure and mechanical characteristics of hot-rolled titanium/steel (Ti/steel) bi-metallic plates, aiming to improve their mechanical performance and deformation compatibility. The interfacial bonding mechanism and growth process of the interfacial TiC layer were studied using multi-scale characterization. The microstructural evolution during annealing and the effect of the TiC layer on element interdiffusion were considered. Results show that the TiC interlayer inhibits Ti and Fe diffusion, preventing undesirable Ti-Fe phases, and the TiC layer thickens towards the Ti side. Higher annealing temperatures and longer times worsened the grain size difference between the Ti and steel layers and produced a thick TiC layer, severely degrading deformation compatibility. Microcracks, caused by severe lattice mismatch, are mostly initial at the α-Fe/TiC interface during plastic deformation. Thin to moderate TiC layers resulted in a combination of ductile and brittle fractures, while thick layers led to brittle fractures. In terms of mechanical properties, the ultimate tensile strength (UTS), yield strength (YS), shear strength, and elongation (EL) of the hot-rolled composite plate were measured at 337 MPa, 232 MPa, 238 MPa, and 29 %, respectively. All annealed samples exhibited a reduction in UTS, YS, and shear strength compared to the hot-rolled state; however, they demonstrated improved EL and deformation compatibility, with the elongation achieving its optimal value at 650 °C-3 h. The annealing, at 650 °C for 3 h, was identified as the optimal condition for post-rolling heat treatment, resulting in a composite plate with a comprehensive mechanical performance characterized by UTS, YS, shear strength, and EL values of 267 MPa, 127 MPa, 171 MPa, and 46 %, respectively.

Microstructure and mechanical properties of butt-welded Ti/steel bimetallic sheet using various multi-principal filler wires

Ti/steel bimetallic sheets have attracted significant attention in various engineering fields. However, achieving high-quality welded joints of Ti/steel bimetallic sheet presents difficulties because of poor metallurgical compatibility and different thermal expansion coefficients between titanium and steel. In this study, four types of multi-principal filler wires with varying contents of Cu, Ni, and Ti elements were designed and manufactured to finish the welding of TA2/Q235 bimetallic sheets. The study investigated the effects of various filler wires on the hardness, tensile strength, corrosion resistance, and microstructure of the welded joints. An interesting finding is that the highest tensile strength of 327±6 MPa was achieved in the welded joint using FeCoNi2Ti0.5 filler wire, with a joint coefficient of ∼79.1 %. The highest hardness in the weld zones was achieved by using FeCoNiTi0.5 filler wire, while the lowest hardness was achieved using FeCoNiCu0.5 filler wire. Dendrite (DR), interdendritic (ID), and eutectic structures were consistently observed in these weld zones. The phases of the DR and ID were identified as Fe2Ti and FCC structures based on EBSD data. A high content of Ni in filler wires could reduce the size and content of the Fe2Ti phase in the weld zones of Ti/steel bimetallic sheets.

Tune Al/Ti to adjust FCC+L21 hetero-structured Ni-based high-entropy alloys for improved mechanical properties and wear resistance

Outstanding mechanical properties of Ni-based superalloy benefit from its coherent γ/γ’ structure via precipitation strengthening of γ matrix (FCC structure) by L12 Ni3Al-type γ’ phase. Back-stress strengthening is another effective strategy to further enhance the FCC+L12 structured Ni-based superalloy. In this work, we extend such approaches to high-entropy alloys (HEAs) by introducing different Al and Ti contents (5 at.% ∼18 at.%) into a Ni-based CrFe2Ni4 alloy to form FCC+L21 heterostructured AlxCrFe2Ni4Tiy HEAs. Detailed microstructural analysis indicates that L12 Ni3(Al,Ti)-type nanoparticles form in a (Ni,Fe,Cr)-rich FCC matrix. The volume fraction of L21 AlNi2Ti-type phase can be varied by adjusting the Al/Ti ratio and concentrations of Al and Ti. Higher Al and Ti contents promote L21 phase formation and higher Al/Ti ratio (>1) prohibits the high Ti-containing compounds such as D024η-Ni3Ti and C14 Laves Fe2Ti phases, which are hard but brittle. Corresponding Young's modulus, Poisson's ratio, hardness, and the bulk to shear modulus ratio (B/G) can be readily modified. Compressive tests demonstrate that Al1.5CrFe2Ni4Ti1.0 alloy with half FCC and half L21 phases possesses the optimal strength-ductility combination (with compressive yield strength of ∼1564 MPa and fracture strain of ∼28 %). DFT calculations were performed to elucidate relevant mechanisms. Sliding wear tests were also performed, which demonstrate superior wear resistance of the HEAs at both room and elevated temperatures, compared with a commercial Ni-based superalloy, UHT-Nickel.

Surface wave phenomenon and microstructure evolution mechanism of electromagnetically levitated ternary Ti-Al-Fe alloy

Electromagnetic levitation technique was performed to investigate the surface wave phenomenon and microstructure evolution mechanism of undercooled ternary Ti50Al30Fe20 alloy. Under the condition of high undercooling, the formation process of surface waves on the levitated alloy surface were directly detected by high-speed camera. The cooling gas provided the external perturbation that promoted surface nucleation, providing the suitable site for surface wave generation. On the rotating semisolid alloy surface, the competition between centrifugal force and surface tension caused the surface wrinkling, leading to the formation of surface waves. The residual liquid phase was solidified in the vortex circulation flow, and the vortex-shape pattern was preserved during rapid solidification. With the increases of undercooling, the microstructure evolved from dendrites and interdendritic lamellar eutectics into uniform anomalous eutectics because of the independent nucleation and competitive growth of (βTi) and TiFe phase. The surface wave was formed only at high undercoolings, indicating this phenomenon was related to the fluidity in eutectic growth. In this case, the uniform microstructure was closer to satisfying the continuum medium hypothesis, and the homogeneous medium reduced the energy damage during wave propagation. In addition, the micromechanical properties were remarkably increased as undercooling rose owing to the microstructural morphology and solute trapping effect.

A novel high entropy composite interlayer for diffusion bonding of TC4 titanium alloy to 316L stainless steel

Titanium/steel hybrid structure exhibit broad prospects in the nuclear industry and aerospace applications. Achieving high-performance titanium/steel bonding is crucial. Herein, the novel AlCoCrNiCuAg/Cu high entropy composite interlayer was designed for vacuum diffusion bonding of TC4 alloy to 316L stainless steel. The effects of bonding temperature, holding time and assembly sequence on the interfacial microstructure and mechanical properties were investigated, and the fracture behaviors were researched. Typical microstructure of the joint bonded at 1010 °C for 90 min via AlCoCrNiCuAg/Cu sequence was TC4/β-Ti/β-Ti+TiFe/TiFe2+χ+σ/α-Fe+χ+σ/316L. With bonding temperature increased, due to the dispersed distribution of the Cuss phase in the Ti-Fe phases, the highest shear strength of 222.8 MPa was achieved at 1010 °C/90 min. The cleavage characteristics were confirmed in the fracture surfaces, suggesting the brittle fracture. The main cracks were located at the junction of the TiFe2+χ+σ and the β-Ti+TiFe layers, further confirmed that the interface appeared immense strain, accelerating the joint fracture.

Exploring the role of Fe in the wear and corrosion resistance of Ti-based alloys produced with conventional powder metallurgy

In this study, the Ti-6Al-XFe alloy was produced by conventional powder metallurgy at varying Fe contents (3.5, 7.0, 10.5, 14.0, 17.5, and 21.0 wt%) to investigate its potential as a substitute for Nb and V. The primary aim was to assess the impact of Fe content on the mechanical, tribological, and electrochemical properties of the alloys, focusing on their suitability for biomedical implants. XRD and SEM analyses revealed a decrease in the α-Ti phase and an increase in the β-Ti and FeTi phases with higher Fe content. The lowest porosity (0.8 %) and highest hardness (348.4 Hv0.2) were observed in the Ti-6Al-17.5Fe alloy. Tensile and flexural strengths peaked at 238.3 MPa and 680 MPa, respectively, in the 17.5Fe alloy. The Ti-6Al-14.0Fe alloy showed the smallest change in specific wear rate (0.274 × 10−6 mm3/N·m) under dry conditions, while the Ti-6Al-7.0Fe alloy had the smallest change (0.565 × 10−6 mm3/N·m) under wet conditions. The 7.0Fe alloy demonstrated the highest corrosion resistance, with the lowest Icorr (1.02 × 10−8 mm3/N·m) and corrosion rate (14.02 × 10−3 mpy), and the highest charge transfer resistance in EIS analysis.

The Determining Influence of the Phase Composition on the Mechanical Properties of Titanium-Iron Alloys after High-Pressure Torsion.

Three titanium alloys with 0.5, 6, and 9 wt.% iron were investigated, and the samples were pre-annealed in three different regions of the Ti-Fe phase diagram, namely β, α+β, and α+FeTi. After annealing, five samples of different phases and structural compositions were studied. They were then subjected to the high-pressure torsion (HPT). The microstructure of the samples before and after HPT treatment was studied using transmission and scanning electron microscopy. The microstructure of the samples obtained during heat treatment before HPT treatment had a fundamental effect on the microstructure after HPT. Grain boundary layers and chains of particles formed during the annealing process made it difficult to mix the material during HPT, which led to the formation of areas with non-uniform mixing of components. Thus, the grain boundary layers of the α-phase formed in the Ti-6wt % Fe alloy after annealing at 670 °C significantly decreased the mixing of the components during HPT. Despite the fact that the microstructure and phase composition of Ti-6wt % Fe alloys pre-annealed in three different regions of the Ti-Fe phase diagram had significant differences, after HPT treatment, the phase compositions of the studied samples were quite similar. Moreover, the measured micro- and nanohardness as well as the Young's modulus of Ti-6wt % Fe alloy had similar values. It was shown that the microhardness of the studied samples increased with the iron content. The values of nanohardness and Young's modulus correlated well with the fractions of β- and ω-phases in the studied alloys.

Analysis of the Microstructure and Mechanical Performance of Resistance Spot-Welding of Ti6Al4V to DP600 Steel Using Copper/Gold Cold-Sprayed Interlayers.

In this article, an attempt was made to join DP600 steel and Ti6Al4V titanium alloy sheets by resistance spot-welding (RSW) using an interlayer in the form of Cu and Au layers fabricated through the cold-spraying process. The welded joints obtained by RSW without an interlayer were also considered. The influence of Cu and Au as an interlayer on the resulting microstructure as well as mechanical properties (shear force and microhardness) of the joints were determined. A typical type of failure of Ti6Al4V/DP600 joints produced without the use of an interlayer is brittle fracture. The microstructure of the resulting joint consisted mainly of the intermetallic phases FeTi and Fe2Ti. The microstructure of the Ti6Al4V/Au/DP600 joint contained the intermetallic phases Ti3Au, TiAu, and TiAu4. The intermetallic phases TiCu and FeCu were found in the microstructure of the Ti6Al4V/Cu/DP600 joint. The maximum tensile/shear stress was 109.46 MPa, which is more than three times higher than for a welded joint fabricated without the use of Cu or Au interlayers. It has been observed that some alloying elements, such as Fe, can lower the martensitic transformation temperature, and some, such as Au, can increase the martensitic transformation temperature.

Microstructure regulation and performance of titanium alloy coating with Ni interlayer on the surface of mild steel by laser cladding

The preparation of Ti-alloy coating on the steel surface via laser cladding is very easy to form Fe-Ti phase and large tensile residual stress, which is not conducive to the performance of Ti-alloy coating. Here, Ti-6Al-4V coating (TC4-coating) was prepared on the mild steel substrate using laser cladding technology with Ni-alloy as the interlayer, and the Fe-Ti phase inside was completely suppressed. Increasing the powder feeding rate and scanning speed can change the undercooling of the alloy melt and the preferred growth orientation of the grains, while limiting the abnormal grain growth and grain boundary segregation, which is beneficial for grain refinement and equiaxed crystal formation. Reducing the scanning speed and powder feeding rate can increase the molten pool lifetime, thereby increasing the dilution rate of the coating and facilitating the formation of Ti2Ni phase. The abundant Ti2Ni inside the coating gives the TC4-coating greater microhardness (>500 HV0.1) and better corrosion resistance (Icorr of 7.00 × 10−8 A·cm−2). Grain refinement of the coating texture caused by the increase of powder feeding rate and scanning speed, as well as the high content of β-Ti phase and martensite structure, can improve the adhesion and shear strength of TC4-coating (386 ± 31 MPa).

To Mix or Not to Mix: Details of Magma Storage, Recharge, and Remobilization during the Pacheco Stage at Misti Volcano, Peru (≤21–2 ka)

Abstract We investigate ten of the most recent tephra-fall deposits emplaced between ≤21 and 2 ka from the Pacheco stage of Misti volcano, Peru, to elucidate magma dynamics and explosive eruption triggers related to magma storage, recharge, and remobilization. Whole-rock, glass, and mineral textures and compositions indicate the presence of broadly felsic, intermediate, and mafic magmas in a chemically and thermally stratified magma storage system (Zones 1–3) that interact to differing extents prior to eruption. Intermediate magmas are defined by plagioclase + amphibole + two-pyroxenes + Fe-Ti oxides and phase equilibria indicate they formed at ~300 to 600 MPa and ~950°C to 1000°C. Intermediate magmas dominate the Pacheco stage and either erupted alone as hybridized magmas or mingled with minor volumes of cool felsic magmas (~800°C) in which only plagioclase + Fe-Ti oxides are stable. Felsic magmas do not exclusively comprise any tephra-fall deposit emplaced during the Pacheco stage but were remobilized by recharge and mixing with intermediate magmas in order to erupt. Furthermore, felsic-hosted amphibole cognate to the intermediate magmas are reacted despite the felsic magmas being water saturated, which suggests they are staged above the amphibole stability limit (≤200 MPa). The cryptic presence of mafic magmas is indicated by high-An plagioclase cores (An74–88), rare anhedral olivine (Fo77–80), and possibly high Mg# augite and amphibole (up to Mg# 84 and 77, respectively). The dearth of basalt to basaltic andesite melts recorded in erupted glasses and exclusivity of high-An plagioclase to crystal cores signals mafic magmas are staged deeper in the crust than the intermediate magmas. Periodic interactions between these magmas tracked via glass compositions and crystal exchange reveal an alternation between the production of mingled magmas and their eruption shortly after a recharge event, followed by a period of homogenization and eruption of hybridized magmas. As such, we identify magma recharge as a key mechanism by which half of the explosive eruptions were triggered in the Pacheco stage. A >100°C increase in Misti’s fumarole temperatures from 1967 to 2018 coincident with changes in fumarolic gas compositions is consistent with degassing of a mafic recharge magma, signaling that Misti could produce similar explosive eruptions in the future.

Influence of intermetallic phase (TiFe) on the microstructural evolution and mechanical properties of as-cast and quenched Ti–Mo–Fe alloys

This study presents the phase analysis, microstructural characteristics, and mechanical property evaluation of the as-cast and quenched Ti–15Mo–xFe alloys with high iron content ranging from 4 to 12 weight percent. All the four alloys were produced in a vacuum-arc melting furnace. Heat treatment in the form of solution treatment was performed in a muffle furnace at a temperature of 1100 °C, with 1-h holding time and the samples were rapidly quenched in ice-brine. X-ray diffractometer (XRD) was used to analyses the phases present in each alloy whereas the optical microscope (OM) was employed to track the microstructural evolution and percentage porosity. The mechanical properties of the alloys were evaluated using a tensile test and compression test method while the micro-Vickers hardness measurements were conducted to evaluate hardness of the alloys. The XRD patterns of as-cast showed peaks belonging to the β and α″ phases and intermetallic B2 TiFe phases. The as quenched XRD peaks illustrated β phase only and Fe·Ti·O2 phases. The as-cast OM micrographs revealed equiaxed β grains, substructures, dendritic structure, and pores forming around the grain boundaries. The quenched OM showed only β equiaxed grains with pores throughout the grain boundaries. The tensile properties such as ultimate tensile strength (UTS) and elastic modulus (E) of as-cast TMF0 were 264 MPa and 79 GPa respectively and these properties changed upon quenching to 411 MPa and 66 GPa respectively. The elastic modulus of TMF1 in as-cast condition was 74 GPa. The UTS and E of TMF1, TMF2, and TMF3 in as-cast and quenched conditions were not recorded due to the fragility of the samples that failed prior to yielding any useful data. The compressive strength in as-cast and in quenched condition decreased with an increase in Fe content. The micro-Vickers hardness in as-cast and quenched conditions showed a similar trend with hardness increasing slightly upon quenching for TMF0, TMF1, and TMF3 alloys but slightly decreased in the case of TMF2. The fracture surfaces of all the as-cast and quenched alloys were comprised of ductile and brittle fracture.

Intermetallic phase evolution and strengthening mechanisms of the titanium and stainless steel lap joints welded by interrupted pulsed arc welding

The study is focused on analyzing the intermetallic phase evolution and strengthening mechanisms of the titanium alloy and stainless steel (Ti-SS) seam-welded joints using interrupted pulsed arc welding (IPAW). The precise adjustment of welding parameters for the IPAW technique allowed for the successful creation of two different joining modes for Ti-SS joints: contact reactive brazing and fusion modes. The homogeneous composition in the brazing joints was achieved by the formation of a diffusion-driven eutectic liquid phase at the joining contact, resulting in an unusual eutectic structure consisting of β-Ti and TiFe. The molten pool at high temperatures caused an uneven distribution of composition and energy throughout the fusion joints. The fusion joints consisted of a Ti-rich layer, containing β-Ti and TiFe phases near the TC4 side, and a Fe-rich layer, containing TiFe2/TiCr2 and α-Fe phases near the 304SS side. The shear-bearing capacity of the joints exhibited an initial increase and subsequent decrease as the heat input increased. The low heat input resulted in the formation of the unwelding zone, which significantly reduced the shear resistance of the joints. With the increase of the heat input, a reduction in shear strength occurred due to the accumulation of TiFe2 brittle phases associated with the shift of the joining mode from the brazing to the fusion. The shear force decreased after reaching its maximum value, despite the joints being fully joined and the joining area expanding.

Study on the microstructure and wear resistance of AlCrCuFeNiTix high entropy alloys for surfacing welding

In order to investigate the effect of Ti element content on the microstructure and wear resistance of AlCrCuFeNiTix (x = 0, 0.3, 0.6, 0.9) high entropy surfacing alloy, a melting electrode gas shielded welding technology was used to prepare AlCrCuFeNiTix high entropy surfacing alloy on the surface of carbon steel plates. The microstructure, phase composition, and wear resistance of the alloy were analyzed. The results show that the phase composition of the surfacing alloy becomes a BCC+FCC solid solution phase, with a much higher content of BCC phase than FCC phase. The microstructure consists of disordered BCC phase rich in Fe and Cr, ordered BCC phase rich in Al and Ni, and FCC phase rich in Cu. The microstructure exhibits typical dendritic (DR) and interdendritic (ID) structures. With the increase of Ti element, hard Fe2Ti phase precipitates in the interdendritic zone, and the micro hardness of the alloy shows an increasing trend. The maximum hardness can reach 636 HV, which is 2.4 times that of the base material. With the increase of Ti element, the friction coefficient of the alloy shows a trend of first decreasing and then increasing, and the wear amount first decreases and then increases. When Ti is 0.6, the wear resistance of the high entropy surfacing alloy reaches its best.

Microstructural evolution and mechanical properties of FeCrNiCuTix high entropy alloys

In this study, the microstructural evolution and mechanical properties of a series of FeCrNiCuTix (x = 0, 0.2, 0.4, 0.6, 0.8, and 1, in mole ratio) high entropy alloys (HEAs) were analyzed in detail to study the influence of Ti content on the HEAs. The microstructures of the alloys transformed from single-phase face-centered cubic (FCC) phase structure to FCC and body-centered cubic (BCC) diphase, finally to FCC, BCC and intermetallic compound (Fe2Ti) phase with the increase of Ti content. The addition of Ti element significantly refined the grain of the alloys. The hardness, strength and tribology tests of the alloys were also carried out. The results indicated that the Vickers hardness, yield strength, and fracture strength increased first and then decreased, the average friction coefficient variation law was just the opposite, and the plastic strain reduced monotonically, with the increase of x values for the alloys. At x = 0.4, the maximum yield strength and fracture strength of the alloy were 1646.89 MPa and 1947.09 MPa, respectively, and the average friction coefficient was a minimum of 0.47, with a hardness value of HV 489.68 and a plastic strain of 13.98%. The maximum hardness value of the alloy was HV 656.19 at x = 0.8. The fracture mechanism of the alloys was from ductile fracture to brittle fracture and the wear mechanism was form of abrasive wear. Accordingly, the FeCrNiCuTi0.4 alloy obtained the optimal mechanical properties overall. This research is of great significance for the development of engineering and structural materials with excellent mechanical properties.

Orientation relationship between TiFeH and TiFe phases in AB-type Ti–Fe–V–Ce hydrogen storage alloy

The partially hydrogenated microstructure of an AB-type Ti–Fe–V–Ce hydrogen storage alloy was investigated using scanning electron microscopy (SEM) with electron backscatter diffraction (EBSD). For the first time, the formation of the orthorhombic β-TiFeH phase was directly observed by using SEM-EBSD. Lamellar structures consisting of TiFeH and body-centered cubic TiFe phases with a (100)TiFeH∥(100)TiFe habit-plane pair were observed. Pole figure analysis was performed to confirm the orientation relationship between the TiFeH and TiFe phases to be [011](100)TiFeH∥[010](100)TiFe. The formation of TiFeH was characterized by simple lattice expansion with a short-range arrangement of H atoms and surface relief. In addition, unidirectional microcracks along the (100)TiFe planes were observed, presumably owing to the dehydrogenation of the TiFeH phase.

Influence of bonding time during diffusion bonding of Ti–6Al–4V to AISI 321 stainless steel on metallurgical and mechanical properties

Diffusion bonding was employed to join AISI 321 stainless steel to Ti–6Al–4V titanium alloy via Cu–Zn foil as the interlayer. The influence of bonding time (30, 45 and 60 min) at 900 °C temperature with the pressure of 2 MPa on the microstructural and mechanical behaviors of the joints is evaluated. The optical and scanning electron microscopes were utilized to examine the microstructural characteristics of the Ti–6Al–4V/Cu–Zn/AISI 321 stainless steel joints. Results displayed that three distinct reaction layers have been created as a result of the brazing process at all joints. It was also found that a longer bonding time led to the widening/expanding of the reaction/diffusion layers. The attained data also showed that bonding time affected the formation of brittle IMCs including CuTi2, CuTi, FeTi, Fe22Zn78 and TiZn3 phases within the interface as a result of the increased diffusivity of reaction elements and subsequently resulted in the reduction of the shear strength of the diffusion bonded joints from 281 MPa for bond made at 30 min to about 174 MPa for bond made at 60 min. Decreasing the shear strength by rising the bonding time can be a sign of expanding the level of interfacial reaction at the joints.

Microstructural evolution and anti-corrosion properties of laser cladded Ti based coating on Q235 steel

Titanium (Ti) based coatings laser cladded on steels could effectively protect steels from corrosion in the marine environment. However, the microstructural evolution and underlying solidification mechanisms for Ti based coatings laser cladded on steels are still unclear due to the nonequilibrium solidification processes during laser cladding. In this study, a Ti based coating was prepared on a Q235 steel by laser cladding. The microstructural evolution and corrosion properties of the coating were systematically investigated by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), electron probe micro-analysis (EPMA) and electrochemical measurements in 3.5 wt% NaCl solution. Four typical regions form in the Ti based coating and the constituent phases evolve from α-Fe + TiFe2 phases to TiFe2 phase, then to TiFe phase, and finally to Fe0.2Ti0.8 (metastable β-Ti) + TiFe + Ti2Fe phases from the fusion interface to the coating surface. Temperature gradients and solidification rates determine the microstructure morphologies of the Ti based coating, and the contents of Fe in the Ti based coating evolve and affect the phase transformations at different distances from the fusion interface. Moreover, the Ti based coating shows better anti-corrosion properties than the substrate. The effect of micro-strain at different regions on the microhardness and corrosion properties is also discussed. This study can be the base of optimizing the microstructure of laser cladded Ti based coatings on steels for better corrosion performances.

Interfacial microstructure evolution and mechanical properties in laser welded Invar alloy/TC4 dissimilar joints

The present study examined the evolution of interfacial microstructure and its effect on the mechanical properties of Invar/TC4 dissimilar joints by laser welding. The results indicated that various intermetallic compounds (IMCs) were formed in the interface layer of the TC4 side, such as Ti2Cu, TiCu and TiNi phases, while the columnar dendrites grown epitaxially perpendicular to the fusion line were observed on the weld seam (WS). Moreover, the boundary between dendrites growing in different directions within the WS was attribute to the high thermal conductivity of the filler metal and the non-equilibrium rapid cooling facilitated by the composition gradient. Besides, excessive heat input intensified the migration of elements and phase transition behavior, leading to the formation of brittle Ti-Fe phases in the interface layer, which significantly weakened the mechanical properties of the dissimilar joints and resulted in brittle fracture characteristics. The strength of the joint exhibits a parabolic distribution with heat input. When the heat input was below 600 J/cm, the joint fractured in the interface layer of the TC4 side, with a maximum tensile strength of 298.4 MPa at 600 J/cm. However, when the heat input exceeded 600 J/cm, the formation of brittle Ti-Fe IMCs contributed to a decrease in joint strength. The investigation provides an efficient and stable method for achieving high-strength Invar/TC4 dissimilar alloy welding.

RADIAL DEPENDENCES OF THE PHASE COMPOSITION, NANOHARDNESS, AND YOUNG’S MODULUS FOR TI-2 WT % FE ALLOY AFTER HIGH-PRESSURE TORSION

The specimens of Ti-2 wt % Fe alloy were annealed at three different temperatures, in the β-Ti, (α-Ti + β-Ti) and (α-Ti + TiFe) fields of the Ti-Fe phase diagram, then water quenched and subjected to high-pressure torsion (HPT). The X-ray diffraction analysis showed that the main phase in all annealed samples was the α phase (more than 90%), while the main phase after HPT was the ω phase. The hardness H and Young’s modulus E were determined by nanoindentation at the center, in the middle of the radius, and near the edge of each specimen. It was found that the H and E values were different for specimens annealed at different temperatures and depended on the radial coordinate of the indentation region. The maximum H values were obtained in the middle of the radius of the specimens. The E values of all specimens decreased from the center to the edge, reaching very low values. The paper discusses structure transformations during HPT, the behavior of the radial dependences of H and E , and probable causes of a strong decrease in E values.