TiAl Research Articles

Anisotropy of microstructure features and tensile properties of Ti–48Al–2Cr–2Nb alloy produced by electron beam powder bed fusion

A Ti–48Al–2Cr–2Nb alloy was produced by electron beam powder bed fusion. The effect of the volume energy density parameter on the forming quality was investigated, and the tissue characteristics, hardness distribution, and mechanical properties of the alloy were analyzed. The results showed that the quality was better when the volume energy density parameter was 21.5–22.5 J/mm3. The microstructure of the alloy has the phenomenon of changing with the forming height: with an increase in the forming height, the forming part produces the phenomenon of strip microstructure along the construction direction, and the regional microstructure variability occurs under the cross section of the same height. The average hardness of the alloy reached 375.2 HV at the bottom, 381.8 HV in the middle, and 389.6 HV at the top, and the standard errors of the hardness values were 12.40, 10.49, and 7.12 HV, respectively, with the microhardness showing a gradual increase along the molding direction, and the homogeneity was gradually better. The transverse tensile strength at room temperature reached 526 MPa, the yield strength reached 461 MPa, and the elongation at break reached 1.24%, while the longitudinal tensile strength reached 486 MPa, the yield strength reached 414 MPa, and the elongation at break reached 1.02%.

Investigation into the stress‒strain compatibility and fracture behaviour of a TC18 titanium alloy with a multistage lamellar microstructure

Understanding the fracture mechanism is essential for optimizing the mechanical properties of titanium alloys. The relationship between fracture behaviour and the multistage lamellar microstructure of the TC18 (Ti–5Al–5Mo–5V–1Cr–1Fe) alloy was investigated via in situ tensile and three-point bending tests. The results indicate that the TC18 alloy, featuring a multistage lamellar microstructure (including a β matrix, primary lamellar α phase, bundles, and secondary lamellar α phase), exhibits an excellent combination of strength and ductility. The precipitation of the secondary lamellar α phase significantly enhances the alloy's strength but weakens the stress‒strain compatibility of the microstructure. This results in a smaller crack-tip plastic zone (CTPZ) and causes dislocations to concentrate more at the grain boundaries and, to a lesser extent, at the phase interfaces. Consequently, in the later stages of crack propagation, microvoids and microcracks tend to form at dislocation pile-ups. With increasing stress, these microvoids and microcracks rapidly coalesce, leading to a greater proportion of intergranular fracture and thus reducing the fracture toughness of the alloy.

Effects of V Addition on the Microstructure and Mechanical Properties of a PM Ti–4Al–3Cu–2Fe Alloy

Effects of V Addition on the Microstructure and Mechanical Properties of a PM Ti–4Al–3Cu–2Fe Alloy

Development of an Al–Ti–Hf Composite Alloy Strengthened with High Volume Fraction of In-situ formed Al3(Ti, Hf)-Type Trialuminide Intermetallic Phase

Development of an Al–Ti–Hf Composite Alloy Strengthened with High Volume Fraction of In-situ formed Al3(Ti, Hf)-Type Trialuminide Intermetallic Phase

Phase equilibria of CaO–Al2O3–CaO·TiO2 system at 1500 °C in hydrogen atmosphere

The phase diagram of CaO–Al2O3-TiOx system is of great importance in guiding the design of metallurgical slag systems for Al–Ti alloy steel, controlling Ti-bearing inclusions in molten steel, and regulating the mineral phase of vanadium-titanium magnetite. In the present work, the high temperature equilibration-quench technique was adopted, and the types and compositions of equilibrium phases were identified by Electron Probe Micro Analysis (EPMA) and X-ray diffraction (XRD). The isothermal section of CaO–Al2O3–CaO·TiO2 system at 1500 °C in H2 atmosphere was constructed for the first time. There are 7 three-phase fields, 10 two-phase fields, and a single liquid phase field. On this basis, according to the theoretical analysis of the crystal structure, the formation energy analysis based on first-principles calculations, and the related theories of defect chemistry, the formation mechanisms of CaTiO3 and Ca3Ti2O7 solid solution with were determined, respectively. Additionally, the experimental phase diagram was utilized to discuss the dissolution type and the equilibrium solubility of typical inclusions (Al2O3, Ti3O5, and CaO·TiO2) in Al–Ti alloy steel.

Deep Cryogenic and Thermal Aging Treatments of Ti–5Al–5Mo–5V–3Cr Alloy Additively Manufactured by Powder Bed Fusion–Laser Beam

The properties of 3D‐printed components via powder bed fusion–laser beam (PBF–LB) depend strongly on the processing parameters, particularly due to the rapid solidification conditions involved. In this study, an innovative post‐treatment strategy combining deep cryogenic treatment (DCT) and thermal aging treatments are introduced to enhance the properties of Ti–5Al–5V–5Mo–3Cr alloy (Ti‐5553) alloy fabricated by PBF–LB. In the results, it is revealed that DCT of as‐built material can refine the grain size and introduce defects and sub‐grain boundaries, thereby improving strength and ductility without significantly altering the microstructure or phase composition. However, applying DCT after aging can significantly improve ductility and maintain strength, primarily by refining β‐phase grains. Conversely, thermal aging followed by DCT of as‐built materials tends to increase strength at the expense of ductility, due to the formation of the ω phase and defects induced by the cryogenic treatment that in turn promote the development of more abundant and finer α phase within grains during aging. In the findings of this research, significant insights and valuable methodologies are offered for optimizing the mechanical properties of Ti‐5553 alloy manufactured by PBF–LB via an extra DCT following thermal aging.

Investigation of the microstructure evolution and mechanical properties of cast Ti–47Al–2Cr–2Nb alloy during ultra-high pressure heat treatment

TiAl alloy is a high-temperature and lightweight material with superior properties, which has been widely used in aerospace industry. and casting is an economical method for its production. However, casting defects has hindered its direct applications in aerospace turbine blades. To minimize casting defects and achieve alloy strengthening, this paper proposed a novel single heat treatment process under ultra-high pressure (UHP) to regulate the microstructure and mechanical properties of the Ti–47Al–2Cr–2Nb alloy. The results indicated that the microstructure achieved overall grain refinement, high temperature and ultra-high pressure stresses jointly induced the γ→α2 phase transformation. After the UHP heat treatment, the hardness of the alloy increased from 287HV to 381HV, and the yield strength and ultimate strength increased by 53 % and 20 %, respectively, without significantly affecting the strain to fracture. Based on the phase transformation behavior and strengthening mechanism, these enhancements in mechanical properties were mainly attributed to the precipitation strengthening of α2 grains and the reduction of lamellar thickness. This suggested that UHP heat treatment was an effective method to improve cast TiAl alloys.

In situ tailoring of precipitation behavior and improving mechanical properties of (Ti2AlC+Y2O3) reinforced TiAl alloy produced by directed energy deposition

A (Ti2AlC + Y2O3) synergistically reinforced Ti–48Al–2Cr–2Nb alloy was prepared by directed energy deposition with in situ tailoring of precipitate formation by induction preheating and thermal cycle. The influence of C and Y2O3 coaddition on the microstructure and high-temperature compressive properties was systematically investigated. The results indicated that Ti2AlC was formed by adding elemental C, and the Ti2AlC phase was mainly distributed in two forms: long rod-shaped Ti2AlC with a micron scale that distributed uniformly in the matrix, and lenticular Ti2AlC particles with nanometer size that distributed along the (α2/γ) lamellar interface. The Y2O3 particles were randomly distributed in the matrix. Columnar grains in vertical cross section along the building direction were completely eliminated by adding C and Y2O3. The high temperature compressive strength increased from 597 MPa to 758 MPa at 850 °C by adding C and Y2O3. Finally, the precipitation mechanism of nano-Ti2AlC was discussed in detail. This work provided a valuable reference for the preparation of high-performance TiAl alloys by in situ tailoring of the precipitates during the DED process.

Investigation of Inclusion Characteristics in Ferrosilicon Killed High Silicon Steels

Industrially, the silicon requirement of liquid steel is often met with ferrosilicon (FeSi) instead of high‐purity silicon addition. FeSi, a silicon‐rich alloy, contains impurities typically inherited from its manufacturing stage. Therefore, FeSi addition results in the formation of complex inclusions in the liquid steel. Herein, a detailed inclusion characterization of the samples obtained from the melting experiments for a wide range of silicon concentrations has been carried out to examine the effect of FeSi impurities. Pure silica inclusions evolve to silica‐ and/or alumina‐based Si–Al–(Ti)–O–(TiN) complex inclusions with the increasing addition of FeSi to the steel melt. Reduction of silica by aluminum or titanium, the presence of titanium in the steel melt, and/or TiN inclusions formed at the periphery of oxide inclusions restrict the growth of oxide inclusions, resulting in small‐sized (average) oxide inclusions. The underlying mechanism of such complex (Si–Al–Ti–O–N)‐based inclusions has been explained with the aid of microstructural characterization and thermodynamic calculations. Moreover, the steel–crucible (alumina) interface has also been investigated for inclusion deposits and crucible–steel interaction.

Stress-induced martensitic transformation during cold rolling of metastable β Ti–5Al–5V–5Mo–3Cr alloy

The present study focuses on modifying the microstructures and mechanical properties of a recently developed metastable β Ti–5Al–5V–5Mo–3Cr (Ti-5553) alloy through cold rolling technique. Three different degrees of deformations (5 %, 10 %, and 20 % thickness reductions) are employed on the as-cast Ti-5553 alloy. Microstructural analysis reveals presence of single β-phase in the as-cast alloy, which is further confirmed through X-ray diffraction technique. Cold rolling however activates different deformation mechanisms with increasing degree of rolling and hence evolve the microstructure as well. While the alloy subjected to the lowest extent of thickness reduction, deforms mainly via slip, that with the highest degree of rolling deforms through formation of slip lines, zigzag slip lines, and deformation bands. Overall, activation of specific twins such as {332} <113>β along the closed packed direction of the β matrix is noted for the optimally cold rolled specimen. Most interestingly, occurrence of stress-induced martensitic phase is also confirmed for all the cold rolled specimens with its volume percentage being directly proportional to the degree of deformation. This cold rolling imparted microstructural modifications also influence the local and global mechanical performance of Ti-5553 alloy. Highest values of hardness and compressive yield strength are noted for the Ti-5553 alloy cold rolled up to the highest extent. This systematic study is the first of its kind to report the influence of cold rolling on the stress induced martensite formation and hence establishes the processing-structure-property correlation for Ti-5553 alloy.

Origin of the enhanced creep properties of high Nb containing TiAl alloys with the addition of C and Y2O3

In this paper, Ti–43Al–6Nb–1Mo–1Cr, Ti–43Al–6Nb–1Mo–1Cr-0.5C and Ti–43Al–6Nb–1Mo–1Cr-0.5C-0.05Y2O3 alloys were prepared by induction skull melting under argon atmosphere. Creep tests were carried out on three alloys to reveal the effects of C and Y2O3 on the creep properties of alloys and to clarify the precipitation behavior of Ti2AlC and B2 phases. The results show that adding C and Y2O3 can significantly reduce the steady-state creep rate and improve the creep properties of the alloy. After adding C and Y2O3, the parallel decomposition of α2 lamellae occurs, and the fine γ lamellae precipitates from coarse α2 lamellae. The lamellar degradation occurs obviously during creep, and the reaction is α2→γ+B2. The B2 phase preferentially grows into α2 lamellae after nucleation at the lamellar interface. Furthermore, the precipitated B2 phase can induce the formation of stacking faults in α2 lamellae. The strengthening mechanism of C is mainly solid solution strengthening and the precipitation hardening. The dynamically precipitated Ti2AlC during creep can hinder the movement of dislocations and improve the bonding strength of the lamellar interface. Y2O3 mainly plays a role of second phase strengthening, which can share the stress of the matrix and prevent the crack propagation. Finally, the voids nucleation and crack propagation process of the alloy are analyzed and summarized.

A Local-Scale, Post-Fire Assessment in a Double-Burned Area: A Case Study from Peloponnisos, Greece

In the summer of 2021, Greece experienced significant forest fires and mega-fires across multiple regions, leading to human casualties and damage to the natural environment, infrastructure, livestock, and agriculture. The current study aims to assess the ecosystem condition in terms of the natural regeneration and soil conditions of an area burnt by a forest fire (2021), specifically in the Ancient Olympia region situated in West Peloponnese (Ilia Prefecture), Greece. A standardized field sampling methodology was applied to record natural regeneration at chosen sites where a forest fire had also previously occurred (in 2007), resulting in the natural re-growth of the Pinus halepensis forest. Furthermore, an analysis was conducted on the geochemical, mineralogical, and sedimentological properties of soils obtained from this location. The findings of the research demonstrate the decline in the established natural regeneration of the Pinus halepensis forest and the overall tree layer. Species characteristic of post-fire ecological succession were observed in the shrub and herb layers, displaying varying coverage. The examination of soil mineralogy, sedimentology, and geochemistry indicated that the soil characteristics in the area are conducive to either natural or artificial regeneration. Ultimately, recommendations for landscape rehabilitation strategies are provided to inform decision-making processes, considering future climate conditions.

Microstructure and properties of Ti55531 alloy subjected to deep cryogenic treatment

The cryogenic treatment of near β Ti–5Al–5Mo–5V–3Cr–1Zr (Ti55531) alloy was conducted using the liquid nitrogen refrigeration method. The microstructure and properties were characterized by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results show that the alloy achieves optimal properties at a cryogenic time of 8h. Compared to samples that were not cryogenically treated, microhardness, ultimate tensile strength (UTS), and elongation increased by 12.9%, 6.8%, and 8.0% respectively. Detailed microstructural characterization indicated that the cryogenic processing can lead to grain refinement, enhanced dislocation density, and accelerate the transformation of the metastable β phase into the stable α phase, resulting in a higher volume fraction of the α phase. After cryogenic treatment, the lath-shaped α phase reorients from a vertical to a parallel orientation, and its average width is reduced. Simultaneously, cryogenic treatment diminished texture strength but enhanced the uniformity of the alloy. Improvements induced by cryogenic treatment are attributed to alloy volume and lattice contraction caused by cold compression forces at cryogenic temperatures, which generate internal stress and grain deflection.

Structure and Properties of the Powder for Additive Synthesis of Alloys Based on Titanium Aluminide TiAl

Structure and Properties of the Powder for Additive Synthesis of Alloys Based on Titanium Aluminide TiAl

Density and surface tension of liquid Al, V and their binary alloys measured by electromagnetic levitation

Both density and surface tension were systematically investigated over a wide temperature and compositional range for the liquid Al–V alloy system. The thermophysical properties were measured in an electromagnetic levitation device. A linear decrease in surface tension and density with increasing temperature was observed for every alloy composition investigated. Additionally, a decrease in density and surface tension was observed for increasing aluminum content among the different probed samples. This decrease is, a strong deviation from an ideal mixing behavior which was experienced for both properties. Different models, including variants of the well-established Butler model, were employed to better describe the compositional dependence of density and surface tension in the liquid Al–V system. The advantages and disadvantages were discussed for each model describing the measured thermophysical property data. Strong similarities were observed when comparing the mixing behavior and segregation effects of the investigated Al–V system with already established works for the liquid Al–Ti system. The results suggest that both vanadium and titanium show similar mixing behavior when alloyed with aluminum.

Жароміцні інтерметалідні сплави та особливості їх легування

The work considers the prerequisites for the development of creep-resistant and heat-resistant alloys, based on intermetallics, taking into account the optimal combination of their physical and mechanical properties, as well as structural characteristics. It is shown that there is a sufficient number of intermetallics, which have a density lower than iron-based alloys, which, in combination with high melting temperatures and heat resistance, makes them promising materials for aerospace application, in particular, for gas turbine engine parts manufacturing. The most suitable creep-resistant and heat-resistant intermetallics can be called aluminides and silicides of titanium, nickel and molybdenum. For these compounds, it is possible to combine high values of specific strength with alloying-favorable types of crystal lattice. One of the most important and common creep-resistant alloys based on intermetallics is Ni3Al with FCC lattice. For this material, complex optimized alloying is the main way to increase creep resistance. The heat resistance of such alloys is significantly increased by applying ceramic coatings. Titanium aluminides Ti3Al and TiAl mainly have only a low density among the advantages. Their fragility at room temperatures and tendency to superplasticity at high temperatures significantly limits their application. The impact of disadvantages may be reduced by applying thermomechanical processing of such materials, which aims to change their structure. Alloying titanium aluminides with a large amount of niobium was chosen as a solution that significantly reduced marked week sides of Ti-Al intermetallic alloys. As a result, this led to the creation of a new alloy based on intermetallic Ti2AlNb with a high set of operational characteristics. Mo-Si and Mo-Si-B can be considered as one of the most perfect systems for creating heat-resistant intermetallic alloys. They combine an acceptable density, high creep and heat resistance, which can be additionally increased by reinforcing with ceramic particles. Keywords: intermetallic-based alloys, creep resistance, alloying, Ni-Al, Ti-Al, Mo-Si, Mo-Si-B.

Investigation on the effect of electroshock treatment on the microstructure and mechanical properties of Ti–45Al–5Nb alloy

This study investigated the effects of electroshock treatment (EST) on the microstructure and mechanical properties of Ti–45Al–5Nb alloy. Microstructure results showed that no new phase was generated after EST, the peak positions of α2 phase and γ phase were shifted, the relative intensity of the diffraction peaks were enhanced, and the grain orientations were varied. The original relatively coarse α2 lamellae decomposed into fine γ+α2 lamellae in a direction parallel to the original γ/α2 lamellae. The segregation of Nb element was weakened and the distribution was more uniform. Texture research showed that after EST with 60 ms and 80 ms, the maximum relative texture intensity of γ phase was enhanced. After EST with 100 ms, the maximum relative texture intensity of γ phase weakened to 17.86, and the grain orientation became dispersed. The texture distribution was more uniform. The maximum relative texture intensity of α2 phase was weakened and the orientation was dispersed after EST. Mechanical property results showed that after EST, the yield strength and fracture strain of the material was improved. The main reason is that the precipitation of γ phase forms fine γ/α2 lamellae. All results indicate that EST provides a new way to manipulate the microstructure and properties of TiAl alloys.

Вплив термічної обробки на структуру і властивості алюмініду титану TI–28Al–7Nb–2Mo–2Cr та його зварних з’єднань

Вплив термічної обробки на структуру і властивості алюмініду титану TI–28Al–7Nb–2Mo–2Cr та його зварних з’єднань

Influence of heat treatment on the structure and properties of Ti‒28Al‒7Nb‒2Mo‒2Cr titanium aluminide and its welded joints

Influence of heat treatment on the structure and properties of Ti‒28Al‒7Nb‒2Mo‒2Cr titanium aluminide and its welded joints

Electromagnetic characterization of MAX phase and MXene in Ti–Al–C ternary system

The present paper set out to investigate the synthesis and electromagnetic characterization of Ti3AlC2 MAX phase and Ti3C2Tx MXene in Ti–Al–C ternary system. In this regard, Ti3AlC2 MAX phase was synthesized using mechanical milling process of TiC, Al, and Ti powder mixtures based on 2TiC–Al–Ti + xAl (x = 0, 0.25, 0.5, 0.75 and 1). The HF acidic etching was also employed to synthesize the Ti3C2Tx MXene. Structural and electromagnetic characterizations of the prepared samples were conducted using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vector network analyzer. The obtained results point to the impossibility of the formation of Ti3AlC2 single-phase structure in stoichiometric system. In other word, development of the Ti3AlC2 single-phase structure is only possible in non-stoichiometric 2TiC–2Al–Ti system. The minimum reflection losses of the prepared Ti3AlC2 MAX phase was estimated to be around −30.73 dB at the matching frequency of 15.25 GHz. The results further revealed that the etching time affects electromagnetic behavior of the MXene. That is, an increase in the etching time brings about a change in the reflection loss (RL) from −24.17 to −5.69 dB within the frequency range of 1–18 GHz.