Editorial

4 pages, 172 KiB

Open AccessEditorial

Microstructure and Mechanical Properties of Titanium Alloys

by Artur Shugurov

Metals 2021, 11(10), 1617; https://doi.org/10.3390/met11101617 - 12 Oct 2021

Cited by 7 | Viewed by 3164

Titanium and its alloys are widely used engineering materials within the aerospace, automotive, energy, and chemical industries [...] Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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12 pages, 1250 KiB

Open AccessFeature PaperArticle

Infrasonic Nanocrystal Formation in Amorphous NiTi Film: Physical Mechanism, Reasons and Conditions

by Evgeny E. Slyadnikov

Metals 2021, 11(9), 1390; https://doi.org/10.3390/met11091390 - 01 Sep 2021

Cited by 2 | Viewed by 1298

Abstract

The physical mechanism, reasons and conditions of nanocrystal formation in an amorphous NiTi metal film, stimulated by infrasonic action, are formulated. Nanostructural elements of an amorphous medium (relaxation centers) containing disordered nanoregions with two-level systems are considered to be responsible for this process. [...] Read more.

The physical mechanism, reasons and conditions of nanocrystal formation in an amorphous NiTi metal film, stimulated by infrasonic action, are formulated. Nanostructural elements of an amorphous medium (relaxation centers) containing disordered nanoregions with two-level systems are considered to be responsible for this process. When exposed to infrasound, a large number of two-level systems are excited, significantly contributing to inelastic deformation and the formation of nanocrystals. The physical mechanism of the nanocrystallization of metallic glass under mechanical action includes both local thermal fluctuations and the additional quantum tunneling of atoms stimulated by shear deformation. A crystalline nanocluster appears as a result of local atomic rearrangement growing increasingly exposed to infrasound. It is possibly unstable in the absence of infrasound. When the radius of the nanocluster reaches a critical value, a potential well appears, in which a conducting electron is localized to form a phason (stable nanocrystal). Estimated values of the phason’s radius and the depth of the nanometer potential well is about 0.5 nm and 1 eV, respectively. It forms a condition of stable phason formation. The occurrence of the instability of the amorphous state and following transformation to the nanostructured state is based on the accumulation of the potential energy of inelastic deformation to a critical value equal to the latent heat of the transformation of the amorphous state into the nanostructured state. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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10 pages, 3677 KiB

Open AccessArticle

Structure and Multistage Martensite Transformation in Nanocrystalline Ti-50.9Ni Alloy

by Tamara M. Poletika, Svetlana L. Girsova, Aleksander I. Lotkov, Andrej N. Kudryachov and Natalya V. Girsova

Metals 2021, 11(8), 1262; https://doi.org/10.3390/met11081262 - 10 Aug 2021

Cited by 6 | Viewed by 1568

Abstract

An electron microscopic study of the evolution of the size, morphology, and spatial distribution of coherent Ti₃Ni₄ particles with a change in the aging temperature in a nanocrystalline (NC) Ti-50.9 at % Ni alloy with an inhomogeneous grain–subgrain B2-austenitic nanostructure [...] Read more.

An electron microscopic study of the evolution of the size, morphology, and spatial distribution of coherent Ti₃Ni₄ particles with a change in the aging temperature in a nanocrystalline (NC) Ti-50.9 at % Ni alloy with an inhomogeneous grain–subgrain B2-austenitic nanostructure has been carried out. It was found that with an increase in the aging temperature, along with a change in the size and shape of Ti₃Ni₄ nanoparticles, their spatial distribution changes from location at dislocations to precipitates at subboundaries. Research has shown that the presence of different types of internal interfaces in the nanostructure contributes to the heterogeneous distribution of coherent Ti₃Ni₄ nanoparticles in the volume of the B2 matrix, which is associated with the precipitation of particles in the region of low-angle subboundaries and the suppression of the Ti₃Ni₄ precipitation in nanograins with high-angle boundaries. The difference in the structural-phase state of nanograins and subgrains regions is the main reason for the implementation of the anomalous R-phase transformation effect in the sequence of multistage martensitic transformations B2↔R↔B19′. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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14 pages, 4975 KiB

Open AccessArticle

Effect of abc Pressing at 573 K on the Microstructure and Martensite Transformation Temperatures in Ti_49.8Ni_50.2 (at%)

by Oleg Kashin, Aleksandr Ivanovich Lotkov, Victor Grishkov, Konstantin Krukovskii, Dorzhima Zhapova, Yuri Mironov, Natalia Girsova, Olga Kashina and Elena Barmina

Metals 2021, 11(7), 1145; https://doi.org/10.3390/met11071145 - 20 Jul 2021

Cited by 4 | Viewed by 1645

Abstract

This paper presents experimental data on the microstructure and martensite transformation temperatures of Ti_49.8Ni_50.2 (at%) after abc pressing (multi-axial forging) to different true strains e from 1.84 to 9.55 at 573 K. The data show that increasing the true strain [...] Read more.

This paper presents experimental data on the microstructure and martensite transformation temperatures of Ti_49.8Ni_50.2 (at%) after abc pressing (multi-axial forging) to different true strains e from 1.84 to 9.55 at 573 K. The data show that increasing the true strain results in grain–subgrain refinement on different scales at a time. With e = 9.55 at 573 K, the average grain–subgrain size measured approximately 130 nm. Decreasing the abc pressing temperature from 723 to 573 K caused a decrease in all martensite transformation temperatures, a change in the lattice parameters, R phase formation, and angular shifts of diffraction peaks and their broadening. The largest change in the microstructure of Ti_49.8Ni_50.2 was provided by abc pressing to e = 1.84. Increasing the true strain to e = 9.55 resulted in a much smaller effect, suggesting that the alloy obtained a high density of structural defects even at e = 1.84. Two possible mechanisms of grain–subgrain refinement are discussed. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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9 pages, 2975 KiB

Open AccessFeature PaperArticle

Behavior of Inelastic and Plastic Strains in Coarse-Grained Ti_49.3Ni_50.7(at%) Alloy Deformed in B2 States

by Dorzhima Zhapova, Victor Grishkov, Aleksandr Lotkov, Victor Timkin, Angelina Gusarenko and Ivan Rodionov

Metals 2021, 11(5), 741; https://doi.org/10.3390/met11050741 - 29 Apr 2021

Cited by 5 | Viewed by 1499

Abstract

The regularities of the change in inelastic strain in coarse-grained samples of the Ti_49.3Ni_50.7 (at%) alloy are studied when the samples are given torsional strain in the state of the high-temperature B2 phase. During cooling and heating, the investigated samples [...] Read more.

The regularities of the change in inelastic strain in coarse-grained samples of the Ti_49.3Ni_50.7 (at%) alloy are studied when the samples are given torsional strain in the state of the high-temperature B2 phase. During cooling and heating, the investigated samples underwent the B2–B19′ martensite transformation (MT); the temperature of the end of the reverse MT was A_f = 273 K. It was found that at the temperature of isothermal cycles “loading-unloading” A_f + 8 K, when the specimen is assigned a strain of 4%, the effect of superelasticity is observed. With an increase in the torsional strain, the shape memory effect is clearly manifested. It is assumed that the stabilization of the B19′ phase in unloaded samples is due to the appearance of dislocations during deformation due to high internal stresses at the interphase boundaries of the B2 phase and the martensite phase during MT. The appearance of dislocations during the loading of samples near the temperatures of forward and reverse MT can also be facilitated by the “softening” of the elastic moduli of the alloy in this temperature range. At a test temperature above A_f + 26 K, the superelasticity effect dominates in the studied samples. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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11 pages, 4262 KiB

Open AccessArticle

Microstructural Features and Surface Hardening of Ultrafine-Grained Ti-6Al-4V Alloy through Plasma Electrolytic Polishing and Nitrogen Ion Implantation

by Marina K. Smyslova, Roman R. Valiev, Anatoliy M. Smyslov, Iuliia M. Modina, Vil D. Sitdikov and Irina P. Semenova

Metals 2021, 11(5), 696; https://doi.org/10.3390/met11050696 - 23 Apr 2021

Cited by 4 | Viewed by 1636

Abstract

This work studies a near-surface layer microstructure in Ti-6Al-4V alloy samples subjected to plasma electrolytic polishing (PEP) and subsequent high-energy ion implantation with nitrogen (II). Samples with a conventional coarse-grained (CG) structure with an average α-phase size of 8 μm and an ultrafine-grained [...] Read more.

This work studies a near-surface layer microstructure in Ti-6Al-4V alloy samples subjected to plasma electrolytic polishing (PEP) and subsequent high-energy ion implantation with nitrogen (II). Samples with a conventional coarse-grained (CG) structure with an average α-phase size of 8 μm and an ultrafine-grained (UFG) structure (α-phase size up to 0.35 μm) produced by equal channel angular pressing were used in the studies. Features of phase composition and substructure in the thin surface layers are shown after sequential processing by PEP and II of both substrates with CG and UFG structures. Irrespective of a substrate structure, the so-called “long-range effect” was observed, which manifested itself in enhanced microhardness to a depth of surface layer up to 40 μm, exceeding the penetration distance of an implanted ion he. The effect of a UFG structure on depth and degree of surface hardening after PEP and ion-implantation is discussed. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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12 pages, 6462 KiB

Open AccessFeature PaperArticle

Transformations of the Microstructure and Phase Compositions of Titanium Alloys during Ultrasonic Impact Treatment. Part I. Commercially Pure Titanium

by Alexey Panin, Andrey Dmitriev, Anton Nikonov, Marina Kazachenok, Olga Perevalova and Elena Sklyarova

Metals 2021, 11(4), 562; https://doi.org/10.3390/met11040562 - 30 Mar 2021

Cited by 11 | Viewed by 1956

Abstract

Experimental and theoretical studies helped to reveal patterns of surface roughening and the microstructure refinement in the surface layer of commercial pure titanium during ultrasonic impact treatment. Applying transmission electron microscopy technique, a gradient microstructure in the surface layer of the ultrasonically treated [...] Read more.

Experimental and theoretical studies helped to reveal patterns of surface roughening and the microstructure refinement in the surface layer of commercial pure titanium during ultrasonic impact treatment. Applying transmission electron microscopy technique, a gradient microstructure in the surface layer of the ultrasonically treated sample, where the grain size is varied from nano- to micrometers was revealed. It was shown that the surface plastic strains of the titanium sample proceeded according to the plastic ploughing mechanism, which was accompanied by dislocation sliding, twinning, and the transformations of the microstructure and phase composition. The molecular dynamics method was applied to demonstrate the mechanism of the phase transformations associated with the formation of stacking faults, as well as the reversible displacement of atoms from their sites in the hcp lattice, causing a change in coordination numbers. The role of the electronic subsystem in the development of the strain-induced phase transformations during ultrasonic impact treatment was discussed. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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14 pages, 8784 KiB

Open AccessArticle

Investigation of the Dynamic Recovery and Recrystallization of Near-β Titanium Alloy Ti-55511 during Two-Pass Hot Compression

by Hande Wang, Jinyang Ge, Xiaoyong Zhang, Chao Chen and Kechao Zhou

Metals 2021, 11(2), 359; https://doi.org/10.3390/met11020359 - 20 Feb 2021

Cited by 6 | Viewed by 1929

Abstract

The two-pass thermal compression behavior of near-β Ti-55511 alloy was investigated. The first-pass restoration mechanisms changed from dynamic recrystallization (DRX) to dynamic recovery (DRV) as the first-pass deformation temperature increased from 700 °C to 850 °C. The occurrence of recrystallization reduced the dislocation [...] Read more.

The two-pass thermal compression behavior of near-β Ti-55511 alloy was investigated. The first-pass restoration mechanisms changed from dynamic recrystallization (DRX) to dynamic recovery (DRV) as the first-pass deformation temperature increased from 700 °C to 850 °C. The occurrence of recrystallization reduced the dislocation density, resulting in a slower grain growth rate in the subsequent process. Because of the static recrystallization (SRX) and β grain growth, the β grain size increased and the morphology became less uniform during the subsequent β holding process, which also changed the restoration mechanism during second-pass compression. The level of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) become weaker during second-pass deformation. The changes in the restoration mechanism and the microstructures slightly increased the peak stress during the second-pass deformation. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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11 pages, 3404 KiB

Open AccessArticle

Performance Analysis of Electrochemical Micro Machining of Titanium (Ti-6Al-4V) Alloy under Different Electrolytes Concentrations

by Geethapriyan Thangamani, Muthuramalingam Thangaraj, Khaja Moiduddin, Syed Hammad Mian, Hisham Alkhalefah and Usama Umer

Metals 2021, 11(2), 247; https://doi.org/10.3390/met11020247 - 02 Feb 2021

Cited by 25 | Viewed by 2814

Abstract

Titanium alloy is widely used in modern automobile industries due to its higher strength with corrosion resistance. Such higher strength materials can be effectively machined using unconventional machining processes, especially the electro-chemical micro machining (ECMM) process. It is important to enhance the machining [...] Read more.

Titanium alloy is widely used in modern automobile industries due to its higher strength with corrosion resistance. Such higher strength materials can be effectively machined using unconventional machining processes, especially the electro-chemical micro machining (ECMM) process. It is important to enhance the machining process by investigating the effects of electrolytes and process parameters in ECMM. The presented work describes the influence of three different combinations of Sodium Chloride-based electrolytes on machining Titanium (Ti-6Al-4V) alloy. Based on the ECMM process parameters such as applied voltage, electrolytic concentration, frequency and duty cycle on response, characteristics are determined by the Taguchi design of experiments. The highest material removal rate (MRR) was achieved by the Sodium Chloride and Sodium Nitrate electrolyte. The combination of Sodium Chloride and Citric Acid achieve highest Overcut and Circularity. The optimal overcut was observed from the Sodium Chloride and Glycerol electrolyte due to the presence of glycerol. The better conicity was obtained from Sodium Chloride and Citric Acid in comparison with other electrolytes. A Sodium Chloride and Glycerol combination could generate better machined surface owing to the chelating effect of Glycerol. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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10 pages, 1944 KiB

Open AccessArticle

Effect of Surface Modification of a Titanium Alloy by Copper Ions on the Structure and Properties of the Substrate-Coating Composition

by Marina Fedorischeva, Mark Kalashnikov, Irina Bozhko, Olga Perevalova and Victor Sergeev

Metals 2020, 10(12), 1591; https://doi.org/10.3390/met10121591 - 27 Nov 2020

Cited by 2 | Viewed by 1734

Abstract

To improve the strength properties, adhesion, and the thermal cycling resistance of ceramic coatings, the titanium alloy surface was modified with copper ions under different processing times. It is found that at the maximum processing time, the thickness of the alloyed layer reaches [...] Read more.

To improve the strength properties, adhesion, and the thermal cycling resistance of ceramic coatings, the titanium alloy surface was modified with copper ions under different processing times. It is found that at the maximum processing time, the thickness of the alloyed layer reaches 12 μm. It is shown that the modified layer has a multiphase structure in addition to the main α and β–titanium phases with the intermetallic compounds of the Ti-Cu system. The parameters of the fine structure of the material are investigated by the X-ray diffraction analysis. It has been found that when the surface of the titanium alloy is modified, depletion occurs in the main alloying elements, such as aluminum and vanadium, the crystal lattice parameter increases, the root-mean-square (rms) displacements of the atoms decrease, and the macrostresses of compression arise. A multilevel micro- and nanoporous nanocrystalline structure occurs, which leads to an increase in the adhesion and the thermal cyclic resistance of the ceramic coating based on Si-Al-N. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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12 pages, 8729 KiB

Open AccessArticle

Effect of Radial Forging on the Microstructure and Mechanical Properties of Ti-Based Alloys

by Lev B. Zuev, Galina V. Shlyakhova and Svetlana A. Barannikova

Metals 2020, 10(11), 1488; https://doi.org/10.3390/met10111488 - 08 Nov 2020

Cited by 2 | Viewed by 2097

Abstract

Radial forging is a reliable way to produce Ti alloy rods without preliminary mechanical processing of their surface, which is in turn a mandatory procedure during almost each stage of the existing technology. In the present research, hot pressing and radial forging (RF) [...] Read more.

Radial forging is a reliable way to produce Ti alloy rods without preliminary mechanical processing of their surface, which is in turn a mandatory procedure during almost each stage of the existing technology. In the present research, hot pressing and radial forging (RF) of the titanium-based Ti-3.3Al-5Mo-5V alloy were carried out to study the specifics of plasticized metal flow and microstructural evolution in different sections of the rods. The structural analysis of these rods was performed using metallography and X-ray diffraction techniques. The X-ray diffraction reveals the two-phase state of the alloy. The phase content in the alloy was shown to vary upon radial forging. Finally, radial forging was found to be a reliable method to achieve the uniform fine-grained structure and high quality of the rod surface. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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10 pages, 3471 KiB

Open AccessArticle

Cyclic Stress Response Behavior of Near β Titanium Alloy and Deformation Mechanism Associated with Precipitated Phase

by Siqian Zhang, Haoyu Zhang, Junhong Hao, Jing Liu, Jie Sun and Lijia Chen

Metals 2020, 10(11), 1482; https://doi.org/10.3390/met10111482 - 06 Nov 2020

Cited by 2 | Viewed by 1506

Abstract

The cyclic stress response behavior of Ti-3Al-8V-6Cr-4Mo-4Zr alloy with three different microstructures has been systematically studied. The cyclic stress response was highly related to the applied strain amplitude and precipitated phase. At low strain amplitude, the plastic deformation was mainly restricted to soft [...] Read more.

The cyclic stress response behavior of Ti-3Al-8V-6Cr-4Mo-4Zr alloy with three different microstructures has been systematically studied. The cyclic stress response was highly related to the applied strain amplitude and precipitated phase. At low strain amplitude, the plastic deformation was mainly restricted to soft α phase, and a significant cyclic saturation stage was shown until fracture for all three alloys. At high strain amplitude, three alloys all displayed an initial striking cyclic softening. However, the softening mechanism was obviously difference. Interestingly, a significant cyclic saturation stage was noticed after an initial cyclic softening for alloy aging for 12 h, which could be attributed to the deformation of {332}<113> twin and precipitation of α″ martensite. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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14 pages, 6438 KiB

Open AccessArticle

Recovery of Scratch Grooves in Ti-6Al-4V Alloy Caused by Reversible Phase Transformations

by Artur R. Shugurov, Alexey V. Panin, Andrey I. Dmitriev and Anton Yu. Nikonov

Metals 2020, 10(10), 1332; https://doi.org/10.3390/met10101332 - 05 Oct 2020

Cited by 8 | Viewed by 2701

Abstract

The deformation behaviors of Ti-6Al-4V alloy samples with lamellar and bimodal microstructures under scratch testing were studied experimentally and using molecular dynamics simulation. It was found that the scratch depth in the sample with a bimodal microstructure was twice as shallow as that [...] Read more.

The deformation behaviors of Ti-6Al-4V alloy samples with lamellar and bimodal microstructures under scratch testing were studied experimentally and using molecular dynamics simulation. It was found that the scratch depth in the sample with a bimodal microstructure was twice as shallow as that measured in the sample with a lamellar microstructure. This effect is attributed to the higher hardness of the sample with a bimodal microstructure and the larger amount of elastic recovery of scratch grooves in this sample. On the basis of the results of molecular dynamics simulation, a mechanism was proposed, which associates the recovery of the scratch grooves with the inhomogeneous vanadium distribution in the β-areas. The calculations showed that at a vanadium content typical for Ti-6Al-4V alloy, both the body-centered cubic (BCC) and hexagonal close-packed (HCP) structures can be more energetically favorable depending on the atomic volume. Therefore, compressive or tensile stresses induced by the indenter could facilitate β

\to

α and α

\to

β phase transformations, respectively, in the vanadium-depleted domains of the β-areas, which contribute to the recovery of the Ti-6Al-4V alloy subjected to scratching. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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13 pages, 3166 KiB

Open AccessArticle

Effect of True Strains in Isothermal abc Pressing on Mechanical Properties of Ti_49.8Ni_50.2 Alloy

by Oleg Kashin, Konstantin Krukovskii, Aleksandr Lotkov and Victor Grishkov

Metals 2020, 10(10), 1313; https://doi.org/10.3390/met10101313 - 30 Sep 2020

Cited by 9 | Viewed by 1522

Abstract

The paper analyzes the microstructure and mechanical properties of Ti_49.8Ni_50.2 alloy (at.%) under uniaxial tension at room temperature after isothermal abc pressing to true strains e = 0.29 − 8.44 at T = 723 K. The analysis shows that as [...] Read more.

The paper analyzes the microstructure and mechanical properties of Ti_49.8Ni_50.2 alloy (at.%) under uniaxial tension at room temperature after isothermal abc pressing to true strains e = 0.29 − 8.44 at T = 723 K. The analysis shows that as the true strain e is increased, the grain–subgrain structure of the alloy is gradually refined. This leads to an increase in its yield stress σ_y and strain hardening coefficient θ = dσ/dε at linear stage III of its tensile stress–strain curve according to the Hall–Petch relation. However, the ultimate tensile strength remains invariant to such refinement. The possible mechanism is proposed to explain why the ultimate tensile strength can remain invariant to the average grains size (d_av). It is assumed that the sharp increase of the ultimate tensile strength σ_UTS begins when (d_av) is less than the critical average grain size (d_av)_cr. In our opinion, for the investigated alloy (d_av)_cr ≈ 0.5 µm. In our study, the attained average grain size is larger the critical one. The main idea of the mechanism is next. In alloys with an average grain size (d_av) less than the critical one, a higher external stress is required for the nucleation and propagation of the main crack. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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14 pages, 4899 KiB

Open AccessArticle

First Principles Study of Bonding Mechanisms at the TiAl/TiO₂ Interface

by Alexander V. Bakulin, Sergey S. Kulkov, Svetlana E. Kulkova, Stephen Hocker and Siegfried Schmauder

Metals 2020, 10(10), 1298; https://doi.org/10.3390/met10101298 - 29 Sep 2020

Cited by 11 | Viewed by 2123

Abstract

The adhesion properties of the TiAl/TiO₂ interface are estimated in dependence on interfacial layer composition and contact configuration using the projector augmented wave method. It is shown that a higher value of the work of separation is obtained at the interface between [...] Read more.

The adhesion properties of the TiAl/TiO₂ interface are estimated in dependence on interfacial layer composition and contact configuration using the projector augmented wave method. It is shown that a higher value of the work of separation is obtained at the interface between the Ti-terminated TiAl(110) surface and the TiO₂(110)_O one than at that with the Al-terminated alloy. An analysis of structural and electronic factors dominating the chemical bonding at the interfaces is carried out. It is shown that low bond densities are responsible for low adhesion at both considered interfaces, which may affect the spallation of oxide scale from the TiAl matrix. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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12 pages, 15107 KiB

Open AccessArticle

Structural Defects in TiNi-Based Alloys after Warm ECAP

by Aleksandr Lotkov, Anatoly Baturin, Vladimir Kopylov, Victor Grishkov and Roman Laptev

Metals 2020, 10(9), 1154; https://doi.org/10.3390/met10091154 - 25 Aug 2020

Cited by 3 | Viewed by 2064

Abstract

The microstructure, martensitic transformations and crystal structure defects in the Ti₅₀Ni_47.3Fe_2.7 (at%) alloy after equal-channel angular pressing (ECAP, angle 90°, route B_C, 1–3 passes at T = 723 K) have been investigated. A homogeneous submicrocrystalline (SMC) [...] Read more.

The microstructure, martensitic transformations and crystal structure defects in the Ti₅₀Ni_47.3Fe_2.7 (at%) alloy after equal-channel angular pressing (ECAP, angle 90°, route B_C, 1–3 passes at T = 723 K) have been investigated. A homogeneous submicrocrystalline (SMC) structure (grains/subgrains about 300 nm) is observed after 3 ECAP passes. Crystal structure defects in the Ti_49.4Ni_50.6 (at%) alloy (8 ECAP passes, angle 120°, B_C route, T = 723 K, grains/subgrains about 300 nm) and Ti₅₀Ni_47.3Fe_2.7 (at%) alloy with SMC B2 structures after ECAP were studied by positron lifetime spectroscopy at the room temperature. The single component with the positron lifetime τ₁ = 132 ps and τ₁ = 140 ps were observed for positron lifetime spectra (PLS) obtained from ternary and binary, correspondingly, annealed alloys with coarse-grained structures. This τ₁ values correspond to the lifetime of delocalized positrons in defect-free B2 phase. The two component PLS were found for all samples exposed by ECAP. The component with τ₂ = 160 ps (annihilation of positrons trapped by dislocations) is observed for all samples after 1–8 ECAP passes. The component with τ₃ = 305 ps (annihilation of positrons trapped by vacancy nanoclusters) was detected only after the first ECAP pass. The component with τ₃ = 200 ps (annihilation of positrons trapped by vacancies in the Ti sublattice of B2 structure) is observed for all samples after 3–8 ECAP passes. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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11 pages, 5590 KiB

Open AccessArticle

Improvement of the Crack Propagation Resistance in an α + β Titanium Alloy with a Trimodal Microstructure

by Changsheng Tan, Yiduo Fan, Qiaoyan Sun and Guojun Zhang

Metals 2020, 10(8), 1058; https://doi.org/10.3390/met10081058 - 06 Aug 2020

Cited by 14 | Viewed by 3900

Abstract

The roles of microstructure in plastic deformation and crack growth mechanisms of a titanium alloy with a trimodal microstructure have been systematically investigated. The results show that thick intragranular α lath and a small number of equiaxed α phases avoid the nucleation of [...] Read more.

The roles of microstructure in plastic deformation and crack growth mechanisms of a titanium alloy with a trimodal microstructure have been systematically investigated. The results show that thick intragranular α lath and a small number of equiaxed α phases avoid the nucleation of cracks at the grain boundary, resulting in branching and fluctuation of cracks. Based on electron back-scattered diffraction, the strain partition and plastic deformation ahead of the crack tip were observed and analyzed in detail. Due to the toughening effect of the softer equiaxed α phase at the grain boundary, crack arresting and blunting are prevalent, improving the crack growth resistance and generating a relatively superior fracture toughness performance. These results indicate that a small amount of large globular α phases is beneficial to increase the crack propagation resistance and, thus, a good combination of mechanical property is obtained in the trimodal microstructure. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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15 pages, 13767 KiB

Open AccessArticle

Correlation between Microstructure and Mechanical Properties of Heat-Treated Ti–6Al–4V with Fe Alloying

by Yongwei Liu, Fuwen Chen, Guanglong Xu, Yuwen Cui and Hui Chang

Metals 2020, 10(7), 854; https://doi.org/10.3390/met10070854 - 28 Jun 2020

Cited by 13 | Viewed by 3142

Abstract

The microstructure and mechanical properties of a newly developed Fe-microalloyed Ti–6Al–4V titanium alloy were investigated after different heat treatments. The volume fraction and the morphological features of the lamellar α phase had significant effects on the alloy’s mechanical performance. A dataset showing the [...] Read more.

The microstructure and mechanical properties of a newly developed Fe-microalloyed Ti–6Al–4V titanium alloy were investigated after different heat treatments. The volume fraction and the morphological features of the lamellar α phase had significant effects on the alloy’s mechanical performance. A dataset showing the relationship between microstructural features and tensile strength, elongation, and fracture toughness was developed. A high aging temperature resulted in high plasticity and fracture toughness, but relatively low strength. The high strength favored the fine α and the slender β. The high aspect ratio of lamellar α led to high strength but low fracture toughness. The alloy with ~84 vol % α exhibited the highest strength and lowest fracture toughness because the area of its α/β-phase interface was the highest. Optimal comprehensive mechanical performance and heat-treatment procedures were thus obtained from the dataset. Optimal tensile strength, yield strength, elongation, and fracture toughness were 999 and 919 MPa, 10.4%, and 94.4 MPa·m^1/2, respectively. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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