Evolution Of Ti Research Articles

Enhanced kinetics of microstructural evolution in Ti–6Al–4V through electropulsing treatment

The post-processing of Ti–6Al–4V, which has traditionally been conducted using furnace heat treatment (FHT), is crucial to attaining the optimum microstructure and mechanical performance. This study investigated the microstructural kinetics induced by the electropulsing treatment (EPT) of an extruded Ti–6Al–4V alloy from 50 to 400 s. The results were compared with the conventional microstructural evolution caused by FHT at the same temperature and duration. The remarkable energy efficiency enabled a rapid heating of EPT specimens. EPT enhances the kinetics of several aspects of microstructural evolution, such as phase transformation, static recrystallization, dislocation mobility, and the resultant suppression of grain growth. These phenomena arose from the promoted atomic diffusion due to the combination of the thermal and athermal effects of the electropulses. Grain refinement, amplified solid-solution hardening, and increased phase interfaces improved the microhardness of the EPT specimens. These results demonstrate the potential of EPT to facilitate favorable microstructural modifications in Ti–6Al–4V.

Quantitative Investigation on the Evolution of Ti(Cx, N1−x) in Ultra-high-Strength Steel Slab During TSCR Process: Precipitation and Redissolution

Quantitative Investigation on the Evolution of Ti(Cx, N1−x) in Ultra-high-Strength Steel Slab During TSCR Process: Precipitation and Redissolution

Structural and Oxidation Behavior of Nanocomposite TiCrN Thin Films

The structural and oxidation behavior of nanocomposite titanium chromium nitride (TiCrN) thin films has been investigated by using x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDS), and field emission scanning electron microscopy (FE-SEM). The TiCrN thin films were deposited on Si substrates by using the reactive DC magnetron sputtering technique from the Ti-Cr mosaic target. After that, the as-deposited thin films were annealed in the air at 500 - 900°C for 2 h. The XRD results showed that the formation oxidation of anataseTiO2, rutile-TiO2, and Cr2O3 which diffraction peak appear from 500°C. The relative intensity of these oxide peaks varied with the annealed temperatures. By observing from FE-SEM, the aggregation of the grain increased with the annealing temperature. The cross-sectional results showed that the thin dense oxide overlayer occurred at 700°C and the oxide thickness increased gradually with the annealing temperature. Meanwhile, underneath the TiCrN grain grew above 700°C and become more void structure after annealing at 700°C. The dramatically increase of the oxygen content was found at 700°C and the evolution of Ti, Cr, N, and O with different elements compositions at various annealing temperatures were investigated from the EDS technique. The oxide layer obviously grows inward indicating the oxidation of TiCrN thin films belongs to inward oxidation. The oxidation rate of the films was increased with the increase of annealing temperature. The activation energy of the oxidation as evaluated by the Arrhenius-type relation was 168 kJ/mol.

In situ melt pool measurements for laser powder bed fusion using multi sensing and correlation analysis

Laser powder bed fusion is a promising technology for local deposition and microstructure control, but it suffers from defects such as delamination and porosity due to the lack of understanding of melt pool dynamics. To study the fundamental behavior of the melt pool, both geometric and thermal sensing with high spatial and temporal resolutions are necessary. This work applies and integrates three advanced sensing technologies: synchrotron X-ray imaging, high-speed IR camera, and high-spatial-resolution IR camera to characterize the evolution of the melt pool shape, keyhole, vapor plume, and thermal evolution in Ti–6Al–4V and 410 stainless steel spot melt cases. Aside from presenting the sensing capability, this paper develops an effective algorithm for high-speed X-ray imaging data to identify melt pool geometries accurately. Preprocessing methods are also implemented for the IR data to estimate the emissivity value and extrapolate the saturated pixels. Quantifications on boundary velocities, melt pool dimensions, thermal gradients, and cooling rates are performed, enabling future comprehensive melt pool dynamics and microstructure analysis. The study discovers a strong correlation between the thermal and X-ray data, demonstrating the feasibility of using relatively cheap IR cameras to predict features that currently can only be captured using costly synchrotron X-ray imaging. Such correlation can be used for future thermal-based melt pool control and model validation.

Grain reorientation and stress-state evolution during cyclic loading of an [formula omitted]-Ti alloy below the elastic limit

High-energy synchrotron x-rays are used to track grain-averaged lattice reorientation and stress-state evolution in Ti–7Al as it is cyclically loaded to 90% of its macroscopic yield stress. This evolution provides clear indication of accumulating plastic strain even though the sample never exceeded the elastic limit. The largest changes in lattice orientation and stress state are observed following the first cycle then evolution continues at a lower rate with subsequent cycles. Variation of the axes about which lattice reorientation occurs is found to be highly dependent on the maximum resolved shear stress and corresponding activation of various families of slip systems.

Incipient dynamic recrystallization and adiabatic shear bands in Ti–7Al studied via in situ X-ray diffraction

The interconnected phenomena of dynamic recrystallization (DRX) and adiabatic shear bands (ASBs) are critical features of dynamic deformation and fracture in metals. Despite their importance, observations of these phenomena have largely been restricted to post-mortem analyses. Here we report on the first in situ X-ray diffraction (XRD) observations of DRX. By combining high strain rate loading via Kolsky bar with high speed X-ray diffraction, time resolved observations of microstructural evolution in Ti–7Al are made. XRD measurements are coupled with explicit finite element simulations to assess the stress, strain, and temperature dependence of the microstructural evolution. These observations reveal a continuous evolution of the microstructure with increasing plastic strain up to a maximum stress. At the maximum stress, the structure ceases evolving and the subsequent softening suggests the onset of shear banding. As a whole, these unique experiments definitively reveal the onset of DRX to be driven by accumulation of plastic strain and not the temperature rise associated with plastic deformation. The observed sequence of events further suggests DRX results in microstructural softening and precedes ASB formation.

Hot deformation characteristics and microstructure evolution of Ti–5Al–3Mo–1.5V alloy

A detailed investigation was conducted to study the concurrent effect of temperature and strain rate on the microstructure evolution in Ti–5Al–3Mo–1.5V dual-phase Titanium alloy. By applying varying strain rates from $$10^{-3} $$ to 10 $$\hbox {s}^{-1}$$ between 1098 and 1298 K at an interval of 50 K, isothermal compression characteristics and microstructural changes were recorded. The sizes of globules, concentrated predominantly at the lamellar kinks, were found to be inversely proportional to the strain rate. Further, a dynamic material model was employed to assess and plot the processing map displaying the safe hot working regime. The apparent hot-working activation energy in the $$\alpha +\beta $$ and $$\beta $$ phase field was 636 kJ/mol and 379 kJ/mol, respectively. A higher activation energy than the self-diffusion threshold of the $$\alpha +\beta $$ and $$\beta $$ field was attributed to lamellae breakup and dynamic recrystallization in the respective phase fields. The microstructure analysis and identified softening mechanisms further helped in concluding the safe hot working regime to be 1248 K and 10 $$^{-3}$$ $$\hbox {s}^{-1}$$ .

Microstructural evolution in Ti–10Al–1Zr–1Mo–1Nb alloy under thermomechanical treatment in β-region

The influence of temperature and strain rate on microstructural evolution in near α-type Ti–10Al–1Zr–1Mo–1Nb alloy was studied under uniaxial compression in the β single-phase-region. Hot compression tests were conducted for up to 75% reduction at temperatures between 1273 K and 1333 K and strain rates between 0.01 s−1 and 5 s−1. The steady-state of the flow behavior revealed that dynamic recovery in the β single-phase was dominant in the microstructural evolution process, and few dynamically recrystallized grains were detected, except in the vicinity of the pre-existing β grain boundaries. Two types of configurations such as lamellar αL and acicular αAC microstructures were developed, which were consistent with the compressive deformation mechanism in the β-region. The αL microstructure consisted of α platelets that were developed via growth of a specific variant, whereas the αAC microstructure consisted of individual α platelets with a different variant in the prior-β matrix. The stress exponent and activation energy were evaluated to determine the deformation mechanism. The heterogeneous nucleation of individual α platelets in the cellular structure (sub-grains) without a specific orientation in the β matrix resulted in the αAC microstructure. In contrast, the substructure as uniformly distributed dislocations in prior-β grains under the viscous motion of dislocations promoted a single variant selection to form αL platelets in the transformation. When the viscous drag dislocation motion in the β-region is dominant, a large crystal rotation is detected in the acicular (side plate) αSP platelets in the vicinity of the prior-β grain boundary.

Influence of Controlled Cooling Rates During Thermal Processing of Ti 6% Al 4% V Alloys Using In-Situ Scanning Electron Microscopy

ABSTRACTWe describe experimental approaches to real time examination of the microstructural evolution of Ti 6%Al 4%V upon cooling from above the beta transus (~995 °C) while imaging in the scanning electron microscope. Ti 6%Al 4%V is a two phase, α+β titanium alloy with high strength and corrosion resistance. The β →α transformation on cooling can give rise to different microstructures and properties through various thermal treatments. Fully lamellar microstructures, bi-modal microstructures, and equiaxed microstructures can each be obtained by accessing different cooling rates upon the final treatment above the beta temperature, each resulting in uniquely enhanced material properties.Utilizing the capabilities of a heating/ tensile stage developed by Kammrath & Weiss Inc., are able to apply real-time imaging techniques in the scanning electron microscope to monitor the development of the microstructure. Annealing temperatures up to 1100 °C are attainable, with cooling rates ranging from 0.1 ° C per second to 3.3 °C per second. This has allowed us to directly observe the formation of lamellae at different annealing temperature/ cooling rate combinations to determine the lamellar microstructure width, separation, and colony size.

Microstructural evolution in the surface of Ti–10V–2Fe–3Al alloy by solution treatments

By solution treatments in vacuum and in air, the surface region of Ti–10V–2Fe–3Al exhibits different microstructures from the interior region of the alloy. When solution treated in vacuum, the microstructure of the specimen is composed of dominant β phase and a few of α″ martensite in surface region, with a large amount of α″ martensite and a little of β phase in interior. When solution treated in air, the specimen is characterized by dominant surficial α phase and interior β phase. In addition, the lattice parameter evolutions of α and β phases were observed in the surface region of the specimens by solution treatment in air. The mechanism for the surface effects is discussed in light of the structural stability and phase evolution in Ti–10V–2Fe–3Al alloy with solution treatments.

Constitutive behavior and microstructural evolution in Ti–Al–Si ternary alloys processed by mechanical milling and spark plasma sintering

Severe plastic deformation is closely related to the microstructural behaviors of intermetallics or grain refinement by mechanical milling and subsequent rapid sintering process, i.e. high energy ball milling and spark plasma sintering. In this study, the Ti–Al–Si ternary powders were synthesized to investigate their phase transformation by plastic deformation during the mechanical milling in each process time and composition. The sintered-bodies Ti–Al–Si ternary alloys were fabricated by spark plasma sintering among the rapidly consolidated powders, except for the distribution of single phases in accordance with the Al-melting. The microstructures of intermetallics in Ti–Al–Si ternary alloys were composed of titanium aluminides and titanium silicides, and even ternary compounds as a τ1-phase. In particular, the twining or stacking faults induced by severe plastic deformation were revealed through crystallographic patterns and microstructural evidence. These defects were caused by the slip system for TiAl3 (fcc) or Ti5Si3 (hcp) phases, depending on the grain refinement and generation of ambient intermetallics. To estimate the possibility of these defects, various approaches were taken to obtain experimental measurement of the twin probability and stacking fault energy derived from TEM and XRD analyses.

Phase transformation and evolution of dislocation structure in the β phase of Ti-17 alloy during hot deformation

The hot deformation behavior and microstructural evolution of Ti–5Al–2Sn–2Zr–4Mo–4Cr (Ti-17) alloy in the β-phase field were examined. Hot compression tests were conducted at temperatures ranging from 700 and 1100 °C and strain rates ranging from 10-3 to 1 s-1. The obtained true stress–true strain curves exhibited steady-state flow behavior at temperatures above the β-transus temperature (Tβ ~ 890 °C). The microstructural observations suggested that the dynamic recovery process represents a dominant mechanism for the β-phase of the alloy. In contrast, the flow softening was identified at 700 °C at a strain rate of 10–3 s–1. The formation of fine acicular α microstructures was noticed in such a deformation condition, indicating that dynamic phase transformation can occur in the metastable β-phase during hot deformation. Such a dynamic phase transformation also occurred preferentially at the initial β-grain boundaries as well as sub-boundaries that created within the βmatrix via dynamic recovery. The β-processing conditions were also examined by constructing processing maps based on the dynamic materials model (DMM).

Effect of alloying additions on work hardening, dynamic recrystallization, and mechanical properties of Ti–44Al–5Nb–1Mo alloys during direct hot-pack rolling

There is significant gap in the understanding of the effect of alloying elements, particularly V and B, on the dynamic recrystallization (DRX) behavior, and the corresponding microstructure evolution in Ti–44Al–5Nb–1Mo-(V, B) alloys during uniaxial hot compression. In this regard, we have studied here the relationship of work hardening rate (θ) and critical strain of dynamic recrystallization (εc) on strain, deformation parameters. The θ values showed typical dynamic recrystallization characteristics, and were sensitive to temperature and strain rate. Deformation mechanism involving twinning-dislocation interactions and phase transformation contributed to characteristics of θ. DRX occurred in Ti–44Al–5Nb–1Mo–2V-0.2B alloys even at higher rolling speed and at ambient temperatures over a wide range, which implied a wider processing window during the direct hot-pack rolling process. Crack-free sheets were directly obtained from the as-HIPed alloys at 1250 oC with rolling speeds of 0.3 m/s, and 10%–20% reduction per pass. Their microstructure, high-temperature tensile properties and fracture mechanisms are discussed. As rolling progressed, Ti–44Al–5Nb–1Mo alloy was characterized by residual lamellae with locally dissolved α2 laths, broadening γ laths, and fine sub-grains. Dislocation-induced DRX and phase transformation of α2/γ lamellae were the primary deformation modes. In contrast, on the addition of V and B, deformation twinning was activated. Multi-phase microstructure was characterized by equiaxed grains of ~ 5–20 μm. The as-rolled sheets of both the alloys exhibited superior performance at 800 oC. Ti–44Al–5Nb–1Mo alloy showed a higher ultimate tensile stress of ~689 MPa, while superior ductility of greater than 75% was obtained for Ti–44Al–5Nb–1Mo–2V-0.2B alloy. The microstructure with different degree of dynamic recrystallization contributed to various aspects of high-temperature tensile properties.

Multi-Length Scale Characterization of Microstructure Evolution and Its Consequence on Mechanical Properties in Dissimilar Friction Stir Welding of Titanium to Aluminum

In dissimilar friction stir welding (FSW), the weld nugget is composed of two elements, which are mechanically mixed. This microstructure helps enhance the mechanical properties when they are homogeneously mixed, and the particles are sub-micron in size. Therefore, it is important to understand the mechanism of the particle formation and their distribution for engineering the mechanical properties of the weld. In the present investigation, dissimilar FSW between commercial purity Al and Ti has been carried out. The weld nugget consisted of distributed Ti particles in an Al matrix. The distribution of the Ti particles in the weld nugget was characterized using X-ray micro-computed tomography (XCT). Microstructural evolution in Ti and Al was examined using a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS), X-ray diffraction and electron back-scattered diffraction (EBSD). Hardness and tensile tests were carried out to determine the integrity of the welds. The XCT result shows that the weld nugget contains Ti particles of variable size. The finer particles of Ti are distributed homogeneously in the weld nugget, unlike large particles. The deformation mechanisms and microstructural evolution of the Ti interface and Al matrix are investigated using EBSD. It is observed that the microstructure of both Ti and Al is substantially refined. However, for a given grain in Al, the boundary is of mixed character, namely low- and high-angle boundaries. Hardness data of the weld indicate large variation within the nugget region. The tensile test sample revealed that the failure of the sample occurs on the Al side of the weld. The fractograph indicates ductile and brittle modes of fracture with a bimodal distribution of dimples at the surface. Lack of twining and fine grains (40 to 5 µm) at the Ti interface indicates high-temperature deformation. Deformation of Ti at low temperature and high strain rate is caused by adiabatic shear banding (ASB). In these shear bands, a high level of grain refinement is observed and is a path for easy crack propagation. It is proposed that the ASB-controlled deformation of Ti leads to a recrystallized microstructure at the interface and fragmentation of Ti. These Ti particles undergo further fragmentation to form smaller particles. On the other hand, microstructural evolution in Al is gradual because of the high stacking fault energy, which leads to continuous dynamic recrystallization (CDRX) through the dynamic recovery (DRV) mechanism. The mechanical properties of the weld depend on the characteristics of particles in the Al matrix. Proper control of the fragmentation and distribution of Ti particles and interface property can lead to superior mechanical properties of the weld.

Goss Orientation Evolution in Ti–5.5Mo–8Al–6Zr Shape Memory Alloy upon Heat Treatment

Goss Orientation Evolution in Ti–5.5Mo–8Al–6Zr Shape Memory Alloy upon Heat Treatment

Synthesis, microstructural and phase evolution in Ti–2Ni and Ti–10Ni binary alloys consolidated by spark plasma sintering technique

The availability of lower-cost titanium with unique properties required for engineering applications such as in automobile, aerospace and biomedical has created a renewed interest in titanium and its alloys. However, poor sinterability due to high affinity of titanium for oxygen results in the production of less dense sintered product. While this may be of benefits in biomedical applications, it is deleterious to engineering applications such as in aviation parts that require high fatigue performance. In order to overcome this challenge, this study synthesized and consolidated Ti–2Ni and Ti–10Ni binary alloys using spark plasma sintering technique. Ti (Gd 1) and Ni elemental powders were mixed together in a TF2 Turbula mixer, at the speed of 101 rpm for 8 h. Sintering was conducted at 850, 1100 and 1200 °C under vacuum using the spark plasma sintering system. The applied pressure, heating rate and holding time were maintained at 50 MPa, 100 °C/min and 10 min respectively. Sample characterization was carried out with the aid of X-ray diffractometer and scanning electron microscope, equipped with energy-dispersive X-ray spectroscopy. The density and hardness of the sintered alloys were obtained using the Archimedes technique and Vickers microhardness tester respectively. The results showed that the relative density and hardness increased with increasing sintering temperature for the sintered Ti–2Ni and Ti–10Ni alloys. Generally, it was observed that increasing the sintering temperature and nickel addition improved the sinterability and densification of the sintered alloy.

Microstructure evolution of Ti–30Nb–(4Sn) alloys during classical and step-quench aging heat treatments

Recent studies involving step-quench (SQ) heat treatments have shown that, unlike classical quench-and-aging (QA) heat treatments, SQ route can favour precipitation mechanisms that are strongly dependent on decomposition of the parent β-phase. In this work, Ti–30Nb and Ti–30Nb–4Sn (wt-%) alloys were subjected to cold-working, recrystallisation and then to either classical or SQ heat treatments at 400°C. Among QA samples, ω-phase is formed in both alloys during the heating ramp. By the SQ route, we found extensive isothermal ω-phase precipitation in Ti–30Nb during aging. On the other hand, a complete suppression of ω-phase in Ti–30Nb–4Sn was observed, thus, α-phase precipitation could take place improving hardness while still preserving a low elastic modulus.

Microstructure evolution and interfacial reaction of TiAl–Si alloy solidified in alumina crucible

The microstructure evolution of Ti–43Al–3Si (at-%) alloy solidified in alumina crucible was investigated by directional solidification technology. After directional solidification, the microstructure of the alloy is consisted of γ-TiAl, α2-Ti3Al, ξ-Ti5Si3 phases and Al2O3 particles. There are three morphologies of ξ phases formed in the alloy, namely, long rod-like, cluster-like with eutectic morphology, and needle-like shape. The volume fraction of ξ phases decreases with increasing growth rates. Al2O3 particles broke from the crucible and enter into the melt by the thermal physical erosion. Al2O3 particles enrich in the liquid phase with the moving of solid-liquid interface, and are captured or entrapped by dendrites during solidification. The Al2O3 particles mainly distributed in the interdendritic region, and some particles exist in dendrites.

Effects of laser shock peening on microstructure and residual stress evolution in Ti–45Al–2Cr–2Nb–0.2B alloy

Laser peening is a novel surface treatment technique for improving the mechanical properties of metal parts' surface. To investigate and evaluate the effect of laser peening on the microstructural changes, texture evolution, and residual stress distribution changes, laser peening experiment was undertaken using Nd:YAG laser system with the pulse–width of 20ns and max pulse–energy of 9J. Micro-hardness measurements of the untreated and treated specimens were carried out with Vickers indenter. Depth-resolved characterization of the residual stresses and strains was achieved using X-ray diffraction. The structure–texture–phase–stress combined analysis was performed based on the X-ray diffraction patterns using the whole pattern fitting method. The relationship between laser peening processing parameters, microstructure, texture, residual stress distribution and hardness are presented and discussed. The results showed that laser peening could improve microstructures and properties of TiAl alloy.

Precipitation processes in the Beta-Titanium alloy Ti–5Al–5Mo–5V–3Cr

Precipitate evolution in Ti–5Al–5Mo–5V–3Cr–0.3Fe wt.% (Ti-5553) has been studied in-situ by small angle neutron scattering (SANS) during a two step ageing heat treatment of 300°C/8h+500°C/2 h. The first heat treatment step precipitates ω, with a corresponding increase in hardness of ∼15% compared to quenched material. The second heat treatment step precipitates fine scale α from the ω phase, with a ∼90% increase in hardness compared to quenched material.The SANS measurements are complemented by atom probe tomography (APT) to give compositional information, ex-situ transmission electron microscopy (TEM) to confirm phase identification and size distribution locally, and X-ray diffraction (XRD) for additional confirmation of phase identification.The ω phase is depleted in all the solute additions following 300°C/8 h ageing heat treatment. The volume fraction of the ω phase from APT is estimated to be ∼7%. SANS modelling is consistent with disc shaped particles for the ω phase. The mean particle diameter increases from ∼7.5 nm to 9.5 nm diameter between 1 h and 8 h heat treatment at 300 °C, while the thickness increases from ∼4 nm to ∼5 nm. The SANS model estimates the volume fraction to be ∼10% for the 8 h heat treatment, using the phase compositions from APT.