Beta Grain Research Articles

Effect of Ce Addition on the Machinability of Ti-6Al-4V Alloy

Ti alloys are difficult to machine, accounting for 50-75% of the final component price, necessitating urgent improvements in machinability to increase their demand in several fields. This study found that adding small amounts of Ce (0.1-2.0wt.%) significantly improves the machinability of Ti-6Al-4V alloy. Here, we systematically analyzed microstructural changes due to Ce addition and their effects on machinability and tensile properties. We found that adding 0.3wt.% Ce results in fine (80-100nm) Ce-oxides dispersion throughout the matrix, which effectively reduces chip length (192mm→12.5mm) and increases tensile strength from 840MPa to 956MPa without a significant decrease in ductility; however, the reduction in cutting torque was minimal (2.5Nm→2.3Nm). On the other hand, when 1.4wt.% Ce was added, Ce-oxide particles were not only finely distributed within the matrix but also coarsely (3μm-5μm) located along the prior beta grain boundaries, resulting in significant reductions in both chip length (192mm→4.5mm) and cutting torque (2.5Nm→1.9Nm). In this case, the tensile strength increased from 840MPa to 909MPa, but ductility slightly decreased due to cleavage fracture. Therefore, the addition of 1.4wt.% Ce is suitable when reducing cutting torque is more important than ductility, while 0.3wt.% Ce is preferable when reducing chip length and maintaining ductility are critical. This study is expected to contribute to expanding the industrial application of Ti components by reducing the machining costs of Ti alloys.

Characterisation of dissimilar metal weldments of titanium alloys Ti-64 and Ti-6246 made using electron beam and rotary friction welding

Abstract Welding of dissimilar Titanium alloys viz. Ti-64 and Ti-6246 by fusion processes is challenging due to their different physical properties. Such alloys find applications in turbine disks and blades. The alloys were welded using Electron Beam Welding (EBW) and Rotary Friction Welding (RFW) processes. In this paper, metallurgical and mechanical properties of welded joints between the Titanium alloys were examined and reported. Microstructures, electron back scattered diffraction (EBSD) analysis, and residual stresses were also examined. The EBW weld was free of defects such as porosity and inclusions. Furthermore, RFW weld was also free of any defects. SEM and EBSD analysis also support this conclusion. The coarse columnar beta grains with thin needle-like alpha can be observed in the fusion zone of the EBW weldments. The grains appeared to have been refined in the deformation zone (DZ) due to dynamic recrystallization (DRX) in the RFW joints. The yield and ultimate tensile strengths of EBW weldments were 977 MPa and 1051 MPa respectively. While that of RFW weldments, 960 MPa and 1039 MPa. The percent elongation of the EBW weldments and RFW weldments was 14.2 and 10.28 respectively. The welds were stronger than the base metal in both the weldments as the fracture occurred in the Ti-64 base metal and not in the weld during tensile test. The microhardness of the fusion zone of EBW weldments was approximately 430 HV to 460 HV. While that of weld nugget of RFW weldments was 380 HV. The mechanical properties indicate that either of the welding processes is suitable for welding the alloys.


Comparative Review of the Microstructural and Mechanical Properties of Ti-6Al-4V Fabricated via Wrought and Powder Metallurgy Processes

This review examines the microstructural and mechanical properties of a Ti-6Al-4V alloy produced by wrought processing and powder metallurgy (PM), specifically laser powder bed fusion (LPBF) and hot isostatic pressing. Wrought methods, such as forging and rolling, create equiaxed alpha (α) and beta (β) grain structures with balanced properties, which are ideal for fatigue resistance. In contrast, PM methods, particularly LPBF, often yield a martensitic α′ structure with high microhardness, enabling complex geometries but requiring post-processing to improve its properties and reduce stress. The study evaluated the effects of processing parameters on grain size, phase distribution, and material characteristics, guiding the choice of fabrication techniques for optimizing Ti-6Al-4V performance in aerospace, biomedical, and automotive applications. The analysis emphasizes tailored processing to meet advanced engineering demands.

Investigation on influence of selective laser melting parameters on mechanical properties of Ti-6Al-4V alloy

This research investigates the effects of process parameters of selective laser melting (SLM) on mechanical and metallurgical properties of titanium alloy Ti-6Al-4V fabricated parts. Key printing parameters including scan speed, laser power, and printing strategies, are analyzed for their impact on properties of printed parts using Taguchi L9 statistical approach. It is found that increasing laser power and scan speed decreases strength in both the longitudinal and transverse directions of the printed samples. The study highlights that the bi-directional printing strategy yields the highest strength in both directions, while the stripe strategy results in the lowest strength. Additionally, higher scanning speeds increase porosity, subsequently lowering the overall strength of the printed components. Microstructural analysis reveals the presence of acicular alpha martensite within the prior beta grains in most samples.

Numerical simulation for β/α transformation of Ti–6Al–4V alloy using a lattice Boltzmann - Cellular automata method

This paper considers the beta/alpha transformation of Ti–6Al–4V alloy using a lattice Boltzmann method (LBM) – cellular automata (CA) coupled method in terms of microstructural evolution during phase transformation. Particularly, the effects of the cooling rate on microstructures such as beta grain size, alpha colony size, and alpha lath thickness were examined as well as the overall morphologies. The LBM and CA were used to implement the diffusion of alloy components and phase transformation, respectively. Additionally, the thermodynamic and kinetic data for simulating the ternary alloy system were obtained from CALPHAD software to utilize the equilibrium phase diagram calculations. The initial states of the beta grain and its composition fields affect the processing of beta/alpha phase transformation and the final alpha + beta phase morphologies. Validation of the proposed method was conducted to compare the simulation results with experimental trends for microstructures of Ti–6Al–4V from the literature. The error in prediction of microstructural morphologies were 20% in the average alpha thickness with deviation of up to 5 μm.

Influence of IP-TIG welding parameters on weld bead geometry, tensile properties, and microstructure of Ti6Al4V alloy joints

Abstract The primary aim of this study is to analyze the influence of inter-pulse tungsten inert gas (IP-TIG) welding parameters (peak current, inter-pulse current, and inter-pulse frequency) on weld bead geometry, tensile properties, and microstructure of Ti6Al4V alloy joints for gas turbine applications. IP-TIG welding principally featured by magnetic arc constriction and pulsing was employed to overcome the high heat input problems in TIG welding of thin Ti6Al4V alloy sheets such as wider bead and HAZ, coarsening of beta grains, inferior ductility, distortion of joints, and atmospheric contamination which significantly deteriorates the mechanical performance of welded sheets. The tensile properties and microhardness of IP-TIG joints were evaluated and correlated to the microstructural features. The microstructural features were analyzed using optical microscopy. The fractured surfaces of tensile specimens were studied using scanning electron microscopy. Results showed that the Ti6Al4V alloy joints developed using peak current of 50 A, inter-pulse current of 30 A, and inter-pulse frequency of 20 kHz exhibited greater strength, hardness and elongation. It showed greater tensile strength of 1030 MPa, yield strength of 981 MPa, and elongation of 10 % and FZ microhardness of 391 HV0.2. It is mainly due to the development of refined grains in fusion zone (FZ).

Effect of processing parameters on microstructure of additively manufactured α+β titanium alloys

The effect of processing parameters on the microstructure was investigated on three α+β alloys, namely Ti6Al4V (Ti64), Ti6Al2Sn4Zr6Mo (Ti6246) and Ti6.5Al3.5Mo1.5Zr0.3Si (TC11) fabricated by laser powder bed fusion (LPBF). Electron Backscattered Diffraction (EBSD) was used to identify microstructural characteristics, including prior beta grains (PBGs) structure, hierarchical lath morphology and orientation. Acicular martensitic (α’) laths form within the PBGs following a crystallographic relationship. The martensite displays a hierarchical structure.

Impact of process parameters on transitions in the microstructural characteristics and mechanical attributes of Ti–6Al–4V alloy joints during FSW

Abstract Transformations in microstructural characteristics and mechanical attributes of friction stir welded 3 mm thick Ti–6Al–4V alloy plates was investigated by employing distinctive tool rotational and traverse speeds. Impact of these parameters on microstructural transitions, generation of flaws, hardness, and tensile properties of the joints were analyzed. Increase in rotational speed from 1200 rpm to 1600 rpm have contributed for escalation in temperature, even above the β transus temperature. Large sized lamellar alpha grains was found to be transformed into finely refined lamellar alpha + altered beta grains in uppermost portion of nugget zone of joints fabricated at 1600 rpm and 50 mm/min combinations. This transformation have occurred due to the impact of the thermal cycles and stirring mechanism. These joints were found to be free from flaws including volumetric related defects, kissing bond, tunnel flaws. Majority of the fabricated joints possessed lowest value of mechanical properties in their heat affected zone and exhibited fracture in this zone. Properties of Ti–6Al–4V alloy joints were evaluated with respect to pseudo index of heat and it was observed that rotational speed of the tool is a dominant parameter in impacting both the mechanical attributes and microstructural transformations of the joints.

Closed-loop temperature controlled solid-state additive manufacturing of Ti-6Al-4V with forging standard out-of-plane tensile properties

Here, we present the first demonstration of additive friction stir deposition of Ti-6Al-4V with closed-loop temperature control, wherein the print head rotation rate is adjusted in real-time to maintain a constant tool temperature during deposition. The as-printed Ti-6Al-4V is fully dense, achieving forging standard tensile properties along both the in-plane and out-of-plane directions. The measured yield strength, ultimate tensile strength, and elongation are 903 MPa, 1000 MPa, and 17% along the in-plane direction, and 948 MPa, 1024 MPa, and 16% along the out-of-plane direction. With closed-loop temperature control, the microstructure is found to be comparable along the thickness direction, contrasting the previous work performed under parameter-controlled conditions. For all the deposition conditions explored in this work, the deposited Ti-6Al-4V exhibits a lamellar microstructure with alpha laths forming inside prior beta grains, indicating higher peak temperatures than the beta transus. The increase of a pseudo heat index leads to an increase in the prior beta grain size and a decrease of the out-of-plane yield strength. Deposition of Ti-6Al-4V is seen to modify the microstructure of the substrate near the interface: the original equiaxed microstructure is replaced by lamellar and bimodal microstructures. We finally discuss the possibility of forming equiaxed microstructures in the as-deposited Ti-6Al-4V and provide evidence for different types of microstructures forming in the same deposition layer, which may be caused by the thermal gradient during reheating.

Effect of friction pressure on microstructure and tensile properties of linear friction welded Ti–6Al–4V alloy joints

This investigation aims to study the influence of friction pressure (FRNP) on the evolution of microstructure and tensile properties of Ti6Al4V alloy joints developed using linear friction welding (LFW) for aeroengine applications. The Ti6Al4V alloy plates of 6 mm thickness were joined using different levels of FRNP from 10 MPa to 30 MPa. The weld joint quality was analyzed employing stereo-zoom microscope. The microstructure of LFW joints was studied using optical (OM), scanning electron (SEM) and transmission electron microscope (TEM). The hardness and tensile properties were evaluated and correlated to the microstructure of joints. The fractographs were studied using SEM and correlated to the hardness. The LF welded Ti6Al4V joints made using the optimum level of FRNP of 20 MPa exhibited greater tensile strength (UTS) of 993 MPa, and elongation (EL) of 8%. It showed notch tensile strength (NTS) of 1073 MPa and notch strength ratio (NSR) of 1.041 revealing ductile fracture. The LF welded Ti6Al4V joints revealed 96.41%, 104.10% and 66.67% of UTS, NTS and EL of base metal. The greater smooth and notch tensile properties of joints are principally imputed to maximum refinement of alpha + beta grains at interface of joint.

Twinning-induced plasticity (TWIP) effect in multi-phase metastable beta Zr-Nb alloys

• Twinning-induced plasticity (TWIP) strategy was first applied in Zr alloys for strain-hardening and ductility enhancements. • Zr-13.8Nb-0.7Hf and Zr-15.5Nb-0.7Hf alloys designed by electron-to-atom ratio exhibit multi-phase microstructures consisting of acicular body-centered tetragonal phase and monoclinic phase in beta grains. • TWIP-enhanced Zr-13.8Nb-0.7Hf alloy resulted in superior strain-hardening rate and ductility when comparing to Zr-15.5Nb-0.7Hf without mechanical twinning. • In-situ traction tests in TEM and SEM-EBSD were conducted to clarify the {332}<113> twinning operation and its interaction with body-centered tetragonal phase. The deformation mechanisms were studied in metastable Zr-13.8Nb-0.7Hf and Zr-15.5Nb-0.7Hf (wt.%) alloys exhibiting complex microstructures due to quenched-in precipitates (acicular body-centered tetragonal phase and globular monoclinic phase) in beta grains. Twinning-induced plasticity (TWIP) effect was observed in Zr-13.8Nb-0.7Hf via {332}<113> twinning operation, resulting in higher strain-hardening rate and uniform elongation than those of Zr-15.5Nb-0.7Hf deforming via only dislocation glide. In-situ characterizations, by applying tensile deformation during electron backscattered diffraction (EBSD) mapping and transmission electron microscopy (TEM) observation, were conducted to clarify the twinning process and the role of quenched-in precipitates when interacting with deformation twins.

Microstructure evolution in compositionally graded Ti(4–12 wt% Mo) prepared by laser directed energy deposition

Compositionally graded Ti(4–12 wt% Mo) alloys were successfully prepared by laser directed energy deposition (L-DED) using two hoppers from Ti and Ti-15Mo master alloy powders. Detailed SEM, EDS and XRD analysis reveals the variation of the microstructure and consequently explains the evolution of the microhardness with the Mo concentration. High laser power is required to dissolve Ti-15Mo particles, to improve the homogeneity of the material at the scale of particle size, and to achieve a smooth linear gradient of the chemical composition. In the bottom part of the samples, the microstructure consists of elongated beta grains of the length of several mm containing big α-Ti laths. With increasing Mo concentration, the volume fraction of α phase decreases. Starting from the composition of about 9 wt% Mo the presence of ω phase was detected. Microhardness values span over a wide range of 270–550 HV and are affected by phase composition. The highest values of microhardness are achieved at around 10 wt% of Mo. However, phase composition and microhardness depend also on the utilized laser power and position in the sample determining the cooling rates. L-DED is capable of producing functionally graded materials (FGM) on the basis of metastable β-Ti alloys providing large variations of mechanical properties within a single sample/product.

Nano mechanical study on a single layer TiC/TI6Al4V-ELI composite manufactured with laser metal deposition

This study investigated the nano mechanical properties of Ti6Al4V-ELI embraced with TiC particles, synthesized with in situ laser metal deposition technique. The 3.85% feed ratio fraction TiC/Ti6Al4V-ELI composite samples were manufactured at four varying energy densities. The beta grain boundary and the acicular alpha primary matrix were found to have diverse morphologies of carbide particles due to the in-situ reaction. The effect of energy density is observed on the microstructure and nano mechanical properties. An average off set of 650 nm was recorded after the nano-indentation in the matrix at a maximum load of 400 mN.

Changes in High Temperature Deformation Behavior by Differences in Energy Dissipation Efficiency of Ti–6Al–4V Alloy

Ti–6Al–4V alloy is widely used as a system material in high temperature and high pressure environments in various industrial fields and is difficult to mechanically machine. Thus, high temperature processing methods such as hot forging, rolling, and hot forming are usually applied. Among various methods for deriving optimal molding conditions during high-temperature processing, the dynamic material model suggests energy dissipation efficiency according to the flow stress of the material. However, the energy dissipation efficiency merely numerically represents the change in flow stress, not the metallurgical behavior of the material. Therefore, it is necessary to understand the difference in energy dissipation efficiency in relation to the high-temperature deformation mechanism. In this study, high temperature compression tests were performed on the Ti–6Al–4V alloy. The temperature range was set at 800°C∼1200°C at intervals of 50°C, and the strain rate was set at 1 × 100/sec∼1 × 10−3/sec at intervals of 10−1/sec. Based on the results of the experiments, flow stress and processing maps were derived, and the high temperature plastic deformation behaviors of Ti–6Al–4V alloy were analyzed in correlation with the microstructural changes and mechanical properties according to temperature and strain rate. And the prior beta grain size according to the difference in energy dissipation efficiency was explained for each condition.

Thermo-Mechanical Fatigue Crack Growth and Phase Angle Effects in Ti6246.

A bespoke TMF crack growth test set-up has been developed and validated for use throughout this study and the effects of phasing between mechanical loading and temperature have been investigated. The study shows that TMF cycles may show increased crack growth rate behaviour when compared to isothermal fatigue. The phase angle of the applied TMF cycle can also affect crack growth behaviour, with in-phase (IP) test conditions showing faster crack growth rates than out-of-phase (OP) test conditions. Propagating cracks interact with the microstructure of the material, in particular, the α/β interfaces within the prior beta grains and supporting fractography evidences subtle differences in fracture mechanisms as a result of phase angle.

Investigations on the effect of build orientation on the properties of wire electron beam additive manufactured Ti-6Al-4V alloy

In the present scenario, wire additive manufacturing is the most effective and efficient technique adopted to realize complex and bulky components in aerospace applications. The current work mainly investigates the heterogeneous and anisotropic behavior of the electron bean wire additive manufactured Ti-6Al-4V. To investigate the effect of build orientation, cuboids were built to extract cylindrical samples with axis parallel to Z-axis, X-axis, Y-axis, and inclined at 45° to the base X-Y plane. Non-destructive inspection using radiography was conducted to ensure the attainment of defect-free samples. Further, the samples were subjected to advanced material characterization techniques. Microstructural features of as-built samples reveal the large columnar prior beta grains attributed to the rapid cooling in the vacuum chamber. Electron backscatter diffraction analysis shows β phase solidified as columnar grains. The martensite structure is observed in the Transmission electron microscopic analysis of the fabricated samples. The tensile samples build at different orientations exhibits the higher yield strength and higher percentage elongation for the sample built along Z-axis. The tensile strength and elongation of the additive built samples are found to be better than that of wrought Ti-6Al-4V. The fractography analysis on the fractured specimen reveals the failure through ductile mode.

Development of ultra-fine grain microstructures in a metastable-β titanium alloy via phase transformation assisted recrystallisation

Generally, in metallic alloys, attaining ultra-fine sub-micron grain sizes by recrystallisation requires severe plastic deformation (SPD), however SPD techniques are difficult to apply to large quantities of material. In this work, we explore a strategy to reach an ultra-fine grained microstructure in a metastable-β titanium Ti-20Nb-6Zr (at.%) by controlled recrystallisation after conventional rolling and annealing. The thermally stable sub-micronic dual phase microstructures are associated with the formation of strain-induced martensite during rolling and its subsequent reversion during annealing. Some specimens were cold-rolled to change most of the β microstructure to stress-induced martensite (SIM); others were “warm rolled” just above the critical temperature for formation of SIM (453 K). The role of SIM in grain refinement was isolated by comparing the microstructural evolution of the two sets of specimens during annealing treatments. The cold rolled specimens produced an effective ultrafine grain recrystallisation, which was identified to start from 723 K, and a final equiaxed alpha-beta microstructure of ~250 nm. In warm rolled specimens without SIM, no new beta grains were observed, only an array of intragranular acicular alpha precipitates of approximately 50 nm thickness.

In situ microstructure property prediction by modeling molten pool-quality relations for wire-feed laser additive manufacturing

Metal additive manufacturing (AM) is sensitive to changes in process or environment variables that potentially significantly impact the part quality. The lack of in-process microstructure monitoring and control for quality assurance of AM parts is the main barrier that prevents the widespread use of AM technologies. To enable in situ quality monitoring of printed part characteristics, we have developed an in-process sensing system integrated with a wire-feed laser AM (WLAM) machine to monitor the molten pool dimensional and temperature profiles, which are a significant indicator of microstructural properties of final parts. The part microstructure characteristics such as Alpha lath thickness and Beta grain size are evaluated comprehensively. A convolutional neural network (CNN) model is developed for establishing the correlations directly from in-process molten pool information to the microstructural properties. The multi-modality CNN (m-CNN) receives both camera and pyrometer sensors as input to improve the property prediction performance. The m-CNN model is investigated, validated, and benchmarked with the traditional Gaussian process regression (GPR) model. The developed model proves the feasibility of in-process microstructural property estimation from molten pool sensing data to provide a pathway for high quality design and control of metallic AM technologies.

Microstructural Evolution, Mechanical Properties, and Preosteoblast Cell Response of a Post-Processing-Treated TNT5Zr β Ti Alloy Manufactured via Selective Laser Melting.

A Ti–34Nb–13Ta–5Zr (TNT5Zr) β Ti alloy with a high strength-to-modulus ratio has been developed, showing its potential to become another candidate material in load-bearing implant applications. This work mainly investigates the microstructural evolution, mechanical properties, and biocompatibility of a post-processing-treated TNT5Zr alloy manufactured via selective laser melting (SLM). Transmission electron microscopy observation shows the existence of the single beta grain matrix and alpha precipitates along the grain boundary in the SLM + HIP manufactured TNT5Zr alloy (TNT5Zr-AF + HIP), and ellipsoidal nano-sized intragranular α″ precipitates (approx. 5–10 nm) were introduced after the subsequent low-temperature aging treatment. The precipitation strengthening enables the SLM + HIP + aging manufactured TNT5Zr (TNT5Zr-AF + HIPA) alloy to show a comparable ultimate tensile strength (853 ± 9 MPa) to that of the reference material (Ti64-AF + HIP, 926 ± 23 MPa). Including the inferior notch-like surface of the test pieces, the slip-band cracking that occurs in this ductile TNT5Zr-AF + HIPA alloy is regarded as the main factor in determining its fatigue strength (170 MPa). In vitro short-term biocompatibility evaluation reveals almost no significant difference in the preosteoblast viability, differentiation, and mineralization between TNT5Zr-AF + HIPA and the reference biomaterial (Ti64-AF + HIP).

Grain size-dependent tensile behaviour in a metastable beta titanium alloy

The present study investigates the effect of beta grain size on the stability of the beta phase in terms of trigger stress and the resultant mechanical properties of metastable beta titanium alloy. The trigger stress has a complex U-shaped relation concerning the beta grain size, which could be due to alternant mechanisms from interface friction and elastic energy. Nevertheless, the residual stress/strain could affect the trigger stress in the small grain size scale. More interestingly, dominant deformation modes are altered by a change of grain size with predominant stress-induced martensite (SIM) at small grain size and prime dislocation at large grain size, leading to grain size-dependent tensile behaviour of a metastable beta titanium alloy.