Fatigue Life Of Titanium Alloy Research Articles

Residual stress, fatigue behavior, and mechanical properties of equal-channel angular pressed commercial pure titanium

Residual stresses, fatigue behavior, and mechanical properties of equal channel angular pressing (ECAP) commercial pure titanium (CP–Ti) are investigated in this study. Residual stresses can significantly affect the performance and reliability of CP-Ti components under cyclic loading conditions. The study focuses on understanding the relationship between ECAP processing, residual stresses, and fatigue behavior in CP-Ti. The ECAP process was employed to produce CP-Ti grade 2 samples, and their fatigue behavior was characterized. The results revealed a significant increment in residual stresses, fatigue strength, microhardness, and tensile strength by ECAP processing on the CP-Ti. The measured fatigue limit of the processed CP-Ti was found to be higher than that of coarse-grained CP-Ti and approaches the fatigue limit of the Ti–6Al–4V alloy. Residual stresses resulting from non-conventional machining processes and surface treatments are known to affect the fatigue life of titanium alloys. Compressive residual stresses have been shown to inhibit the growth rate of fatigue cracks and improve fatigue life. Understanding the effect of residual stresses on the fatigue behavior and mechanical properties of ECAP-processed CP-Ti is crucial to optimizing the design and ensuring the long-term durability of CP-Ti components in engineering applications.

Significant improvement in fatigue life of titanium alloy induced by superlattice coating

The purpose of this paper is to investigate the effect of the TiN coating and the TiN/AlN superlattice coating on the fatigue performance of titanium alloys. The effect of the coating on the fatigue property of the titanium alloy is studied through the coating-substrate interaction. The results show that the TiN/AlN superlattice coating with high hardness and fracture toughness inhibits strain localization on the surface, changes the location of fatigue crack initiation and improves the fatigue strength at 107 cycles by 23.7%. Dislocation redistribution and “secondary slip” are found in the titanium alloy to eliminate stress concentration.

Experimental study on the effect of dwell-fatigue life of titanium alloy for pressure hull

Titanium alloy is widely applied in the pressure hull of the manned submersible for its good mechanical properties. The operations of the manned submersible include diving, cruising and ascent. The load spectrum of the pressure hull is a typical dwell-fatigue process. The dwell effect is known to induce a reduction in the fatigue life of titanium alloys at room-temperature. The dwell fatigue of the new titanium alloy is the key issue to ensure a safe submersible operation. In this paper, the dwell-fatigue behavior of a new titanium alloy for pressure hull is investigated. It is found that the accumulated strain at the final rupture increases with the increase of dwell time, and the total cycle decreases. The total cycle life of the specimen decreases, and the accumulated strain increases with increasing peak stress level. The introduction of the dwell time at the peak stress will significantly reduce the dwell-fatigue life and the mechanism is due to the accumulation of the plastic strain.

Significant Improvement in Fatigue Life of Titanium Alloy Induced by Superlattice Coating

Significant Improvement in Fatigue Life of Titanium Alloy Induced by Superlattice Coating

An Entropy-Based Neighborhood Rough Set and PSO-SVRM Model for Fatigue Life Prediction of Titanium Alloy Welded Joints.

In order to obtain comprehensive assessment of the factors influencing fatigue life and to further improve the accuracy of fatigue life prediction of welded joints, soft computing methods, including entropy-based neighborhood rough set reduction algorithm, the particle swarm optimization (PSO) algorithm and support vector regression machine (SVRM) are combined to construct a fatigue life prediction model of titanium alloy welded joints. By using an entropy-based neighborhood rough set reduction algorithm, the influencing factors of the fatigue life of titanium alloy welded joints such as joint type, plate thickness, etc. are analyzed and the reduction results are obtained. Fatigue characteristic domains are proposed and determined subsequently according to the reduction results. The PSO-SVRM model for fatigue life prediction of titanium alloy welded joints is established in the suggested fatigue characteristic domains. Experimental results show that by taking into account the impact of joint type, the PSO-SVRM model could better predict the fatigue life of titanium alloy welded joints. The PSO-SVRM model indicates the relationship between fatigue life and fatigue life influencing factors in multidimensional space compared with the conventional least-square S-N curve fitting method, it could predict the fatigue life of the titanium alloy welded joints more accurately thus helps to the reliability design of the structure.

Effect of Mechanical Properties on Fatigue Life of Titanium Alloy Ti-6Al-4V Manufactured by Electron Beam Melting

Effect of Mechanical Properties on Fatigue Life of Titanium Alloy Ti-6Al-4V Manufactured by Electron Beam Melting

Effect of Different Shot Peening Treatments on Fatigue Life in Ti Alloy

The effects of peening conditions on the surface characteristics and fatigue life of titanium alloy was investigated using microshot peening, ultrasonic shot peening, and multiple shot peening. The use of microshot peening technology with minute media has become more widespread in consideration of the reduction of the notch effect in the material surface. The ultrasonic shot peening that uses media of several millimeters in size with ultrasonic vibration has attracted attention as a means to reduce the surface roughness. In the present study, an air-type and an ultrasonic type machine were used. In the microshot peening process, the media used was high-carbon cast steel and the hard powder, with an average diameter of 0.1 mm. The workpiece was commercial titanium alloy Ti-6Al-4V. In the microshot peening (MSP), work hardening was evident to the depth of approximately 0.3 mm from the surface. This depth was approximately three times the diameter of the media. However, the influence of the peening time on the hardness distribution was not great. In the ultrasonic shot peening (USP), work hardening was deeper in the material. This is because the diameter of the media used for ultrasonic machining was large. On the other hand, in the combined shot peening (CSP), a degree of hardness was higher at the top surface. However, the hardness patterns and values were pretty much identical to ultrasonic shot peening. The fatigue limit was thought to be greater in the microshot peening experiment because the work-hardened layer was formed near the workpiece surface.

Surface integrity generated with peripheral milling and the effect on low-cycle fatigue performance of aeronautic titanium alloy Ti-6Al-4V

ABSTRACTMachining-induced surface integrity has an important effect on reliability and service life of the components used in the aerospace industry where titanium alloy Ti-6Al-4V is widely applied. Characterisation of machining-induced surface integrity and revealing its effect on fatigue life are conducive to structural fatigue life optimisation design. In the present study, surface topography, residual stress, microstructure and micro-hardness were first characterised in peripheral milling of titanium alloy Ti-6Al-4V. Then, low-cycle fatigue performances of machined specimens were investigated on the basis of the tension-tension tests. Finally, the effects of surface integrity factors (stress concentration factor, residual stress and micro-hardness) on fatigue performances were discussed. Results show that stress concentration can reduce the fatigue life while increasing the residual compressive stress, and micro-hardness is beneficial to prolonging the fatigue life, but when the surface material of the specimen is subjected to plastic deformation due to yield, the residual stress on the surface is relaxed, and the effect on the fatigue performance is disappeared. Under the condition of residual stress relaxation, the stress concentration factor is the main factor to determine the low-cycle fatigue life of titanium alloy Ti-6Al-4V. While for the specimens with no residual stress relaxation, micro-hardness was the key factor to affect the fatigue life, followed by residual stress and stress concentration factor, respectively.

Using Cavitation Peening to Improve the Fatigue Life of Titanium Alloy Ti-6Al-4V Manufactured by Electron Beam Melting

Although Electron Beam Melting (EBM) is an innovative technology, the fatigue properties of materials manufactured by EBM may be lower than those of casted and wrought materials due to defects and surface roughness. In order to enhance the fatigue life of components or structures manufactured by EBM, a mechanical surface treatment technology, e.g., peening, would be effective because peening introduces high compressive residual stress at the surface which can extend the fatigue life considerably. In the present study, specimens were manufactured by EBM using titanium alloy Ti-6Al-4V powder. Two types of specimens were prepared: as-built and as-machined specimens. Specimens of each type were treated by cavitation peening or shot peening. The fatigue lives of the specimens were evaluated by a plate bending fatigue tester. The residual stress and surface roughness were also evaluated. The results obtained showed that the fatigue strength of as-built specimens can be improved by 21% by cavitation peening or shot peening, and the fatigue life under particular applied stresses can also be extended by 178% by cavitation peening.

Prediction of Cold Dwell-Fatigue Crack Growth of Titanium Alloys

The dwell effect of the material can reduce the fatigue lives of titanium alloys at room temperature. A unified fatigue life prediction method developed by the authors’ group is modified in this paper to predict dwell-fatigue crack growth taking into account the effects of dwell time and maximum stress. The modified model can be successfully used to predict the crack growth rate and calculate the fatigue life of different titanium alloys under pure fatigue and dwell-fatigue conditions. It is validated by comparing prediction results with the experimental data of several titanium alloys with different microstructures, dwell time, hydrogen contents, stress ratios and stress levels .

FE Modelling of Residual Stresses and Validation Using Chip-Mechanism and Microstructural Analysis of Ultrasonic Vibration Assisted Turning of Ti Alloy Ti-6Al-4V

Ultrasonic assisted turning (UAT) is a novel manufacturing technology, where high frequency vibrations are imposed on the movement of a cutting tool. A 2D FE transient simulation is developed in DEFORM, where ultrasonic vibrations of frequency 20 kHz and amplitude of 20 μm are provided to the cutting tool in the direction of cutting velocity. The prediction of residual stress distribution is carried out using elasto-plastic finite element simulations. Experimental analysis is carried out in measuring the strain at the cutting tool during CT and UAT along with the chip mechanism and chip microstructure study to validate the residual stress distribution. The ultrasonic vibrations yield a considerable improvement in compressive residual stresses which ultimately benefits in improving fatigue life of titanium alloys.

Fatigue Life of Titanium Alloys Fabricated by Additive Layer Manufacturing Techniques for Dental Implants

Additive layer deposition techniques such as electron beam melting (EBM) and laser beam melting (LBM) have been utilized to fabricate rectangular plates of Ti-6Al-4V with extra low interstitial (ELI) contents. The layer-by-layer deposition techniques resulted in plates that have different surface finishes which can impact significantly on the fatigue life by providing potential sites for fatigue cracks to initiate. The fatigue life of Ti-6Al-4V ELI alloys fabricated by EBM and LBM deposition techniques was investigated by three-point testing of rectangular beams of as-fabricated and electro-discharge machined surfaces under stress-controlled conditions at 10 Hz until complete fracture. Fatigue life tests were also performed on rolled plates of Ti-6Al-4V ELI, regular Ti-6Al-4V, and CP Ti as controls. Fatigue surfaces were characterized by scanning electron microscopy to identify the crack initiation site in the various types of specimen surfaces. The fatigue life data were analyzed statistically using both analysis of variance techniques and the Kaplan-Meier survival analysis method with the Gehan-Breslow test. The results indicate that the LBM Ti-6Al-4V ELI material exhibits a longer fatigue life than the EBM counterpart and CP Ti, but a shorter fatigue life compared to rolled Ti-6Al-4V ELI. The difference in the fatigue life behavior may be largely attributed to the presence of rough surface features that act as fatigue crack initiation sites in the EBM material.

접촉피로 파라미터의 개발

In this study, new multi-axial, critical plane based, fretting fatigue crack initiation parameter is developed by the addition of a new term into the Modified Shear Stress Range(MSSR) parameter. The newly developed parameter (MSSR') is then used to evaluate fretting fatigue life of titanium alloy, Ti-6A1-4V with various contact conditions. Finite element analysis is also used in order to obtain stress distribution on the contact surface during fretting fatigue test, which is then used for the calculation of fretting fatigue parameter. The MSSR' parameter shows better performance in predicting fretting fatigue lives from the conventional fatigue data, and less scattering within fretting fatigue data with different contact geometries.

Improvement of the fatigue life of titanium alloys for biomedical devices through microstructural control

A limited number of reports exist regarding the systematic investigation or comparison of the fatigue strength of titanium alloys for medical devices, including plain, fretting and notch fatigue, for improvement through various treatments and processes, with respect to related microstructures. This article focuses on the changes and improvements in fatigue strength of newly developed β-type and practically used α + β-titanium alloys for medical devices through heat treatments, thermomechanical treatments and surface modifications.

Total fatigue life prediction for Ti-alloys airframe structure based on durability and damage-tolerant design concept

Based on the concept of the damage-tolerance and durability design, the total fatigue life of titanium alloys is divided into three phases: crack initiation (0–0.3 mm), short crack growth (0.3–2 mm) and long crack growth (2 mm– a C). Among these three phases, different prediction models are accepted due to different failure mechanisms. A computer program was developed to predict the total fatigue life of the titanium alloy structure. Fatigue testing is also conducted for two types of ELI grade titanium alloy to verify the prediction models. The predicted fatigue life agrees well with experimental results.

Investigation of the dwell period’s influence on the fatigue crack growth of a titanium alloy

The dwell effect, which is known to induce a reduction in the fatigue life of titanium alloys at room temperature, is related to early crack initiation. The present results support faster crack growth rates. The governing mechanisms are identified by mean of scanning electron microfractographic observations. The potential role of the atmosphere is examined through comparative testing performed in air and in high vacuum in order to distinguish the specific contributions of cold creep and environment assistance.

The structure and fatigue life of titanium alloys processed by electrical pulses

The structure and properties of VT3-1 titanium alloy processed by electrical pulses are investigated. The electric pulse processing improves the fatigue life of titanium specimens, as follows from high-cycle fatigue tests.

Influence of thin coatings deposited by a dynamic ion mixing technique on the fatigue life of TITANIUM ALLOYS

The technique of dynamic ion mixing involving a physical vapour deposition method and a simultaneous ion implantation has been used in order to improve the fatigue resistance of two titanium alloys. This process allows the deposition of adherent NiTi and SiC amorphous coatings of the order of 1 μm thick. Both treated substrates have been tested at room temperature in the low cycle fatigue range, revealing significant fatigue life improvement. NiTi and SiC films modify the surface deformation mechanisms of fatigued materials and largely suppress or delay crack initiation. These effects depend, however, on the nature of the film, the microstructure of the substrate and the stress amplitude applied during the fatigue tests. To explain the fatigue results, the mechanical properties of these thin films have been characterized by different techniques: scratch-tests, micro-Vickers indentations, Young's modulus measurements by a resonant frequency method and “fracture stress” determination by in situ tensile tests. The results have shown that their mechanical properties are very different to those of the corresponding classically deposited solid materials and are influenced by the film thickness. The results are discussed according to the mechanical properties of the coatings and the substrate deformation and damage modes associated with their microstructure.

Effect of the dimensions of the alpha- and beta-phases on the fatigue life of titanium alloys

1. The cyclic life of (α+β)-titanium alloys depends on the size of the β-transformed phase. The maximum fatigue life has the VT6 alloy whose structure contains the smallest β-transformed phase. 2. The volume percentage of the initial α-phase and β-transformed phase as well as the dimensions of the α-phase have no effect on the cyclic life of (α+β)-titanium alloys.