On the work hardening of titanium: new insights from nanoindentation

Fitzner, Arnas; Palmer, J. L.; Gardner, Ben; Thomas, Matthew; Preuss, Michael; Fonseca, João Quinta da

doi:10.1007/s10853-019-03431-w

Cited by 36 publications

(9 citation statements)

References 28 publications

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“…The declination angle is the angle between the crystal c-axis and the indent loading direction and was combined with the hardness measurement for each indent that did not interact with a grain/ phase boundary. The results of this are presented in Figure 7 (e), which shows that grains which have a small angle between their c-axis and the sample surface normal are harder, in good agreement with trends measured in the literature [38,39].…”

Section: Bulk Materialssupporting

confidence: 88%

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Quantifying the effect of oxygen on micro-mechanical properties of a near-alpha titanium alloy

Gardner

Gopon

Magazzeni

et al. 2021

Journal of Materials Research

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Titanium alloys are widely used in the aerospace industry, yet oxygen ingress can severely degrade the mechanical properties of titanium alloy components. Atom probe tomography (APT), electron probe microanalysis (EPMA) and nanoindentation were used to characterise the oxygen-rich layer on an in-service jet engine compressor disc, manufactured from the titanium alloy TIMETAL 834. Oxygen ingress was quantified and related to changes in mechanical properties through nanoindentation studies. The relationship between oxygen concentration, microstructure, crystal orientation and hardness has been explored through correlative hardness mapping, EPMA and electron backscatter diffraction (EBSD). It has been found that the hardening effects of microstructure and crystallography are only significant at very low-oxygen concentrations, whereas interstitial solid solution hardening dominates by order of magnitude for higher oxygen concentrations. The role of microstructure on oxygen ingress has been studied and oxygen ingress along a potential α/β interface was directly observed on the nanoscale using APT.

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Section: Bulk Materialssupporting

confidence: 88%

“…The results of this are presented in Fig. 7e, which shows that grains which have a small angle between their c-axis and the sample surface normal are harder, in good agreement with trends measured in the literature [42,43].…”

Section: Bulk Materialssupporting

confidence: 88%

Quantifying the effect of oxygen on micro-mechanical properties of a near-alpha titanium alloy

Gardner

Gopon

Magazzeni

et al. 2021

Journal of Materials Research

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“…Porous structures inevitably contain features that cause the stress to concentrate and hence initiate plastic deformation. The resulting strain hardening of the deforming region locally increases the yield strength in that region [224][225][226]. However, the material continues to fail as the strain hardening cannot raise the yield strength at a rate greater than the increase in stress due to the reduced area of the deformation.…”

Section: Discussionmentioning

confidence: 99%

Mechanical performance of highly permeable laser melted Ti6Al4V bone scaffolds

Arjunan

Demetriou

Baroutaji

et al. 2020

Journal of the Mechanical Behavior of Biomedical Materials

125

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Critically engineered stiffness and strength of a scaffold are crucial for managing maladapted stress concentration and reducing stress shielding. At the same time, suitable porosity and permeability are key to facilitate biological activities associated with bone growth and nutrient delivery. A systematic balance of all these parameters are required for the development of an effective bone scaffold. Traditionally, the approach has been to study each of these parameters in isolation without considering their interdependence to achieve specific properties at a certain porosity. The purpose of this study is to undertake a holistic investigation considering the stiffness, strength, permeability, and stress concentration of six scaffold architectures featuring a 68.46-90.98% porosity. With an initial target of a tibial host segment, the permeability was characterised using Computational Fluid Dynamics (CFD) in conjunction with Darcy's law. Following this, Ashby's criterion, experimental tests, and Finite Element Method (FEM) were employed to study the mechanical behaviour and their interdependencies under uniaxial compression. The FE model was validated and further extended to study the influence of stress concentration on both the stiffness and strength of the scaffolds. The results showed that the pore shape can influence permeability, stiffness, strength, and the stress concentration factor of Ti6Al4V bone scaffolds. Furthermore, the numerical results demonstrate the effect to which structural performance of highly porous scaffolds deviate, as a result of the Selective Laser Melting (SLM) process. In addition, the study demonstrates that stiffness and strength of bone scaffold at a targeted porosity is linked to the pore shape and the associated stress concentration allowing to exploit the design freedom associated with SLM.

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“…The improved fatigue behavior from shot peening is attributed to the introduced compressive residual stresses, which led to localized increases of hardness at the surface of samples [29] and stress-induced cold worked microstructural changes such as deformation twins (Figures 9-11). This induced cold work resulted in the formation and growth of tensile deformation twins, which, in turn, resulted in increasing the hardness of the material even though the exact mechanism is still being contested in the scientific literature [37]. The localized increase in hardness and related microstructural cold-work changes made it more difficult for crack initiation to occur at the surface of shot-peened parts, as it occurred in untreated samples, despite their slightly rougher surface finish even after polishing in comparison with untreated fatigue samples.…”

Section: Discussionmentioning

confidence: 99%

Fatigue Improvement of Additive Manufactured Ti–TiB Material through Shot Peening

DiCecco

Mehdi

Edrisy

2021

Metals

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In this work, fatigue improvement through shot peening of an additive manufactured Ti–TiB block produced through Plasma Transferred Arc Solid Free-Form Fabrication (PTA-SFFF) was investigated. The microstructure and composition were explored through analytical microscopy techniques such as scanning and transmission electron microscopy (SEM, TEM) and electron backscatter diffraction (EBSD). To investigate the isotropic behavior within the additive manufactured Ti–TiB blocks, tensile tests were conducted in longitudinal, diagonal, and lateral directions. A consistent tensile behavior was observed for all the directions, highlighting a nearly isotropic behavior within samples. Shot peening was introduced as a postmanufacturing treatment to enhance the mechanical properties of AM specimens. Shot peening led to a localized increase in hardness at the near-surface where stress-induced twins are noted within the affected microstructure. The RBF-200 HT rotating-beam fatigue machine was utilized to conduct fatigue testing on untreated and shot-peened samples, starting at approximately 1/2 the ultimate tensile strength of the bulk material and testing within low- (<105 cycles) to high-cycle (>105 cycles) regimes. Shot-peened samples experienced significant improvement in fatigue life, increasing the fitted endurance limit from 247.8 MPa for the untreated samples to 318.3 MPa, leading to an increase in fatigue resistance of approximately 28%.

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On the work hardening of titanium: new insights from nanoindentation

Cited by 36 publications

References 28 publications

Quantifying the effect of oxygen on micro-mechanical properties of a near-alpha titanium alloy

Quantifying the effect of oxygen on micro-mechanical properties of a near-alpha titanium alloy

Mechanical performance of highly permeable laser melted Ti6Al4V bone scaffolds

Fatigue Improvement of Additive Manufactured Ti–TiB Material through Shot Peening

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