Mechanical Surface Treatments on the High‐Strength Alpha‐Titanium Alloy KS 120

Kiese, J.; Zhang, Jiulai; Schauerte, Oliver; Wagner, Lothar

doi:10.1002/3527606580.ch51

Cited by 1 publication

(1 citation statement)

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“…The aim of this investigation is the realization of a microstructure which exhibits a microstructure gradient depending on the surface distance, which improves the properties relevant for the application of cyclically stressed components, particularly the strength of aircraft components subjected to cyclic loading in the HCF (High Cycle Fatigue) and LCF (Low Cycle Fatigue) regimes. Microstructure gradients can be generated by thermomechanical treatment in general [20][21][22] and in Ti alloys [23][24][25][26][27] and thermochemical treatments [28][29][30][31][32], such as THT [33,34]. By employing THT (a process similar to ref.…”

Section: Introductionmentioning

confidence: 99%

Feasibility of THT-Induced Microstructure Gradients and Their Effects on Fatigue Properties in Additively Manufactured Cylindrical and in Conventionally Manufactured Tube-Like Ti-6Al-4V Specimens

Schmidt,

El-Chaikh,

Danzig

et al. 2024

Preprint

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Technical components should be produced sustainably and are subject to growing demands in terms of durability and reliability. To meet these expectations, the development of thermochemical processes is auspicious. Titanium alloys, which have a comparatively high gas solubility, allow temporary hydrogen (H) loading, often called thermo hydrogen treatment (THT). THT causes lattice deformation and reduces the β transformation temperature. These effects enable an adjustment of the microstructure, which improves the mechanical properties as compared to those produced conventionally. Furthermore, the process is applicable to complex geometries that cannot be surface hardened by mechanical surface treatment techniques. The investigation presented intends to realize a local microstructure gradient in additively via laser-powder bed fusion (L-PBF) manufactured cylindrical Ti–6Al–4V specimens by changing the distribution and morphology of strengthening precipitates as well as the β grain size depending on the distance to the surface, which should improve the material fatigue properties. To evaluate the mechanical properties of such THT-induced microstructure gradients, the resulting change in fatigue life in the LCF and HCF range was determined by stress-controlled cyclic deformation tests. Besides, the resulting microstructure was characterized by means of XRD and TEM. In addition to the additively manufactured and thermo hydrogen treated cylindrical specimens, conventionally produced tube-like specimens were thermo hydrogen treated and examined. For the THT-induced microstructure gradients, numerically simulated H concentration profiles as well as experimentally determined hardness profiles were used for the evaluation of the THT process. The study shows that H-loading at 500°C and H-degassing at 750°C, followed by aging at 550°C, allows the establishment of a microstructure gradient that shows an 8% improvement in fatigue properties compared to a reference condition without THT. The reason for this improvement is an increased volume fraction secondary alpha phase in the near-surface area of the specimens. Moreover, the results show that the process is applicable a tube-like specimen with varying wall thicknesses.

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