“Secondary electron hyperspectral imaging (SEHI) is an innovative SEM-based analysis tool allowing spatially-resolved chemical analysis beyond elemental composition”.

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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.

A method is presented for the registration and correlation of property maps of materials, including data from nanoindentation hardness, Electron Back-Scattered Diffraction (EBSD), and Electron Micro-Probe Analysis (EPMA). This highly spatially resolved method allows for the study of micron-scale microstructural features, and has the capability to rapidly extract correlations between multiple features of interest from datasets containing thousands of data points. Two case studies are presented in commercially pure (CP) titanium: in the first instance, the effect of crystal anisotropy on measured hardness and, in the second instance, the effect of an oxygen diffusion layer on hardness. The independently collected property maps are registered using affine geometric transformations and are interpolated to allow for direct correlation. The results show strong agreement with trends observed in the literature, as well as providing a large dataset to facilitate future statistical analysis of microstructure-dependent mechanisms. Graphical abstract

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We present new developments of the laser-induced transient grating spectroscopy (TGS) technique that enable the measurement of large area 2D maps of thermal diffusivity and surface acoustic wave speed. Additional capabilities include targeted measurements and the ability to accommodate samples with increased surface roughness. These new capabilities are demonstrated by recording large TGS maps of deuterium implanted tungsten, linear friction welded aerospace alloys, and high entropy alloys with a range of grain sizes. The results illustrate the ability to view the grain microstructure in elastically anisotropic samples and to detect anomalies in samples, for example, due to irradiation and previous measurements. They also point to the possibility of using TGS to quantify grain size at the surface of polycrystalline materials.

It is well known that titanium and some titanium alloys creep at ambient temperature, resulting in a significant fatigue life reduction when a stress dwell is included in the fatigue cycle. It is thought that localised time dependent plasticity in 'soft' grains oriented for easy plastic slip leads to load shedding and an increase in stress within a neighbouring 'hard' grain * Corresponding author E-mail address: yi.xiong@materials.ox.ac.uk (Yi Xiong) have a significant effect on stress redistribution to hard grain orientations during cold dwell fatigue. Author ContributionsThis work formed part of a larger testing campaign proposed by AJW and carried out at Diamond Light Source by YX, PK, CTN, DMC, CMM & AJW. PK oversaw preparation of test pieces and preliminary characterisation undertaken by YX, CMM and PK. CTN and PK setup and guided use of the ETMT system. YX, PK, DMC and AJW developed data analysis procedures. YX carried out crystal plasticity simulations supervised by ET who supplied the UMAT code. YX drafted the initial manuscript, with all authors contributing to and agreeing the final version.

A statistical framework is presented enabling optimal sampling and analysis of constant life fatigue data. Protocols using Bayesian maximum entropy sampling are built based on conventional staircase and stress step methods, reducing the requirement of prior knowledge for data collection. The Bayesian Staircase method shows improved parameter estimation efficiency, and the Bayesian Stress Step method shows equal accuracy to the standard method at larger step size allowing experimentalists to lessen concerns of loading history. Statistical methods for determining model suitability are shown, highlighting the influence of protocol. Experimental validation is performed, showing the applicability of the methods in laboratory testing.