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Highlights  Residual stress and phase analysis at the microscale at interface and coping edge  X-ray diffraction and Raman spectroscopy show comparable results  Cross validation using ring-core focused ion beam and digital image correlation  Monoclinic and highly stressed regions identified close to interface  Phase transformation volumetric expansion is the origin of porcelain failure

Full In-plane Strain Tensor (FIST) analysis at the micro-scale is crucial for improving the evaluation of residual stress and the understanding of the origins of mechanical failure in many applications ranging from civil structures to energy systems and micro-electronics. This study presents the analytical background and experimental implementation of a Focused Ion Beam (FIB) milling and Digital Image Correlation (DIC) based technique that uses material removal and strain relief monitoring to perform precise, reliable and rapid quantification of micro-scale residual stress.The nature of semi-destructive FIB milling overcomes the main limitations of X-Ray Diffraction (XRD) strain tensor quantification: unstrained lattice parameter estimates are not required, analysis is performed in within a precisely defined 3D microscale volume, both amorphous and crystalline materials can be studied and access to X-ray/neutron facilities is not required.The FIST FIB milling and DIC experimental technique is based on extending the interpretation of strain relief observed for the ring-core milling geometry to quantify the strain variation with azimuthal angle. The approach benefits from the high magnitude of strain relief, excellent precision and the simplicity of the analytical approach associated with this method. In-plane strain analysis is reported for a sample of commercial interest: a porcelain veneered Yttria Partially Stabilised Zirconia (YPSZ) dental prosthesis, for which the results were also compared with micro-beam synchrotron X-ray diffraction. Since the two methods sample different gauge volumes and mechanical states (approaching plane stress for ring-core milling and through-thickness averaging that approaches plane strain for XRD), the important matter of correlating the two sets of measurements arises and requires addressing. Complex variable and Finite Element (FE) methods are used to connect the two states, demonstrating that valid comparisons can be drawn. The analysis revealed excellent agreement between the principal stress orientation and values, led to realistic residual stress estimates which closely matched literature measurements ( ≈ 460 MPa) and produced upper and lower bounds for the (101) interplanar crystal lattice spacing of YPSZ in the range 2.9586 − 2.9596 Å, closely matching published values. Highlights• Full in-plane strain tensor measured by ring-core Focused Ion Beam (FIB) milling• Absolute strain measurement at the μm-scale for amorphous & crystalline materials• Comparative X-ray diffraction study validates experimental FIB results• Lattice parameter and stress state in Zr prosthesis sample match literature values• Surface vs bulk residual stress state relationships was identified and validated

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Articles you may be interested inGrain and the concomitant ferroelectric domain size dependent physical properties of Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics fabricated using powders derived from oxalate precursor route Yttria Stabilised Zirconia (YSZ) is a tough, phase-transforming ceramic that finds use in a wide range of commercial applications from dental prostheses to thermal barrier coatings. Micromechanical modelling of phase transformation can deliver reliable predictions in terms of the influence of temperature and stress. However, models must rely on the accurate knowledge of single crystal elastic stiffness constants. Some techniques for elastic stiffness determination are well-established. The most popular of these involve exploiting frequency shifts and phase velocities of acoustic waves. However, the application of these techniques to YSZ can be problematic due to the micro-twinning observed in larger crystals. Here, we propose an alternative approach based on selective elastic strain sampling (e.g., by diffraction) of grain ensembles sharing certain orientation, and the prediction of the same quantities by polycrystalline modelling, for example, the Reuss or Voigt average. The inverse problem arises consisting of adjusting the single crystal stiffness matrix to match the polycrystal predictions to observations. In the present model-matching study, we sought to determine the single crystal stiffness matrix of tetragonal YSZ using the results of timeof-flight neutron diffraction obtained from an in situ compression experiment and Finite Element modelling of the deformation of polycrystalline tetragonal YSZ. The best match between the model predictions and observations was obtained for the optimized stiffness values of C11 ¼ 451, C33 ¼ 302, C44 ¼ 39, C66 ¼ 82, C12 ¼ 240, and C13 ¼ 50 (units: GPa). Considering the significant amount of scatter in the published literature data, our result appears reasonably consistent. V C 2014 AIP Publishing LLC. [http://dx.

The high failure rate of the Yttria Partially Stabilized Zirconia (YPSZ)-porcelain interface in dental prostheses is influenced by the micro-scale mechanical property variation in this region. To improve the understanding of this behavior, micro-scale fracture toughness profiling by nanoindentation micropillar splitting is reported for the first time. Sixty 5 μm diameter micropillars were machined within the first 100 μm of the interface. Berkovich nanoindentation provided estimates of the bulk fracture toughness of YPSZ and porcelain that matched the literature values closely. However, the large included tip angle prevented precise alignment of indenter with the pillar center. Cube corner indentation was performed on the remainder of the pillars and calibration between nanoindentation using different tip shapes was used to determine the associated conversion factors. YPSZ micropillars failed by gradual crack propagation and bulk values persisted to within 15 μm from the interface, beyond which scatter increased and a 10% increase in fracture toughness was observed that may be associated with grain size variation at this location. Micropillars straddling the interface displayed preferential fracture within porcelain parallel to the interface at a location where nano-voiding has previously been observed and reported. Pure porcelain micropillars exhibited highly brittle failure and a large reduction of fracture toughness (by up to ~90%) within the first 50 μm of the interface. These new insights constitute a major advance in understanding the structure-property relationship of this important bi-material interface at the micro-scale, and will improve micromechanical modelling needed to optimize current manufacturing routes and reduce failure.

Objectives: Residually strained porcelain is influential in the early onset of failure in Yttria Partially Stabilised Zirconia (YPSZ)porcelain dental prosthesis. In order to improve current understanding it is necessary to increase the spatial resolution of residual strain analysis in these veneers. Methods: Few techniques exist which can resolve residual stress in amorphous materials at the microscale resolution required. For this reason, recent developments in Pair Distribution Function (PDF) analysis of X-ray diffraction data of dental porcelain have been exploited. This approach has facilitated high-resolution (70 µm) quantification of residual strain in a YPSZ-porcelain dental prosthesis. In order to cross-validate this technique, the sequential ring-core focused ion beam and digital image correlation approach was implemented at a step size of 50 µm. This semidestructive technique exploits microscale strain relief to provide quantitative estimates of the near-surface residual strain. Results: The two techniques were found to show highly comparable results. The residual strain within the veneer was found to be primarily tensile, with the highest magnitude stresses located at the YPSZ-porcelain interface where failure is known to originate. Oscillatory tensile and compressive stresses were also found in a direction parallel to the interface, likely to be induced by the multiple layering used during fabrication.