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Recent studies into the origins of failure of yttria partially stabilised zirconia–porcelain veneered prosthesis have revealed the importance of micro-to-nano scale characterisation of this interface zone. Current understanding suggests that the heat treatment, residual stresses and varying microstructure at this location may contribute to near-interface porcelain chipping. In this study the chemical, microstructural and mechanical property variation across the interfacial zone has been characterised at two differing length scales and using three independent techniques; energy dispersive X-ray spectroscopy, transmission electron microscopy and micropillar compression. Energy dispersive X-ray spectroscopy mapping of the near-interface region revealed, for the first time, that the diffusional lengths of twelve principal elements are limited to within 2–6 μm of the interface. This study also revealed that 0.2–2 μm diameter zirconia grains had become detached from the bulk and were embedded in the near-interface porcelain. Transmission electron microscopy analysis demonstrated the presence of nanoscale spherical features, indicative of tensile creep induced voiding, within the first 0.4–1.5 μm from the interface. Within zirconia, variations in grain size and atomistic structure were also observed within the 3 μm closest to the interface. Micropillar compression was performed over a 100 μm range on either side of the interface at the spatial resolution of 5 μm. This revealed an increase in zirconia and porcelain loading modulus at close proximities (< 5 μm) to the interface and a decrease in zirconia modulus at distances between 6 and 41 μm from this location. The combination of the three experimental techniques has revealed intricate details of the microstructural, chemical and consequently mechanical heterogeneities in the YPSZ–porcelain interface, and demonstrated that the length scales typically associated with this behaviour are approximately ± 5 μm. [ABSTRACT FROM AUTHOR]

We report a fluxing technique for ZrMo 2 O 8 single crystal growth. The volatility of MoO 3 coupled with the limited temperature range of its stability with the liquid phase makes the single crystal growth of ZrMo 2 O 8 a formidable challenge. Single crystal growth of ZrMo 2 O 8 was carried out in a horizontal tubular furnace using a platinum boat and utilizing Li 2 MoO 4 as a fluxing agent. The synthesized faceted crystals were up to 3 mm along the maximum dimension. Laue and single crystal X-ray diffraction confirmed the monoclinic crystal structure having a space group C 1 2/c 1 (S.G#15), and a single crystallographic domain within the crystals. Reduced elastic modulus and hardness were determined to be 108±4 GPa and 6.4±0.2 GPa respectively using nanoindentation. Appearance of additional peaks in Raman spectra of the indented region when compared with the fresh crystal indicated a possible pressure induced phase transformation during indentation. [ABSTRACT FROM AUTHOR]

Abstract: ZrW2O8 is known for its isotropic negative thermal expansion over a wide of range of temperature from −272 to 777°C. However, ZrW2O8 melts incongruently at 1257°C and is stable only over a short temperature interval between 1105 and 1257°C. This makes the growth of single crystals a formidable challenge. In order to study the intrinsic properties of this compound, a repeatable, viable single crystal growth strategy is required. Here we report a simple, self-seeding, self-fluxing single crystal growth process which resulted in single crystals of ZrW2O8 up to about 4mm in size. Grown crystals were characterized by X-ray diffraction (XRD), Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. Mechanical properties of the crystals were studied using nanoindentation. [Copyright &y& Elsevier]

Abstract: Statistical design of experiments was used to investigate the effect the process parameters on electrophoretic deposition (EPD) of alumina onto steel substrates from its suspension in iso-propanol. The process parameters considered were (i) concentration of particles in the suspension (solid loading), (ii) electrode separation, (iii) applied potential, and (iv) deposition time on the quantity of ceramic particles electrophoretically deposited. A 24 full factorial matrix, with four repetitions of the center point, was used to develop the predictive regression equation for deposition of alumina per unit area of the electrode in the design space. The results show that particle concentration has the most dominant effect with more than 50% contribution to the deposited amount. A good correlation was obtained between predicted and experimental values suggesting that the model can predict data accurately in the experimental matrix. [Copyright &y& Elsevier]

Mechanical size effects are a well known phenomenon when the sample volume is reduced or the characteristic length of the microstructure is changed. While size effects in micropillar compression (smaller is stronger) or due to grain refinement (Hall-Petch) are well understood, this is less so in fracture mechanics. Given this lack of knowledge, the main question addressed in this work is: What happens to the fatigue crack growth properties when extrinsic size effects play a role? To answer this question, nanocrystalline nickel cantilevers, ranging in width from 5 to ▪, were subjected to fatigue crack growth. The crack growth rates and stress intensity factors were calculated and the Paris exponent in the stable crack growth regime was determined. It was found that the results scatter more strongly for the smaller cantilevers compared to the larger cantilevers. Results are interpreted in terms of plastic zone size and ligament size which are found to be critical for small cantilevers. • Scatter of Paris Exponents increases with decreasing microcantilever dimensions. • Differences in the extent of grain growth are associated with the different stages of fatigue crack initiation and growth. • Fatigue pre-crack ensures consistent crack growth experiments in ductile samples. [ABSTRACT FROM AUTHOR]

In situ mechanical testing in combination with direct observation and analysis holds the key to enhanced understanding of deformation mechanisms in materials. Due to its high precision, good spatial resolution and practicality in scanning electron microscopes, electron backscatter diffraction is a powerful technique for probing the surface of crystalline materials. This paper reports in situ micro-cantilever experiments on single crystal tungsten performed inside a scanning electron microscope in combination with high angular resolution electron backscatter diffraction. The evolution of stresses reaching values in the GPa range, as well as the distribution of geometrically necessary dislocations were analysed in the loaded state, revealing the details of deformation behaviour. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fracture behaviour of BaTiO3 thin film attached to different substrates were studied using microcantilever facture experiments. • These experiments revealed a significant effect of the substrate elastic modulus on the fracture toughness of the films. • Increase in fracture toughness of the bi-layered system was found as the crack tip approach the film-substrate interface. • Presence of ductile interface shielded the crack tip and changed the crack trajectory. • These measurements provide a template for design of thin films with increased fracture resistance. Damage tolerance of a thin film attached to a substrate is dependent on several parameters such as film thickness, film orientation, residual stresses, nature of interfaces, microstructure and defects present. Here we study the fracture resistance and crack growth trajectory in BaTiO 3 thin films attached to elasticially stiff substrates using micromechanical experiments and finite element modeling. Microcantilever fracture tests are carried out on bi-layered systems of BaTiO 3 film on Pt-Si and SrTiO 3 substrates to study the effect of interfaces, texture and elastic mismatch on fracture toughness. The substrates in the bi-layers are chosen to force the crack to experience a shielding effect in terms of a decrease in the crack driving force. Experiments revealed an unexpectedly large increase in fracture toughness when the crack tip is closer to a stiffer substrate, qualitatively matching the predictions from the numerical model. The bi-layered films attached to the substrate showed 125% (on Pt-Si) and 160% (on SrTiO 3) increase in fracture toughness compared to the free-standing films, for the first time, revealing the significant effect of elastic modulus of the substrate on improving the fracture resistance at such micrometer length scales. [ABSTRACT FROM AUTHOR]

Alumina (Al 2 O 3) remains one the most important engineering ceramic for industrial applications. In addition to the α phase, transition alumina phases have interesting characteristics. Controlling the obtained phase structure from alumina melt requires processes with extreme cooling rates and therefore limits the tailoring capabilities. This study investigates how the cooling rate of pure alumina affects its microstructural properties and phase structure in plasma-based processing. The paper reports phase changes in micron sized granulated alumina particles in high-temperature plasma spheroidization and compares the results to plasma sprayed alumina coatings. Both plasma processes involve melting of the material followed by subsequent rapid cooling. Direct comparison on the alumina phase transitions is obtained for the two methodically distinct processing routes, creating unique microstructures due to difference in their cooling rates. • Alumina properties can be adjusted by controlling the cooling rate in melt quenching. • The alumina phase structure can be reprogrammed to fit a specific application. • Plasma spheroidization allows a new way to study the intermediate phases in alumina. [ABSTRACT FROM AUTHOR]

The stress required to activate twinning of the longitudinal < 11 2 ¯ ] { 111 } system in the lamellar γ-TiAl phase of the alloy Ti-45Al-2Nb-2Mn (at.%)-0.8 vol.% TiB 2 was measured at several temperatures up to 700 °C by in situ micropillar compression of soft mode oriented γ-TiAl/α 2 -Ti 3 Al lamellar stacks. The lamellae undergoing deformation twinning were identified by electron backscatter diffraction orientation mapping. In some cases, such lamellae were not constrained by domain or colony boundaries and longitudinal twinning was the only deformation mechanism observed based on digital image correlation strain maps. The resolved shear stress for such unconstrained twinning was found to increase monotonically with temperature from 25 °C to 700 °C. This is consistent with the stacking fault energy increasing with temperature as found in many metallic alloys, suggesting that the increased ease of deformation twinning at high temperature in bulk TiAl alloys is due to the increased ease with which the twinning shear can be accommodated by the neighbouring domains and lamellae with increasing temperature, rather than a thermal softening of the intrinsic twinning mechanism. [ABSTRACT FROM AUTHOR]

Gadolinium doped ceria is a well-known oxygen ion conduction material for solid fuel cell electrolytes. With its centrosymmetric average lattice and relatively low bulk dielectric constant it does not look interesting for electromechanical applications. However, a giant electrostriction (ES) effect was recently found in Ce 0.8 Gd 0.2 O 2−x thin films. It was explained by the dynamic response of oxygen vacancies to an external electric field. In this work, the giant ES response has been reproduced in sputter deposited thin films. The proper transverse bulk ES coefficient has been derived from the measured clamped value. For this purpose, the Young's modulus was measured by nanoindentation. The highest ES coefficient was found as 9.0 × 10 −19 (m/V) 2 for the strain coefficient, and 2.3 × 10 −7 N/V 2 for the effective stress coefficient. Specific growth conditions must be chosen in order to obtain a microstructure exhibiting the giant ES effect. There is evidence for a higher oxygen deficiency than needed to compensate the gadolinium dopants (Gd’). It was observed that the nature of the bottom electrode impacts on the size of the effect. The highest response was obtained at films grown on Al bottom electrodes. To learn more on the mechanisms of the giant ES effect, a bipolar cycling was performed to test the delay time for the ionic reorientation in changing the sign of polarization, as observed in the stress loop. The maximal response was observed below 100 Hz in this bipolar mode, showing that the time for 180° reorientation amounts to several milliseconds. [ABSTRACT FROM AUTHOR]

[Display omitted] • The research novelty lies in evaluating the tribological and biological properties of Nickel Free Stainless Steel (NiFSS) produced through laser bed powder diffusion for metals (PBF-LB/M) additive manufacturing. • Optimized process parameters for PBF-LB/M fabrication of NiFSS resulted in samples with a relative density of 98.469% and fully ferritic microstructure in the as-built state. • Tribological experiments assessed NiFSS at constant load and sliding speed using an automated Bio-Tribometer, showing promising friction coefficients and wear rates relevant to implant applications. • NiFSS exhibited reduced Coefficient of Friction and wear rates compared to PBF-LB/M built austenitic 316L SS, attributed to its superior hardness and elastic modulus. • Biocompatibility testing with pre-osteoblastic MC3T3-E1 cells indicated better cell viability on PBF-LB/M built NiFSS compared to PBF-LB/M built 316L SS. • The present study suggests the potential of PBF-LB/M fabricated NiFSS for use in biomedical devices, particularly in joint arthroplasty applications. Due to the risk of releasing carcinogenic nickel ions from conventional 316L stainless steel under a corrosive human body environment, a new variant of steel termed nickel-free stainless steel (NiFSS) has been investigated. The present study investigates the tribological properties and biocompatibility of NiFSS manufactured via laser powder bed fusion (PBF-LB/M). The ferritic NiFSS exhibited significantly lower coefficient of friction (0.08 to 0.28) and wear rate (1.60 × 10-6 mm3/Nm to 6.60 × 10-6 mm3/Nm) compared to reported values for austenitic 316L SS, under both dry and simulated body fluid (SBF) conditions and various sliding geometries. This improvement is attributed to the superior hardness (3.394 ± 0.1340 GPa) and elastic modulus (238 ± 9.0797 GPa) of NiFSS. To assess the biocompatibility, the viability of mouse pre-osteoblastic MC3T3-E1 cells was evaluated with an Alamar Blue assay when the cells were cultured on top of PBF-LB/M built NiFSS and 316L SS samples. The results indicated that even though cell growth was most optimal on regular cell culture plastic, cell viability was better maintained on PBF-LB/M built NiFSS compared to 316L SS. Therefore, the results of the present study propose that PBF-LB/M fabricated NiFSS holds promise for application in biomedical devices for joint arthroplasty. [ABSTRACT FROM AUTHOR]

This paper studied the formation mechanism of white layer of a next generation nickel-based superalloy formed under severe plastic deformation induced by a mechanical material removal process. A graded microstructure of the white layer in the nickel-based superalloy has been revealed for the first time, which is composed of (i) a "dynamic recrystallisation" layer formed by nanocrystalline (∼200 nm) grains at the vicinity of the surface and (ii) a "dynamic recovery" layer with subgrain microstructures extending further into the subsurface. The mechanism of surface grain refinement was identified based on the results obtained via crystallographic and chemical analysis, as well as in-situ micro-mechanics experiments in the scanning electron microscope. It is found that in the top surface layer not only grain refinement but also the γ′ phase dissolution occurs, changing drastically from the bulk material. Furthermore, it is shown how the high plastic strain and cutting temperature along the subsurface causes grain refinement in the white layer and grain elongation in the subsurface. The γ′ precipitates in the recrystallisation layer are dissolved during the machining process, while the ultra-high cooling rate suppresses the further precipitation of this phase, resulting in the supersaturation of γ grains or minimized γ′ precipitates in the top surface layer. Hence, the grain refinement does not result in an increase of mechanical stiffness but a deterioration of mechanical properties due to the dissolution of the strengthening phase γ', which leads to a lower strength and increased ductility. Machining is generally treated as a cold-working process. However, according to our findings hot-working with dynamic recrystallisation and recovery, as well as phase evolution, occurs in the white layer of nickel-based superalloys. Image 1 [ABSTRACT FROM AUTHOR]

Abstract The distribution of strain in hard mode oriented lamellar stacks of the two-phase γ-TiAl/α 2 -Ti 3 Al alloy Ti-45Al-2Nb-2Mn (at.%)-0.8 vol% TiB 2 was measured at several temperatures up to 633 °C by in situ micropillar compression, complemented by electron backscatter diffraction orientation mapping and digital image correlation strain mapping of a thermally stable surface Pt speckle pattern. Post-mortem transmission electron microscopy further identified the finest scale deformation structures. It was found that slip and twinning transverse to the lamellae operates within discreet bands that zigzag across the lamellar structure. The shear strain within each band is approximately constant across the pillar width. This is inconsistent with current energetic models for transverse twin formation in γ-TiAl, which assume independent, non-interacting twins. This is explained using a mathematical formulation for the stress required to operate this transverse mechanical twinning as a function of strain. This study has elucidated how the multi-scale combination of several transverse twinning systems on different {111} planes in γ-TiAl lamellae can relieve the elastic stresses generated at a lamellar interface by the primary (highest Schmid factor) twinning system. It is thought that the facilitation of this mechanism will promote the ductilisation of lamellar γ-TiAl alloys. This is crucial for an increased damage tolerance and ease of component manufacture, leading to a more widespread use of γ-TiAl alloys. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract The occurrence of plasticity below the macroscopic yield stress during tensile monotonic loading of nearly lamellar Ti-45Al-2Nb-2Mn(at%)-0.8 vol% TiB 2 at both 25 °C and 700 °C, and in two conditions of lamellar thickness, was measured by digital image correlation strain mapping of a remodelled Au surface speckle pattern. Such initial plasticity, not necessarily related to the presence of common stress concentrators such as hard particles or cracks, could occur at applied stresses as low as 64% of the general yield stress. For a same applied strain it was more prominent at room temperature, and located as slip and twinning parallel to, and near to or at (respect.) lamellar interfaces of all types in soft mode-oriented colonies. These stretched the full colony width and the shear strain was most intense in the centre of the colonies. Further, the most highly operative microbands of plasticity at specimen fracture were not those most active prior to yielding. The strain mapping results from polycrystalline tensile loading were further compared to those from microcompression testing of soft-mode stacks of lamellae milled from single colonies performed at the same temperatures. Combined with post-mortem transmission electron microscopy of the pillars, the initial plasticity by longitudinal dislocation glide was found to locate within 30–50 nm of the lamellar interfaces, and not at the interfaces themselves. The highly localised plasticity that precedes high cycle fatigue failure is therefore inherently related to the lamellar structure, which predetermines the locations of plastic strain accumulation, even in a single loading cycle. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

[Display omitted] • Metal micropillars were synthesized by template-assisted electrodeposition. • Mechanical testing was performed at cryogenic temperatures and high strain rates. • Structure-property relationships were identified for a large range of conditions. • The deformation mechanism was identified to be collective dislocation nucleation. • 3D Microlattices showcase the promise of the method for complex microarchitectures. Template-assisted electrodeposition is a promising microscale additive manufacturing technique allowing to deposit pure metals with high resolution. To allow the application-relevant design of metamaterials, it is necessary to establish microstructure-mechanical property relationships under extreme conditions. In this work, a novel process based on two-photon lithography was used to synthesize arrays of nanocrystalline nickel micropillars and complex microlattices. This allowed high throughput mechanical testing using a newly developed in situ nanoindenter at unprecedented combination of cryogenic temperatures (160 to 300 K) and strain rates (0.001 to 500 s−1). Strain rate sensitivity was found to increase from ∼ 0.004 at 300 K to ∼ 0.008 at 160 K. Thermal activation analysis showed a decrease in activation volume from 122b3 at 300 K to 45b3 at 160 K and an activation energy of 0.59 eV in line with collective dislocation nucleation as the rate limiting mechanism. Transmission Kikuchi Diffraction allowed quantifying microstructural changes during deformation. As such, a deformation map along with the responsible deformation mechanisms has been ascertained for additively micromanufactured nanocrystalline nickel at unique combinations of extreme temperatures and strain rates. Further, rate-dependent compression of microlattices and complementary finite element simulations using the results from micropillars as constitutive models exemplified the promise of such metal microarchitectures in space and aviation applications. [ABSTRACT FROM AUTHOR]