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Haptic rendering enables people to touch, perceive, and manipulate virtual objects in a virtual environment. Using six cascaded identical hollow disk electromagnets and a small permanent magnet attached to an operator's finger, this paper proposes and develops an untethered haptic interface through magnetic field control. The concentric hole inside the six cascaded electromagnets provides the workspace, where the 3D position of the permanent magnet is tracked with a Microsoft Kinect sensor. The driving currents of six cascaded electromagnets are calculated in real-time for generating the desired magnetic force. Offline data from an FEA (finite element analysis) based simulation, determines the relationship between the magnetic force, the driving currents, and the position of the permanent magnet. A set of experiments including the virtual object recognition experiment, the virtual surface identification experiment, and the user perception evaluation experiment were conducted to demonstrate the proposed system, where Microsoft HoloLens holographic glasses are used for visual rendering. The proposed magnetic haptic display leads to an untethered and non-contact interface for natural haptic rendering applications, which overcomes the constraints of mechanical linkages in tool-based traditional haptic devices. [ABSTRACT FROM AUTHOR]

SUMMARY: Rendering of rigid objects with high stiffness while guaranteeing system stability remains a major and challenging issue in haptics. Being a part of the haptic system, the behavior of human operators, represented as the mechanical impedance of arm, has an inevitable influence on system performance. This paper first verified that the human arm impedance can unconsciously be modified through imposing background forces and resist unstable motions arising from external disturbance forces. Then, a reliable impedance tuning (IT) method for improving the stability and performance of haptic systems is proposed, which tunes human arm impedance by superimposing a position-based background force over the traditional haptic workspace. Moreover, an adaptive IT algorithm, adjusting the maximum background force based on the velocity of the human arm, is proposed to achieve a reasonable trade-off between system stability and transparency. Based on a three-degrees-of-freedom haptic device, maximum achievable stiffness and transparency grading experiments are carried out with 12 subjects, which verify the efficacy and advantage of the proposed method. [ABSTRACT FROM AUTHOR]

As a rare earth hexaaluminate, LaMgAl 11 O 19 (LMA) has been one of the most promising materials used as thermal barrier coatings (TBCs). A large amount of amorphous phase, however, often exists in the plasma-sprayed LMA coating and significantly reduces the service lifetime of TBCs. In this study, La 1- x Gd x MgAl 11 O 19 (x = 0, 0.2, 0.4, 0.6, and 0.8) ceramic powders are synthesised by solid-state reaction, and all of these powders are employed to prepare the corresponding coatings. The phase compositions and microstructures of samples are examined by X-ray diffraction and scanning electron microscopy, respectively. The linear thermal expansion behaviour and thermal cycling behaviour of the coatings are also analysed. The results show that the amorphous phase content is decreased and the thermal expansion behaviour is improved by doping the coatings with Gd 2 O 3. The thermal cycling lifetime of the coating, however, basically remains unchanged. [ABSTRACT FROM AUTHOR]

Atmospheric plasma-sprayed (APS) coatings have a layered structure as well as lower strain tolerance and a shorter lifetime than EB-PVD coatings. In this study, TBCs composed of a LaMgAl 11 O 19 (LMA) top coat and a NiCrAlY bond coat were prepared by APS coupled with dry-ice blasting to implant vertical microcracks in the top coat. The thermal cycling lifetime and CMAS corrosion behaviour of LMA-TBCs with pre-implanted vertical microcracks were investigated in detail. The results show that the LMA top coat possesses an improved proportion of vertical microcracks and that the corresponding TBC has an improved thermal cycling lifetime. The vertical microcracks in the top coats, which not only reduce the thermal stress but also improve the strain tolerance of TBCs, dramatically contribute to the improvement in the thermal cycling lifetime. Surprisingly, the CMAS corrosion resistance of LMA-type TBCs with implanted vertical microcracks is better than that of conventional TBCs with a typical layered structure. [ABSTRACT FROM AUTHOR]

ZrO 2 co-stabilized by CeO 2 and TiO 2 with stable, nontransformable tetragonal phase has attracted much attention as a potential material for thermal barrier coatings (TBCs) applied at temperatures > 1200 °C. In this study, ZrO 2 co-stabilized by 15 mol% CeO 2 and 5 mol% TiO 2 (CTZ) and CTZ/YSZ (zirconia stabilized by 7.4 wt% Y 2 O 3 ) double-ceramic-layer TBCs were respectively deposited by atmospheric plasma spraying. The microstructures, phase stability and thermo-physical properties of the CTZ coating were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric-differential scanning calorimeter (TG-DSC), laser pulses and dilatometry. Results showed that the CTZ coating with single tetragonal phase was more stable than the YSZ coating during isothermal heat-treatment at 1300 °C. The CTZ coating had a lower thermal conductivity than that of YSZ coating, decreasing from 0.89 W m −1 K −1 to 0.76 W m −1 K −1 with increasing temperature from room temperature to 1000 °C. The thermal expansion coefficients were in the range of 8.98 × 10 −6 K −1 – 9.88 ×10 −6 K −1 . Samples were also thermally cycled at 1000 °C and 1100 °C. Failure of the TBCs was mainly a result of the thermal expansion mismatch between CTZ coating and superallloy substrate, the severe coating sintering and the reduction-oxidation of cerium oxide. The thermal durability of the TBCs at 1000 °C can be effectively enhanced by using a YSZ buffer layer, while the thermal cycling life of CTZ/YSZ double-ceramic-layer TBCs at 1100 °C was still unsatisfying. The thermal shock resistance of the CTZ coating should be improved; otherwise the promising properties of CTZ could not be transferred to a well-functioning coating. [ABSTRACT FROM AUTHOR]

In this study, perovskite-type SrCeO 3 was proposed and investigated as a novel thermal barrier coating (TBC) material for applications above 1200 °C. Results indicated that SrCeO 3 has a low thermal conductivity, decreasing from 2.84 W/(m⋅K) to 1.74 W/(m⋅K) with increasing temperatures from room temperature to 800 °C. The thermal expansion coefficients are in a range of 9.67 × 10 −6 K −1 -10.6 × 10 −6 K −1 , which are comparable to those of the traditional yttria stabilized zirconia (YSZ). The results of thermogravimetric-differential scanning calorimeter (TG-DSC) analyses and long-term annealing tests indicated that SrCeO 3 has excellent phase stability from room temperature to 1300 °C. The above merits suggested that SrCeO 3 has a good potential for TBC applications at temperatures higher than 1200 °C. Therefore, plasma sprayed SrCeO 3 coating was further produced and characterized. However, coated samples failed very early during thermal cycling. The low fracture toughness (1.09 MPa m 1/2 ), high sintering activity and coating composition deviation are deemed to be the major factors which lead to the early spallation of SrCeO 3 coating. Finally, methods for the improvement of the thermal shock life of SrCeO 3 TBC were proposed. [ABSTRACT FROM AUTHOR]

In this study, LaMgAl 11 O 19 (LMA) thermal barrier coatings (TBCs) were deposited by atmospheric plasma spraying with different spraying powers. The effects of spraying power on the amorphous phase content, microstructure and porosity of the coatings were investigated using X-ray diffraction and scanning electron microscopy. The thermal expansion behavior, microhardness and bonding strength of the coatings were also studied. Results indicated that the amorphous phase content of the coatings increased with the spraying power increasing, while the porosity of the coatings exhibited an opposite trend. Coating with high amorphous phase content suffered large volume shrinkage and exhibited low thermal expansion coefficient (TEC). Bonding strength and microhardness of the coatings increased with the spraying power increasing from 22 to 32 kW and then decreased from 32 to 42 kW. Thermal cycling behavior of LMA coatings at 1100 °C was also investigated. Spallation of the TBCs was mainly correlated with the formation of thermally grown oxides and mismatch of TECs between the topcoat and the substrate, which were influenced by the microstructure and the amorphous phase content of the coatings. The longest lifetimes were achieved on LMA coating deposited at 32 kW, owing to its relatively low amorphous phase content and the highest bonding strength. [ABSTRACT FROM AUTHOR]

Plasma sprayed coatings were fabricated from nanostructured yttria-stabilized zirconia powders (n-YSZ) with different crystalline grain sizes, prepared via sintering of nano ZrO 2 -4 mol% Y 2 O 3 powders at different temperatures. The hot corrosion behaviour of both n-YSZ powders and their corresponding coatings with sodium metavanadate (NaVO 3 ) were investigated at 700 °C. During hot corrosion, NaVO 3 reacts with Y 2 O 3 in YSZ to form YVO 4 , leading to a tetragonal to monoclinic destructive phase transformation of YSZ. The crystalline grain size of n-YSZ powders did not affect the hot corrosion mechanisms of both the n-YSZ powders and their corresponding coatings. However, compared with n-YSZ powders, the coatings were more easily corroded, and the coatings formed from starting powders with crystalline grain sizes <30 nm featured better degradation resistance to hot corrosion. [ABSTRACT FROM AUTHOR]

Graphical abstract Two stages are involved in SrCeO 3 under V 2 O 5 attack: the first stage involves a dissolve-precipitation process and the subsequent involves a grain boundary attack process with Sr2+ leaching out from SrCeO 3 grains. Highlights • At 700 °C or 900 °C, V 2 O 5 reacted with SrCeO 3 ceramic to form Sr 2 V 2 O 7 , CeO 2 and CeVO 4. • At 1250 °C, the main corrosion products were Sr 3 V 2 O 8 and CeO 2. • The corrosion zone comprised of several regions, each with a different composition. • The hot corrosion mechanism was explained by phase diagram and lewis acid-base rule. • A model describing the formation of the corrosion zone was established. Abstract Hot corrosion behaviour of SrCeO 3 ceramic in molten V 2 O 5 was studied at 700–1250 °C. Sr 2 V 2 O 7 , CeO 2 and CeVO 4 were the main reaction products at 700 °C and 900 °C, while only Sr 3 V 2 O 8 and CeO 2 can be detected at 1250 °C. The corrosion zone was divided into several layers. Both the structure and composition of the corrosion zones were dependent on the corrosion temperature. The microstructure of corrosion zone appeared to have evolved in two major stages, including a first dissolve-precipitation process and a subsequent grain boundary attack process. Finally, a model describing the formation of the corrosion layer was established. [ABSTRACT FROM AUTHOR]

The wear resistance of chromium oxide (Cr 2 O 3 ) coatings could be improved by doping modification and changing the structural scale, etc. In this study, micrometric Cr 2 O 3 coatings were doped with different additives, CeO 2 and Nb 2 O 5 . Moreover, Cr 2 O 3 coatings were deposited from nanostructured feedstock by the combination process of plasma spraying and dry-ice blasting. The correlation between the microstructure, chemical components and tribological properties of plasma-sprayed Cr 2 O 3 -based coatings was discussed based on the investigation of their porosity, hardness and friction behaviors. The results showed that the composite coatings doped with additives exhibited a higher microhardness, corresponding to a lower porosity than pure Cr 2 O 3 coating under the identical plasma-spray condition. CeO 2 constituent was found to improve the wear resistance of Cr 2 O 3 coating while Nb 2 O 5 incorporation corresponds to a steep rise in the friction coefficient. The mismatch of coefficient of thermal expansion (CTE) between Cr 2 O 3 and Nb 2 O 5 lamellae facilitated the origin of fatigue cracks and the formation of microfracture pits. Although the combination process promotes a porosity reduction, the nanostructured Cr 2 O 3 (n-Cr 2 O 3 ) coatings present a lower microhardness than micrometric coatings, due to their loosen microstructure from insufficient plasma power compared to microscaled coatings. The wear mechanisms of both the micro- and nanometric Cr 2 O 3 coatings are fatigue cracks and material transfer. [ABSTRACT FROM AUTHOR]

Calcium-magnesium-alumino-silicate (CMAS) attack is a significant failure mechanism for thermal barrier coatings (TBC). In this study, La 2 (Zr 0.7 Ce 0.3 ) 2 O 7 (LZ7C3) TBC prepared by electron-beam physical vapor deposition was found to be highly effective in resisting CMAS infiltration for prolonged durations (24 h, 1250 °C), while conventional Y 2 O 3 -stabilized ZrO 2 TBC was completely penetrated by molten CMAS within 30 min. This resistance was achieved through crystallization of CMAS as a result of high-temperature chemical interactions between LZ7C3 coating and CMAS glass. The crystalline products, mainly consisted of La-Ce apatite and C-ZrO 2 , tended to form a sealing layer and can effectively prevent CMAS from further infiltration. [ABSTRACT FROM AUTHOR]