Effect Of Thermal Mismatch Research Articles

Effect of Thermal Mismatch on Fracture Characteristics of Porcelain Veneered Lithia-Based Disilicate Posterior Ceramic Crown

(1) Background: Dental glass–ceramics shrink during crystallization, complicating restoration manufacturing. Thermo-pressure molding was introduced to address this, with lithium disilicate crystals providing high strength. Residual tensile stresses can influence the chipping strength of single tooth crowns. (2) Methods: Insync dentine was layered onto three lithia-based disilicate core ceramics (Amber Press, IPS e.max Press) for microtensile bond strength tests. The Vickers test assessed the residual tensile stress and interfacial bonding. Porcelain-veneered posterior ceramic crowns were fabricated and subjected to axial loading, measuring fracture loads (three per group). (3) Results: A chemical bonding layer formed at the interface, which was thicker in the Insync-IPS e.max Press and increased with more firings. The ultimate tensile bond strength was 28.5 MPa for the four-times-fired Insync-Amber Press, similar to the twice-fired Insync-IPS e.max Press. No residual tensile stress was found in the Insync-Amber Press; the Insync-IPS e.max Press showed crack growth within 250 μm of the bonded interface. The average fracture resistance was twice as high for the Insync-Amber Press. (4) Conclusions: The Insync-Amber Press exhibited better thermal harmony with no crack growth, while the IPS e.max Press showed crack growth due to residual tensile stress. Insync-Amber Press posterior ceramic crowns had significantly greater fracture resistance than Insync-IPS e.max Press crowns.

The effect of boron anomaly on the dielectric properties and thermal expansion of barium borosilicate glasses for 3D packaging systems

Barium borosilicate (BBS) glass is a potential three-dimensional system packaging and sensor cover material. In this study, we prepared glass samples with different SiO2/B2O3 ratios based on the revised model of Dell and Bray and discussed the effect of boron anomaly on dielectric and thermal properties through Raman spectroscopy. The results indicate that the [BO4] tetrahedrons are beneficial in reducing the dielectric constant and dielectric loss to a certain extent, while the improvement in the coefficient of thermal expansion (CTE) is attributed to the depolymerization of the glass network by the [BO3] triangles. After the disappearance of the boron anomaly, a certain amount of dielectric performance is sacrificed in exchange for an increase in the CTE. When the substitution rate of B2O3 for SiO2 reaches 15.12 mol%, the CTE of the sample increases to 8.43 × 10−6/°C, in addition, the dielectric constant and dielectric loss decrease to 4.90 and 0.0071 (@1 GHz), respectively. In summary, this work provides a suitable method for preparing glass with a high coefficient of expansion and low dielectric loss to address the thermal mismatch effect of different materials in electronic packaging systems.

Design, Modeling, and Experimental Validation of an Active Microcatheter Driven by Shape Memory Effects.

Microcatheters capable of active guidance have been proven to be effective and efficient solutions to interventional surgeries for cardiovascular and cerebrovascular diseases. Herein, a novel microcatheter made of two biocompatible materials, shape memory alloy (SMA) and polyethylene (PE), is proposed. It consists of a reconfigurable distal actuator and a separate polyethylene catheter. The distal actuator is created via embedding U-shape SMA wires into the PE base, and its reconfigurability is mainly dominated by the shape memory effect (SME) of SMA wires, as well as the effect of thermal mismatch between the SMA and PE base. A mathematical model was established to predict the distal actuator's deformation, and the analytical solutions show great agreement with the finite element results. Structural optimization of such microcatheters was carried out using the verified analytical model, followed by fabrication of some typical prototypes. Experimental testing of their mechanical behaviors demonstrates the feasibility of the structural designs, and the reliability and accuracy of the mathematical model. The active microcatheter, together with the prediction model, will lay a solid foundation for rapid development and optimization of active navigation strategies for vascular interventions.

Fatigue behaviour analysis of thermal cyclic loading for through-silicon via structures based on backstress stored energy density

Through-silicon via (TSV) structures are widely used in microelectronic due to the ease of chip interconnection. Few research has focused on investigating the fatigue properties of TSV structures using crystal plasticity finite element (CPFE) simulations. As the process of TSV structures approaches the micron scale, the effects of anisotropic microstructure and grain size on their fatigue behaviours will become necessary. The present work aims to use CPFE simulations to investigate the fatigue properties of TSVs at the microscale. Finite element models with realistic EBSD morphology and orientation are established for four TSV structures with different grain sizes, and CPFE simulations with thermal cyclic loading from −55℃ to 125℃ are performed. From the energy point of view, the stored energy density based on backstress and strain gradient is proposed as a fatigue indicator parameter (FIP). CPFE simulation results show that low-angle grain boundaries (LAGBs) and high-angle grain boundaries (HAGBs) dominate crack initiation at the top, bottom or edges of the TSV structure, which is still mainly due to the thermal mismatch effect caused by the difference in the coefficients of thermal expansion of the materials. The crack initiation in the internal structure is mainly caused by symmetric grains containing twin boundaries (TBs), or trigrain boundaries, and this is different from the macroscopic simulations. Combined with the local FIPs concentration distribution, the backstress stored energy density is able to capture more details than the cumulative plastic strain because of its direct correlation with the strain gradient, and validates its effectiveness as a FIP.

Effect of B4C particle size and TiB2 content on the mechanical properties of B4C composites and their dynamic mechanical properties

AbstractB4C–MAS and B4C–TiB2–MAS ceramic composites were prepared by hot pressed sintering. The effects of particle size of B4C and TiB2 content on the microstructure and general mechanical properties of the ceramic composites were investigated by using X‐ray diffractometer, scanning electron microscope, and universal testing machine. The strengthening and toughening mechanism of ceramic composites is mainly attributed to the addition of magnesium–aluminosilicate (MAS) and thermal mismatch effect of TiB2. When the TiB2 content was 20 wt.%, the bending strength, fracture toughness, and Vickers hardness of B4C–TiB2–MAS ceramic composites were 375 MPa, 4.42 MPa·m1/2, and 23.9 GPa, respectively, and its relative density could reach 99.7%. The dynamic mechanical properties of B4C–TiB2–MAS ceramic composites were investigated at strain rates of 2000–6000 s−1 using a Separate Hopkinson Pressure Bar (SHPB) device. The results showed that the B4C–TiB2–MAS ceramic composites exhibited significant strain rate sensitivity. The dynamic compressive strength of the ceramic composites increased from 4634 to 5734 MPa with increasing strain rate in the tested strain rate range.

Mechanism of phase structure modulating damping in Fe73Ga27 alloy

The magnetostriction and damping performance of Fe–Ga alloy are closely related to the phase structure. In this paper, the phase structure of Fe73Ga27 alloy was regulated by homogenization + aging treatment. The results show that the Fe73Ga27 alloy with modified-D03 phase has higher damping performance at lower amplitudes, and the damping peak is nearly 1.3 times that of only solution-treated alloy. The modified-D03 phase with tetragonal structure leads to local tetragonal distortion of the matrix, which enhances the magnetostriction and magneto-mechanical damping. In addition, the presence of the modified-D03 phase also increases the sensitivity of the alloy to stress. The Fe73Ga27 alloy with L12 phase as the main phase has higher damping performance at higher amplitudes. When the amplitude is higher than 3 × 10−4, the damping value is more than 1.6 times that of only solution-treated alloy. The mismatch between the L12 phase and matrix with body-centered cubic structure greatly improves the nonmagnetic damping. The strain mismatch between the L12 phase and the matrix causes interfacial sliding under load to provide interfacial damping. The high-density dislocation due to the thermal mismatch effect enhances dislocation damping.

Tuning high and low thermal expansion coefficients of Li2O–BaO–Al2O3–B2O3–SiO2/quartz LTCC composites by replacing quartz partly with α-Al2O3 or ZrO2

Low-temperature co-fired ceramics (LTCC) with adjustable coefficients of thermal expansion (CTE) based on Li 2 O–BaO–Al 2 O 3 –B 2 O 3 –SiO 2 /quartz LTCC composites (glass/ceramics) have been employed in electronic packaging to address the interface thermal mismatch problem caused by different thermal expansion coefficients. In the present study, sintering behavior, phase structure, and CTE of LTCC composites is controlled by replacing quartz partly with α-Al 2 O 3 or ZrO 2 . Accordingly, LTCC composites with the highest and lowest CTE values are achieved. The results show that the major phases of α-Al 2 O 3 substituted LTCC composites are hexacelsian, β-spodumene, and virgilite. Correspondingly, CTE values are in the range of 5.67–8.62 × 10 −6 /°C. Whereas, ZrO 2 substituted LTCC composites have exhibited increased CTE values to 12.27 to 13.2 × 10 −6 /°C with major phases of cristobalite, hexacelsian, and bazirite. Moreover, the negative effects of phase transformation of hexacelsian can be inhibited to a certain extent upon substitution of α-Al 2 O 3 up to 15 wt%. This work provides suitable methods for preparing LTCC composites with gradient CTE and resolving the thermal mismatch effects at different interfaces (e.g., chip/LTCC, metal electrode/LTCC) in electronic packaging structures.

Highly Sensitive Temperature Sensor Based on Coupled-Beam AlN-on-Si MEMS Resonators Operating in Out-of-Plane Flexural Vibration Modes.

This paper reports a type of highly sensitive temperature sensor utilizing AlN-on-Si resonators with coupled-beam structures of double- and triple-ended-tuning-fork (D/TETF). For both resonators, the out-of-plane flexural mode is adopted as it favors the effect of thermal mismatch between the composite layers inherent to the AlN-on-Si structure and thus helps attain a large temperature coefficient of resonant frequency (TCF). The analytical model to calculate TCF values of D/TETF AlN-on-Si resonators is provided, which agrees well with the finite-element simulation and experimental results. The resonant temperature sensor is built by closing the loop of the AlN-on-Si resonator, a transimpedance amplifier, a low-pass filter, and a phase shifter to form an oscillator, the output frequency of which shifts proportionally to the ambient temperature. The measured sensitivities of the temperature sensors using D/TETF resonators are better than -1000 ppm/°C in the temperature range of 25°C~60°C, showing great potential to fulfill the on-chip temperature compensation scheme for cofabricated sensors.

Improvement in microstructure uniformity and mechanical properties of surface modified graphene reinforced Ni-based composites by laser deposition

Graphene (Gr) is regarded as one of the promising nano reinforcement of metal matrix composites (MMCs) to improve the comprehensive performance owing to its superior physical and mechanical properties recently. However, the agglomeration and survivability at high-temperature of Gr as well as the compatibility between Gr and metal, have severely restricted the application of Gr in MMCs. Herein, the surface modification coupled with a mixing method without ball-milling was employed to protect Gr from the structural damage. Then, the modified Gr (CoFe@Gr) reinforced Ni-based alloy composites were fabricated via laser deposition technique in an argon protective atmosphere. The results showed that the pristine Gr nanosheets were successfully incorporated into composites, but some of them were transformed into the nanospheres while others formed “core-shell” structure with carbides under the high-energy laser irradiation. Compared with alloys adding Gr directly, the addition of CoFe@Gr composite powders not only promoted the uniform distribution of the second phases in matrix phase but also inhibited the generation of the pores defects resulted from the burning of Gr without surface modification. The changes in microstructure contributed to the lower coercivity of composites. Moreover, the micro-hardness and compressive strength values of composites were increased by 12.55% and 45.50% as compared with that of as-deposited alloys, respectively. This was mainly attributed to the improved interface compatibility between Gr and Ni matrix, the thermal mismatch effect and the second phase strengthening effect. This work is expected to provide a technique guidance for Gr reinforced MMCs that the fabrication conditions requiring high temperature.

Microstructure and Properties of SnO2‐rGO Reinforced Copper Matrix Composites Fabricated by Molecular‐Level Mixing Method and Spark Plasma Sintering

Herein, the SnO2‐rGO compound powders are synthesized by reducing the graphene oxide with the SnCl2+HCl solution, and the SnO2‐rGO reinforced Cu matrix composites with uniform microstructure are successfully fabricated via molecular‐level mixing method along with spark plasma sintering. The hardness of the Cu matrix composite increases progressively with more incorporation of SnO2‐rGO content. At 0.1 wt% SnO2‐rGO, the yield strength and tensile strength of the Cu matrix composite are 305 and 350 MPa, which are, respectively, increased by 56% and 43% as compared to pure Cu. When the SnO2‐rGO content is beyond 0.2 wt%, the fractograph of the SnO2‐rGO/Cu bulk composite presents obvious tear ridges, and the fracture mode changes from ductile fracture to brittle fracture. With the introduction of SnO2 nanoparticles, the (Cu, Sn) solid solution formed at the interface between rGO and Cu matrix promotes the interface bonding. The strengthening mechanism of the SnO2‐rGO/Cu bulk composite can be ascribed to the dominant load transfer, supplemented by grain refinement and thermal mismatch effect.

Multilayered microstructures with shape memory effects for vertical deployment

This paper presents a fabrication and characterization of multilayered microstructures with shape memory effects enabling large vertical deployment under electro-thermal actuation. Our previous research demonstrated vertical deployment of such microstructures by the effect of thermal mismatch. Development of equiatomic NiTi layers in the multilayered microstructure is investigated further for shape memory effects. Multilayered microstructures are built by sputtered NiTi layers and a lift-off process. Negative photoresist ma-N1420 enables clean lift-off of 500 nm thick NiTi layers by forming a significant undercut profile after development. The parametric study on co-sputter powers for Ti and Ni50Ti50 targets suggests that 100 W RF on Ti target and 200 W DC on Ni50Ti50 target can deposit Ni49.62Ti50.38 layers. X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM) were used to study the crystal structures and surface topography of NiTi layers. XRD results of post-annealed Ni49.62Ti50.38 layers show coexistence of austenite and martensitic phases at room temperature, suggesting that the transformation temperature of such NiTi layers should be approximate 20 °C. The surface topography of Ni49.62Ti50.38 layers reveals substantial increase of surface roughness at ambient conditions after the annealing. Experimental verification of the multilayered microstructure for vertical deployment was carried out by Signatone Probe Station and Dual Scanning Electron Microscope/Focused Ion Beam (SEM/FIB) system. A vertical deployment of the two-dimensional (2D) multilayered microstructures for three-dimensional (3D) can be detected by applying a constant voltage of 0.04 V, and the expected 3D deployment displacement is enlarged from 2 μm to 10 μm by introducing the shape memory effect.

Thermal Mismatch Effect and High-Temperature Tensile Performance Simulation of Hybrid CMC and Superalloy Bolted Joint by Progressive Damage Analysis

The hybrid CMC and superalloy bolted joints have exhibited great potential to be used as thermostructural components of reusable space transportation systems, given the respective strengths of these two materials. In the high temperature excursion of the hybrid joints with the aircrafts and space vehicles, the substantial difference in thermal expansion coefficients of CMC and superalloy materials will induce complex superposition of initial assembly stress, thermal stress, and tensile stress around fastening area, which might lead to unknown failure behavior of joint structure. To address this concern, a finite element model embedded with progressive damage analysis was established to simulate the thermostructural behavior and high-temperature tensile performance of single-lap, single-bolt C/SiC composite and superalloy joint, by using the ABAQUS software. It was found that the initial stiffness of the CMC/superalloy hybrid bolted joints decreases with the rise of applied temperature under all bolt-hole clearance levels. However, the load-bearing capacity varies significantly with the initial clearance level and exposed temperature for the studied joint. The thermal expansion mismatch generated between the CMC and superalloy materials led to significant changes in the assembly preload and bolt-hole clearance as the high-temperature load is applied to the joint. The evolution in the thermostructural behavior upon temperature was then correlated with the variations in stiffness and failure load of the joints. The provided new findings are valuable for structural design and practical application of the hybrid CMC/superalloy bolted joints at high temperatures in next-generation aircrafts.

The effect of thermal mismatch on the thermal conductance of Al/SiC and Cu/diamond composites

Thermal mismatch at the interface is inevitable in the manufacturing process of metal matrix composites. The relationship between strain and thermal conductivity of metal is obtained. The plastic strain region caused by thermal mismatch and its effect on thermal conductance of Al/SiC and Cu/diamond are acquired and discussed using the finite element method. It is found that the average strain is independent of particle size and proportional to the ratio of particle radius to distance. The strain will affect the thermal conductivity of composites in two ways. One is to decrease the effective thermal conductivity of matrix, which is more significant for the Al/SiC system than the Cu/diamond system, but it has a relatively small impact on the thermal conductivity of composites. The other is to reduce the interfacial thermal conductance (ITC) by weakening interfacial bonding and scattering phonon transport, making the effective thermal conductivity of reinforcement and thermal conductivity of composites decrease, which has a bigger impact on composites with high thermal conductance reinforcements. The results also show that there is an increase of thermal conductivity of composites with ITC in a specific region determined by particle size, and the composite reinforced with large particles has a higher thermal conductivity at low ITC because of the low density of interface. Our work is important for understanding the effect of thermal mismatch on thermal conductance of metal matrix composites and provides a way to bridge the relationship between mechanical behavior and physical properties.

Finite element analysis of the effect of thermal cycles and ageing on the interface delamination of plasma sprayed thermal barrier coatings

The present study provides a numerical simulation of the interface crack development in thermal barrier coatings, deposited using plasma spray method. The proposed model benefited from the SEM image obtained from our previous experimental studies so that the geometry was placed in a model with the dimensions of the tested specimens. In this study, the longitudinal and lateral growth effects of TGO, the creep effect of all coating layers, and the effect of thermal mismatch between layers were investigated on the stress distribution of the coating. The results obtained from previous experimental observations revealed that the separation occurs in the TC/TGO interface. Therefore, in the numerical study, it was defined as the cohesive layer. The separation of cohesive layer in various thermal ageing periods was further explored alongside the cooling-heating thermal cycles. The results obtained by the finite element analysis indicated that as the thermal ageing period increased, the interface separation was enlarged and cracks started to nucleate from other points of the interface. Separation behavior of TC/TGO interface was evaluated once increasing ageing period and thermal cycles.

Multi-Layer Cold Spray Coating: Strain Distribution

In this paper, we report the effect of multi-layer cold spray deposition on the residual stress formation in the coating and substrate. A method is proposed to separately measure the thermal and mechanical residual stresses induced in cold spray coating. Fiber Bragg Grating (FBG) sensors were employed for in situ monitoring of the strain evolution during the cold spray of multi-layer coating Al7075-Zn on AZ31B Magnesium substrates. Utilizing the capability of the FBG sensors in recording both thermal and mechanical strain gradients, first the effect of temperature on the substrate was investigated when the sample was only treated under carrier gas temperature. Then, the sensors were employed to evaluate the mechanical strain behavior of substrate during the coating process and cooling. Therefore, the effect of thermal mismatch on inducing mechanical strains was observable during the process. Finally, the interaction between the peening process of cold spray and thermal mismatch after cooling was studied. It is shown that the thermal expansion coefficient (CTE) plays a critical role in residual stress development in the substrate and consequently affects the mechanical properties of the coated sample. Hence, careful selection of layers in multilayer deposition can provide desired residual stress in the coating and substrate.

Effect of Co on thermal and mechanical properties of Si3N4 based ceramic tool material

The use of ceramic cutting tools is limited due to their inherent brittleness. In this paper, metal phase Co is considered to strengthen Si3N4 based ceramic tool materials. The effects of Co on room-temperature and high-temperature mechanical properties and thermal shock resistance of the material are studied. Compared with the composite without Co, the addition of Co can improve room-temperature fracture toughness of Si3N4 based ceramic material at the cost of reducing its hardness. The flexural strength decreases a little in accordance with the reduced relative density. As the testing temperature increases, the fracture toughness first increases gradually and then decreases sharply while the flexural strength decreases gradually. Due to the oxidation inhibition effect, the Co-containing composite maintains higher flexural strength and fracture toughness than the Co-free composite at the specified test temperatures. The critical thermal shock temperature difference of the composite with Co is higher than that without Co, although before reaching the difference its residual bending strength is lower due to pores and thermal mismatch effect. The addition of Co can also inhibit the growth of thermal shock microcracks and improve the thermal fatigue resistance of Si3N4 ceramic material.

Strengthening analyses and mechanical assessment of Ti/Al2O3 nano-composites produced by friction stir processing

The present work investigates strengthening mechanisms and mechanical assessment of Ti/Al2O3 nano-composites produced by friction stir processing of commercially pure titanium using nano-sized Al2O3 with different volume fractions and particle sizes. Microstructural analyses were conducted to characterize the grain size of matrix, size and dispersion of reinforcing particles. The mean grain size of the composites ranged from ~0.7 to 1.1μm that is much lower than 28μm of the as-received material. Reduction of grain size was found to be in agreement with Rios approach (based on energy dissipated during the motion of an interface through particle dispersion), and showed deviation from Zener pinning model. Scanning and transmission electron microscopies revealed a near uniform dispersion of Al2O3 nano-particles, with only a small fraction of widely spaced clusters. The maximum compression yield strength of the fabricated nano-composite (Ti/3.9%vol of 20nm-Al2O3) was found to be ~494MPa that is ~1.5 times higher than that of the as-received material. Strengthening analyses based on grain refining (Hall–Petch approach), load transfer from matrix to reinforcements, Orowan looping, and enhanced dislocation density due to thermal mismatch effects were carried out considering Al2O3 reinforcement with different volume fractions and sizes. However, Hall–Petch approach was found to be the dominant mechanism for the enhancement of yield strength.

Leak behavior of steam generator tube-to-tubesheet joints under creep condition: Experimental study

To address concerns regarding excessive leakage from throughwall cracks in steam generator tube-to-tubesheet joints under severe accident conditions, leak rate testing was conducted using tube-to-collar joint specimens. The tube interior and the interface between tube and collar (crevice) were pressurized independently using nitrogen gas. The leak rate through the crevice was almost zero when the specimens were pressurized at ∼500 °C; this low leak rate is attributed to thermal mismatch effects preventing much leakage. The near zero leak rate was maintained until the onset of large leakage at higher temperatures. The leak rate behavior after the onset of the large leakage was not much affected by the crevice length or heat-to-heat variation of Alloy 600 tubes. This suggests that once the crevice gap opens, the creep rate of the low alloy steel collar becomes dominant. Specimens with different tube diameters behaved essentially the same way. To simulate a flawed steam generator tube in the tubesheet, the crevice region was pressurized through a hole in the tube. This simulation resulted in essentially the same behavior as those specimens whose tubes and crevices were pressurized independently. Oxidation of low alloy steel collars in air tests can increase the flow resistance, and thus tests using nitrogen gas would provide more conservative leak rate data.

Effect of thermal mismatch induced residual stresses on grain boundary microcracking of titanium diboride ceramics

The effect of thermal mismatch induced residual stresses on grain boundary microcracking in titanium diboride (TiB2) ceramics has been studied by finite element method. A cohesive zone model was used to simulate the microcracking initiation in four-point bending specimens. In particular, the microcracking was assumed to occur at a grain boundary which is located in the center of the specimen, surrounded by a thermally anisotropic area. The predicted failure strength appears to be significantly reduced by the presence of residual stresses when the cohesive energy of the microstructure is small. The failure load from experiments has been used to determine the critical damage parameters for microcracking initiation in both pristine and aluminum-infiltrated TiB2. A viscous regularization technique is employed in the simulations to improve the rate of convergence of the solution and the effect of the value of the viscosity parameter on the simulation results, has been investigated. The effect of grain size, grain orientation, and number of employed thermally anisotropic grains, on the microcracking is also discussed.

Experimental Studies of Sealing Mechanism of a Dismountable Microsystem-to-Macropart Fluidic Connector for High Pressure and a Wide Range of Temperature

As fluidic microelectromechanical devices are developing and often attached to, or embedded in, large, complex, and expensive systems, the issues of modularity, maintenance, and subsystem replacement arise. In this work, a robust silicon connector suitable for high-pressure applications—likely with harsh fluids—in the temperature range of +100 to [Formula: see text] C is demonstrated and tested together with a stainless steel nipple representing a simple and typical macropart. With a micromachined circular membrane equipped with a 5 μm high ridge, this connector is able to maintain a leak rate below [Formula: see text] scc/s of gaseous helium with a pressure of up to 9.7 bar. Degradation of the sealing performance on reassembly is associated with the indentation of the ridge. However, the ridge makes the sealing interface less sensitive to particles in comparison with a flat reference. Most evaluation is made through the so-called heat-until-leak tests conducted to determine the maximum working temperature and the sealing mechanism of the connector. A couple of these are followed by cryogenic testing. The effect of thermal mismatch of the components is discussed and utilized as an early warning mechanism.