Thermal Mismatch Research Articles

Effect of thermal mismatch strain on the self-assembly of nanorods in YBCO/NRs nanocomposite films

This study presents a thermoelastic model to investigate the impact of thermal mismatch strain, resulting from distinct thermal expansion coefficients between the film matrix and nanorods, on the self-assembly of nanorods in YBCO/NRs nanocomposite films. An accurate understanding of thermal mismatch strain generated during nanocomposite film preparation is vital for controlling the self-assembly of artificial nanorods in such films. In this model, we calculated the total elastic energy density of the film matrix and nanorods, considering both lattice and thermal mismatch strains, to analyze the effect of thermal strain on the diameter of c-oriented nanorods in YBCO nanocomposite films. The calculated nanorod diameter values match experimentally measured values for BaZrO3 and BaSnO3 nanorods. Furthermore, compared to results that only consider lattice mismatch strain, the proposed model yields closer calculation values to experimental measurements by incorporating the impact of thermal mismatch strain. The thermal mismatch strain also affects the spacing between two adjacent nanorods, having the most profound effect on BSO nanorods compared to BZO and BHO nanorods. These findings contribute to understanding the mechanisms involved in nanorod self-assembly and provide insights to optimize the design of YBCO/NRs nanocomposite films.

Thermal ecology shapes disease outcomes of entomopathogenic fungi infecting warm-adapted insects

The thermal environment is a critical determinant of outcomes in host-pathogen interactions, yet the complexities of this relationship remain underexplored in many ecological systems. We examined the Thermal Mismatch Hypothesis (TMH) by measuring phenotypic variation in individual thermal performance profiles using a model system of two species of entomopathogenic fungi (EPF) that differ in their ecological niche, Metarhizium brunneum and M. flavoviride, and a warm-adapted model host, the mealworm Tenebrio molitor. We conducted experiments across ecologically relevant temperatures to determine the thermal performance curves for growth and virulence, measured as % survival, identify critical thresholds for these measures, and elucidate interactive host-pathogen effects. Both EPF species and the host exhibited a shared growth optima at 28 °C, while the host’s growth response was moderated in sublethal pathogen infections that depended on fungus identity and temperature. However, variances in virulence patterns were different between pathogens. The fungus M. brunneum exhibited a broader optimal temperature range (23–28 °C) for virulence than M. flavoviride, which displayed a multiphasic virulence-temperature relationship with distinct peaks at 18 and 28 °C. Contrary to predictions of the TMH, both EPF displayed peak virulence at the host's optimal temperature (28 °C). The thermal profile for M. brunneum aligned more closely with that of T. molitor than that for M. flavoviride. Moreover, the individual thermal profile of M. flavoviride closely paralleled its virulence thermal profile, whereas the virulence thermal profile of M. brunneum did not track with its individual thermal performance. This suggests an indirect, midrange (23 °C) effect, where M. brunneum virulence exceeded growth. These findings suggest that the evolutionary histories and ecological adaptations of these EPF species have produced distinct thermal niches during the host interaction. This study contributes to our understanding of thermal ecology in host-pathogen interactions, underpinning the ecological and evolutionary factors that shape infection outcomes in entomopathogenic fungi. The study has ecological implications for insect population dynamics in the face of a changing climate, as well as practically for the use of these organisms in biological control.

Topologically protected hierarchical buckling modes of compressed thin films on Winkler substrates

Patterns created by buckling of thin films on substrates have important applications in many fields such as functional devices and surface engineering. Introducing hierarchy to such patterns may further enhance their functionalities. However, unpredictable geometrical and material defects may disturb the formation of patterns. It is thus attractive to construct robust hierarchical buckling patterns that are insensitive to defects. Here, inspired by the construction of topologically protected localized states insensitive to defects in wave mechanics, a thin film of finite length bonded on a simple Winkler substrate is quantitatively designed by just varying its width continuously. Under the action of specific compressive stresses within such a continuous thin film owing to thermal mismatch between the film and substrate, there really exists a hierarchical film-buckling mode generated by topologically protected localization. Conditions under which the topologically protected localization exists are given explicitly, and the underlying mechanism is intuitively demonstrated from the mechanical point of view. Moreover, an analytical solution for the decay rate of localization is obtained as a satisfactory second-order approximation, from which the associated influencing factors are clearly identified. This work is expected to provide a theoretical guidance for the design and optimization of hierarchical patterns in film/substrate systems via the concept of topology.

Fan-out panel-level package warpage and reliability analyses considering the fabrication process

With the continuous advancement of IC packaging technology, 3D and 2.5D packaging systems have emerged as the prevailing trends. The advantages of large area and high I/O density have made fan-out panel-level packaging (FOPLP) been considered as one of the best package types for 3D and 2.5D packaging applications. The discussions about FOPLP have been popular recently. Warpage and reliability of FOPLP are the main concerns of packaging engineers. However, it was found that warpage and reliability of FOPLP are strongly related to the fabrication process but not many research works have been published. Thus, reliability analysis procedure considering the residual stress of fabrication process was proposed in this paper to observe warpage and stress distribution during fabrication process. Then, this research procedure facilitates subsequent fatigue life calculations and predicts reliability of the package.First, the thermal stresses and warpage of the redistribution layer-first (RDL-first) process were conducted for an entire panel. Next, warpage and thermal stress analyses were conducted for a strip encapsulated with an epoxy molding compound (EMC) during compression molding. Then, a reliability analysis was conducted with an IC unit and incorporated the consideration of the residual stress induced during the fabrication processes.The compression molding analysis utilized the pressure–volume–temperature–cure (P–V–T–C) model to account for both the volume shrinkage caused by a thermal mismatch and the chemical shrinkage. Furthermore, dual shift factor model was used to model the viscoelastic behavior of EMC in this study during PMC analysis effectively.An observation of the stress distribution for an IC unit revealed that the maximum stress position was at the solder ball near the periphery, with a stress value of 147.309 MPa. The fatigue life calculated using the modified Coffin–Manson fatigue model was 417 cycles.

Oxygen permeation mass transfer modeling and onion-like micromechanical modeling to predict the effect of multilayered interface on oxidation resistance and mechanical properties of composites

To predict oxidative damage of interfaces and fibers under high temperature aerobic environment and mechanical strength of composites before and after oxidation, oxygen permeation mass transfer modeling and onion-like micromechanical modeling of multilayered interface were proposed. The oxygen mass transfer theory and oxidation damage theory of PyC interface were used to establish the two models. The oxidative damage of PyC interface was extended to (PyC-SiC)n multilayered interface, and transformation of SiC phase and microcracks caused by thermal mismatch were also considered. The law of oxygen permeation mass transfer and the evolution of fiber oxidative damage in the “Carbon fiber/(PyC-SiC)n multilayered interface” region were revealed. The mechanical strength of composites under different interface layers was researched, resembling an onion-like wrapping in layers from the core outwards. Furthermore, Cf@(PyC-SiC)n/SiC(n = 1/2/3/4) composites were prepared by chemical vapor infiltration (CVI) method. The mechanical properties of the composites were tested before and after oxidation. A comparison was made between the experimental and predicted tensile strengths before and after oxidation. The predicted results of tensile strength were found to be in good agreement with the experimental ones. In addition, the results show that PyC-SiC multilayered interface has a positive effect on the tensile strength of the composites, mainly as the cracks are deflected and branched by the multilayered interface to promote the multistage pull-out of the fibers. With the increase of interface number, the oxygen diffusion path was lengthened and zigzagged, reducing the oxidative damage of fiber and interface.

Low residual stress SiC coatings on C/CA composites by a strategy of matching their expansion behaviors to improve thermal shock resistance

The poor thermal shock resistance of coated C/CA composites limits the applications with rapid temperature fluctuations due to the huge thermal mismatch between the coating and the substrate. A facile strategy of tailoring coefficient of thermal expansion (CTE) of C/CA is proposed to match their thermal deformation behaviors. The optimized C/CA by heat treatment has a positive correlation between CTE and temperature, and thus the as-prepared SiC coating has a decreased macroscopic residual strain of 80.7% due to their coordinated thermal response compared to the original C/CA. Meanwhile, benefited from the structural improvement of larger pore size and higher degree of graphitization of C/CA, a significantly decreased tensile stress of 60.3% in the coating is achieved due to the formation of small SiC spheres in the carbon network. Resultantly, the coated C/CA shows remarkably improved thermal shock resistance with narrower and fewer microcracks, and lower mass and linear cyclic ablation rates of 0.252 mg/s and 0.607 μm/s, respectively.

Comprehensive material study of Ge grown by aspect ratio trapping on Si substrate

High-quality monolithic Ge-on-Si is sought for CMOS-compatible optoelectronic devices. We examine the structural characteristics of Ge-on-Si grown by the aspect ratio trapping (ART) method on a SiO2/Si(001) template in pre-patterned holes. Transmission electron microscopy and surface topography analysis revealed high-quality Ge islands overgrown from the ART holes in SiO2. The superior crystal quality of Ge ART growth was also confirmed by comparing x-ray diffraction (XRD) data of Ge ART and Ge planar epilayer samples. The XRD and micro-Raman data additionally show a small residual strain in the islands which vanishes by reducing the hole diameter from 280 nm to 180 nm, while leading to only a minor increase in the crystallographic inclinations of the Ge islands from 0.34 deg to 0.54 deg. With finite element method simulations, we find that the small residual strain in Ge originates during the cool-down from growth to room temperature because of thermal expansion coefficient mismatch between Ge and SiO2. A tensile force develops along the [001] axis of the Ge pillar whose faster shrinkage to the room temperature volume is restricted by the oversized surface island.

Quasi van der Waals Epitaxy of Single Crystalline GaN on Amorphous SiO2/Si(100) for Monolithic Optoelectronic Integration.

The realization of high quality (0001) GaN on Si(100) is paramount importance for the monolithic integration of Si-based integrated circuits and GaN-enabled optoelectronic devices. Nevertheless, thorny issues including large thermal mismatch and distinct crystal symmetries typically bring about uncontrollable polycrystalline GaN formation with considerable surface roughness on standard Si(100). Here a breakthrough of high-quality single-crystalline GaN film on polycrystalline SiO2/Si(100) is presented by quasi van der Waals epitaxy and fabricate the monolithically integrated photonic chips. The in-plane orientation of epilayer is aligned throughout a slip and rotation of high density AlN nuclei due to weak interfacial forces, while the out-of-plane orientation of GaN can be guided by multi-step growth on transfer-free graphene. For the first time, the monolithic integration of light-emitting diode (LED) and photodetector (PD) devices are accomplished on CMOS-compatible SiO2/Si(100). Remarkably, the self-powered PD affords a rapid response below 250µs under adjacent LED radiation, demonstrating the responsivity and detectivity of 2.01×105 A/W and 4.64×1013Jones, respectively. This work breaks a bottleneck of synthesizing large area single-crystal GaN on Si(100), which is anticipated to motivate the disruptive developments in Si-integrated optoelectronic devices.

Experiment and Numerical Simulation on Thermal Cycling Performance of YSZ-Based Sealing Coatings with “Brick-Mud” Layered Structure

The failure of premature thermal cycling spalling off is the bottleneck problem currently faced by yttrium oxide partially stabilized zirconia (YSZ) ceramic-based sealing coatings. Studies on the thermal cycling performance of coatings with “brick-mud” structures were carried out by experimental and simulation methods in this paper. The results showed that, as the thickness of “mud” layer increased, the bonding strength of the “brick-mud” structure coatings gradually decreased. When the thickness of the “mud” layer was about 3 μm and 10 μm, the thermal cycling lives of the T1 and T2 coatings were improved by 90.0% and 135.7%, respectively, compared with conventional coating (T0 coating), while that of the T3 coating (containing thick “mud” layers of about 20 μm) was decreased by 81.4%. The stress field of M2 “mud” layers with different thicknesses was subjected to a comprehensive effect by thermal mismatch stress and pores in “brick” layer. Compared with the medium and thick “mud” layers, the thin “mud” layer sustained obvious larger σ22 max and σ12 max, indicating its potential for the preferential initiation of transverse microcracks. In addition, the thin “mud” layer withstood the largest σ11 max and had the strongest potential for longitudinal crack growth. Both transverse and longitudinal cracking could consume energy during thermal cycling and reduce the stress concentration at the top coating/bond coating interface. These were the main reasons for the improvements in the thermal cycling performances of the T1 and T2 coatings. The degree of crack deflection and the capacity of energy dissipation in the “mud” layer increased significantly with its thickness. However, the propagation length of transverse cracks also gradually increased in the meantime. Especially when the “mud” layer was 20 μm, the length of the transverse cracks increased rapidly. Thus, early interlayer delamination failure occurred in the T3 coating during thermal cycling.

Optimization of elution conditions and comparison of emerging biocompatible columns on the resolving power and detection sensitivity of oligonucleotides by ion-pairing reversed-phase liquid chromatography mass spectrometry

A generic performance comparison strategy has been developed to evaluate the impact of mobile-phase additives (ion-pairing agent / counter ion systems), distinct stationary phases on resulting resolving power, and MS detectability of oligonucleotides and their critical impurities in gradient IP-RPLC. Stationary-phase considerations included particle type (core-shell vs. fully porous particles), particle diameter, and pore size. Separations were carried out at 60°C to optimize mass transfer (C-term). The incorporation of an active column preheater mitigated thermal mismatches, leading to narrower peaks and overcoming peak splitting. Acetonitrile as organic modifier outweighed methanol in terms of peak-capacity generation and yielded a 30% lower back pressure. Performance screening experiments were conducted varying ion-pairing agents and counter ions, while adjusting gradient span achieved an equivalent effective retention window. Hexafluoromethylisopropanol yielded superior chromatographic resolution, whereas hexafluoroisopropanol yielded significantly higher MS detection sensitivity. The 1.7 µm core-shell particle columns with 100 Å pores provided maximum resolving power for small (15–35 mers) oligonucleotides. Sub-min analysis for 15–35 polyT ladders was achieved operating a 50 mm long column at the kinetic performance limits. High-resolution separations between a 21-mer modified RNA sequence oligonucleotides and its related (shortmer and phosphodiester) impurities and complementary strand were obtained using a coupled column set-up with a total length of 450 mm.

Improving Electromigration Resistance of Fine‐Pitch Redistributed Layer Using Graphene‐Doped Twinned Copper Composites

The electromigration (EM) behavior of graphene‐doped twinned copper composite (GC–Cu) and nanotwinned copper (NT–Cu) redistributed layers (RDLs) are investigated. Firstly, the GC–Cu has longer lifetimes under various test conditions. For example, the GC–Cu RDL took 291 h to reach a 20% resistance increase, while the NT–Cu RDL took 117 h under the same condition of 120 °C and 106 A cm−2. Secondly, thinner oxidation layer and slighter voiding phenomena are detected on GC–Cu RDLs. When the line width and spacing (L/S) of RDL decreased from 20/20 μm to 10/10 μm, new failure modes, i.e., fracture of oxide layer, separation between the oxide layer and copper matrix are also detected, demonstrating the increasing thermal mismatch. Combined with the finite element analysis (FEA), there is simultaneous current aggregation and stress concentration around the voids, which should further cause the degradation of RDL. Above all, this study gives insights into the material design in the fine‐pitch RDL structure.

Microstructure and Properties of Aluminum-Graphene-SiC Matrix Composites after Friction Stir Processing.

Enhancing the mechanical properties of conventional ceramic particles-reinforced aluminum (Al 1060) metal matrix composites (AMCs) with lower detrimental phases is difficult. In this research work, AMCs are reinforced with graphene nanosheet (GNS) and hybrid reinforcement (GNS combined with 20% SiC, synthesized by shift-speed ball milling (SSBM), and further fabricated by two-pass friction stir processing (FSP). The effect of GNS content and the addition of SiC on the microstructure and mechanical properties of AMCs are studied. The microstructure, elemental, and phase composition of the developed composite are examined using SEM, EDS, and XRD techniques, respectively. Mechanical properties such as hardness, wear, and tensile strength are analyzed. The experimental results show that the GNS and the SiC are fairly distributed in the Al matrix via SSBM, which is beneficial for the mechanical properties of the composites. The maximum tensile strength of the composites is approximately 171.3 MPa in AMCs reinforced by hybrid reinforcements. The tensile strength of the GNS/Al composites increases when the GNS content increases from 0 to 1%, but then reduces with the further increase in GNS content. The hardness increases by 2.3%, 24.9%, 28.9%, and 41.8% when the Al 1060 is reinforced with 0.5, 1, 2% GNS, and a hybrid of SiC and GNS, respectively. The SiC provides further enhancement of the hardness of AMCs reinforced by GNS. The coefficient of friction decreases by about 7%, 13%, and 17% with the reinforcement of 0.5, 1, and 2% GNS, respectively. Hybrid reinforcement has the lowest friction coefficient (0.41). The decreasing friction coefficient contributes to the self-lubrication of GNSs, the reduction in the contact area with the substrate, and the load-bearing ability of ceramic particles. According to this study, the strengthening mechanisms of the composites may be due to thermal mismatch, grain refinement, and Orowan looping. In summary, such hybrid reinforcements effectively improve the mechanical and tribological properties of the composites.

Parks may not be effective enough to improve the thermal environment in Shanghai (China) as our modified H3SFCA method suggests

Anthropogenic warming and rapid urbanization have exacerbated the deterioration of urban thermal environments, increasing interest in the ability of parks to regulate local climates. However, their potential to mitigate local thermal discomfort and spatial mismatch in supply and demand is poorly understood. We 1) examined the cooling effects of Shanghai's parks via a thermal comfort index, 2) identified the role of parks in improving local thermal environments by comparing thermal discomfort and park cooling capacity, and 3) explored the spatial mismatch between the demand for thermal discomfort mitigation and the supply of park cooling based on multiple park accessibility. The extent of park cooling is inversely related to the level of urbanization, while cooling intensity is positively associated with urbanization. Only 20.65% of the parks effectively mitigate local thermal discomfort, highlighting the need for improvements. Cooling accessibility increases from the city center to the periphery, with 22.70% of areas lacking access to park cooling services within a 15-min radius. Further improvements can enhance the thermal comfort of accessible parks by 49.55%. Priority adaptation is required in old urban areas and key development zones in peripheral urban areas to meet the needs of their large populations. Our study contributes to the study of urban thermal discomfort mitigation via parks in the context of climate adaptation planning.

Single step silicon carbide heteroepitaxy on a silicon wafer at reduced temperature

A single step growth approach for wafer-scale homogeneous cubic silicon carbide (3C-SiC) heteroepitaxy, using chemical vapour deposition (CVD), on a silicon (Si) substrate is demonstrated. Residual biaxial tensile strain causing a wafer bow is eliminated in the 3C-SiC epilayer via in-situ defects engineering and heteroepitaxy at reduced temperature. Thermal mismatch between the 3C-SiC epilayer and substrate is minimised by a substantial reduction of growth temperature, down to ∼1000 °C. Heteroepitaxy of high quality, fully relaxed 3C-SiC epilayers with minimal wafer bow is demonstrated, made possible by careful process optimisation. Unusually very high growth rate of 3C-SiC of > 10 µm/hr is achieved. At the same time the epilayer is free from any other silicon carbide (SiC) polytype inclusions. Moreover, the reduced growth temperature unlocks the ability to deposit high quality 3C-SiC epilayers within traditional Si-based cold walled CVD reactors, enabling the growth of such thin films on unprecedently high volumes and wafer diameters up to 300 mm and above.

Interface Reliability Modeling of Coaxial Through Silicon Via Based on WOA-BP Neural Network

Abstract Due to the complex structure and thermal mismatch of coaxial through silicon via (TSV), cracks easily occur under thermal load, leading to interface delamination or spalling failure. The reliability issue of coaxial TSV is important for its application in three-dimensional packaging, so it is of great significance to predict the crack trend and evaluate the reliability of coaxial TSV. In this paper, an algorithm model with the combination of whale optimization algorithm (WOA) and back propagation (BP) neural network for the reliability prediction of coaxial TSV is proposed. Based on finite element method (FEM), the training and validation datasets of the energy release rates (ERR) of the crack at the critical interface are calculated to construct the deep learning neural network. Six key structure parameters affecting the reliability of coaxial TSV are selected as the input values of the BP neural network. The maximum relative error of whale optimization algorithm optimized back propagation (WOA-BP) neural network model is 0.88%, which is better than the prediction results of the traditional BP and genetic algorithm (GA) optimized BP models. The WOA-BP neural network model was also compared with BP and GA-BP neural network models with four error metric models. It is verified that WOA-BP neural network model has the best prediction performance. The proposed model can be used to achieve improved prediction accuracy for the interface reliability of coaxial TSV under complex structural conditions since it has higher accuracy and stronger robustness.

Strain accumulation and relaxation on crack formation in epitaxial AlN film on Si (111) substrate

The formation of cracks is often observed in the epitaxial growth of ultrawide-bandgap aluminum nitride (AlN) semiconductor films on economical and versatile silicon (Si) substrates due to the significant differences in in-plane lattice parameters and thermal expansion coefficients between the film and the substrate, which hampers the development of template, buffer layer, and device structure with a relatively thick AlN layer for devices. The present study aims to elucidate the conditions of crack formation through a simple but comprehensive estimation of strain energy accumulation and relaxation by lattice strain, misfit dislocation density, and crack formation. Strain energy in the epitaxial film from lattice and thermal mismatches is evaluated by an elastic strain equation tailored to the epitaxy of the hexagonal crystal structure. The effects of temperature, thickness, and dislocation density on the lattice and dislocation strain energies of the film are also considered. Finally, the comparison in the changes in the total strain energy and cleavage energy with decreasing temperature shows that cleavage energy is higher than strain energy if the film is thinner than 400 nm but becomes lower than the strain energy if the film is thicker than 400 nm during cooldown, suggesting the crack formation, which matches well with experimental observations.

Strengthening mechanisms and wear performance of Al/APC/micro-B4Cp hybrid composites prepared by HTCDC process and hot extrusion

An Al/APC/micro-B4Cp hybrid composites were fabricated using the hydrothermal carbonized deposition on chips (HTCDC) process and hot extrusion process. The microstructure and mechanical properties and wear resistance of the Al/APC/micro-B4Cp hybrid composites were characterized. APC spheres and irregular micro-B4Cp could be observed on the Al chips surface after the HTCDC process, and the micro-B4Cp were also coated with an APC film. Al/APC/micro-B4Cp hybrid composites were prepared by hot extrusion from the Al chips covered with APC and micro-B4Cp. With the increase of micro-B4Cp content, the α-Al grain sizes of composites decrease from 18.8 µm to 12.8 µm, because the dispersed micro-B4Cp in the composites can pin the grain boundaries, hinder the migration of grain boundaries, and inhibit the growth of recrystallized grains. The highest values were obtained when the micro-B4Cp content was 3 wt%, and the UTS and hardness values of Al/APC/B4Cp hybrid composites (223.66 MPa and 101.8HV) were increased by 14.07% and 24%, respectively, compared with Al/APC composite. The results of the YS calculation show that thermal mismatch strengthening is the main strengthening mechanism, followed by grain-refined strengthening, and load transfer strengthening. Because the APC of the self-lubricating effect can form a lubrication film on the wear surface during sliding, the COF and wear rate of the Al/APC composite are low. When the micro-B4Cp is added to the matrix, the micro-B4Cp will strip the APC film from the wear surface, so the COF increases. However, the addition of micro-B4Cp can greatly increase the hardness of the composite, as a consequence that the wear rate of the composite material is still low(1.44 ×10−5 mm3/Nm).

Multi-layered environmental barrier coatings designed on basis of YbTaO4-Ta2O5 composites for protecting SiCf/SiC composites

YbTaO4-Ta2O5 composites were designed and different multi-layered YbTaO4-Ta2O5/Yb2Si2O7/Si (YbT-T/YbDS/Si) as well as YbTaO4-Ta2O5/Si (YbT-T/Si) environmental barrier coatings (EBCs) were put forward to protect SiC fiber reinforced silicon carbide (SiCf/SiC) ceramic matrix composites (CMCs). The thermal cycling and the water-vapor/oxygen corrosion behavior of different multi-layered EBCs were compared. Results indicated that the thermal cycling lifetime of the bi-layered YbT-T/Si EBCs was similar with the tri-layered YbT-T/YbDS/Si ones. The ultimate failure of these two EBCs was induced by the cracking of the SiCf/SiC substrates as well as the vertical cracks associated with the thermal mismatch stress among different layers. However, the tri-layered EBCs exhibited greater resistance to water-vapor/oxygen corrosion than the bi-layered ones, primarily due to that the tri-layered YbT-T/YbDS/Si EBCs contained significantly less cracks than the bi-layered ones, limiting the transport of reactant (oxygen and/or water vapor) to reach Si bond coat.

Toughening and strengthening of Cu-coated carbon nanotubes reinforced AZ61 magnesium matrix nanocomposites by improving interfacial bonding

Interfacial modification without damaging the structure of carbon nanotubes (CNTs) is urgently needed to improve the performance of CNTs reinforced metal matrix nanocomposites. To fabricate CNTs/AZ61 nanocomposite with strong interfacial bonding, copper-coated CNTs (0.15–2.4 vol%) and AZ61 powder were employed through the process of ball milling mixing, vacuum hot pressing and extrusion. The powder and nanocomposites were characterized by HRTEM, SEM, XRD and compressive test to study the distribution of reinforcements, microstructures, interfacial structure and compression behavior. During the high-temperature fabrication process, in-situ interfacial reactions occurred between Cu particles of CNTs and Mg, Al and Zn elements in AZ61 matrix. As a result, the formation of interfacial reaction phases, such as AlCu3, Al2Cu, Cu2Mg, CuMg2, Cu0.61Zn0.39 and MgAl2C2 phases, and their diffused and/or coherent interface significantly strengthen the interfacial bonding. With only 0.15 vol% CNTs, the work of fracture and compression strength of the composite are 40 % and 20 % higher than those of pure AZ61, respectively. The dominating toughening mechanisms are the load transfer role of scattered CNTs and fine-grain effect. The dominating strengthening mechanisms are thermal mismatch and Orowan strengthening.

Phonon dynamic behaviors induced by amorphous layers at heterointerfaces.

An amorphous layer is commonly found at the interfaces of heterostructures due to lattice and thermal mismatch between dissimilar materials. While existing research has explored the impact of these layers on interfacial thermal transport, a comprehensive understanding of the underlying microscopic mechanisms remains essential for advancing thermal nanodevice development. Through phonon wave packet simulations, we investigated the dynamic behaviors of phonons crossing the amorphous interlayer at the GaN/AlN interface from the mode level. Our results highlight the amorphous layer's capability to notably adjust the polarization properties of incoming phonons, culminating in phonon localization. By examining transmission outcomes on a per-mode basis, we demonstrate the amorphous layer's impediment on phonon transport. Notably, this resistance escalates with an increase in the amorphous layer thickness (L), with certain high-frequency TA phonons showing unexpectedly high transmissivity due to polarization conversion and inelastic scattering at the amorphous interface. In addition, we observe that the amorphous layer prompts multiple reflections of incident phonons, instigating discernible from the two-beam interference equation. Finally, in pursuit of enhanced phonon transport, we employ annealing techniques to optimize the interface morphology, leading to the recrystallization of the amorphous layer. This optimization yields a substantial enhancement of interfacial thermal conductance by up to 38% for L = 3 nm.