Effects of the In Situ Growth of CNTs on Ti-Coated Diamond Surfaces on the Mechanical Properties of Diamond/Aluminum Composites.

Diamond/aluminum composites have attracted significant attention as novel thermal management materials, with their interfacial bonding state and configuration playing a crucial role in determining their thermal conductivity and mechanical properties. The present work aims to evaluate the bending strength and thermal conductivity of CNT-modified Ti-coated diamond/aluminum composites with multi-scale structures. The Fe catalyst was encapsulated on the surface of Ti-coated diamond particles using the solution impregnation method, and CNTs were grown in situ on the surface of Ti-coated diamond particles using the plasma-enhanced chemical vapor deposition (PECVD) method. We investigated the influence of interface structure on the thermal conductivity and mechanical properties of diamond/aluminum composites. The results show that the CNT-modified Ti-coated diamond/aluminum composite exhibits excellent bending strength, reaching up to 281 MPa, compared to uncoated diamond/aluminum composites and Ti-coated diamond/aluminum composites. The selective bonding between diamond and aluminum was improved by the interfacial reaction between Ti and diamond particles, as well as between CNT and Al. This led to the enhanced mechanical properties of Ti-coated diamond/aluminum composites while maintaining acceptable thermal conductivity. This work provides insights into the interface's configuration design and the performance optimization of diamond/metal composites for thermal management.

Endoplasmic reticulum stress interferes with the development of type 1 regulating T cells.

BACKGROUND: A variety of stimuli can cause endoplasmic reticulum (ER) stress, which is a common cellular reaction. It is not yet clear how ER stress contributes to the pathogenesis of ulcerative colitis (UC). The deregulation of regulatory T cell (Treg) is associated with UC. The goal of this study is to shed light on how ER stress affects Treg's development. METHODS: CD4+ CD25- T cells were isolated from blood samples collected from UC patients and healthy control (HC) subjects. ER stress-associated molecule expression in CD4+ CD25- T cell was assessed by RNA sequencing and RT-qPCR. RESULTS: The presence of ER stress in peripheral CD4+ CD25- T cells was observed in patients with UC compared to HC subjects. The induction of ER stress in HC CD4+ CD25- T cells by polyclonal activation was made worse by the presence of 3-methyl-4-nitrophenol (MNP; a common environmental pollutant). Exposure to MNP in culture resulted in an increase in the expression of ring finger protein 20 (Rnf20) in CD4+ CD25- T cells. The synergistic effects of MNP and ER stress on the reduction of IL-10 levels in CD4+ CD25- T cells are mediated by Rnf20, which prevents the development of Tr1 cells. Inhibition of Rnf20 resulted in the development of Tr1 cells from CD4+ CD25- T cells in UC patients. CONCLUSIONS: The synergistic effects of ER stress and MNP interfere with the development of Tr1 cells. The development of Tr1 from CD4+ CD25- T cells in patients with UC is re-established by Rnf20 inhibition.

Influence of Interface on Mechanical Behavior of Al-B4C/Al Laminated Composites under Quasi-Static and Impact Loading.

In this study, Al-B4C/Al laminated composites with high interlayer bonding strength were fabricated by integrated hot-pressed sintering accompanied with hot rolling. The mechanical properties and interface behavior of the Al-B4C/Al laminated composites were investigated under quasi-static and impact loading. The results show that the Al-B4C/Al laminated composites obtain a high interface bonding strength, because no interlayer delamination occurs even after fractures under quasi-static and impact loads. The Al-B4C/Al laminated composites exhibit a better comprehensive mechanical performance, and the fracture can be delayed due to the high bonding strength interface. Moreover, laminated composites can absorb more impact energy than the monolithic material under impact loading due to the stress transition and relaxation.

5-HT modulates the properties of dendritic cells to interfere with the development of type 1 regulating T cells.

BACKGROUND: 5-hydroxytryptamine (5-HT, serotonin) is a major mediator in allergic reactions. The number of tolerogenic dendritic cell (tolDC) and regulatory T cell is reduced in allergic disorders. The mechanism is unclear. The objective of this study is to elucidate the role of 5-HT in interfering with tolDC generation and regulatory Type 1 T cell (Tr1 cell). METHODS: BALB/c mice were treated with 5-HT-containing nasal instillations. The frequency of tolDC and Tr1 cell was evaluated by flow cytometry. RESULTS: Following treatment with 5-HT nasal instillations for one week, the frequency of tolDC and Tr1 cell was significantly reduced in the respiratory tissues. Higher levels of SOS1 were detected in DCs isolated from the airway tissues of mice treated with 5-HT. A complex of SOS1 and c-Maf was detected in DCs in response to 5-HT stimulation. The expression of IL-10 was suppressed by the presence of 5-HT. The induction of Tr1 cell by DC was substantially compromised by 5-HT. CONCLUSIONS: 5-HT inhibits the expression of IL-10 in DCs. DCs primed with 5-HT lose the ability to induce Tr1 cells.

Targeting the RhoA-GEF-H1 pathway of mast cells attenuates experimental airway allergy.

Mast cells are the major effector cells in allergic diseases. RhoA and its downstream pathway is associated with the pathogenesis of airway allergy. The objective of this study is to test a hypothesis that modulating the RhoA-GEF-H1 axis in mast cells can attenuate airway allergy. An airway allergic disorder (AAD) mouse model was employed. Mast cells were isolated from AAD mouse airway tissues to be analyzed by RNA sequencing. We observed that mast cells isolated from the respiratory tract of AAD mice were resistant to apoptosis. Mast cell mediator levels in nasal lavage fluid were correlated with apoptosis resistance in AAD mice. Activation of RhoA in AAD mast cells was related to resistance to apoptosis. Mast cells isolated from the airway tissues in AAD mouse exhibited strong RhoA-GEF-H1 expression. The RhoA-GEF-H1 axis was associated with the lower FasL expression in AAD mast cells. Activation of the RhoA-GEF-H1 axis promoted the production of mediators in mast cells. Inhibition of GEF-H1 facilitated the SIT-induced mast cell apoptosis and enhanced the therapeutic efficacy of AAD. In conclusion, RhoA-GEF-H1 activities are associated with resistance to apoptosis in mast cells isolated from sites of allergic lesions. The state of apoptosis resistance in mast cells is associated with the state of AAD disease. Inhibition of GEF-H1 restores the sensitivity of mast cells to apoptosis inducers, and alleviates experimental AAD in mice.

Effect of Lattice Constants and Precipitates on the Dimensional Stability of Rolled 2024Al during Isothermal Aging.

The change in material dimensional will lead to the decline of instrument accuracy and reliability. In this paper, the characterization and analysis of the lattice constant, precipitates, and dislocation density of the material by X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveals the reason why the relative dimensional change in the rolled 2024Al is one order of magnitude lower than that of the as-cast 2024Al during isothermal aging. Compared with as-cast 2024Al, the dislocation density of rolled 2024Al is higher, the lattice constant decreases less before and after aging, and the precipitates have orientation and more content, resulting in the dimensional change in rolled 2024Al being smaller than that of as-cast 2024Al. In addition, two main reasons for decreasing the dimensional change in rolled 2024Al are discussed: the decrease in lattice constant, the formation and growth of the S phase before and after aging.

Effect of Interfacial Strength on Mechanical Behavior of Be/2024Al Composites by Pressure Infiltration.

In this paper, two kinds of Be/2024Al composites were prepared by the pressure infiltration method using two different beryllium powders as reinforcements and 2024Al as a matrix. The effect of interfacial strength on the mechanical behavior of Be/2024Al composites was studied. Firstly, the microstructure and mechanical properties of the two composites were characterized, and then the finite element analysis (FEA) simulation was used to further illustrate the influence of interfacial strength on the mechanical properties of the two Be/2024Al composites. The mechanical tensile test results show that the tensile strength and elongation of the beryllium/2024Al composite prepared by the blocky impact grinding beryllium powder (blocky-Be/2024Al composite) are 405 MPa and 1.58%, respectively, which is superior to that of the beryllium/2024Al composite prepared by the spherical atomization beryllium powder (spherical-Be/2024Al composite), as its strength and elongation are 331 MPa and 0.38%, respectively. Meanwhile, the fracture of the former shows brittle fracture of beryllium particles and ductile fracture of aluminum, while the latter shows interface debonding. Further FEA simulation illustrates that the interfacial strength of the blocky-Be/2024Al composite is 600 MPa, which is higher than that of the spherical-Be/2024Al composite (330 MPa). Therefore, it can be concluded that the better mechanical properties of the blocky-Be/2024Al composite contribute to its stronger beryllium/aluminum interfacial strength, and the better interfacial strength might be due to the rough surface and microcrack morphology of blocky beryllium particles. These research results provide effective experimental and simulation support for the selection of beryllium powder and the design and preparation of high-performance beryllium/aluminum composites.

Effect of Nanoscale W Coating on Corrosion Behavior of Diamond/Aluminum Composites.

The stability of diamond/aluminum composite is of significant importance for its extensive application. In this paper, the interface of diamond/aluminum composite was modified by adding nanoscale W coating on diamond surface. We evaluated the corrosion rate of nanoscale W-coated and uncoated diamond/aluminum composite by a full immersion test and polarization curve test and clarified the corrosion products and corrosion mechanism of the composite. The introduction of W nanoscale coating effectively reduces the corrosion rate of the diamond/aluminum composite. After corrosion, the bending strength and thermal conductivity of the nanoscale W-coated diamond/aluminum composite are considerably higher than those of the uncoated diamond/aluminum composite. The corrosion loss of the material is mainly related to the hydrolysis of the interface product Al4C3, accompanied by the corrosion of the matrix aluminum. Our work provides guidance for improving the life of electronic devices in corrosive environments.

Substance P promotes immunotherapy efficacy for airway allergy.

Background: Allergen-specific immunotherapy (AIT) has been employed in the treatment of allergic diseases for many years. However, the effectiveness of AIT requires improvement. Substance P (SP) can interact with immune cells, modulate immune cell activity, and regulate immune reaction. The purpose of this study is to use SP as an immune regulator to enhance the therapeutic efficacy of AIT. Methods: An established mouse model of the airway allergy disorder (AAD) was employed with ovalbumin as a specific antigen. The AAD response was evaluated through established procedures. AAD mice were treated with AIT employing SP as an immune regulator. Dendritic cells were isolated from the airway tissues by magnetic cell sorting, and were analyzed by RNA sequencing (RNAseq). Results: We observed that after sensitization with ovalbumin, mice exhibited AAD-like symptoms, serum specific IgE, and Th2 polarization. The presence of SP in the course of sensitization prevented the development of AAD. Treating mice with SP by nasal instillations induced IL-10, but not TGF-ß, in dendritic cells of the airway tissues. The most differentially expressed genes (DEG) in the dendritic cells were those related to the IL-10 expression, including Il10, Tac1r, and Mtor. The gene ontology analysis showed that these DEGs mainly mapped to the tachykinin-PI3K-AKT-mTOR pathway. The addition of SP substantially enhanced the therapeutic efficacy of AIT for AAD by inducing antigen specific type 1 regulatory T cells (Tr1 cells). Conclusion: Acting as an immune regulator, SP promotes the therapeutic efficacy for AAD by inducing antigen specific Tr1 cells in the airway tissues.

Designed Synthesis of Compartmented Bienzyme Biocatalysts Based on Core-Shell Zeolitic Imidazole Framework Nanostructures.

For complex cascade biocatalysis, multienzyme compartmentalization helps to optimize substrate transport channels and promote the orderly and tunable progress of step reactions. Herein, a simple and general synthesis strategy is proposed for the construction of a multienzyme biocatalyst by compartmentalizing glucose oxidase and horseradish peroxidase (GOx and HRP) within core-shell zeolite imidazole frameworks (ZIF)-8@ZIF-8 nanostructures. Owing to the combined effects of biomimetic mineralization and the fine regulation of the ZIF-8 growth process, the uniform shell encloses the seed (core) surface by epitaxial growth, and the bienzyme system is accurately localized in a controlled manner. The versatility of this strategy is also reflected in ZIF-67. Meanwhile, with the ability to covalently bind divalent metal ions, lithocholic acid (LCA) is used as a competitive ligand to improve the pore structure of the ZIF from a single micropore to a hierarchical micro/mesopore network, which greatly increases mass transfer efficiency. Furthermore, the multienzyme cascade reaction is exemplified by the oxidation of o-phenylenediamine (OPD). The findings show that the bienzyme assembly strategy significantly affects the biocatalytic efficiency mainly by influencing the utilization efficiency of the intermediate (Hydrogen peroxide, H2 O2 ) between the step reactions. This study sheds new light on facile synthetic routes to constructing in vitro multienzyme biocatalysts.

Signals from the TAFA4-PTEN-PU.1 axis alleviate nasal allergy by modulating the expression of FcεRI in mast cells.

The high-affinity IgE receptor, FcεRI, plays a key role in the antigen-induced mast cell activation. Regulations for FcεRI are not yet well understood. TAFA4 is a molecule derived from neuron tissues, and has immune regulation functions. This study aims to clarify the role of TAFA4 in the regulation of FcεRI expression in mast cells. Nasal secretions were collected from patients with allergic rhinitis (AR) and healthy control (HC) subjects. TAFA4 levels of nasal secretions were evaluated by ELISA. A mouse model AR was developed using ovalbumin as the specific antigen. Negative correlation between TAFA4 and tryptase levels in nasal secretions was observed. TAFA4 could suppress the antigen-related mast cell activation. TAFA4 modulated the transcription of Fcer1g (FcεRI γ gene) in mast cells. Signals from the TAFA4-PTEN-PU.1 axis restricted FcεRI expression in mast cells. Administration of TAFA4 attenuated experimental AR. TAFA4 suppressed the expression of FcεRI in mast cells of airway tissues. TAFA4 can down regulate the expression of FcεRI in mast cells to suppress experimental AR. The data suggest that TAFA4 has translation potential to be developed as an anti-allergy therapy.

Rnf20 inhibition enhances immunotherapy by improving regulatory T cell generation.

BACKGROUND: Allergic disorders are common all over the world. The pathogenesis of allergy is unclear. Therapies for allergic disorders require improvement. Endoplasmic reticulum (ER) stress is one of the factors influencing immune response. The purpose of this study is to improve the effectiveness of immunotherapy for experimental respiratory allergy by targeting the ER stress signal pathway. METHODS: Committed CD4+ T cells were isolated from blood samples collected from patients with allergic rhinitis (AR) and TCR ovalbumin transgenic mice. The effects of TCR engagement and 3-methyl-4-nitrophenol (MNP) on inducing ER stress in committed CD4+ T cells were evaluated. RESULTS: ER stress was detected in antigen-specific CD4+ T cells (sCD4+ T cells) of AR patients. The environmental pollutant MNP increased the expression of the X-binding protein-1 (XBP1) in the committed CD4+ T cells during the TCR engagement. XBP1 mediated the effects of MNP on inhibiting regulatory T cell (Treg) generation. The effects of MNP on induction of protein 20 (Rnf20) in CD4+ T cells were mediated by XBP1. Inhibition of Rnf20 rescued the Treg development from MNP-primed sCD4+ T cells. The ablation of Rnf20 improved the immunotherapy of AR through the restoration of the Treg generation. CONCLUSIONS: ER stress can be detected in CD4+ T cells in TCR engagement. Exposure to MNP exacerbates ER stress in committed CD4+ T cells. Regulation of the ER stress-related Rnf20 expression can restore the generation of Treg from CD4+ T cells of subjects with allergic diseases.

XBP1 is required in Th2 polarization induction in airway allergy.

Rationale: Th2 polarization plays a central role in the pathogenesis of allergic diseases such as airway allergy. The underlying mechanism is not fully understood yet. X-box-binding protein-1 (XBP1) can regulate immune cell activities upon exposing stressful events. The role of XBP1 in the development of Th2 polarization has not yet been explored. Methods: Mice carrying Xbp1-deficient CD4+ T cells were employed to observe the role of XBP1 in the induction of airway allergy. A cell culture model was established to evaluate the role of XBP1 in facilitating the Th2 lineage commitment. Results: We found that Xbp1 ablation in CD4+ T cells prevented induction of Th2 polarization in the mouse airway tract. XBP1 was indispensable in the Th2 lineage commitment. XBP1 mediated the effects of 3-methyl-4-nitrophenol (MNP) on facilitating inducing antigen-specific Th2 response in the airways. Exposure to MNP induced expression of XBP1 in CD4+ T cells. RhoA facilitated the binding between XBP1 and GATA3 in CD4+ T cells. XBP1 induced GATA3 phosphorylation to promote the Il4 gene transcription. Modulation of the RhoA/XBP1 axis mitigated experimental allergic response in the mouse airways. Conclusions: A potential therapeutic target, XBP1, was identified in this study. XBP1 was required in the development of skewed Th2 response in the airways. Inhibiting XBP1 alleviated Th2 polarization-related immune inflammation in the airways. The data suggest that inhibiting XBP1 has the translation potential for the treatment of airway allergy.

5-HT is associated with the dysfunction of regulating T cells in patients with allergic rhinitis.

The dysfunction of regulating T lymphocytes (Treg) is associated with the pathogenesis of many diseases. 5-hydroxytryptamine (5-HT) is capable of interacting with immune cells. The objective of the present study is to shed light on the role of 5-HT in regulating Treg activities. Blood samples were collected from patients with perennial allergic rhinitis (AR). Tregs were isolated from blood samples by magnetic cell sorting. The levels of 5-HT and other cytokines were determined by enzyme-linked immunosorbent assay. The results showed that serum 5-HT levels in patients with AR were higher than in healthy control (HC) subjects. A positive correlation was identified in the data between 5-HT concentrations and AR-related cytokine concentrations in the serum. A negative correlation was found between serum levels of 5-HT and the peripheral frequency of Treg. Exposure to 5-HT enhanced the expression of IL-6 and IL-21 in dendritic cells (DC). Co-culture of 5-HT-primed DCs with Tregs led to the conversion of Th17 cells. STAT3 blockade efficiently abolished the 5-HT-associated conversion of Th17 cells from Tregs. In summary, patients with AR exhibited higher serum concentrations of 5-HT. 5-HT-primed DCs could convert Tregs to Th17 cells.

Effects of Fiber Volume Fraction and Length on the Mechanical Properties of Milled Glass Fiber/Polyurea Composites.

Composites of polyurea (PU) reinforced with milled glass fiber (MGf) were fabricated. The volume fraction and length of the milled glass fiber were varied to study their effects on the morphological and mechanical properties of the MGf/PU composites. The morphological attributes were characterized with scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The SEM investigations revealed a uniform distribution and arbitrary orientation of milled glass fiber in the polyurea matrix. Moreover, it seems that the composites with longer fiber exhibit better interfacial bonding. It was found from the FTIR studies that the incorporation of milled glass fiber into polyurea leads to more phase mixing and decreases the hydrogen bonding of the polyurea matrix, while having a negligible effect on the H-bond strength. The compression tests at different strain rates (0.001, 0.01, 0.1, 1, 2000 and 3000 s-1) and dynamic mechanical properties over the temperature range from -30 to 100 °C at 1 Hz were performed. Experimental results show that the compressive behavior of MGf/PU composites is nonlinear and strain-rate-dependent. Both elastic modulus and flow stress at any given strain increased with strain rate. The composites with higher fiber volume fraction and longer fiber length are more sensitive to strain rate. Furthermore, the elastic modulus, stress at 65% strain and energy absorption capability were studied, taking into account both the effect of fiber volume fraction and mean fiber length. It is noted that an increase in fiber volume fraction and fiber length leads to an increase in elastic modulus, stress at 65% strain and absorbed energy up to ~103%, 83.0% and 137.5%, respectively. The storage and loss moduli of the composites also increase with fiber volume fraction and fiber length. It can be concluded that the addition of milled glass fiber into polyurea not only improves the stiffness of the composites but also increases their energy dissipative capability.

Dispersion and Preparation of Nano-AlN/AA6061 Composites by Pressure Infiltration Method.

Nanomaterials play an important role in metal matrix composites (MMC). In this study, 3.0 wt.%, 6.0 wt.%, and 9.0 wt.% nano-AlN-particles-reinforced AA6061 (nano-AlN/AA6061) composites were successfully prepared by pressure infiltration technique and then hot extruded (HE) at 500 °C. The microstructural characterization of the composites after HE show that the grain structure of the Al matrix is significantly refined, varying from 2 to 20 µm down to 1 to 3 µm. Nano-AlN particles in the composites are agglomerated around the matrix, and the distribution of nano-AlN is improved after HE. The interface between AA6061 and nano-AlN is clean and smooth, without interface reaction products. The 3.0 wt.% nano-AlN/AA6061 composite shows an uppermost yield and supreme tensile strength of 333 MPa and 445 MPa, respectively. The results show that the deformation procedure of the composite is beneficial to the further dispersion of nano-AlN particles and improves the strength of nano-AlN/AA6061 composite. At the same time, the strengthening mechanism active in the composites was discussed.

Enhancing the Strengthening Effect of Graphene-Nanoplates in Al Matrix Composites by Heterogeneous Matrix Design.

In the present work, the properties of graphene-nanoplates/aluminum (GNPs/Al) composites with a heterogeneous matrix design were investigated. The advantage of the heterogeneous matrix was investigated by the finite element method. Then, 0.6 wt.% (GNPs/6061Al)/2024Al (heterogeneous matrix) and 0.6 wt.% GNPs/6061Al composites were prepared by ball milling, pressure infiltration technology, and hot extrusion. The aggregation of GNPs was eliminated and the interlayer slide of GNPs was observed. Mechanical property test results show that the mechanical properties of the heterogeneous matrix composite are better than that of a homogeneous matrix composite, including strength, elastic modulus, and plasticity. It is assumed that the heterogeneous matrix design enhances the non-uniform stress field during the deformation treatment. This improves the dispersion of GNPs, grain refinement, and produces the few-layer graphene (FLG), thus enhancing the strengthening effect of GNPs. Meanwhile, heterogeneous matrix design is thought to introduce more hardening mechanisms to increase the plasticity of materials and improve the intrinsic trade-off of strength and toughness.

Semaphorin-3 Promotes Specific Immunotherapy Effects on Experimental Food Allergy.

Sustaining higher frequency of mast cells in the allergic lesion site has been recognized. Factors causing high numbers of mast cells in the local tissues are not fully understood yet. RAS signaling plays a role in sustaining certain cell activities. This study is aimed at elucidating the role of RAS activation in the apoptosis resistance induction in mast cells and at employing semaphorin 3A to regulate RAS activities in sensitized mast cells and alleviating the allergic response in the intestine. A food allergy (FA) mouse model was developed. Mast cells were isolated from FA mouse intestinal tissues by flow cytometry. Mast cell apoptosis was assessed by staining with annexin V and propidium iodide. We found that aberrantly higher p21-activated kinase-1 (Pak1) expression in FA mast cells was associated with mast cell aggregation in the intestine. Sensitization increased Pak1 expression and apoptosis resistance in intestinal mast cells. RAS and Pak1 mutually potentiated each other in sensitized mast cells. Semaphorin 3A (sema3A) suppressed the Pak1 expression and RAS activation in mast cells. sema3A restored the apoptosis sensitivity in sensitized mast cells. Administration of sema3A potentiated allergen-specific immunotherapy in experimental FA. In conclusion, mast cells of FA mice showed higher Pak1 expression and high RAS activation status that contributed to apoptosis resistance in mast cells. Administration of sema3A restored the sensitivity to apoptosis inducers and promoted the therapeutic effects of specific immunotherapy on experimental FA.

Effect of Microstructure on the Dimensional Stability of Extruded Pure Aluminum.

High-performance extruded aluminum alloys with complex textures suffer significant dimension variation under environmental temperature fluctuations, dramatically decreasing the precision of navigation systems. This research mainly focuses on the effect of the texture of extruded pure aluminum on its dimensional stability after various annealing processes. The result reveals that a significant increment in the area fraction of recrystallized grains with <100> orientation and a decrement in the area fraction of grains with <111> orientation were found with increasing annealing temperature. Moreover, with the annealing temperature increasing from 150 °C to 400 °C, the residual plastic strain after twelve thermal cycles with a temperature range of 120 °C was changed from -1.6 × 10-5 to -4.5 × 10-5. The large amount of equiaxed grains with <100> orientation was formed in the microstructure of the extruded pure aluminum and the average grain size was decreased during thermal cycling. The area fraction of grain with <100> crystallographic orientation of the sample annealed at 400 °C after thermal cycling was 30.9% higher than annealed at 350 °C (23.7%) or at 150 °C (18.7%). It is attributed to the increase in the proportion of recrystallization grains with <100> direction as the annealing temperature increases, provided more nucleation sites for the formation of fine equiaxed grains with <100> orientation. The main orientation of the texture was rotated from parallel to <111> to parallel to <100> after thermal cycling. The change in the orientation of grains contributed to a change in interplanar spacing, which explains the change in the dimension along the extrusion direction during thermal cycling.

Spark Plasma Sintering of AlN/Al Functionally Graded Materials.

In this paper, six-layer AlN/Al gradient composites were prepared by a spark plasma sintering process to study the influences of sintering temperature and holding time on the microstructure and mechanical properties. The well-bonded interface enables the composite to exhibit excellent thermal and mechanical properties. The hardness and thermal expansion properties of the composite exhibit a gradient property. The hardness increased with the volume fraction of AlN while the CTE decreased as the volume fraction of AlN. The thermal expansion reaches the lowest value of 13-14 ppm/K, and the hardness reaches the maximum value of 1.25 GPa, when the target volume fraction of AlN is 45%. The simulation results show that this gradient material can effectively reduce the thermal stress caused by the mismatch of the thermal expansion coefficient as a transmitter and receiver (T/R) module. This paper attempts to provide experimental support for the preparation of gradient Al matrix composites.