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Novel plastic deformation was exhibited in amorphous oxides, attributed to the metastable state of amorphous phase with free volume and disordering structure; however, metastable degrees can be quite different in amorphous phases, and the effect of metastability on plastic deformation was never reported in amorphous oxides. In this work, the metastable degree of amorphous phase was controlled by adjusting the temperature in powder calcination, and evaluated through free volume and disordering degree, using the true density of amorphous powder, DSC and 27 Al MAS-NMR. Under compression at 500 °C, the sample with lowest metastability exhibited brittle fracture; however, the other two with higher metastable degrees displayed plastic strain of 3.5% and 5.2%. The enhanced plastic deformation benefited from higher metastability was mainly attributed to easier formation of shear bands. For amorphous phase with higher metastability, the atomic mobility and local free volume were larger, which could improve the formation of shear bands and promote the plasticity according to free volume theory. This work could inspire new methods to improve the plastic deformation in amorphous materials. [ABSTRACT FROM AUTHOR]

Porous alumina ceramics with inter-locked plate-like structure were successfully fabricated by the tert -butyl alcohol-based gel-casting method. The effects of Al/Si mole ratio on the structure and properties of the obtained products were investigated. The formation process of the inter-locked structure was analyzed. The products fabricated with the one-step method, in which the growth of plate-like alumina and the formation of the inter-locked structure were combined together, exhibited a high porosity of 76.21%, a compressive strength of 0.525 MPa and a low thermal conductivity of 0.495 W/mK, while the products fabricated by the two-step method after sintered at 1500 °C using the grinded powders after 700 °C heat-treatment as the starting materials possessed a relatively high compressive strength of 4.80 MPa. The obtained porous alumina ceramics were promising flexible insulant materials for the application in high-temperature field. [ABSTRACT FROM AUTHOR]

The feature of "curing at low temperature, directly used in extreme conditions" made the adhesion technique more suitable for engineering application. The superalloy was successfully bonded at high temperatures by a multi-components modified, phenix-silicone-based adhesive, through forming various ceramics and intermetallics. The intermetallization process not only modified the thermal expansibility of adhesive, but also improved the compositional continuity and reaction extent around bonding interface. With the heating temperature increasing from 500 °C to 1000 °C, various high-temperature-resistant phases in turn generated in adhesive, and the chemical reactions on interfaces became more and more intense. Eventually, the room temperature shear strength of joints calcined at 700 °C reached the maximum value of 28.3 MPa, and the high temperature strength was still up to 18.4 MPa at 800 °C. Moreover, after 6 thermal cycles, the residual strength for joints calcined at 700 °C almost remained ∼13 MPa. The exclusive adhesive absolutely facilitated the repair and connection of engineering superalloy. Image 1 • The convenient use is "one-time connection at room-temperature, valid to 1000 °C without post-processing". • The CTE of adhesive is matched well with superalloys. • The reaction transition layer greatly guaranteed the bonding performance. [ABSTRACT FROM AUTHOR]

Abstract A modified superalloy-used heat-resistant adhesive, which can cure at room temperature and provide excellent bonding effect in a wide temperature range from RT to 1000 °C, was prepared from silicone resin as matrix, and Ni, Al, B 4 C, low-temperature-melting glass powder as additives. After pre-calcination, the bonding strength of adhesive reached 30.1 MPa after 700°C-calcination and maintained above 15.7 MPa during the whole heating process as the mixture of Ni-based intermetallics, heat-resistant ceramic generated and high viscosity glass generated in the adhesive. Without pre-calcination, the bonding strength still kept above 10.5 MPa during test from RT to 900 °C and decreased to 4.3 MPa at 1000 °C. Graphical abstract Image 1 Highlights • This adhesive provides excellent bonding strength from room temperature to 1000 °C for superalloys joining. • The bonding effect of adhesive at high temperatures is estimated by high-temperature shear test. • The practical use is "one-time joining at room temperature, valid to 1000 °C without post-processing". • This adhesive can be used not only for the manufacture of superalloy components but also for the repair of broken parts. [ABSTRACT FROM AUTHOR]

A novel heat-resistant phosphate-based adhesive for bonding superalloys was developed from phosphates as matrix, and B 4 C, Si as well as low temperature melting Zn-B-Al-Si-R glass as fillers. It can cure at room temperature (RT) and provide no less than 5 MPa in a wider temperature range of RT-1000 °C. The addition of these fillers boosted the thermal expansion of adhesive, improved the structure of bonding area, and provided reactant sources for heat-resistant components. After calcination at 1000 °C, the bonding strength reached the maximum of 7.8 MPa as more heat-resistant ceramics and high-temperature melting glass generated in adhesive, and deeper chemical reactions happen on interface. This novel adhesive greatly facilitated the repair of superalloys, especially for non-weight-bearing superalloy slices or flakes. [ABSTRACT FROM AUTHOR]

Mullite fibrous ceramics with a two-dimensional planar random structure was prepared via a pressure infiltration method. The in-plane and out-of-plane mechanical properties, thermal expansion coefficients and thermal conductivities were compared. MoSi 2 -borosilicate glass coatings were applied on two adjacent surfaces of the as-prepared mullite fibrous ceramics via an in-situ reaction method. The bonding strength and thermal shock resistance of the two coatings were compared. Results show that higher crosslinking degree and more fiber orientating in the planes resulted in the fact that the in-plane compressive and tensile strength of the ceramics were 4.6 times and 2.1 times higher than the out-of-planes values, respectively. The in-plane CTE (Coefficient of Thermal Expansion), thermal conductivity and permeability were also higher than the out-of-plane ones. The interface bonding strength of Coating B (coated perpendicular to the planes) was higher than that of Coating A (coated parallel to the planes), because of the better mechanical locking at the interface and the higher tensile strength of the substrate. Besides, Coating B presented a better thermal shock resistance because the CTE of the substrate parallel to Coating B was closer to the CTE of the coating, and the substrate was more complaint parallel to Coating B so that could absorb some of the thermal stress by deformation. [ABSTRACT FROM AUTHOR]

Buoyancy material with high temperature resistance was successfully prepared through a tert-butyl alcohol gelcasting process. Borosilicate glass (BG) and hollow glass microspheres (HGMs) with different average diameters were used as the matrix and the filler, respectively. Results show that the compressive strength increased with the decrease of the mean diameter of HGMs, and the sample consisting of the filler of HGMs with a small average diameter exhibited high compressive strength of 25.04 MPa. Young's modulus values of the composite sintered at 700 °C and 750 °C were distributed over in the range of the values predicted from Ashby-Gibson model to Hashin-Shtrikman model and other moduli values agreed well with that of Past model prediction. Weibull moduli ( m ) reflecting the variation degree of the sample compressive strength were in the range of 5–15. The compressive strength of the composites composed of the HGMs with small average particle size tested at 500 °C was as high as 7.94 MPa. [ABSTRACT FROM AUTHOR]

A type of buoyancy material with excellent temperature resistance was successfully prepared through a molding method, and the hollow glass microspheres (HGMs) and silicon oxide (SiO 2 ) were used as the filler and the matrix, respectively. The effect of sintering temperature on mechanical performance, microstructure, and high-temperature performance of the HGMs/SiO 2 composite were investigated in the study. The HGMs/SiO 2 composite exhibited low density (0.47–0.53 g/cm 3 ), high porosity (66.7–75.6%), low thermal conductivity (0.18–0.27 W/(m·K)), and relatively high compressive strength (3.8–5.2 MPa) properties. The values of Weibull moduli m used to predict the variation degree of compressive strength during the compression process was in the range of 5–15 and its values for the samples sintered at 850 °C was 14.64. Two stages namely elastic stage and fracture stage were shown in the stress-strain curves and in the elastic stage, the stress increased linearly with increasing of the strain until reaching the maximum stress. In the fracture stage, the sample gradually destroyed with further increasing of the strain until complete failure. The compressive strength of the HGMs/SiO 2 composites tested at high-temperature was larger than that of the one tested at room temperature. The HGMs/SiO 2 composite exhibited low density, low thermal conductivity and excellent temperature resistance properties and can be used as the structural material or buoyancy material in the deep sea field in the near future. [ABSTRACT FROM AUTHOR]

Two infrared radiating coatings with borosilicate glass as binder and MoSi 2 as emittance agent were prepared on mullite fibrous ceramics by an in-situ reaction method and a two-step method, respectively. The in-situ reaction coating was prepared from Si, B 2 O 3 and MoSi 2 , in which borosilicate glass was obtained through the in-situ reaction of Si, B 2 O 3 and O 2 . By contrast, the two-step method included the preparation of borosilicate glass powders by a melt-quench technique and then coating preparation with MoSi 2 and the glass powders. The structure, phase composition, thermal endurance, infrared radiation property and impact resistance of the two coatings were compared. The results showed that the in-situ reaction coating was denser, and much less MoSi 2 therein was oxidized during sintering (11.3%) than that in the two-step coating (67.0%), resulted from the oxygen diffusion barrier formed by molten B 2 O 3 at approximately 450 °C. The in-situ reaction coating possessed better thermal endurance due to its higher MoSi 2 content and denser structure. In addition, the in-situ reaction coating had higher emissivity (0.787) and better impact resistance (0.051 J) than the two-step coating (0.706, 0.038 J). [ABSTRACT FROM AUTHOR]

A modified polymer adhesive characterized by “one-time connection at low-temperature without post-treatment” was developed for joining mullite ceramic. Without pre-calcination, the bonding strength of cured adhesive maintained above 6.5 MPa during the whole heating process and even reached 24.8 MPa at 1300 °C. After pre-calcination at 1300 °C, the adhesive obtained the optimum bonding performance as much more heat-resistant ceramics and high-temperature melting glass generated in adhesive. Its bonding strength kept about 45 MPa during test from RT to 700 °C, while the value decreased to 28.5 MPa at 1300 °C because of the melting of newly-formed glass. With increasing thermal-cycling times at 1300 °C, the value could maintain at about 35.2 MPa. [ABSTRACT FROM AUTHOR]

A SiC whisker reinforced phosphate adhesive was developed for bonding carbon/carbon composites. A kind of spine-like SiCw with a large specific surface area was synthesized at first and then was chosen as the reinforcement phase. It was found that the mechanical performance of adhesive was promoted by the appropriate amount (1 wt.%) of SiCw within the whole heat-treatment temperature range, while the excessive whisker content caused a side effect. With the temperature increasing, the variation of composition and structure of adhesive was closely related to the reinforcing effect of whiskers at different temperatures. Moreover, the reinforcement effect from 900 °C to 1500 °C was better than that below 900 °C. At 1300 °C, the fracture displacement could be extended by 100%, which was attributed to the influence of both spine-like SiCw and the newly-formed slender SiCw. [ABSTRACT FROM AUTHOR]

A new practical phosphate adhesive was prepared based on aluminum and phosphate as matrix and SiO 2 and B 4 C as additives, which can be applied to join oxide and non-oxide ceramics under air and argon atmospheres. After being cured at room temperature, the as-received joints do not need subsequent processing and can keep stable shear strength within the whole heat treatment process. Its bonding effect for mullite under air was better than that for SiC under argon. The shear strength of mullite joints could be up to 14.5 MPa after treatment at 1300 °C, while that of SiC joints was about 9 MPa. [ABSTRACT FROM AUTHOR]