Ultra-high Gravity Research Articles

Evaluation of ultra-high degree gravity field models: a case study of Eastern Tibetan Plateau and Sichuan Province

This study validates the ultra-high-degree gravity field models in terms of the internal error estimate and the external precision. Internal error estimate is evaluated by geoid error degree variance and cumulative geoid height errors. The evaluation of the external precision is carried out using observed ground gravity data sets in Qinghai-Tibet Plateau and Sichuan Basin of mainland China. The results show that the geoid degree error is at the millimeter level, and the accumulated geoid error is at the centimeter level, and SGG-UGM-2 has the highest precision in terms of geoid errors. However, in terms of gravity anomaly, the GECO model has the highest precision of 37.080 mGal in the Qinghai-Tibet Plateau, and after terrain correction, its precision can reach 28.907 mGal, an improvement of 22%. In the Sichuan Basin, EGM2008 performs best with a precision of 7.202 mGal; the precision of EGM2008 becomes 6.648 mGal after terrain correction. These results mean that the terrain correction must be considered in the area where topography varies largely, while when the terrain is relatively flat, the effect of terrain on gravity can be ignored.

Anti-penetration performance of high entropy alloy–ceramic gradient composites

A high-entropy alloy–ceramic gradient composite of TiC–TiB2/75vol% Al0.3CoCrFeNi was successfully prepared by combustion synthesis under an ultra-high gravity field, which is a low-cost method with high efficiency. The ceramic particles were gradient distributed in the Al0.3CoCrFeNi matrix, and the hardness of the composite material gradually decreased along the thickness direction. The anti-penetration performance of the gradient composites was simulated using the ANSYS/LS-DYNA explicit simulation program. The results demonstrate that the distribution of the ceramic particles strongly affected the mechanical properties and the anti-penetration performance of the composites. With the same total ceramic volume fraction, the gradient composites exhibit better anti-penetration performance than the corresponding ceramic–metal interlayer composites. The more uneven the ceramic distribution, the greater the elastic modulus and yield stress of the surface layer and, thus, the better the anti-penetration performance.

Fabrication of ceramics/high-entropy alloys gradient composites by combustion synthesis in ultra-high gravity field

The gradient ceramic/metal composite of TiC-TiB2/Al0.3CoCrFeNi was prepared by combustion synthesis under ultra-high gravity field. Right after the formation of the mixture by combustion, the ceramics and metals are separated in an ultra-gravity field due to the difference in mass density, resulted in a gradient distribution of ceramics (TiC-TiB2) along the gravitational field in the high-entropy alloy (Al0.3CoCrFeNi) matrix. The hardness of the material shows a significant gradient change.

Application of Geoid Anomalies to the Tectonic Research in the East Asian Continental Margin

In this paper, we calculated multi-scale residual geoid anomalies with the method of geoid separation processing, according to EGM2008 ultra-high order gravity field model, remove-restore technique and Stokes integral. The East Asian continental margin was selected as the study area. The residual geoid anomalies have been calculated by programming. On the basis of residual geoid anomalies at various orders, the interlayer geoid anomalies at different depths were calculated to depict the spatial distribution characteristics of the residual geoid. Finally, we conducted a detailed geophysical interpretation for the study area according to the geoid anomalies in combination with other geophysical datasets. Four conclusions can be outlined as follows: 1) it is impracticable that geoid anomalies are used in the interpretation of the shallow objects due to the influence of the terrain; 2) the anomalies of residual geoid can reflect the intensity of small-scale mantle convection in the asthenosphere; 3) the interlayer geoid anomalies can reflect the magmatic activities associated with the mantle convection and mantle plume in different scales; 4) the study of the geoid may provide an approach for the research of the subduction zone, mantle convection and mantle plume.

TiB 2 -based Ceramic/1Cr18Ni9Ti Stainless Steel Composite Produced by Combustion Synthesis in Ultra-high Gravity Field

Abstract Based on fusion bonding and atomic interdiffusion between the ceramic and stainless steel, the TiB2-based ceramic/1Cr18Ni9Ti stainless steel composite with chemical composition gradient was produced by combustion system in ultra-high gravity field (CSUGF). The presence of chemical reaction in explosive combustion and the subsequent thermal-vacuum circumstance induced by liquid products in ultra-high gravity make stainless steel partially fused, resulting in fusion bonding. XRD, FESEM and EDS results show that the interface has a good bonding, and the intermediate exhibits three dimensional network ceramic-metal graded microstructure considered as a result of intensive interdiffusion of atomics. Vickers hardness profile reveals the quasi-parabola relationship of the hardness to the testing distance from the ceramic matrix to the steel substrate. Meanwhile, interfacial shear fracture of the composite presents the mixed mode consisting of intercrystalline fracture along TiB2 platelets and ductile fracture in Fe-Ni-Cr alloy, presenting interfacial shear strength (325±25) MPa.

Analysis of the impact on the gravity field determination from the data with the ununiform noise distribution using block-diagonal least squares method

The block-diagonal least squares method, which theoretically has specific requirements for the observation data and the spatial distribution of its precision, plays an important role in ultra-high degree gravity field determination. On the basis of block-diagonal least squares method, three data processing strategies are employed to determine the gravity field models using three kinds of simulated global grid data with different noise spatial distribution in this paper. The numerical results show that when we employed the weight matrix corresponding to the noise of the observation data, the model computed by the least squares using the full normal matrix has much higher precision than the one estimated only using the block part of the normal matrix. The model computed by the block-diagonal least squares method without the weight matrix has slightly lower precision than the model computed using the rigorous least squares with the weight matrix. The result offers valuable reference to the using of block-diagonal least squares method in ultra-high gravity model determination.

Observation and Manipulation of a Capillary Jet in a Centrifuge-Based Droplet Shooting Device

We report observation and manipulation of a capillary jet under ultra-high centrifugal gravity in a proposed capillary-based fluidic device for the synthesis of microparticles in a centrifugal tube called Centrifuge-Based Droplet Shooting Device (CDSD). Using a high-speed camera, we directly observed the dripping to jetting transition of a viscous capillary jet of water and Sodium alginate solution generated from a glass capillary-orifice of a diameter of O (100) m under centrifugal gravity ranging from 190 to 450 g. A non-dimensional analysis shows that the mechanism of the dripping-jetting transition in the CDSD may follow that previously reported for a dripping faucet under standard gravity. We also fabricated calcium alginate microparticles by gelating droplets of sodium alginate solution obtained in the break-up of the capillary jet in the jetting regime and demonstrated fabrication of microbeads-on-a-string structures. We confirmed that the jetting regime of the capillary jet could be used to fabricate smaller particles than that of the dripping regime. The results show that the CDSD would be a more useful device to fabricate various polymeric structures and understand the physics of fluid jets under ultra-high gravity.

Interfacial failure mechanism in tungsten fiber reinforced copper-based composites fabricated by combustion synthesis melt infiltration under ultra-high gravity

Abstract Tungsten fiber reinforced copper-based composites were successfully fabricated by a new method called combustion synthesis melt infiltration under ultra-high gravity. Between the tungsten fibers and the copper matrix, an interlayer consisting of W18O49 needles was observed at the surface of the pickled tungsten fibers. The interfacial strength was measured by the push-out test. For the tungsten fibers with a WO3 surface layer, the failure happened at the interface between the WO3 layer and the copper matrix by the debonding failure mechanism. For the case with the formation of a W18O49 interlayer, the failure happened at the interface between the W18O49 interlayer and tungsten fibers by the brittle failure model, which improved the interfacial strength.

Microstructures and Toughening of TiC-TiB2Ceramic Composites with Cr-Based Alloy Phase Prepared by Combustion Synthesis in High-Gravity Field

Micro-nanocrystalline microstructures which are characterized by TiB2platelets of the average thickness close to or smaller than 1 μm can be achieved in nearly full-density solidified TiC-TiB2ceramic composites with Cr-based alloy phases by combustion synthesis in ultra-high gravity field of 2500 g. The filler phases in ceramic composites are actually Cr-based alloy with a little solidified solution of Ni atoms and Al atoms. The hardness, flexural strength, and fracture toughness of the materials are 18.5 ± 1.5 GPa, 650 ± 35 MPa, and 16.5 ± 1.5 MPa⋅m0.5, respectively. The improved fracture toughness of TiC-TiB2ceramic composites results from crack deflection, crack bridging, and pull-out by a large number of fine TiB2platelets and plastic deformation with some Cr-based alloy phases.

Ballistic Performance of Laminated Composite with TiB<sub>2</sub> Based Ceramic to Ti-6Al-4V Alloy in Continuously-Graded Microstructure

Laminated composite of TiB2 based ceramic to Ti-6Al-V alloy in graded microstructure were achieved by combustion synthesis in ultra-high gravity field. XRD and FESEM results showed the presence of the graded microstructures at the joint which was characterized by multilevel (TiC1-x-TiB-TiB2 + TiB2-Ti-TiC1-x-TiB + TiB2-TiC1-x-TiB-Ti + TiB-TiC1-x-Ti + TiC1-x-Ti) and multiscale (micro-submicro-nano) of the size and the distribution of TiB2 phases and TiB phases. It was considered that liquid fusion, atomic interdiffusion and a series of metallurgical reaction during solidification were reasoned for the continuously-graded microstructure from the ceramic to Ti alloy. Ballistic mass effectiveness coefficients of TiB2 based ceramic and the laminated composite with TiB2 based ceramic to Ti alloy were calculated to be 3.25 and 7.35 respectively by DOP test. The continuously-graded microstructures at the joint from the ceramic to Ti ally was considered to effectively reduce acoustic impedance mismatch between the ceramic and the metal, resulting in the enhanced ballistic performance of the target against the projectile by initiating intensive shear coupling effect.

Microstructure modification and fracture behavior of solidified TiC–TiB2 ceramic prepared by combustion synthesis in ultra-high gravity field

A series of solidified TiC–TiB2 were fabricated by combustion synthesis integrated with ultra high gravity, and the ceramics were comprised of TiB2 primary phases, irregular TiC secondary phases, a few of Al2O3 inclusions and Cr-based metallic phases. Obviously, the increased high gravity field promoted phase separation of Al2O3 droplets from the molten reaction products, which resulted in not only the rapidly reduced Al2O3 inclusions but also the refined microstructure and the improved homogeneity. When high gravity acceleration reached 2500 g, the ultrafine-grained microstructure with the average thickness of TiB2 platelets smaller than 1 μm was achieved. More and more fine TiB2 platelets with aspect ratio of 4–6 participated in the toughening mechanism of crack bridging and subsequent pullout, the maximum fracture toughness could amount to 16.5 ± 1.0 MPa m0.5. Because of rapidly reduced Al2O3 inclusions, the refined microstructure and the improved homogeneity were obtained in the near full-density composite, the maximum flexural strength of 982 ± 20 MPa was also simultaneously achieved in the solidified TiC–TiB2 composite at 2500 g.

Laminated Composite of Solidified TiC-TiB<sub>2</sub> Ceramic to 1Cr18Ni9Ti Stainless Steel Achieved by Combustion Synthesis in High-Gravity Field

By combining mechanical activation and combustion synthesis in ultrahigh gravity field, the laminated composite of TiB2based ceramic to stainless steel was achieved in continuously-graded composition and microstructure, and within the Fe-Cr based intermediate Ti-Fe enriched carbides and fine TiB2platelets decreased gradually in size and volume fraction from the ceramic to stainless steel. Because of the sequent presence of thermal explosion, the dissolution of the molten stainless steel to TiC-TiB2liquid, the formation of diffusion-controlled concentration gradient from the ceramic liquid to the alloy liquid, the rapid sequent solidification of the ceramic and the alloy, the laminated composite is achieved in multilevel, scale-span hybrid microstructure that the different-size, different-morphology Fe-Cr alloy phases alternate with TiB2platelets and irregular TiC grains in size from micrometer to micro-nanometer.

Microstructures and Crack Propagation in the Joint of Solidified TiC-TiB<sub>2</sub> to Ti-6Al-4V Prepared by Reactive Fusion Bonding in Ultrahigh Gravity Field

By taking combustion synthesis in ultrahigh gravity field to prepare solidified TiC-TiB2 composite ceramic, laminated composite of the ceramic to Ti-6Al-4V was achieved by fusion bonding and atomic inter-diffusion, and within the joint there formed the unique microstructure of multiscale (micrometer-micro/nanometer-nanometer) and multilevel characterized by size and distribution of TiB2 and TiB due to the presence of a series of metallurgical reaction including peritectic reaction of solidified and Ti liquid, direct growth of TiB solids from liquid Ti and subsequent eutectic reaction of TiB solids and liquid Ti. FEMSEM images of crack propagation paths at the joint showed despite the contribution from crack bridging of micro-nanometer TiB2 and TiB platelets to crack propagation resistance, residual stress toughening and subsequent crack pinning by micro-nanometer TiB2 ,TiB platelets and needle-like nanometer TiB grains as well as ductile phase toughening and bridging toughening by Ti metallic phases became the primary resistances to crack propagation, thereby presenting the delayed fracture behavior in the joint, so that shear fracture usually occurred at the solidified Ti alloy rather than the joint, and shear strength of 375 ± 55 MPa was achieved between the solidified ceramic and Ti alloy.

Effects of Ball Milling Processing on Solidified TiC-TiB<sub>2</sub> Composites Prepared by Combustion Synthesis in High Gravity Field

By combining ball milling processing with combustion synthesis in ultrahigh gravity field, the solidified TiC-TiB2 composite was achieved with fine-grained and ultrafine-grained microstructure. It is considered that taking balling milling processing to mechanically activate powder blend promotes thermal explosion to occur in ultrahigh gravity field by reducing ignition temperature, increases sharply the actual temperature of full-liquid product, thereby not only accelerating liquid-liquid separation of TiC-TiB2 liquid and Al2O3 droplets, but also refining the solidified microstructure by enhancing undercooling of TiC-TiB2 liquid, finally, brings about a series of dramatic improvements in densification and mechanical properties of the ceramic.

Tailoring of interfaces in amorphous silicon–germanium multilayers on the atomic scale by ultra-high gravity

Amorphous Si/Ge multilayers containing diffuse interfaces have been prepared, heated in an ultra-centrifuge and subsequent interface structure modifications observed by X-ray reflectivity. The thickness of the Si/Ge and Ge/Si interface zones became asymmetrical owing to various effects occurring on the different atoms parallel to the direction of gravity-induced diffusion. The technique could prove useful for tuning physical (electronic, magnetic or optical) properties of layered structures.

Melt Modification and Microstructure Homogeneity of Solidified TiC-TiB<sub>2 </sub>Composites Prepared by Combustion Synthesis in Ultrahigh Gravity Field

By introducing (CrO3+Al) high-energy thermit into (Ti+B4C) system and designing adiabatic temperature of reactive system as 3000°C,3200°C, 3400°C, 3600°C and 3800°C respectively, a series of solidified TiC-TiB2were prepared by combustion synthesis in ultrahigh gravity field with the acceleration 2000 g. XRD, FESEM and EDS results showed that the solidified TiCTiB2were composed of a number of TiB2primary platelets, irregular TiC secondary grains, and a few of isolated Al2O3inclusions and Cr-based alloy. Because of the enhanced Stokes flow in mixed melt with the increased adiabatic temperature, Al2O3droplets were promoted to float up and separate from TiC-TiB2-Me liquid while constitutional distribution became more and more uniform in TiC-TiB2-Me liquid, resulting in not only the sharply-reduced Al2O3inclusions in the solidified ceramic but also the refined microstructure and the improved homogeneity in the ceramic, and ultrafine-grained microstructure with a average thickness of TiB2platelets smaller than 1μm began to appear in near-full-density ceramic as the adiabatic temperature exceeded 3600°C, so the densification, fracture toughness and flexural strength of the ceramic were enhanced with the increased adiabatic temperature of the reactive system.

Composition Modification and Mechanical Properties of Solidified TiB<sub>2</sub>-Based Ceramic Prepared by Combustion Synthesis in Ultra-High Gravity Field

The solidified TiC-TiB2 ceramics with excessive Ti mole content were prepared through adjusting the Ti additional agent in combustion system with ultra-high-gravity of 2000 g, and the ceramics were comprised of TiB2 primary phases, irregular TiC1-x secondary phases, a few of Al2O3 inclusions and Cr-Ti-Al metallic phases. The additional Ti content resulted in not only the rapidly-reduced Al2O3 inclusions but also the refined microstructure and the improved homogeneity in the solidified microstructure. As the Ti additional agent was increased, more and more Ti atoms could participate in the formation of nonstoichiometric TiC1-x phases and Cr-Ti-Al metallic phases. The maximum fracture toughness of 18.5 ± 1.0 MP · m0.5 in current solidified TiC-TiB2composite was achieved because of the less Al2O3 inclusions, the refined microstructure and the Ti-rich Cr-Ti-Al metallic phases obtained in the near-full-density composite. The high fracture toughness contributed from not only mechanism of crack deflection, crack-bridging and pull-out by a large number of fine TiB2 platelets, but also the ductile fracture toughening result from plastic deformation of Cr-Ti-Al metallic phases.

Composite of TiC-TiB<sub>2</sub> Ceramic with Ti-6Al-4V Alloy Prepared by Combustion Synthesis in Ultrahigh Gravity Field

Based on taking combustion synthesis into high-gravity field to fabricate high-hardness bulk solidified TiC-TiB2 composite, layered composite of solidified TiC-TiB2 ceramic to Ti-6Al-4V alloy was obtained by the introduction of Ti-6Al-4V alloy plates at the bottom of graphite crucible. XRD, FESEM and EDS results showed that the layered composite was achieved in multi-scale (micron/submicron/micro-nanometer) and multi-level (TiC1-x-TiB-TiB2 + TiB2-Ti-TiC1-x-TiB + TiB2-TiC1-x-TiB-Ti + TiB-TiC1-x-Ti + TiC1-x-Ti + Ti) graded microstructure between the ceramic and Ti alloy, which was characterized by size and distribution of TiB2 and TiB, thereby paving a new way for developing light-weight materials for special engineering.

Effects of Ultra-High Gravity Field on the Microstructure and Mechanical Properties of Solidified TiC-TiB2 Ceramic Prepared by Combustion Synthesis

Based on increasing the acceleration of high-gravity field from 500 g to 2500 g, a series of TiC-TiB2 composites are prepared by combustion synthesis in high-gravity field, and microstructure modification, microstructure homogeneity and mechanical properties of TiC-TiB2 composites are discussed in terms of liquid-liquid separation of TiC-TiB2 and Al2O3 in high gravity field. XRD, FESEM and EDS results showed that by increasing the acceleration of high gravity field, Al2O3 inclusions in the ceramic decreased both in volume fraction and size due to the enhanced separation of TiC-TiB2 liquid and Al2O3 liquid, while the enhanced Stokes flow induced by the enhanced liquid-liquid separation also promoted the constitutional homogeneity of TiC-TiB2 melt, thereby bringing about the refinement of the solidified microstructures, finally, making Vickers hardness and fracture toughness of the composites increase with the acceleration of high gravity field.

Fracture Behavior of Solidified TiC-TiB<sub>2</sub> Ceramic Prepared by Combustion Synthesis in Ultra-High Gravity Field

A series of TiC-TiB2 ceramics were prepared by combustion synthesis in ultra-high gravity field, the microstructure, fracture behavior and toughening mechanism of the composite ceramic are discussed. The maximum fracture toughness of 13.1 MPa · m0.5 is achieved in TiC-66.7%TiB2, very close to the values (10~15 MPa · m0.5) of fiber-reinforced ceramic composite, contributed from the intensive coupled toughening mechanisms of crack deflection, frictionally crack-bridging and pull out by a large number of fine TiB2 platelets and ductile phase toughing caused by a few Cr-Al metallic phases.