Study of high pressure sintering behavior of CBN composites starting with CBN-Al mixtures

Cubic boron nitride(CBN) composites starting with CBN-Al mixtures were sintered on WC-16 wt%Co substrate under static high pressure of 5.0 GPa at temperatures of 800 to 1 400℃for 30 min.Vickers hardness of the sintered samples increased with increasing CBN content and the highest hardness of 32.7 GPa was achieved for the CBN-5 wt%Al specimens sintered at 1 400℃.The reactions between CBN and Al started to occur at about 900℃and the reaction products strongly depended on the Al content,sintering temperature and Co diffused from the substrates according to the x-ray diffraction(XRD) observations.The CBN composite sintered at 1 200℃from a CBN-15 wt%Al mixture showed the best cutting performance.

Ferroelectric behaviour of 30nm BaTiO3 ceramics prepared by high pressure assisted sintering

Dense nanocrystalline BaTiO3 ceramics with a homogeneous grain size of 30 nm was obtained by pressure assisted sintering. The ferroelectric behaviour of the ceramics was characterized by the dielectric peak at around 120 ℃, the P-E hysteresis loop and some ferroelectric domains. These experimental results indicate that the critical grain size for the disappearance of ferroelectricity in nanocrystalline BaTiO3 ceramics fabricated by pressure assisted sintering is below 30 nm. The ferroelectric property decreasing with decreasing grain size can be explained by the lowered tetragonality and the ＇dilution＇ effect of grain boundaries.

Effects of sintering pressure and temperature on microstructure and tribological characteristic of Cu-based aircraft brake material

A novel Cu-based P/M aircraft brake material was prepared and the effects of sintering pressure and temperature on microstructure and tribological characteristic were investigated. For the constant sintering temperature, when the sintering pressure increases from 0.5 MPa to 1.5 MPa, the porosity, wear loss and friction coefficient decrease remarkably. When the sintering pressure increases from 1.5 MPa to 2.5 MPa, the porosity further decreases but in a little degree and wear behaviors are improved slightly. However, once the sintering pressure is larger than 2.5 MPa, it has no obvious effect on microstructure and tribological characteristic. For the constant sintering pressure, when the sintering temperature increases from 900 ℃ to 930 ℃, the sintered density remarkably increases, and wear behaviors are obviously improved. For further increasing sintering temperature to 1 000 ℃, the density keeps on increasing, but wear behaviors change slightly.

High-pressure sintering and magnetic properties of Fe_(86)Zr_(11-x)Nb_xB_3(x=5.5, 6) amorphous alloys

The thermal stability of milling Fe86Zr11-xNbxB3（x=5.5, 6） melt-spun strip powders and the influence of high-pressure sintering conditions on phase component and grain size of bulk alloys were investigated by X-ray diffractometry（XRD）, differential scanning calorimetry（DSC） and scanning electron microscopy（SEM）. The results show that milling melt-spun powder remains in the amorphous state, and the crystallization temperature of which is 480530℃, the apparent activation energy Ep of crystallization process is 294.1219.5kJ/mol. The increasing Nb content can increase crystallization temperature and decrease Ep. Under the sintering conditions of 5.5GPa/3min, when Pw is 1150W, single phase α-Fe nanocrystalline （20.626.7nm） bulk alloy with relative density higher than 99.0% can be obtained. Under the sintering conditions of 5.5GPa/1150W/3min, the magnetic properties of these nanocrystalline bulk alloys are Fe86Zr5.5Nb5.5B3 alloy, Bs=1.15T, Hc=5.08kA·m-1; Fe86Zr5Nb6B3 alloy, Bs=1.26T, Hc=4.27kA·m-1.

Recent advances of high-pressure generation in a multianvil apparatus using sintered diamond anvils

The tried and tested multianvil apparatus has been widely used for high-pressure and hightemperature experimental studies in Earth science. As a result, many important results have been obtained for a better understanding of the components, structure and evolution of the Earth. Due to the strength limi- tation of materials, the attainable multianvil pressure is generally limited to about 30 GPa （corresponding to about 900 km of the depth in the Earth） when tungsten carbide cubes are adopted as second-stage anvils. Compared with tungsten carbide, the sintered diamond is a much harder material. The sintered diamond cubes were introduced as second-stage anvils in a 6--8 type multianvil apparatus in the 1980s, which largely enhanced the capacity of pressure generation in a large volume press. With the development of material synthesis and processing techniques, a large sintered diamond cube （14 ram） is now available. Recently, maximum attainable pressures reaching higher than 90 GPa （corresponding to about 2700 km of the depth in the Earth） have been generated at room temperature by adopting 14-mm sintered diamond anvils. Using this technique, a few researches have been carried out by the quenched method or combined with synchrotron radiation in situ observation. In this paper we review the properties of sintered diamond and the evolu- tion of pressure generation using sintered diamond anvils. As-yet unsolved problems and perspectives for uses in Earth Science are also discussed.

Structural, Pasting, and Thermal Properties of Ultra-high Pressure-treated Lotus Seed Starch

Lotus seed starch （15%, w/w） was subjected to ultra-high pressure （UHP） at 500 MPa for 10～60 min. The effects of UHP on the structural, pasting, and thermal properties of starch were investigated using solid-state 13C CP/MAS NMR, differential scanning calorimetry （DSC）, HPSEC-MALLS-RI, and a rapid visco analyzer. The 13C CP/MAS NMR results revealed a reduction in the relative crystallinity and peak intensity of the crystalline state with increasing the UHP time. The molecular weight of native starch was 1.433 × 107 Da, which was higher than that of the UHP-treated starch. Viscograms of UHP-treated starch revealed an increase in paste viscosity, peak time, and pasting temperature and a reduction in breakdown and setback viscosity compared to the native starch. Furthermore, the DSC results showed a reduction in gelatinization temperature and gelatinization enthalpy with increasing the UHP time.

Computational Analysis of Selective Laser Sintering of Inconel 625

A two-dimensional multi-physics finite element model is developed to simulate the Selective Laser Sintering(SLS)process using Inconel 625 powders.The validity of the developed model is first assessed by comparing its results with experimental data.Various factors such as phase transition,recoil pressure,surface tension,and theMarangoni force are considered.The study’s findings underscore that the morphology and thermal-fluid dynamics of the molten pool in the SLS process are predominantly shaped by the influence of the Marangoni force and recoil pressure acting on its surface.The recoil pressure at the front of the laser spot rises exponentially with temperature,making the liquid metal move downward,and creating a depression at the pool’s head.It also causes particles to splash from the pool’s rear edge.The study explores the influence of the backward Marangoni force,where hightemperature liquid flows from the front to the rear of the molten pool,creating a vortex and moving the pool in the rear.Process parameters like laser intensity,scan speed,and spot size were analyzed.The findings indicate that higher laser power lower scanning speed and laser beam spot size lead to increased width and depth of the molten pool.

Effects of ultra-high hydrostatic pressure on foaming and physical-chemistry properties of egg white

The influences of ultra-high hydrostatic pressure treatment on foaming and physical properties (solubility, hydrophobicity and sulfhydryl content) of egg white were investigated. A pressure range of 0-500 MPa, time range of 0-20 min and pH range of 7.5-8.5 were selected. The foaming property of egg white is improved by 350Mpa and 10min. The treatment resulted in in- crease of sulfhydryl content of egg white, while solubility and hydrophobicity were significantly decreased.

Fabrication and residual stresses of aluminum nitride ceramics sintered at high-pressure

High-density AlN ceramics were fabricated without sintering additives at high pressure(5.0 GPa) and temperature(1300～1800℃).The sintered bodies were characterized by XRD,SEM and micro-Raman spectroscopy(MRS).Controlling fracture mode was intragranular when the sintering temperature was as low as 1400℃under 5.0 GPa.The values of residual stresses due to the distortion of the AlN lattice were assessed using the Micro-Raman Spectroscopy(MRS).The residual compression stress of the AlN ceramics sintered at 5.0 GPaand 1700℃for 125 min is 2.0 GPa.The residual compression stress is increased according to the extension of the sintering time.

Analysis on performance and test of a new type of ultra-high pressure pipe joint

Analysis as well as application of ultra-high pressure hydraulic system and elements has become a trend. The structure and operation principle of a new type of ultra-high pressure pipe joint is introduced. The structure of the new type of ultra-high pressure pipe joint is simple and is easy to be produced. The finite element model on two working conditions( preload condition with 30 N·m torque and static-loading condition with 70 MPa pressure) is built and computed. The width of contact area,the equivalent stress status,as well as the contact pressure status are plotted and analyzed. According to the national standard,test on air-tightness,blasting,and cyclic endurance is conducted and the results show that the new type of ultra-high pressure pipe joint has the sealability for ultra-high pressure up to 70 MPa,and the DN6 ultra-high pressure pipe joint can provide effective seal under70 MPa fluid pressure. The research can provide a thinking and method on designing ultra-high pressure pipe joint and push forward the development of ultra-high pressure hydraulic system.

Enzymatic Hydrolysis of Hairtail Surimi in an Ultra-High Pressure Bioreactor

Amino acids have been extracted from Hairtail surimi using enzymes in an ultra-high pressure bioreactor. The extraction efficiency of different enzymes including papain, trypsin, and proteases (acid, neutral, alkaline) also has been evaluated, and it has been discovered that neutral protease behaved the best. The amino acids were analyzed using automatic amino acid analyzer, and the enzymatic digestion conditions were optimized. For neutral protease, the optimal condition was 50℃, 250 MPa, pH 7.0. Material to liquid ratio of enzyme is 6%. More than 29 amino acids were detected after 24 hours of hydrolysis;the enzymatic hydrolysis rate can reach 83.29%. The results show that enzymatic digestion under ultra-high-pressure provides a very promising approach to extract amino acids from Hairtail surimi.

THERMAL MODELLING OF COLLISIONAL OROGENY: IMPLICATIONS FOR THE ULTRA-HIGH PRESSURE METAMORPHISM

The petrological research on the ultra high pressure metamorphism (UHP) of collisional orogen indicates that the upper crustal rocks is subducted to depths exceeding 100 km, and returned to the surface rapidly. In this study, we investigate the thermal structure of collisional orogen as a slab of continental lithosphere being subducted beneath an overriding wedge of continental lithosphere by the 2 D finite element method. The advection heat transfer due to the accretion of orogenic wedge is considered. The wedge is composed of the upper crust materials through the accretion from the down going plate to the upper plate. For identifying the significance of the geometric and/or kinetic factors on the thermal structure of continental subduction, the different combinations of parameters, including dip angle of subduction zone, accretion or erosion rates, and the convergence velocity etc., are used in modelling. The time span of continental subduction in our calculation is less than 30 Ma, according to the short duration of ultra deep subduction of continental slab suggested by the preservation of metastable pre peak low pressure mineralogy assemblage in the garnet of UHP rocks. Therefore, the steep dip angle of down going plate and/or low rate of accretion favour the ultra deep subduction of upper crust materials, especially for the slower down going slab. Meanwhile, taking the erosion rate as the level of exhumation rate of UHP rocks in some orogens (i.e., 1-2 km/Ma or more) does not result in the anatexis melting of crust of the overriding plate, due to the cooling effect of the rapid down going slab. However, the temperature structures of all models are generally cooler than those recovered by thermobarometric studies of the UHP rocks. This implies the significant increase of temperature after the rapid subduction of continental slab. Following the method of Davies and von Blackenburg (1998), we show that the slab breakoff can occur at the depth exceeding 100 km. Thermal modelling on the post subduction stage shows the heating related to the plate breakoff can cause the higher temperature recorded by the exhumed UHP rocks. The higher geotherm during post subduction stage leads to the weak strength of the orogenic wedge, and favours the faster upward movement of the UHP rock slices as ductile agents. The lower temperature gradient of the subduction slab predicted by modelling suggests the cold subducting slab could have transported significant fluids to mantle depth, not released during subduction. Accordingly, the absence of coeval calc alkalic magmatism in UHP orogens might resulted from the lower temperature as well as the fluid free circumstance, both are related to the rapid subduction of cold plate. Therefore, shear heating is not needed for explanation the thermal evolution of UHP orogen. On the other hand, the post collisional or late stage granitic plutonism is closely related to the deep seated heat producing materials of the accretion wedge.

Application of pre-alloyed powders for diamond tools by ultrahigh pressure water atomization

Copper, iron and cobalt based pre-alloyed powders for diamond tools were prepared by ultrahigh pressure water atomization（UPWA） process. Pre-alloyed powders prepared by different processes including UPWA, conventional water atomization （CWA） and elemental metal mechanical mixing （EMMM） were sintered to segments and then compared in mechanical properties, holding force between matrix and diamond, fracture morphology of blank and sintering diamond section containing matrix. The results showed that the pre-alloyed powder prepared by UPWA exhibits the best mechanical properties including the relative density, the hardness and the bending strength of matrix sinteredsegment. Sintered segments fractography of UPWA pre-alloyed powder indicatesmechanical mosaic strength and chemical bonding force between the pre-alloyed powder and the diamond, leading to the great increase in the holding force between matrix and diamond. The mechanical performance andthe service life of diamond tools were greatly improved by UPWA pre-alloyed powders.

A Breakthrough in Pressure Generation by a Kawai-Type Multi-Anvil Apparatus with Tungsten Carbide Anvils

Expansion of the pressure range of Kawai-type multi-anvil presses (KMAPs) with tungsten carbide (WC) anvils is called for, especially in the field of Earth science. However, no significant progress in pressure generation has been made for 40 years. Our recent studies have expanded the pressure generation of a KMAP with WC anvils to 65 GPa, which is the world record for high-pressure generation in this device and is more than 2.5 times higher than conventional pressure generation. We have also successfully generated pressures of about 50 GPa at high temperatures. This work reviews our recently developed technology for high-pressure generation. High-pressure generation at room temperature and at high temperature was attained by integration of the following techniques:① a precisely aligned guideblock system,② a high degree of hardness of the second-stage anvils,③ tapering of the second-stage anvil faces,④ a high-pressure cell consisting of materials with a high bulk modulus, and ⑤ high thermal insulation of the furnace. Our high-pressure technology will facilitate investigation of the phase stability and physical properties of materials under the conditions of the upper part of the lower mantle, and will permit the synthesis and characterization of novel materials.

Evolution of carbides and carbon content in matrix of an ultra-high carbon sintered steel during heat treatment process

DTA, thermal expansion, XRD, and SEM were used to evaluate the effect of quenching temperature on the mechanical properties and microstructure of a novel sintered steel Fe-6Co-1Ni-5Cr-5Mo-1C. Lattice parameters and the mass fraction of carbon dissolved in the matrix of the steel quenched were investigated. It is discovered that the hardness of the steel increases with quenching temperature in the range of 840-900℃ and remains constant in the range of 900 to 1100℃. It decreases rapidly when the temperature is higher than 1100℃. The mass fraction of carbon dissolved in the matrix of the steel quenched at 840℃ is 0.38, but when the quenching temperature is increased to 1150℃, it increases to 0.98. The carbides formed during sintering are still present at grain boundaries and in the matrix of the steel quenched at low quenching temperatures, such as 840℃. When the quenching temperature is increased to 1150℃, most of the carbides at grain boundaries are dissolved with just a small amount of spherical M23C6 existing in the matrix of the quenched steel.

Polycrystalline cubic boron nitride prepared with cubic-hexagonal boron nitride under high pressure and high temperature

Polycrystalline cubic boron nitride(Pc BN)compacts,using the mixture of submicron cubic boron nitride(c BN)powder and hexagonal BN(h BN)powder as starting materials,were sintered at pressures of 6.5–10.0 GPa and temperature of1750℃without additives.In this paper,the sintering behavior and mechanical properties of samples were investigated.The XRD patterns of samples reveal that single cubic phase was observed when the sintering pressure exceeded 7.5 GPa and h BN contents ranged from 20 vol.%to 24 vol.%,which is ascribed to like-internal pressure generated at grain-to-grain contact under high pressure.Transmission electron microscopy(TEM)analysis shows that after high pressure and high temperature(HPHT)treatments,the submicron c BN grains abounded with high-density nanotwins and stacking faults,and this contributed to the outstanding mechanical properties of Pc BN.The pure bulk Pc BN that was obtained at 7.7 GPa/1750℃possessed the outstanding properties,including a high Vickers hardness(~61.5 GPa),thermal stability(~1290℃in air),and high density(~3.46 g/cm^(3)).

Characterization of diamond MWCNTs composite fiber synthesized under high pressure and high temperature

A regrown composite fiber was synthesized during the sintering of diamond under high pressure 5.8 GPa and high temperature 1500℃for 1 min,using 3wt%MWCNTs as additive.SEM observation of the fiber after alkali and acid treatment revealed that the outer layer of the fiber is composed of nano-polycrystalline diamond.EDS,XPS,XRD and Raman spectrum analysis further identified that the fiber is composed of MWCNTs in the inner part and nano-polycrystalline diamond in the out layer.It is proposed that the untransformed MWCNTs may act as a template for the regrown outer layer of nano diamond fiber under high pressure and high temperature.

Grain-refining fabrication of nanocrystalline(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy ceramics by ultra-high pressure sintering

As an important A_(2)B_(2)O_(7)-type ceramic,(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy pyrochlore pos-sesses promising properties such as high melting point,high chemical durability,and low thermal conductivity.However,the low sintering ability limits its application in thermal barrier coating and radioactive waste immobilization.It usually needs long-term high-temperature soaking to achieve full density,but with inevitable grain growth.In this work,dense and grain-refined nanocrystalline(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramics were prepared with ultra-high pressure sintering(UHPS)method under 10 GPa at a low temperature of 800℃.The densification behavior,microstructure evo-lution,and properties of the UHPS-ed samples were then investigated.The grain size of as-prepared(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramic was only 151 nm,which is 40%smaller than that of raw pow-der.In addition,it exhibited advantageous properties including both high hardness and aqueous durabil-ity.Plastic deformation under ultra-high pressure was believed as the dominant densification mechanism responsible for grain refinement and property improvement.

Cyclic Pulsating Pressure Enhanced Segregating Structuration of Ultra-High Molecular Weight Polyethylene/Graphene Composites as High-performance Light-Weight EMI Shields

Currently,the enhancement in electromagnetic interference(EMI)performance of polymeric composite generally relies on either improving electrical conductivity(σ)for stronger electromagnetic(EM)reflections or tailoring structure for higher EM resonances.Herein,we proposed a novel technique called cyclic pulsating pressure enhanced segregating structuration(CPP-SS),which can reinforce these two factors simultaneously.The structural information was supplied by optical microscopy(OM)and scanning electron microscopy(SEM),both of which confirmed the formation and evolution of segregate structured ultra-high molecular weight polyethylene(UHMWPE)/graphene composites.Then,the result showed that CPP-SS can significantly improve theσof samples.Ultimately,advanced specific EMI shielding efficiency of 31.1 d B/mm was achieved for UHMWPE/graphene composite at 1-mm thickness and a low graphene loading of 5 wt%.Meanwhile,it also confirmed that the intrinsic disadvantage of poor mechanical properties of conventional segregated structure composites can be surpassed.This work is believed to provide a fundamental understanding of the structural and performance evolutions of segregated structured composites prepared under CPPSS,and to bring us a simple and efficient approach for fabricating high-performance,strong and light-weight polymeric EMI shields.

Theoretical and experimental investigation on vertical tank technology for sinter waste heat recovery

In the present work, the gas flow pressure drop and gas–solid heat transfer characteristics in sinter bed layer of vertical tank were studied experimentally on the basis of the homemade experimental setup. The gas flow pressure drop through the sinter bed layer was measured with different gas velocity and particle diameters, as well as the sinter and air temperatures. The influences of gas superficial velocity and particle diameter on the gas flow pressure drop and gas solid heat transfer in sinter bed layer were analyzed in detail. The revised Ergun's correlation and gas solid heat transfer correlation were obtained according to the regression analysis of experimental data. It is found that, the pressure drop of unit bed layer height gradually increases as a quadratic relationship with increasing the gas superficial velocity, and decreases as an exponential relationship with the increase of sinter particle diameter. For a given sinter temperature, the heat transfer coefficient in sinter bed layer increases with increasing the gas superficial velocity, and increases with decreasing the sinter particle diameter. In addition, the heat transfer coefficient also gradually increases with increasing the sinter temperature at the same gas superficial velocity and sinter particle diameter. The mean deviations between the experimental data obtained from this work and the values calculated by the revised Ergun's correlation and the experimental heat transfer correlation are 7.22% and 4.22% respectively, showing good prediction.