Preparation of ZrB_2 Ceramics by Self-propagating High-temperature Synthesis and Hot Pressing Sintering

ZrB2 ceramics were prepared by self-propagating high-temperature synthesis（SHS） and were sintered by hot pressing（HP）.The effects of the granularities and doses of raw materials in Zr-B2O3-Mgon SHS process and product were investigated.XRD and combustion temperature curves prove that the ideal SHS reactants of Zr-B2O3-Mg are 50μm Zr powder,75μm B2O3 powder and 400μm Mg powder with 45% excessive.The particle sizes of SHS product,acid-leached product,sintered product are 2-5μm,0.5-2μm,2-10μm respectively.Chemical analysis indicates that the acid-leached product consists of ZrB2（94.59%）,ZrO2（3.87%）,and H3BO3（1.54%）,The sintered product has a relative density of 95.4%.

Study on Squeeze Casting Metal-zirconium Composite Die Material by Hot Press Sintering

ZrO_(2)-5CrMnMo composite samples were prepared by hot press sintering.When NiCoCrAlY powders were used as the bonding layer and the different mixtures of NiCoCrAlY alloy and 3YSZ (3mol% yttria stabilized zirconia) ceramic powders were used as the transition layers,the connection between zirconia ceramic and 5CrMnMo steel were strengthened.Three composite samples with different structures were fabricated by heat spraying and hot press sintering.Shear and thermal shock cycle tests were conducted to characterize connection strength and thermal shock resistance of these samples.The shear strength reached 95.69 MPa,and the heating shock cycles achieved to the maximum value of 27.7 times.Microstructures and connection interfaces were analyzed by scanning electron microscopy.The hardness and wearing resistance of 3YSZ coat and 5CrMnMo substrate were compared,and the heat insulation property of composite samples were also discussed.It is shown that these composite materials fabricated in this research are benefited to be used as squeeze casting dies.

Formation and Sintering Behavior of Nanocrystalline Fe-Ni Powder by Mechanical Alloying

The solid sintering behavior and mechanical properties of Fe-Ni powders prepared by mechanical alloying of elemental powders and hot pressing sintering in vacuum atmospheres were investigated. It was observed that the microstructure of the powder particles evolves in three stages. The alloy powder with average grain size of 20-30 nm was obtained. The sinter densification depends crucially on the particle rearrangement and the large amount of internal strain introduced during milling. The theoretical density of over 95 % was obtained after hot pressing sintering at 800 ℃ for 30 min with pressure of 50 MPa. No significant grain growth was observed during sintering. And also relatively high hardness was obtained.

Wear resistance performance of high entropy alloy–ceramic coating composites synthesized via a novel combined process

Titanium nitride(TiN), characterized by its high hardness and strength, was widely used as ceramic coating to improve the wear resistance of matrix materials. In this work, AlCrFeNiTi_(x) high-entropy alloy(HEA) powders were synthesized by direct electrochemical reduction in molten salt from the mixed metal oxides. Then,TiN ceramic coating on the AlCrFeNiTi_x bulk HEA containing the topologically close-packed(TCP) phase(σphase, Laves phase, and Ti_(3)Al phase) was prepared by vacuum hot pressing sintering, where nitride element come from boron nitride parting agent sprayed on the graphite mold. The effect of titanium content on the crystal structure, microstructure, hardness, and wear resistance of the products were investigated by X-ray diffraction, field emission scanning electron microscope, field emission electron-probe microanalysis,Vickers hardness tester, and friction–abrasion testing machine. The bulk HEAs exhibit excellent hardness and its hardness increases significantly with the increase of titanium content. The wear mechanism changes from both of predominantly delamination and accompanied oxidative wear to single delamination wear,which is due to ultra-high melting point and high hot hardness of TiN, that can effectively prevent the oxidation and deformation of the worn surface. Formation of the ceramic coatings containing the TiN second phase and TCP phase are the key factor to AlCrFeNiTi_x alloy with the excellent hardness and wear properties.

In Situ Reaction Strengthening and Toughening of B_(4)C/TiSi_(2)Ceramics

B_(4)C-SiC-TiB_(2)ceramics were prepared by in situ reactive hot-pressing sintering with TiSi_(2)as an additive.The reaction pathways of TiSi_(2)and B_(4)C were investigated.The sintering was found to be a multistep process.The reaction started at approximately 1000℃,and TiB_(2)was formed first.Part of Si and C started to react at 1300℃,and the unreacted Si melted at 1400℃to form a liquid phase.TiSi_(2)predominantly affected the intermediate sintering process of B_(4)C and increased the sintering rate.Due to the unique reaction process of TiSi_(2)and B_(4)C,a large number of aggregates composed of SiC and TiB_(2)were generated.The results showed that composite ceramics with the optimal flexural strength of 807 MPa,fracture toughness of 3.2 MPa·m1/2,and hardness of 32 GPa,were obtained when the TiSi_(2)content was 10 wt%.

Hot pressing sintering process and sintering mechanism of W-La_(2)O_(3)-Y_(2)O_(3)-ZrO_(2)

The W-La_(2)O_(3)-Y_(2)O_(3)-ZrO_(2)materials were prepared by vacuum hot pressing sintering process.The microstructure was characterized by scanning electron microscopy(SEM).The effects of sintering temperature,sintering pressure,holding time and heating rate on relative density,hardness and microstructure were studied.The sintering activation energy of the powder was calculated.Based on the result,the best sintering parameters by vacuum hot pressing sintering are as follows:sintering temperature of 1600℃,sintering pressure of 60 MPa and holding time of 60 min.The heating rate is 10℃·min^(-1)from room temperature to 1000℃and 4℃·min^(-1)from1000 to 1600℃.Using this process,the grain size is about3 lm in diameter with relative density at 99.7%,and the hardness is HV 528.5.The sintering characteristic index(n)of the specimen is 4,and the sintering mechanism mainly depends on the diffusion from the surface to the intragranular in the volume diffusion.The sintering activation energy of W-La_(2)O_(3)-Y_(2)O_(3)-ZrO_(2)material is286.2 k J·mol^(-1),which indicates that the powder has higher activity in sintering process.

Al_2O_3 PARTICLE REINFORCED COPPER MATRIX COMPOSITE USING FOR CONTINUOUS CASTING MOULD

A kind of Cu base composite reinforced by 0 1μm Al 2O 3 particles were prepared by hot pressing and sintering process for steel continuous casting mould. The microstructure and properties were studied. The results show that the Al 2O 3 particle distribution is uniform, and the particles refine the grain size. The tensile fracture is a mixture of quasi cleavage and dimple due to the moderate interface strength. As a result, the composite has better soft resistance and wear resistance than those of Cu and Cu alloy. With increase in super fine Al 2O 3, the density and electric conductivity of the composite decrease, but hardness and strength increase.

Fabrication and Microstructure of BN Matrix Composites with Electrical Conductivity

BN ceramic is an advanced engineering ceramics with excellent thermal shock resistance, good workability and excellent dielectricity.TiB 2 ceramic has excellent electric conductivity,high melting points, and corrosion resistance to molten metal.Therefore,the composite consisting of BN and TiB 2 ceramics is expected to have a combination of above mentioned properties,thereby can be used as self heating crucible.In this paper,hot pressing technology was used to fabricate the high performance BN TiB 2 composite materials.microstructure and electric conducting mechanism were studied,and the relationship between the microstructure and physical property was discussed.The results show that the microstructure of composites has a great influence on the physical property of composites.The BN TiB 2 composites with excellent mechanical strength and stable resistivity can be obtained by optimizing the processing parameter and controlling the microstructure of composites.

Effect of Powder Particle Size on Microstructure and Mechanical Property of Ni-Based P/M Superalloy Product

The solid sintering behavior and mechanical properties of Fe Ni powders prepared by mechanical alloying of elemental powders and hot pressing sintering in vacuum atmospheres were investigated. It was observed that the microstructure of the powder particles evolves in three stages. The alloy powder with average grain size of 20-30 nm was obtained. The sinter densification depends crucially on the particle rearrangement and the large amount of internal strain introduced during milling. The theoretical density of over 95 % was obtained after hot pressing sintering at 800 ℃ for 30 min with pressure of 50 MPa. No significant grain growth was observed during sintering. And also relatively high hardness was obtained.

Synthesis and Microstructure of Partly-oriented Bismuth Layer Structure Ferroelectrics Ceramics SrBi_4Ti_4O_(15)

SrBi4Ti4O15 powder was synthesized by conventional solid state synthesis （ CS ） and molten salt synthesis （ MSS ） . MSS method can synthesize plate-like SrBi4Ti4O15 at lower temperature （900℃） than CS method. Plate-like form becomes more distinct when the synthesis temperature increases. This would help cause the grain orientation of the ceramics after sintering. The sintered samples of MSS had grain orientation at （0,0, 10） plane. The degree of （0,0,10） grain orientation F was 62.1% . Hot pressing made （0,0,10） grain orientation more distinct （ F = 85.7% ）. The microstructures of the sintered samples were detected by SEM. Due to the grain orientation the density of samples fabricated by MSS was lower than that of prepared by CS.

Formation of Fe-19 wt%Cr-9 wt%Ni Nanocrystalline Alloy with Excellent Corrosion Resistance: Phase Transition and Microstructure

In this paper,microstructure characteristics and phase transitions of Fe-19 wt%Cr-9 wt%Ni nanocrystalline alloy are comprehensively studied during the mechanical alloying and hot pressing sintering processes.Corrosion resistance of the sintered Fe-19 wt%Cr-9 wt%Ni nanocrystalline alloy samples is further analyzed.During the mechanical alloying process,Fe-19 wt%Cr-9 wt%Ni nanocrystalline alloy powders mainly composed of metastable ferrite phase are obtained after mechanical alloying for 8,16 and 24 h,respectively.In the subsequent hot pressing sintering process,the phase transitions(from ferrite to austenite)occur from 650 to 750°C for Fe-19 wt%Cr-9 wt%Ni alloy powders milled for 24 h.When the sintering temperature is raised to 1050°C for 1 h,the ferrite phase has transformed into austenite phase completely,and the obtained grain size of sintered Fe-19 wt%Cr-9 wt%Ni alloy is around 40 nm.Electrochemistry test of the sintered Fe-19 wt%Cr-9 wt%Ni alloy has been operated in 0.5 mol L^(-1) H_(2)SO_(4) solution to show the corrosion resistance properties.Results show that the sintered Fe-19 wt%Cr-9 wt%Ni alloy exhibits excellent corrosion resistance,which is proved by higher self-corrosion potential,lower self-corrosion current density and larger capacitive reactance,compared with that of commercial 304 stainless steel.