IPS e.max press热压铸造陶瓷全冠及二氧化锆全瓷冠对前牙修复患者牙龈健康美观度的影响

目的:比较IPS e.max press热压铸造陶瓷全冠及二氧化锆全瓷冠对前牙修复患者牙龈健康、美观度的影响,为前牙美学修复的材料选择提供临床参考。方法:以2021年5月至2022年5月于我院接受前牙修复的104例患者为研究对象,以随机数字表法分为两组,分别52例。观察组、对照组分别以IPS e.max press铸瓷全冠、二氧化锆全瓷冠修复,比较两组患者的临床修复效果及修复后的牙龈指数、菌斑指数、龈沟出血指数、龈沟液炎性因子水平。结果:观察组边缘密合度、继发龋情况均优于对照组(P<0.05);修复后,观察组牙龈指数、菌斑指数等显著小于对照组,龈沟液IL-6、IL-8及TNF-α水平显著低于对照组(P<0.05);修复12个月后,观察组PES评分高于对照组(P<0.05)。结论:相比于二氧化锆全瓷冠,IPS e.max press铸瓷全冠具有良好的前牙美学修复效果,可降低龈沟液炎性因子水平,改善牙龈健康,并能提高前牙美观度。

Using HyperCoal to prepare metallurgical coal briquettes via hot-pressing

HyperCoal was prepared from low-rank coal via high-temperature solvent extraction with N-methylpyrrolidone as an extraction solvent and a liquid-to-solid ratio of 50 mL/g in a high-temperature and high-pressure reactor. When HyperCoal was used as a binder and pulverized coal was used as the raw material, the compressive strength of the hot-pressed briquettes(each with a diameter of 20 mm and mass of 5 g) under different conditions was studied using a hot-pressing mold and a high-temperature furnace. The compressive strength of the hot-pressed briquettes was substantially improved and reached 436 N when the holding time period was 15 min, the hot-pressing temperature was 673 K, and the HyperCoal content, was 15 wt%. Changes in the carbonaceous structure, as reflected by the intensity ratio between the Raman G-and D-bands(IG/ID), strongly affected the compressive strength of hot-pressed briquettes prepared at different hot-pressing temperatures. Compared with cold-pressed briquettes, hot-pressed briquettes have many advantages, including high compressive strength, low ash content, high moisture resistance, and good thermal stability; thus, we expect that hot-pressed briquettes will have broad application prospects.

Interfacial reaction process of the hot-pressed WC/2024Al composite

12 vol%WCp/2024Al composite was fabricated from mixed powders by hot-pressing at various tempera-tures. Investigation of the interfacial reaction between the WC phase and the Al alloy matrix was performed by X-ray diffraction （XRD）, transmission electron microscope （TEM） and energy dispersive spectroscopy （EDS）. A multiple layer interface structure, which is composed of Al/ WAl12/AlnC3/WC, is found to form by the interfacial reaction during hot-pressing. Further study shows that the AlaC3 layer forms along with a given crystal orientation of WC phase and might retard the interfacial reaction process.

MICROSTRUCTURES OF TiAl BASED ALLOYS PREPARED BY HOT PRESSING ELEMENTAL POWDERS

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Flow characteristics of aluminum coated boron steel in hot press forming

The flow characteristics of aluminum coated boron steel in hot press forming were investigated.Furthermore,the effects of aluminum coated layer on press forming were analyzed during deep drawing.The results show that aluminum coated boron steel exhibits a high sensitivity on temperature and strain rate.Aluminum coating layer appears in surface flaking in a temperature range of 700-800 ℃,but smooth surface is formed above 900 ℃.

Porous bulk metallic glass fabricated by powder hot pressing

A synthesis method for the production of porous bulk metallic glass (BMG) was introduced. This method utilizes the su- perplastic forming ability of amorphous powder in the supercooled liquid (SCL) state and intenerating salt mixture as a placeholder to produce BMG foam by using a hot die pressing method. Scanning electron microscope (SEM), X-ray diffraction (XRD) and dif- ferential scanning calorimetry (DSC) were employed to characterize the morphologies of foaming structure, the crystallization and the percentage of crystallization of the as-produced porous BMG. The results suggested that the formation of porous structure by su- perplastic forming process is feasible. Good bonding effect was observed between amorphous powder particles. Less than 6.5% of crystalline phases were formed during hot pressing, and less than 5.5% of residual salt was enclosed in the foam. To remove any re- sidual salt particles, salt preforms with three-dimensional network and good connectivity is necessary.

Synthesis of high-purity Ti_2AlN ceramic by hot pressing

High-purity Ti2AlN ceramic was prepared at 1300 ℃ by hot pressing(HP)of Ti/Al/TiN powders in stoichiometric proportion.The sintered product was characterized using X-ray diffraction(XRD)and MDI Jade 5.0 software(Materials Data Inc,Liverpool,CA).Scanning electron microscopy(SEM)and electron probe micro-analysis(EPMA)coupled with energy-dispersive spectroscopy(EDS)were utilized to investigate the morphology characteristics.The results show that Ti2AlN phase is well-developed with a close and lamellar structure.The grains are plate-like with the size of 3-5 μm,thickness of 8-10 μm and elongated dimension.The density of Ti2AlN is measured to be 4.22 g/cm3,which reaches 97.9% of its theory value.The distribution of Ti2AlN grains is homogeneous.

Diffusion behavior of Nb element in high Nb containing TiAl Alloys by reactive hot pressing

Diffusion behavior of Nb in elemental powder metallurgy high Nb containing TiAl alloys was investigated. The results show that Nb element dissolves into the matrix by diffusion. Pore nests are formed in situ after Nb diffusion. With the increase in hot pressing temperature, the diffusion of Nb will be more sufficient, and the microstructure is more homogeneous. Nb element diffuses completely at 1400℃. Meanwhile, compression deformation and agglomeration phenomena of pores are observed in some pore nests. Hot isostatic pressing （HIP） treatment can only efficiently decrease but not eliminate porosity completely.

Effects of aluminum and titanium on the microstructure of ODS steels fabricated by hot pressing

Three oxide-dispersion-strengthened(ODS)steels with compositions of Fe-14Cr-2W-0.2V-0.07Ta-0.3Y_2O_3(wt%,so as the follows)(14Y),Fe-14Cr-2W-0.2V-0.07Ta-1Al-0.3Y_2O_3(14YAl),and Fe-14Cr-2W-0.2V-0.07Ta-0.3Ti-0.3 Y_2O_3(14YTi)were fabricated by hot pressing.Transmission electron microscopy(TEM)was used to characterize the microstructures and nanoparticles of these ODS steels.According to the TEM results,14Y,14YAl,and 14YTi ODS steels present similar bimodal structures containing both large and small grains.The addition of Al or Ti has no obvious effect on the microstructure of the steels.The spatial and size distribution of the nanoparticles was also analyzed.The results indicate that the average size of nanoparticles in the 14YTi ODS steel is smaller than that in the 14YAl ODS steel.Nanoparticles such as Y_2O_3,Y_3Al_5O_(12) and YAlO_3,and Y_2Ti_2O_7 were identified in the 14Y,14YAl,and 14YTiODS steels,respectively.

Effect of La_2O_3 on microstructure and high-temperature wear property of hot-press sintering FeAl intermetallic compound

FeAl intermetallic compound with different contents of rare earth oxide La2O3 addition was prepared by hot pressing the mechanically alloyed powders.Effect of La2O3 on microstructure and high-temperature wear property of the sintered FeAl samples was investigated in this paper.The results showed that 1 wt.% La2O3 addition could refine the microstructure and increase the density of the FeAl intermetallic compound,and correspondingly improved the high-temperature wear resistance.SEM and EDS analyses of the wo...

Fabrication of Ni_3Al by hot pressing from element powders

Ni3Al intermetaUic was synthesized by hot pressing from element powders of nickel, aluminum, and boron. The influences of parameters on the properties of Ni3Al were investigated. The parameters include the particle size of nickel powder, adding or without boron powder, hot pressing temperature, etc. The properties include the density of hot-pressed samples, resultant redo of Ni3A1 phase, and bending strength. The microstructures of hot-pressed samples were investigated by X-ray diffraction and scan electronic microscopy, and the properties, such as density and bending strength, were also measured. The results show that a higher bending strength was obtained under the same hot pressing conditions by the fine nickel powder than the coarse one, and there is little difference about density. Boron powder added in this process accelerates the formation of Ni3Al and markedly increases the hot pressed density. In the temperature range of this study, the density increases along with the hot pressing temperature. Full dense Ni3Al samples were obtained under the condition of 860℃, 10 min, 45 MPa from Ni-22.89A1-0.5B powder.

Mechanical and wear properties of Al-Al_3Mg_2 nanocomposites prepared by mechanical milling and hot pressing

β-A13Mg2 intermetallic was used as a reinforcing agent to improve the mechanical properties of an aluminum matrix. Different amounts of A13Mg2 nanoparticles （ranging from 0wt% to 20wt%） were milled with aluminum powders in a planetary ball mill for 10 h. Consolidation was conducted by uniaxial pressing at 400β under a pressure of 600 MPa for 2 h. Microstructural characterization confirms the uniform distribution of A13Mg2 nanoparticles within the matrix. The effects of nano-sized A13Mg2 content on the wear and mechanical properties of the composites were also investigated. The results show that as the A13Mg2 content increases to higher levels, the hardness, compressive strength, and wear resistance of the nanocomposites increase significantly, whereas the relative density and ductility decrease. Scanning electron microscopy （SEM） analysis of worn surfaces reveals that a transition in wear mechanisms occurs from delamination to abrasive wear by the addition of A13Mg2 nanoparticles to the matrix.

Effect of ball milling time on microstructure and properties of Laves phase NbCr_2 alloys synthesized by hot pressing

Laves phase NbCr2 alloys with a composition of Nb-66.7Cr (molar fraction, %) were prepared by mechanical alloying and hot pressing. The microstructures and properties of the Laves phase NbCr2 alloys, prepared from elemental niobium and chromium powders under various ball milling time by hot pressing at 1 250 ℃ for 0.5 h, were investigated. The results indicate that if the ball milling time is longer than 40 h, the synthesizing reaction of Laves phase NbCr2 can be accomplished much sufficiently. Then the nearly full-dense Laves phase NbCr2 alloys can be prepared by hot pressing from ball milled powders with more than 40 h. The hot pressing sample with homogeneous and fine microstructure made from 40 h ball milled powders has the optimum microstructure and properties. It has a relative density of 98.1%, Vickers hardness of 11.4 GPa, compress strength of 1 981 MPa and fracture toughness of 4.82 MPa·m1/2. The effect of fine grain toughening is fully realized.

JOINING OF TiAl BASEDALLOYS BY HOT PRESSING

By hot pressing in an inert atmosphere, the joining interface between coarse lamellar structures and that between a coarse lamellar structure and a fine duplex structure of a Ti 33Al 3Cr(%, mass fraction) alloy, and the effect of heat treatment on the microstructure at the interfaces have been studied. The results showed that the microstructure at the interface between two coarse lamellar structures depends on the orientations of lamellae. And microcavities are found at such interfaces. After heat treatment at 1 250 ℃, the recrystallization structure widened. As to the interface between a coarse lamellar structure and a fine duplex structure, a new duplex structure formed within the original duplex structure at the interface and further widened after subsequent heat treatment at 1 250 ℃ for 4 h. Microcavities are rare at such interfaces, and the joining appears better than that between two coarse lamellar structures.

Synthesis and properties of bulk nanocrystalline Mg_2Si through ball-milling and reactive hot-pressing

Bulk nanocrystalline Mg2Si(n-Mg2Si) was prepared by mechanical milling and reactive hot-pressing in vacuum and its mechanical properties were characterized. The results indicate that the grain sizes of Mg and Si decrease non-monotonously with increasing ball-to-powder mass ratio(BPR). The content of Mg2Si phase increases with increasing milling time; however, pure Mg2Si phase cannot be obtained by direct ball milling. Moreover, monolithic is Mg2Si phase can only be obtained when as much as 10% of excess Mg was blended in the raw mixtures. The relative density (D) and fracture toughness as well as hardness of bulk Mg2Si samples can be raised effectively by increasing the pressure in hot-pressing. After hot-pressing at 400 ℃ for 60 min under 1.5 GPa, highly dense(D>98%) n-Mg2Si (d=60 nm) was obtained, whose fracture toughness (KIC≈1.46 MPa·m1/2) and Vickers hardness (HV≈ 4.38 Gpa) are superior to those of conventional coarse-grained Mg2Si.

Synthesis of Ti_2AlC by hot pressing and its mechanical and electrical properties

Ti2AlC bulk material was synthesized by hot pressing of mixture powders of TiC, Ti, Al and active carbon. The phase compositions of resultant product at different temperature were detected by X-ray diffractometer. The microstructures of the samples were observed by SEM. Finally, the mechanical properties and thermal properties of the sample at 1400 ℃ were measured. The results show that high purity Ti2AlC material with little Ti3AlC2 can be synthesized by hot pressing 0.5TiC/1.5Ti/1.0Al/0.5C at 1 400 ℃. Ti2AlC exhibits high mechanical properties and metallic electrical properties. Its fracture toughness is 7.0 MPa·m1/2, its flexural strength is 384 MPa at room temperature, and its electrical conductivity is 2.56×106 Ω1·m-1 at room temperature.

Comparative study of β-Si_3N_4 powders prepared by SHS sintered by spark plasma sintering and hot pressing

β-Si3N4 powders prepared by self-propagating high-temperature synthesis （SHS） with additions of Y2O3 and Al2O3 were sintered by spark plasma sintering （SPS）. The densification, microstructure, and mechanical properties of Si3N4 ceramics prepared using this method were compared with those obtained by hot pressing process. Well densified Si3N4 ceramics with finer and homogeneous microstructure and better mechanical properties were obtained in the case of the SPS technique at 200°C lower than that of hot pressing. The microhardness is 15.72 GPa, the bending strength is 716.46 MPa, and the fracture toughness is 7.03 MPa·m1/2.

Microstructure and mechanical properties of hot isostatically pressed cermets with TiN coatings

To increase the adhesion strength between the coating and the substrate, sintered Ti（C,N）-based cermets were selected and deposited with monolayer TiN using a multiarc ion-plating technique; subsequently, hot isostatic pressing （HIPhag） treatment was performed at 1000℃ using nitrogen pressure up to 110 MPa. The mechanical properties of cermets after a coating process and subsequent HIPing treatment have been evaluated with respect to the hardness, the residual stress, and the coating adhesion. The results show that atter the HIPing process, there was a higher increase ha critical load ha the TiN-coated cermets with lower surface roughness compared with those with higher surface roughness. In all cases, the residual stress was found to be compressive. The effects of substrate surface roughness and posttreatment on the adhesion strength of the coatings were thus investigated. It was also fotmd that the HIPing posttreatment process is well suited for hacreasing the adhesion strength between the coating and the substrate.

Diffusion Bonding of Al6061 and Cu by Hot Isostatic Pressing

Diffusion bonding between Al and Cu was successfully performed by hot isostatic pressing(HIP). To improve the strength of diffusion bonding joint, pure nickel foils with different thickness were used as intermediate layer. Microstructure of the interface between Al and Cu was investigated by X-ray diffraction(XRD) technique, secondary electron microscopy(SEM), and nano-indentation tests. When the temperature was 500 ℃ and held for 3 h with a processing pressure of 50 MPa, Al and Cu could be bonded with its interface formed by several diffusion layers. With the addition of Ni interlayer, the diffusion of aluminum atoms was effectively hindered, and the interface became smoother. The tensile strength of bonded joints increases with increasing the thickness of Ni interlayer, which contributes to a reduction in the thickness of intermetallic compounds(IMCs) and well bonding quality of Al-Cu joints.

Repetitious-Hot-Pressing Technique in Hot-Pressing Process

A new pressing method was proposed for hot-pressing process. Experimental results indicated that the porosity in Al2O3/TiC/ Ni/Mo (hereafter called AI2O3/TiC composite) composite compacts decreases by 6% after adopting this new technique, compared to traditional hot-pressing technique under the same sintering temperature. The flexural strength and Vicker hardness increase from 883 MPa to 980 MPa and from 16 GPa to 21.1 GPa, respectively. A theoretical model was given to analyze the densification mechanism of the composite in the process of repetitious-hot-pressing.