Porous FeAl alloys via powder sintering:Phase transformation,microstructure and aqueous corrosion behavior

This study investigates the phase transformation and microstructure of porous Fe Al parts sintered from elemental powder mixtures using in-situ neutron diffraction and in-situ thermal dilatometry.A single B2 structured Fe Al phase was determined in the sintered Fe Al alloy.The combined effects of the Kirkendall porosity,transient liquid phase,and phase transformations associated with powder sintering all contribute to the swelling phenomenon of the final sintered part.The aqueous corrosion test indicates that the corrosion products include iron oxides in the porous Fe Al parts.The accumulation of corrosion products blocks the pore channel and decreases pore size and permeability over the soaking time.

Particle Size Distribution,Powder Agglomerates and Their Effects on Sinterability of Ultrafine Alumina Powders

An intensive study of the particle size distribution of four commercial ultrafine alumina powders to obtain information about the powder agglomeration and relate them to the compactibility and the sinterability has been made.

Densification Model for Porous Metallic Powder Materials

A new mechanical model for powder metallurgy compaction is presented. In this model, various amount of voids can be introduced into a continuous solid, therefore porosity can be conveniently controlled. The elastic-plastic finite element method was used to analyze the sintered powder material. The model was used to simulate compressing of a sintered cylinder. MSC.Marc of MSC. Software Corporation was applied here, and the sintered powder model was built in MSC.Mentat. The sintered cylindrical powder metallurgy part is treated as a piece of normal metal with pores in the model. The metal block is considered as cylinder with a radius of 6.0 mm and a total height of 10.0 mm. Young’s module was assumed to be 4 000 MPa. Poisson’s ratio was 0.269. The initial yield stress is 210 MPa. Friction coefficient used for the upper and lower contact surfaces is 0.3. Coulomb principle is adopted. Considering axisymmetricity, just half a section is analyzed. Totally there are 1 240 elements. Experiment was carried out by a computer controlled a universal tensile testing machine. During the experiment, the sample was prepared from highly compressible water atomized iron powder with 0.6wt% polymeric lubricant. Particle size is about 100～150 μm. The comparison was performed using a sintered cylindrical sample. The green compact was sintered at 1 140 ℃ for 2 hours. Initially, H0 is 10.20 mm, Φ0 is 12.01 mm and the initial relative density is 0.789. After pressing, H is 7.30 mm, Φ1 is 13.10 mm, Φ2 is 14.64 mm and relative density is 0.88. The load-displacement curves agree with the experimental results very well. Plastic deformation of metallic material is mostly caused by the slipping of crystal lattice. Although very small, a metal powder particle is composed of metallic crystal. Mechanical properties of a powder particle should be very close to their as solid metal counterpart.

A NEW MECHANISM OF ULTRASOUND ATTENUATION IN SINTERED METAL POWDERS

This paper analyzes the anomalous power-law dependence of the ultrasound attenuation on frequency by means of a percolation model. It was suggested that the anomaLous ultrasound attenuation is associated with strongly localized eigen modes (to be called fracton) in disordered systems. There exits a steplike increase in the density of vibrational states at crossover frequency ω(co).Computer simulation of vibration spectrum in disordered system is also reported. The density of vibrational states is consistent with the results of relevant experiment outlined above.

A Study on Synthesis Kinetics of YBa_2Cu_3O_x High Tc Superconductor Powder

The synthesis kinetics of YBa_2Cu_30_x supercon- ductor was studied through comparing the calcina- tion (sintering) processes of different kinds of powders. It was shown that the temperature of synthesis of YBa_2Cu_30_x phase can be lowered from 950℃ to 800℃ through direct calcination of multiphase powder with uniform chemical com- position. The stress which is caused by the volume change during synthetic reaction breaks the particles. It facilitates the formation of highly active superfines of superconductor.

Influence of aluminium nitride as a foaming agent on the preparation of foam glass-ceramics from high-titanium blast furnace slag

To effectively reuse high-titanium blast furnace slag （TS）, foam glass-ceramics were successfully prepared by powder sintering at 1000℃. TS and waste glass were used as the main raw materials, aluminium nitride （AIN） as the foaming agent, and borax as the fluxing agent. The influence of the amount of A1N added （lwt%-5wt%） on the crystalline phases, microstructure, and properties of the produced foam glass-ceramics was studied. The results showed that the main crystal phases were perovskite, diopside, and augite. With increasing A1N content, a transformation from diopside to augite occurred and the crystallinity of the pyroxene phases slightly decreased. Initially, the aver- age pore size and porosity of the foam glass-ceramics increased and subsequently decreased; similarly, their bulk density and compressive strength decreased and subsequently increased. The optimal properties were obtained when the foam glass-ceramics were prepared by adding 4wt% AIN.

Mierostrueture and Properties of Coating from Cemented Carbide on Surface of Hl3 Steel

The microstructures and properties of coating from cemented carbide on the substrate of H 13 by vacuum powder sintering were studied. The effect of sintering temperature on the microstructures of coating was discussed. The interface characteristics between coating and H 13 steel substrate, microhardness distribution and wear resistance in the coating were analyzed. The coating from cemented carbide with thickness of 1-3 mm by vacuum powder sintering at temperature ranging from 1280℃to 1300 ℃ was obtained. The experimental results indicated that the coating with microhardness of HV 1600 favorable to wear resistance is strongly bonded with the H 13 steel substrate by mutual diffusion and penetration of Fe,Cr, Mo,V in substrate towards the coating and W, Co,Ni in coating towards the substrate.

Research on fabricating technique of Ba-Al-S:Eu sputtering target

Ba-Al-S-Eu sputtering target for blue emitting phosphors was prepared by powder sintering method. XRD patterns showed that the main components of the target were barium tetra aluminum sulfide （BaAl4S7）, bariutm sulfide （BaS）, and europium sulfide （EuS）. In the samples, part of the barium and aluminum are formed into barium aluminum oxide （BaAl2O4） with the impurity element of oxygen. The PL characteristic spectra of the target showed the 470 nm blue emission obviously, and the Ba-Al-S thin films also transmitted a purple-blue emission at the position of 440 nm.The results indicated that this method was suitable for the fabrication of the Ba-Al-S：Eu sputtering target.

Preparation and Characterization of Copper-Nickel Bulk Nanocrystals

Copper-nickel nanoparticle was directly prepared by flow-levitation method （FL） and sintered by vacuum sintering of powder （VSP） method. Several characterizations, such as transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）, differential thermal analysis （DTA）, and energy-dispersive X-ray spectroscopy （EDX） were used to investigate the prepared nanostructures. The results of the study show that FL method could prepare high purity Cu-Ni nanocrystals of uniform spheres with size distribution between 20 and 90 nm. After sintering the bulk nanocrystalline copper-nickel has obvious thermal stability and the surface Webster hardness increases with the rising sintering temperature. At the temperature of 900 ℃, the specimen shows higher surface Webster hardness, which is about two times of traditional materials. When the sintering temperature arrives at 1 000 ℃ the relative density of bulk nanocrystals can reach 97.86 percent. In this paper, the variation tendency of porosity, phase and particles size of bulk along with the changing of sintering temperature have been studied.

Forced boiling of nonazeotropic immiscible mixture in a supercapillary microchannel array for ultra-high heat flux removal with chip junction temperature below 85℃

In this study,a structure-optimized two-phase microchannel heat sink with sintered submicron nucleation sites was developed and tested.The copper-based microchannels had a rectangular cross-section with an equivalent hydraulic diameter of 222μm.The subcooled flow boiling characteristics were comprehensively compared between pure HFE-7100 and a non-azeotropic,immiscible binary mixture of HFE-7100 and water,considering heating areas of 1 and 5 cm^(2).The total heating power input to the test section were 100–1500 and 250–3000 W for a 1 and 5 cm^(2)heat source,respectively,with a flow rate ranging from 50 to150 L/h.Compared to pure HFE-7100,the non-azeotropic immiscible binary mixture of HFE-7100/water in the sintered porous microchannels exhibited a much higher overall heat transfer coefficient and lower power consumption.To maintain the junction temperature of a high power electronic chip below 85℃,the proposed supercapillary microchannel heat sink could effectively dissipate the heat flux of 1275 W/cm^(2)over 1 cm^(2)heat source and 500 W/cm^(2)over 5 cm^(2)heat source.In addition,the volume ratio of the binary mixture strongly influence the two-phase flow heat transfer characteristics.An optimal volume ratio exist in terms of the thermal resistance–pumping power minimization(HFE-7100:water=2:8 is recommended in this study).The findings of this investigation on the flow boiling properties of non-azeotropic immiscible mixtures help fill a gap in the related field.

Direct reduction of hematite powders in a fluidized bed reactor

Ultrafine hematite powder was reduced to produce ultrafine iron powder in a 50%Ar-50%H2 atmosphere at 450-550 ℃ in a fluidized bed reactor. The ultrafine hematite powder shows the typical agglomerating fluidization behavior with large agglomerates fluidized at the bottom of the bed and small agglomerates fluidized at the upper part of the bed. It was found that defluidization occurred even at the low temperature of 450 C with low metallization rate. Defluidization was attributed mainly to the sintering of the newly formed iron particles. Granuation was employed to improve the fluidization quality and to tackle the defluidization problem, where granules fluidized like a Geldart＇s group A powder. Granulation was found to effectively reduce defluidization during reduction, without however sacrificing reduction speed. The asreduced iron powders from both the ultrafine and the granulated hematite exhibited excellent sintering activity, that is, fast sintering at temperature of as low as ~580℃, which is much superior as compared to that of nano/ultrafine iron powders made by other processes.

Preparation,Structure and Mechanical Properties of Nickel Based Porous Spherical Superalloy

The porous superalloy materials with hollow spherical pores were fabricated by using metal powder sintering process. The scanning electron microscope （SEM） observation was applied to the test samples and it revealed that the pores of the porous material exhibited a uniform distribution and the apertures were of same size in principle. The sintering necks appeared between adjacent particles on metal skeleton after sintering. The mechanical properties of the test samples were analyzed and the result showed that this kind of materials possessed excellent energy absorption capability, and the compression resistance decreased with increasing the porosity and aperture.