Atomic force microscope study of WC-10Co cemented carbide sintered from nanocrystalline composite powders

In order to compare the spark plasma sintedng （SPS） process plus hot isostatic press （HIP） with vacuum sintedng plus HIP, an investigation was carried out on the topography, microstructure and gain size distribution of nanocrystalline WC-10Co composite powder and the sintered specimens prepared by SPS plus HIP and by vacuum sintering plus HIP by means of atomic force microscopy （AFM）. The mechanical properties of the sintered specimens were also investigated. It is very easy to find cobalt lakes in the specimen prepared by vacuum sintering plus HIP process. But the microstructure of the specimen prepared by SPS plus HIP is more homogeneous, and the grain size is smaller than that prepared by vacuum sintering plus HIP. The WC-10Co ultrafine cemented carbide consolidated by SPS plus HIP can reach a relative density of 99.4%, and the transverse rupture strength （TRS） is higher than 3540 MPa, the Rockwell A hardness （HRA） is higher than 92.8, the average grain size is smaller than 300 nm, and the WC-10Co ultrafine cemented carbide with excellent properties is achieved. The specimen prepared by SPS with HIP has better properties and microstructure than that prepared by vacuum sintering with HIP.

Co-based Amorphous/Nanocrystalline Composite Coatings Deposited by Arc Ion Plating

Cobalt-based amorphous/nanocrystalline composite coatings have been grown by arc ion plating together with a specimen cooling system. With decreasing substrate temperature, the coatings undergo significant structure evolution. The degree of crystallization first decreases and subsequently increases as confirmed by X-ray diffraction. The cluster size first decreases and then remains constant as confirmed by transmission electron microscopy. The effect of substrate temperature on the evolution of the structure has been studied as a result of a competition between nucleation thermodynamics and kinetics of crystalline growth. With decreasing the substrate temperature, the microhardness and the critical load of the composite coatings firstly increased, and then remained almost constant. And the saturation magnetization revealed the opposite trend over the same range. The essence of these phenomena was ascribed to the microstructural variations caused by the decrease of the substrate temperature.

Effect of Zr on Microstructure and Magnetic Properties of Nanocrystalline (Nd, Pr)FeB/α-Fe Composite Alloys

For nanophase (Nd, Pr)FeB/α-Fe composite alloys were prepared by melt spinning, the appreciable addition of Zr reduces their average grain size. Observed by atom force microscopy (AFM), the average grain diameter of crystallized ribbons on their free surface, reduces from 175 nm of Zr-free alloy to 79 nm of Zr-1at%, by about 55%. If the concentration exceeds 1%, the effects of Zr on fining grain size are evidently weakened. The average grain size on free surface of Zr-1.5at% is 72 nm. With the addition of 1at% Zn, the bonded magnets has the best combination of properties: B_r=0.675 T, H_(ci)=616 kA·m^(-1), (BH)_(max)=77 kJ·m^(-3). Below 1at%, the coarser grains lead to a lower magnetic property. Beyond 1at%, the layer of Zr-rich intergranular phase will thicken, which results in weakening of the exchange coupling among adjacent grains, and then causes degrading of magnetic properties of magnets.

Microstructure and Hydrogen Absorption Pro-perties of Mg/MmNi_(5-x) (CoAlMn)_x Composite Prepared by Mechanical Alloying

The microstructure ofthe Mg/MmNi5-x (CoAlMn )x composite hydrogen storage material preparedby the method of mechanical alloyingwas characterized by X-ray diffraction, SEM and particle size distribution analysis. By measuring PCTcurves, the hydrogen absorption properties of the composite was evaluated.The results show that nanocrystallinecomposite structure can be obtainedunder adequate ball milling condition. The reactive activation and hydrogen absorption capacity are improved compared with the sole MmNi5-x(CoAlMn)x alloy. The effect ofmagnesium on the microstructure andhydrogen absorption properties of thecomposite were also evaluated.

Study on the diamond/ultrafine WC-Co cermets interface formed in a SPS consolidated composite

Nanocrystalline WC-Co composite powder and coated tungsten diamond by using vacuum vapor deposition were consolidated by the spark plasma sintering （SPS） process to prepare diamond-enhanced WC-Co cemented carbide composite materials. The interface microstructures between coated tungsten diamond and WC-Co cemented carbide matrix were investigated by scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDXS）. The results showed that there is a transitional layer between the diamond and the matrix, in which the carbon content is 62.97wt.%, and the content of cobalt in the transitional zone is 6.19wt.%; the content of cobalt in the WC-Co cemented carbide matrix is 6.07wt.%, in which the carbon content is 15.95wt.%, and the content of cobalt on the surface of diamond is 7.30wt.%, in which the carbon content is 80.38wt.%. The transitional zone prevents the carbon atom of the diamond from spreading to the matrix, in which the carbon content does coincide with the theoretical value of the raw nanocomposite powders, and the carbon content forms a graded distribution among the matrix, transitional zone, and the surface of diamond; after the 1280℃ SPS consolidated process the diamond still maintains a very good crystal shape, the coated tungsten on the surface of the diamond improves thermal stability of the diamond and increases the bonding strength of the interface between the diamond and the matrix.

Dependence of Magnetic Properties of Rapidly Quenching (Nd,Pr)_x (FeCoZr)_(94-x)B_6 Bonded Magnets on Rare Earths Content

By using sub-overquenching and annealing method which has a wide processing window, (Nd, Pr), ( Fe-CoZr)(94-x)B-6(x = 12, 10.5, 10, 9) bonded magnets were prepared and the effect of rare earths content on magnetic properties was investigated. Being spun at sub-ove.quenching speed the as-spun ribbons consist of amorphous phases mixed with fine crystallites. After crystallization under optimum annealing conditions and bonded with 3.25% (mass fraction) epoxy, the magnets obtained the optimum magnetic properties. The rare earths content directly determines the magnetic properties. With the reduction of rare earths content, B-r increases but H-ci and (BH)(max) decrease. x = 10 is the critical value for the magnetic proper-ties change. Below this value, Br increases slowly meanwhile H-ci and (BH)(max) decrease strongly because alloy contains extra fractions of soft magnetic phase which are not coupled with the hard magnetic phase.. This experimental result is consistent with the calculated results using the model of volume fraction of soft magnetic phase coupled completely suggested.

Influences of Carbon Content on the Properties and Microstructure of Ultrafine WC-10Co Cemented Carbide

WC-10Co nanocrystalline composite powders prepared by spray pyrogenation-continuous reduction and carburization technology were consolidated by vacuum sintering plus hot isostatic pressing （HIP）. Influences of carbon content on properties and microstructure of ultrafine WC-10Co cemented carbide were investigated. The results show that the relative density of the ultrafine WC-10Co cemented carbides can reach 99.72%, and the transverse rupture strength （TRS） was higher than 3 890 MPa, Rockwell A hardness （HRA） was higher than 92.5, the average grain size was less than 460 nm, when carbon content in nanocrystalline composite powder was 5.54wt% and the ball-milled time was 48 hours, ultrafine WC-10Co cemented carbide with excellent properties and homogeneous microstructure was obtained.

Influence of microstructure on the corrosion resistance of Fe–44Ni thin films

An Fe–44Ni nanocrystalline（NC） alloy thin film was prepared through electrodeposition. The relation between the microstructure and corrosion behavior of the NC film was investigated using electrochemical methods and chemical analysis approaches. The results show that the NC film is composed of a face-centered cubic phase（γ-（Fe,Ni）） and a body-centered cubic phase（α-（Fe,Ni）） when it is annealed at temperatures less than 400℃. The corrosion resistance increases with the increase in grain size, and the corresponding corrosion process is controlled by oxygen reduction. The NC films annealed at 500℃ and 600℃ do not exhibit the same pattern, although their grain sizes are considerably large. This result is attributed to the existence of an anodic phase, Fe0.947Ni0.054, in these films. Under this condition, the related corrosion process is synthetically controlled by anodic dissolution and depolarization.