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Journal ArticleDOI

Electroless nickel-phosphorus coating on Ti and Al elemental powders

31 Jul 2001-Scripta Materialia (Elsevier BV)-Vol. 45, Iss: 2, pp 183-189

AboutThis article is published in Scripta Materialia.The article was published on 2001-07-31. It has received 31 citation(s) till now. The article focuses on the topic(s): Electroless nickel & Metal powder. more

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Journal ArticleDOI
Abstract: In this paper, infiltration behavior of W/Cu composite compacts made from coated tungsten powder has been investigated. For this purpose, tungsten particles were coated with Ni, Ni–P and Ni–Cu–P using electroless plating technique. Then the coated tungsten powders were compacted under selective pressures for control infiltrated copper in range 10–20 wt%. Infiltration process was carried out at 1300 °C under a reducing atmosphere. The effect of pre-coat of tungsten particles on microstructure, contiguity and density of infiltrated W/Cu compacts was evaluated by OM/SEM, EDS and Archimedes methods. It was found that electroless plating of tungsten particles leads to more homogeneity microstructure so relative density of 99.3% was achieved for infiltrated compacts. The contiguity of W–W particles in the microstructure of composite made from Ni–Cu–P coated tungsten powder was lower than to other ones.

62 citations

Journal ArticleDOI
Abstract: Combustion of activated aluminum was studied by four different methods: microscopic imaging of the preignition process, digital imaging of the combustion process at pressures up to 64 bar in air, nitrogen, and carbon dioxide, TGA, and DSC. Activation by three fundamentally different methods was found effective in enhancing both the ignitability and the burn rate. The complex fluoride coating prevented agglomeration completely in all stages of combustion, while the nickel and cobalt coatings promoted agglomeration of aluminum oxide at combustion, but prevented the agglomeration of the aluminum metal before combustion. Nickel coating catalyzed aluminum nitride formation, accelerating burn rate more than other coatings in air and in nitrogen, while complex fluoride coating was most effective in carbon dioxide. Carbon coagulation in carbon dioxide quenched burning in many cases at higher pressures than 8 bar. The complex fluoride activation accelerated combustion in CO 2 extremely effectively, but did not prevent carbon shell formation and subsequent quenching at high pressures. Ni coating negated the effects of carbon coagulation in CO 2 , but enhanced the burn rate only slightly. Co coating reduced the carbon shell formation, but did not accelerate combustion in CO 2 . Only the Ni coating applied in large amounts promoted combustion in nitrogen.

55 citations

Journal ArticleDOI
Abstract: In the present research, tungsten particles were coated using nickel/nickel–phosphorus electroless plating technique. The coated tungsten powders were pressed under constant pressure to achieve compact material of cylindrical shape with same porosity. Then, attained compacts were infiltrated/penetrated by liquid copper under the hydrogen atmosphere in order to obtain W–15 wt.% Cu composites. The coated/uncoated powders as well as its infiltrated compacts were characterized by optical microscopy (OM) as well as scanning electron microscopy (SEM), EDS and XRD methods. The microstructure, relative density and specific resistivity of composites were compared. The microstructural observations revealed that the infiltration behavior can be improved in the compacts prepared by both nickel and nickel–phosphorus coated tungsten powders, in comparison with uncoated ones. In addition, it was found that relative density may be raised from 95% by nickel electroless plating, that leads to decrease specific resistivity from 6 to 4 µΩ cm. Enhancement of electrical conductivity of infiltrated W–15 wt.% Cu compacts prepared by electroless nickel coated tungsten powders was related to its higher density.

45 citations

Journal ArticleDOI
Abstract: In this paper nickel (Ni)-coated tungsten carbide (WC) composite powders have been synthesized by ultrasonic-assisted electroless plating with a simplified pretreatment at room temperature as the conventional sensitization and activation steps have not been employed. The growth mechanism of Ni layers and surface morphologies and composition of initial WC powders, pretreated WC powders and Ni-coated WC powders were analyzed by field emission scanning electron microscopy, and energy dispersion spectrometry. The results shows that uniform Ni-coated WC composite powders were successfully synthesized without conventional sensitization and activation steps by ultrasonic-assisted electroless plating at room temperature. The growth mechanism of Ni layers appears as follows: the surfaces of pretreated WC powders appear step-like defects which act as activated sites. Nucleation and the growth of nickel grains take place on the activated sites of pretreated WC powder, and the process repeats continuously on the lath particles with reticulate structure on the as-coated surfaces of previously deposited Ni-cells, finally Ni cells grow up and merge into a layer.

44 citations

Journal ArticleDOI
Abstract: Ni 3 Al–hBN–Ag intermetallic matrix composite coating was prepared on Ni-based superalloy by reactive sintering. The crystalline phase and microstructure of the coating were examined by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The results showed that the hBN particles pretreated by electroless nickel plating and hot-dip aluminizing and Ag particles with a size of several micrometers were homogeneously dispersed in the Ni 3 Al matrix, and the composite coating had strong interfacial bonding with a fine and dense microstructure. During the reactive sintering, an exothermic reaction between Ni and Al associated with a transient liquid phase occurred, leading to in situ synthesis of the densified Ni 3 Al matrix in the coating with a high tensile strength of more than 70 MPa. The high-temperature tribological properties evaluated on a ball-on-disc test rig showed that the coating possessed self-lubricating properties from room temperature to 800 °C due to a synergetic lubricating action of Ag and hBN.

34 citations

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01 Jan 1985
Abstract: This book contains over 50 selections. Some of the titles are: Order-disorder behavior of grain boundaries in a two-dimensional model ordered alloy; Dislocation reactions at grain boundaries in Ll/sub 2/ ordered alloys; Creep cavitation in a nickel aluminide; Effects of elastic anisotropy on the anomalious yield behavior of cubic ordered alloys; and Processing technology for nickel aluminides.

2,121 citations

01 Jan 1979

393 citations

Ian M. Watt1
30 Jun 1985
Abstract: 1. Microscopy with light and electrons 2. The electron microscope family 3. Rudiments of specimen preparation and interpretation of micrographs 4. Specialised techniques in electron microscopy 5. Examples of the use of electron microscopy Appendix 1: Production and measurement of high vacua Appendix 2: Vacuum deposition of thin metallic and carbon films for electron microscopy Appendix 3: X-ray generation and analysis Appendix 4: Electron sources for electron microscopes.

168 citations

Journal ArticleDOI
Abstract: The effects of Cr additions to y-base alloys have been investigated, using bulk materials consolidated from rapid solidification-processed ribbons. The composition ranges studied were 0 to 4 at. pet Cr and 44 to 54 at. pet Al. It was found that Cr additions do not affect the deformation behavior of single-phase γ alloys. However, they significantly enhance the plasticity of Al-lean duplex alloys which contain grains of single-phase γ and grains of lamellar γ/α2. Other Cr effects on microstructure, phase stability, site occupancy, and deformation sub-structures were characterized and correlated to the observed mechanical behavior. It was concluded that the ductilization effect of Cr in duplex alloys is partially due to the tendency of Cr to occupy Al lattice sites. Ductilization is also partially due to the ability of Cr to modify the Al partitioning and, therefore, the thermal stability of transformed α2 laths.

143 citations

Journal ArticleDOI
Abstract: Solidification microstructures of arc-melted, near-equiatomic TiAl alloys containing boron additions are analyzed and compared with those of binary Ti-Al and Ti-B alloys processed in a similar fashion. With the exception of the boride phase, the matrix of the ternary alloy consists of the same α2 (DO19) and γ (Ll0) intermetallic phases found in the binary Ti-50 at. pct Al alloy. On the other hand, the boride phase, which is TiB (B27) in the binary Ti-B alloys, changes to TiB2 (C32) with the addition of Al. The solidification path of the ternary alloys starts with the formation of primary α (A3) for an alloy lean in boron (∼1 at. pct) and with primary TiB2 for a higher boron concentration (∼5 at. pct). In both cases, the system follows the liquidus surface down to a monovariant line, where both α and TiB2 are solidified concurrently. In the final stage, the α phase gives way to γ, presumably by a peritectic-type reaction similar to the one in the binary Ti-Al system. Upon cooling, the α dendrites order to α2 and later decompose to a lath structure consisting of alternating layers of γ and α2.

106 citations