Akira Ikenaga

Boriding of nickel by the powder-pack method

Abstract Boriding of nickel (Ni) has been performed by means of a powder-pack method using boriding powder that contains no silicon. In this study, the boride layer was analyzed with an X-ray diffractometer and electron probe microanalyzer (EPMA). We studied the high-temperature hardness and the friction and wear characteristics of the layer. The results showed that the boride layer was composed of Ni 2 B and that the high-temperature hardness of borided Ni was higher than that of untreated Ni. The friction and wear properties of Ni were improved by boriding.

Enhanced densification of combustion synthesized Ni–Al intermetallic compound by Si addition

Abstract Ni–Al intermetallic compound was combustion synthesized from a powder mixture of elemental Al, Ni, and Si and was simultaneously bonded with spheroidal graphite cast iron substrate (FCD). By heating a powder mixture of elemental Al and Ni, exothermal reaction occurred at about 873 K to form Ni–Al intermetallic compound. However, the synthesized compound included a large volume of voids or unreacted regions. It was confirmed that Si addition as well as applying pressure were effective to decrease the voids or unreacted regions. It is considered that higher flowability of Al–Si liquid enhanced the densification of Ni–Al compound. The identification and growth behavior of the reaction layers formed in the interface between compound layer and FCD substrate was investigated.

Dissimilar joining of nickel aluminide with spheroidal graphite cast iron and Cu alloy by hot pressing

Abstract Joining of copper alloys (BC6) on spheroidal graphite cast iron (FCD) is effective to enhance the wear resistance of sliding parts. By applying combustion synthesis to a joining to FCD and BC6 has possibilities to enable the process at a lower temperature or for a shorter time. In this study, we examined the application of this process as joining of FCD and BC6 by using Ni–Al–Si compact as filler. Then the effects of the interface microstructure on joining were examined. As a substrate, FCD and BC6 cut into a column of 10.5Ø × 3 mm were prepared. Ni, Al and Si powders were mixed in the composition of Ni–28 at.%(Al–8 at.%Si), or Ni–78 at.%(Al–8 at.%Si). These powders were die-pressed with a load of 400 MPa for 60 s to the disc shape compact of 10 mm in diameter and 0.5 mm or 0.25 mm in thickness. Dense Ni–Al–Si intermetallic compound coating layer was formed by the combustion synthesis from the elemental mixture of Ni, Al and Si, and was simultaneously bonded with the FCD and BC6 substrate. The composition of the filler was Ni3Al, Al3Ni2 and Ni solid solution. Unreacted Ni was almost consumed by the reaction with Al–Si. Densification was achieved in the interface between filler and substrate as well as in the filler due to molten Al–Si in the filler during hot pressing infiltrates well into the interface between filler and substrates and the boundary of each powder. Reaction layer of Ni–Al–Cu was formed in the interface between filler and BC6 achieving chemically bonding. q 2003 Elsevier Ltd. All rights reserved.

In-Situ Joining of Combustion Synthesized Ni-Al Alloys with Al Casting Alloy

We focused on the surface reinforcement of Al casting alloys with Ni-Al intermetallic compounds by in-situ combustion reaction to improve the surface properties of Al casting components. Microstructure and phase formation behavior of Ni-Al based intermetallic compounds synthesized by combustion reaction were investigated in terms of thermal and phase analysis using scanning electron microscope(SEM) equipped with energy dispersive x-ray spectrometer (EDS) and x-ray diffractometer(XRD) in Ni-Al intermetallic compounds. Three kinds of nickel aluminides, NiAl3, NiAl and Ni3Al, were synthesized by emission heat from the Al molten metal in order to form a coating layer of intermetallic phase simultaneously on the solidifed Al alloy surface. The synthesized shapes and microstructures of nickel aluminides were varied by casting temperature, Si contents, and the mixing ratio of elemental powders. The synthesized reaction products formed in nickel aluminides were observed to be different depending on the mixing ratio of elemental powders. The reaction layer of about 25m thickness was formed at the interface, and it mainly consisted of NiAl3 phase by the reaction between liquid molten Al alloy and solid Ni powders in green compact. With this information, we successfully produced a coating layer of Ni3Al intermetallic compound onto the casting Al alloy surface using molten metal heat without any additional process. These findings led us to conclude that a near-net shaped nickel aluminide coating layer can be formed using this unique process.

Residual Stress and Wear Characteristics of Ni3Al Coating Layer

The Ni3Al intermetallic compound is of great interest because of its oxidation, corrosion-resistance, and high melting point. The low-temperature hot press + thermal diffusion process method is a technique that uses the thermal reactive diffusions between the elements that compose the intermetallic compound. In this method the powder mixture is heated and be able to generate the diffusions of the powder elements by keeping the heating temperature comparatively lower temperature with other technique. The authors evaluated the preparation conditions and joining quality in Ni3Al coating layer of particular interest is the residual stress due to the different mechanical properties of the coating and the substrate and its effect on the interface joining quality. It is known that residual stresses were generated by the difference in the coefficient of thermal expansion (CTE) of coating and substrate during cooling process. Such a residual stress caused by the differences of mechanical properties has strong influence on composite material strength. X-ray stress measurement techniques has been developed for experimental determination of residual stresses. In this paper, the Ni3Al intermetallic compound was coated on spheroidal graphite cast iron and austenite stainless steel using the reactive sintering method. Wear characteristics and residual stress on these intermetallic compound layers were investigated to evaluate the effect of substrate materials on coating layer properties.

Effects of Casting Conditions on the Mold Filling Characteristics of Mg Alloy in the EPC Process

Mold filling characteristics in the Mg Expendable Pattern Casting(EPC) process were investigated in terms of casting conditions such as reduced pressure, pouring temperature and casting modulus including foam materials. With increasing pouring temperature up to 775oC the filling velocity increased. However, the filling velocity decreased at temperatures above 775oC. This is likely due to the increase of back pressure. Concerning the effect of reduced pressure on filling velocity, it increased sharply at lower reduced pressure while became stable at higher reduced pressure. In thick pattern, high reduced pressure would be needed to obtain high filling velocity. In expanded polystyrene(EPS) patterns, mold filling was found to be faster in the thick pattern than thin pattern at temperatures below 750oC. This propensity was observed to be reverse at pouring temperatures above 750oC. In polymethyl methacrylate(PMMA) patterns, the filling velocity almost leveled off without showing a dependence of pouring temperature. This result is attributed to the difference in gas pressure between EPS and PMMA patterns during the EPC process.

Dissimilar Joining of Nickel Aluminide Intermetallic Compound with Spheroidal Graphite Cast Iron by Using Combustion Synthesis

Nickel aluminide based intermetallic compounds were combustion synthesized from a powder mixture of elemental Al, Ni, and Si and were simultaneously bonded with spheroidal graphite cast iron substrate (FCD). Addition of Si to the elemental mixture of Al and Ni was confirmed to be effective both to the densification of combustion synthesized intermetallic compounds and to the joining between compounds and FCD. When the composition of precursor was Ni-69at%Al-9at%Si (Al/Si is the ratio of the eutectic composition), Al3Ni and Al6Ni3Si were mainly combustion synthesized. In the interface between compounds and FCD, reaction layers were formed to the thickness of 10 µm and the constituent phases were identified as Al7Fe2Si, FeAl3 respectively. In the four point bending test of the dissimilar joints prepared by heating at 973 K for 300 s, the brittle fracture did not occurred around the joint interface but mainly in the inside of nickel aluminide coating. The interface of reaction layers with 10 µm were chemically well bonded. The sample with Ni-69at%Al-9at%Si coating exhibited highest bonding strength of about 56 MPa because of the smallest void ratio of the obtained compounds.

Boriding of Nickel in Fluidized Bed

Bonding is useful in surface hardening nickel (Ni) in many surface treatments. Although Ni boronized by powder-pack bonding with amorphous boron and by gas bonding with BCl3 has been reported, few reports cover bonding in a fluidized bed. We analyzed the treated layer using X-ray diffraction (XRD), glancing incidence X-ray diffraction, glow discharge emission spectrometry (GDS), and electron probe microanalyzer (EPMA). High-temperature microhardness and friction and wear characteristics of boronized Ni were studied, with the following results:(1) Bonding Ni at a high temperature over a long time in a fluidized bed showed flaking of the treated layer due to Ni siliconization.(2) The Knoop hardness was 1300HK for the sample boronized 7.2ks at 1073K. The boride layer was about 25μm thick and consisted mainly of Ni2B and Ni3B.(3) The high-temperature microhardness of boronized Ni is higher than that of untreated Ni below about 800K.(4) Friction properties and wear resistance to SUJ2 and SUS304 were improved by Ni bonding.