Elsevier

Advanced Powder Technology

Volume 30, Issue 10, October 2019, Pages 2101-2109
Advanced Powder Technology

Original Research Paper
Synthesis and structural control of Fe-based porous layer on Fe substrate for joining with resin parts using combustion reaction

https://doi.org/10.1016/j.apt.2019.06.024Get rights and content

Highlights

  • An open-cell Fe/TiB2 composite layer was synthesized on a Fe substrate.

  • The combustion reactions among Fe, Ti, and B powders were applied.

  • Higher peak temperature changed pore morphology from open to semi-closed.

  • Higher peak temperatures promoted bonding between the substrate and porous layer.

  • The changes in the porous structure was assessed with the calculated phase diagram.

Abstract

A porous Fe/TiB2 composite layer was synthesized on an Fe substrate by a powder metallurgy process using combustion reactions among Fe, Ti, and B to achieve Fe/resin joints through interpenetrating phase layers. The effects of Fe particle size and the blending ratio of the raw powder mixture on the porous structure, roughness of the top surface of the porous layer, and adhesiveness between the porous layer and Fe substrate were investigated. The peak temperature measured with a thermocouple increased with increasing Fe particle size and blending ratio of Ti and B. An increase in the peak temperature does not affect the porosity of the porous layer. Higher peak temperatures increase the pore size and change the pore morphology from open to semi-closed (although pores are not completely isolated). The change in pore morphology prevents the exposure of pores on the top surface of the porous layer, resulting in decreasing surface roughness. Moreover, an increase in the maximum temperature promotes bonding between the Fe substrate and porous layer. These results are discussed in view of the thermodynamic assessment using the calculated equilibrium phase diagram.

Introduction

Weight reduction of vehicle bodies has been intensively studied with a view to reducing CO2 emission and effectively utilizing energy. Multi-material structures have received much attention, in which the most suitable material (e.g., steels, light metals, carbon-fiber-reinforced plastics (CFRPs)) is used for each component of the vehicle [1]. Vehicles then can be designed considering the balance among low cost, high strength, and low weight. Thus, it is essential to establish technologies to join dissimilar materials like metals and resins.

One of the direct joining methods is mechanical interlocking using the anchor effect. Metal and resin can be interlocked by infiltrating resin into dimples formed on the metal surface. The surface structure of the metal is important to obtain high joint strength. Many promising processes to modify and control the structure of metal surfaces, such as laser irradiation, chemical etching, and sandblasting, have been reported [2], [3], [4], [5], [6], [7], [8]. There have been many studies on the shear strength at the joint interface in the case of mechanical interlocking. However, the tensile strength perpendicular to the interface has not been widely investigated.

Recently, Suzuki et al. proposed a novel concept of mechanical interlocking via an “interpenetrating phase layer (IPL)” [9], [10]. Resin is infiltrated into open porous layer formed on the metal surface to interlock the metal/resin three-dimensionally. High bonding strength can be achieved in all directions because of the three-dimensional interlocking in the IPL. Suzuki et al. joined Al with epoxy resin via a porous Al layer fabricated by the space holder method using NaCl [11]. High joint efficiency (87% of resin strength) in the direction normal to the joint interface was achieved [10]. It was also clarified that the fracture mode changes depending on the volume fraction of resin in the IPL. In the present study, we have attempted to synthesize an Fe-based porous layer in order to achieve an Fe/resin joint via the IPL. Processes to fabricate porous Fe include continuous casting [12], [13], the metal hollow sphere (MHS) method [14], [15], metal powder slurry processing [16], [17], and the space holder method using polymethylmethacrylate (PMMA) or polystyrene [18], [19], [20]. Recently, Ito et al. reported that Fe-based porous materials can be synthesized by combustion reactions among Fe, Ti, and B [21]. An open-cell porous Fe/TiB2 composite is synthesized in a very short time by the heat of reaction to form TiB2 from Ti and B. Also, if the reactions are induced on a Fe substrate, it is expected that the large amount of heat will lead to good bonding between the porous layer and substrate. Thus, the combustion reaction of the Fe-Ti-B system is a promising process to synthesize porous layer for joining with resins. In the present study, porous Fe/TiB2 composites were synthesized on an Fe substrate. The effects of Fe particle size and the blending ratio of the raw powder mixture on the porous structure, surface structure of the porous layer, and adhesiveness between the porous layer and substrate were investigated.

Section snippets

Materials and methods

In this study, Fe powders (purity > 99.9%) with various particle sizes (dFe < 53 μm, <150 μm), Ti powder (purity: 99.9%, particle size < 45 μm), and B powder (purity: 99%, particle size < 45 μm) were used as starting materials. Fig. 1 shows secondary electron images (SEIs) of the raw powders used in the present study. These powders were dry blended for 30 min. The molar ratio of Ti and B was fixed at 1:2 to synthesize TiB2. The volume fractions of TiB2 (VTiB2) were set at 40, 50, 60, and 70% on

Results

Fig. 5 shows (a, b) the temperature profiles measured with the thermocouple when Fe powders with (a) dFe < 53 μm and (b) dFe < 150 μm were used and the (c) change in the maximum temperature (TMax) observed during the reaction as a function of VTiB2. When the heating temperature exceeded approximately 1150 °C, the temperature sharply increased. The sharp rise in temperature is due to the combustion reaction among Fe, Ti, and B. Note that the exothermic reaction finished in a very short time

Discussion

In the present study, an Fe-based porous layer was synthesized on an Fe substrate using the combustion reaction of the Fe-Ti-B system. The effects of the volume fraction of TiB2 (VTiB2) and Fe particle size (dFe) on the porous structure and microstructure of the porous layer were investigated. Porous layers in all the samples were composed of Fe/TiB2 composites and exhibited 30% porosity (Figs. 6 and 11(a)). Fe-rich regions without TiB2 were observed when the maximum temperature was below

Conclusion

The effects of the volume fraction of TiB2 (VTiB2) and Fe particle size (dFe) on the porous structure of an Fe-based porous layer synthesized on an Fe substrate by the combustion reaction among Fe, Ti, and B powders was investigated. The main results are as follows.

  • The pore size in the porous layer increases with both increasing VTiB2 and dFe while porosity is almost constant.

  • The surface roughness of the top surface of the porous layer decreased with both increasing VTiB2 and dFe.

  • The bonding

Declaration of Competing Interest

None.

References (28)

Cited by (2)

  • Joint strength of Fe/epoxy resin hybrid structure via porous Fe/TiB<inf>2</inf> composite layer synthesized by in-situ reaction process

    2021, Journal of Materials Processing Technology
    Citation Excerpt :

    The bonding ratio (α), which reflects the adhesiveness of the porous layer/Fe substrate was quantified. The detailed definition of bonding ratio was given in Suzuki et al. (2019). To evaluate the tensile joint strength, the samples soaked into the two-component epoxy resin was cut into rods after curing the resin.

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