Brazing can be considered as an attractive method for joining sintered steel components since it can be integrated into the sintering process. The behavior and quality of the joint rely on the braze filler design. Among others, the interaction between the base material and the filler depends on the brazing temperature, wettability, infiltration ability, holding time, and sintering atmosphere. The use of this joining technique in components based on FeCuC is very common, and in this case the presence of a second liquid phase during sintering can limit the response of braze fillers. In this study, with the aim of analyzing the effect of the base steel composition, a NiCu-based brazing will be used together with different Fe-base substrates for sinter-brazing tests: iron is considered as the reference, FeC to assess the carbon addition effect, and finally FeCCu substrate tries to explain the interaction between the two liquid phases (the molten brazing alloy and the Cu transient liquid phase). Characterization of the final joint is supported with SEM and LOM microscopy, and EDS is used for determining the distribution of the alloying elements. Moreover, liquid phase features such as infiltration capacity and diffusion are evaluated by using image analysis. On the other hand, the study is completed with wetting evaluation of the brazing alloy.

Introduction

The production of components through the powder metallurgy technology is characterized by its ability for producing large batches at a low cost and with close tolerances, although there are some restrictions on the complexity of the obtained parts. These restrictions can be overcome through joining techniques, since they allow the combination of different materials and the processing of complex parts impossible to obtain by uniaxial compaction.

Within the different joining techniques, the sinter-brazing process offers a competitive advantage thanks to the excellent mechanical properties and low dimensional distortion that can be achieved, without increasing the number of steps in the manufacturing route of a certain component. This technique consists on a joining process of metallic components, in which an additional material in liquid state is used and it is known as the brazing alloy. It is carried out in a furnace and the brazing process occurs while the parts to braze are being sintered. The melting point of the filler is lower than the sintering and melting temperature of the base material, so that it wets the substrates without melting themselves.

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