Active metal brazing is a key method allowing the convenient joining of ceramics. In order to make an appropriate use of the outstanding high temperature resistance of ceramics, filler materials with an elevated application temperature are under development. Currently, there are no commercially available active filler materials devoid of noble metals with a melting point above 1.300°C, which is limiting the use of brazed high temperature stable components of SiC.
The composition Ni62Ta38 with a melting temperature of 1.390°C was selected from the binary system Ni-Ta. The aim of the presented work is to develop a high temperature resistant filler alloy devoid of noble metals for active metal brazing of SiC. For this reason the processing behavior of the filler material and the phase formation inside the alloy and the diffusion-transition zone are investigated.
The thermal stability of the joints generated by reactive filler alloys is mostly determined by the phases forming the diffusion-transition zone. To estimate the thermal stability of the joints the interface reactions were calculated by the thermochemical software FactSage®. The calculations show a favored reaction of Ni with the Si from SiC to NiSi. Ta reacts with the residual C to TaC. However the thermochemical software doesn’t consider the kinetics of the interface reactions.
The use of a laser supported brazing technology allows to reduce the processing time up to less than 60s (depend from the thickness of the joining seam), what makes this technology interesting for the investigation of short-term chemical reactions. The laser joint samples were loaded in a high temperature furnace over 5 hours and 900°C to control the thermal stabilities of the phases in the braze material and compared with the phase formation during a furnace brazing process.
The filler material and the joints were executed using a 3kW diode laser with a wavelength of 808nm to 940nm allowing the variation of processing times between 2s and 120s.
The quality of the joints and the formation of chemical phases was analyzed by SEM-EDX and X-ray diffractometric measurements. A processing time less than 60s leads to the formation of the intermetallic phases TaNi, Ta2Ni, NiSi and TaC in contrast to Ta3Ni, NiSi and TaC formed in processes longer than 60s.
The experimental results confirm the suitability of the Ni62Ta38 alloy for the active metal brazing of SiC by laser and by conventional furnace heating technology.