Evolution behavior of microstructure and properties of Cu-20Sn-15Ti filler metal regulated by Si
To improve the microstructure and properties of Cu-Sn-Ti brazing alloy through component control,the ef-fect of Si on the microstructure and properties of Cu-20Sn-15Ti brazing filler metals was studied using scanning elec-tron microscopy,X-ray diffraction,and EDS energy spectrum analysis.The results show that the microstructure of Cu-20Sn-15Ti brazing filler metal is composed of large-sized polygonal CuSn3Ti5 phase,eutectic structure and α-Cu phase.A small amount of Si(≤2.0wt%)refines the polygonal-shaped CuSn3Ti5 phase in the brazing filler metal and gener-ates small-sized Si3Ti5 phase.In contrast,a larger amount of Si(≥3.0wt%)differentiates the polygonal-shape CuSn3Ti5 phase,reduces the proportion of eutectic structure,and increases the content and size of the Si3Ti5 phase.When the Si content increases to 5.0wt%,the filler metal no longer generates polygonal-shaped CuSn3Ti5 phase and eutectic struc-ture.Instead,Ti primarily forms Ti5Si3 phase,and the microstructure mainly consists of Ti5Si3 phase,α-Cu phase,Cu41Sn11 phase,and a small amount of strip-shaped CuSn3Ti5 phase.Compared with Cu and Sn,Si has a stronger chem-ical affinity with Ti and preferentially reacts with Ti to form Ti5Si3 phase.The three-dimensional structure of Ti5Si3 phase is prismatic and exhibits agglomerated growth characteristics.The coarse strip Ti5Si3 phase has central or lateral pore defects,which are mainly related to the growth mechanism.As the Si content increases,the shear strength of the filler metals shows a trend of"increasing-decreasing-increasing",and the fracture morphology transitions from a mixed morphology of quasi-cleavage fracture and cleavage fracture to cleavage fracture.The CuSn3Ti5 phase is prone to break-age and cracking,becoming the source of cracking.The presence of coarse CuSn3Ti5 phase in different states can deteri-orate the shear strength of the brazing filler metals to some extent.
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