Investigation On Microstructure Evolution And Young’s Modulus Of Directionally Solidified Cu-50at.%Sn Peritectic Alloy

In recent years,numerous studies have been carried out by scholars on the solidification in peritectic alloys.However,most of the studies are based on the peritectic alloy systems in which the peritectic phase is the solid solution phase with high solid solubility,while there are still much less studies on peritectic alloy systems containing intermetallic compound phases with low or no solid solubility.The precise measurement of mechanical properties such as Young’s modulus is very important in the development of metallic materials.Present measurement methods are mostly contact tests,which affects the accuracy of the test results.Therefore,this paper is based on the study of the Cu-50 at.%Sn peritectic alloy containing the intermetallic phases Cu₃Sn and Cu₆Sn₅with low solubilities.The Young’s modulus of the primary phase Cu₃Sn and the peritectic phase Cu₆Sn₅were obtained through the Brillouin light scattering non-destructive testing technique.The specific results are as follows:The directional solidification structure with growth velocity（V）,temperature gradient（G）and growth distance（l）as single variables are analyzed.The results show that the primary phase Cu₃Sn grows as the leading phase throughout the entire directional solidification growth zone,while the peritectic phase Cu₆Sn₅no longer precipitates after the certain distance.Therefore,this paper concentrates on the effect of changes in solidification conditions on the solidification structure of the quenched solid-liquid interface.When the temperature gradient and growth distance are constant,the primary phase Cu₃Sn undergoes the transition from the cellular→cellular/dendritic→dendritic structure as the growth velocity increases.At the same time,the size and spacing of the Cu₃Sn phase both decrease with increasing growth velocity.When the growth velocity and growth distance are constant,the primary phase Cu₃Sn transforms from massive and dendritic to the cellular structure as the temperature gradient increases.When the growth velocity and temperature gradient are constant,the primary phase Cu₃Sn changes from massive with cellular/dendritic to cellular structure as the growth distance increases,while the slight refinement in the size of Cu₃Sn phase occurs.The tip distance between the experimentally obtained primary phase Cu₃Sn and peritectic phase Cu₆Sn₅has been accurately measured in different solidification conditions to analyze the growth behaviour of the peritectic Cu₆Sn₅phase during directional solidification.When both the temperature gradient and growth distance are constant,the tip distance between the above two phases increases from 12.8 mm to 23mm as the growth velocity increases.When both the growth velocity and growth distance are constant,the tip distance decreases from 15.3 mm to 10.7 mm for 1μm/s and from 17.5 mm to 11.3 mm for 5μm/s as the temperature gradient increases.When the growth velocity and temperature gradient are constant,the tip distance increases from 12.1 mm to 16.4 mm for 1μm/s and from 10.2 mm for 5μm/s as the growth distance increases.In addition,the growth behaviour of the peritectic phase Cu₆Sn₅was explained in combination with the solute partitioning model and tip temperature model from previous studies.Nanoindentation experiments are carried out for Cu-50at.%Sn peritectic alloys to analyze the load-displacement curves of the primary phase Cu₃Sn and peritectic phase Cu₆Sn₅at different growth velocity as the temperature gradient and growth distance were constant.The results show that the maximum load for both the Cu₃Sn and Cu₆Sn₅phases increases as the growth velocity increases.The Young’s modui of the Cu₃Sn and Cu₆Sn₅phases is measured with the continuous stiffness method at different growth velocity,and the Young’s modui of both of the above phases change slightly as the growth velocity increases.The Young’s modui for the Cu₃Sn and Cu₆Sn₅phases was 115.12±9.54 GPa and 105.4±9.32 GPa through combining the test results from various growth velocity,respectively.Single-phase samples of the Cu₃Sn and Cu₆Sn₅phases required for the Brillouin light scattering test are prepared by long-term thermal stabilization.Non-destructive optical experiments are carried out on single-phase samples in different directions through Brillouin light scattering based on the tandem multichannel Fabry-Pérot interferometer.The independent elasticity coefficient matrices and Young’s modui of the Cu₃Sn and Cu₆Sn₅phases can be calculated by analyzing the Brillouin spectra.The calculated results are slightly lower than the results obtained using nanoindentation measurements in this and previous studies.The above phenomenon is attributed to the plastic deformation reinforcement produced by the indenter pressing into the surface of the sample in the nanoindentation experiment.Therefore,it is important to explore non-contact Brillouin light scattering to measure the Young’s modui of different phase in bulk alloy materials.