Observation Of Intermetallic Compound And Hydrogen Bubble Behaviors In Al-Ni Alloy By Synchrotron Radiography

The growth behavior of Al₃Ni intermetallic compounds,hydrogen bubbles and their interaction during the directional solidification of hypereutectic Al-Ni alloy were investigated by synchrotron radiation.Two main growth patterns of primary Al₃Ni phase,I-like and V-like,appeared during solidification,and I-like Al₃Ni phase grew faster than V-like phase due to its smaller energy density and less specific surface area.The growth of I-like phase was mainly affected by undercooling and Ni concentration.We also found that V-like Al₃Ni phase can evolve into M-like phase during solidification.The size of Al₃Ni intermetallic compound is largely related to alloy composition and pulling rate.The closer the alloy composition is to the eutectic composition and the larger the pulling is,the finer the Al₃Ni intermetallic compound will be.In addition,the Al₃Ni intermetallic compound will become finer with the directional solidification going on.The growth of hydrogen bubbles was mainly affected by hydrogen concentration,the interaction with intermetallic compounds,internal pressure and bubble size.The bubble growth can be divided as three stages.In the first stage,hydrogen bubbles grew stochastically in Al alloy melt,and the growth velocity was determined by hydrogen concentration.In the second stage,local bubble deformation happened under the squeeze of intermetallic compounds,and the increase of hydrogen concentration and its gradient at the bubble-liquid interface contributed to the accelerated growth.In the third stage,the hydrogen concentration gradient ahead of the bubble-liquid interface became negative.So bubbles began to shrink.And the increasing pressure resulting from the decreasing contact angle between bubbles and intermetallic compounds can result in the decrease of bubble dimension by increasing hydrogen solubility.With bubble size decreasing,spheroidization phenomenon happened.