Study On Preparation And Microstructure Of Copper Matrix Composites Reinforced By Rare Earth Oxides

Due to their excellent high-temperature mechanical properties and radiation resistance,oxide dispersion strengthened(ODS)copper alloys have become the main candidates for heat sink materials of divertors in thermonuclear fusion experimental reactors.Nanosized oxide particles are uniformly distributed in the alloys.Their properties largely rely on the type,size and volume fraction of the particles,as well as the processing method of the alloys.These alloys are mainly prepared by mechanical alloying.Usually,Cu and Y₂O₃ powders are chosen as raw materials for mechanical alloying.In this process,Y and O are dissolved into Cu powder via high-energy ball milling.Due to the high thermal stability of Y₂O₃,the ball-miling time has to be extremely long,resulting in a low efficiency.Therefore,in this study,instead of Y₂O₃,Cu₂O or Ti O₂ with lower stability are selected as oxygen sources for mechanical alloying.As a result,nano-oxide particles form through in situ reactions between the disovled oxygen and Y in the raw powders.Four powder systems,Cu-Y-Cu₂O(pure Cu powder,pure Y powder and Cu₂O powder),Cu-Y-Ti O₂(pure Cu powder,pure Y powder and Ti O₂ powder),(Cu,Y)_atomized-Cu₂O(atomized(Cu,Y)powder and Cu₂O powder)and(Cu,Y)_atomized-Ti O₂(atomized(Cu,Y)powder and Ti O₂ powder)are applied in this research.Influence of powder types on the mechanical alloying process is studied.The mechanism of mechanical alloying has been revealed.Finally,nano-Y₂O₃ and nano-Y₂Ti₂O₇ dispersion strengthened Cu alloys are obtained by spark plasma sintering.The main results are as follows:(1)Compared with the Cu-Y-Cu₂O/Ti O₂ system,the(Cu,Y)_atomized-Cu₂O/Ti O₂ powder system has a smaller size and a more uniformly distributed Y after ball-milling for the same period.This suggests that the use of atomized powder facilitates the mechanical alloying process.(2)With increasing ball-milling time,the powder size varies and finally reaches a steady state after 48 hours.In addition,Y is gradually homogenized into the Cu matrix.The alloying process is substantially achieved after ball-milling for 48 hours.(3)Nanosized Y₂O₃ and Y₂Ti₂O₇ particles are formed in the as-sintered(Cu,Y)_atomized-Cu₂O and(Cu,Y)_atomized-Ti O₂ systems,respectively.They are mostly spherical.After annealing,more nano particles precipitate.Due to the severe internal strain in the ball-milled powders,nano-crystalline Cu matrix is formed in the as-sintered material.After annealing,the grain size increases.