Investigation On The Microstructural Formation Of In-situ Cu-Hi（TiH₂）-B Composites Sintered In Powder Metallurgy System

With the development of modern science and technology,the requirements for the comprehensive performance of conductive Cu-based composite materials are increasing.Borides have become attractive reinforcement for strengthening copper due to high electrical conductivity and mechanical properties.The purpose of this paper is to study the formation mechanism of reinforcement and the microstructural evolution of Cu matrix to prepare copper matrix composites with excellent properties by controlling the properties of reinforcement and matrix.In this paper,Ti and B powders were firstly mixed in a planetary ball miller.The Cu powders were then blended with ball-milled powders,and subsequently cold compacted into green body.These compacts finally were sintered in a furnace.The effects of different sintering temperatures and heating rate on the composites were investigated and the formation mechanism of reinforcement was discussed by the thermodynamic and kinetic assessments.In addition,the microstructural evolution of Cu matrix and the sintered materials during the preparation of composites by different ball milling systems of Cu-Ti-B powder combined with hot-pressing sintering were also analyzed.The main results are as follows:(1)Hybrid TiB2 particles and TiB whiskers reinforced copper matrix composites have been successfully prepared by sintering the green body of ball-milled Ti,B powder and mixed Cu powder.Microstructure analysis showed that there is a competitive behavior between TiB whistles and TiB2 particles,where the relative content of the two reinforcements was varying with sintering temperature and heating rate.(2)Thermal/kinetic assessments indicated that the formation of both TiB and TiB2 in copper is thermodynamically favored.This competitive growth of the two depends mainly on the change of growth mode.The entire reaction process of Ti and B atoms was controlled by the initial Zener growth and the later Dybkov growth.(3)After the B powder participates in ball milling process,Cu powder would be refined and it was easy to form twins inside.B atoms tended to segregate at the twin boundaries to pinning the twins and kept them until the sintering was completed.Some twins disappeared due to the recovery and recrystallization of the Cu matrix during the sintering process.Twins in the matrix can hinder cracks propagation and electron migration,which could increases hardness and reduces electrical conductivity.