Investigation On Microstructure And Properties Of TiB₂/Cu Composites Prepared By Spray Deposition

In order to improve the softening temperature of copper alloys,the addition of TiB2 particles with high hardness,high melting point,good wear resistance,and good electrical conductivity to copper to improve the high temperature strength of the composite materials is a more commonly used strengthening method.However,TiB2/Cu composites prepared by traditional methods have problems such as uneven distribution of reinforcing phase and severe particle agglomeration.Reactive spray deposition is a new method for preparing particle-reinforced metal matrix composites by combining in-situ reaction with rapid solidification.The prepared composites have the advantages of small size and dispersed uniform distribution of the reinforcing phase,good interface bonding,simple process and low cost.In this paper,TiB2/Cu composites were prepared by spray deposition.The atomization,reactive deposition and densification process in spray deposition were discussed.The influence of atomization process parameters on the particle size distribution and morphology of the powders were investigated using Cu-Ti alloys in the atomization stage.The internal morphology,composition and theoretical solid solubility of the prepared powders were analyzed.The TiB2/Cu composites were prepared by spray deposition on the basis of atomization.First,the spray deposition process parameters were optimized,and then the prepared billets were analyzed for composition,microstructure and properties.The deposited billets were densification treatment by hot pressing sintering and cold deformation.The results show that:(1)The alloy powders prepared by the gas atomization method had the characteristics of small particle size,good sphericity and a small amount of irregular powder.The best atomization process parameter was atomization pressure of 5MPa,superheat of 300?,and nozzle diameter of 4mm.The atomized powder was composed of dendrite and equiaxed crystal.The internal grain size of 50-150?m powders was about 10?m.(2)The smaller the particle size of the powders,the greater the degree of lattice distortion in the powders and the higher the content of titanium in the powders.Theoretical calculation of solid solubility of 50-100?m powders were about 2.0wt.%.The content of titanium in the powder prepared by vacuum gas atomization was about 2.1wt.%,and the content of oxygen was 0.03wt.%;the content of titanium in the powders of 50-100?m was about 1.8wt.%.(3)The best technological parameter for spray deposition were atomization pressure of 3MPa,nozzle diameter of 3.5mm,superheat of 300?,and air flow rate of 15L/min.The density of the deposited billet was 8.1g/cm3.The deposition billet prepared by spray deposition method had different properties in different positions.The electrical conductivity of edge region was about 10%IACS and the hardness was 60HB.The electrical conductivity of central region was 22%IACS,and the hardness was between 70-80HB.The content of titanium and boron in the deposition billet was about 3wt.%and 1-1.5wt.%,respectively.The hardness and electrical conductivity of the deposited billet prepared by 15L/min gas flow rate were 93HB and 13%IACS respectively.Boron powder on the particle surface reacted with titanium element to form TiB2 phase particles.(4)The properties of the deposited billets were greatly improved by hot pressing sintering.The deposition billet prepared by 15L/min gas flow rate was sintered at 990?.The density,electrical conductivity,hardness,tensile strength and elongation of the deposited billet were 8.5g/cm3,17.5%IACS,126HB,240MPa.The fracture mode was brittle fracture.After sintering,new TiB2 particles were formed at grain boundaries,but TiB2 particles agglomerated seriously at grain boundaries.(5)After 40%cold rolling,the deposited billet prepared by 15L/min gas flow rate had a density of 8.53g/cm3,an electrical conductivity of 20%IACS,a hardness of 155HB,a tensile strength of 520Mpa,and an elongation rate of 4.1%.The fracture mode was brittle fracture.After 40%cold rolling,the properties of the deposited billet with different boron content increased obviously.the electrical conductivity of the deposited billet increased first and then decreased,the tensile strength and the elongation rate of the deposited billet decreased gradually.Fracture mode of the deposited billet from plastic fracture to brittle fracture.