Effect Of Trace Hf On Properties And Microstructure Of Cu And Cu-0.6Cr Alloy

Hafnium?Hf?has the characteristics of plasticity,easy processing,high temperature and corrosion resistance,and is used in both atomic reactors and nickel-based superalloys.As an element associated with Zr,the properties of Hf are similar to those of Zr.When added to copper,it can greatly increase the recrystallization temperature of copper,while maintaining the strength while maintaining high electrical conductivity.The precipitation strengthening effect also exists in the addition of Hf to copper.The solubility of Hf in copper is higher than that of Zr?Hf is 0.4at%,Zr is 0.12at%?at eutectic temperature,which has more room for performance improvement.Faced with the increasing requirements for the strength of high-copper alloys and the heat resistance of high-strength and high-conductivity copper alloys,it is of great significance to try to develop new alloys and corresponding processing techniques.In this paper,Cu-Hf and Cu-0.6Cr-Hf alloys were studied.Three different Hf content Cu-Hf alloys and two different Hf content Cu-0.6Cr-Hf alloys were vacuum-melted and cast,solid solution,cold rolling,aging and other deformation heat treatment processes for the alloy,testing the mechanical properties and physical properties of Vickers hardness,tensile strength,elongation,electrical conductivity,softening temperature,etc.The effects of Hf on the properties and microstructure of copper and copper-chromium alloys were systematically studied by means of metallographic microscope?OM?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and energy dispersive spectroscopy?EDS?.,explored the existence form of Hf in the alloy,after analysis,the following conclusions are obtained:?1?When the amount of Hf added reaches a certain level,it has the effect of refining crystal grains;the solution temperature of three Cu-Hf and two Cu-0.6Cr-Hf alloys should be 950°C;the aging temperature of Cu-Hf alloy is The performance is better at 450°C.From the comprehensive performance point of view,the softening temperature of Cu-0.15Hf alloy is 525°C,and the softening temperature of Cu-0.4Hf and Cu-0.9Hf alloy can reach 550°C;Cu-0.15Hf and Cu-0.4 The hardness of Hf alloy after aging can reach 140HV0.5,160HV0.5,respectively.Their electrical conductivity is above 80%IACS,and the hardness of Cu-0.9Hf alloy can reach 180HV0.5 after aging,and the conductivity can reach 80%IACS.As the Hf content increases,the peak hardness and the maximum tensile strength of the alloy increase.?2?The two Cu-0.6Cr-Hf alloys have better performance at aging temperature of500°C.From the comprehensive performance,the hardness and electrical conductivity of Cu-0.6Cr-0.15Hf alloy after aging are above 180HV0.5 and The hardness and electrical conductivity of the 80%IACS,Cu-0.6Cr-0.9Hf alloy after aging are 210 HV0.5 and 70%IACS,respectively.The softening temperature of Cu-0.6Cr-0.15Hf and Cu-0.6Cr-0.9Hf alloy can reach 580°C.The addition of trace amounts of Hf in copper-chromium alloy can greatly increase the softening temperature as the Zr element.The softening temperature of Cu-Cr-Hf alloy is slightly higher than that of Cu-Cr-Zr alloy,but with the increase of Hf content,the increase of alloy softening temperature is gradually reduced.?3?The addition of Hf element increases the hardness of the alloy in the as-cast state.In the deformation heat treatment process,it can always hinder the growth of the grain and improve the heat resistance of the alloy.This effect increases as the Hf content increases.?4?The precipitated phase precipitated by Cu-Hf alloy exhibits a short rod shape.The particle size of the Cu-Hf alloy after aging at 450°C is only about 20 nm,which has little effect on the hardness.After a sufficiently long aging time,the precipitated phase exhibits the most stable state,which is Cu₅Hf of cubic AuBe₅ type,and the precipitated phase at this time is Cu₅Hf of face-centered cubic structure.The precipitated phase containing Hf precipitated by Cu-Cr-Hf alloy is the same as that in Cu-Hf alloy,and exhibits a short rod shape.The precipitate containing Hf is similar to the Zr phase contained in Cu-Cr-Zr alloy,and is not in a stable state.It is a metastable phase that changes with the aging.