Study On Preparation And Friction Properties Of Recycled Copper Matrix Composites By Powder Metallurgy

Recovering copper from electronic waste is an important way of copper recycling.In the early stage,our research group has recovered recycled copper alloy powder from waste printed circuit boards through mechanical and physical methods（hereinafter referred to as"this method"）.Compared with traditional pyrometallurgical or hydrometallurgical technologies,this method has the advantages of green,low carbon,lower cost and short process flow.In this thesis,on the basis of recycled copper alloy powder,the recycled copper matrix friction material was prepared by adding lubricating phase and reinforcement,and the application of recycled copper powder was studied.Firstly,Cu matrix friction materials of the same standard brand were prepared from electrolytic pure copper powder and recycled copper powder obtained by this method.The effects of sintering temperature and holding time on the microstructure,physical and mechanical properties and friction properties of the two friction materials were studied.Then,（Fe Ni Mn Al_x）₅₀Cu₅₀ high entropy alloy was prepared by mechanical alloying and spark plasma sintering.The effects of Al on the microstructure,mechanical properties and friction properties of the high entropy alloys were studied.High entropy alloy composites with copper coated graphite as lubricating phase were prepared by adding solid lubricating components to high entropy alloys.The effect of copper coated graphite on the friction and wear properties of the composites was studied.The main results are as follows:（1）Under different sintering processes,the physical,mechanical and friction properties of pure copper matrix composites and recycled copper matrix composites have little difference,and the change rules are similar.All properties meet the requirements of standard brand materials,indicating that recycled copper powder can replace electrolytic pure copper powder to prepare composites with the same properties.When the sintering temperature is 825℃and the holding time is 1.5 h,the friction and wear properties of the material are the best.When the load is 10 N,the average friction coefficient of pure copper and recycled Cu matrix composites is 0.11 and 0.12,the standard deviation is 0.008 and 0.006 respectively.The wear rate is0.79×10^-7 cm³/J、0.9×10^-7 cm³/J respectively,and the standard deviation is 0.08 and 0.03respectively.Indicating that the pure copper matrix composite shows better wear performance,but the recycled copper matrix composite shows better friction and wear stability.（2）High-entropy alloying of recycled copper alloy powders to prepare（Fe Ni Mn Al_x）₅₀Cu₅₀series high-entropy alloys.The high entropy alloy powders were completely alloyed after 60 h ball milling and formed a single FCC phase solid solution.After spark plasma sintering at950℃,the high entropy alloy formed a multiscale grain structure of ultrafine grains（Cu-rich phase）+micron grains（Fe-Mn-rich phase）.With the increase of Al,the plasticity of（Fe Ni Mn Al_x）₅₀Cu₅₀ alloy decreases while the strength and hardness increase.This is mainly because the hard and brittle Ni-Al phase（B2 structure）is formed in the high-entropy alloy after adding 10 at.%Al,and more Al elements produce solid solution strengthening in the matrix.（3）Al content and friction load have an important effect on the friction and wear properties of high entropy alloys prepared from recycled copper.With the increase of Al content,the friction coefficient and wear rate of（Fe Ni Mn Al_x）₅₀Cu₅₀ first decreased and then increased.It shows that adding Al can reduce the friction coefficient and wear rate of high entropy alloy.The friction coefficient and wear rate of(Fe₃₂Ni₃₂Mn₁₆Al₂₀)₅₀Cu₅₀ under different loads increase with the increase of load.The main reasons for the increase of friction coefficient are that the increase of load leads to more micro bumps entering the contact state between the high entropy alloy and the friction pair,the increase of contact area and the grain boundary effect in the microcrystal region of the high entropy alloy.（4）By adding copper coated graphite to(Fe₃₂Ni₃₂Mn₁₆Al₂₀)₅₀Cu₅₀,a high entropy alloy based self-lubricating composite was prepared.After adding copper coated graphite,the friction coefficient and wear rate of the high entropy alloy composite decreased significantly,and the friction stability of the composite improved.When the load is 25 N,the friction coefficient of the material decreases from 0.74（C=0 wt.%）to 0.10（C=3 wt.%）,and the wear rate increases from 1.41×10^-6cm³/J（C=0 wt.%）reduced to 3.43×10^-10 cm³/J（C=3 wt.%）,the wear rate of the composite is three orders of magnitude lower than that of the initial high entropy alloy.