Microstructure,mechanical Properties And Tribological Performance Of Wear Resistant High Entropy Copper Alloys Containing CuMnNi

The high entropy copper alloy is a new member of high entropy family,which had redesigned based on the ternary Cu-Mn-Ni alloy solid solution system by gradually adding Zn,Al and Sn elements to the equimolar ratio CuMnNi high entropy alloy.The high entropy copper alloy is considered as a new generation high-performance structural materials of copper and replace the conventional copper alloy due to its excellent mechanical properties result of multi-principal component and simple phase structure.However,until now,the tribological properties of high entropy copper alloy are rarely studied.In this thesis,the CuMnNi Zn_x(x=10,20,30 and 40 wt.%),CuMnNi Al_x(x=0,5,10 and 15 wt.%)and CuMnNi ZSn_x(x=0,5,10,15 and 20 wt.%)HEAs were designed based on the principle of solid solution pahse formation in the HEAs and prepard them using Cu,Mn,Ni,Zn,Al and Sn powders by induction melting technique.The phase compositions,microstructure and mechanical properties are systematically investigated.Moreover,the tribological behaviors of these HEAs at room temperature are study,and the wear mechanism are discussed as well.The main results are listed as follows:1.The CuMnNiZn_x HEAs have uniform dendrite and interdendritic structure without casting defects appear.As the the Zn content was raised to 40 wt.%,the composition of CuMnNi Zn_xHEAs were evolved from a single face-centered cubic(FCC)structure to FCC+BCC(body-centered cubic)duplex structure.In these HEAs with single FCC structure,the strong solid solution strengthening effect casued by Zn atomic made the hardness,yield strength,compressive strength and fracture toughness of HEAs significantly increased with the increase of Zn content.The formation of the BCC phase has a significant strengthening effect on the CuMnNi Zn₄₀high entropy copper alloy,however,the BCC phase will deteriorate the plasticity and toughness of the material.At room temperature,the HEAs with FCC structure have show a high friction coefficient and poor wear resistance while the BCC phase has a good anti-friction and anti-wear effect,so that the friction coefficient and wear rate of CuMnNi Zn₄₀high-entropy copper alloy are approximately to 0.49 and 2.41×10^-4mm³/N·m,respectively.2.The results indicated that the CuMnNi high entropy alloy is only composed of a solid solution phase with a FCC structure,and had good plasticity and toughness.The addition of Al element promotes the formation of BCC structure,and its relative content increases with the increase of Al element.At the same time,the hardness and yield strength of CuMnNi Al_xHEAs have a significantly increased.The content ratio of the FCC structure and the BCC structure in the CuMnNi Al₁₀HEAs reaches the best combination,which makes the alloy has excellent comprehensive mechanical properties.At room temperature,the CuMnNi Al₁₀HEA shows better wear resistance(the wear rate is about 1.34×10^-4mm³/N·m)than conventional wear-resistant aluminum bronze C6161 due to the its BCC phase plays a good supporting effects during the friction process,so that the HEA has shows a smaller coefficient of friction and wear rate.3.The microstructure of interdendritic region in CuMnNi Al₁₀HEA is obviously different from the same region of the others HEAs.Thence,a new HEA composed by Cu₃₅Mn₃₂Ni₁₉Al₁₄which is based on the EDS analysis results from this region,had been designed and prepard.After this,the effect of annealing temperature on phase compositions,microstructure,mechanical and tribological properties were studied.The results indicated that Cu₃₅Mn₃₂Ni₁₉Al₁₄HEA was composed by FCC phase and BCC phase,and the FCC phase is a typically lamellar structure which formed by stacking needle-like crystal grains.After annealing treatment,the grain size of acicular grain in FCC phase increased obviously with the increase of annealing temperature,and the content of the BCC phase in the H650 and H850 alloys increased gradually casued by thermal diffusion motion of Ni ang Al atoms.Therefore,the content increasing of BCC phase is help to improve the strength and hardness of HEAs,but causesd the wear resistancea of HEAs decreased slightly.4.Cu Mn NiSn_x HEAs are mainly composed of FCC+L2₁ phases,the addition of Sn produced a high solid solution strengthening effect on the FCC phase of the alloy and promoted the formation of the L2₁phase.The L2₁phase is a typical brittle structure,and the increased in content is not conducive to the improvement of the ductility of HEAs.However,the L21 phase exhibits a good anti-friction and anti-wear effect during the friction process,so that the Cu Mn NiSn₂₀HEA has shows a smaller wear rate with 10^-5mm³/N·m level.