【作者】 李建；

【导师】 刘祖铭；

【作者基本信息】 中南大学 ， 材料与化工（专业学位）， 2023， 硕士

【摘要】 Cu-Cr-Nb系合金具有优异的力学性能、导电性、导热性和高温稳定性,在航空航天发动机等高热通量领域具有广阔的应用前景。目前航空航天和国防工业的发展对高性能铜合金的需求日益增多,但如何调控合金的显微组织,提高其综合性能,是Cu-Cr-Nb系合金面临的难题。本研究旨在通过选区激光熔融（SLM）工艺优化和Ti微合金化,调控合金的显微组织,制备高密度的Cu-Cr-Nb-Ti合金。通过优化热处理工艺,提高Cu-Cr-Nb-Ti合金的性能,实现强度和导电率的良好匹配,为制备高性能的铜合金提供支持。主要内容与结果如下:（1）采用氩气雾化制备的Cu-2.01Cr-0.92Nb-0.18Ti（at.%）合金粉末,粒径分布集中,球形度良好,无空心粉末。使用激光功率325W、扫描速率800 mm/s制备的成形件缺陷最少,相对密度达到99.26%。相近体能量密度制备的Cu-Cr-Nb-Ti合金成形件的相对密度存在较大差异。扫描速率低于800 mm/s制备的成形件表面缺陷以飞溅的液滴和球化现象为主,内部缺陷以剥蚀导致的孔隙为主。扫描速率高于800 mm/s制备的成形件的表面出现明显的起伏现象,且随着激光功率的增加而不断增加,低激光功率制备的合金因输入能量低而出现未融合孔隙,高激光功率制备的合金出现锁孔。（2）SLM制备的Cu-Cr-Nb-Ti合金XY面由熔池道中心的细晶和两侧的粗晶组成,不同工艺制备的合金晶粒的平均尺寸均在24～55μm范围内。XZ面组织由水滴状晶粒、长柱状晶和等轴晶组成。提高扫描速率或激光功率,晶粒择优取向程度减弱。合金中弥散分布着细小的FCC型C15-Cr₂Nb相,尺寸为28～50 nm,且Ti原子富集在大尺寸Cr₂Nb相中。325 W和800 mm/s制备的Cu-Cr-Nb-Ti合金的显微硬度、抗拉强度和伸长率最高,分别为139 HV_0.2、416 MPa和27.8%,导电率为15.6%IACS。（3）Cu-Cr-Nb-Ti合金经过500℃/30 min时效处理后,综合性能最优异,显微硬度为260 HV_0.2,屈服强度为622 MPa,极限抗拉强度为728 MPa,伸长率为16.3%,导电率为59.4%IACS。合金XY面显微组织为粗晶和细晶交替出现的双峰晶粒尺寸结构,弥散分布着25～50 nm和小于10 nm的双尺度FCC型C15-Cr₂Nb相,Ti原子富集在大尺寸Cr₂Nb相中。这些第二相有效地钉扎位错,使晶粒内位错密度增加。增加时效时间或提高时效温度,Cu-Cr-Nb-Ti合金的平均晶粒尺寸略微减小,择优取向程度明显减弱,Cr₂Nb相结构不发生转变,尺寸无明显长大,但Cr₂Nb相发生明显团聚。图58幅,表7个,参考文献113篇更多还原

【Abstract】 Cu-Cr-Nb alloys have broad application prospects in high heat flux fields such as aerospace engines,which have excellent mechanical properties,electrical conductivity,thermal conductivity,and high temperature stability.At present,the development of aerospace and national defense industries has increasingly increased the demand for high-performance copper alloys.However,how to control microstructure of alloys and improve comprehensive properties are challenges for Cu-Cr-Nb alloys.The purpose of this study is to prepare high density Cu-Cr-Nb-Ti alloy and control microstructure of alloy by optimizing the selective laser melting（SLM）process and Ti microalloying.By optimizing the heat treatment process,we improve the performance of Cu-Cr-Nb-Ti alloy,and achieve a good match between strength and conductivity.It provides support for the preparation of high-performance copper alloys.The main contents and results are as follows:（1）Cu-2.01Cr-0.92Nb-0.18Ti（at.%）alloy powder was prepared by argon atomization.The particle size distribution is centralized.The powders were spheroidal and no pores were observed.As-built sample manufactured by laser power of 325 W and scanning speed of 800 mm/s has the least defects,and the relative density reaches 99.26%.There are significant differences in the relative densities of Cu-Cr-Nb-Ti alloy samples prepared with similar volumetric energy densities.The surface defects of as-built samples prepared at a scanning speed lower than 800mm/s are mainly splashed droplets and balling phenomenon,while the internal defects are mainly pores caused by denudation.The surfaces of as-built samples prepared by a scanning speed higher than 800 mm/s have significant fluctuations,which increase continuously with the increase of laser power.Samples prepared by low laser power have lack-of-fusion（LOF）pores due to low input energy,while samples prepared by high laser power have keyholes.（2）The XY plane of SLMed Cu-Cr-Nb-Ti alloy is composed of fine grains in the center of the molten track and coarse grains on both sides.The average grain size of XY planes of all samples is in the 24～55μm range.The microstructure of the XZ plane is composed of water-drop grains,long columnar grains,and equiaxed grains.The degree of grain-preferred orientation of as-built samples decreases as scanning speed or laser power increases.Fine FCC type C15-Cr₂Nb phases with size of 28～50 nm are dispersed,and Ti atoms are enriched in large-sized Cr₂Nb phase.The Cu-Cr-Nb-Ti alloy prepared by 325 W and 800 mm/s has the highest microhardness,tensile strength,and elongation,namely 139 HV_0.2,416MPa,and 27.8%,respectively,and the electrical conductivity is15.6%IACS.（3）After direct aging at 500℃/30 min,the Cu-Cr-Nb-Ti alloy has the optimum comprehensive properties,with a microhardness of 260 HV_0.2,a yield strength of 622 MPa,an ultimate tensile strength of 728 MPa,an elongation of 16.3%,and an electrical conductivity of 59.4%IACS.The microstructure of XY plane of the alloy is a bimodal grain size structure with alternating coarse grains and fine grains,and bimodal scale FCC type C15-Cr₂Nb phases of 25～50 nm and less than 10 nm are dispersed.Ti atoms are enriched in large-sized Cr₂Nb phase.The second phases effectively anchor dislocations,increasing the dislocation density within the grain.With increasing aging time or temperature,the average grain size of the alloy decreases slightly,and the degree of grain-preferred orientation decreases significantly.The structure of Cr₂Nb phases does not change and the size does not grow significantly,but Cr₂Nb phases obviously agglomerates.更多还原