【作者】 徐凯；

【导师】 赵玉涛；

【作者基本信息】 江苏大学 ， 材料工程（专业学位）， 2016， 硕士

【摘要】 随着对镍基单晶合金性能要求的不断提高,发达国家已研制出第五代单晶合金。目前,国际上提高镍基单晶合金性能通常是在合金中添加贵重金属铼(Re)和钌(Ru),但是Re和Ru的增加,不仅合金成本和密度大幅增加,而且对合金的单晶成型能力也带来不利影响,因此关于如何在保证合金性能的基础上降低Re、Ru含量的研究具备十分重要的意义。本文主要在第三代镍基单晶合金基础上采用电子空位理论、d电子理论以及相图分析(CLAPHAD)法设计一种低铼第三代镍基单晶合金,在保证合金高温性能的基础上降低合金的密度、成本,并采用真空感应熔炼与定向凝固技术制备出单晶试样,研究熔体过热与热处理工艺对合金微观组织变化规律,研究结果表明:通过电子空穴法、d电子理论法以及相图分析(CLAPHAD)法进行合金设计得到以下较好的合金成份范围:Cr:3%,Co:9.5-10.5%,W:7.5-8%,Mo:1%,Ta:5.5-6%,Al:6%,Hf:0.1-0.2%,Ti:0-0.5%,Nb:0.2-0.5%,Re:3.5%,其余为Ni。其中Nv≦2.3、Md≦0.985、(W+Mo)≦3.5%(at%)以及Ta/(W+Mo)在0.5-1之间,并通过相图分析,其组织稳定性基本达到第三代单晶合金要求。新型单晶合金铸态组织呈枝晶状,枝晶干与枝晶间存在着严重成份偏析,Al、Ti、Ta、Nb、Cr偏析于枝晶间,而Re、W、Mo、Co偏析于枝晶间。在相同的抽拉速度(3mm/min)条件下,随着熔体过热温度的增高,枝晶干与枝晶间成份偏析降低;单晶合金中一次枝晶间距与二次枝晶间距均降低,其中一次枝晶间距降幅达40-60μm;枝晶间(γ+γ’)共晶组织由大的片状转变为小块状;γ’尺寸也显著变小,立方度提高。采用DTA实验分析可知合金的(γ+γ’)共晶组织在1445℃溶解。通过对比几种不同的固溶处理工艺,确定新型单晶合金的固溶处理工艺为:1300℃,4h+1310℃,6h+1320℃,8h,+1330℃,8h A.C。在该固溶处理条件下合金中共晶组织基本消除,枝晶干与枝晶间成份偏析大大降低。随一次时效温度的增加,新型单晶合金的γ’相尺寸不断增大,其立方度先增大后减小,在1180℃时单晶合金γ’尺寸达到最大,立方度最高。并在1200℃时出现棱角钝化现象。在时效冷却后发现基体通道中有二次γ’析出,并随着时效温度提高与时效时间延长,二次γ’相增大。新型单晶合金在相同固溶处理后经过870℃/24h与900℃/20h的二次时效,合金中的γ’相均有所长大,立方度有所提高;在1180℃/24h+870℃/24h处理后,γ’相更加均匀,排列规整。因此新型单晶合金的热处理工艺为:1300℃,4h+1310℃,6h+1320℃,8h,+1330℃,8h A.C+1180℃/24h+870℃/24h。更多还原

【Abstract】 With the continuous improvment of performance requirements of nickel base single crystal alloy, the fifth generation single crystal alloys had been developed in developed countries. At present, the increase of nickel base single crystal superalloy performance is usually added in the elements of rhenium(Re) and ruthenium(Ru). However, with the content of Re and Ru increased, not only had the cost and density of the alloy been increased, but also brought adverse effects. Therefore, study of how to reduce the content of Re and Ru in the alloy and assurance the single crystal superalloy properties has a important significanceThis paper mainly designed a new third generation of nickel base single crystal superalloy with low rhenium in the base of third generation nickel base single crystal superalloy by the electron vacancy theory, d-electron theory and thermodynamic analysis method, as far as possible to reduce the cost and density and ensure properties of superalloy, and manufactured the single crystal specimens by using the vacuum induction melting and directional solidification technique. The paper studied the refinement rule of melt superheat and heat treatment process on microstructure. The results show that:By electron vacancy theory, the d-electron theory method and caculate of phase diagram method for alloy design and got the following better alloy composition range: Cr:3%,Co:9.5-10.5%, W:7.5-8%, Mo:1%, Ta:5.5-6%, Al:6%, Hf:0.1-0.2%, Ti:0-0.5%, Nb:0.2-0.5%,Re:3.5%, remaining for Ni. The Nv was less than 2.3. Md was less than 0.985.(W+Mo)(at%) is less than 3.5%. The value of Ta/(W+Mo) was in 0.5-1. Through the caculate of phase diagram analysis, the microstructure stability basically reached the requirements of the third generation single crystal superalloy.The morphology of the as-cast new single crystal alloy shows a dendrite structure, and there are serious component segregation between dendrite and interdendtrite. Al, Ti, Ta, Nb, Cr were enriched in dendritic and Re, W, Mo, Co were enriched in interdendritic.In the same pulling speed(3mm / min) conditions, with the superheating temperature increased, composition segregation was reduced between dendrite and interdendritic. Both primary dendrite arm spacing and dendrite arm spacing were decreased in the new single crystal superalloy. Especially the decline of primary dendrite spacing reached 40-60 μm. The eutecticmicrostructure(γ+γ’) in interdentritic changed from large sheet to small block and the size of γ’phase was decrease but the cubic degree increase.The test result by DTA shows the eutectic microstructure of new single crystal superalloy is dissolved at 1445 ℃. Through observing the structure of different processing dissolution,Determine the optimal processing dissolution is 1300℃,4h +1310℃,6h+1320℃,8h+1330℃,8h A.C. In this dissolution, eutectic organization of the alloy was basically disappeared and segregation components between the dendrite and interdendritic is markedly reduced. With an increase of aging temperature, γ’ phase size of the new single crystal alloy was increasing and the cubic degree was increased first and then decreased. The γ’ phase size and cubeic degree reached the maximun at 1180 ℃. The γ’ phase appeared angular passivation phenomenon in 1200 ℃.When the aging is above 1200℃ and cooled at the air cooling condition, the secondary γ’ phase can precipitate within the matrix channel. Increasing the aging temperature or prolonging the aging time, the number and size of secondary γ’ phase are increased.The γ’ phase size of new single crystal superalloy which were in the same solid solution treatment were increased after the secondary aging in 870℃/24 h and 900℃/20 h, and the cubic degree increased,too. The γ’ phase after aging in 1180℃/4h+870℃/24,A.C was more uniform and regulae. Therefore, the heat treatment process of the new 3rd single crystal superalloy is1300℃,4h+1310℃, 6h +1320℃,8h,+1330℃,8h A.C+1180℃/24h+870℃/24h。更多还原