【作者】 王旭；

【导师】 陈瑞润；

【作者基本信息】 哈尔滨工业大学 ， 材料与化工（专业学位）， 2022， 硕士

【摘要】 近年来,航空航天技术发展迅猛,因此对于航空发动机部件的要求越来越高,例如耐高温性能、抗疲劳性能。如今的航空发动机叶片的首选材料是Ni基高温合金,但是它也面临着服役温度受限,重量略重等问题,而Nb-Si合金作为优秀的超高温合金有着高熔点低密度的优点,使得它在航空航天热端部件领域备受青睐。目前Nb-Si合金抗氧化性能和部分高温性能已经符合要求,面临最严峻的问题就是其室温断裂韧性不足,这是导致Nb-Si高温合金不能在工业中进行应用的主要原因。近年来,对于Nb-Si基合金采用合金化的工艺方法已经有较多研究,由于目前添加合金化元素一般集中于Ti、Cr、Al、Zr等常见元素,而对于采用稀土元素进行变质处理或者元素替代方法提升相关性能的研究较少。因此本文主要通过研究Ru、Gd、Zr合金化及采用Zr元素等原子百分比替代Ti对Nb-Si超高温合金相组成、微观组织、力学性能方面的影响,对开发新型Nb-Si基超高温合金具有实际意义,本文主要研究内容和结果如下:首先通过真空非自耗电弧炉熔炼16种不同成分合金,其名义成分分别为Nb-16Si-24Ti-x Zr、Nb-16Si-（24-x）Ti-x Zr、Nb-16Si-24Ti-x Ru、Nb-16Si-24Ti-x Gd（均为原子百分比）。后续通过XRD、SEM、EDS、EMPA等分析手段以及Gleeble1500X、电子万能试验机设备等进行力学性能实验。研究不同合金化元素对相转变、凝固路径、微观形貌等影响,结果表明:Ru添加0.5at.%、1at.%时能够有效地促进共析反应的进行,但在添加2at.%时,并不会起到促进效果。在添加0.5at.%Ru时,合金中出现共晶组织能够有效提高合金的力学性能。随着Ru的添加合金的室温断裂韧性、室温压缩性能和高温拉伸性能三者变化趋势一致均是先增大后减小,在添加0.5at.%Ru达到最大值其合金的室温断裂韧性为8.88MPa·m^1/2,较基体合金提升了26.14%,室温压缩性能为2066MPa,高温拉伸强度取得最大值为223.2MPa,同比增长27.3%。在添加0.5at.%的Ru后合金裂纹扩展方式和断裂方式也出现变化,说明共晶组织有效地抵抗裂纹的扩展,断口形貌中也出现了撕裂棱等韧性断裂特征。向基体合金Nb-16Si-24Ti添加Gd时γ-Nb5Si3相先出现后消失,说明适量添加Gd能够有效促进共析转变。同时Gd元素的添加影响微观组织形貌,在添加0.05at.%Gd时初生Nbss相体积较大,连续性最好。但添加过量的Gd会在组织途中观察到白色物质,经实验分析出该物质是Gd析出相,严重影响合金的力学性能,在裂纹扩展过程中被裂纹直接穿过为脆性相。随着Gd的添加,合金室温断裂韧性先增加后减小,在添加0.025at.%是达到最大,为7.81MPa·m^1/2,同比基体合金增长10.9%。其他力学性能变化趋势不明显,但适量添加Gd均会较基体合金有所提高。在向Nb-16Si-24Ti合金中添加Zr或用Zr等原子比替代Ti时合金中均出现γ-Nb5Si3相衍射峰。在Nb-16Si-24Ti-x Zr系合金中,随着Zr元素含量的增加,合金中共晶组织增多,在添加16at.%Zr时,出现较多花瓣状共晶,在裂纹扩展过程中使裂纹偏转幅度巨大,有效地抵抗裂纹的扩展。室温断裂韧性也随着Zr的增加而增加,Nb-16Si-24Ti-16Zr的室温断裂韧性为12.47MPa·m^1/2,较基体合金提高77.4%,高温压缩强度也在添加16at.%Zr达到最大值为443.6MPa。在Nb-16Si-（24-x）Ti-x Zr系合金中,随着Zr等原子比替代Ti元素的增加,合金中初生Nbss组织连续性发生变化,在用24at.%Zr完全替代Ti时,Nbss相连续性较好,并没有出现元素富集现象。合金的室温断裂韧性随着替代元素含量的增加先增加后降低,合金Nb-16Si-8Ti-16Zr室温断裂韧性最高为8.60MPa·m^1/2,相较于基体合金Nb-16Si-24Ti提高22.2%,高温压缩强度先上升后下降,同样时合金Nb-16Si-8Ti-16Zr具有最高的高温压缩强度为674.8MPa同比增长59.4%。更多还原

【Abstract】 In recent years,aerospace technology has developed rapidly,so the requirements for aero-engine components are getting higher and higher,such as high temperature resistance and fatigue resistance.Today’s preferred material for aero-engine blades is Ni-based superalloy,but it also faces problems such as limited service temperature and slightly heavier weight.As an excellent superalloy,Nb-Si alloy has the advantages of high melting point and low density,making It is favored in aerospace hot end components.At present,the oxidation resistance and some high-temperature properties of Nb-Si alloys have met the requirements.The most serious problem is the insufficient fracture toughness at room temperature,which is the main reason that Nb-Si superalloys cannot be used in industry.In recent years,there have been many studies on the alloying process of Nb-Si-based alloys.Since the current addition of alloying elements is generally concentrated in common elements such as Ti,Cr,Al,Zr,and the use of rare earth elements for modification treatment or There are few studies on the relative performance improvement of element substitution methods.Therefore,this paper mainly studies the effects of Ru,Gd,Zr alloying and the substitution of Ti by atomic percentages of Zr elements on the phase composition,microstructure and mechanical properties of Nb-Si superalloys.With practical significance,the main research contents and results of this paper are as follows:First,16 alloys with different compositions were melted in a vacuum nonconsumable arc furnace,and their nominal compositions were Nb-16Si-24Ti-x Zr,Nb-16Si-（24-x）Ti-x Zr,Nb-16Si-24Ti-x Ru,Nb-16Si-24Ti-x Gd（Atomic percentage）.Follow-up mechanical properties experiments were carried out through XRD,SEM,EDS,EMPA and other analysis methods,as well as Gleeble1500 X,electronic universal testing machine equipment,etc.The effects of different alloying elements on phase transformation,solidification path,and microscopic morphology were studied.The results show that the addition of Ru at 0.5at.% and 1at.% can effectively promote the eutectoid reaction,but when the addition of 2at.will not promote the effect.When adding 0.5at.%Ru,the appearance of eutectic structure in the alloy can effectively improve the mechanical properties of the alloy.With the addition of Ru,the room temperature fracture toughness,room temperature compressive properties and high temperature tensile properties of the alloys all increase first and then decrease.The room temperature fracture toughness of the alloy reaches the maximum value when0.5at.% Ru is added.8.88MPa·m^1/2,which is 26.1% higher than that of the base alloy,the room temperature compressibility is 2066 MPa,and the high temperature tensile strength reaches the maximum value of 223.2MPa,a year-on-year increase of 27.3%.After the addition of 0.5at.% Ru,the crack propagation mode and fracture mode of the alloy also changed,indicating that the eutectic structure effectively resisted the crack propagation,and ductile fracture characteristics such as tearing edges also appeared in the fracture morphology.When adding Gd to the base alloy Nb-16Si-24 Ti,the γ-Nb5Si3 phase appeared first and then disappeared,indicating that the proper amount of Gd addition can effectively promote the eutectoid transformation.At the same time,the addition of Gd element affects the microstructure and morphology.When 0.05 at.%Gd is added,the volume of the primary Nbss phase is larger and the continuity is the best.However,when excessive Gd is added,a white substance will be observed on the way of the structure.The experimental analysis shows that this substance is a Gd precipitation phase,which seriously affects the mechanical properties of the alloy,and is directly penetrated by the crack as a brittle phase during the crack propagation process.With the addition of Gd,the fracture toughness of the alloy at room temperature increases first and then decreases,and reaches the maximum at 7.81MPa·m^1/2 with the addition of 0.025 at.%,an increase of 10.9% over the base alloy.The change trend of other mechanical properties is not obvious,but an appropriate amount of Gd will be improved compared with the base alloy.When adding Zr to the Nb-16Si-24 Ti alloy or replacing Ti with the same atomic ratio of Zr,the diffraction peaks of γ-Nb5Si3 phase appear in the alloy.In Nb-16Si-24 Tix Zr alloys,with the increase of Zr element content,the eutectic structure of the alloy increases.When 16 at.% Zr is added,more petal-like eutectic appears,which deflects cracks during crack propagation.The amplitude is huge and effectively resists the propagation of cracks.The room temperature fracture toughness also increases with the increase of Zr.The room temperature fracture toughness of Nb-16Si-24Ti-16 Zr is12.47MPa·m^1/2,which is 77.4% higher than that of the base alloy.The high temperature compressive strength also reaches the maximum with the addition of 16 at.%Zr.The value is 443.6MPa.In Nb-16Si-（24-x）Ti-x Zr alloys,with the increase of the atomic ratio of Zr to replace Ti elements,the microstructure continuity of primary Nbss in the alloy changes.When 24 at.% Zr is used to completely replace Ti,The Nbss phase has good continuity and no element enrichment phenomenon.The room temperature fracture toughness of the alloy increases first and then decreases with the increase of the content of the substitute elements.The room temperature fracture toughness of the alloy Nb-16Si-8Ti-16 Zr is up to 8.60MPa·m^1/2,which is 22.2% higher than that of the base alloy Nb-16Si-24 Ti,the high-temperature compressive strength first increased and then decreased.At the same time,the alloy Nb-16Si-8Ti-16 Zr had the highest hightemperature compressive strength of 674.8MPa,increase of 59.4%.更多还原