2018材料前沿第四讲.ppt

材 料 科 学 与 工 程 前 沿,航空航天高温结构材料High-Temperature Structural Materials in Aerospace,北京航空航天大学 材料学院 2018 年 4 月，沙江波,七、Nb-Si基高温合金,T/W ratio 20,What materials could be qualified？,T/W:Thrust to Weight Ratio for Aero-Engine,Ceramics matrix composites Good strength and oxidation resistance at HT;Brittle,difficult to processC/C composites Low density,good strength at HT;Poor oxidation resistance&Difficult to processNb/Si based intermetallics(composites)Good formability,and Comprehensive advantage in mechanical performance at HT Poor ductility and oxidation resistance,元素周期表,Nb具有良好的室温塑韧性，机械加工性和高的熔点（2447C，超过Ni约1000C)，以及热传导率大,热膨胀系数小,弹性系数大,密度小,到熔点都保持稳定b.c.c.承温能力：12001700C.可以采用多种方式强化、韧化和改善抗氧化 性:1、强化,固溶强化 Mo,W,Hf,Cr,Al,Si 等能与Nb形成置 换固溶体，W、Mo最强金属间化合物NbSS/Nb3Al(Nb-Al二元合金)和 NbSS/Nb5Si3（Nb-Si二元合金)，NbSS 提供韧性而Nb3Al和Nb5Si3提供高温强度 韧/脆两相结构，NbSS：Solid solution，固溶体特殊热加工定向凝固（DS:directional solidification），热等静压(HIP:hot isostatic pressing),热挤出（HE:hot extrusion),粉末冶金等,2、韧化 合金化-Hf、Ti元素对NbSS韧化 减少Si含量-Si减少，Nb5Si3减少，塑韧性上升 改变组织形态-Mo，W等元素倾向形成片状组 织改善NbSS和Nb5Si3形态 3、抗氧化：基体抗氧化+涂层 Cr-NbCr2有利于抗氧化 Si-SiO2有利于抗氧化，Ti有利于抗氧化,合金元素对Nb性能的影响,1、,Nb-Si binary diagram,Nb5Si3High melting point:2520 CModerate density:6.1 gcm-3Toughness:KIC=13 MPam1/2NbSSGood ductility at RT,Alloys with NbSS and Nb5Si3:Can be stable up to very high temperature(1670C),Nb-18Si-15W-10Mo-10Ti(AIST,JUTEMI and TOHUKU Uni.In Japan)Target Appl.Temperature:1500CAlloyed with high W and MoHigh strength:650MPa at 1500C Poor toughness,ductility and oxidation resistanceHigh density:910 g/cm3,Nb-24.7Ti-16Si-8.2Hf-2.0Cr-1.9AlTarget Appl.Temperature:1200CAlloyed with high Ti and HfHigh toughness:20MPam1/2Low creep rateLow density:6.58 g/cm3Poor oxidation resistance,Nb-18Ti-17.22Si-8.7Hf-20Cr-2.5AlTarget Appl.Temperature:1200CAlloyed with high Cr and TiGood oxidation resistance Low density:6.57.5 g/cm3Poor mechanical properties,高温强度,室温断裂韧性,高温抗氧化性,Balance the toughness,strength and oxidation resistance by optimizing and controlling microstructure of NbSS,Silicide and Cr2Nb phases,Our work on Nb-Si based alloys focus:Target Appl.Temperature:1250C1350C To balance the toughness,strength&oxidation resistance Application:Vane of aero-engine,R&D of Nb-Si based alloys in present work,Nb-Si-Ti-Cr系合金宏合金化、组织和性能,Typical compositions of studied alloys:,Based on Nb-Si-Ti phase diagram,Cr is added to investigate relationship between composition and phases of NbSS、Nb5Si3 and Cr2Nb,and optimize phases constitution and proportion,Ti：22 at%,toughening Nb and decreasing eutectoid temperature of Nb3Si NbSS+Nb5Si3;Si：12 at%16at%，hypo-eutectic,avoid large primary Nb5Si3;Cr：2 at%17 at%，determining phase evolution of NbSS/Nb5Si3/Cr2Nb;Assistant elements：2Hf+2Al;Compositions:Nb-(12,14,16)Si-22Ti-2Hf-2Al-(2,6,10,14,17)Cr,Tri-phase NbSS+Nb5Si3+Cr2 Nb obtained with Cr 6 at.%,NbSS+Nb5Si3+Nb3Si,NbSS+Nb5Si3+Cr2Nb,NbSS+Nb5Si3+Cr2Nb,NbSS+Nb5Si3+Cr2Nb,NbSS+Nb5Si3+Cr2Nb,NbSS+Nb5Si3+Cr2Nb,NbSS,Typical Microstructures of as-cast 16 at%Si alloys with different Cr content,Typical Microstructures of as-cast 12,14 at%Si alloys with different Cr content,Tri-phase NbSS+Nb5Si3+Cr2 Nb obtained with Si+Cr 21 at.%,Typical Microstructures of heat-treated 16 at%Si alloys with different Cr content,铸态相组成与微观组织与Si和Cr的关系,0.2%yield strength increases with an increasing Si content,and a decreasing Cr content;2.The strength of 16Si-2Cr is the maximum,about 320MPa at 1250C.,KQ decreases with an increasing Si and Cr contents,and heat treatment improves fracture toughness;2.Heat-treated alloy with 2%Cr shows the best toughness,1415 MPam1/2,Weight change shows a decreasing tendency with an increasing Cr content16Si-17Cr shows the minimum weight change of about 50mg/cm2 for 100hThe weight gain of the substrate with Mo(Al,Si)2 coating is 7.8 mg/cm2 after oxidation for 100 h.,氧化动力学曲线,Solidification paths of Nb-Si and Nb-Si-Mo,Eutectic structure NbSS/Nb5Si3,组织控制,Alloying with Mo changes the solidification paths and results in the formation of NbSS/Nb5Si3 lamellar structure,DS eutectic structures of NbSS/Nb5Si3,Growth direction,Full lamellated eutectic of NbSS/Nb5Si3 in Nb-18Si-10Mo alloy can obtained by directional solidification(Growth rate:5mm/h),NbSSNb5Si3,室温弯曲断裂形貌NbSS/Nb5Si3,室温弯曲断裂形貌NbSS/Nb5Si3/Cr2Nb,桥接、分叉，界面分离、绕过机制,高温压缩断裂形貌,硅化物压塌，裂纹在硅化物内或界面扩展,Cast blades of Nb-16Si-22Ti-2Cr-2Al-2Hf,GE公司制备的Nb-Si超高温金属间化合物高温结构材料的叶片目前还没有装机试车的报道,预计2012年出现低压涡轮叶片，2015年出现更复杂的高压涡轮叶片,室温塑性和强韧性匹配；抗氧化性和涂层设计；定向凝固叶片加工技术。,进一步开展的工作,粉末粒度对Nb-16Si合金组织及断裂韧性影响,粉末冶金Nb-Si合金,高强度,高韧塑性,纳米金属材料：强度比普通金属高一个量级，但几乎无拉伸塑性,Yinmin Wang,Mingwei Chen,Fenghua Zhou and EnMa,NATURE,VOL 419,31 OCTOBER 2002:912-915,结构材料,难以兼具,纳米晶中引入微米级粗晶粒，材料兼具高强度高塑性！,粗晶Cu,1.粉末粒度及形貌对Nb-16Si组织及韧性影响,0 同时提高材料的强度和韧塑性,Nb-Si基合金中，NbSS和Nb5Si3相具有不同尺寸配合的时，对合金性能的影响？,采用传统制备工艺（As-cast,DS）难以在Nb-Si合金中实现NbSS和Nb5Si3相不同尺寸配合,DS,As-cast,3.1 粉末粒度对Nb-16Si组织及断裂韧性影响,Nb-Si合金同样是一种强度高，塑韧性低的合金,不同粒度Nb和Nb5Si3粉制备,1.1 试验方案,1 粉末粒度对Nb-16Si组织及断裂韧性影响,粉末混合,粉末混合方式：无球干混；转速：300 rpm；球磨时间：2h,烧结,烧结工艺：SPS；烧结温度：1350；压力：40MPa；保压时间：10min；氩气保护,块体合金,1 粉末粒度对Nb-16Si组织及断裂韧性影响,Nb+Nb5Si3粉末粒度配合,Nb/Nb5Si3合金相对密度,1 粉末粒度对Nb-16Si组织及断裂韧性影响,1.2 试验结果及分析,显微组织,83.80-86.37,83.80-43.60,83.80-2.85,37.38-86.37,