【作者】 曾岗；

【导师】 韩杰才；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2007， 博士

【摘要】 本文采用X射线衍射（XRD）、扫描电镜（SEM）、原子力显微镜（AFM）和透射电子显微镜（TEM）以及力学测试方法深入系统地研究了采用电子束物理气相沉积（EB-PVD）制备的0.3mm厚的Ni20.3Cr4.6Co2.1Al合金薄板制备态和热处理态组织演变规律和力学性能。并研究了制备态和经800℃/16h处理的合金薄板在800℃、900℃和1000℃空气中的氧化行为,采用SEM对氧化试样的表面和截面形貌进行研究,采用小角XRD、XPS和EDAX对其相组成和成分分布进行分析。研究结果表明:制备态Ni20.3Cr4.6Co2.1Al合金薄板相组成为γ-Ni基固溶体,不存在第二相。组织致密均匀,晶粒尺寸为500nm左右;亚结构主要为孪晶,没有发现位错存在。制备态合金薄板的纳米硬度为5.57 GPa,弹性模量E为221.33GPa;常温拉伸抗拉强度σb为1033 MPa,合金薄板伸长率δ为0.6%,呈脆性断裂。800℃时拉伸抗拉强度σb为107 MPa,合金薄板伸长率δ为1.02%。经600℃长时间热处理后,Ni20.3Cr4.6Co2.1Al合金薄板仍为γ-Ni基固溶体单相组织,亚结构仍然为孪晶,没有发现位错存在。晶粒随保温时间的延长而长大,而TEM像中的应变条纹消失,XRD分析表明存在（220）晶面的择优生长。热处理温度达到800℃,晶粒明显长大,亚结构为孪晶和位错,1000℃处理后发现有第二相析出。薄板在600℃以下温度处理时,其断裂强度随处理温度升高而降低,其伸长率随温度升高而稍微有些增加。600℃处理16h,断裂强度σb为780 MPa,伸长率δ仅为4 %。800℃保温16h时,合金薄板的常温断裂强度σb增加到825 MPa,伸长率δ增加到14 %,属于延性断裂;随后其断裂强度随处理温度升高而降低,其伸长率随温度升高而稍微有些增加。合金薄板在不同温度下保温16h后,在800℃拉伸时,伸长率是随着保温温度的升高拉伸强度越来越大,其拉伸性能在800℃保温16h时的800℃拉伸强度σb值最高,为63 MPa,其伸长率δ达246 %。但在900℃保温16h处理后合金薄板的800℃拉伸强度σb却开始下降24 MPa,而伸长率δ却增加到336%,均为延性断裂。细晶Ni20.3Cr4.6Co2.1Al薄板高温氧化动力学与常规镍基合金的氧化动力学不同,800℃氧化时,初期氧化动力学近似符合抛物线规律,而长期氧化动力学符合立方规律;合金900℃氧化时,氧化初始阶段动力学符合三次方规律,而氧化后期动力学符合四次方规律;合金1000℃氧化时,氧化初始阶段动力学近似的近似符合抛物线规律,而氧化后期动力学近似符合立方规律。制备态Ni20.3Cr4.6Co2.1Al合金800℃初期氧化阶段的氧化产物主要是NiO和少量的Cr2O3;长时间氧化时氧化产物主要是NiO、NiCr₂O₄以及Cr2O3。合金900℃初始氧化阶段的氧化产物主要是NiO、Cr2O3和NiCr₂O₄;长时间氧化以后氧化膜外层的氧化产物主要是NiO,氧化初期在氧化膜的晶界处形成了富Al区域。合金1000℃初始氧化阶段的氧化产物主要是NiO和Cr2O3,而在长期氧化时氧化膜主要是由NiO为主,Cr2O3和NiCr₂O₄为辅的复合层。经800℃/16h退火处理后的细晶Ni20.3Cr4.6Co2.1Al合金薄板,在800℃空气中氧化动力学氧化初期符合四次方规律,随后氧化非常缓慢,长时间暴露后合金薄板氧化增重不明显。氧化产物主要是NiO、Cr2O3和NiCr₂O₄。900℃空气中氧化动力学符合立次规律,氧化产物主要是NiO、Cr2O3和NiCr₂O₄。1000℃空气中暴露时存在脱落,退火处理后薄板1000℃暴露空气中表面生成的氧化产物是单一的针状Al2O3。研究发现细晶Ni20.3Cr4.6Co2.1Al在800℃、900℃和1000℃空气中氧化动力学与经典的抛物线规律存在明显的偏差,主要由于细晶化后氧化物形核率极大提高,形成微晶态氧化膜,氧化膜中的扩散由晶格扩散为主变为以晶界短路扩散为主,改变了氧化膜的生长动力学,对细晶合金高温氧化动力学规律进行探讨,导出其遵守x2=At1-n.更多还原

【Abstract】 The microstructure evolution and mechanical properties of Ni20.3Cr4.6Co2.1Al alloy sheet about 0.3mm thickness deposited by electron beam physical vapor deposition （EB-PVD） technology were systematically investigated by means of X-ray diffactometry （XRD）, sanning electron microscopy （SEM）, atom force microscopy （AFM） and transmission electron microscopy （TEM） as well as mechanical test method. In addition, oxidation behaviors of as-deposited and annealed Ni-Cr-Al alloys at 800°C, 900°C and 1000°C were investigated.The results show that the average sizes of as-deposited Ni20.3Cr4.6Co2.1Al alloy sheet composed only ofγphase was about 500nm.The substructures were （111） twins mainly without dislocations.For the as-deposited alloy sheet, the nano-hardness, elastic modulus E, room temperature tensile strengthσb and elongationδwas 5.57GPa, 221.33GPa, 1033MPa and 0.6%, respectively. Obviously, it was brittle fracture. Andσb tensile strength and elongation of as-deposited alloy sheet at 800℃was 107 MPa and 1.02%, respectively.The heat-treated Ni-11.5Cr-4.5Co-0.5Al sheet by EB-PVD at 600°C for different time consists ofγ-Ni-based single-phase with twins sub-structure and without dislocation. The grain size grows up with the extension of holding time. And the strain stripes disappear in TEM Micrograph. XRD analysis shows there is （220） crystal face of preferred orientation. When the heat-treatment temperature reaches 800°C, the grain grew up significantly, the sub-structure for the twins and dislocations. And the second phase precipitation was found when the sheet annealed at 1000℃.The Ni20.3Cr4.6Co2.1Al alloy sheet by EB-PVD annealed below 600°C, the fracture strength slightly reduced and the elongation slightly increased with temperature increasing. Annealed at 600℃for 16 h, the fracture strengthσb of sheet reduced to 780 MPa, and elongationδup to only 4%. Annealed at 800℃for 16 h, the room temperature tensile strengthσb and elongationδof alloy sheet increased to 825 MPa and 14%, respectively. The fracture belongs to ductile fracture. Subsequently the fracture strength slightly reduced and the elongation slightly increased with temperature increasing. The alloy sheet annealed at different temperature for 16 h, the 800°C tensile strength and elongationδof sheet annealed at 800℃for 16 reached 63 MPa and 246%, respectively. But annealed at 900℃for 16 h, the 800℃tensile strengthσb has begun to drop 24 MPa, and elongationδhas grown to 336%. And they were ductile fracture.The oxidation dynamics was different for the microcrystalline Ni20.3Cr4.6Co2.1Al sheet and conventional nickel-base alloy. Exposed at 800℃or 1000℃in air, the oxidation kinetics of microcrystalline Ni-11.5Cr-4.5Co-0.5Al alloy sheet followed a parabolic power law at initial oxidation stage and cubical power law for long oxidation terms. And the oxidation kinetics follows a cubical power law at initial oxidation stage and fourth power law for long oxidation terms at 900℃in air.As-deposited Ni20.3Cr4.6Co2.1Al alloy sheet exposed at 800℃in air, the oxidation products are mainly NiO and a small number of Cr2O3 at early stages, mainly NiO, NiCr₂O₄ and Cr2O3 after prolonged oxidation. Exposed at 900℃in air, the oxidation products are NiO, Cr2O3 and NiCr₂O₄ at initial stage. And the scale grain boundary formed Al-regional at the initial stage. After prolonged oxidation, the oxidation product is mainly NiO. The oxidation products are NiO and Cr2O3 at early stages, mainly by NiO, Cr2O3 and secondarily of NiCr₂O₄ composite layer after prolonged oxidation at 1000℃in air.After annealed of microcrystalline Ni20.3Cr4.6Co2.1Al sheet, the oxidation kinetic curves of alloy sheet at 800℃in air follow a fourth power rate law at initial oxidation stage, then very slow oxidation, and the final stage of the alloy sheet is almost not oxidized. The oxidation products are mainly NiO, Cr2O3 and NiCr₂O₄. The oxidation kinetic curves of alloy sheet at 900℃in air follow a cubic power rate law. And the oxidation products are mainly NiO, Cr2O3 and NiCr₂O₄. Exposed at 900℃in air of annealed sheet, the oxidation product is a single needle Al2O3, and Oxide layer peeling occurred.The oxidation kinetics of microcrystalline Ni20.3Cr4.6Co2.1Al failed to obey the parabolic law at 800°C、900°C and 1000°C in air. It was suggested that the oxide scale turned in to microcrystalline state since the nuclear probability of oxide was extremely increased for this kind of microcrystalline alloy. The short circuit diffusion through oxide scale was dominant. An expression, x2=At1-n has been derived for the oxidation kinetics of microcrystalline alloy based upon the model of short circuit diffusion.更多还原