基于二维面探的高温合金GH4169残余应力分析

目的 通过二维面探X射线衍射法测试高温合金GH4169的残余应力.方法 由于GH4169是Ni基高温合金,Ni合金在Cr靶下有较强衍射峰,因此采用Cr靶来测试GH4169合金的残余应力.二维面探仪有500个探测头,均匀分布在一个面上,根据每一个探测器测得的衍射角变化,就能得到500个方向上的应变值,再根据应力与应变之间的关系,就可以计算出材料的残余应力.结果 GH4169合金的德拜环只有一个衍射峰,而且衍射峰的强度随着角度α的变化而变化.这说明该材料的应力取向不均匀,存在较为明显的织构.该材料表面主应力方向上的残余应力测试值为-968 MPa,误差为62 MPa;切向上的残余应力测试值为24 MPa,误差为43 MPa.由于测试的GH4169合金是经过喷丸处理的,主应力方向上受残余压应力,而其测试结果 确为负值,说明此次测试结果 可信.结论 通过二维面探X射线衍射方法 测试材料残余应力从原理和实际操作上都是可行的,并成功测试出GH4169合金的残余应力.经喷丸处理后的GH4169材料受残余压应力的作用,且应力分布不均匀,存在较为明显的织构.     

镍基高温合金GH4169高温变形流动应力模型研究

镍基高温合金GH4169热模拟压缩实验结果表明:变形温度的升高和应变速率的减小使该合金高温变形时的峰值应力和稳态应力显著降低,变形温度会影响其进入稳态变形时变形程度的大小.基于高温合金GH4169高温变形时的流动应力特征,运用模糊神经网络理论建立了该合金高温变形时的流动应力模型.计算与实验的流动应力的最大误差为10.18%,平均误差为2.11%,该模型的计算精度明显高于由回归法建立的高温合金GH4169高温变形时的流动应力模型.     

GH4169合金经高温及应力时效处理后的组织演变及性能

以GH4169高温合金为研究对象,通过对其进行不同条件下的高温时效以及高温应力时效处理后,进行拉伸和疲劳寿命测试,研究其微观组织演变、剩余强度和疲劳寿命以及其相关机理。结果表明,GH4169合金在550℃时效时组织稳定;650℃高温时效后γ″相开始出现粗化,在应力作用下发生γ″→δ转变,强度和寿命降低;700℃高温时效后晶内γ″相向δ相转变明显,耦合应力进一步促进了相的转变。高温耦合应力的环境下表面发生氧化开裂大大降低了GH4169合金的疲劳寿命。     

C含量对GH4169合金显微组织及力学性能的影响

为了研究C元素含量对GH4169合金显微组织及力学性能的影响,采用真空感应熔炼、均匀化热处理、锻造和固溶处理得到C含量分别为0.025%、0.044%和0.072%的三种GH4169合金,通过热力学计算和差示扫描量热法研究了不同C含量GH4169合金的平衡相析出行为,并结合显微组织观察、X射线衍射相分析和室温拉伸试验,分析了C含量对GH4169合金显微组织、室温拉伸性能和加工硬化指数的影响。结果表明：C含量的增加会促进GH4169合金中MC和M23C6碳化物的析出,富Nb的MC碳化物含量随C含量的增加呈线性趋势增加。C含量的增加会抑制δ相的析出,对γ′相的析出无显著影响。随C含量的增加,固溶态GH4169合金的晶粒得到细化,室温强度升高,断后伸长率降低,加工硬化指数降低,均匀塑性变形能力降低。MC碳化物及其引起的微孔是导致合金室温拉伸断裂的主要原因。     

多场耦合作用下GH4169合金变形行为与强韧化机制

研究了脉冲电流/温度/应力多场耦合作用下,镍基GH4169合金的变形行为与强韧化机理。结果表明,GH4169合金在脉冲电流/温度/应力作用下,GH4169合金变形抗力降低、塑性变形能力提高,在高温下脉冲电流的引入加剧了原子热振动、金属晶格Pereils力下降,由此降低了合金变形抗力,增强了合金塑性变形协调能力。而当GH4169合金经脉冲电流/温度场耦合时效处理,则可以显著提高合金的高温强度和韧性,脉冲电流/温度耦合作用提高了合金基体空位缺陷密度,促进了其在随后高温变形过程中析出大量数纳米级新γ"相强化相,而脉冲电流/温度场耦合时效处理过程中析出、粗化的γ"相以及其与合金高温变形中新析出数纳米级γ"相的协同作用,使合金实现了强韧化。     

GH4169、GH4169plus和GH4738高温合金组织稳定性

为了获得不同沉淀硬化相作用的高温合金在高温长期时效过程中的组织稳定性的对比规律,对3种应用最为广泛的高温合金GH4169、GH4169plus、GH4738经720℃时效后的显微组织和硬度变化进行了对比分析。结果表明,合金的组织稳定性与晶界相和弥散强化相有关,晶界碳化物较晶界δ相稳定,γ'相较γ″相有更好的稳定性,但同为γ'相,组织稳定性还与其和基体的错配度有关。对比3种合金,随时效时间的延长,GH4169plus合金的稳定性稍次于GH4738合金,但要优于GH4169合金。     

单晶DD3与细晶GH4169高温合金摩擦焊接界面表征

采用SEM,TEM及EDS对制造焊接式整体涡轮叶盘所用的单晶DD3与细晶GH4169高温合金摩擦焊接界面进行了研究.结果表明,焊合区存在一条以GH4169合金为主的摩擦变形带,两侧单晶和细晶合金的热力影响区均形成了动态再结晶晶粒;连接界面处于两侧合金的动态再结晶晶粒之间,通过连接界面上的共有晶粒和共有晶界实现了两侧合金的连接;成分过渡主要发生在连接界面处的共有晶粒内和共有晶界处.TEM分析位置的共有晶粒(C2)与相邻GH4169动态再结晶晶粒(C3)具有特殊的取向关系:[1ˉ14]C2∥[1ˉ10]C3和(220)C2∥(220)C3;在摩擦焊热循环及焊后热处理作用下,共有晶粒、两侧动态再结晶晶粒都存在γ'相析出,γ'相呈细小的球形分布,并与γ基体共格,但未发现有γ"相析出.     

热处理对3D打印制备GH4169合金组织与性能的影响

通过选区激光熔化(SLM)技术三维打印(3D priting)制备了GH4169合金板状试样,并对其进行了热处理。采用三维原子探针技术(3DAP)以及附带原位拉伸功能的扫描电镜(SEM)对热处理前后试样的显微组织及力学性能进行了检测。结果表明,打印态GH4169合金中熔池和晶粒内部均为凝固枝晶组织,合金元素分布均匀。经过热处理后,基体中形成了大量细小γ″相和γ′相;拉伸试验结果显示,3D打印GH4169合金热处理后具有更优的力学性能,这归因于枝晶组织的消失、有害δ相的减少以及大量纳米级γ″相和γ′相在基体中的析出。     

激光冲击处理对GH4169合金应力回火稳定性的影响

利用激光冲击波对GH4169合金表面进行了强化处理,通过扫描电镜观察了激光冲击处理后其表面形貌的变化,用X射线应力仪测定了激光冲击处理后GH4169合金600℃和800℃回火处理后残余应力分布规律,并分析了残余应力产生机理.结果表明,激光冲击处理后GH4169合金残余压应力为-400 MPa以上;在800℃回火处理使残余应力值下降20%,600℃回火处理对其残余应力没有影响,回火稳定性较好.     

超瞬态凝固增材制造梯度整体涡轮叶盘用高温合金粉末特性研究I：盘体用合金粉末

本文针对超瞬态凝固增材制造梯度整体涡轮叶盘用高温合金粉末特性开展研究。根据合金的承温能力和JMatPro相平衡计算结果,分别选用GH4169和K418作为盘体心部和轮盘边缘部位材料,DZ4125作为叶片材料。采用真空感应熔炼氩气雾化制粉(VIGA)制备高温合金粉末,筛分至53-105μm粒度范围,采用差示扫描量热分析（DSC）、场发射扫描电镜（FESEM）、电子探针（EPMA）、激光粒度仪、动态图像粒度粒形分析仪以及综合粉体性能测试仪对高温合金粉末的相变温度、显微组织、元素偏析行为、粒度、粒形、松装密度、振实密度和流动性进行了系统表征。结果表明：K418合金固液温度范围比G4169合金窄,K418合金的γ′和MC碳化物的开始析出温度均比GH4169高,过渡区(GH4169+K418)混合成分合金主要强化相的析出温度介于GH4169和K418两种合金之间。GH4169和K418合金粉末形貌主要为球形和近球形。表面和截面显微组织主要呈树枝晶结构,所含元素中偏析倾向较强的元素有Ti、Nb、Zr和Mo,均富集分布于枝晶间,而偏析倾向弱的元素包括Ni、Cr、Fe和Al,高温合金粉末元素偏析类型与铸造镍基高温合金相近,但粉末组织更为细小均匀。激光衍射和动态图像分析法测得的粉末粒度值接近,GH4169的D50分别为79.1μm和76.2μm,K418的D50分别为67.8μm和65.6μm。动态图像法测得2种合金均具有较好的球形度,GH4169和K418的SPHT均值分别为0.91和0.90。所选GH4169和K418高温合金粉末具有相近的松装密度、振实密度和流动性,其松装和振实密度分别达到合金理论密度的50%和60%,压缩度在13.3~15.5%范围,粉末具有较好的流动性（18.5~20.4 s?(50 g)-1）。     

Crystallography using an X-ray free-electron laser

An X-ray free-electron laser (XFEL) produces short pulses (10–50 fs) of intense (mJ μm^?2 at 120 Hz) X-rays, with high transverse coherence. Such pulses open novel spectroscopic and scattering methods for static and time-resolved studies of matter, and many are based on X-ray crystallography. With serial femtosecond crystallography, the XFEL allows high-resolution structural determination on sub-micron protein crystals. Although the XFEL pulse is destructive, its short duration ensures that effectively undamaged material is probed. Coherent scattering features provide information on the physical crystal form and may assist in determining the crystallographic phase. By introducing synchronized optical laser pulses, one can perform ‘pump-probe’ measurements of dynamic properties, on the sub-picosecond timescale. These include photo-initiated structural modifications in biomolecules, photo-excited lattice vibrations and photo-driven structural phase transitions. As with synchrotron radiation, the XFEL wavelength can be tuned to atomic resonances, allowing time-resolved resonant-diffraction measurements, which are particularly sensitive to selected order parameters (lattice, charge, spin, and orbital) in magnetic or correlated electron materials. Finally, it is anticipated that the special properties of XFEL pulses will allow entirely new types of X-ray scattering measurements, such as ptychographic crystallography on 2D bio-crystals, correlation-function determination of nanoparticle geometry and nonlinear crystallographic mixing of optical and X-ray pulses.     

The effects of the combined substitution of Y and Ga on the crystallographic structure of Nd2−xYxFe17−yGay intermetallic compounds

The effects of the combined substitution of Y and Ga on the crystallographic structure of Nd_2−xY_xFe_17−yGa_y compounds with x = 0, 0.5, 1.0, 1.5 and y = 0, 1, 2, 3 have been investigated using X-ray and neutron powder diffractions. Rietveld refinements of the diffraction data indicate that all the samples crystallize in the rhombohedral Th₂Zn₁₇-type structure with only small amounts of alpha iron. It is found that the addition of Ga atoms lessens the decreasing rates of the a-axis and unit cell volume V on the Y content but almost does not affect the decreasing rates of the c-axis. However, the substitution of Y has a positive effect on the increasing rates of the a-axis and unit cell volume V on the Ga content but has a very slight effect on the increasing rate of the c-axis. The c/a ratio of Nd_2−xY_xFe_17−yGa_y as a function of Ga content exhibits a different increase for different Y content owe to the combined effects of Y and Ga on the crystallographic structure. The substitution of Y is found to have little effect on the site occupancy of Ga in Nd_2−xY_xFe_17−yGa_y. The combined effects of Y and Ga on the bond lengths and ASBL of Nd_2−xY_xFe_17−yGa_y indicate that more bonds detrimental to ferromagnetic exchange can be modulated into the desirable ferromagnetic exchange distance range through suitable combined substitution, which provides a valuable way to improve the magnetic properties of rare earth-transition intermetallic compounds.     

Structural study on Zr0.39Ni0.61 and (Zr0.39Ni0.61)D0.59 amorphous alloys by neutron and X-ray diffraction

Neutron and X-ray diffraction and reverse Monte Carlo (RMC) simulation were performed on Zr_0.39Ni_0.61 and (Zr_0.39Ni_0.61)D_0.59 amorphous alloys to investigate the rearrangement of metal atoms due to the deuterium absorption. The RMC models showed that the Zr–Zr distances slightly increase but the Zr–Ni and Ni–Ni distances remain virtually unchanged after the deuterium absorption. Additionally, the Voronoi polyhedral analysis of the RMC configurations showed that there is not much difference in the local structure around Zr and Ni between Zr_0.39Ni_0.61 and (Zr_0.39Ni_0.61)D_0.59 amorphous alloys.     

The crystal structure of (Nb0.75Cu0.25)Sn2 in the Cu-Nb-Sn system

During the processing of superconducting Nb₃Sn wire, several intermediate intermetallic phases including a previously encountered Cu-Nb-Sn phase show up. The yet unknown crystal structure of this phase is now identified by a combination of different experimental techniques and database search to be of the hexagonal NiMg₂ type with a proposed composition of about (Nb_0.75Cu_0.25)Sn₂. The structure determination started from an evaluation of the lattice parameters from EBSD Kikuchi patterns from quenched material suggesting hexagonal or orthorhombic symmetry. A database search then led to the hexagonal NiMg₂ type structure, the presence of which was confirmed by a Rietveld analysis on the basis of high energy synchrotron X-ray powder diffraction data. Assuming a partial substitution of Nb in orthorhombic NbSn₂ by Cu, the change of the valence electron concentration provokes a structural transformation from the CuMg₂ type for NbSn₂ to the NiMg₂ type for (Nb_0.75Cu_0.25)Sn₂. In the previous literature the (Nb_0.75Cu_0.25)Sn₂ phase described here has occasionally been referred to as Nausite.     

马氏体点阵参数与含碳量的定量关系:新的X射线衍射实验研究

发现了一个多晶马氏体X射线衍射的新的实验规律 ,并能用X射线衍射理论进行满意的解释。实验现象支持低碳马氏体为体心立方结构的假说。观察到马氏体中的碳原子有序—无序分布有关的立方—正方转变 ,并且从实验上确立了该转变的临界点 ,建立了一个马氏体点阵参数随固溶碳量变化的新经验方程。本文的实验方法及根据实验数据所获得的回归方程可成为钢中α相 (过饱和 )含碳量的实用的标定办法 (特别在低碳范围 )。     

Neutron diffraction from fibers

The X-ray diffraction technique has greatly improved our understanding of the function and properties of filamentous systems of biological and organic polymers by providing structural information at a molecular level. Although X-ray diffraction remains the primary method for determining fiber structures, neutron diffraction is an important supplementary technique. Neutron diffraction has some distinct advantages over the X-ray technique for providing certain types of structural information. This review describes the results from neutron diffraction studies of fibers and discusses the future prospects for this emerging technology.     

Asymmetric X-Ray Diffraction

Abstract

Physical phenomena characteristic of asymmetric X-ray diffraction schemes for perfect crystals, including diffraction under conditions of specular reflection, have been considered in detail. The principles underlying asymmetric crystal monochromators, achievements in obtaining narrow collimated X-ray beams, and the latest results on the application of asymmetric schemes in the investigation of thin subsurface layers are stated; along with the fundamentals of asymptotic Bragg diffraction, specific features of the grazing Bragg-Laue scheme and the analysis of amorphous sublayers with the use of the surface Bragg peak. Emphasis is placed on the application of asymmetric diffraction schemes in the method of X-ray standing waves to increase sensitivity (in recording of photoelectrons, fluorescence, and Compton scattering) and to study the characteristic features of the diffraction process in strongly asymmetric geometry.     

Subsolidus phase relations of the SrO–Ta2O5–CuO system at 900 °C in air

The subsolidus phase relations of the SrO–Ta₂O₅–CuO system were investigated in air. The samples were equilibrated at 900 °C. The ternary oxide Sr₃Ta₂CuO₉ compound is stable under these conditions. This phase presents a solid solution range, its actual composition being Sr₃Ta_2−xCu_1+xO_9+δ with 0.0 ≤ x ≤ 0.2. Up to about 5 at.% Cu can be incorporated in the Sr_3−xTa_1+xO_5.5+δ phase. Similarities with the SrO–Nb₂O₅–CuO system are discussed.