Ti-6Al-4V钛合金网篮组织与拉伸性能 定量关系研究

建立钛合金显微组织-拉伸性能定量关系对于组织性能的控制及优化具有重要意义。本文基于定量金相学和体视学原理,利用多元非线性回归方法建立了Ti-6Al-4V钛合金网篮组织-拉伸性能定量关系模型。模型自变量包括片状α相厚度、片状α相长宽比,因变量为合金的室温拉伸性能。经验证表明,所建立的多元回归模型对合金的拉伸性能具有较高的预测精度,说明模型的构建方法是可行的。     

Ti-6Al-4V合金网篮组织与拉伸性能定量关系研究

建立钛合金显微组织-拉伸性能定量关系对于组织-性能的控制及优化具有重要意义。基于定量金相学和体视学原理,利用多元非线性回归方法建立了Ti-6Al-4V合金网篮组织-拉伸性能定量关系模型。模型自变量包括片状α相厚度、片状α相长宽比,因变量为合金的室温拉伸性能。经验证表明,所建立的多元回归模型对合金的拉伸性能具有较高的预测精度,预测值与实验值相吻合。     

(α+β)两相钛合金显微组织的定量分析和表征

基于体视学方法,结合计算机图形处理,建立一套钛合金显微组织定量测量和表征的方法.对钛合金中片层和等轴两类典型组织进行定量表征,其参数包括:片层α的厚度、体积分数、形态、取向,初生α相尺寸、体积分数,总α相体积分数.分析实例表明,建立的钛合金显微组织定量表征方法精度高、重现性好,为后续建立显微组织-力学性能预测模型奠定了基础.     

新型TC21钛合金热处理工艺参数与显微组织演变的关系研究

TC21钛合金是新型的高强韧损伤容限型钛合金，其模锻件为网篮组织，锻后热处理工艺采用双重退火工艺。本研究采用金相法、SEM等方法系统研究了TC21钛合金模锻件的锻后热处理工艺和显微组织演变规律。试验分析了TC21钛合金模锻件锻后第1次退火加热温度、第2次退火加热温度和保温时间等工艺参数条件下的初生α相数量、形状以及网篮组织形貌特征的变化规律，为TC21钛合金模锻件获得高强、高韧和损伤容限优良综合性能奠定基础。     

薄板TC4钛合金TIG电弧和激光焊接接头晶粒尺寸与微观组织

对薄板TC4钛合金进行TIG电弧和激光焊接技术研究,重点分析了TIG焊接电流、焊接速度和激光输出功率对TC4钛合金焊接接头晶粒尺寸、微观组织和显微硬度的影响规律. 试验结果表明,在实现薄板TC4钛合金完全熔透的条件下,激光焊接具有更小热输入,接头焊缝区和热影响区宽度也显著降低. TIG焊接接头晶粒尺寸随热输入增加,呈现增加趋势. 随距焊缝中心位置增加,焊接接头晶粒尺寸均逐渐降低. TC4钛合金激光焊接接头焊缝区呈现魏氏组织特征,针状α'马氏体细小. 近缝热影响区组织为网篮状α'马氏体,而近母材热影响区为未转变α相和针状α'马氏体的双相组织. 随距焊缝中心位置增加,马氏体生成量逐渐减少,焊缝显微硬度值呈现降低趋势;同时相比于TIG焊接,TC4激光焊接接头具有更高的显微硬度.     

钛合金显微组织与性能定量关系的模型

提出利用软计算方法定量分析钛合金显微组织与性能的关系。在实现钛合金显微组织的定量分析和参数化表征的基础上,探讨以钛合金显微组织特征参数为输入变量、以性能为预测输出变量的组织与性能定量关系模型的构建方法。依据长期实践中得到的组织影响性能的定性规律及热加工工艺对组织特征的影响程度,提出定量关系模型显微组织信息预处理过程中组织特征参数评价取舍原则。运用人工神经网络建立Ti-17合金组织与室温拉伸力学性能的定量关系模型,研究建模的具体方法。该模型对各项性能指标具有较高的预测精度,说明提出的建模思想合理和模型构建方法可行     

钛合金固态相变的归纳与讨论(Ⅷ)——利用三类α相设计三态组织

针对钛合金复杂显微组织结构设计和认识需求，在传统钛合金金相学理论知识基础上，对钛合金的显微组织结构进行了进一步解析，指出钛合金的显微组织结构可以从形态学和结构学两个方面理解。以形态学为基础，提出钛合金中的α相可以根据生成阶段的不同，分为一次α相、二次α相和三次α相，并对三类α相进行了定义。最后，以两相钛合金为例，说明如何利用三类α相设计三态组织，从而更好地协调不同性能对组织要求的冲突性。     

激光沉积TA15钛合金退火处理工艺及网篮组织变形机制研究

以TA15钛合金球形粉末为原料,采用激光沉积制造技术制备TA15钛合金厚壁件。通过光学显微镜(OM)、扫描电子显微镜(SEM)等方法研究了α+β两相区退火处理对TA15钛合金室温拉伸性能和显微组织的影响,并对网篮组织在拉伸过程中的变形机制进行讨论。结果表明：经α+β两相区不同温度退火后,显微组织为网篮组织或近网篮组织,退火温度对α相的形貌尺寸具有明显影响;退火后力学性能仍表现出方向上的各向异性：沉积方向上强度较低,塑性较好,而垂直沉积方向上强度高,塑性较差;粗大的层间区组织滑移变形具有“开路”作用,而柱状晶晶界对α相的滑移产生一种“固定”作用;显微硬度值随退火温度升高变化不大,显微硬度值受α相含量影响;网篮组织中的α片层组织在应力的作用下由原来近似正交方向逐渐向近似平行于应力方向变形,α片层组织的交错排列导致滑移变形时互相产生阻力;α+β两相区退火处理后的两种方向上断口形貌相似,断裂方式相同,均为韧性断裂。     

激光沉积TA15钛合金退火处理工艺及网篮组织变形机制

以TA15钛合金球形粉末为原料,采用激光沉积制造技术制备TA15钛合金厚壁件。通过光学显微镜(OM)、扫描电子显微镜(SEM)等方法研究了α+β两相区退火处理对TA15钛合金室温拉伸性能和显微组织的影响,并对网篮组织在拉伸过程中的变形机制进行讨论。结果表明:经α+β两相区不同温度退火后,显微组织为网篮组织或近网篮组织,退火温度对α相的形貌尺寸具有明显影响;退火后力学性能仍表现出方向上的各向异性:沉积方向上强度较低、塑性较好,而垂直沉积方向上强度高、塑性较差;粗大的层带区组织滑移变形具有"开路"作用,而柱状晶晶界对α相的滑移产生一种"固定"作用;显微硬度值随退火温度升高变化不大,显微硬度值受α相含量影响;网篮组织中的α片层组织在应力的作用下由原来近似正交方向逐渐向近似平行于应力方向变形,α片层组织的交错排列导致滑移变形时互相产生阻力;α+β两相区退火处理后的2种方向上断口形貌相似,断裂方式相同,均为韧性断裂。     

铸造钛合金α层的组织与形成机理

利用熔模铸造的方法制备了铸造Ti-6Al-4V合金试样,通过金相、电子探针、显微硬度测试等技术研究了铸造钛合金表面α层的组织和形成机理。结果表明,铸造钛合金试样表面均形成了α层,显微组织特征为呈"网篮"状排列的粗大片状α相组织。α层形成机理主要与型壳材料中间隙氧原子和碳原子向合金基体扩散有关。显微硬度测试得到的α层深度略大于金相结果。为完整去除α层,以硬度测试的结果更为可靠。     

A framework for automated analysis and simulation of 3D polycrystalline microstructures. Part 2: Synthetic structure generation

This is the second of a two-part paper intended to develop a framework for collecting data, quantifying characteristics and subsequently representing microstructural information from polycrystalline materials. The framework is motivated by the need for incorporating accurate three-dimensional grain-level morphology and crystallography in computational analysis models that are currently gaining momentum. Following the quantification of microstructural features in the first part, this paper focuses on the development of models and codes for generating statistically equivalent synthetic microstructures. With input in the form of statistical characterization data obtained from serial-sectioning of the microstructures, this module is intended to provide computational modeling efforts with a microstructure representation that is statistically similar to the actual polycrystalline material.     

Three-dimensional simulation of intermetallic compound layer growth in a binary alloy system

We present three-dimensional phase-field simulations of the thickening of intermetallic compound (IMC) layers and their microstructural evolution during soldering and aging in a binary alloy system. The focus was on the grain growth in the IMC layer, since the grain boundary (GB) provides a high-diffusivity path and affects the thickening kinetics of the IMC. The radial grain growth of the IMC was analogous to Ostwald ripening when the phase interface was rounded, while it followed normal grain growth with planar phase interface. The thickening mode of the IMC layer was dependent upon the microstructural evolution within the IMC layer with high diffusivity along the GBs. The simulation results successfully confirm literature models on the effect of GB diffusion on IMC thickening.     

Predicting phase equilibrium,phase transformation,and microstructure evolution in titanium alloys

Phase transformation and microstructural evolution in commercial titanium alloys are extremely complex. Traditional models that characterize microstructural features by average values without capturing the anisotropy and spatially varying aspects may not be sufficient to quantitatively define the microstructure and hence to allow for establishing a robust microstructure-property relationship. This article discusses recent efforts in integrating thermodynamic modeling and phase-field simulation to develop computational tools for quantitative prediction of phase equilibrium and spatiotemporal evolution of microstructures during thermal processing that account explicitly for precipitate morphology, spatial arrangement, and anisotropy. The rendering of the predictive capabilities of the phase-field models as fast-acting design tools through the development of constitutive equations is also demonstrated. For more information, contact Y.-Z. Wang, Department of Materials Science & Engineering, Ohio State University, 2041 College Road, Columbus, OH 43221, USA; (614) 292-0682; fax (614) 292-1537; e-mail wang.363@osu.edu.     

MODELING OF MICROSTRUCTURAL EVOLUTION IN MICROALLOYED STEEL DURING HOT FORGING PROCESS

~~MODELING OF MICROSTRUCTURAL EVOLUTION IN MICROALLOYED STEEL DURING HOT FORGING PROCESS~~1 C.A. Hernandez, S.F. Medina and J. Ruiz, Acta Materialia 44 (1996) 155. 2 P.D. Hodgson and R.K. Gibbs, ISIJ International 32 (1992) 1329. 3 S.I. Kim, Y. Lee and S.M. Byon, Journal of Materials Processing Technology 140 (2003) 84. 4 A. Laasraoui and J.J. Jonas, Metall. Trans. 22A(1991) 1545. 5 S.F. Medina and J.E. Mancilla, ISIJ International …     

Modeling of precipitation hardening in pre-aged AlMgSi(Cu) alloys

A new analytical method to estimate the evolution of the relative volume fraction of precipitates during artificial aging of pre-aged AlMgSi(Cu) alloys in the underaged regime is introduced. The analytical results demonstrate that the precipitation processes in AlMgSi(Cu) alloys are isokinetic in commercially relevant temperature ranges. The theory of transformations is used to model isothermal and non-isothermal aging kinetics in isokinetic systems where the precipitate nuclei pre-exist at the start of aging and definite precipitate contents are reached at the end of transformation. A simple physically based model is also developed for the prediction of the average size of precipitates during artificial aging of pre-aged alloys, when “growth” is the controlling mechanism of precipitation. The microstructural models are combined with a previously developed yield strength model and the evolution of yield strengths during isothermal and non-isothermal aging of AlMgSi(Cu) alloys, with various pre-aging histories, are modeled. The analytical method and the microstructural and yield strength models are validated using experimental results.     

金属板料冲压数值模拟中的宏观硬化模型研究现状

金属板料冲压数值模拟的精度取决于所应用的材料模型是否能够对材料的弹塑性行为提供准确描述。对于考察材料力学响应在变形过程中的变化,采用宏观硬化模型,并将微观结构特征整合在宏观内变量中,是一种合适的方法。文章结合微观结构演化,讨论了对金属材料宏观硬化的4种基本方式(各向同性硬化、运动硬化、旋转硬化、畸变硬化)及其限制;根据对不同应变路径变化下材料性能变化的描述,归纳了近年来较为典型的板料宏观硬化模型研究,并指出其不足之处及需要进一步研究的内容。同时,就金属板料冲压的宏观硬化模型研究需要注意的问题进行讨论。     

Thermodynamic analysis of the effect of C,Mn and Al on microstructural evolution of lightweight steels

The effect of alloying elements carbon, manganese and aluminum on the microstructural evolution of lightweight steels during a typical steel production process has been investigated experimentally and on the basis of a thermodynamic calculation. It is proposed how the information from thermodynamic calculations should be utilized for the interpretation of microstructural evolution during a real steel production process. It is demonstrated that the equilibrium thermodynamic calculation can be successfully utilized for the interpretation of non-equilibrium microstructural evolution after some calibration.     

Studying and modeling surface gas nitriding for titanium alloys

In this article, experimental studies for the nitriding of four titanium alloys at different temperatures and for different periods of time are summarized. The studies focused on microstructural changes in relation to the alloy composition and processing parameters; microindentation hardness testing on the nitrided titanium alloys to analyze their hardness evolution; and the corrosion behavior of titanium alloys before and after gas nitriding in response to the corrosive condition. In addition, models were developed to simulate and monitor the evolution of surface layers during the gas nitriding of titanium alloys.     

A yield strength model for the Al-Mg-Si-Cu alloy AA6111

A yield strength model is developed for the Al-Mg-Si-Cu alloy AA6111. The evolution of the strength of precipitates, as obstacles to dislocation motion, during various stages of aging is modeled according to the theories for strengthening mechanisms, as well as the microstructural and mechanical behavior of the alloy. The precipitation hardening component of yield strength is modeled for conditions where precipitates act as either strong or weak obstacles. The dislocation breaking angles for various stages of aging at 180 °C is estimated and the applicability of both strong and weak obstacle models examined. It is found that although the weak obstacle model could be a better choice for describing the very early aging stages and/or the low temperature processes, the entire aging period in the temperature range of 160–220 °C is well described by applying the strong obstacle model. The modeling results are related to the microstructural evolution in this alloy system.