1.1 在本标准中，给出了测量金属添加剂制造（AM）零件制造后相对密度和密度评估试样的指南。 1.2 在本指南中，参考了通常用于测量零件相对密度的标准测试方法，并详细说明了PBF-LB零件使用的任何程序更改或建议。可以根据用户的判断，根据具体情况考虑对其他类型的金属AM工艺的扩展性。 1.3 本指南适用于AM零件相对密度测量方法的选择过程，以平衡成本、精度、复杂性、零件破坏和零件尺寸问题。 1.4 孔径、形状和分布及其与AM工艺和材料相关的影响超出了本指南的范围；然而，在各种密度测量方法的背景下讨论了每种方法获得这些度量的能力。 1.5 单位- 以国际单位制表示的数值应视为标准。本标准中不包括其他计量单位。 1.6 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的使用者有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.7 本国际标准是根据世界贸易组织技术性贸易壁垒委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认的标准化原则制定的。 ====意义和用途====== 5.1 概述: 5.1.1 本指南旨在支持PBF-LB工艺和参数开发、零件验收标准和工艺控制测试。 5.1.2 缺陷和缺陷- 在AM中，制造完全致密的零件仍然是一个挑战，因为该工艺本质上会在零件中引入体积缺陷，从而降低零件的相对密度（即，增加孔隙率或零件中存在的小空隙使其不完全致密）和机械性能。 5.1.2.1 当缺陷的尺寸、形状、位置或临界程度达到零件验收不可接受的程度时，将其称为缺陷。 5.1.2.2 缺陷或缺陷的形成由制造工艺、构造参数、原料和几何因素决定。因此，准确测量制造零件的相对密度是确定零件和工艺质量的重要初始步骤。 5.1.2.3 体积缺陷的数量、尺寸和形状会影响零件的机械性能，尤其是在循环载荷下。这些数据可以指示不规则形状（例如LOF孔隙或微裂纹）或球形孔隙（例如小孔或截留气体孔隙），并通过指定标准来确定可接受性。 虽然这些指标可以量化，但在本指南中，将强调每种方法获取这些数据的一般能力，但不会对这些数据类型提出详细建议，而是将重点放在相对密度测量上。 5.1.3 不确定性和误差- 用户应考虑本指南中考虑的每种测量技术对各种尺寸的特征具有不同的敏感性。由于采样尺寸、检测分辨率、表面条件的影响、实验设置或对理论材料密度的依赖，测量方法也将具有不同的潜在系统误差或测量不确定性。重要的是要考虑到这些影响以及测量中的自然统计变异性。 应对名义上相同的试样进行多次测量，以量化统计不确定度。系统不确定度的贡献不会因重复测量次数的增加而减少。当测量相对密度接近100%的试样时，所选测量技术的系统不确定度量化对于将测量和系统变化与AM过程驱动的变化区分开来变得更加重要。根据测量是否支持工艺开发（例如，确定适当的制造参数）或零件验收（例如，零件鉴定），在确定不确定性和变化的作用时，可以采用不同的严格程度。 5.1.4 重复性和再现性- 由于不确定性和误差可能通过操作员的变化而引入测量过程。对于依赖于大量手动试样制备或操作的方法，如阿基米德、比重计、超声波和金相学，建议执行量规重复性和再现性（gage R&R），这是一个确定测试方法重复性和重现性的过程。请参阅指南 1782年 以获得执行此过程评估的指导。 5.2 方法选择: 5.2.1 在评估方法时，了解不同方法的各种属性之间的比较可能是有益的。在里面 图1 ，给出了比较这些不同方法及其质量的汇总矩阵。 图1 本指南中评估的测试方法的比较矩阵 5.2.2 使用多种方法- 可能希望使用多种方法来确定相对密度。例如，使用低分辨率XCT来测量较大的零件缺陷，使用金相学来识别较小工艺缺陷的数量，这可能是产生准确缺陷数据的一种非常有用的方法。另一种提高测量精度的方法是采用多种原理相似的方法，如比重瓶法和阿基米德法。 5.2.3 无损检测方法- 阿基米德、超声波、比重计和XCT是无损检测方法，而金相方法需要对零件进行破坏才能获得相对密度测量。 所有的无损检测方法都可以用来表征零件的相对密度；然而，随着零件尺寸的增加，这些方法可能会变得难以使用。阿基米德需要一个更大的专用相对密度计算装置，该装置对于适当的精度来说可能很昂贵，但仍然是成本最低的选择，XCT和超声波结果高度依赖于几何形状和尺寸，许多比重计设备无法处理更大的零件体积（许多比重计配备用于处理1cm的样本体积 3. 至3.5厘米 3. ，但也有一些可以处理高达10厘米的 3. )。虽然这些方法中的几种可能不适合表征较大的零件体积，但所有方法都可以提供相对密度。 低成本和快速的测量方法，如阿基米德，可以用作生产过程中的过程开发或统计过程控制数据的手段。 5.2.4 孔隙形态数据- 除了整体零件相对密度外，金相和XCT方法还可以提供单个缺陷的相对密度测量和特定几何细节（即尺寸、纵横比和形状）。然而，对于用于XCT的金相方法或体素大小，金相和XCT测量高度依赖于数据的分辨率，无论是检查的切片、图像数量还是显微镜分辨率，或其组合。阿基米德法、超声波法和比重计法在测量相对密度时不提供这些类型的数据。 5.2.5 基于理论材料密度的相对密度测量- 阿基米德、超声波和气体比重计方法在计算相对密度时依赖于理论材料密度值。所选择的理论材料密度值可能是系统误差的来源。材料密度取决于成分。每种材料都有一个成分规格和该成分的允许变化。这与制造过程中的材料蒸发相结合，可能导致材料密度值与材料供应商或在线来源报告的值不同。用户应谨慎使用报告值，并确保理论密度代表材料（即，从特定材料批次、从最终材料测量或从可靠的数据库等）。 5.2.5.1 对于依靠比较测量材料密度和理论材料密度来计算试样相对密度的方法，应使用以下公式: 5.3 具体方法建议: 5.3.1 阿基米德法- 阿基米德方法具有很高的成本效益、无损性和相对非几何依赖性；然而，操作人员、零件尺寸、零件表面光洁度、流体截留、流体蒸发、温度、水纯度、吸收的气体、表面孔隙或裂纹以及气泡可能会给工艺带来大量变化。使用这种方法，对于完全致密的材料，相对密度测量的不确定度可以达到约0.1%。 与零件尺寸相结合的变化源将增加这种不确定性。然而，培训和一致的实践可以最大限度地减少测量之间差异的影响。此外，阿基米德测量有两个主要的ASTM国际标准，试验方法 B962型 和 2011年3月 .试验方法 2011年3月 是专门为测量孔隙率小于2%的零件的材料密度而设计的，因此被推荐为PBF-LB零件的测量方法。这两种方法的主要区别在于试验方法 B962型 要求流体浸渍以处理表面连接的孔隙率和试验方法 2011年3月 没有。如果试样在浸入水中时质量增加，则使用试验方法 B962型 ，如果试样没有增加质量，则试验方法 2011年3月 适用。建议在浸入水中时搅拌PBF-LB试样，以减少零件表面可能存在的任何气穴。此外，AM的一个优点是能够实现高复杂度——使用这种方法的潜在误差源是内部通道或液体覆盖整个体积的能力。使用此方法时，建议进行多次测量并计算标准偏差。 5.3.2 气体比重计法- 气体比重计要求试样在试验过程中不含可能放气的污染物，不应与置换气体发生反应，并且应具有足够的强度，以避免在加压气体环境中变形。 此外，该方法应仅用于测量具有高相对密度的零件，因为该方法使用气体来确定体积。具有表面孔隙率或互连孔隙结构的样品（无论是通过工艺缺陷还是通过设计）将测量骨骼体积，导致相对密度测量不准确。这种方法的原理与阿基米德相似；然而，它不具有与使用液体进行体积位移相关的那么多潜在误差源。该方法的不确定性是零件尺寸和设备容量的函数。有几个公式可以计算设备制造商的不确定性； 但是，它将是特定于设备和零件的。请注意，比重计确定的体积可以根据正在生产的零件的CAD尺寸直接与理论零件体积进行比较。差异可以直接指向生产零件中闭合孔隙的体积。试验方法 B923 用于测量骨骼或材料密度。虽然该试验方法主要用于测定金属粉末的骨架密度，但也发现它可用于测定传统粉末冶金方法生产的零件的骨架体积和密度。请注意，最好尝试选择比重瓶容量和样本容器配置，以使被测样本占据尽可能多的样本容器体积。 对于任何商业气体比重瓶来说，生产的零件可能太大，如果是这样，则应选择另一种列出的方法。使用此方法时应进行多次测量，并计算标准偏差。 5.3.3 超声波法- 超声波相对密度表征在应用中受到零件几何形状的限制，并受到AM零件中固有的小零件尺寸和表面粗糙度引起的误差。应使用具有简单几何形状（例如立方体）和抛光表面的较大样本零件进行数据采集。请注意，该方法通常用作无损检测方法，而不是用于相对密度测量。测量速度的变化可能表明零件内部存在裂纹或缺陷。 通过超声波检测接收到的这些数据可以评估为实践中提供的几个方程 第494页 以计算材料密度。然后可以将其与理论材料密度进行比较，以计算相对密度测量值。然而，需要几个材料常数，例如泊松比或杨氏模量。为了确定准确的值，需要进行额外的测试，这可能很麻烦。否则，可能需要使用供应商或在线来源来估计这些值，这些值可能不能代表真实值或包括不确定性因素。由于这些因素与测量固有的测量可变性相结合- 制造AM零件，这不是测量PBF-LB零件相对密度的首选方法。 5.3.4 XCT方法- XCT提供了高度描述性的数据，如孔径、形状和分布。然而，它确实需要昂贵的设备，而且时间密集。使用XCT可以获得高分辨率（体素大小约为1µm至5µm）分析；然而，样本尺寸有限，需要更小的零件、更长的扫描时间，而且通常成本更高。低分辨率XCT可以评估较大的零件，但无法检测细微的细节或较小的缺陷。应记录成功的参数和软件处理步骤，以确保可重复性。此外，用于过滤噪声和灰度阈值的软件工具可能会导致不确定性和变化，因为分析中可能会遗漏一些孔隙。 可能需要进行大量迭代以找到合适的扫描和处理参数，并且应对操作员进行培训。在这种方法中，分辨率由体素大小决定；然而，不确定性也可能由此产生。如果选择较大的体素大小，则在相对密度计算中可以不考虑较小的气孔。此外，为识别孔隙而选择的阈值标准是另一个误差源。 5.3.5 金相学与连续切片法- 孔隙率的冶金检查需要对零件或试样进行机械切片，并使用实践中所述的仪器 1245欧元 ，一种配有明场物镜和数字成像的光学显微镜。 图像分析软件生成二进制图像，并对白色背景下的黑色像素进行计数，反之亦然。这是一种相对低成本的相对密度测量技术。然而，由于这是一种破坏性方法，因此，在生产环境中，它更适用于试样，而不是实际零件。如果对生产零件进行剖切，请检查关键设计位置和容易出现气孔的区域。从中导出相对密度数据的微观图像是2D的，并且需要平面的体视学的数学关系来确定不确定性。使用该方法时，应在多个方向和多个抛光深度拍摄完整样本区域的多张图像。 该方法中存在大量来自系统和采样来源的不确定性。由于未对整个试样进行测量，因此可能会遗漏临界孔隙。另一种方法，如比重计，应用于产生样品的可靠相对密度测量值。自动连续切片和成像允许广泛的数据收集，使用冶金方法从样品中捕获大量显微照片。然而，所涉及的资本设备和生成大量图像的时间使得这种方法成本高昂。可以在抛光方向上缝合连续切片图像，以呈现样品的高分辨率3D数据。 连续切片可以通过获取大量的图像数据来降低金相方法的不确定性。在样品制备过程中应特别小心，以确保将残留划痕降至最低。

1.1 In this standard, guidelines for measuring post-manufacturing relative density of metallic additive manufactured (AM) parts and density assessment test specimens are given. 1.2 In this guide, standard test methods commonly used to measure part relative density and details any procedural changes or recommendations for use with PBF-LB parts are referenced. Extensibility to other types of metallic AM processes may be considered on a case-by-case basis with user discretion. 1.3 This guide is intended to be applied during the selection process of methods to measure the relative density of AM parts to balance cost, accuracy, complexity, part destruction, and part size concerns. 1.4 Pore size, shape, and distribution and their implications relative to the AM process and material are beyond the scope of this guide; however, each method’s ability to obtain these metrics is discussed in the context of the various density measurement methods. 1.5 Units— The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard. 1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 General: 5.1.1 This guide is intended to support PBF-LB process and parameter development, part acceptance criteria, and process control tests. 5.1.2 Flaws and Defects— Fabricating fully dense parts continues to be a challenge in AM as the process intrinsically introduces volumetric flaws into a part reducing the part relative density (that is, increasing porosity or the presence of small voids in a part making it less than fully dense) and mechanical performance. 5.1.2.1 When a flaw reaches a size, shape, location, or criticality that makes it becomes unacceptable for part acceptance, it will be referred to as a defect. 5.1.2.2 Flaw or defect formation is governed by the manufacturing process, build parameters, feedstock, and geometric factors. Therefore, accurate measurement of fabricated part relative density is an important initial step in determining part and process quality. 5.1.2.3 The quantity, size, and shape of the volumetric flaws influences mechanical performance of a part, particularly under cyclic loading. These data could indicate irregularly shaped (for example, LOF pores or microcracking) or spherical porosity (for example, keyhole or entrapped gas porosity) and determine acceptability by assigning criteria. While these metrics can be quantified, in this guide, the general capabilities of each method to capture this data will be highlighted, but detailed recommendations on these data types will not be made and rather the focus will be on relative density measurements. 5.1.3 Uncertainty and Error— Users should consider that each measurement technique considered in this guide has differing sensitivities to various sized features. The measurement methods will also have different potential systematic errors or measurement uncertainties due to sampling sizes, detection resolution, effect of surface condition, experimental set-up, or reliance on a theoretical material density. It is important that these effects are taken into consideration as well as the natural statistical variability in the measurements. Multiple measurements of nominally identical test specimens should be made to enable the quantification of statistical uncertainty. Systematic uncertainty contributions will not be reduced by greater numbers of repeated measurements. When measuring specimens with relative densities close to 100 % quantification of systematic uncertainty for the selected measurement technique(s) becomes more critical to separate measurement and systematic variation from variation driven by the AM process. Differing levels of rigor can be applied when determining the role of uncertainty and variation depending on whether the measurement is in support of process development (for example, identifying appropriate fabrication parameters) or part acceptance (for example, part qualification). 5.1.4 Repeatability and Reproducibility— As uncertainty and error can be introduced into the measurement process through operator variation. Performing gage repeatability and reproducibility (Gage R&R), a process that determines a test method’s repeatability and reproducibility, is recommended for methods that rely on significant manual specimen preparation or operation such as Archimedes, pycnometry, ultrasonic, and metallography. Refer to Guide E2782 for guidance on performing this process evaluation. 5.2 Method Selection: 5.2.1 When evaluating methods, it may be beneficial to understand how the various attributes compare from method to method. In Fig. 1 , a summary matrix comparing these various methods and their qualities is given. FIG. 1 Comparison Matrix of the Test Methods Evaluated in This Guide 5.2.2 Using Multiple Methods— It can be desirable to use multiple methods to determine relative density. For example, using low-resolution XCT to measure larger part flaws and metallography to identify the quantity of smaller process flaws could prove to be a highly useful way of producing accurate flaw data. Another approach to strengthen measurement accuracy is by implementing multiple methods that operate on similar principles, such as pycnometry and Archimedes. 5.2.3 Non-destructive Methods— Archimedes, ultrasonic, pycnometry, and XCT are nondestructive methods, while metallographic methods require part destruction to get relative density measurements. All the nondestructive methods can be used to characterize part relative density; however, as part size increases, these methods can become cumbersome to use. Archimedes requires a much larger and dedicated setup for relative density calculation that can be expensive for the appropriate accuracy but remains the least cost-intensive option, XCT and ultrasonic results are highly geometry and size dependent, and many pycnometry devices cannot handle larger part volumes (many pycnometers are equipped to handle specimen volumes of 1 cm 3 to 3.5 cm 3 , however there are some that can handle up to 10 cm 3 ). While several of these methods may not be suitable for characterizing larger part volumes, all can provide relative density. Low-cost and quick measurement methods, such as Archimedes, can be used as a means of process development or data for statistical process control during production. 5.2.4 Pore Morphology Data— Metallographic and XCT methods can provide relative density measurements and specific geometric details (that is, size, aspect ratio, and shape) of individual flaws in addition to the overall part relative density. However, metallographic and XCT measurements are highly dependent on the resolution of the data, whether that is the sections examined, quantity of images, or microscope resolution, or a combination thereof, for metallographic methods or voxel size used for XCT. Archimedes, ultrasonic, and pycnometry methods do not provide these types of data when measuring relative density. 5.2.5 Relative Density Measurements Relying on Theoretical Material Density— Archimedes, ultrasonic, and gas pycnometry methods rely on theoretical material density values in the calculation of relative density. The theoretical material density value selected is a possible source of systematic error. Material density is composition dependent. Each material will have a compositional specification and an allowable variation of that composition. This combined with material vaporization during fabrication could lead to a different material density value than the reported value by a material vendor or online source. The user should use caution on the reliance of a reported value and ensure the theoretical density is representative of the material (that is, from the specific material lot, measured from final material, or from a reliable database such). 5.2.5.1 For methods relying on comparing the measured and theoretical material densities to calculate the relative density of the specimen, the following formula should be used: 5.3 Method Specific Recommendations: 5.3.1 Archimedes Method— The Archimedes method is highly cost effective, nondestructive, and relatively non-geometry dependent; however, a significant amount of variation can be introduced into the process from the operator, part size, surface finish of the part, fluid entrapment, evaporation of fluid, temperature, water purity, absorbed gases, surface pores or cracks, and bubbles. Uncertainties of approximately 0.1 % for relative density measurements can be achieved for fully dense materials using this method. The sources of variation combined with part size will increase this uncertainty. However, training and consistent practices can minimize the effects of variation between measurements. Additionally, there are two main ASTM International standards for Archimedes measurements, Test Methods B962 and B311 . Test Method B311 is specifically designed for measuring material density of parts with less than 2 % porosity volume and is, therefore, recommended as the measurement method for PBF-LB parts. The major difference between the two methods is that Test Methods B962 require fluid impregnation to deal with surface-connected porosity and Test Method B311 does not. If a specimen increases in mass while submerged in water, use Test Methods B962 , and if the specimen does not gain mass, then Test Method B311 is applicable. Agitating the PBF-LB specimens while submerged is recommended to reduce any air pockets that may exist on the part’s surface. Additionally, a benefit of AM is the ability to achieve high complexity—a potential source of error using this method would be internal channels or the ability for the liquid to cover the entire volume. It is recommended to take multiple measurements when using this method and compute a standard deviation. 5.3.2 Gas Pycnometry Method— Gas pycnometry requires that specimens be free of contaminants that may outgas during the test, shall not react with the displacing gas, and shall have sufficient strength to avoid deformation in the pressurized gas environment. Additionally, this method should only be used to measure parts with high relative densities since this method uses a gas to determine volume. Specimens with surface porosity or interconnected pore structures (whether through process defect or by design) will measure the skeletal volume, resulting in an inaccurate relative density measurement. This method functions on similar principles to that of Archimedes; however, it does not possess as many potential sources of error related to using a liquid for volume displacement. Uncertainty in this method is a function of part size and equipment capacity. There are several equations to calculate uncertainty from the equipment manufacturer; however, it will be equipment and part specific. Note that pycnometry determines a volume that can be compared directly to theoretical part volume based upon CAD dimensions of the part being produced. Differences can point directly to the volume of closed porosity in the produced part. Test Method B923 is used for measurement of skeletal or material density. While this test method is primarily for determination of skeletal density of metal powders, it has also been found to be useful for determination of skeletal volume and density of parts produced by traditional powder metallurgy methods. Note that it is best to try to choose a pycnometer capacity and specimen container configuration that result in the specimen under test occupying as much of the specimen container volume as possible. It can occur that a produced part is too large for any commercial gas pycnometers, and if so, another listed method shall be selected. Multiple measurements should be taken when using this method and compute a standard deviation. 5.3.3 Ultrasonic Method— Ultrasonic relative density characterization is limited in application by part geometry and suffers errors induced by small part sizes and surface roughness inherent in AM parts. Larger specimen parts with simple geometries (for example, cubes) and polished surfaces to measure from should be used for data capture. Note that this method is typically used as an NDT method and not for relative density measurement. Changes in measured velocity can be indicative of cracking or flaws within parts. These data received through ultrasonic testing can be evaluated into several equations provided in Practice E494 to calculate material density. This can then be compared to theoretical material density to compute a relative density measurement. However, several material constants such as Poisson’s ratio or Young’s modulus are required. To determine accurate values, additional testing is required, which can be cumbersome. Otherwise, vendor or online sources may need to be used to estimate these values, which may not be representative of the true values or include uncertainty considerations. Because of these factors combined with measurement variability inherent to measuring as-built AM parts, this is not a preferred method for measuring relative density of PBF-LB parts. 5.3.4 XCT Method— XCT provides highly descriptive data, such as pore size, shape, and distribution. However, it does require costly equipment and is time intensive. High-resolution (voxel size of ~1 µm to 5 µm) analysis is obtainable using XCT; however, there is a limitation on specimen size, requiring smaller parts, longer scanning times, and often more cost. Low resolution XCT can evaluate larger parts but is unable to detect fine details or smaller flaws. Successful parameters and software processing steps should be recorded to ensure repeatability. Additionally, the software tools used to filter noise and the grayscale thresholding can lead to uncertainty and variation as some pores can be missed in the analysis. Significant iterating may be required to find the proper scanning and processing parameters and operators should be trained. Resolution is governed by voxel size in this method; however, uncertainty can arise from this as well. Smaller gas pores can be unaccounted for in relative density computation if a larger voxel size is selected. Additionally, the thresholding criteria selected for identifying pores are another source of error. 5.3.5 Metallography and Serial Sectioning Method— Metallurgical examination of porosity requires mechanical sectioning of the part or test specimen and an apparatus such as described in Practice E1245 , a light microscope equipped with brightfield objectives and digital imaging. Image analysis software produces a binary image and counts black pixels against a white background or vice versa. This is a relatively low-cost relative density measurement technique. However, as it is a destructive method, it is, therefore, more applicable to test specimens than actual parts in a production setting. If sectioning a production part, examine critical design locations and areas prone to porosity. The microscopic images from which relative density data are derived are 2D and require mathematical relationships of stereology for planar surfaces to determine uncertainty. Multiple images of the full specimen area in several orientations and at multiple polishing depths should be taken when using this method. A significant amount of uncertainty exists within this method from systematic and sampling sources. Critical pores can be missed as the whole specimen is not measured. Another method, such as pycnometry, should be used to generate reliable relative density measurements of a specimen. Automated serial sectioning and imaging allows for expansive data collection that captures a significant number of micrographs from a specimen using metallurgical methods. However, the capital equipment involved and time to generate a large quantity of images makes this method costly. Serial sectioning images can be stitched in the polishing direction to render high resolution 3D data of the specimen. Serial sectioning can be used to reduce the uncertainty of the metallographic method by taking a large quantity of image data. Special care should be taken during the specimen preparation procedure to ensure minimal residual scratching.