Additive manufacturing letters最新文献_第7页

Continuous carbon fiber 3D printing with interweaving deposition for enhanced mechanical performance in fused filament fabrication 连续碳纤维3D打印与交织沉积，以提高机械性能的熔丝制造

IF 4.2 Q2 ENGINEERING, MANUFACTURING

Additive manufacturing letters

Pub Date : 2025-07-01 Epub Date: 2025-05-09 DOI: 10.1016/j.addlet.2025.100289

A. ElSherbiny, A.J. Qureshi, P. Mertiny

Additive manufacturing (AM) has revolutionized modern manufacturing by enabling the rapid prototyping and production of complex geometries with minimal material waste. Among AM techniques, Fused Filament Fabrication (FFF) is widely used for polymer-based manufacturing but exhibits limitations in high-performance applications due to insufficient mechanical properties. To address these shortcomings, this study focuses on advancing a standard FFF system to integrate Continuous Carbon Fiber (CCF) and implement interweaving deposition patterns, with the goal of enhancing structural performance and integrity. Representative volume element modeling and finite element analysis were conducted to evaluate the mechanical behavior, with results validated through experimental mechanical testing. The results confirm that CCF reinforcement improves the mechanical performance of printed components, particularly in the raster direction, although variations in response highlight the influence of material imperfections and non-linearities. The study demonstrates the potential of advanced CCF 3D printing in addressing the limitations of traditional FFF and provides insights for further advancements in polymer composite AM.

增材制造（AM）通过在最小的材料浪费下实现复杂几何形状的快速原型和生产，彻底改变了现代制造业。在增材制造技术中，熔融长丝制造（FFF）广泛用于基于聚合物的制造，但由于机械性能不足，在高性能应用中受到限制。为了解决这些缺点，本研究着重于推进一种标准的FFF系统，以集成连续碳纤维（CCF）并实现交织沉积模式，以提高结构性能和完整性。通过具有代表性的体元建模和有限元分析对其力学行为进行了评价，并通过实验力学试验对结果进行了验证。结果证实，CCF增强提高了印刷部件的机械性能，特别是在光栅方向上，尽管响应的变化突出了材料缺陷和非线性的影响。该研究展示了先进的CCF 3D打印在解决传统FFF局限性方面的潜力，并为聚合物复合材料AM的进一步发展提供了见解。

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引用次数: 0

Towards fully 3D printed dielectric elastomer actuators—A mini review 迈向完全3D打印的介电弹性体致动器-一个小型回顾

IF 4.7 Q2 ENGINEERING, MANUFACTURING

Additive manufacturing letters

Pub Date : 2025-07-01 Epub Date: 2025-07-25 DOI: 10.1016/j.addlet.2025.100304

Rollo Pattinson , Nathan Ellmer , Mokarram Hossain , Rogelio Ortigosa , Jesús Martínez-Frutos , Antonio J. Gil , Anil Bastola

Dielectric elastomer actuators (DEAs) have attracted the interest of researchers in soft robotics and biomimetics, due to their versatile capabilities, explored through numerical analysis and experimentation. Advances in computational simulation techniques have accelerated numerical studies on DEAs, enabling even design optimisation for improved performance. However, as computational models grow in sophistication, the fabrication methods required often exceed the capabilities of traditional manufacturing. Additive manufacturing, in particular 3D printing, offers a promising solution to the challenges of realising intricate multi-functional designs developed through topology optimisation. Its precision and ability to create complex geometries make it well-suited for translating computational designs into functional DEA devices. This mini-review examines recent progress in 3D printing for DEA fabrication, emphasising its role in bridging the gap between computational design and physical devices. It also highlights emerging technologies and key challenges that must be addressed to fully realise topologically optimised DEA designs.

介电弹性体致动器（dea）由于其多用途的性能，通过数值分析和实验进行了探索，引起了软机器人和仿生学研究人员的兴趣。计算模拟技术的进步加速了dea的数值研究，甚至可以优化设计以提高性能。然而，随着计算模型越来越复杂，所需的制造方法往往超过传统制造的能力。增材制造，特别是3D打印，为实现通过拓扑优化开发的复杂多功能设计的挑战提供了一个有前途的解决方案。它的精度和创建复杂几何形状的能力使其非常适合将计算设计转化为功能DEA设备。这篇迷你评论研究了DEA制造3D打印的最新进展，强调了其在弥合计算设计和物理设备之间差距方面的作用。它还强调了必须解决的新兴技术和关键挑战，以充分实现拓扑优化DEA设计。

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引用次数: 0

Superior mechanical properties of a high temperature Co-based superalloy fabricated by laser powder bed fusion 激光粉末床熔合制备的高温钴基高温合金具有优异的力学性能

IF 4.7 Q2 ENGINEERING, MANUFACTURING

Additive manufacturing letters

Pub Date : 2025-07-01 Epub Date: 2025-07-28 DOI: 10.1016/j.addlet.2025.100311

Liuhao Miao , Huiliang Wei , Jiashun Yue , Rong Chen , Yuanhong Qian , Xiaopeng Li , Zhiguang Zhu , Tingting Liu , Wenhe Liao

Laser powder bed fusion (LPBF) of high temperature superalloys with superior mechanical properties are highly desired. However, the correlations between the process, microstructure and ambient/high temperature mechanical properties for the typical Co-based superalloy Haynes 188 remain unclear. In this work, the process development, the ambient and high temperature mechanical properties for LPBF of Haynes 188 were systematically explored. Samples with relative density over 99.9 % were achieved. Unprecedented ambient temperature strength-ductility were obtained, with yield strength of 756 MPa, tensile strength of 1067 MPa, and elongation of 60.2 %, respectively. Moreover, high temperature mechanical properties such as the steady-state creep rate of 1.04×10⁻⁴ s⁻¹ at 750 °C and 270 MPa were firstly reported. Additionally, the yield strength of Haynes 188 at 980 °C reached 276 MPa. Microstructural analysis revealed that nano-scale M₆C/M₂₃C₆ carbides pinned dislocations, while dense dislocation networks and refined sub-grains suppressed dynamic recovery. The obtained achievements can provide valuable insights for additive manufacturing of complex and high-performance Haynes 188 components.

激光粉末床熔合（LPBF）是一种具有优良力学性能的高温合金。然而，典型co基高温合金Haynes 188的工艺、显微组织与环境/高温力学性能之间的相关性尚不清楚。本文系统地探讨了haynes188 LPBF的工艺发展、环境力学性能和高温力学性能。样品的相对密度在99.9%以上。获得了前所未有的室温强度-塑性，屈服强度为756 MPa，抗拉强度为1067 MPa，伸长率为60.2%。此外，还首次报道了在750℃和270 MPa下的稳态蠕变速率1.04×10−4 s⁻¹等高温力学性能。Haynes 188在980℃时的屈服强度达到276 MPa。显微组织分析表明，纳米尺度的M6C/M23C6碳化物固定了位错，而密集的位错网络和细化的亚晶粒抑制了动态恢复。所获得的成果可以为复杂高性能Haynes 188部件的增材制造提供有价值的见解。

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引用次数: 0

A new approach to laser DED as a repair technology with laser mesh deposition 用激光网状沉积技术修复激光DED的新方法

IF 4.2 Q2 ENGINEERING, MANUFACTURING

Additive manufacturing letters

Pub Date : 2025-07-01 Epub Date: 2025-07-11 DOI: 10.1016/j.addlet.2025.100301

Thomas Girerd , Richard Adamson , Andres Gameros , Marco Simonelli , Andy Norton , Adam Thomas Clare

Controlling the heat input and exploring alternate feedstocks for DED is necessary to improve the versatility of DED as a repair technique. In this research, a new DED method using metallic mesh feedstocks and laser beam oscillations. This method is shown to have good stability, repeatability and good bonding with the substrate comparable to other DED processes. The best depositions show a dilution above 40 % and a height of >1.2 mm. The deposits show similar results to wire DED and powder DED with low dilution levels producing dense clads with no large pores and some grain refinements at the edges of the tracks. This then manifests as a potentially viable repair process with the advantage of a more flexible material input facilitating the delivering of the feedstock material for hard to access repair operations.

Furthermore, this process has shown its capability to be used with various energy profiles and mesh density paving the way for a better control of the microstructure for complex repair operations. This new DED alternative method has shown its capability to run efficiently with various scan strategies and feedstocks. Hence, laser mesh deposition could be used to deposit material on inhomogeneous surfaces by using carefully designed scanning strategies and mesh density during the process increasing the repair capabilities of DED.

控制热输入和探索DED的替代原料是提高DED作为一种修复技术的通用性所必需的。本文研究了一种利用金属网格原料和激光束振荡的DED方法。与其他DED工艺相比，该方法具有良好的稳定性、可重复性和与衬底的良好结合。最好的沉积表现为稀释度在40%以上，高度为1.2 mm。该沉积的结果与低稀释水平的线状DED和粉末DED相似，形成致密的包层，没有大的孔隙，在轨迹边缘有一些晶粒细化。这是一种潜在可行的维修工艺，其优点是材料输入更灵活，便于为难以进入的维修作业提供原料材料。此外，该工艺已显示出可用于各种能量分布和网格密度的能力，为复杂修复操作中更好地控制微观结构铺平了道路。这种新的DED替代方法已经显示出其在各种扫描策略和给料下有效运行的能力。因此，激光网格沉积可以通过精心设计的扫描策略和网格密度在非均匀表面上沉积材料，从而提高DED的修复能力。

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引用次数: 0

Dual-matrix interface strength of 3D printed continuous carbon fiber reinforced composites: Quantitative assessment methodology and critical influencing factors 3D打印连续碳纤维增强复合材料双基体界面强度：定量评估方法及关键影响因素

IF 4.2 Q2 ENGINEERING, MANUFACTURING

Additive manufacturing letters

Pub Date : 2025-07-01 Epub Date: 2025-07-14 DOI: 10.1016/j.addlet.2025.100303

Xiaofei Lou , Lei Dong , Xin'an Tang , Xiaohui Nan , Teng Zhang , Li Zhao

In 3D printed continuous carbon fiber reinforced dual-matrix composites, the resin matrix in the carbon fiber prepreg filament is not the same with the matrix in the composite, and the dual-matrix interface plays an important role on the mechanical properties of structures. In this paper, a method for testing the interface shear strength (IFSS) of the dual-matrix is proposed. The interfaces between carbon fiber reinforced polyamide-6 prepreg filament and different polylactic acid matrices are selected, and the strengths of the dual-matrix interface are investigated under different printing temperatures, printing speeds, layer thicknesses, and prepreg filament volume fractions. The results show that the polylactic acid matrix with lower crystallinity is capable to form stronger interface with the polyamide-6 material. The printing temperature and printing speed need to be controlled within a certain range to ensure a reasonable viscosity range and printing quality, which will achieve a higher dual-matrix IFSS. The increase of prepreg filament volume fraction and the decrease of layer thickness are conducive to the improvement of dual-matrix interfacial properties. In addition, finite element analysis based on the cohesive model is used to analyze the interface debonding behavior, which validates the test method proposed in this paper.

在3D打印连续碳纤维增强双基复合材料中，碳纤维预浸长丝中的树脂基体与复合材料中的基体不相同，双基体界面对结构的力学性能起着重要作用。本文提出了一种双基体界面抗剪强度测试方法。选择了碳纤维增强聚酰胺-6预浸丝与不同聚乳酸基体的界面，研究了不同打印温度、打印速度、层厚和预浸丝体积分数下双基体界面的强度。结果表明，结晶度较低的聚乳酸基质能与聚酰胺-6材料形成较强的界面。印刷温度和印刷速度需要控制在一定的范围内，以保证合理的粘度范围和印刷质量，这将实现更高的双矩阵IFSS。预浸丝体积分数的增加和层厚的减小有利于双基体界面性能的改善。此外，采用基于内聚模型的有限元分析方法对界面脱粘行为进行了分析，验证了本文提出的试验方法的有效性。

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引用次数: 0

Columnar-to-equiaxed transitions in additively manufactured face-centered cubic multi-principal element alloys 增材制造面心立方多主元素合金的柱向等轴转变

IF 4.2 Q2 ENGINEERING, MANUFACTURING

Additive manufacturing letters

Pub Date : 2025-07-01 Epub Date: 2025-04-14 DOI: 10.1016/j.addlet.2025.100283

Mengyao Zheng , Yu Liao , Zheng Zhou , Hao Zhang , Chuanwei Li , Zhong Long , Jianfeng Gu

Columnar-to-equiaxed transition (CET) represents a critical microstructural characteristic in additively manufactured alloys. Precise control over CET is essential for achieving high-performance metallic components through additive manufacturing. In this study, two face-centered cubic multi-principal element alloys (MPEAs), namely CoCrNi and FeCoCrNi, were fabricated via laser directed energy deposition. The influence of process parameter and alloy composition on the CET of the two MPEAs was investigated. The results demonstrated that pronounced CET phenomena were observed in both MPEAs as the laser power increased and the scanning speed decreased. However, significant variations were noted in their CET parameters, equiaxed grain fraction, and crystallographic texture. Subsequently, the impact of process parameters on temperature gradient, solidification rate, and molten pool morphology was investigated via finite element modelling, revealing the formation mechanisms of the grain morphology and texture in additively manufactured CoCrNi and FeCoCrNi alloys. Additionally, the results of thermodynamic calculation revealed significant differences in the growth restriction factors between the two MPEAs, thereby explaining the distinct CET behaviors observed in the two MPEAs.

柱状到等轴转变（CET）是增材制造合金中一个重要的显微组织特征。通过增材制造实现高性能金属部件，对CET的精确控制至关重要。本研究采用激光定向能沉积法制备了CoCrNi和feccrni两种面心立方多主元素合金（mpea）。研究了工艺参数和合金成分对两种mpea的效率的影响。结果表明，随着激光功率的增大和扫描速度的降低，两种mpea都出现了明显的CET现象。然而，它们在CET参数、等轴晶粒分数和晶体织构方面存在显著差异。随后，通过有限元模拟研究了工艺参数对温度梯度、凝固速率和熔池形貌的影响，揭示了CoCrNi和feccrni合金晶粒形貌和织构的形成机制。此外，热力学计算结果揭示了两种mpea之间生长限制因子的显著差异，从而解释了两种mpea中观察到的不同的CET行为。

{"title":"Columnar-to-equiaxed transitions in additively manufactured face-centered cubic multi-principal element alloys","authors":"Mengyao Zheng , Yu Liao , Zheng Zhou , Hao Zhang , Chuanwei Li , Zhong Long , Jianfeng Gu","doi":"10.1016/j.addlet.2025.100283","DOIUrl":"10.1016/j.addlet.2025.100283","url":null,"abstract":"<div><div>Columnar-to-equiaxed transition (CET) represents a critical microstructural characteristic in additively manufactured alloys. Precise control over CET is essential for achieving high-performance metallic components through additive manufacturing. In this study, two face-centered cubic multi-principal element alloys (MPEAs), namely CoCrNi and FeCoCrNi, were fabricated via laser directed energy deposition. The influence of process parameter and alloy composition on the CET of the two MPEAs was investigated. The results demonstrated that pronounced CET phenomena were observed in both MPEAs as the laser power increased and the scanning speed decreased. However, significant variations were noted in their CET parameters, equiaxed grain fraction, and crystallographic texture. Subsequently, the impact of process parameters on temperature gradient, solidification rate, and molten pool morphology was investigated via finite element modelling, revealing the formation mechanisms of the grain morphology and texture in additively manufactured CoCrNi and FeCoCrNi alloys. Additionally, the results of thermodynamic calculation revealed significant differences in the growth restriction factors between the two MPEAs, thereby explaining the distinct CET behaviors observed in the two MPEAs.</div></div>","PeriodicalId":72068,"journal":{"name":"Additive manufacturing letters","volume":"14 ","pages":"Article 100283"},"PeriodicalIF":4.2,"publicationDate":"2025-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143859350","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Cross-modality transfer for DED-LB/M: AI-based prediction of schlieren phenomena from coaxial imaging d - lb /M的跨模态转移：基于人工智能的同轴成像纹影现象预测

IF 4.2 Q2 ENGINEERING, MANUFACTURING

Additive manufacturing letters

Pub Date : 2025-07-01 Epub Date: 2025-06-25 DOI: 10.1016/j.addlet.2025.100298

Benedikt Brandau , João Sousa , Rico Hemschik , Frank Brueckner , Alexander F.H. Kaplan

Real-time process monitoring is essential for ensuring stability and defect control in directed energy deposition - laser beam/metal (DED-LB/M). Schlieren imaging has proven to be a valuable tool for detecting refractive index variations in the process zone, providing insights into gas flow behaviour, shielding gas efficiency and process plume dynamics. However, schlieren imaging typically requires specialized optical setups, making integration into industrial systems challenging. This study explores an artificial intelligence-driven cross-modality transfer approach that enables the prediction of schlieren-induced refractive index variations from coaxial imaging data, eliminating the need for a dedicated schlieren setup. A background-oriented schlieren system was used to capture reference data, while a coaxial camera recorded the melt pool and surrounding process zone during DED-LB/M. A machine learning model was trained on the combined dataset, establishing correlations between schlieren activity and intensity variations in the coaxial images. The model successfully predicted schlieren-induced disturbances, allowing for the indirect detection of gas flow instabilities and shielding gas deficiencies. The results demonstrate that artificial intelligence-based analysis of coaxial imaging can provide schlieren-equivalent process information, making it possible to monitor refractive index variations, detect process deviations and improve defect prediction in real time. This approach enhances process monitoring capabilities in DED-LB/M, enabling cost-effective, scalable and easily integrable monitoring solutions for industrial applications.

实时过程监控是保证定向能沉积-激光束/金属（ed - lb /M）工艺稳定性和缺陷控制的关键。纹影成像已被证明是一种有价值的工具，用于检测过程区的折射率变化，提供对气体流动行为、保护气体效率和过程羽流动力学的见解。然而，纹影成像通常需要专门的光学设置，使得集成到工业系统具有挑战性。本研究探索了一种人工智能驱动的跨模态转移方法，该方法能够从同轴成像数据中预测纹影诱导的折射率变化，从而消除了对专用纹影设置的需要。采用面向背景的纹影系统捕获参考数据，同轴相机记录了d- lb /M过程中的熔池和周围工艺区域。在组合数据集上训练机器学习模型，建立纹影活动与同轴图像强度变化之间的相关性。该模型成功地预测了纹影引起的扰动，允许间接检测气体流动不稳定性和保护气体缺陷。结果表明，基于人工智能的同轴成像分析可以提供纹影等效的工艺信息，从而可以实时监测折射率变化，检测工艺偏差并改进缺陷预测。这种方法增强了ed - lb /M的过程监控功能，为工业应用提供了经济高效、可扩展且易于集成的监控解决方案。

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引用次数: 0

Chamfer distance for non-linear registration of Triply Periodic Minimal Surface lattices 三周期极小曲面格非线性配准的倒角距离

IF 4.2 Q2 ENGINEERING, MANUFACTURING

Additive manufacturing letters

Pub Date : 2025-07-01 Epub Date: 2025-07-14 DOI: 10.1016/j.addlet.2025.100299

Michela Lapenna , Francesco Faglioni , Keerthana Chand , Bardia Hejazi , Rita Fioresi , Giovanni Bruno

We present a 3D image registration technique for non-linear deformation estimation in Additive Manufacturing processes. The methodology involves comparing X-ray Computed Tomography (XCT) data with Computer Aided Design (CAD) models for Triply Periodic Minimal Surface (TPMS) lattices and employs the Chamfer distance to refine mesh non-linear deformations.

提出了一种用于增材制造过程中非线性变形估计的三维图像配准技术。该方法包括将x射线计算机断层扫描（XCT）数据与三周期最小表面（TPMS）网格的计算机辅助设计（CAD）模型进行比较，并使用倒角距离来细化网格非线性变形。

引用次数: 0

Part distortion monitoring in additive manufacturing using machining 增材制造中零件变形监测

IF 4.2 Q2 ENGINEERING, MANUFACTURING

Additive manufacturing letters

Pub Date : 2025-07-01 Epub Date: 2025-06-06 DOI: 10.1016/j.addlet.2025.100295

Jaydeep Karandikar , Akash Tiwari , Josh Harbin , Christopher Tyler , Scott Smith , Derril Vezina , Rob Caron

In additive manufacturing, accumulation of residual stresses can result in severe part distortion from the desired preform shape. Current methods for in-situ part distortion monitoring in additive manufacturing typically require expensive sensors, or capital equipment, and require time-consuming post-processing to understand the shape deviation. This paper presents an in-situ method, in the context of hybrid manufacturing, for part distortion detection using machining of additively manufactured parts. As a surrogate, three test artifacts were used to represent different distorted geometries. The tool axis positions from the machine tool controller and the cutting power were monitored during a facing operation. Cutting power data was used to detect the tool entry and exit in the workpiece using a novel approach with power standard deviation metric. The workpiece geometry and distorted configuration was subsequently predicted for positional and rotational deviations to within 2 mm accuracy using synchronized tool position data with cutting power. The proposed method can be used in a hybrid (additive and subtractive) machine tool to periodically check part distortion in the additive build. The method is applicable for any additive process and is low-cost and computationally inexpensive.

在增材制造中，残余应力的积累会导致零件严重变形。目前在增材制造中进行原位零件变形监测的方法通常需要昂贵的传感器或资本设备，并且需要耗时的后处理才能了解形状偏差。本文提出了一种在混合制造背景下，利用增材制造的零件加工进行零件畸变检测的原位方法。作为代理，三个测试工件被用来表示不同的扭曲几何。在加工过程中，通过机床控制器监测刀具轴的位置和切削功率。采用一种新的功率标准差度量方法，利用切削功率数据检测刀具在工件中的进出。随后，利用同步刀具位置数据和切削功率，预测了工件几何形状和变形结构的位置和旋转偏差，精度在2mm以内。该方法可应用于加减法混合机床中，对加式制造中的零件畸变进行周期性检测。该方法适用于任何增材工艺，成本低，计算成本低。

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引用次数: 0

Improved corrosion resistance of selective laser melted NiTi alloys via nanosecond pulsed laser annealing treatment for biomedical application 生物医学用纳秒脉冲激光退火提高选择性激光熔化NiTi合金的耐蚀性

IF 4.2 Q2 ENGINEERING, MANUFACTURING

Additive manufacturing letters

Pub Date : 2025-07-01 Epub Date: 2025-07-15 DOI: 10.1016/j.addlet.2025.100306

Chao Yang , Tao Long , An Yan , Hongwei Ma , Haizhou Lu , Liang Liang , Weisi Cai

NiTi alloys, known for their excellent biocompatibility, have broad application prospects in the biomedical field, making surface quality and corrosion resistance critical for practical applications. This study employs nanosecond pulsed laser annealing to improve the surface properties of NiTi alloys fabricated by selective laser melting (SLM). The results show that laser annealing significantly reduces surface roughness, with the average roughness (Ra) decreasing from 8.76 µm to 1.42 µm. Meanwhile, potential dynamic polarization analysis conducted at 37 °C in Hank’s solution indicates that laser annealing effectively enhances corrosion resistance, with the corrosion potential shifting positively from -0.68 V to -0.23 V and the corrosion current density decreasing from 3.580 μA·cm⁻² to 0.151 μA·cm⁻². This improvement is attributed to the reduction in surface roughness, grain refinement, and the formation of a more stable oxide layer through laser annealing. This study not only validates the potential of laser annealing for surface modification of SLMed NiTi alloys but also provides valuable insights for their further optimization in biomedical applications.

NiTi合金具有良好的生物相容性，在生物医学领域具有广阔的应用前景，其表面质量和耐腐蚀性对实际应用至关重要。采用纳秒脉冲激光退火技术改善选择性激光熔化制备的NiTi合金的表面性能。结果表明：激光退火能显著降低表面粗糙度，平均粗糙度（Ra）由8.76µm降至1.42µm；同时，对Hank’s溶液在37°C下进行的电位动态极化分析表明，激光退火有效地提高了材料的耐蚀性，腐蚀电位从-0.68 V正移到-0.23 V，腐蚀电流密度从3.580 μA·cm⁻²下降到0.151 μA·cm⁻²。这种改进归因于表面粗糙度的降低，晶粒细化，以及通过激光退火形成更稳定的氧化层。该研究不仅验证了激光退火在SLMed NiTi合金表面改性中的潜力，而且为其在生物医学应用中的进一步优化提供了有价值的见解。

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引用次数: 0