Cold gas dynamic manufacturing: A non-thermal approach to freeform fabrication

This paper reports on the development of a novel freeform fabrication technique using a cold spray (CS) system. In the CS process, metallic powder particles are accelerated in a supersonic gas jet and impacted with a substrate at speeds in excess of 600 m/s. The non-melting nature of its deposition mechanism ensures that the sprayed material is free from thermally induced tensile stresses, while the underlying substrate remains unchanged. The process is seen as a viable method for additive manufacturing because of its high deposition rates and controllable spray jet. A process was developed to investigate the potential of non-thermal freeform fabrication and was coined Cold Gas Dynamic Manufacturing (CGDM). Here, additive and subtractive techniques were combined to enable the production of complex geometries. Whereas most CS facilities concentrate on the application of wear or corrosion-resistant coatings, CGDM is dedicated to the production of freeform components, whilst still retaining an inherent coating ability. The process can produce functional forms using novel manufacturing strategies that are unique to CS. This paper presents information on the process, and details the various strategies employed during component fabrication. It was possible to construct components from many materials, including titanium, which exhibited freeform surfaces, internal channels and embedded devices. A breakdown of the process economics is also provided, with and without helium recycling.     

激光增材制造钛合金微观组织和力学性能研究进展

激光选区熔化(SLM)技术与激光熔化沉积(LMD)技术在航空航天、生物医疗等领域的应用具有巨大潜力,但由于成形的Ti6Al4V合金构件存在较差的表面质量、较大的残余应力以及内部孔洞等问题,影响了构件的力学性能,从而制约了其大规模的应用。针对这一现状,首先概述了激光选区熔化技术与激光熔化沉积技术的制造原理,比较了2种增材制造技术的成形参数及其特点,并分析了2种不同成形技术的自身优势以及适用场合。其次,从2种增材制造技术成形钛合金的工艺参数入手,综述了激光功率、扫描速度、激光扫描间距、铺粉厚度、粉床温度等参数对SLM工艺成形钛合金的影响,以及激光功率、扫描速度、送粉速率等参数对LMD工艺成形钛合金的影响。发现成形工艺参数直接影响了粉末熔化程度、熔合质量和成形显微结构,从而影响成形件的组织与力学性能。此外,综述了不同的扫描策略对两种增材制造技术成形钛合金的表面质量与力学性能的影响,可以发现在不同扫描策略下同一试样表面的不同区域表面质量、残余应力以及抗拉强度存在较大差异,同一扫描策略下试样的不同表面之间也存在各向异性。最后,探讨了不同热处理工艺对钛合金微观组织和力学性能的影响,通过合适的热处理能够降低成形构件应力,并调控组织相变和性能。     

Cold Spraying of Armstrong Process Titanium Powder for Additive Manufacturing

Titanium parts are ideally suited for aerospace applications due to their unique combination of high specific strength and excellent corrosion resistance. However, titanium as bulk material is expensive and challenging/costly to machine. Production of complex titanium parts through additive manufacturing looks promising, but there are still many barriers to overcome before reaching mainstream commercialization. The cold gas dynamic spraying process offers the potential for additive manufacturing of large titanium parts due to its reduced reactive environment, its simplicity to operate, and the high deposition rates it offers. A few challenges are to be addressed before the additive manufacturing potential of titanium by cold gas dynamic spraying can be reached. In particular, it is known that titanium is easy to deposit by cold gas dynamic spraying, but the deposits produced are usually porous when nitrogen is used as the carrier gas. In this work, a method to manufacture low-porosity titanium components at high deposition efficiencies is revealed. The components are produced by combining low-pressure cold spray using nitrogen as the carrier gas with low-cost titanium powder produced using the Armstrong process. The microstructure and mechanical properties of additive manufactured titanium components are investigated.     

冷喷涂技术及其系统的研究现状与展望

与传统的热喷涂相比,冷喷涂具有沉积温度低、沉积效率高、孔隙率低,以及粉末在沉积过程中不易发生氧化、分解、相变和纳米结构材料的晶粒长大等问题,这使得氧化敏感、温度敏感和相变敏感等材料的高质量涂层制备成为可能.更值得一提地是,近年来冷喷涂工艺与设备的大力发展使冷喷涂作为一种快速固态成形工艺,在金属增材制造和航空航天等关键零...     

冷喷涂过程中气固两相流动行为及喷涂工艺优化研究新进展

冷喷涂技术因其固态沉积特性及突出的冶金优势,在金属或金属基复合材料涂层制备、增材制造与修复再制造等领域获得了国内外研究者的广泛关注。 近十年来,国内外对冷喷涂技术的基础理论研究也取得了重要进展。 冷喷涂粒子加速加热行为是结合机理研究的先决条件。 因此,文中结合作者多年的研究经验,对冷喷涂过程中气固两相流动行为及喷涂工艺优化的最新进展进行了综述。 首先,分析了冷喷涂喷嘴内外的气体流动特性;其次,讨论了冷喷涂粒子的加速与加热行为;然后,阐述了冷喷涂过程中工艺参数优化的策略;最后,给出了相关研究的发展方向。     

Elimination of porosity in directly fabricated titanium via cold gas dynamic spraying

Cold gas dynamic spray (cold spray) is a deposition technology in which particles achieve supersonic velocities. Commercial purity titanium (CP Ti) is directly fabricated to exploit the potential for cold spray to be utilised as a new fabrication technology. Deposition parameters for elimination of porosity were identified. Results show that using helium as the deposition gas has a significant influence on the elimination of pores. The volume fraction of porosity decreased with a decrease in the distance between the nozzle and the substrate. Furthermore, a decrease in average particle size led to a reduction in porosity of the deposited material. The results show that the directly fabricated CP Ti exhibits a higher hardness compared with wrought CP Ti. Optimisation of cold spray parameters led to a significant reduction of pores in directly fabricated parts.     

碳钢双丝与单丝等离子弧增材制造成形及组织特征分析

针对传统丝材等离子弧增材制造碳钢效率低、质量高的特点,提出了一种"双填丝+压缩等离子弧"增材制造工艺,并采用该工艺增材制造了试样,对比分析了双填丝与单填丝增材制造试样的成形尺寸、显微组织特征和力学性能.结果表明,相对于单填丝等离子弧增材制造工艺,采用新型双填丝等离子弧增材制造工艺,在相同的工艺条件下,熔敷效率提高了0.97倍;平均晶粒尺寸由18.75 μm细化到13.47 μm;试样纵向拉伸抗拉强度提高了62.64 MPa,横向拉伸抗拉强度提高了67.52 MPa;试样有效层的平均显微维氏硬度由158.95 HV0.5增加到175.34 HV0.5.     

冷喷涂增材制造技术研究现状及应用与挑战

冷喷涂增材制造技术是一种固态增材方法,其依靠粉末颗粒塑性变形形成结合,增材构件几乎没有氧化、相变及晶粒长大、裂纹等缺陷,较低的沉积温度对基体热影响较小,同时具有增材效率高和制造大构件等优势,已受到多个国家研究团队的关注,被认为是一种强大而有用的增材制造及增材修复技术。鉴于目前冷喷涂增材制造技术受到各国学者和工业界越来越多的关注,本文试图在阐述冷喷涂设备的基础上,总结典型冷喷涂沉积体（Cu、Al、Ti及Ta等材料）组织结构与性能,重点介绍冷喷涂增材制造技术在国防领域的应用和新进展。同时,也指出了目前冷喷涂增材制造技术存在的挑战。最后对冷喷涂增材制造技术发展尚存的问题与发展方向进行了展望。     

TC4钛合金电弧增材制造叠层组织特征

采用CMT电弧增材制造技术制造了TC4钛合金薄壁墙构件，并对其组织特征进行了研究. 结果表明，在电弧增材制造过程中，受其热输入、多次热循环及冷却速度的影响，在其构件中产生了从高温保留下来的贯穿数个堆积层的原始β柱状晶晶界、水平层带条纹、马氏体组织和网篮组织等. 显微硬度显示，中下部区域硬度相对较高，平均硬度为336HV 0.1，上部显微硬度有明显降低，平均硬度为323.3HV 0.1.     

Comparison of the Properties of Cold-Sprayed Cu-0.5Cr-0.05Zr Alloys after Various Heat Treatments Versus Forged and Vacuum Plasma-Sprayed Alloys

In this work, Cu-0.5Cr-0.05Zr (wt.%) samples obtained by the cold spray process were studied regarding the microstructure and the mechanical properties versus several heat treatments. Ultimate tensile strength higher than 600 MPa, yield strength of 570 MPa and Vickers hardness HV0.2 of about 200 were obtained. Comparison of these results with those obtained by forging or vacuum plasma spraying highlighted the ability of the cold spray technique to produce dense Cu-Cr-Zr deposits with low oxygen content, low level of residual stresses and high mechanical properties.     

The Effects of Low Frequency on the Microstructure and Mechanical Properties of High-Strength Al-Mg Aluminum Alloys by Wire and Double-Pulsed Arc Additive Manufacturing

An innovative and high deposition efficiency process, the double-pulsed arc additive manufacturing process, is used to produce high-strength Al-Mg wall components. This dissertation investigates the electrical parameter acquisition, bead appearance, porosity morphology, microstructure and mechanical properties of additively manufactured high-strength Al-Mg wall components and how these are affected by the low frequency of the double-pulsed arc additive manufacturing process. Then, using this process at different low frequencies of 0, 1, 3, 5, 7 and 9 Hz, multilayer deposition experiments were performed. It can be observed that the deposit porosity is obviously eliminated compared with cold metal transfer (CMT) process. The bead appearance of the deposited aluminum wall varies clearly with low frequencies, and at a low frequency of 3 Hz, its appearance is the best of all. The optical observation of microstructure proves that the average grain size varies significantly with low frequency, and at a low frequency of 1 Hz, it is the smallest. In addition, the deposited wall showed maximum mean microhardness and maximum ultimate tensile strength at a low frequency of 3 Hz. Considering the deposited porosity and mechanical priorities, double-pulsed arc additive manufacturing with a frequency of 3 Hz is more suitable for making high-strength Al-Mg wall components than at other low frequencies.     

Microstructure and Mechanical Properties of Ti6Al4VAlloy by Laser Integrated Additive Manufacturing with Alternately Thermal/Mechanical EffectsEI北大核心CSCD

To meet the requirements of the long fatigue life and high reliability of the key components of the aeroengine as well as solve the challenges of"structure control"and"performance control"based on the fact that plastic deformation can effectively eliminate internal stress and close metallurgical defects generated by the thermal effect, a laser integrated additive manufacturing technology with alternately thermal/mechanical effects is developed. In this study, Ti6Al4V alloy was chosen as the research object. The distributions of residual stress and metallurgical defects and the microstructural evolution of the formed components were systematically studied. The effects of surface laser shock peening (LSP) and interlayer LSP without coating (LSPwC) treatments on mechanical properties were investigated using a tensile test. The results showed that after LSP, tensile residual stress was transformed into compressive residual stress. Additionally, laser shock waves could effectively improve the metallurgical defects in selective laser melting (SLM)-formed components. Moreover, high-density dislocation structures and numerous twins in two directions were produced in coarse alpha' martensite by laser shock waves, which jointly promoted the grain refinement of a' martensite. The ultimate tensile strength and elongation of Ti6Al4V fabricated by the laser integrated additive manufacturing technology with alternately thermal/mechanical effects reached 1543 MPa and 15.53%, which are 46.5% and 91.5% higher than those of the SLM-formed components, respectively, yielding a good combination of strength and ductility.     

‘Cold spray +’ as a new hybrid additive manufacturing technology: a literature review

ABSTRACT

Cold spray (CS) is a new solid state coating technique that has attracted considerable attention as it is quite suitable for mass production of metallic materials or metal matrix composites. More recently, cold spray additive manufacturing (CSAM) has been proposed to fabricate/repair components or produce welding joint. However, inherently deficient in ductility/plasticity of CSAMed materials limits its application. Therefore, many hybrid processes have been proposed to further explore CS, which can be grouped together as ‘cold spray +’ hybrid processes (laser, shot peening and friction stir processing). This review will summarise the state-of-the-art of the ‘cold spray +’ processes to show their abilities and their effectiveness. Recommendations for further research and development have been incorporated to help widespread the process.     

Residual stress development in cold sprayed Al,Cu and Ti coatings

Residual stresses play an important role in the formation and performance of thermal spray coatings. A curvature-based approach where the substrate–coating system deflection and temperature are monitored throughout the coating deposition process was used to determine residual stress formation during cold spray deposition of Al, Cu and Ti coatings. The effect of substrate material (carbon steel, stainless steel and aluminium) and substrate pre-treatment (normal grit blasting, grit blasting with the cold spray system and grinding for carbon steel substrate) were studied for all coating materials with optimized deposition parameters. Mainly compressive stresses were expected because of the nature of cold spraying, but also neutral as well as tensile stresses were formed for studied coatings. The magnitudes of the residual stresses were mainly dependent on the substrate/coating material combination, but the surface preparation was also found to have an effect on the final stress stage of the coating.     

激光能量输入对直接激光沉积莫来石陶瓷组织性能的影响

研究了激光能量密度对直接激光沉积熔体自生莫来石陶瓷孔隙/密度、微观组织和力学性能的影响.结果表明,较低激光能量密度(15 J/mm2)所制备的陶瓷样件边缘分布有尺寸较大的气孔,使得样件整体孔隙率较高,且表面粘粉严重,这与成形扫描速度大和硅酸盐熔体粘度高有关.而较高激光能量密度(90 J/mm2)虽然可以获得表面光滑、莫...     

Microstructure,mechanical and corrosion properties of electron-beam-melted and plasma-transferred arc-welded WC_P/NiBSi metal matrix composites

As one of the new additive manufacturing processes,electron beam melting(EBM)has seen its promising potential in the fabrication of metal matrix composites(MMCs)components with complex geometries.In this work,WC_P/NiBSi MMCs were fabricated by EBM and plasma-transferred arc welding(PTAW)for a comparative study.The microstructures of both samples were examined using a scanning electron microscope(SEM)equipped with an electron backscattered diffraction(EBSD)detector.The macrohardness was tested using a Rockwell hardness method(Type C),while the microhardness was measured using different loadings(0.5-1.0 N)based on different phases.The anti-abrasion performance was tested as per the ASTM G105 standard.The corrosion behavior of the MMCs was also assessed by potentiodynamic polarization.The results indicate that the EBM bulk and the PTAW cladding MMCs exhibit different microstructures due to the different local solidification conditions.This is believed to lead to the varied mechanical properties and corrosion resistance of the MMCs,and the possible mechanisms were also discussed.     

Mechanical Performance of Cold-Sprayed A357 Aluminum Alloy Coatings for Repair and Additive Manufacturing

Cold-sprayed coatings made of A357 aluminum alloy, a casting alloy widely used in aerospace, underwent set of standard tests as well as newly developed fatigue test to gain an information about potential of cold spray for repair and additive manufacturing of loaded parts. With optimal spray parameters, coating deposition on substrate with smooth surface resulted in relatively good bonding, which can be further improved by application of grit blasting on substrate’s surface. However, no enhancement of adhesion was obtained for shot-peened surface. Process temperature, which was set either to 450 or 550 °C, was shown to have an effect on adhesion and cohesion strength, but it does not influence residual stress in the coating. To assess cold spray perspectives for additive manufacturing, flat tensile specimens were machined from coating and tested in as-sprayed and heat-treated (solution treatment and aging) condition. Tensile properties of the coating after the treatment correspond to properties of the cast A357-T61 aluminum alloy. Finally, fatigue specimen was proposed to test overall performance of the coating and coating’s fatigue limit is compared to the results obtained on cast A357-T61 aluminum alloy.     

搅拌摩擦增材制造技术研究现状与发展趋势

现有的高能束增材制造技术在成形大型高性能金属构件时存在适用材料范围有限、能源利用率低以及成形件各向异性等工艺特点,搅拌摩擦增材制造是近年来发展起来的一项新型固相增材制造技术,其无液态金属熔凝过程的成形特征为铝合金、镁合金等易氧化轻质合金的高性能快速制备提供了新的增材制造途径。文中首先指出现有高性能金属构件增材制造技术应用的局限性,重点介绍搅拌摩擦增材制造技术的工艺原理、性能优势及应用现状。综述了国内外所开展的主要搅拌摩擦增材制造技术现状,包括同轴送料式、预置料式等类别,进而展示了搅拌摩擦增材制造技术在轻质大型结构件增材制造及特征结构添加,梯度材料与涂层制备,缺陷损伤修复及新型复合材料制备等方面的应用潜力。最后,对搅拌摩擦增材制造技术的发展趋势进行了展望。通过文中综述,以期推动该技术在国内航空航天等领域大型轻质材料构件的制备方面实现应用。 创新点： (1)为解决现有激光/电子束等高能束增材制造技术在轻质材料构件应用方面的局限性,文中对搅拌摩擦增材制造这一新型固相增材制造技术开展调研分析,其无液态金属熔凝的成形特性使得制件不会形成与快速凝固相关的缺陷,如孔隙率、热烈纹、元素偏析、稀释、微细分散氧化物聚集以及高残余应力,具有更高成形效率、更大成形尺寸、更优的力学性能。 (2)文中通过对搅拌摩擦增材制造技术的工艺特性与应用现状分析,总结出了该技术在轻质大型结构件增材制造、特征结构添加、梯度材料与涂层制备、缺陷损伤修复及新型复合材料制备等方面具备较大的应用潜力。     

冷喷涂增材制造关键技术

近些年来,冷喷涂技术得到快速的发展,并逐渐形成了一门新的增材制造方法。 但由于目前存在的诸多技术壁垒以及居高不下的制造成本,使得冷喷涂增材制造技术尚未得到广泛的应用。 文中从技术与应用的角度出发,对冷喷涂增材制造目前存在的一些关键技术问题以及未来发展的方向进行梳理与讨论,同时也提出了一些适用的解决方案。 目的是为促进该技术实现更高价值的制造过程,从而推动冷喷涂增材制造技术的发展。     

Utilization of Titanium Particle Impact Location to Validate a 3D Multicomponent Model for Cold Spray Additive Manufacturing

Cold spray is a solid-state rapid deposition technology in which metal powder is accelerated to supersonic speeds within a de Laval nozzle and then impacts onto the surface of a substrate. It is possible for cold spray to build thick structures, thus providing an opportunity for melt-less additive manufacturing. Image analysis of particle impact location and focused ion beam dissection of individual particles were utilized to validate a 3D multicomponent model of cold spray. Impact locations obtained using the 3D model were found to be in close agreement with the empirical data. Moreover, the 3D model revealed the particles’ velocity and temperature just before impact—parameters which are paramount for developing a full understanding of the deposition process. Further, it was found that the temperature and velocity variations in large-size particles before impact were far less than for the small-size particles. Therefore, an optimal particle temperature and velocity were identified, which gave the highest deformation after impact. The trajectory of the particles from the injection point to the moment of deposition in relation to propellant gas is visualized. This detailed information is expected to assist with the optimization of the deposition process, contributing to improved mechanical properties for additively manufactured cold spray titanium parts.