Get Involved: Charles Ward,Integrating Materials and Manufacturing Innovation

End Notes

Get Involved: Charles Ward, Integrating Materials and Manufacturing Innovation     

Machinability of Al 6061 Deposited with Cold Spray Additive Manufacturing

Additive manufacturing techniques such as cold spray are translating from research laboratories into more mainstream high-end production systems. Similar to many additive processes, finishing still depends on removal processes. This research presents the results from investigations into aspects of the machinability of aluminum 6061 tubes manufactured with cold spray. Through the analysis of cutting forces and observations on chip formation and surface morphology, the effect of cutting speed, feed rate, and heat treatment was quantified, for both cold-sprayed and bulk aluminum 6061. High-speed video of chip formation shows changes in chip form for varying material and heat treatment, which is supported by the force data and quantitative imaging of the machined surface. The results shown in this paper demonstrate that parameters involved in cold spray directly impact on machinability and therefore have implications for machining parameters and strategy.     

Assessing Reliability of Cold Spray Sputter Targets in Photovoltaic Manufacturing

Cold spray has been used to manufacture more than 800 Cu-In-Ga (CIG) sputter targets for deposition of high-efficiency photovoltaic thin films. It is a preferred technique since it enables high deposit purity and transfer of non-equilibrium alloy states to the target material. In this work, an integrated approach to reliability assessment of such targets with deposit weight in excess of 50 lb. is undertaken, involving thermal-mechanical characterization of the material in as-deposited condition, characterization of the interface adhesion on cylindrical substrate in as-deposited condition, and developing means to assess target integrity under thermal-mechanical loads during the physical vapor deposition (PVD) sputtering process. Mechanical characterization of cold spray deposited CIG alloy is accomplished through the use of indentation testing and adaptation of Brazilian disk test. A custom lever test was developed to characterize adhesion along the cylindrical interface between the CIG deposit and cylindrical substrate, overcoming limitations of current standards. A cohesive zone model for crack initiation and propagation at the deposit interface is developed and validated using the lever test and later used to simulate the potential catastrophic target failure in the PVD process. It is shown that this approach enables reliability assessment of sputter targets and improves robustness.     

In Situ Monitoring of Particle Consolidation During Low Pressure Cold Spray by Ultrasonic Techniques

This study attempts to test the viability of the examination of the cold spray process using acoustic methods, specifically in situ testing during the actual spray process itself. Multiple composites studied by flat and multi-channel transducers as well as the results of actual online measurements are presented. It is shown that the final thickness as well as the dynamics of buildup can be evaluated (including plotting rates of buildup). Cross sections of the coating thickness are also easy to obtain and show true profiles of the coating. The data can also be used to generate real estimates for nozzle speed and spray diameter. Finally, comparisons of real thickness and acoustically estimated thickness show a close linear relationship. The data clearly show that online acoustic measurement is a viable method for estimating thickness buildup.     

AgSnO2触点涂层的组织与性能

采用高能球磨方法制备Ag-SnO₂复合粉末,将球磨粉末冷喷涂到铜基板上,能够获得几毫米厚度的较致密的AgSnO₂触点涂层。850 ℃退火后涂层发生进一步致密化并且在原始粉末颗粒边界形成富银区,涂层材料硬度略为降低。电弧侵蚀和电接触试验表明,冷喷涂的AgSnO₂涂层材料具有低而稳定的接触电阻,能够满足触点的基本性能要求。     

Cold Spray Deposition of Freestanding Inconel Samples and Comparative Analysis with Selective Laser Melting

Cold spray offers the possibility of obtaining almost zero-porosity buildups with no theoretical limit to the thickness. Moreover, cold spray can eliminate particle melting, evaporation, crystallization, grain growth, unwanted oxidation, undesirable phases and thermally induced tensile residual stresses. Such characteristics can boost its potential to be used as an additive manufacturing technique. Indeed, deposition via cold spray is recently finding its path toward fabrication of freeform components since it can address the common challenges of powder-bed additive manufacturing techniques including major size constraints, deposition rate limitations and high process temperature. Herein, we prepared nickel-based superalloy Inconel 718 samples with cold spray technique and compared them with similar samples fabricated by selective laser melting method. The samples fabricated using both methods were characterized in terms of mechanical strength, microstructural and porosity characteristics, Vickers microhardness and residual stresses distribution. Different heat treatment cycles were applied to the cold-sprayed samples in order to enhance their mechanical characteristics. The obtained data confirm that cold spray technique can be used as a complementary additive manufacturing method for fabrication of high-quality freestanding components where higher deposition rate, larger final size and lower fabrication temperatures are desired.     

Deposition of multicomponent coatings by Cold Spray

Cold Spray multicomponent coatings are deposited by a new powder injection method that consists of separate injection of each component of the powder mixture into a different zone of the carrier gas stream. Temperature and velocity of 10-40 µm-sized aluminium and copper particles at the nozzle outlet are calculated. It is shown that these values depend considerably on the location of the point where the powder was injected into the gas stream. The method is experimentally validated by producing a composite aluminium-copper coating.     

Metallization of Various Polymers by Cold Spray

Previous results have shown that metallic coatings can be successfully cold sprayed onto polymeric substrates. This paper studies the cold sprayability of various metal powders on different polymeric substrates. Five different substrates were used, including carbon fiber reinforced polymer (CFRP), acrylonitrile butadiene styrene (ABS), polyether ether ketone (PEEK), polyethylenimine (PEI); mild steel was also used as a benchmark substrate. The CFRP used in this work has a thermosetting matrix, and the ABS, PEEK and PEI are all thermoplastic polymers, with different glass transition temperatures as well as a number of distinct mechanical properties. Three metal powders, tin, copper and iron, were cold sprayed with both a low-pressure system and a high-pressure system at various conditions. In general, cold spray on the thermoplastic polymers rendered more positive results than the thermosetting polymers, due to the local thermal softening mechanism in the thermoplastics. Thick copper coatings were successfully deposited on PEEK and PEI. Based on the results, a method is proposed to determine the feasibility and deposition window of cold spraying specific metal powder/polymeric substrate combinations.     

Microstructure and Mechanical Properties of Ti-Ta Composites Prepared Through Cold Spray Additive Manufacturing

In this study, an innovative approach was used to fabricate Ti-Ta composite biomaterials through cold spray additive manufacturing followed by a diffusion treatment. The microstructure and mechanical properties of the composites were investigated in detail using field emission scanning electron microscopy, electron backscatter diffraction, 3D X-ray computed tomography, tensile test, nanohardness test and resonance vibration test. The obtained results indicated that the prepared composites have inhomogeneity in their microstructure and composition. A unique microstructure, composed of Ti-rich, Ta-rich and diffusion regions, was evolved in the composites due to incomplete diffusion between Ti and Ta splats. Further, Kirkendall pores were formed in the composites due to uneven diffusion of the two phases (of Ti and Ta) during high-temperature heat treatment. The prepared composites simultaneously showed low elastic modulus and high tensile strength which is required for a good biomaterial. Low elastic modulus was associated with the residual pores and the alloying effect of Ta in Ti, while high tensile strength was related to the solid solution strengthening effects. The obtained results indicated that the prepared Ti-Ta composites have a great potential to become a new candidate for biomedical applications.     

Influence of Spray Materials and Their Surface Oxidation on the Critical Velocity in Cold Spraying

The critical velocity is an important parameter in cold spraying, which determines the deposition efficiency under a given spray condition. The critical velocity depends not only on materials types, but also on particle temperature and oxidation conditions. In the present paper, three types of materials including copper, 316L stainless steel, Monel alloy were used to deposit coatings by cold spraying. The critical velocities of spray materials were determined using a novel measurement method. The oxygen content in the three powders was changed by isothermal oxidation at ambient atmosphere. The effect of oxygen content on the critical velocity was examined. It was found that the critical velocity in cold spray was significantly influenced by particle oxidation condition besides materials properties. The critical velocity of Cu particles changed from about 300 m/s to over 610 m/s with the change of oxygen content in powder. It is evident that the materials properties influence the critical velocity more remarkable at low oxygen content than at high oxygen content. The results suggest that with a severely oxidized powder the critical velocity tends to be dominated by oxide on the powder surface rather than materials properties.     

Mechanical Characteristics of Al-Co-Ce Coatings Produced by the Cold Spray Process

Gas atomized feedstock particles of an Al-13Co-26Ce alloy system were sprayed using the Cold Spray deposition technique. The microstructures of the coatings produced are examined and the mechanical characteristics, in particular the bending fatigue and the bond strength, of the Al-Co-Ce coatings are reported. The results show that the Al-Co-Ce coatings improved the fatigue behavior of AA 2024-T3 specimens when compared to uncoated and Alclad specimens. During the bond strength tests, the bonding agent failed and no delamination of the coating from the substrate occurred. The microstructural features of the feedstock powder were also found in the coatings. It is suggested that the increase in the fatigue properties of the specimens can be attributed to the residual compressive stresses induced in the coatings and to the high adhesion strength of the coatings to the substrates. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Phase Stability of Al-5Fe-V-Si Coatings Produced by Cold Gas Dynamic Spray Process Using Rapidly Solidified Feedstock Materials

In this study, aluminum alloy Al-5Fe-V-Si (in wt.%) feedstock powder, produced by rapid solidification (RS) using the gas atomization process, was selected to produce high-temperature resistant Al-alloy coatings using the cold gas dynamic spraying process (CGDS). The alloy composition was chosen for its mechanical properties at elevated temperature for potential applications in internal-combustion (IC) engines. The CGDS spray process was selected due to its relatively low operating temperature, thus preventing significant heating of the particles during spraying and as such allowing the original phases of the feedstock powder to be preserved within the coatings. The microstructure and phases stability was investigated by means of Scanning Electron Microscopy, transmission electron microscopy, X-ray diffraction and differential scanning calorimetery techniques. The coatings mechanical properties were evaluated through bond strength and microhardness testing. The study revealed the conservation of the complex microstructure of the rapid solidified powder during the spray process. Four distinct microstructures were observed as well as two different phases, namely a Al₁₃(Fe,V)₃Si silicide phase and a metastable (Al,Si) _x (Fe,V) Micro-quasicrystalline Icosahedral (MI) phase. Aging of the coating samples was performed and confirmed that the phase transformation of the metastable phases and coarsening of the nanosized precipitates will occurs at around 400 °C. The metastable MI phase was determined to be thermally stable up to 390 °C, after which a phase transformation to silicide starts to occur.     

Numerical Analysis of Cold Spray Particles Impacting Behavior by the Eulerian Method: A Review

Numerical simulations have been widely used to study particles impacting behavior in cold spraying. Among the used simulation methods, the Eulerian frame becomes increasingly attractive for its absence of mesh distortion which happens in the Lagrangian frame. It has been proved that particle deformation behaviors upon impacting calculated by the Eulerian method are well comparable to the experimental observations. In this review article, the literature on modeling particle impacting by the Eulerian method was summarized. In the second part, the Eulerian method was detailedly introduced. In the third part, the particle/substrate impacting behavior, and its influencing factors, i.e., mesh resolution, particle impacting velocity, preheating (particle or/and substrate) and oxide film, were summarized. Additionally, the prediction of critical velocity and residual stresses by using the Eulerian method was also discussed in detail. Finally, the current issues, problems and prospects existing in the Eulerian simulations of particle impacting were explored.     

冷喷涂纳米结构NiCrAlY涂层在氩气气氛中的氧化行为

采用冷喷涂方法在镍基高温合金基体(Incone1738)上沉积纳米结构NiCrAIY涂层,通过扫描电镜与能谱分析、X射线衍射,研究了在Ar气氛下热处理温度对氧化膜组织结构及成分的影响.结果表明,在Ar气氛下,经900℃处理后,涂层表面局部生成针状θ～Al2O3.在1000℃以上热处理后,涂层表面生成的球状的α-Al2O3,氧化膜均匀连续覆盖在涂层表面,但局部较厚的氧化膜呈现双层结构,外层为Cr2O3或尖晶石氧化物,内层为α-Al2O3且连续均匀.     

熔融金属喷射沉积技术的发展与应用

喷射沉积是１种快速凝固材料制备新技术。本文叙述该技术的产生及应用发展和原理。在贵金属材料领域将有重要的应用 。     

Novel Method of Aluminum to Copper Bonding by Cold Spray

Cold spray bonding (CSB) has been proposed as a new method for joining aluminum and copper. At high speeds, solid Al particles impacted the groove between the two substrates to form a bond between Al and Cu. Compared to traditional welding technologies, CSB does not form distinct intermetallic compounds. Large stainless steel particles were introduced into the spray powders as in situ shot peen particles to create a dense Al deposit and to improve the bond strength of joints. It was discovered that introducing shot peen particles significantly improved the flattening ratio of the deposited Al particles. Increasing the proportion of shot peen particles from 0 to 70 vol.% decreased the porosity of the deposits from 12.4 to 0.2%, while the shear strength of joints significantly increased. The tensile test results of the Al-Cu joints demonstrated that cracks were initiated at the interface between the Al and the deposit. The average tensile strength was 71.4 MPa and could reach 81% of the tensile strength of pure Al.     

Velocity of the Particles Accelerated by a Cold Spray Micronozzle: Experimental Measurements and Numerical Simulation

In the current study, velocities of aluminum, zinc, and copper particles accelerated in an axisymmetric cold spray micronozzle are numerically simulated and experimentally measured. It is found that aluminum and zinc particles can be accelerated to velocities close to the critical values in a supersonic nozzle with 1-mm exit diameter, 0.5-mm throat diameter, and 20-mm length when helium is used as the process gas. The diameter of the particle jet delivered by the micronozzle does not exceed 1.3 mm for any of the types of the tested powders.