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1. Nondestructive Evaluation of Additively Manufactured Metal Components with an Eddy Current Technique

   B. Schneider, B ; Shoaib, M ; Taheri, H ; Koester, L ; Bigelow, T ; Bond, L ( January 2018 , ASNT 27th Research Symposium Proceedings)

   The ability of Additive Manufacturing (AM) processes to ensure delivery of high quality metal-based components is somewhat limited by insufficient inspection capabilities. The inspection of AM parts presents particular challenges due to the design flexibility that the fabrication method affords. The nondestructive evaluation (NDE) methods employed need to be selected based on the material properties, type of possible defects, and geometry of the parts. Electromagnetic method, in particular Eddy Current (EC), is proposed for the inspections. This evaluation of EC inspection considers surface and near-surface defects in a stainless steel (SS) 17 4 PH additively manufactured sample and a SS 17 4 PH annealed plates manufactured traditionally (reference sample). The surfaces of the samples were polished using 1 micron polishing Alumina grit to achieve a mirror like surface finish. 1.02 mm (0.04”), 0.508 mm (0.02”) and 0.203 mm (0.008”) deep Electronic Discharge Machining (EDM) notches were created on the polished surface of the samples. Lift off and defect responses for both additive and reference samples were obtained using a VMEC-1 commercial instrument and a 500 kHz absolute probe. The inspection results as well as conductivity assessments for the AM sample in terms of the impedance plane signature were compared to response of similar features in the reference sample. Direct measurement of electromagnetic properties of the AM samples is required for precise inspection of the parts. Results show that quantitative comparison of the AM and traditional materials help for the development of EC technology for inspection of additively manufactured metal parts. 

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2. Effects of Printing Layer Orientation on the High-Frequency Bending-Fatigue Life and Tensile Strength of Additively Manufactured 17-4 PH Stainless Steel

   https://doi.org/10.3390/ma16020469  

   Ghadimi, Hamed ; Jirandehi, Arash P. ; Nemati, Saber ; Ding, Huan ; Garbie, Abdelrahman ; Raush, Jonathan ; Zeng, Congyuan ; Guo, Shengmin ( January 2023 , Materials)

   In this paper, small blocks of 17-4 PH stainless steel were manufactured via extrusion-based bound powder extrusion (BPE)/atomic diffusion additive manufacturing (ADAM) technology in two different orientations. Ultrasonic bending-fatigue and uniaxial tensile tests were carried out on the test specimens prepared from the AM blocks. Specifically, a recently-introduced small-size specimen design is employed to carry out time-efficient fatigue tests. Based on the results of the testing, the stress–life (S-N) curves were created in the very high-cycle fatigue (VHCF) regime. The effects of the printing orientation on the fatigue life and tensile strength were discussed, supported by fractography taken from the specimens’ fracture surfaces. The findings of the tensile test and the fatigue test revealed that vertically-oriented test specimens had lower ductility and a shorter fatigue life than their horizontally-oriented counterparts. The resulting S-N curves were also compared against existing data in the open literature. It is concluded that the large-sized pores (which originated from the extrusion process) along the track boundaries strongly affect the fatigue life and elongation of the AM parts. 

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3. Fatigue Behavior and Cyclic Deformation of Additive Manufactured NiTi

   https://doi.org/10.1016/j.jmatprotec.2017.10.006  

   Bagheri, A. ; Mahtabi, M.J. ; Shamsaei, N. ( October 2017 , Journal of materials processing technology)

   The aim of this study is to experimentally investigate the fatigue behavior of additively manufactured (AM) NiTi (i.e. Nitinol) specimens and compare the results to the wrought material. Additive manufacturing is a technique in which components are fabricated in a layer-by-layer additive process using a sliced CAD model based on the desired geometry. NiTi rods were fabricated in this study using Laser Engineered Net Shaping (LENS), a Direct Laser Deposition (DLD) AM technique. Due to the high plateau stress of the as-fabricated NiTi, all the AM specimens were heat-treated to reduce their plateau stress, close to the one for the wrought material. Two different heat treatment processes, resulting in different stress plateaus, were employed to be able to compare the results in stress- and strain-based fatigue analysis. Straincontrolled constant amplitude pulsating fatigue experiments were conducted on heat-treated AM NiTi specimens at room temperature (~24°C) to investigate their cyclic deformation and fatigue behavior. Fatigue lives of AM NiTi specimens were observed to be shorter than wrought material specifically in the high cycle fatigue regime. Fractography of the fracture surface of fatigue specimens using Scanning Electron Microscopy (SEM) revealed the presence of microstructural defects such as voids, resulting from entrapped gas or lack of fusion and serving as crack initiation sites, to be the main reason for the shorter fatigue lives of AM NiTi specimens. However, the maximum stress level found to be the most influential factor in the fatigue behavior of superelastic NiTi. 

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4. Life Prediction for Directed Energy Deposition‐Manufactured 316L Stainless Steel using a Coupled Crystal Plasticity–Machine Learning Framework

   https://doi.org/10.1002/adem.202201429  

   Ye, Wenye ; Zhang, Xing ; Hohl, Jake ; Liao, Yiliang ; Mushongera, Leslie T. ( March 2023 , Advanced Engineering Materials)

   Additively manufactured stainless steels have become increasingly popular due to their desirable properties, but their mechanical behavior in structural parts is not yet fully understood. Specifically, the impact of columnar microstructures on fatigue behavior is still unclear. A typical directed energy deposition (DED)‐fabricated 316L stainless steel microstructure consists of distinct zones with equiaxed and columnar grains. To answer the question of how these zones of a DED‐fabricated 316L stainless steel microstructure affect the local mechanical behavior individually, such as the fatigue strength, stress/strain distribution, and fatigue life, crystal plasticity simulations are conducted to investigate the influence of microstructure on local mechanical behavior such as fatigue strength, stress/strain distribution, and fatigue life. The simulations find that columnar microstructures exhibit better fatigue strength than equiaxed structures when the load is parallel to the major axis of the columnar grains, but the strength decreases when the load is perpendicular. This study also uses machine learning to predict fatigue life, which shows good agreement with crystal plasticity modeling. The study suggests that the combined crystal plasticity–machine learning approach is an effective way to predict the fatigue behavior of additively manufactured components.

    

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5. Characterization of Additively Manufactured Metals from ADDERE Printing

   Foster, J. ; Kumpaty, S. ; Coen, L. ; Perkins, A. ; Gengler, M. ; Woida, S. ( November 2022 , ASME International Mechanical Engineering Congress and Exposition)

   IMECE2022-88299 Midwest Engineered Systems Inc. has created a novel laser wire metal deposition process, ADDere manufacturing. ADDere has a much higher deposition rate than powder bed fusion, making it ideal for large components. In this project, the mechanical properties of ADDere printed materials were tested and compared to typical values found in ASM publications to show the quality of materials manufactured by the ADDere printing process. A detailed material analysis was performed on samples made from Ti-6Al-4V and 17-4 PH stainless steel. This work builds upon an earlier study of samples made from 17-4 PH that were produced using a single direction pattern. In this project, the 17-4 PH samples were printed in a cross hatched pattern, and testing results were compared to existing data from single direction samples of the previous research. The Ti-6Al-4V samples were created in two builds. One using the uni-directional method and the other with the crossed pattern. Testing specimens were removed from the samples using a water jet cutter and further machined into ASTM tensile bars and metallurgic mounts to perform a thorough material evaluation. The Ti-6Al-4V sample met the expected values in the ASM literature, and the cross hatched 17-4 PH exhibited a higher hardness and better microstructure than the single direction samples from the previous work. It was also observed that when the Ti64 samples were manufactured in the cross hatched pattern, the properties indicated slight improvement and more homogeneity than those printed in single layer direction. The obtained results indicate that ADDere’s printing process can produce highly refined materials that are customizable with their expected uses. This work showcases an excellent industry collaboration of an undergraduate research experience. 

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