This study examines the influence of RF/DC sputtering deposition parameters on the microstructural evolution and mechanical properties of NbMoTaW high-entropy alloy (HEAs) films. HEAs films were deposited via magnetron sputtering at pressures of 0.25 Pa, 0.5 Pa, and 1.0 Pa, with varying thicknesses of 500 nm and 2000 nm. The results demonstrate that both sputtering pressures and film thicknesses significantly influence grain growth and hardness, obeying the Hall-Petch relationship. A breakdown in the Hall-Petch effect was observed at larger grain sizes, likely due to grain boundary sliding. These findings provide a comprehensive understanding of how both deposition and film thickness can be optimized to enhance the performance of NbMoTaW films.

SAC305 (96.5 wt% Sn, 3 wt% Ag, 0.5 wt%Cu) solder is increasingly becoming popular due to its reliability good characteristics and performance in addition to the environmental concerns and regulations that restrict the use of lead in nano/microelectronic products. In nano/microelectronics, manufacturing smooth solder coatings free of defects such as voids and cracks, which can compromise joint reliability is crucial. Magnetron sputtering offers a high degree of control over film thickness and composition, resulting in films with excellent uniformity and adhesion. Despite these advantages, fabricating continuous and robust SAC305 films using magnetron sputtering remains a difficult task with limited research addressing these Challenges. To address these challenges and obtain an enhanced surface morphology property, we focus on fabricating SAC305 thin films by optimizing the magnetron sputtering parameters including sputtering power and pressure, and by using various substrates. Field emission-scanning electron microscopy imaging, energy-dispersive X-ray spectroscopy, X-ray diffraction, and atomic force microscopy were used to evaluate the quality of the thin films.

To compare hardness versus strain rate data from different kinds of indentation creep test can be challenging. It is often difficult to determine whether measured differences in material response along different loading paths, such as constant load creep or load relaxation, are real or merely arise as artifacts from the analysis. We argue that the difficulty lies in how indentation strain rate is defined. For traditional definitions of strain rate, such as ε̇_h , which measures the rate of penetration, or ε̇_A , which measures the growth of indent area, material response might seem path-dependent even when it is not. We introduce a new definition of plastic strain rate, ε̇_irr , which is based on irreversible work and is well-posed in the sense that it gives the same results from different loading paths when deformation is path-independent. This property frees experimenters to isolate and explore deformation mechanisms that respond differently along different loading paths, which is useful for revealing the influences of time and strain rate on evolution of structure. ε̇_irr is important for exploring path-dependence in high-hardness/modulus (≳ 0.02) materials like ceramics and polymers. For low-hardness-modulus materials other measures of strain rate suffice.

This study presents an optimization of the process parameters for the effect of copper (Cu) donor material percentage on the friction stir welding (FSW) of AA6061-T6 alloy. Extensive factorial experiments were conducted to determine the significance of the rotational speed (ω), the transverse speed (v), the interface coefficient of friction (μ), and the Cu donor material percentage in the plunge, left, right, and downstream zones. Design Expert 13 software was used to identify the number of simulation experiments to be conducted using the Abaqus simulation software. From Design Expert 13, which is a thorough multi-objective optimization analysis software, we were able to identify ideal welding parameters such as a rotational speed of 1222 rpm, transverse speed of 1.1 mm/s, the coefficient of friction of 0.9, and a 19% donor material percentage for the plunge zone. Significant findings demonstrate that increasing the Cu donor material substantially reduced the temperature from 502 °C to 134 °C when the Cu content is increased from 0% to 50%. This integrated modeling and optimization approach provides a practical procedure to identify the best experimental parameters for the process and a new understanding to guide advances for high-quality FSW of aluminum alloys. This work offers a methodology for optimizing the FSW parameters aligned with multifaceted thermomechanical physics.

Virginia State University's Manufacturing Engineering program is surrounded by organizations from the aerospace industry and Research and Development sectors including Rolls Royce, NASA Langley Research Center, and Commonwealth Center for Advanced Manufacturing (CCAM). With support from NASA and industry, a design and manufacturing course has been created to introduce students to state-of-the-art principles of "Advanced Manufacturing Engineering for the Aerospace Industry." We use modern aircraft and industry practices as examples for students to illustrate topics of how design, aerodynamics, propulsion, structure, and performance are influenced by aerospace materials, manufacturing processes, quality systems, and industry regulations. We aim to prepare future technical specialists and/or business leaders for the aerospace industry. This paper details the process, challenges, and strategies associated with implementing this course.

Beam exit windows are crucial components of any particle accelerator as they provide an interface between the beamline vacuum and target material at atmospheric media. For high beam power machines, special materials and designs are required to withstand high radiation and mechanical loads, while minimizing energy loss during transition and maximizing window lifetime. This research investigates the impact of electron beam exposure to bulk CrMnV and CrMnTiV high entropy alloys (HEAs) with the primary goal of identifying suitable candidate materials for the design of robust and durable exit window settings. The selection criteria include intrinsic characteristics, power dissipation, and mechanical responses. According to the thermodynamic calculations, both equiatomic CrMnV and the addition of 7% of Ti with equiatomic CrMnV yield solid-solutions phases. The structural and mechanical properties of CrMnV and CrMnTiV samples were tested using field emission scanning electron microscopy, atomic force microscopy, scanning electron microcopy with energy dispersive x-ray spectroscopy, x-ray diffraction, and nanoindentation before and after exposure to a dose of ∼66 kGy from a 10 MeV e-beam accelerator. Despite exhibiting beam transmission characteristics comparable to Cr and V, the indentation hardness of HEAs exceeded that of the Cr and V samples by five to six times. The examination of the CrMnTiV irradiated samples revealed organized deformation patterns depicting new features, which we suspect twinning and twin boundaries due to the addition of Ti to CrMnV. Ti, a hexagonal-close-packed crystal structure, is commonly known for deformation twinning behavior.

This study investigates the surface morphology, mechanical properties including the strain rate sensitivity of the hardness in indentation creep, and electrical resistivity of SAC05 (96.5 %Sn-3 %Ag-0.5 %Cu) thin films sputtered onto Si and SiO2 substrates using RF and DC magnetron. Various deposition parameters, including DC and RF powers and pressures, were optimized for a continuous and robust film. Among the 16 samples analyzed, the optimal surface was obtained at RF 200 W and 0.32 Pa pressure, as confirmed by FE-SEM. Before polishing, the film exhibited a rough surface with an average grain size of similar to 1 mu m a thickness of similar to 2 mu m. Post-polishing, the film displayed a uniform 1.5 mu m thickness and a mean surface roughness (Ra) of 14.9 nm. The electrical resistivity of SAC305 on the SiO2 substrate was 19.6 mu Omega.cm, while the strain rate sensitivity, m, for SAC305 on the Si substrate was 0.12 +/- 0.02.

In this research effort, we explore the use of a donor material to help heat workpieces without wearing the tool or adding more heat than necessary to the system. The donor material would typically be a small piece (or pieces) of material, presumably of lower strength than the workpiece but with a comparable melting point. The donor, a sandwich material, is positioned between the tool head and the material to be welded, where the tool initially plunges and heats up in the same manner as the parent material that is intended for welding. The donor material heats up subsequent to tool penetration due to friction and as a result heats up the material beneath it. This preheating technique softens the harder parent material, which helps to minimize tool wear and produce better weld performance. The goal is to investigate the use of the donor material as a preheating technique that minimizes wear and tear on the tool head without negatively impacting the structural properties of the weld. To demonstrate the donor material concept, a combination of Cu-Al, Cu-1045 Carbon steel (CS), and Al-1045 CS sets of donor and parent materials were used in the simulation, in addition to control samples Al-Al and CS-CS. We simulated two thicknesses of donor material 25 and 50% of the parent material thickness, respectively. The simulation suggests that the donor material concept generates phenomenal results by reducing the temperature and axial forces for the friction stir welding of aluminum AA6061 and carbon steel 1045. It also assists downstream during welding, resulting from frictional mechanical work which is converted into stored heat.

This paper investigates the surface morphology, mechanical properties, and electrical resistivity of SAC305 thin films deposited on Si and SiO2 substrates through RF magnetron sputtering. Various deposition parameters were tested using both DC and RF power sources at different pressures and powers to produce robust continuous films. The most optimal surface morphology, with an average grain size of ~1 µm and a thickness of ~2 µm, was accomplished at a pressure of 2.4 mTorr and 200-Watt power. After polishing, a uniform thickness of 1500 nm with a mean roughness (Ra) of 14.9 nm was obtained. The samples contained polycrystalline β-Sn grains at (200) diffraction planes with a preferred orientation 2θ of 30.70°. Although the XRD pattern did not indicate any Ag peaks, weak peaks of Ag3Sn were observed at 2θ of 37.60° and 39.59°, corresponding to diffraction planes (020) and (211) respectively. The electrical resistivities of the SAC305 thin film deposited on the SiO2 substrate and of the bulk SAC305 samples were measured as 19.6 µΩ·cm and 13.7 µΩ·cm, respectively. It was noted that changes in hold time at peak loads or the rate of loading in the creep experiments did not significantly influence the creep properties of the SAC305 bulk or thin films material.

This study aims to explore the impact of e-beam irradiation on the mechanical and structural characteristics of four different polycrystalline metals (Ni, Cr, V, and Ti), in both bulk and thin film forms. Thin metal films are fabricated using magnetron sputtering. The primary goal is to identify suitable metal candidates for growing thin films, which could serve as exit windows for e-beam accelerators. This selection is based on their properties, power dissipation capabilities, and the effects of irradiation on mechanical attributes such as hardness, ductility, defect density, and strength. For the bulk polycrystalline metal samples, a series of nanoindentation tests has been conducted before and after e-beam irradiation to investigate changes in hardness and elastic modulus. Additionally, to compare performance with the bulk samples, thin metal films are subjected to the same procedure before and after irradiation, allowing for the evaluation of film hardness, moduli, and creep properties. Results indicate that irradiated bulk samples of Ni, Cr, and V become harder, whereas Ti experiences softening. There is no significant irradiation effect on modulus for all for polycrystalline metal samples. To understand the underlying reasons behind these effects, both the fabricated metal films and bulk metal samples undergo comprehensive characterization tests for their microstructural properties, elastic behavior, and chemical composition. This involves the utilization of SEM with EDS, FESEM and AFM to analyze microstructure and surface attributes of the films, followed by X-ray diffraction to gain insight into film morphology and lattice orientation.

In this study, the influence of post weld heat treatment (PWHT) on the microstructure and mechanical properties of a copper (Cu) donor material assisted friction stir welding (FSW) of AA6061-T6 aluminum alloy has been investigated. Cu assisted FSW joints of AA6061-T6 alloy were prepared at an optimized constant tool rotational rate of 1400 rpm and welding speed at 1 mm/s. The Cu donor material of 20% thickness with respect to the workpiece thickness was selected to assist the FSW joining at the plunge stage. FSWed AA6061-T6 samples were prepared using solid solution treatment at 540 °C for 1 hour followed by quenching in water at room temperature. It was then artificially aged at 180 °C for 6 hours and 24 hours followed by air cooling. The microstructure and tensile fractured surfaces were analyzed using scanning electron microscope and optical microscope. The microstructure depicts an additional grain refinement in the stir zone (SZ) due to the occurrence of recovery and recrystallization with increasing aging time. Vickers micro hardness indicates a softening effect due to the dissolution of hardening precipitates. Hardness recovery is most likely attributed to the uniform distribution of fine hardening precipitates at all aging time levels. The maximum hardness was 92.5 HV at the SZ and the tensile properties were significantly improved by 20 % after solution heat treated at 540 °C for 1 hour followed by artificial aging at 180 °C for 24 hours.

This research investigation focuses on copper (Cu) donor material assisted friction stir welding (FSW) of AA2024-T4 and AA6061-T6 plates of 6.35 mm thickness. FSW joints were prepared at optimized process parameters of 1400 rpm and welding speeds of 1, 2, or 3 mm/s. The Cu donor material of 25% and 50% thickness with respect to the workpiece thickness were selected to assist the FSW joining during the plunge stage. The downward force generated in the FSW process was gradually decreased after introducing the Cu donor material because more heat was produced in the donor material and conducted to the base plate. The temperature profiles that the inclusion of the Cu donor material increased the temperature at the beginning of the welding process. The welded joints were characterized in terms of the micro-hardness and tensile properties. Defect-free joints could be obtained when placing high strength AA2024 alloy at the advancing side of the weld with 25% thick donor material. From the hardness profiles, it is observed that the hardness decreases from the base metal of AA 2024 to the center of the weld followed by thermomechanical affected zone (TMAZ) and the heat affected zone (HAZ). The hardness measurements are lower in the TMAZ and HAZ where tensile failure occurs. The maximum tensile strength improved by 130% with 25% Cu donor material as compared to the as welded samples. SEM Fractography images confirmed mixed modes of brittle and ductile fracture surfaces with tearing ridges and finer dimples after the inclusion of donor material in FSW.

In this research, magnetron sputtering is employed to fabricate thin films of high entropy alloys. The target materials are derived from VCrMn and VCrMnTi systems. The focus is to pinpoint suitable candidates for robust and long-lasting beam exit windows in e-beam accelerators. The selection process considers their inherent characteristics, their capacity to dissipate power, and how they respond to irradiation in terms of mechanical traits like hardness, ductility, defect density, and strength. For the bulk alloy samples of VCrMn and VCrMnTi, a sequence of nanoindentation tests has been executed to evaluate hardness and elastic modulus. The outcomes reveal that both the hardness and modulus are notably greater than those of any individual metal samples. It is anticipated that fabricated alloy films with same compositions will exhibit robust qualities in terms of mechanical properties, including ductility, defect density, and strength. The incorporation of additional titanium (Ti) alloying elements into the high entropy alloys (HEAs) of VCrMn is projected to enhance electron transmission. The fabricated films have undergone thorough analysis and testing to comprehend their microstructural attributes and chemical composition which involves the utilization of SEM with EDS, FESEM, AFM to investigate microstructural and surface properties of the films. Subsequently, X-ray diffraction has been employed to acquire insights into the morphology and lattice orientation of the films.

Friction stir welding of high-strength materials such as steels is the impeded by the lack of the vast heat input needed to start the process. Contact friction is considered the most dominant source of heat generation for FSW steels which tends to cause severe wear conditions of the tool hear. To relieve the extreme wear conditions that occur on the tool heads because of FSW steels, we introduce the non-mixing Cu donor stir material to friction stir welding of aluminum alloys. The elastic properties of the Cu donor assisted friction stir welded aluminum alloys are measured using nanoindentation. The hardness and elastic modulus were measured for two regions, the base metal (BM) and the stir zone (SZ). The measurements were conducted for 20% and 60% Cu non-heat treated (NHT) and heat-treated (HT) samples. The nanomechanical properties were measured using nanoindentation with the continuous stiffness method (CSM) in depth control. The HT samples are softer than the NHT samples as expected. However, the 20% Cu NHT and HT samples depicted the same hardness at the SZ. Similar results were observed for the 60% Cu donor stir samples. It therefore concluded that the SZ is softer than the BM for the 20% and 60% Cu donor stir material as expected. The hardness of the weld at the SZ is similar to the hardness of the Al6061-T6 plate, suggesting that the Cu donor stir material did not impact the hardness properties of the Al6061-T6 plate due to the depletion of the Cu donor stir material during the welding process, an important result of the concept of the donor material. The elastic moduli of the Cu donor stir welded samples vary between 75~85 GPa at a depth of indentation of ~4600 nm , which are different from the elastic moduli of Cu 110 ( 117.2 GPa ) and similar to the elastic modulus of aluminum alloys ( 68.9 GPa ), an important outcome.

This paper investigates the surface morphology, mechanical properties, and electrical resistivity of 96.5Sn–3.0Ag–0.5Cu (SAC305) thin films deposited on Si and SiO2 substrates through RF magnetron sputtering. Various deposition parameters were tested using both DC and RF power sources at different pressures and powers to produce robust continuous films. The most optimal surface morphology, with an average grain size of ∼1 μm and a thickness of ∼2.2 μm, was accomplished at a pressure of 2.4 mTorr and 200 W power. After polishing, a uniform thickness of 1800 nm with a mean roughness (Ra) of 14.9 nm was obtained. The samples contained polycrystalline β-Sn grains at (200) diffraction planes with a preferred orientation 2θ of 30.70°. Although the XRD pattern did not indicate any Ag peaks, weak peaks of Ag3Sn were observed at 2θ of 37.60° and 39.59°, corresponding to diffraction planes (020) and (211), respectively. The electrical resistivity of the SAC305 thin film deposited on the SiO2 substrate and of the bulk SAC305 samples were measured as 19.6 and 13.7 μΩ cm, respectively. It was noted that changes in hold time at peak loads or the rate of loading in the creep experiments did not significantly influence the creep properties of the SAC305 bulk or thin film material.

Electronic packaging industries are in an ongoing transition to lead free soldering due to the adverse effect on environment and human health [1]. Sn-Ag-Cu (SAC) have been recognized as promising alternatives due to its low eutectic temperature, higher wettability and strength, superior resistance to creep and thermal fatigue. Surface roughness has a significant influence on mechanical parameters determined nanoindentation tests. Although research has been conducted to analyze the mechanical properties of bulk SAC material, there have been limited prior studies on SAC thin films and their mechanical properties since fabricating a smooth SAC thin film is a fundamental challenge. SAC thin films with four different Sn–Ag–Cu ternary eutectic composition: 96.5Sn-3.0Ag-0.5Cu, 95.5Sn-3.8Ag–0.7Cu, 95.5Sn-3.9Ag–0.6Cu & Sn-4.0Ag–0.5Cu will be deposited using RF magnetron sputtering with different deposition rates and annealed at various temperature to fabricate a smooth continuous film. Figures 1 and 2 depict SAC05 deposited using RF magnetron sputtering at Figure 1: SEM image of SAC-05 surface at 10,000X. 20W, 2.4 mTorr pressure, and argon flow flow rate of 20.5 sccm. Surface morphology will be examined using Field emission Scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Crystallinity of the deposited film will be examined using X-ray diffraction (XRD). Mechanical properties will be studied using nanoindentation [2]. Properties of the thin film will be compared with the bulk material with similar eutectic composition. References M. Abtew G. Selvaduray. (2000). Lead-free Solders in Microelectronics. Materials Science & Engineering. a Review Journal., 27(5-6), 95. Long, X., Wang, S., Feng, Y., Yao, Y., & Keer, L. M. (2017). Annealing Effect on Residual Stress of Sn-3.0Ag-0.5Cu Solder Measured by Nanoindentation and Constitutive Experiments. Materials Science and Engineering: A, 696, 90-95. Figure 1

In this research, copper (Cu) donor material-assisted friction stir welding (FSW) of AA6061-T6 alloy was studied. Cu-assisted FSW joints of AA6061-T6 alloy were prepared at a constant tool rotational rate of 1400 rpm and various welding speeds at 1 mm/s and 3 mm/s. The Cu donor material of different thickness (i.e., 20%, 40%, and 60%) with respect to the workpiece thickness was selected to assist the FSW joining at the plunge stage. It is observed that the downward force generated in the FSW process was gradually decreased after introducing Cu donor material with incremental thicknesses with respect to workpiece at the plunge stage. Post-weld analysis was characterized in terms of microstructure and mechanical properties. The results of microstructure analysis at the stir zone (SZ) show the formation of finer grains due to dynamic recrystallization and plastic deformation. Micro-hardness tests reveal that the hardness decreased from the base metal (BM) to the SZ across the heat-affected zone (HAZ) and thermo-mechanically affected zone (TMAZ). The lowest value of hardness appeared in the TMAZ and HAZ where tensile failure occurs. With increasing welding speed, the average hardness in the SZ decreased due to lower heat input and faster cooling rate. Tensile test plots show no significant change in ultimate tensile strength with or without Cu donor material. Fractography of tensile tested samples shows both ductile and brittle like structure for given welding parameters. This proposed work of FSW with Cu donor material is promising to increase tool life due to the decrement of the downforce during plunge and throughout the welding stage. Meanwhile, the inclusion of donor material did not compromise the weld quality in terms of the mechanical properties and micro-hardness.

High Entropy Alloys (HEAs) and Refractory High-Entropy Alloys (RHEAs) are novel potential materials for high-temperature applications [1]. NbMoTaW, a RHEAs, such as the one in Fig. 1, possess superior mechanical properties, combining high strength, outstanding thermal stability, and resistance to softening at high temperatures [2]. The influence of adding Vanadium [3], Tantalum [4], and Rhenium [5] to NbMoTaW alloys on the bulk mechanical behavior was investigated by the previous studies. In this research, the effect of adding Rhenium with different (R e0 , Re 0.5 , R e1 ) on the microstructure and the mechanical properties of NbMoTaW thin films will be nvestigated. The larger the enthalpy of mixing in negative values, the higher the binding force between the elements, which has been enhanced with Rhenium addition. As for the entropy of mixing, it increased from 11.53 to 13.38 for R e0 and R e1 , respectively. The higher the mixture entropy suggests a more stable solid solution. This is confirmed by calculating the thermodynamic parameters proposed by Yang et. Al [6] where they suggested that a mixture with δ < 6.6 and Ω > 1.1 correspond to solid solution formation. The anticipated crystal structure for the three samples is BCC structure according to the valence electron concentration (VEC) theory, where the VEC values were less than 6.87 as suggested by Gou et. Al [7]. The RexNbMoTaW HEAs thin films are fabricated using RF magnetron sputtering. The film thickness, deposition power, and temperature impact on the films’ characteristics are studied. Field emission (FE-SEM), X-ray diffraction (XRD), and nanoindentation are used to investigate the RexNbMoTaW thin films’ crystal structure, surface morphology, and mechanical properties. The mechanical properties of the thin films will be compared with their counterpart bulk materials. References Kim, H., et al., International Journal of Refractory Metals and Hard Materials, 2019. 80: p. 286-291. Feng, X., et al., Materials Letters, 2018. 210: p. 84-87. Senkov, O.N., et al., Intermetallics, 2011. 19(5): p. 698-706. Han, Z.D., et al., Materials Science and Engineering: A, 2018. 712: p. 380-385. Zhang, J., et al., Journal of Alloys and Compounds, 2020. 827. Yang, X. and Y. Zhang, Materials Chemistry and Physics, 2012. 132(2-3): p. 233-238. Guo, S., et al., Journal of Applied Physics, 2011. 109(10): p. 103505. Figure 1

The choice of a material and the engineering design that is intended to lead to a beam exit window capable of sustaining mechanical and thermal loads in a high-radiation environment, while minimizing the beam loss and maximizing the window lifetime is discussed. Thin titanium windows have been typically used in industrial accelerators in the tens of kW beam power [1]. The focus of this research is to conduct fundamental studies related to the choice of a material, from a material science point of view, for MW-class beam exit windows and an engineering design, including parameters such as the window size, thickness, and cooling scheme, suitable for industrial accelerators. CrMnV and CrMnTiV HEAs were selected for this study. According to Yang et al., [2], 1.1 and 6.6% should be expected as the criteria for forming high entropy stabilized solid solution phases. The two parameters of the CrMnV and CrMnTiV alloys are and respectively. Therefore, the two alloys are expected to be solid solution. The mechanical properties of CrMnV and CrMnTiV solid solution HEAs exit window prior to E-beam irradiation were measured using nanoindentation. The nanoindentation testing was carried out using XP Nanoindenter tester equipped with a three-sided diamond Berkovich indenter tip with maximum displacement of 2000 nm. The hardness is measured as 5.2 and 6.1 GPa for the bulk CrMnV and CrMnTiV solid solution HEAs at a depth of indentation of 900 nm respectively, Fig. 1. We also observe that both solid solution CrMnV and CrMnTiV HEAs depict indentation size effect. References Chmielewski A.G., Zimek, Z., Panta P., Drabik W., Radiat. Phys. Chem. 45 1029 (1995). Yang, X. and Y. Zhang, Prediction of high-entropy stabilized solid-solution in multi-component alloys. Materials Chemistry and Physics, 2012. 132 (2-3): p. 233-238. Figure 1