Additive Friction Stir Research Articles

Additive friction stir deposition of SS316: Effect of process parameters on microstructure evolution

Solid state nature of additive friction stir deposition (AFSD) additive manufacturing process is very advantageous in terms of defect formation and microstructural refinement in the material. Current study presents the process optimization, microstructural evolution and kinetics of recrystallization for AFSD deposited low stacking fault energy material - SS316. As deposited microstructure shows equiaxed ultra fine grains with an average grain size of ~5.0 ± 0.5 μm. Shear deformation at high temperature during processing leads to the operation of restoration mechanisms. Observation of necklace type microstructure in the as deposited SS316 is attributed to discontinuous dynamic recrystallization during processing. Recrystallization kinetics of the AFSD SS316 is characterized using Johnson-Mehl-Avarami-Kolmogorov (JMAK) model. Deformation – thermal cycling during AFSD process resulted in inconsistent recrystallization kinetics. Variation in strain, strain rate and temperature during processing with processing parameters result in varying microstructure and tool wear. High strength-ductility combination and sustained work hardening in as deposited SS316 appear to arise from transformation and twinning during deformation, leading to the formation of hierarchical twins and martensitic phase after deformation. • A high strength and work hardening alloy – SS316 is additively manufactured using a novel additive friction stir deposition. • Porosity free builds with fine equiaxed grain structure is formed in as deposited material as a result of discontinues dynamic recrystallization during processing. • Microstructure of the deposited material and the tool wear during processing varied with variation in the process parameters. • Activation of twining and transformation during deformation resulted in excellent tensile properties with yield strength of 415 ± 10 MPa and ductility 75 ± 5% in as deposited material.

Ballistic Evaluation of Aluminum Alloy (AA) 7075 Plate Repaired by Additive Friction Stir Deposition Using AA7075 Feedstock

In this work, Additive Friction Stir Deposition (AFSD) was employed for ballistic repair of AA7075-T6511 plates. After penetration with 7.62 × 51 mm FMJ rounds, the AA7075-T6511 plates were repaired by AFSD using the same AA7075-T6511 feedstock material. The repaired plates were impacted and penetrated with the same 7.62 × 51 mm FMJ rounds, and the surface damage characteristics including the initial and residual velocities were compared against the control wrought plates. The AFSD process successfully repaired the damaged control plates with the same alloy, without any observable defects such as large cracks or pores prior to impact tests. Although the surface appeared pristine other than milling marks, the surface damage characteristics of the repaired plates were significantly different than the control plates. The increase of spalling and petalling with the repaired material can be attributed to the thermomechanical processing of AFSD, which would alter the control T6511 temper of the feedstock due to coarsening of strengthening precipitates. A cross-sectioned repaired plate was analyzed using microhardness plots and optical microscopy to illustrate the effectiveness of the AFSD process for ballistic repair by depositing the same material into the damaged area. Despite the surface damage discrepancy, the repaired plates performed similarly to the control plates with respect to initial and residual velocities.Graphical

Precipitation in AA6063 produced from swarf using additive friction stir deposition

• AA6063 via additive friction stir deposition (AFSD) refines the harmful Fe containing particles present in the swarf and exhibits a relatively refined and equiaxed grain structure. • A precipitation gradient is formed during AFSD but post heat treatment readily produces a uniform structure. • Heat-treated AFSD AA6063 shows a wrought-like property. Additive friction stir deposition (AFSD) is an emerging additive manufacturing technology with the unique capability to create large-scale, free-form depositions without melting. It has the added benefit of accepting input material that is readily formed from swarf. The present work addresses questions that have arisen over the impact of the process on the precipitation in 6063 aluminium alloys (AA6063). The mechanical properties and microstructure throughout the deposit was assessed and characterized in T4, T5 and T6 conditions using a combination of transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). In the as-deposited condition, the degree of precipitation was highly heterogeneous across the different printed layers, resulting in a significant hardness gradient from the bottom to the top of the deposit. Such gradients in hardness and precipitation could be eliminated through the use of a T6 heat treatment. Additionally, the EBSD result shows that the deposited AA6063 exhibited a relatively refined and equiaxed grain structure, which evolved via continuous dynamic recrystallization during deposition. These results emulate those observed for 6xxx-series alloy deposits formed from primary material. This work demonstrates the capacity of AFSD as a viable method of solid state Al recycling, creating depositions with wrought-like properties when an adequate post-deposition heat treatment is conducted.

Deformation based additive manufacturing of a metastable high entropy alloy via Additive friction stir deposition

Additive friction stir deposition (AFSD) is a novel solid-state additive manufacturing process which offers unique capability of producing 3-D parts with no solidification related defects and having homogeneous, equiaxed microstructure. However, to fulfill the full potential of the process for structural applications, AFSD needs intense process optimization for a wide range of alloys with excellent mechanical properties. The present study explored AFSD of a novel metastable high entropy alloy (HEA), CS-HEA (Fe 40 Mn 20 Co 20 Cr 15 Si 5 (at.%)), enabled with transformation and twinning induced plasticity during deformation. Intense shear deformation at elevated temperature and strain rate during AFSD led to the operation of restoration mechanisms such as recovery, recrystallization, and grain growth which resulted in refined grains with excellent strength and work hardenability. The average grain size for as-deposited CS-HEA is 3.0 ± 0.5 µm, and the average tensile yield strength of as-deposited CS-HEA is 450 ± 20 MPa. The microstructural variation and mechanical response of the alloy as a function of process parameters were correlated to the AFSD process variables, phase transformation, and recrystallization kinetics. Further, the interaction between recrystallization kinetics and transformation kinetics on microstructural evolution of the material was explored. Additionally, the microstructure and stacking fault energy of the alloy were used to predict the mechanical response of the deposited material using a five parameter work hardening model. • A Metastable high entropy alloy, CS-HEA is additively manufactured using a deformation based additive manufacturing process – additive friction stir deposition. • Operation of discontinuous dynamic recrystallization during AFSD deposition of CS-HEA led to formation of refined equiaxed grain structure in as deposited state. • Variation in AFSD processing parameters affected the microstructure of the alloy, higher heat input resulted in larger grain size with higher fraction of high temperature γ phase. • γ→ε transformation and twinning in ε phase provided excellent strength-ductility combination in as deposited state.

Embedded QR code for part authentication in additive friction stir deposition

This paper describes an approach for authentication of parts produced by additive friction stir deposition (AFSD) using an embedded QR tag. The manufacturing steps are: produce the QR tag by laser micromachining, deposit the base layers for the part using AFSD, machine a pocket in the top layer, insert the tag with the QR code(s) facing toward the printed material, and deposit the following layers over the QR tag to embed it within the part. Authentication is then provided using CT scanning to image the QR code at the known location within the AFSD part.

A pseudo thermo-mechanical model linking process parameters to microstructural evolution in multilayer additive friction stir deposition of magnesium alloy

Additive friction stir deposition has been proposed as a disruptive manufacturing process; involving complex thermo-mechanical mechanisms during multilayer material deposition. The current efforts have attempted to develop a FEM based pseudo-mechanical thermal model accounting for heat generation due to friction and plastic dissipation during multilayer additive friction stir deposition. The primary motivation for development of the model was to seek an understanding of thermo-mechanical mechanisms and their impact on microstructural evolution during additive friction stir deposition. The predicted temperature–time profiles agreed well with the experimentally derived ones. The computational predictions indicate rise of the peak temperatures up to 0.8 times the melting temperature of Mg-alloy. In addition, the Zener-Holloman parameter, Ze evaluated using the computational model was correlated with the microstructural evolution during the deposition process. The unique thermo-mechanical processing conditions during additive friction stir deposition led to dynamic recrystallization followed by grain coarsening. A significant extent of texture strengthening was observed in the AFSD processed samples. The already established phenomenological relationship between Ze and grain size was used to predict the grain size in the present work. The computational predictions indicate that the recrystallized grain size ranged from 4 to 6 µm, and the post deformation grain coarsening varied in the range of 4–24 µm, thereby providing reasonable agreement with the experimental observations.

Residual Stress Distributions in AA6061 Material Produced by Additive Friction Stir Deposition

Residual Stress Distributions in AA6061 Material Produced by Additive Friction Stir Deposition

A Review on Solid-State-Based Additive Friction Stir Deposition

Additive manufacturing (AM) is an important technology in Industry 4.0. In recent years, solid-state-based additive friction stir deposition (AFSD) has attracted much attention, as it can avoid the inherent defect of melting and rapid solidification in electron beam-based or laser-based AM technologies. The macro and micro laws, finite element simulation, and engineering application technology of the AFSD process are still in their early stages. This paper mainly reviews the equipment, mechanism, the effect of process parameters on macro/micro characters, and the engineering applications of the AFSD process. Further, based on the complex loading conditions during the AFSD process, some perspectives are proposed, including the characterization method, unified constitutive model, novel composite manufacturing technology, and systematic study of the AFSD process.

Towards underwater additive manufacturing via additive friction stir deposition

Given the challenges in feed material supply and quality control, metal additive manufacturing has rarely been implemented in austere environments, especially underwater. This paper explores the underwater operation potential of an emerging solid-state additive technology: additive friction stir deposition, wherein material feeding and bonding are enabled by mechanical forces with minimal influences from water. It is demonstrated that additive friction stir deposition of 304 stainless steel can be successfully performed with the print head and substrate immersed in water. High temperature is reached in the deposition zone (>60% melting temperature); the material deposition behavior is similar to that in typical open-air operation. The as-deposited material is fully-dense, having fewer annealing twins and a substantially smaller grain size than the feed material (4.98 μm vs. 31.44 μm). Such microstructural changes stem from dynamic recrystallization caused by the large strain and high temperature introduced during deposition. In addition to grain refinement, small equiaxed dispersoids (∼2–3 μm or less) are formed and evenly distributed in the austenite steel matrix. Rich in Cr, Mn, and O, these particles likely result from the reaction between the elements in stainless steel and water at elevated temperatures.

Additive friction stir deposition of AZ31B magnesium alloy

The current work explored additive friction stir deposition of AZ31B magnesium alloy with the aid of MELD® technology. AZ31B magnesium bar stock was fed through a hollow friction stir tool rotating at constant velocity of 400 rpm and translating at linear velocity varied from 4.2 to 6.3 mm/s. A single wall consisting of five layers with each layer of 140×40×1 mm3 dimensions was deposited under each processing condition. Microstructure, phase, and crystallographic texture evolutions as a function of additive friction stir deposition parameters were studied with the aid of scanning electron microscopy including electron back scatter diffraction and X-ray diffraction. Both feed material and additively produced samples consisted of the α-Mg phase. The additively produced samples exhibited a refined grain structure compared to the feed material. The feed material appeared to have a weak basal texture, while the additively produced samples experienced a strengthening of this basal texture. The additively produced samples showed a marginally higher hardness compared to the feed material. The current work provided a pathway for solid state additive manufacturing of Mg suitable for structural applications such as automotive components and consumable biomedical implants.

Closed-Loop Temperature and Force Control of Additive Friction Stir Deposition

Additive Friction Stir Deposition (AFSD) is a recent innovation in non-beam-based metal additive manufacturing that achieves layer-by-layer deposition while avoiding the solid-to-liquid phase transformation. AFSD presents numerous benefits over other forms of fusion-based additive manufacturing, such as high-strength mechanical bonding, joining of dissimilar alloys, and high deposition rates. To improve, automate, and ensure the quality, uniformity, and consistency of the AFSD process, it is necessary to control the temperature at the interaction zone and the force applied to the consumable feedstock during deposition. In this paper, real-time temperature and force feedback are achieved by embedding thermocouples into the nonconsumable machine tool-shoulder and estimating the applied force from the motor current of the linear actuator driving the feedstock. Subsequently, temperature and force controllers are developed for the AFSD process, ensuring that the temperature at the interaction zone and the force applied to the feedstock track desired command values. The temperature and force controllers were evaluated separately and together on setpoints and time-varying trajectories. For combined temperature and force control with setpoints selected at a temperature of 420 °C and a force of 2669 N, the average temperature and force tracking errors are 5.4 ± 6.5 °C (1.4 ± 1.6%) and 140.1 ± 213.5 N (5.2 ± 8.0%), respectively.

A critical review on process metrics–microstructural evolution–process performance correlation in additive friction stir deposition (AFS-D)

A critical review on process metrics–microstructural evolution–process performance correlation in additive friction stir deposition (AFS-D)

A multi modal approach to microstructure evolution and mechanical response of additive friction stir deposited AZ31B Mg alloy

Current work explored solid-state additive manufacturing of AZ31B-Mg alloy using additive friction stir deposition. Samples with relative densities ≥ 99.4% were additively produced. Spatial and temporal evolution of temperature during additive friction stir deposition was predicted using multi-layer computational process model. Microstructural evolution in the additively fabricated samples was examined using electron back scatter diffraction and high-resolution transmission electron microscopy. Mechanical properties of the additive samples were evaluated by non-destructive effective bulk modulus elastography and destructive uni-axial tensile testing. Additively produced samples experienced evolution of predominantly basal texture on the top surface and a marginal increase in the grain size compared to feed stock. Transmission electron microscopy shed light on fine scale precipitation of Mg_{17}Al_{12} within feed stock and additive samples. The fraction of Mg_{17}Al_{12} reduced in the additively produced samples compared to feed stock. The bulk dynamic modulus of the additive samples was slightly lower than the feed stock. There was a sim, 30 MPa reduction in 0.2% proof stress and a 10–30 MPa reduction in ultimate tensile strength for the additively produced samples compared to feed stock. The elongation of the additive samples was 4–10% lower than feed stock. Such a property response for additive friction stir deposited AZ31B-Mg alloy was realized through distinct thermokinetics driven multi-scale microstructure evolution.

Elucidating the influence of temperature and strain rate on the mechanics of AFS-D through a combined experimental and computational approach

In this study, the temperature and strain rate dependent physics of Additive Friction Stir Deposition (AFS-D) are elucidated for the first time. Candidate constitutive models are selected to account for the severe plastic deformation and wide ranges of temperature and strain rate inherent to AFS-D. Torsion mechanical tests are performed to capture AA6061 stress dependency on temperature and strain rate. Four constitutive models, including a low fidelity-calibrated one, are applied to single-layer AFS-D simulations. The robust meshfree method, smoothed particle hydrodynamics (SPH), provided the framework for constitutive model comparison. Utilizing the SPH simulations, peak values, temperature contours, effective stress contours, effective plastic strain contours, build profiles, and simulation run time are all compared to reveal hidden mechanisms of AFS-D processing. This work highlights the importance of constitutive model selection, which can lead to improved simulation results by accurately capturing plastic stress dependence on strain, strain rate, and temperature.

Evaluation of additive friction stir deposition of AISI 316L for repairing surface material loss in AISI 4340

Additive technologies provide a means for repair of various failure modes associated with material degradation occurring during use in aggressive environments. Possible repair strategies for AISI 4340 steel using AISI 316L deposited by additive friction stir deposition (AFSD) were evaluated under this research by metallography, microhardness, and wear and mechanical testing. Two repair geometries were investigated: groove-filling and surface cladding. The former represents repair of localized grinding to eliminate cracks, while the latter represents material replacement over a larger area, for example, to repair general corrosion or wear. The 316L deposited by AFSD exhibited a refined microstructure with decreased grain size and plastic strain, ~ 12% lower strength, and 5–12% lower hardness than the as-received feedstock. Wear testing by both two-body abrasion and erosion by particle impingement indicated that the wear resistance of the 316L cladding was as good as, or better than, the substrate 4340 material; however, there was some evidence that the resistance to intergranular corrosion was compromised due to the formation of carbides or sigma phase. In both repair geometries, the microstructure of the substrate beneath the deposited material exhibited heat affected zones where the substrate appeared to have austenized to a depth of ~ 4 mm during the deposition process, and transformed to martensite or bainite during cooling. This report constitutes an initial evaluation of a novel approach to the repair of structural steel components damaged by microcracking, wear, or corrosion, with potentially broad applicability to the marine, aerospace, and heavy duty off-road industries.

Review on latest trends in friction-based additive manufacturing techniques

Additive manufacturing comprises layer-by-layer construction of 3D parts using computer controls. This present-day study reveals a list of novel concepts for additive manufacturing, where the addition of material is achieved in solid-state. Materials joined by solid-state techniques exhibits properties beyond those exhibited by material joined by conventional techniques. This has been investigated in both theoretical and experimental manner in length. However, with the development of additive manufacturing techniques, a wide range of possibilities for fabricating complex structures have been identified, which can never be accomplished by conventional techniques. Research on metal-based additive manufacturing has been comparatively less as these products deprive lateral and transverse strength and have issues of anisotropy, making them unfit for structural applications. Moreover, these techniques are not cost-effective. So to overcome these issues, methods incorporating friction into additive manufacturing have been developed. These solid-state techniques use the principle of layer-by-layer deposition. Most of these techniques utilize the principle of selective deposition of materials to form the desired material layer. In this literature review, different advances, approaches, features, and principles of friction-based material joining techniques alongside additive manufacturing are discussed in detail, which recommends new openings for researchers to work in interdisciplinary research to fabricate structures that can exhibit unique properties. This literature portrays an extensive account of the contemporary methods in the fabrication of structures using friction-based additive manufacturing techniques and highlights areas that are worth further research and necessitate a consistent effort on account of the aforementioned disciplines to advance the modernistic technique. Initially, a brief review of different solid-state additive manufacturing techniques is presented, followed by a comprehensive summary of friction stir-based additive manufacturing techniques such as friction assisted seam welding (FASW), additive friction stir (AFS) process, and friction stir additive manufacturing (FSAM) process.

Microstructure Evolution of Al6061 Alloy Made by Additive Friction Stir Deposition.

In this paper, the phase structure, composition distribution, grain morphology, and hardness of Al6061 alloy samples made with additive friction stir deposition (AFS-D) were examined. A nearly symmetrical layer-by-layer structure was observed in the cross section (vertical with respect to the fabrication-tool traversing direction) of the as-deposited Al6061 alloy samples made with a back-and-forth AFS-D strategy. Equiaxed grains were observed in the region underneath the fabrication tool, while elongated grains were seen in the “flash region” along the mass flow direction. No clear grain size variance was discovered along the AFS-D build direction except for the last deposited layer. Grains were significantly refined from the feedstock (~163.5 µm) to as-deposited Al6061 alloy parts (~8.5 µm). The hardness of the as-fabricated Al6061 alloy was lower than those of the feedstock and their heat-treated counterparts, which was ascribed to the decreased precipitate content and enlarged precipitate size.

A solid-state additive manufacturing method for aluminum-graphene nanoplatelet composites

A low-power solid-state additive manufacturing process termed additive friction stir deposition (AFS-D) successfully deposited a bulk 6061 aluminum alloy - 2.5 wt.% graphene nanoplatelet (GNP) metal matrix composite. Post-deposition, the build exhibited a macrostructure with undulating onion-ring-like patterns similar to friction stir welding features. Optical and scanning electron microscopy (SEM) observed GNPs distributed within and along grain boundaries with the GNPs reduced in widths from 4,000 µm (pre-deposit) to 200 nm (post-deposit) through this solid-state deposition process. Differences in particle dispersion between the retreating and advancing sides of deposited material were also observed and quantified. Raman spectroscopy confirmed the graphitic nature of the GNPs in the matrix after deposition, which also showed an increase in disorder in the GNPs. The fully dense deposition consisted of microhardness across the cross section, varying from 45 to 70 HV, where higher hardness was correlated to the location of the GNP dispersions.

Microstructure and mechanical properties of Ti6Al4V alloys fabricated by additive friction stir deposition

The additive friction stir deposition (AFSD) of Ti6Al4V alloy was successfully performed over a wide processing window. The microstructures were examined based on the high atemperature β grain size, grain boundary α formation and the propensity of variant selection as a function of process parameters. The analysis revealed that a reduction in deposition temperature could be achieved by the change in AFSD parameters, resulting in major reduction of prior β grain size and refinement of as-deposited α phase structure. This resulted in significant improvements of ductility and strength in the as-deposited state with ductility values up to ∼20% and maximum yield and ultimate tensile strengths values of 1010 MPa and 1233 MPa, respectively.

Evaluation of Microstructure and Mechanical Properties of Al-Zn-Mg-Cu Alloy Repaired via Additive Friction Stir Deposition

Abstract A novel solid-state additive manufacturing (AM) process, additive friction stir deposition (AFS-D), provides a new pathway for additively repairing damaged nonweldable aerospace materials that are susceptible to induced thermal gradients within the microstructure. In this work, we quantify the microstructural evolution and mechanical performance of an additively repaired AA7075-T651 (Al-Zn-Mg-Cu) via the AFS-D process. To evaluate the AFS-D process for repairing high strength aluminum alloys, the AFS-D technique was used to additively fill a linear groove that was machined into an AA7075-T651 plate. After repairing the plate with the AFS-D process, the repaired plate was subjected to standard T6 heat treatment. The results of this study show that the heat-treated AFS-D repair did not exhibit any significant grain growth and demonstrated an increase in the average Vickers hardness in the repair compared with the wrought 7075-T651 control. Tensile and fatigue behavior was investigated for heat-treated repair and compared with the wrought AA7075-T651 control. The heat-treated repair exhibited wrought-like tensile properties for yield stress (YS) and ultimate stress; however, the heat-treated repair had significant scatter in the elongation to failure. Additionally, the mean fatigue behavior of the heat-treated repairs displayed a reduction in cycles to failure compared with the wrought control. Lastly, a microstructure-sensitive fatigue life model was used to elucidate process-structure-property fatigue mechanism relations of the heat-treated repair and wrought AA7075.