Showing papers on "Residual stress published in 2022"

Additive manufacturing of Ti-6Al-4V alloy- A review

Abstract: The most popular additive manufacturing (AM) technologies to produce titanium alloy parts are electron beam melting (EBM), selective laser melting (SLM) and directed energy deposition (DED). This investigation explores mainly these three techniques and compares these three methods comprehensively in terms of microstructure, tensile properties, porosity, surface roughness and residual stress based on the information available in the literature. It was found that the microstructure is affected by the highest temperature generated and the cooling rate which can be tailored by the input variables of the AM processes. The parts produced from EBM have strength comparable to that of conventionally fabricated counterparts. SLM and DED yield superior strength, which can be up to 25% higher than traditionally manufactured products. Due to the presence of larger tensile residual stress, surface roughness and porosity, AM fabricated parts have lower fatigue life compared to those of from traditional methods. EBM parts have slightly lower fracture toughness (i.e., lower fatigue life) than conventionally produced parts while SLM and DED have significantly lower fracture toughness. Annealing, hot isostatic pressing, stress relief and additional machining processes improve the characteristics of parts produced from AM. Ti–6Al–4V alloy parts fabricated via AM may have limited applications despite the high demands in aerospace or biomedical engineering. Since rapid product development using 3D printers leads to significant cost reductions more recently, it is expected that more opportunities may soon be available for the AM of titanium alloys with newer AM processes such as cold spray additive manufacturing (CSAM) and additive friction stir deposition (AFSD).

In situ SEM study on tensile fractured behavior of Al/steel laser welding-brazing interface

Abstract: Microcracks initiated and propagated behaviors in Al/steel interface determined interfacial bonding strength and this was observed by in situ scanning electron microscopy (SEM) technology. Interface without or with discontinuous intermetallic compound (IMC) had low bonding strength owing to insufficient metallurgical bonding. When interface was joined with 2–3 μm serration–shaped τ5–Fe1.8Al7.2Si, largest bonding strength of 205 MPa was obtained. Microcracks initiated at protrusion of τ5–Fe1.8Al7.2Si and then propagated to τ5–Fe1.8Al7.2Si layer and τ5–Fe1.8Al7.2Si/Al interface. When interface was joined with 3–5 μm θ–Fe(Al,Si)3 + τ5–Fe1.8Al7.2Si, microcracks initiated at root of IMC layers and the interfacial bonding strength was 150 MPa. When interface was joined with 5–10 μm θ–Fe(Al,Si)3 + τ5–Fe1.8Al7.2Si, microcracks initiated and propagated along IMC layer. Lower interfacial bonding strength (106 MPa) was produced owing to large lattice mismatch between θ–Fe(Al,Si)3 and τ5–Fe1.8Al7.2Si, microdefects and higher residual stress. When interface was joined with 10 μm η–Fe2(Al,Si)5 + θ–Fe(Al,Si)3 + τ5–Fe1.8Al7.2Si, microcracks initiated and propagated along η–Fe2(Al,Si)5 layer or steel/η–Fe2(Al,Si)5 interface. Lowest bonding strength (64 MPa) was obtained resulted from pre–generated microcracks in η–Fe2(Al,Si)5 layer, largest residual stress, crystal defects and abnormal aggregation of Si.

X-ray Diffraction Techniques for Mineral Characterization: A Review for Engineers of the Fundamentals, Applications, and Research Directions

Abstract: X-ray diffraction (XRD) is an important and widely used material characterization technique. With the recent development in material science technology and understanding, various new materials are being developed, which requires upgrading the existing analytical techniques such that emerging intricate problems can be solved. Although XRD is a well-established non-destructive technique, it still requires further improvements in its characterization capabilities, especially when dealing with complex mineral structures. The present review conducts comprehensive discussions on atomic crystal structure, XRD principle, its applications, uncertainty during XRD analysis, and required safety precautions. The future research directions, especially the use of artificial intelligence and machine learning tools, for improving the effectiveness and accuracy of the XRD technique, are discussed for mineral characterization. The topics covered include how XRD patterns can be utilized for a thorough understanding of the crystalline structure, size, and orientation, dislocation density, phase identification, quantification, and transformation, information about lattice parameters, residual stress, and strain, and thermal expansion coefficient of materials. All these important discussions on XRD analysis for mineral characterization are compiled in this comprehensive review, so that it can benefit specialists and engineers in the chemical, mining, iron, metallurgy, and steel industries.

Microstructural evolution and tensile property enhancement of remanufactured Ti6Al4V using hybrid manufacturing of laser directed energy deposition with laser shock peening

Abstract: Laser-directed energy deposition (LDED) provides an attractive and cost-effective way to remanufacture high-value engineering components. However, the LDED manufactured (LDEDed) components are usually characterized by large columnar grains along the deposition direction, leading to mechanical anisotropy. Meanwhile, higher performance is usually required in the damaged regions. In this paper, the effects of interlayer laser shock peening (LSP) treatment, namely, an innovative laser hybrid additive manufacturing technology combined LDED with LSP, on microstructural evolution and mechanical performance of Ti6Al4V alloy were investigated. Particularly, the microstructural features between adjacent deposited layers were clarified using scanning electron microscope (SEM) and transmission electron microscopy (TEM) observations. The results indicated that the epitaxial growth of columnar grains caused by LDED was inhibited, and fine equiaxed grains were formed between deposited layers due to the recrystallization behavior. Besides, the microhardness and tensile property of the LDEDed specimen were significantly improved by the interlayer LSP treatment. Consequently, the laser hybrid additive manufacturing -generated dominant mechanism of the microstructural evolution and tensile property enhancement was revealed. • LSP was combined with LDED to realize the laser hybrid remanufacturing. • Epitaxial growth of columnar grains in the LDEDed specimen was inhibited by LSP. • The micro-hardness of the LDEDed specimen was significantly improved by LSP. • A good combination of UTS and ductility was achieved in the LDED-LSPed specimen. • The mechanism of the tensile property enhancement by LHAM was revealed.

Review on residual stresses in metal additive manufacturing: formation mechanisms, parameter dependencies, prediction and control approaches

Abstract: Metal additive manufacturing (MAM) technology has great application potential in the aerospace, medical and energy fields with its high material utilization efficiency to achieve the manufacturing of metal parts of any shape. However, the extreme thermal, mechanical, and metallurgical coupling in MAM process leads to large residual stresses in the manufactured samples. Residual stress has a significant effect on the dimensional stability, corrosion resistance, crack growth resistance and mechanical properties of MAM samples. As a result, residual stress can be regarded as a key factor in controlling costs, enhancing product efficiency and quality. To help researchers and engineers attain up-to-date information and knowledge about residual stress in MAM, the current paper provides a comprehensive review in this field, especially the formation mechanisms, the influence of process parameters, prediction and control methods.

Numerical Study on Welding Residual Stress Distribution of Corrugated Steel Webs

Abstract: Residual stresses are an inevitable result of the welded fabrication process of corrugated steel webs (CSWs), resulting in structures with high and unpredictable stress fields, causing unexpected failures. The residual stress field is affected by structural parameters and the welding path of CSWs. This study proposes the welding process simulation method for CSWs with element birth and death technology. The optimization design method of heat source parameters is proposed. The feasibility of the simulation method is verified by comparing the numerical results with the experimental results of relevant literature. As a part of the study, a comparison of residual stress fields upon cooling welded CSWs with bending angles of 30, 45, and 60 degrees is presented. Thereafter, the effect of two types of single-sided welding paths and double-sided welding construction processes on residual stress distribution is discussed. Generally, the study results have shown that the equivalent residual stress near the weld reaches the maximum 344 MPa, which is very close to the Q345 steel yield strength. The size of the bending angle has no major effect on the residual stress distribution pattern, but it influences the residual stress value at the bending position. The residual stress at the bending position increases with the bending angle of CSWs. Different welding paths significantly impact the residual stress of the weld toe, and selecting a reasonable welding path can effectively reduce the residual stress value by 20 to 40 MPa.

Evolution of residual stress behavior in selective laser melting (SLM) of 316L stainless steel through preheating and in-situ re-scanning techniques

Abstract: • The influence of preheating techniques on the resultant modifications in residual stress profile of SLM fabricated components was investigated. • Powder bed preheating and baseplate pre heating techniques in SLM were compared for a wide range of temperatures. • In-situ rescanning was also observed as a possible reduction technique for residual stresses in SLM fabricated components. • Relationships between rescanning parameters and the residual stress profile were also established. The premature fractures, cracks, distortions, and delamination in selective laser melting manufactured components are among the most prominent challenges. These issues in selective laser melting manufactured components restrict their widespread application. Residual stresses are among the most common reasons for these behaviors. Post processing techniques are therefore used for most of the selective laser melting fabricated components to either eliminate or decrease these stresses. However, this increases the production time and fabrication costs. Therefore, in process techniques to reduce these residual stresses are of paramount importance in promoting the largescale production of metallic components. In this paper, a finite element method-based investigation of preheating and in-situ rescanning techniques during selective laser melting of 316L stainless steel is presented. The influence of various preheating temperatures on the final residual stress profile was observed. Similarly, the variations in residual stresses with different rescanning parameters were also investigated. Both baseplate and powder bed preheating procedures were observed to have considerable effects on the residual stresses. The residual stresses were significantly decreased with increasing preheating temperatures. Baseplate and powder bed preheating at 400 °C were observed to have decreased the residual stresses from 353.57 MPa (stress values without preheating or rescanning) to 27 MPa and 30 MPa, respectively. In-situ rescanning was also observed to be beneficial in decreasing the stresses in SLM fabricated components. However, their influence is relatively smaller in comparison with the preheating. No significant influence of rescanning on the stress distribution was also observed.

Additive manufactured high entropy alloys: A review on the microstructure and properties

Abstract: High entropy alloys (HEAs) are promising multi-component alloys with unique combination of novel microstructures and excellent properties. However, there are still certain limitations in the fabrication of HEAs by conventional methods. Additive manufactured HEAs exhibit optimized microstructures and improved properties, and there is a significantly increasing trend on the application of additive manufacturing (AM) techniques in producing HEAs in recent years. This review summarizes the additive manufactured HEAs in terms of microstructure characteristics, mechanical and some functional properties reported so far, and provides readers with a fundamental understanding of this research field. We first briefly review the application of AM methods and the applied HEAs systems, then the microstructure including the relative density, residual stress, grain structure, texture and dislocation networks, element distribution, precipitations and the influence of post-treatment on the microstructural evolution, next the mechanical properties consisting of hardness, tensile properties, compressive properties, cryogenic and high-temperature properties, fatigue properties, creep behavior, post-treatment effect and the strengthening mechanisms analysis. Thereafter, emerging functional properties of additive manufactured HEAs, namely the corrosion resistance, oxidation behaviors, magnetic properties as well as hydrogen storage properties are discussed, respectively. Finally, the current challenges and future work are proposed based on the current research status of this topic.

Study on microstructure and properties of Fe-based amorphous composite coating by high-speed laser cladding

Abstract: Fe-Co-B-Si-Nb amorphous coatings were deposited on 45 medium carbon steel under different scanning speeds by high-speed laser cladding technology. The results showed that the surface roughness of the coating became lower and the surface of the coating became smoother with the increase in scanning speed. In addition, the residual tensile stress and the thermal expansion coefficient decreased with the increase in the scanning speed. When the scanning speed was 80.38 m/min, the residual tensile stress was 106.13 ± 24.03 MPa. The residual stress was reduced by more than 50% compared with the scanning speed of 37.68 m/min. The XRD and TEM observation results of the coating at the scanning speed of 80.38 m/min showed a large volume fraction of amorphous phase and some crystalline dendrites. Under the scanning speed of 80.38 m/min, the cooling rate at the top of the coating could reach 1.08 × 105 °C/s, which greatly increased the amorphous formation ability. The hardness and wear resistance properties of the coating were also tested and analyzed. Better performance of the coatings was obtained when the scanning speed was higher.

Additive manufacturing: A machine learning model of process-structure-property linkages for machining behavior of Ti-6Al-4V

Abstract: Prior studies in metal additive manufacturing (AM) of parts have shown that various AM methods and post-AM heat treatment result in distinctly different microstructure and machining behavior when compared with conventionally manufactured parts. There is a crucial knowledge gap in understanding this process-structure-property (PSP) linkage and its relationship to material behavior. In this study, the machinability of metallic Ti-6Al-4V AM parts was investigated to better understand this unique PSP linkage through a novel data science-based approach, specifically by developing and validating a new machine learning (ML) model for material characterization and material property, that is, machining behavior. Heterogeneous material structures of Ti-6Al-4V AM samples fabricated through laser powder bed fusion and electron beam powder bed fusion in two different build orientations and post-AM heat treatments were quantitatively characterized using scanning electron microscopy, electron backscattered diffraction, and residual stress measured through X-ray diffraction. The reduced dimensional representation of material characterization data through chord length distribution (CLD) functions, 2-point correlation functions, and principal component analysis was found to be accurate in quantifying the complexities of Ti-6Al-4V AM structures. Specific cutting energy was the response variable for the Taguchi-based experimentation using force dynamometer. A low-dimensional S-P linkage model was established to correlate material structures of metallic AM and machining properties through this novel ML model. It was found that the prediction accuracy of this new PSP linkage is extremely high (>99%, statistically significant at 95% confidence interval). Findings from this study can be seamlessly integrated with P-S models to identify AM processing conditions that will lead to desired material behaviors, such as machining behavior (this study), fatigue behavior, and corrosion resistance.

Fatigue behaviour of notched laser powder bed fusion AlSi10Mg after thermal and mechanical surface post-processing

Abstract: Laser powder bed fusion (LPBF) as an additive manufacturing technology offers high potential to fabricate parts with complex geometries layer-by-layer. However, these parts have inhomogeneous microstructure and very poor surface quality in their as-built condition. The presence of high surface irregularities especially in the downskin surfaces is a challenging issue that can directly influence their mechanical performance especially under fatigue loading conditions. Hence, applying post-treatments to modulate these imperfections can play a critical role. In this study, the individual and hybrid effects of different post-treatments including T6 heat treatment and shot peening on microstructure, mechanical properties and fatigue behaviour of LPBF V-notched AlSi10Mg specimens were investigated. Two different shot peening processes were applied on both as-built and heat treated specimens using steel and ceramic shots with different Almen intensity, shot diameter and shot hardness. The specimens were comprehensively characterized in terms of microstructural features, surface morphology and surface roughness. Mechanical properties including microhardness and residual stresses were measured and fatigue behaviour of the specimens was determined using a stair-case method; fracture surfaces were also critically analyzed. The results of the analysis performed both on the smooth section and the notched section (including notch root, up and down skin areas) indicated the importance of the choice of shot peening parameters with respect to the target geometry and its material properties. In this case, the shot peening treatment with smaller media and lower intensity was more efficient in terms of surface modification and homogenization especially in the downskin surfaces leading to higher fatigue strength. The significant finding of this study is that by pairing the heat treatment and shot peening, the effect of the presence of the notch can be masked obtaining almost the same fatigue strength for the notched specimens as the un-notched counterparts.

Fatigue behaviour of notched laser powder bed fusion AlSi10Mg after thermal and mechanical surface post-processing

Abstract: Laser powder bed fusion (LPBF) as an additive manufacturing technology offers high potential to fabricate parts with complex geometries layer-by-layer. However, these parts have inhomogeneous microstructure and very poor surface quality in their as-built condition. The presence of high surface irregularities especially in the downskin surfaces is a challenging issue that can directly influence their mechanical performance especially under fatigue loading conditions. Hence, applying post-treatments to modulate these imperfections can play a critical role. In this study, the individual and hybrid effects of different post-treatments including T6 heat treatment and shot peening on microstructure, mechanical properties and fatigue behaviour of LPBF V-notched AlSi10Mg specimens were investigated. Two different shot peening processes were applied on both as-built and heat treated specimens using steel and ceramic shots with different Almen intensity, shot diameter and shot hardness. The specimens were comprehensively characterized in terms of microstructural features, surface morphology and surface roughness. Mechanical properties including microhardness and residual stresses were measured and fatigue behaviour of the specimens was determined using a stair-case method; fracture surfaces were also critically analyzed. The results of the analysis performed both on the smooth section and the notched section (including notch root, up and down skin areas) indicated the importance of the choice of shot peening parameters with respect to the target geometry and its material properties. In this case, the shot peening treatment with smaller media and lower intensity was more efficient in terms of surface modification and homogenization especially in the downskin surfaces leading to higher fatigue strength. The significant finding of this study is that by pairing the heat treatment and shot peening, the effect of the presence of the notch can be masked obtaining almost the same fatigue strength for the notched specimens as the un-notched counterparts.

Residual monotonic mechanical properties of bimetallic steel bar with fatigue damage

Abstract: When a reinforced concrete structure experiences an earthquake and does not collapse, irreversible damage in the reinforcement is caused by the fatigue load, which affects the residual bearing capacity of the structure significantly. Stainless-clad bimetallic steel bars (BSBs) are a new type of coated reinforcement with effective resistance to corrosion. In this study, to accurately evaluate the residual bearing capacity of a concrete structure reinforced with BSBs following an earthquake, it is tested with different fatigue damage ratios. Thereafter, the monotonic stress–strain nonlinear performance, failure behaviour , and residual mechanical properties of BSBs with fatigue damage are explored. The evolution law of the mechanical properties of BSBs with fatigue damage is analysed. A monotonic stress–strain model of the BSB that considers the impact of fatigue damage is proposed. The test results indicate that the stainless-steel cladding of the BSB does not demonstrate apparent buckling following fatigue damage. Cracks are observed on both sides of the rib teeth. When the fatigue damage ratio is 0.6, a fracture occurs at the maximum crack caused by the fatigue damage. When the fatigue damage ratios are 0.2 and 0.4, fractures occur in the necking region of the upper or lower part of the specimen. Fatigue damage leads to the disappearance of the yield platform from the monotonic stress–strain curve of the BSB. The yield strength of the BSB decreases significantly owing to the fatigue damage ratio. The ultimate strength is barely affected by the fatigue damage ratio. Fatigue damage has an adverse effect on the deformation capacity of the BSB. With an increase in the fatigue strain amplitude and fatigue damage ratio, elongation following the fracture of the BSB gradually decreases. This study provides solid theoretical and experimental bases for the engineering application of BSBs, particularly in the post-earthquake evaluation of concrete structures reinforced with BSBs. • Fatigue damage leads to the disappearance of the yield platform from the monotonic stress–strain curve of the BSB. • The fracture position of the BSB with fatigue damage is affected by the damage ratio. • Effects of fatigue damage on the properties of the BSB mechanical parameter are summarised. • A nonlinear predictive model of the BSB with fatigue damage is proposed.

Numerical modeling and experimental verification of residual stress distribution evolution of 12Cr2Ni4A steel generated by shot peening

Abstract: Shot peening is a widely used surface strengthening technique which can improve the fatigue life of metal components by introducing reasonably distributed compressive residual stress. The accurate prediction of residual stress distribution of parts is a tough challenge in the simulation of shot peening. In this paper, the numerical calculation of the residual stress of shot peening is investigated with 12Cr2Ni4A steel as the target. A two-dimensional Gaussian distribution model is proposed to calculate the number of impact shots. A method is proposed to calculate shot peening coverage using displacement and displacement gradient, which increases the identification accuracy of peened surface topography and provides a scientific method for coverage calculation. A random multi-shot finite element model for high strength steel is established considering the elastoplastic of shot. The effects of the process parameters, initial surface morphology and initial residual stress on the residual stress distribution after shot peening are investigated. The accuracy of the proposed method is verified by comparing the measured and simulated results.

Evolution of temperature and residual stress behavior in selective laser melting of 316L stainless steel across a cooling channel

Abstract: Purpose The current investigation aims at observing the influence of the cooling channel on the thermal and residual stress behavior of the selective laser melting (SLM)316L uni-layer thermo-mechanical model. Design/methodology/approach On a thermo-mechanical model with a cooling channel, the effect of scanning direction, parallel and perpendicular and scan spacing was simulated. The effect of underlying solid and powder bases was evaluated on residual stress profile and thermal variables at various locations. Findings The high heat dissipation of solid base due to high cooling rates and steep thermal gradients can reciprocate with smaller melt pool temperature and melt pool size. Given the same scan spacing, residual stresses were found lower when laser scanning was perpendicular to the cooling channel. Moreover, large scan spacing was found to increase residual stresses. Originality/value Cooling channels are increasingly being used in additive manufacturing; however, their effect on the residual stress behavior of the SLM component is not extensively studied. This research can serve as a foundation for further inquiries into the impact of base material design such as cooling channels on manufactured components using SLM.