Large Residual Stresses Research Articles

Quantitative analysis of deformation characteristics and corrosion properties of high energy laser shock peened Ni-based superalloy

This study examines the influence of high-energy laser shock peening (LSP) using 7 J and 10 J pulse energies on the sub-surface deformation characteristics of Inconel 718 superalloy. High-magnitude compressive residual stresses were induced into the samples after LSP with large residual stress depths of the order of 2 mm – the experimental observations were in good agreement with finite element analyses of the LSP process. The propagation of intense shock waves led to an increased strain hardening and dislocation densities that were experimentally quantified by synchrotron diffraction and transmission electron microscopy. Microscopic analyses revealed highly refined grain structure only at the surface without much refinement observed in the residual depth region. Alongside high degree of strain hardening, a profuse amount of adiabatic shear bands was observed in the hardened depth, indicative of simultaneous strain localisation under such high laser pulse energy. These bands occurred along common slip planes in the Ni γ-matrix and could be potential areas of instability leading to failure. The LSP-treated samples exhibited improved corrosion resistance, with higher laser pulse energy peened samples performing better.

The impact of various curing methods on the curing process of polymer-fiber composites analyzed using analytical approach

Ti/Gf/Cf represents a novel form of hybrid fiber metal laminates (HFMLs) that successfully blend the benefits of titanium alloy, glass fiber reinforced plastic (GFRP), and carbon fiber reinforced plastic (CFRP). These materials have garnered attention in the field of engineering due to their exceptional levels of stiffness, strength, and shear resistance. The quality of HFMLs during the curing process was significantly impacted by the chosen curing method. Moreover, the use of multiple types of fibers complicated the optimization of curing parameters in HFMLs. A comprehensive study was conducted using a multi-physics field coupling finite element method to investigate the impact of various curing methods on the development of temperature distribution, curing degree, and curing stress in HFMLs during the curing process. By integrating thermal transmission equations, curing kinetics, and viscoelastic mechanical models, a detailed curing simulation model was established. Increasing the cooling rate from 1 °C to 5 °C was shown to raise the maximum curing stress by 4.7 MPa. Additionally, higher curing temperatures were found to induce internal curing stress due to variations in thermal properties. Insufficient insulation times were observed to exacerbate non-uniform temperature distribution and curing degree fields in HFMLs, potentially leading to increased internal stress. To mitigate the generation of large residual stress, it is recommended to lower the heating and cooling rates, reduce curing temperatures, and extend the insulation time appropriately during the curing process of HFMLs. The primary goal of this research was to accurately predict the evolution of curing parameters in HFMLs under different curing regimes, which were impacted by the chosen curing method. The results of the study demonstrated that rapid changes in temperature during heating and cooling stages can lead to uneven curing, resulting in the accumulation of residual stress within the laminates.

Investigation of surface finish and fatigue life of laser Powder Bed fused Ti-6Al-4V

In this fact-pacing world of technological advancement, the rise of additive manufacturing (AM) has found immense applications of metallic alloys such as Ti6Al4V to manufacture key components in automotive, aerospace and healthcare sectors. However, fatigue characteristics of such additively manufactured metal alloys is noticeably weak, and as such requires post-processing. In this study, AM Ti6Al4V manufactured by Laser Powder Bed Fusion (L-PBF) was treated by Hydrodynamic Cavitation Abrasive Finishing (HCAF) and Laser Cavitation Peening (LCP) to observe the improvement in surface roughness as well as fatigue performance. Our investigations revealed a substantial improvement in surface quality post-HCAF processing. Notably, the surface roughness of AM Ti6Al4V specimens showed a significant reduction of about 91.2 %, post surface treatment. However, Laser Cavitation Peening (LCP) treated sample demonstrates a significantly enhanced fatigue strength of 393 ± 22 MPa at 107, which was 1.75 times better than that of as-built one, i.e., 224 ± 16 MPa. This difference can be attributed to the distinct surface modification mechanisms of each technique. LCP, utilizing laser-induced shock waves, likely induces large compressive residual stresses, leading to better fatigue resistance.

Microstructure and Properties of Ni-WC Composite Plasma Clad

aims: This study aims to improve the surface properties of 45 steel to broaden its applications. background: 45 Steel is an important material for the development of human society and civilisation,and plays an important role in human production and life. Ni-based composite coatings are widely used in metal workpieces to improve the surface properties and expand its applications. objective: In this study, Ni-WC composite coating was prepared on 45 steel substrates by plasma cladding. The microstructure, microhardness, residual stress, and corrosion resistance properties were analyzed to examine various influencing factors. method: In this study, the plasma cladding technique was employed to produce Ni-based cladding with different WC contents on 45 steel surfaces. The microstructure, phase structure, microhardness, residual stress, and corrosion resistance of Ni-based cladding coatings were investigated. result: The results showed that the coatings are made up mostly of Ni3Fe, Cr23C6, Cr7C3, WC, and W2C phases. conclusion: The microhardness of the Ni-based alloy coatings is greatly increased due to the presence of WC hard phase on the Ni matrix. The highest microhardness is more than tripling that of the substrate with the addition of 60% WC. In addition, the largest residual stress at the center of the cladding channel is more than five times higher than the substrate affected zone. The corrosion resistance of 45 steels containing Ni-based coatings increases in acidic, neutral and alkaline environments due to the formation of passivation films. other: none

Crack mitigation in additively manufactured AlCrFe2Ni2 high-entropy alloys through engineering phase transformation pathway

The far-from-equilibrium solidification during additive manufacturing often creates large residual stresses that induce solid-state cracking. Here we present a strategy to suppress solid-state cracking in an additively manufactured AlCrFe2Ni2 high-entropy alloy via engineering phase transformation pathway. We investigate the solidification microstructures formed during laser powder-bed fusion and directed energy deposition, encompassing a broad range of cooling rates. At high cooling rates (104−106 K/s), we observe a single-phase BCC/B2 microstructure that is susceptible to solid-state cracking. At low cooling rates (102−104 K/s), FCC phase precipitates out from the BCC/B2 matrix, resulting in enhanced ductility (~10 %) and resistance to solid-state cracking. Site-specific residual stress/strain analysis reveals that the ductile FCC phase can largely accommodate residual stresses, a feature which helps relieve residual strains within the BCC/B2 phase to prevent cracking. Our work underscores the value of exploiting the toolbox of phase transformation pathway engineering for material design during additive manufacturing.

Vat Photopolymerization of Sepiolite Fiber and 316L Stainless Steel-Reinforced Alumina with Functionally Graded Structures.

Alumina (Al2O3) ceramics are widely used in electronics, machinery, healthcare, and other fields due to their excellent hardness and high temperature stability. However, their high brittleness limits further applications, such as artificial ceramic implants and highly flexible protective gear. To address the limitations of single-phase toughening in Al2O3 ceramics, some researchers have introduced a second phase to enhance these ceramics. However, introducing a single phase still limits the range of performance improvement. Therefore, this study explores the printing of Al2O3 ceramics by adding two different phases. Additionally, a new gradient printing technique is proposed to overcome the limitations of single material homogeneity, such as uniform performance and the presence of large residual stresses. Unlike traditional vat photopolymerization printing technology, this study stands out by generating green bodies with varying second-phase particle ratios across different layers. This study investigated the effects of different contents of sepiolite fiber (SF) and 316L stainless steel (SS) on various aspects of microstructure, phase composition, physical properties, and mechanical properties of gradient-printed Al2O3. The experimental results demonstrate that compared to Al2O3 parts without added SF and 316L SS, the inclusion of these materials can significantly reduce porosity and water absorption, resulting in a denser structure. In addition, the substantial improvements, with an increase of 394.4% in flexural strength and an increase of 316.7% in toughness, of the Al2O3 components enhanced by incorporating SF and 316L SS have been obtained.

Progressive Induction Hardening: Measurement and Alteration of Residual Stresses

Progressive induction hardening is an in-line steel heat treatment method commonly used to surface harden powertrain components. It produces a martensitic case layer with a sharp transition zone to the base material. This rapid process will induce large residual stresses, where a compressive state in the case layer will shift to a tensile state in the transition zone. For fatigue performance, it is important to quantify the magnitude and distribution of these stresses, and moreover how they depend on material and processing parameters. In this work, x-ray diffraction in combination with a layer removal method is used for efficient and robust quantification of the subsurface stress state, which combines electropolishing with either turning or milling. Characterization is done on C45E steel samples that were progressively induction hardened using either a fast or slow (27.5 or 5 mm/s, respectively) scanning speed. The results show that although the hardening procedures will meet arbitrary requirements on surface hardness, case depth and microstructure, the subsurface tensile stress peak magnitude is doubled when using a fast scanning speed. However, the near-surface compressive residual stresses are comparable. In addition, the subsurface tensile residual stress peak is compared with the on-surface tensile stresses in the fade-out zone.

Optimizing the high-frequency magnetic properties of soft magnetic composites via surface nanoengineering

Owing to the presence of large residual internal stress during cold compaction, it is difficult to optimize the multiple high-frequency magnetic properties of amorphous soft magnetic composites (ASMCs) simultaneously. Here, a surface nanoengineering strategy was proposed to address the above dilemma by constructing a stress buffer layer composed of amorphous nano-particles, between amorphous powder and insulation coating. The amorphous FeSiBCCr@x wt.% FeB (x = 0.5, 1, 3) composite powders with core-shell structures were successfully prepared via an in-situ chemical reduction method. Especially, when the composite ratio of nano-particles is 1 wt.%, the comprehensive properties of the ASMC reach the best balance. Compared with the FeSiBCCr ASMC, the saturation magnetization of the modified ASMC enhances from 153 to 171 emu/g. Meanwhile, the core loss decreases by 28.25 %, while the effective permeability increases by 25 % and can stabilize to ∼20 MHz. Therefore, our work provides a strategy for achieving superior comprehensive soft magnetic properties of ASMCs via surface nanoengineering, which presents enormous application potential in high-frequency electric devices.

Microstructure regulation and performance of titanium alloy coating with Ni interlayer on the surface of mild steel by laser cladding

The preparation of Ti-alloy coating on the steel surface via laser cladding is very easy to form Fe-Ti phase and large tensile residual stress, which is not conducive to the performance of Ti-alloy coating. Here, Ti-6Al-4V coating (TC4-coating) was prepared on the mild steel substrate using laser cladding technology with Ni-alloy as the interlayer, and the Fe-Ti phase inside was completely suppressed. Increasing the powder feeding rate and scanning speed can change the undercooling of the alloy melt and the preferred growth orientation of the grains, while limiting the abnormal grain growth and grain boundary segregation, which is beneficial for grain refinement and equiaxed crystal formation. Reducing the scanning speed and powder feeding rate can increase the molten pool lifetime, thereby increasing the dilution rate of the coating and facilitating the formation of Ti2Ni phase. The abundant Ti2Ni inside the coating gives the TC4-coating greater microhardness (>500 HV0.1) and better corrosion resistance (Icorr of 7.00 × 10−8 A·cm−2). Grain refinement of the coating texture caused by the increase of powder feeding rate and scanning speed, as well as the high content of β-Ti phase and martensite structure, can improve the adhesion and shear strength of TC4-coating (386 ± 31 MPa).

Analysis of lattice deformation originated from residual stress on performance of aluminum nitride-based bulk acoustic wave resonators

With the development of MEMS technology to the nanometer scale, the influence of different process conditions on the performance of nano-devices can be calculated through the microscopic changes of materials. During the manufacturing process, the large residual stress from the film stack significantly influences the performance of devices, thereby reducing the wafer yield. Herein, we apply density functional theory to MEMS processes to reveal the intrinsic mechanism of how residual stress affects the performance of aluminum nitride-based bulk acoustic wave (BAW) resonators on an 8-inch high-resistance silicon wafer. The variation rule of physical properties of piezoelectric material aluminum nitride with different residual stresses is calculated via first-principles calculations. Through theory formula derivation, the piezoelectric-coupling constant (Kt2) of the bulk acoustic wave resonator is positively correlated with tensile residual stress, and the resonant frequency (fp, fs) is negatively correlated with tensile residual stress. The measurement results show that the average shifts of Keff2 is 0.12 % within −137 MPa and 183 Mpa residual stress, which is an excellent match with the theory prediction.

Crack mitigation strategies for a high-strength Al alloy Al92Ti2Fe2Co2Ni2 fabricated by additive manufacturing

Laser powder bed fusion is capable of fabricating aluminum (Al) alloy parts with great geometrical flexibility and rapid prototyping for various industries. However, high strength Al alloys generally suffer from solidification cracks due to the steep thermal gradient associated with the laser fusion process. Here, we report several strategies to mitigate the hot crack susceptibility of a high strength Al92Ti2Fe2Co2Ni2 alloy. Routine processing parameter optimization based on varying laser power and scanning speed has to trade off porosity for producing crack-free parts, making it not suitable for load-bearing structural applications. Furthermore, secondary printing parameters, including laser strip length, laser defocus, scanning strategies, etc., improved printability but were insufficient to eliminate all the cracks. Crack morphology and residual stress measurements indicate that the cracks are generated in the solid state driven by large tensile residual stress, instead of solidification cracking or liquation cracking. Thus, an attempt was made to alleviate the residual stress in a controlled manner. By properly introducing a compliant, sacrificial, scaffold support structure to regulate crack propagation, near fully dense, crack-free parts could be successfully printed. The results were further verified by micro computed tomography, showing that cracking could be arrested in the support before propagating through the parts. This method can be readily applied to other alloy systems without modifying the chemistry.

Surface shot peening of cast SiCw/Al composites

ABSTRACT The surface shot peening treatment was carried out on the as-cast SiCw/Al composites, and the distribution of the residual stresses in the surface matrix was measured, the X-ray diffraction method for the yield strength of the surface matrix of the composites was established to explore the strengthening effect of the surface shot peening. The results show that the surface matrix of the composites after shot peening shows a large compressive residual stress state, and the FWHM, that is, the microstructure strengthening effect, is significantly increased., resulting in an increase in the yield strength of the surface matrix of the composites.

Effects of residual stress and microstructure on extremely anisotropic grain growth in nanotwinned Cu films

In this study, the thermal stability and microstructural evolutions of nanotwinned copper (NT-Cu) films under thermal cycling are investigated. The microstructures and residual stresses were tuned by the electroplating current density. It was found that the thermal stability of the NT-Cu films decreased with an increase in current density. The texture transition from (111) to (100) suggests that the extremely anisotropic grain growth (EAGG) was driven by the minimization of strain energy. Bending beam technic was employed to measure the residual stress in the NT-Cu films. Large residual stress in the NT-Cu films is also considered a main driving force for the transition to the (100)-oriented texture. Additionally, strain energy, surface/interface energy, grain boundary energy, and twin boundary energy were calculated, and the results supported the experimental results.

Research on the Deformation Prediction Method for the Laser Deposition Manufacturing of Metal Components Based on Feature Partitioning and the Inherent Strain Method

Laser deposition manufacturing (LDM) has drawn unprecedented attention for its advantages in manufacturing large-scale and complex metal components. During the process of LDM, a large thermal gradient is generated due to thermal cycling and heat accumulation. As a result, large residual stress and deformation are formed in the LDM metal components. Then, the dimensional accuracy of the metal components becomes poor. To achieve deformation control and increase dimensional accuracy, the deformation prediction of metal components is very meaningful and directional. However, the traditional thermoelastic–plastic method can only achieve deformation prediction for small-scale LDM metal components. Because of the low computational efficiency, it is extremely difficult to meet deformation prediction demand for large-scale metal components. Based on feature partitioning and the inherent strain method, a rapid deformation prediction method is proposed for large-scale metal components in this manuscript. Firstly, to solve the problem of poor consistency of formation quality due to the randomness of the partition process, the partitioning process was established according to typical geometric features. Secondly, the inherent strain values for different partitions were obtained by considering the effects of the extraction method, mesh size, equivalent value layer, and partition size on the inherent strain values. Then, using the inherent strain method, the deformation of large-scale components was predicted rapidly. Comparing the simulation results with the experimental results, the following conclusions were obtained. The deformation predicted by the method proposed in this manuscript is consistent with the deformations predicted using the traditional thermoelastic–plastic method and the experimental method. Significantly, applying the method proposed in this manuscript to predict the deformation of LDM metal components, computational efficiency is improved by 27.25 times compared with results using the conventional thermoelastic–plastic method.

Effect of laser shock peening on wear resistance of M50 steel

The effects of laser shock peening (LSP) on the surface state and wear resistance of M50 steel are studied by microstructure observation, hardness, and residual stress detection. Results show that after LSP, the carbides on the surface of steel are broken and micro-pits appear. After removing the surface carbide damage by electrolytic polishing, the number of sub-surface carbides increases, and the maximum content is 26.1%. After LSP, the wear resistance of the steel is improved because LSP causes a large residual compressive stress on the surface. The wear performance of the sample after removing the surface damage becomes better, which is related to the elimination of many crack sources and the larger residual compressive stress.

Study on Welding Deformation Correction of TC4 Titanium Alloy Panel Parts

Aiming at the problem that TC4 titanium alloy panel parts after welding have large internal residual stress and obvious panel deformation, which can’t meet the requirements of the parts, the viscoelastic plastic model of titanium alloy panel parts is established by finite element analysis, and the welding deformation-thermal alignment collaborative simulation environment is established by ANSYS, and the welding deformation and thermal alignment process are analyzed by numerical simulation. The law of shape correction when the correction temperature is 600 °C, 650 °C, 700 °C and the holding time is 3600s, 5400s and 7200s, respectively, and the calculation formula of springback rate is established to evaluate the effect of thermal shape correction, so as to optimize the heat treatment correction process. The results show that the correction temperature and holding time have obvious influence on the correction effect. When the correction temperature is 700 °C and holding time is 7200s, the correction effect is the best, and the springback rate is controlled below 25%, which meets the requirements of machining accuracy.

Laser deposition of titanium layer to enhance two-way shape memory behavior of Nitinol sheet

One of the long-standing mechanical challenges associated with shape memory alloys (SMAs) is achieving and stabilizing an evolving two-way shape memory effect (TWSME) through thermomechanical training/cycling. In most martensitic NiTi SMAs that exhibit zero TWSME at room temperature, the TWSMEs typically require hundreds of cycling repetitions to track trivial values. This demonstrates a promising solution to overcome this challenge. The surface of NiTi SMA sheets was treated by depositing a certain number of titanium (Ti) powder layers on the NiTi surface using a laser beam. The results showed that a unique TWSME of approximately 12% with good stability was achieved after 100 cycles when the optimum number of five Ti layers was deposited, which was much higher than that of the NiTi sheet (0.3% TWSME) and the sample with a single-time laser path irradiation (1.8%). This was attributed to the low coefficient of thermal expansion of the Ti vs. NiTi sheet, which prevented reverse bending during heating, and the formation of Ti-rich intergranular Ti2Ni(Ox) precipitates, which hindered dislocation movement. Meanwhile, in this sample, owing to the generation of a large residual tensile stress and a large heat-affected zone that led to a reduction in plastic zones, the one-way shape memory effect (OWSME) was retained at values above 90% with good stability over cycling. However, the introduction of additional Ti layers can cause problems in terms of oxygen accumulation within the NiTi sheet, which should be considered when designing a product.

Relief of Residual Stress in Bulk Thermosets in the Glassy State by Local Bond Exchange.

The covalently cross-linked network gives thermosets superior thermal, mechanical, and electrical properties, which, however, squarely makes the large residual stress that is inevitably induced during preparation hardly relieved in the glassy state. In this work, an incredible reduction in residual stress is successfully achieved in bulk thermosets in the glassy state through introducing highly dynamic thiocarbamate bonds by "click" reactions of thiols and isocyanates. Due to the excellent dynamic behaviors of thiocarbamate bonds, local network rearrangement is achieved through thermal stimulation, while the strong 3D cross-linked network is well maintained. Ultimately, a decrease by 44% in residual stress is detected by simply annealing samples at 30°C below glass transition temperature (Tg), during which they could well maintain more than 98.4% of the storage modulus. After the annealing, more uniform residual stress distribution is also observed, showing a 32% decline in sample standard deviation. However, the residual stress of epoxy resin, a typical thermoset as a reference, changes little even after annealing at Tg. The results prove it a feasible strategy to reduce residual stress in bulk thermosets in the glassy state by introducing proper dynamic covalent bonds.

Re-evaluation of fatigue design curves for offshore wind monopile foundations using thick as-welded test specimens

The dominant majority of existing offshore wind turbines are supported using monopile foundations which are fabricated by welding thick steel plates. In the current fatigue design recommendations for welded steel structures, which are commonly used in the design of monopile structures, the initial inverse slope of the S-N curve is fixed to −3. The historic rationales for this assumption are the ease of fatigue life calculations, the effect of long-range residual stresses that were not originally captured in the test data on thin welded specimens, and analogy with fatigue crack growth. While this introduces an unquantified level of conservatism to deterministic fatigue calculations, it was an acceptable (and wise) assumption when the S-N design curves were generated a few decades ago; however, current designs and assessments require more accurate calculations and the need to more confidently quantify the likelihoods attached to these evaluations. In the present study, it is argued that unlike large braced structures (e.g. jackets) in which long-range residual stresses may remain in place as fatigue cracks propagate, in circumferential welds of monopile structures the natural relaxation of residual stresses, in the absence of long-range residual stresses, must be accounted for by performing fatigue tests on thick welded samples. This paper presents a thorough analysis of the fatigue test results obtained from 50 mm thick as-welded samples with representative profiles of residual stresses that exist in monopiles. Basic and advanced statistical approaches were employed in the analysis and higher values of inverse slope were found using the large thickness test data. The results from this study are compared with the recommended fatigue design curves available in international standards. The outcomes from this research draw important observations concerning the need to employ an appropriate value of inverse slope in the design of monopile structures by excluding the conservative approach imposed by a fixed value of −3 which was originally implemented for braced structures with the assumption of large and long-range residual stresses.

Anisotropic growth of nano‐precipitates governed by preferred orientation and residual stress in an Al‐Zn‐Mg‐Cu alloy

Through an understanding of diffusion, precise control of the size distribution of nano-precipitates can be essential to developing superior properties in precipitation-strengthened alloys. Although a significant influence of crystallographic orientation on the diffusion process is known to exist in low-symmetry hexagonal close-packed alloys, such anisotropic diffusion is still unidentified in high-symmetry cubic alloys. In this work, we reveal the diffusion-controlled coarsening induced anisotropic growth process of nano-precipitates in an Al-Zn-Mg-Cu alloy. Our experimental and theoretical studies demonstrate that with an increase in the residual stress, the diffusion-controlled coarsening rate is slow along the 〈112〉 fiber texture in the alloy matrix with smaller grain sizes. As such, we find that the diffusion activation energy will be increased along the preferred orientation with largest residual stress, which leads to a reduced diffusion-controlled coarsening rate. Specifically, we demonstrate that the increase in the volume fraction of nano-precipitates originates from the rapid grain-boundary controlled coarsening of the grain-boundary precipitates. Based on these results, an underlying microstructural design strategy is proposed, involving the crystallographic orientation, the residual stress and the grain boundaries to manipulate the precipitate size distribution in this class of alloys.