Reduction Of Residual Stress Research Articles

Effects of processing parameters and heat treatment on the microstructure and magnetic properties of the in-situ synthesized Fe-Ni permalloy produced using direct energy deposition

The present work investigated the correlations between heat treatment and the microstructure and magnetic properties of the in situ alloyed Fe-50%Ni samples manufactured using laser-based direct energy deposition under different production conditions. The samples with high relative density were directly synthesized from the pure Fe and Ni elemental powders. In addition, a fine FCC microstructure with relatively elongated grains in the building direction was observed in the as-print samples. After applying short-time heat treatment, the grain morphology remained unchanged, while the grain size and microhardness were slightly increased and decreased, respectively. This also caused the reduction in internal residual stresses and, subsequently, partial stress relaxation in the microstructure. According to the electron probe microanalysis results, the simultaneous Fe and Ni depletion/enrichment formed during the in-situ alloying was practically decreased after applying short time heat-treatment, resulting in the significant improvement of magnetic properties, as compared to the as-built ones. The maximum magnetization, coercivity, and curie temperature of ~170 emg/g, 1.8 Oe, and 530 °C, respectively, were obtained in the optimum processed sample, which were significantly higher than those of other soft magnetic permalloys produced by additive manufacturing methods.

Oxygen-Induced Residual Stress Reduction of Cubic Boron Nitride Films: Reinterpretation of Ye’s Results Considering Interfacial Turbostratic Boron Nitride Layer

Oxygen-Induced Residual Stress Reduction of Cubic Boron Nitride Films: Reinterpretation of Ye’s Results Considering Interfacial Turbostratic Boron Nitride Layer

Residual Stress Reduction with the LTT Effect in Low Carbon Manganese-Steel through Chemical Composition Manipulation Using Dissimilar Filler Material in Laser Beam Welding

This paper investigates the manipulation of chemical composition of a laser weld by dissimilar filler material and its effect on residual stress. The aim is to minimize residual stresses in the weld seam. In order to negate residual stresses, dissimilar combinations of low-carbon manganese steel (S235JR) base material with high-alloyed solid filler wires (G19 9 and G25 20), as well as similar combinations with low-alloyed solid filler wire G3Si1 are analyzed. The goal of the paper is to show that the so-called low-transformation-temperature effect can be used to induce residual compressive stresses in a weld without the use of specially manufactured filler wires. Chemical compositions are generated within a laser-beam-welding process by means of dilution, proving that the concept of in situ alloying is usable in order to affect the martensite formation on a weld. Dilatometry measurements show that a varying Cr and Ni content in a weld reduces the phase-transformation temperature and increases dilatation. EBSD analysis indicates that a fully martensitic weld with a negligible amount of retained austenite is created while the base material preserves its ferritic-pearlitic microstructure. Residual stress measurements with the hole-drilling method demonstrate a reduction in longitudinal tensile residual stresses, whereby the magnitude of the induced residual compressive stresses depend on the Ms temperature. As a result of this research, it was proven that a reduction in tensile residual stress by means of targeted alloying with conventional materials in low-carbon manganese steel is possible. Under the experimental conditions, residual stress in the weld seam could be reduced to 0 MPa. In some cases, even compressive residual stress in the weld could be achieved.

Evolution Behaviors and Reduction Mechanism of Curing Residual Stresses in GLARE Laminates under a Hot-Pressing Condition.

Nowadays, variable preparation, forming and processing methods of fiber metal laminates are constantly developing to meet the requirements of different application fields, hence the characteristics and evolution of residual stresses under different manufacturing conditions deserve more attention. In this work, the evolution behaviors of curing residual stresses in GLARE under a hot-pressing condition were studied, and the residual stress reduction mechanism was also explained. Results suggested the FE prediction models of the entire cure process, verified by the fiber Bragg grating (FBG) sensors, were more precise than the traditional elastic model. Moreover, the stress evolution during the cure process mainly occurred in the cooling stage, in which the different coefficient of thermal expansion (CTE) of aluminum and GFRP played a major role. Meanwhile, curing shrinkage stress in the GFRP layer during the holding stage at curing temperature obviously influenced the final stress level. The residual stresses in GFRP layers differed by 9.6 MPa under a hot-pressing and autoclave condition, in which the convection heat transfer condition played a major role as it caused lower thermal stress in the holding stage and a smaller temperature gradient in the cooling stage. Considering this, a lower cooling rate could be a feasible way to obtain GLARE with lower residual stress under a hot-pressing condition.

Influence of Laser Polishing on the Material Properties of Aluminium L-PBF Components

In this study, the influence of laser polishing on the microstructural and mechanical properties of additively manufactured aluminium AlSi10Mg Laser Powder Bed Fusion (L-PBF) parts is analysed. The investigation is carried out on a 5-axis laser cell equipped with 1D Scanner optics driven by a solid-state disc laser at a wavelength of 1030 nm. Laser polishing is performed with pulsed or continuous laser radiation on samples in the initial L-PBF state or after stress relief treatment in a furnace. The metallurgical investigation of the remelting zone with a depth of 101–237 µm revealed an unchanged and homogeneous chemical composition, with a coarsened α-phase and a changed grain structure. The hardness within the remelting zone is reduced to 102–104 HV 0.1 compared to 146 HV 0.1 at the L-PBF initial state. Below the remelting zone, within the heat affected zone, a reduced microhardness, which can reach a thickness up to 1.5 mm, occurs. Laser polishing results in a reduction in residual stresses and resulting distortions compared to the L-PBF initial state. Nevertheless, the re-solidification shrinkage of the polished surface layer introduces additional tensions, resulting in sample distortions well above ones remaining after a stress relieve heat treatment of the initial state. The mechanical properties, analysed on laser polished flat tensile specimens, revealed an increase in the ultimate elongation from 4.5% to 5.4–10.7% and a reduction in the tensile strength from 346 N/mm2 to 247–271 N/mm2 through laser polishing. Hence, the strength resulting from this is comparable to the initial L-PBF specimens after stress relieve heat treatment.

Enhanced pitting resistance of directed energy deposition 316L stainless steel by post-manufacturing heat treatment

The effect of the post-manufacturing heat treatment (PMHT) on the pitting resistance of the directed energy deposition (DED) 316L stainless steel was evaluated. In an as-manufactured DED 316L, a fully austenitic microstructure with typical cellular structure and large columnar grains was observed. The cellular structure was retained after the PMHT of 850 °C/2 h but fully removed by the PMHT of 1150 °C/1 h, while large columnar grains survived in both cases. Both PHMTs significantly improved the pitting resistance of the DED 316L. Especially, the pitting potential of the DED 316L after the PMHT of 1150 °C/1 h was comparable to that of 2205 duplex stainless steel. The excellent pitting resistance of DED 316L after the PMHT of 1150 °C/1 h was caused by the reduction of residual stress, elimination of cellular structure, and presence of large columnar grains.

Investigating residual stress evolution in the deposition process of diamond-like carbon film through molecular dynamics

Diamond-like carbon (DLC) films possess excellent tribological properties, such as low friction and high wear resistance. However, DLC films detach easily owing to the high residual stress, which limits their application on mechanical sliding surfaces. To overcome this problem, it is crucial to clarify the residual stress generation mechanism in DLC films. In this study, molecular dynamics simulations were conducted on the deposition process of a DLC film to clarify the residual stress generation mechanism. The results suggest that sp3 hybridization clusters are nucleated in the sp2 formed on the film surface, and sp3 clusters grow in the sp2 carbon through the sp2 → sp3 bond change during the film growth process. The bond length of sp3 was approximately 8.5% larger than that of sp2 under stress-free bulk conditions. Thus, when the sp2 → sp3 bond change occurs under construction by surrounding atoms, compressive stress is generated in the sp3 cluster, which increases with the growth of the sp3 cluster. Based on the results, we conclude that the nucleation and growth of sp3 clusters in sp2 result in residual compressive stress in the DLC film. We believe that the present mechanism clarification of the stress development process in DLC films will facilitate the development of new methods for residual stress reduction.

A numerical formalism towards finding a good component orientation in laser powder bed fusion

• Mathematical formulation of several of objectives considered when deciding how to orient a part during LPBF. • Consideration of printing cost as a metric affecting orientation decisions. • Reduction of complex distortion and residual stress results to a representative variable manageable by multi-objective optimization. • Discontinuity in distortion and residual stress results make it difficult to use machine learning tools. Monte-Carlo optimization is not as sensitive to discontinuities. • The frequency of distortion computations is analyzed to achieve reasonably reliable predictions with least possible computational effort. Several manufacturing constraints and objectives are considered when choosing a build orientation for laser powder bed fusion (LPBF) parts. Some of them are inversely proportional to one another making it necessary to formalize an optimization scheme with weighting factors enabling engineers to decide which of them is most relevant for the application under consideration. Several of the considered cost functions are quick to calculate (e.g. down skin area). The reduction of residual stresses and distortion are on the other hand computationally intensive and are not easily considered in an optimization scheme. Solution sampling in 3 angular directions is therefore utilized to create a response surface describing the part distortion in arbitrary orientations. The response surface accuracy is studied before applying it together with 7 other cost functions within a multi-objective Monte-Carlo optimization scheme.

Creep rupture ductility of ferritic creep resistant steels

ABSTRACT The creep rupture ductility of not only creep strength enhanced ferritic steels but also conventional 2.25Cr-1Mo steels was investigated, focusing on the remarkable decrease in ductility in the long term. The decrease was well described as a function of yield ratio of applied stress and appeared at about 50% of the 0.2% offset yield stress at the creep test temperature with decrease in the yield ratio. A trade-off relation between creep rupture strength and creep rupture ductility was found for Grade T/P23 steels. The similar trade-off relation between creep strength and ductility was observed also for conventional 2.25Cr-1Mo steels. A remarkable drop in creep rupture ductility of quenched and tempered 2.25Cr-1Mo steels was found in conjunction with a large drop in creep rupture strength. This remarkable drop was considered to be caused by microstructural changes due to the inhomogeneous progress of recovery of tempered martensitic microstructure. A modified heat treatment process with intermediate tempering on partially quenched dual phase microstructure was found to have a beneficial effect on creep rupture ductility for Grade P92 steel. This was considered to be the result of the reduction in residual stress introduced by martensitic phase transformation accompanied with shape change and volume expansion.

Evaluation of the effect of heat treatment on the structure parameters and cold resistance of metals produced by additive electric arc growth

In this work, we studied the influence of the type and mode of heat treatment on the structure and parameters of cold resistance of 09Mn2Si and 07Cr25Ni13 steels obtained by additive electric arc growth. It is shown that, under optimal printing conditions, a relatively uniform and fine-grained material structure is observed in 09Mn2Si steel, while a dendritic structure is observed in the 07Cr25Ni13 alloy. Heat treatment of the investigated alloys leads to a more uniform distribution of structural components in metals, and in steel 07Cr25Ni13 the dendrites are destroyed, which leads to a decrease in the anisotropy of material properties. Also, heat treatment leads to a significant reduction in internal residual stresses in the material. The results of the study of impact strength in a wide range of low temperatures show that in the initial state after surfacing, the investigated alloys have a significant anisotropy of impact strength (up to 8 and 25% for alloy 09Mn2Si and 07Cr25Ni13, respectively). Heat treatment significantly reduces the anisotropy of the properties of the studied alloys and increases the values ​​of impact strength. So for steel 09Mn2Si after heat treatment, an increase in impact strength by more than 1.5 times is observed over the entire temperature range. The studies carried out made it possible to identify the temperature range of the ductile-brittle transition and the impact strength of 09Mn2Si and 07Cr25Ni13 alloys, which is of great practical importance in the manufacture of parts and structural elements of the Northern version.

Research on reduction of residual stress in girth welds of large-diameter natural gas pipes by ultrasonic

ABSTRACT Excessive residual stress of the girth weld in pipes will directly damage the pipe strength during its operation. Accurate measurement and effective reduction of the residual stress can ensure the safety of natural gas pipes during their service. In this paper, an X80-type large-diameter natural gas pipe section with girth welds is taken as the research object. The coercive force method is used to characterize the residual stress of the girth weld and its surroundings, and then the distribution law of the residual stress of the girth weld and its surroundings is obtained based on the measurement results of the Blind-hole method; the ultrasonic impact method was used to reduce the girth weld residual stress, and the effect of the ultrasonic impact method on the residual stress reduction was studied by comparing changes of the distribution characteristics of the coercive force in the girth weld and its surroundings before and after the residual stress reduction in the natural gas pipes. Lastly, the in-situ test specimen is made to carry out the uniaxial tensile test so as to study the effect of the ultrasonic impact method on the tensile mechanical properties of pipe welds. This study clarifies the influence law of the ultrasonic impact on the mechanical properties of weld toe materials, and provided technical theoretical guidance for the reduction of field residual stress in natural gas pipes.

RETRACTED ARTICLE: Effect of cooling process on reducing residual stress of hot rolled high strength strip

ABSTRACT In order to analyse the influence of different laminar cooling technology on residual stress of steel strip, a finite-element model of strip was established with ABAQUS and FORTRAN named basic model. The evolution of temperature, phase transformation and stress of the strip during cooling process were expressed with coupling calculation. Other four finite-element models were established based on the basic model by changing its initial condition and boundary condition. The new models represented four cooling technology named edge masking, sparse cooling, posterior cooling and initial transverse temperature difference controlling. The results show that the stress distribution on strips tends to be high compressive stress on edge and tensile stress on middle section. The effect of the four cooling technologies on the residual stress reduction is ranked as initial transverse temperature difference controlling, sparse cooling, edge masking and posterior cooling.

Uphill Quenching to Reduce Residual Stress in Aluminium Alloy 7449 Hollow Structures

BackgroundUphill quenching (UHQ) of heat treatable aluminium alloy components is a long established but rarely practiced or investigated method of reducing residual stresses. The efficacy of the technique has not been quantified on thin walled structures before and this investigation will address that deficiency.ObjectiveTo quantify the impact of uphill quenching on thin walled structure with regards to residual stress and warpage, and compare and contrast to both quenching into cold water and a 30% polyalkylene glycol (PAG) solution.MethodsRectilinear hollow boxes were made from the very high strength aerospace aluminium alloy 7449. These were heat treated and aged using a variety of processing methods including uphill quenching from -196 °C to 100 °C using steam. Residual stresses have been characterised using neutron and x-ray diffraction.ResultsCompared to conventional quenching into cold water, both PAG and UHQ are shown to significantly lower the residual stresses. However, while PAG quenching results in a large uniform reduction in both residual stress and warpage, UHQ is much more localised and limited to regions adjacent to direct steam impingement. These regions are also warped. The depth of penetration of the stress relief during UHQ is shown to be 5 mm.ConclusionsWhile uphill quenching is shown to be capable of locally stress relieving an aluminium alloy, it is far less effective compared to PAG quenching.

Damage-tolerant material design motif derived from asymmetrical rotation

Motifs extracted from nature can lead to significant advances in materials design and have been used to tackle the apparent exclusivity between strength and damage tolerance of brittle materials. Here we present a segmental design motif found in arthropod exoskeleton, in which asymmetrical rotational degree of freedom is used in damage control in contrast to the conventional interfacial shear failure mechanism of existing design motifs. We realise this design motif in a compression-resisting lightweight brittle material, demonstrating a unique progressive failure behaviour that preserves material integrity with 60–80% of load-bearing capacity at >50% of compressive strain. This rotational degree of freedom further enables a periodic energy absorbance pattern during failure yielding 200% higher strength than the corresponding cellular structure and up to 97.9% reduction of post-damage residual stress compared with ductile materials. Fifty material combinations covering 27 types of materials analysed display potential progressive failure behaviour by this design motif, thereby establishing a broad spectrum of potential applications of the design motif for advanced materials design, energy storage/conversion and architectural structures.

Numerical investigation of sequential cuts residual stress considering tool edge radius in machining of AISI 304 stainless steel

Residual stress affects component performance, and the existence of pre-stress changes the residual stress of machined surfaces as well, emphasizing the importance of studying the evolution of residual stress in sequential cutting. This paper reports a numerical investigation of the machining-induced residual stress profile of sequential cuts for orthogonal cutting of AISI 304, considering the effects of edge radius and cutting depth. A Coupled Eulerian-Lagrangian (CEL) model is employed for the first time to stably simulate the evolution of residual stress of multiple sequential cuts. The effectiveness of the proposed method is verified by comparing the chip formation and surface residual stress between simulated and experimental results. The cutting force and cutting temperature, as well as mechanical and thermal loads, are extracted to explain the generation and evolution of residual stress in sequential cutting. It is found that the residual stress on the machined surfaces will decrease during sequential cutting, and a stable value can be reached after approximately six sequential cuts. With the progress of sequential cutting, a larger honed tool edge radius and cutting depth will lead to a slower reduction of residual stress.

Process Parameters Optimisation for Mitigating Residual Stress in Dual-Laser Beam Powder Bed Fusion Additive Manufacturing

Laser beam powder bed fusion (PBF-LB) additive manufacturing (AM) is an advanced manufacturing technology that manufactures metal components in a layer-by-layer manner. The thermal residual stress (RS) induced by the repeated heating–melting–cooling–solidification processes of AM is considered to limit the wider uptake of PBF-LB. A dual-laser beam PBF-LB strategy, with an additional auxiliary laser and reduced power, working in the same powder bed simultaneously, was recently proposed to lower RS within the manufactured components. To provide insights into the optimum PBF-LB AM configurations and process parameters for dual-laser PBF-LB, this study proposed three different coordinated heating strategies (i.e., parallel heating, post-heating, and preheating) of the auxiliary heat source. The temperature fields and RS of dual-laser beam PBF-LB, for Ti-6Al-4V with different process parameters, were computationally investigated and optimized by the thermo-mechanically coupled 3D models. Compared with the single beam PBF-LB, parallel heating, post-heating, and post-heating strategies were proved as effective approaches to reduce RS. Among these, the preheating scanning is predicted to be more effective in mitigating RS, i.e., up to a 10.41% RS reduction, compared with the single laser scanning. This work could be beneficial for mitigating RS and improve the mechanical properties of additively manufactured metal components.

Influence of Ambient Temperature on Part Distortion: A Simulation Study on Amorphous and Semi-Crystalline Polymer.

Semi-crystalline polymers develop higher amounts of residual stress and part distortion (warpage) compared to amorphous polymers due to their crystalline nature. Additionally, the FDM processing parameters such as ambient temperature play an important role in the resulting residual stresses and part distortion of the printed part. Hence, in this study, the effect of ambient temperature on the in-built residual stresses and warpage of amorphous acrylonitrile-butadiene-styrene (ABS) and semi-crystalline polypropylene (PP) polymers was investigated. From the results, it was observed that increasing the ambient temperature from 50 °C to 75 °C and further to 120 °C resulted in 0.22-KPa and 0.37-KPa decreases in residual stress of ABS, but no significant change in the amount of warpage. For PP, increasing ambient temperature from 50 °C to 75 °C led to a more considerable decrease in residual stress (0.5 MPa) and about 3% increase in warpage. Further increasing to 120 °C resulted in a noticeable 2 MPa decrease in residual stress and a 3.4% increase in warpage. Reduction in residual stress in both ABS and PP as a result of increasing ambient temperature was due to the reduced thermal gradients. The enhanced warpage in PP with increase in ambient temperature, despite the reduction in residual stress, was ascribed to crystallization and shrinkage.

Finite element analysis, prediction, and optimization of residual stresses in multi-pass arc welding with experimental evaluation

Prediction and reduction of unwanted tensile Residual Stress of welded stainless-steel plates is presented in this paper. Validated finite element analysis and Artificial Neural Network (ANN) is employed to simulate and mathematically model the process, respectively. Taguchi design of experiments tool is utilized to generate input data for finite element analyses and also to choose the most accurate ANN structures. RSs are minimized using three methods: Taguchi suggestion, Comprehensive factorial search, and Particle Swarm Optimization, whose accuracy and response pace increases and decreases respectively in this order. Furthermore, adding and removing extra weld lines was proposed to reduce unwanted residual stresses by up to 50%. Finally, the shapes and amounts of results are experimentally verified using contour method and proposed novel application of roughness testing. Micro-grain structures of the welded samples were also investigated, and RSs were discussed considering metallography images.

Residual stress control of 316 L stainless steel using pulsed-wave laser additive manufacturing

In this paper, 316 L stainless steel were fabricated by direct laser deposition (DED) using both continuous-wave (CW) and pulsed-wave (PW) laser modes. Effects of laser modes on residual stress, geometric dislocation density (GND) and solid phase transformation with a given heat energy input were investigated. Results showed that PW mode tends to generate less concentrated, lower residual stress than that CW mode does, which the decline range was reached about 42% at the joint of the deposition and the substrate and approximately 75% on the deposition respectively. This is determined by the process characteristics of PW mode. Firstly, the relatively small temperature gradient in PW mode directly causes small thermal stress. Secondly, the characteristic of periodic temperature history and an improved cooling rate of molten pool in PW mode leads to more thermal stress relaxation. The released thermal stress can be used as a driving force for the formation of dislocations at grain boundaries. In addition, solid phase transformation does not occur with PW mode, which has little contribution to the reduction of residual stress.

Silicon carbide/enamel composite coatings for steel corrosion protection: Microstructure, thermal expansion behavior, and anti-corrosion performance

Vitreous enamel coating has been utilized to protect metallic substrates against corrosion and has proven to be effective. Herein, a new low-temperature sintering silicon carbide/enamel composite coating was produced and compared to pure enamel coating. The microstructure, thermal expansion behavior, and anti-corrosion performance of the prepared coatings were evaluated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), dilatometric test, and electrochemical measurements (open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and linear polarization resistance (LPR)). The results indicated that the composite coatings had gradually matched thermal expansion with the steel substrate due to the inclusion of silicon carbide and the raised porosity, which further resulted in the reduction of residual stress and the eradication of surface microcracks. The microstructural alterations increased the anti-corrosion effectiveness of composite coatings, according to the early electrochemical testing (at 24 h). Particularly, the polarization resistance (Rp) of a composite coating containing 7.5 wt% silicon carbide addition was found to be 20 times greater than that of the pure enamel coating. These results imply that the silicon carbide/enamel composite coating outperforms the pure enamel coating and can provide effective corrosion protection for steel.