High Compressive Residual Stress Research Articles

Prediction of residual stress depth profiles in case-carburized gears

Residual stresses have a significant influence on the load carrying capacity of gears. High near-surface compressive residual stresses can increase pitting strength and tooth root bending strength up to 50%. Tooth flank fracture (TFF) is a gear fatigue failure mode, which is in contrast to pitting or tooth root breakage not initiated at the surface or close to the surface but in larger material depths beneath the active gear flank. Therefore, the residual stresses in larger material depths are decisive for TFF. In these larger material depths, the residual stress conditions are almost unknown up to now. It is assumed that tensile residual stresses are present in these areas, which can negatively influence the TFF load carrying capacity. So far, no validated methods are known to estimate or predict these tensile residual stresses. As a result, the tensile residual stresses could not be considered in the calculation methods for the risk of TFF at all until recently.This paper presents a method to predict the residual stresses in case-carburized gears based on comprehensive numerical simulations of case-carburizing processes of different-sized gears. The calculated residual stress profiles also consider the tensile residual stresses in larger material depths.

Residual stress depth profiles self-developed in cathodic arc deposited Ti-Al-N coatings prepared at different constant substrate bias values

Ti-Al-N coatings were prepared by cathodic arc deposition on Inconel 718 substrates at different values of constant substrate bias voltage, aiming to produce samples with different self-developed residual stress (RS) depth profiles through the thickness of the coatings. RS profile measurements and structural characterization were performed on a laboratory-scale x-ray diffraction system (x-ray energy of 8 keV) and in a synchrotron x-ray radiation facility (x-ray energy of 15 keV). Mechanical testing to obtain hardness and Young’s modulus values was performed by instrumented nanoindentation. The results indicate higher compressive RS at the film/substrate interface that decays to lower compressive stress or mild tensile stress at the film surface. Surface hardness and the compressive RS value of the coating increase with larger values of the substrate bias voltage. By comparing the stress characterization done on a laboratory scale and at the synchrotron facility, one observes a generally good agreement, indicating that these analyses may be conducted at a smaller scale and with less costly equipment, and still maintain a reliable precision. The work presents and reviews in detail the methodology of the RS depth-profile analysis. The highest hardness of 31.1 GPa and near-substrate compressive RS around −10 GPa were obtained for a bias of −100 V. Transmission electron microscopy results indicate that regions with higher compressive stresses are found to have smaller columns and denser structure, while portions of the same sample with mild compressive or tensile stresses present larger column size and are richer in hexagonal phases. The findings demonstrate the complex interplay between stress, microstructure, and ultimately mechanical properties in industrially produced Ti-Al-N coatings and indicate that any successful strategy to mitigate stress development should consider the inhomogeneous self-developed stress gradients present even in coatings deposited under constant and controlled conditions.

Machinability of extruded H13 tool steel: Effect of cutting parameters on cutting forces, surface roughness, microstructure, and residual stresses

The production of H13 tool steel (TS) by material extrusion (MEX) is a promising method in various applications, but as-built surface roughness does not comply with the quality requirements. Hence, this study investigated the effects of cutting parameters on tool wear, cutting forces, surface quality, microhardness, structure, and residual stresses when machining H13 TS produced by MEX. Dry machining (DM) proved advantageous in certain indicators such as tool wear and cutting forces in comparison to the flood cooling (FC). The lowest surface roughness (0.08 µm) was achieved at the cutting speed of 80 m/min, feed per tooth of 0.005 mm, and FC which corresponded to a 41 % decrease compared to DM under same conditions. Surface microhardness increased by 20 % after machining, decreasing with distance from the surface. The highest compressive residual stresses were observed under FC, while the DM resulted in a 78.2 % decrease in residual stresses due to a partial annealing effect caused by higher surface temperature. Overall, DM exhibited great potential for achieving high-quality surfaces with a favorable structure and residual stresses. This study´s novelty and robustness lie in its significant contribution to practical industrial applications, such as mold and core production.

Microstructure, corrosion resistance and wear properties of laser directed energy deposited CrCoNi medium-entropy alloy after cyclic deep cryogenic treatment

ABSTRACT Subjected to repeated heating and cooling, laser directed energy deposited (LDED) parts always possess considerable residual stress, which severely limits their industrial applications. In this work, cyclic deep cryogenic treatment (CDCT) was performed to finely tune the residual stress and microstructure of LDED-fabricated CrCoNi medium-entropy alloy (MEA). With increasing number of CDCT cycles, crystalline defects within the sample became denser due to the repeated visco-plastic deformation. The compressive residual stress (CRS) of the sample was estimated to be 361.9 ± 16.8 MPa after 30 cycles of CDCT, 64.2% higher than that in the as-built condition. Due to the existence of dense crystalline defects and high CRS, the corrosion and wear rates of CDCT-treated CrCoNi MEA were significantly decreased compared with the as-built condition. This work demonstrated CDCT as an effective means for regulating the residual stress, microstructure, and surface performance of LDED-fabricated MEA.

Surface integrity and corrosion resistance of 18CrNiMo7-6 gear steel subjected to combined carburized treatment and wet shot peening

Typically, a cost-effective and versatile carburizing process is used to improve the surface integrity of high-value-added gear components. In this study, carburized treatment and wet shot peening (WSP) were applied to increase the corrosion resistance of 18CrNiMo7-6 gear steel. The surface integrity and corrosion resistance after carburizing and combined treatment (carburized treatment + WSP) were analyzed. The results indicated that the combined treatment converted the retained austenite surface layer within approximately 45 μm from the surface into the martensitic phase, with a 13.9 % reduction in equivalent grain size and a 23.6 % increase in dislocation density compared with carburizing. Furthermore, electrochemical experiments in a 3.5 wt% NaCl solution indicated that the combined treatment process increased the corrosion resistance compared with carburizing (55.4 % lower corrosion current density and a higher Fe2+/Fe3+ ratio). Despite the high surface roughness obtained with combined treatment, the improved corrosion resistance is primarily ascribed to the high compressive residual stress and dislocation density. This study provides insights into the surface strengthening design of 18CrNiMo7-6 gear steel for corrosive environments—particularly the synergistic strengthening effect of carburizing and WSP.

Investigation of the Machined Surface Integrity of WC-High-Entropy Alloy Cemented Carbide

A fine-grained WC-15wt%Al0.5CoCrFeNi cemented carbide was prepared through a vacuum and gas pressure sintering. For achieving high surface integrity, diamond wheel grinding serves as the primary molding process for the machining of WC cemented carbide. To reveal the influence of grinding on the surface integrity of fine-grained WC-HEA cemented carbide, studies were conducted on grinding force, surface microstructure, surface roughness, residual stress, microhardness, and bending strength. The morphological analysis of the ground surface indicated a transition in the material removal mechanism of WC-HEA cemented carbide from ductile removal to brittle removal, with brittle removal becoming predominant as the depth of grinding increases. With the increasing depth of grinding, the grinding force increases, and the grinding force increases while the surface roughness decreases. Correspondingly, there is an improvement in both hardness and bending strength. Additionally, grinding induces high residual compressive stress on the surface, with a maximum compressive stress of 1795 MPa. The bending strength of the material is found to be dependent on the residual stress.

Laser peening without coating fabricated superhydrophobic aluminum alloy with favorable mechanical properties

This study prepared 2024-T351 aluminum alloy surfaces with excellent hydrophobic properties by laser peening without coating(LPwC) and post-treatment process (silane solution immersion modification treatment). The surface morphology, microhardness, roughness and residual stress of the specimens before and after LPwC were characterized. Besides, the surface composition and droplet contact angle of the specimens before and after LPwC were measured to investigate the mechanism of enhancing the hydrophobic properties by LPwC. The results showed that after LPwC treatment, the surface of the specimen was uniformly distributed with a large number of micro-nano porous structures and the surface roughness was significantly increased. After the modification treatment with fluorosilane solution, the F element on the surface of the specimen significantly increased, the surface energy decreased, the droplet contact angle rose to above 150°, and the sliding angle dropped to below 10°, which imparted the superhydrophobicity on the surface. After LPwC treatment, the grain size of the specimen near-surface layer was reduced, and high magnitude residual compressive stress was generated inside the matrix, which increased the microhardness of material. The as-prepared superhydrophobic surface exhibits excellent water flow repellency and favorable mechanical properties, which promoted the application of superhydrophobic preparation process in the aerospace field.

Pulsed-dc bias magnetron sputtered TiB2 ceramic coating

Titanium diboride, TiB2, is well known as a ceramic material with a hexagonal structure which presents various attractive properties, such as high hardness and excellent corrosion, thermal oxidation, and wear resistance. However, one drawback of TiB2 coatings is their poor adhesion to substrate materials due to high compressive residual stress after deposition. The present study aimed to assess whether a PVD-TiB2 coating with both high hardness and sufficiently good adhesion to the substrate and good wear properties can be developed by a closed-field unbalanced magnetron sputtering system using pulsed-dc biasing. The TiB2 coating deposited on AISI M2 steel substrates was characterized in terms of the structural, mechanical and tribological property. From the experimental results, it can be concluded that a closed-field unbalanced magnetron sputtering system using pulsed-dc biasing can be used to produce a TiB2 coating with sufficiently good adhesion (82 N), and high hardness (2300 HK0.01), and low friction (0.34) under given deposition conditions. The deposition conditions, particularly substrate biasing and rotation, which inhibited the formation of (001) orientation, played a role in the coating's lack of superhardness.

In-process approach for editing the subsurface properties during single-lip deep hole drilling using a sensor-integrated tool

Single-lip deep-hole drilling (SLD) is characterized by high surface quality and compressive residual stress in the subsurface of the drill hole. These properties depend significantly on the thermomechanical conditions in the machining process. The desired subsurface properties can be adjusted in-process via process monitoring near the cutting zone with a sensor-integrated tool and closed loop control when the thermomechanical conditions are maintained in the optimum range. In this paper, a method is presented to control the thermomechanical conditions to adjust the properties in the subsurface. The process model integrated in the controller is implemented as a soft sensor and takes into account the residual stresses, the roughness, the hardness and the grain size in the surface as well as in the subsurface depending on the process control variables, such as the feed rate and cutting speed. The correlation between the process variables, the thermomechanical conditions of the cutting process and the subsurface properties are investigated both experimentally and by finite element (FE) simulations. Within a justified process parameter range, characteristic fields for the soft sensor were established for each property. In addition, the procedure of controller design and the employed hardware and interfaces are presented.

The Influence of Spraying Parameters and Powder Sizes on the Microstructure and Mechanical Behavior of Cold-Sprayed Inconel®625 Deposits

Cold spraying (CS) of high-strength materials, e.g., Inconel®625 is still challenging due to the limited material deformability and thus high critical velocities for achieving bonding. Further fine-tuning and optimization of cold spray process parameters are required, to reach higher particle impact velocities and temperatures, while avoiding nozzle clogging. Only then, sufficiently high amounts of well-bonded particle–substrate and particle–particle interfaces can be achieved, assuring high cohesive strength and minimum amounts of porosities. In this study, Inconel®625 powder was cold sprayed on carbon steel substrates, using N2 as propellant gas under different spray parameter sets and different powder sizes for a systematic evaluation. Coating microstructure, porosity, electrical conductivity, hardness, cohesive strength, and residual stress were characterized in as-sprayed condition. Increasing the process gas temperature or pressure leads to low coating porosity of less than 1% and higher electrical conductivity. The as-sprayed coatings show microstructures with highly deformed particles. X-ray diffraction reveals that powder and deposits are present as γ-solid-solution phase without any precipitations. The deposits show high microhardness and compressive residual stresses, which is attributed to work hardening and peening effects. The optimized deposits reach almost bulk material properties and are thus well suited for industrial applications.

Control concept for the regulation of the surface layer properties using consecutive cuts in cryogenic hard turning of AISI 52100

In this study, a control concept for the simultaneous adjustment of the workpiece residual stresses and the surface roughness when cryogenic hard turning AISI 52100 is presented. The turning process is comprised by two consecutive cuts in which the process parameters vary, focusing on roughing and finishing; i.e. first a high, then a low depth of cut. On the first cut, the surface residual stress is adjusted via the cutting speed. On the second cut, the surface roughness is minimized by adjusting the feed rate while maintaining high compressive residual stresses. The surface residual stresses are determined by XRD and hole drilling measurements. For the estimation of the residual stresses the passive force is used. Based on these results, a control concept is presented which makes several assumptions that are partly validated by experiments.

Residual Stresses in Ribbed Reinforcing Bars.

Ribbed reinforcing bars (rebars) are used for the reinforcement of concrete structures. In service, they are often subjected to cyclic loading. In general, the fatigue performance of rebars may be influenced by residual stresses originating from the manufacturing process. Knowledge about residual stresses in rebars and their origin, however, is sparse. So far, residual stress measurements are limited to individual stress components, viz., to the non-ribbed part of the rebar surface. At critical points of the rebar surface, where most of the fatigue cracks originate, i.e., the foot radius regions of transverse ribs, the residual stress state has not yet been investigated experimentally. To extend the knowledge about residual stresses in rebars within the scope of this work, residual stress measurements were carried out on a rebar specimen with a diameter of 28 mm made out of the rebar steel grade B500B. In addition, numerical simulations of the TempCoreTM process were carried out. The results of the experimental investigations show tensile residual stresses in the core and the transition zone of the examined rebar specimen. Low compressive residual stresses are measured at the non-ribbed part of the rebar surface, while high compressive residual stresses are present at the tip of the transverse ribs. The results of the numerical investigations are in reasonable accordance with the experimental results. Furthermore, the numerical results indicate moderate tensile stresses occurring on the rebar surface in the rib foot radius regions of the transverse ribs. High stress gradients directly beneath the rebar surface, which are reported in the literature and which are most likely related to a thin decarburized surface layer, could be reproduced qualitatively with the numerical model developed.

Microstructure and wear behaviors of 17-4 PH stainless steel fabricated by laser cladding with post laser shock peening treatment

Laser cladding (LC) technology provides an attractive and cost-effective way to prepare wear-resistant coating on high-value engineering components. However, the thermal effect of coating will lead to a large amount of residual tensile stress in the coating, which seriously affects the wear performance. This paper investigated the influence of laser shock peening (LSP) on the microstructure and wear behaviors of wire-based LC 17-4 PH coating. Results showed that there was no laser remelting phenomenon during LSP process, and all residual austenite in cladding layer transformed into martensite after LSP treatment, accompanied by a more compact and uniform microstructure. LSP can introduce severe plastic deformation to form dislocation structures on the top surface of the coating, which lead to grain refinement through dynamic recrystallization (DRX), and the average grain size decreased from 4.15 μm to 1.81 μm when the laser energy is 9J. Meanwhile, the high strain rate plastic deformation induced by LSP generated high residual compressive stress on the material surface, with a maximum value of 500 MPa. The surface microhardness of the cladding layer increased by 100HV after LSP treatment, reaching to a peak of 458HV at a laser power of 9J, and gradually decreased along the depth direction, presenting a gradient distribution. After LSP treatment, GCr15 steel counter ball was used to simulate the sliding friction of solid particles under real working conditions. Results showed that the friction coefficient (COF) and wear rate of 17-4 PH coating were significantly reduced. Furthermore, the wear type changed from dominative adhesive to slight abrasive wear. The improvement of microhardness and wear properties were attributed to the combined effects of Hall-Petch and Taylor hardening strengthening.

Effect of supersonic fine particle bombardment on microstructure evolution and tribological properties of GCr15SiMn bearing steel

The surface of GCr15SiMn bearing steel was strengthened by supersonic fine particle bombardment (SFPB), and the effects of different impact times on the microstructure, mechanical properties and friction and wear properties of the material were studied. The results show that the surface roughness of GCr15SiMn steel samples increases and the grain is refined after SFPB. As the impact time prolongs, the grain size gradually decreases. When the bombardment time is 180 s, the surface grain size of the sample reaches 12.7 nm. The microhardness of the sample gradually increases and tends to stabilize with the increase of the impact time. The residual compressive stress layer is produced on the surface of the sample after SFPB and the residual compressive stress shows a trend of first increasing and then decreasing with rising the impact time. The friction coefficient and wear rate of GCr15SiMn bearing steel decreases after SFPB. The wear mechanism of the sample changes from mixture of adhesive wear and oxidation wear, accompanied by slight abrasive wear (before SFPB) to the abrasive wear, supplemented by adhesive wear (after SFPB). The wear resistance is improved by the of the grain refinement and the formation of a high residual compressive stress layer.

Mitigating Stress Corrosion Cracking of 304L and 316L Laser Welds in a Salt Spray through Micro-Shot Peening

Two austenitic stainless steel (ASS) plates, 304L and 316L, were cold-rolled (304R and 316R) with a 10% reduction in thickness and then subjected to laser welding. Cold rolling caused slight surface hardening and introduced residual tensile stress into the ASS plates. The susceptibility to stress corrosion cracking (SCC) of the welds (304RW and 316RW) was determined using the U-bend test pieces in a salt spray. To highlight the stress concentration at the weld’s fusion boundary (FB), the top weld reinforcement was not ground off before bending. Moreover, micro-shot peening (MSP) was performed to mitigate the SCC of the welds by imposing high residual compressive stress and forming a fine-grained structure. Cold rolling increased the susceptibility of the 304R specimen to pitting corrosion and intergranular (IG) microcracking. Moreover, pitting corrosion and SCC were found more often at the FBs of the 304RW. The corrosion pits of the peened 304RW (304RWSP) were finer but greater in amount than the those of the un-peened one. The results also indicated that the 316L ASS welds with MSP were resistant to the incidence of pitting corrosion and SCC in a salt spray. The better reliability and longer service life of dry storage canisters could be achieved by using 316L ASS for the construction and application of MSP on it.

Effect of microstructure evolution induced by LP on hydrogen permeation behavior of 316L stainless steel

In order to investigate the hydrogen permeation behavior of 316L stainless steel during the microstructural evolution induced by laser peening (LP), an electrochemical hydrogen charging system for initial hydrogen charging of LPed and non-LPed specimen was developed. Afterward, the microhardness, residual stress, and microstructures of the samples were determined and analyzed. Finally, electrochemical hydrogen permeation experiments were undertaken to verify LP's influence on hydrogen permeation parameters of 316L. The results showed that LP reduced the hydrogen-induced hardening rate of the alloy and additionally invoked high magnitude compressive residual stress on its surface. At the layer close to the face of the specimen, the grain refinement rate was as high as 56.18%, which was accompanied by the appearance of high-density dislocations. Compared with the non-LPed sample, the hydrogen permeation time increased significantly, and the saturation current density in steady state hydrogen permeation also decreased gradually.

Surface Morphology Analysis of Laser Shock Peened 20CrMnTi Steel: A Statistical Evaluation

Surface morphology impacts material performance and durability significantly. To gain a deeper understanding of the impact of laser shock peening (LSP) treatment on the surface morphology of materials and to explore more optimized LSP treatment strategies, this study presents an investigation into the surface morphology of 20CrMnTi steel following LSP treatment. Through the application of statistical analysis, the study examines the induced surface morphology variations resulting from both single-point repetitive LSP and multiple LSP treatments. Experimental results demonstrate significant alterations in surface roughness and peak height distribution after LSP treatments, accompanied by the presence of high amplitude compressive residual stress (CRS). Moreover, the depth of laser-induced indentations is found to be closely related to the number of impacts, and the incidence angle of the laser exhibits a discernible influence on the directional texture and periodicity of the impacted surfaces. This investigation also proposes a method for estimating surface morphology variations after LSP treatment by means of analysis of impact patterns, thereby offering the potential for enhancing the friction and wear performance of the impacted surfaces through the adjustment of the impact region position during multi-layer LSP treatment.

Wear and residual stress in high-feed milling of AISI H13 tool steel

Abstract With the new manufacturing technologies, it has been possible to machine hard metals efficiently. During high-speed machining (HSM) of high-strength steel, the poor surface integrity of the workpiece affects the performance of the process. Surface roughness, microstructure, microhardness and residual stress are key performance indices for surface integrity directly controlled by tool wear and cutting parameters. In this study, high-feed milling (HFM) of a pocket on test samples made of DIN 1.2344 ESR mould steel with 55 HRc hardness was carried out on the CNC vertical milling machine. Three different cutting speeds and five different feed rates were used. At the end of the machining, tool wear was measured using a microscope. Subsequently, X-ray diffraction and hole drilling procedures were used to quantify residual stresses on machined test specimens. The results showed that under cutting conditions, the highest tensile residual stress was attained at f z = 0.78 mm·tooth−1, v = 127.58 m·min−1, and the highest compressive residual stress at f z = 0.5 mm·tooth−1, v = 127.58 m·min−1, on the workpiece surface. The most suitable cutting parameters were reported as f z = 0.63 mm·tooth−1 and v = 70 m·min−1 cutting speed when tool wear and residual stresses are considered together.

Precise peening of Cr–Mo steel using energy-intensive multifunction cavitation in conjunction with a narrow nozzle and positron irradiation

A new metalworking technique referred to as positron and laser assisted magnetic energy intensive multifunction cavitation (PLMEI-MFC) using a narrow nozzle was developed and applied to SCM440 Cr–Mo steel. The effects of varying the laser wavelength and power were initially assessed without positron irradiation. In this system, water jet cavitation (WJC) bubbles were subjected to ultrasonication in a magnetic field and the resulting cavitation clouds were irradiated with laser beams having wavelengths of 450 or 405 nm and with ultraviolet light. Exposure to a broad range of ultraviolet light having a peak at 365 nm was found not to contribute to the generation of residual stress in the metal. Because the narrow nozzle produced small WJC bubbles, high compressive residual stress and significant hardness were imparted to an insulated thin specimen having a low heat capacity. The flow rate of the narrow nozzle was also shown to greatly affect the processing rate. In this system, electrons and positrons in the bubbles evidently underwent annihilation to generate γ-rays and other forms of energy such that energy was concentrated in the bubbles. This PLMEI-MFC processing dramatically improved the surface strength of Cr–Mo steel specimens. Employing this peening apparatus with positron irradiation provided a stress increase of 1160 MPa based on converting tensile residual stress into compressive residual stress. This PLMEI-MFC system using a narrow nozzle allows compressive residual stress to be applied to the surface of steel without generating peening marks.

Advantages in the production of power transmitting gears by fineblanking

Fineblanking of gears has an enormous time and cost saving potential as well as the potential to significantly reduce CO2 emissions compared to conventional manufacturing of gears. Conventional manufacturing of gears consists of at least three steps such as milling, case hardening, and grinding. With fineblanking, only one manufacturing step is necessary. However, the load-carrying capacity regarding different gear fatigue failure modes, such as pitting or tooth root breakage, is stated significantly lower for the commonly used shear-cutting steels compared to the conventional case-hardened gears made out of high-strength hardened steels. This work shows the possibility of utilizing compressive residual stresses that are induced by the fineblanking process to increase the load-carrying capacity regarding tooth root breakage up to the level of case-carburized gears. Pinions and wheels made of S355MC (1.0976) and S500MC (1.0984) are fineblanked using parameters determined in previous works with a focus on the induction of high compressive residual stresses into the finished products. The variants are investigated regarding, e.g., cut surface characteristics, hardness, and residual stresses. For the two steels, as well as a stress relived variant, the tooth root bending strength is also determined in pulsator tests with the fineblanked pinions.