Decrease In Residual Stress Research Articles

Investigation of the correlation between mechanical chip morphology and surface residual stress for Ti6Al4V alloy

A numerical simulation analysis of mechanical chip morphology and residual stress for Ti6Al4V alloy was conducted under different cutting speed and feed rate. Johnson-Cook constitutive model and shear failure model were selected in the simulation procedure. The correlations between the mechanical chip morphology and surface residual stress were detailed. The results show that the chip morphology characterized with the degree of serration Gs and the serrated frequency f has a direct impact on residual stress distribution. With the increase of the degree of serration Gs, the maximum residual tensile stress decreases, while with the increase of the serrated frequency f, the maximum residual compressive stress increases on the surface. The research of the present paper provides a new way to understand and evaluate residual stress distribution for titanium alloy mechanical process.

Wear mechanism in high-speed superabrasive grinding of titanium alloy and its effect on surface integrity

Single-layer electroplated cBN wheels offer several advantages over conventional wheels when grinding difficult-to-cut materials, in terms of improved workpiece surface integrity issues, such as lower grinding burn, fewer surface defects, and generation of compressive residual stresses. However, grinding behaviour e.g., grinding forces, temperature, and surface integrity, changes with wheel use while employing single-layer wheels due to progressive wheel wear as dressing is not conducted for them. Therefore, wheel wear and associated grindability studies like grinding forces and surface integrity are essential for the implementation of these wheels in the industry. The present study evaluates the wear mechanism of the electroplated cBN wheel and its effect on the grindability of Ti–6Al–4V. High grinding speeds (40 & 60 m/s) were employed under different cutting fluids environments (water-based soluble oil emulsion in minimum quantity cooling lubrication (MQCL) as well as in flood cooling modes and neat oil in MQCL regime). A lower cutting speed of 20 m/s is also chosen for benchmarking purpose. Grit fracture is found to be the primary mode of wheel wear. An elaborate discussion on the mechanism of cBN grit fracture is presented. It is observed that thermal shock-induced fracture has a dominant effect on wheel wear, and consequently, water-based fluid provided 2–4 times higher radial wear than neat oil up to 40 m/s. Because of lower radial wear, neat oil provided only 0–10% increase in grinding forces, 0–10% decrease in compressive residual stress, and almost the same level of surface redeposition with the progression of cumulative material removal. On the other hand, water-based fluid yielded 30–100% rise in grinding forces, 10–75% decrease in compressive residual stress, and a higher level of surface redeposition.

Properties of Cryogenic Treated Cemented Carbides (WC-Co)

The present paper explores the effects of deep cryogenic treatment (DCT) on the properties of WC-Co cemented carbides. The investigation involved four different cemented carbide (CC) grades. Two of them were coarse-grained WC with grain sizes larger than 6 μm and binder fractions of 10 and 15 wt. %. The other two were fine-grained with WC grains of 0.5-0.8 μm and the same binder fractions of 10 and 15 wt. %. Their specimens were ground and polished to prepare them for DCT. In each specimen, one half of this polished surface was used for testing the properties of the CC before cryogenic treatment. The post-DCT properties were then determined on the other half. Properties of the cemented carbides prior to and after DCT were studied using optical and scanning electron microscopy, X-ray diffraction, hardness testing according to Vickers scale followed by calculation of fracture toughness KIC and a ball-on-disk test of the wear resistance of the surface. One of the findings was that cryogenic treatment led to a decrease in residual stresses and to lower fracture toughness KIC in the CC.

Improvement in uniformity of alloy steel by pulsed magnetic field treatment

This article reports that the uniformity of the alloy steel 20Cr2Ni4A is improved by using pulsed magnetic treatment. The pulsed magnetic field with 1, 4 and 9T was applied on the tempered samples. Meanwhile the microstructures were characterized using transmission electron microscopy and magnetic force microscopy, and mechanical properties tested to verify the effect of the proposed process. It shows the contact fatigue life of alloy steel increases by 42.11% after magnetic treatment. Range of residual stresses narrows down along with rise of magnetic induction strength. The microstructures of dislocations, precipitates, and magnetic domains become more uniform under pulsed magnetic field. Besides, dislocations and precipitates were observed to transit from intergranular agglomeration to intracrystalline distribution. The energy of the external magnetic field promotes the dislocation slip and reduces high dislocation density on grain boundaries, which results in a decrease of residual stress.

Surface oxidation of nanocrystalline CVD TiB2 hard coatings revealed by cross-sectional nano-analytics and in-situ micro-cantilever testing

Nanocrystalline TiB2 coatings grown by chemical vapour deposition (CVD) are employed e.g. as hard protective coatings on cemented carbide cutting tools, owing to their high wear resistance, hardness and melting point, as well as superior thermal stability. This work applied novel cross-sectional nano-analytical techniques to investigate the effects of prolonged surface oxidation of a CVD bi-layer coating of ~3.4 μm thickness, consisting of a nanocrystalline TiB2 protective top layer and a TiN diffusion-barrier bottom layer. Synchrotron X-ray diffraction with a nano-focussed 70 nm beam revealed cross-sectional phase compositions and residual stress gradients in the coating in as-deposited and oxidised states. Transmission electron microscopy showed a clear oxidation front, the existence of a ~400 nm thick zone of coexistence of TiB2 and rutile TiO2, which coincided with a marked decrease in compressive residual stress, as well as an overlying morphologically stratified TiO2 layer. In-situ micro-cantilever experiments confirmed the structural integrity of the TiB2 phase below the coexistence zone, where no significant oxidation-induced change in fracture stress was detected, while Young's modulus decreased by ~25%. In conclusion, the pursued nano-analytics approach revealed detailed cross-sectional correlations between oxidation-related coating disintegration, microstructure, residual stresses and mechanical properties.

The metallurgical behaviors and crystallographic characteristic on macro deformation mechanism of 316 L laser-MIG hybrid welded joint

A 10 mm 316 L stainless steel plate was joined using multi-layer laser-MIG hybrid welding. Results showed that unmixed zone and “real” fusion zone (FZ) existed near the fusion line. Frequently met dendritic ferrite (δ) and newly encountered spherical nanoscale particles trapped in austenite (γ) were only observed in the latter region. Chemically, these particles turned out a SiO2 phase. From base metal to FZ, δ morphology was altered from originally linear to relatively diversely dendritic. Meantime, γ exhibited a converse manner where previously randomly oriented equiaxed was replaced by coarse, columnar and textured. Accordingly, a comparably high Schmidt factor in γ phase was obtained in FZ. Moreover, δ exhibited a relatively higher stress level than γ which presented a decrease in residual stress with grain coarsening in heat affected zone. In FZ, δ fraction displayed a dramatical increase with special BCC-FCC orientation relations established. Finally, tensile test and fracture appearance implied that FZ was exactly the weakest link of the whole welded joint in spite of a qualified strength achieved. In summary, lack in Σ3, largely increased δ fraction, high Schmidt factor in γ and especially being rich in SiO2 particles collectively led to the micro-void coalescence fracture in FZ.

High-temperature Mechanical Properties and Their Influence Mechanisms of ZrC-Modified C-SiC Ceramic Matrix Composites up to 1600 °C.

In order to understand the influence of the mechanisms of ZrC nanoparticles on the high-temperature mechanical properties of C-SiC ceramic matrix composites, the mechanical properties were measured from room temperature (RT) to 1600 °C under vacuum. The microstructures features were characterized by scanning electron microscopy. In comparison with the composites without ZrC nanoparticles, the ZrC-modified composite presented better mechanical properties at all temperatures, indicating that the mechanical properties could be improved by the ZrC nanoparticles. The ZrC nanoparticles could reduce the residual silicon and improve the microstructure integrity of composite. Furthermore, the variation of flexural strength and the flexural modulus showed an asynchronous trend with the increase of temperature. The flexural strength reached the maximum value at 1200 °C, but the highest elastic modulus was obtained at 800 °C. The strength increase was ascribed to the decrease of the thermally-induced residual stresses. The degradation of mechanical properties was observed at 1600 °C because of the microstructure deterioration and the formation of strongly bonded fiber–matrix interface. Therefore, it is concluded that the high temperature mechanical properties under vacuum were related to the consisting phase, the matrix microstructure, and the thermally-induced residual stresses.

Использование шумов Баркгаузена для определения остаточных напряжений после алмазного выглаживания патрубков высокого давления

The results of residual stress definition after a valve unit diamond smoothing of high-pressure fittings are shown. In the paper there is used Barkhausen noise method allowing the definition of the residual stress level at a great depth as compared with the X-ray method. There is presented a procedure for the definition of residual stresses according to a ratio of a magnetoelastic parameter – deformation. The advantage of the diamond smoothing as a method of FSD allowing the decrease of tensile residual stresses and the increase compression stresses on a contact surface of fittings units is shown.

Effects of Pulsed Magnetic Fields of Different Intensities on Dislocation Density, Residual Stress, and Hardness of Cr4Mo4V Steel

To study the effects of pulsed magnetic fields of different intensities on the dislocation density, residual stress, and hardness of Cr4Mo4V steel, magnetic treatment is conducted at 0, 1.0, 1.3, 1.5, 2.0, and 2.5 T. The dislocation density and residual stress are measured using Electron Backscatter Diffraction (EBSD) and X-ray technique, respectively. The results reveal the dislocation density and compressive residual stress decrease at lower magnetic fields such as 1.0 T and 1.3 T, while they increase at higher magnetic fields such as 2.0 T and 2.5 T. The average value of kernel averaged misorientation (KAM) and compressive residual stress decrease about 10.4% and 15.8%, respectively, at 1.0 T, while they increase about 5.88% and 18.2%, respectively, at 2.5 T. The average value of hardness decreases about 3.5% at 1.0 T, from 817 HV to 787 HV. With the increments of intensities, the hardness of the treated samples increases. The hardness essentially remains unchanged at 2.0 T and 2.5 T. The reason for the dislocation motion under the action of pulsed magnetic fields is discussed.

Experimental and Numerical Simulation to Study the Reduction of Welding Residual Stress by Ultrasonic Impact Treatment.

In this study, the effects of ultrasonic impact treatment (UIT) on the residual stress in a repair welding joint are investigated by experimental and finite element methods. A three-dimensional numerical analysis approach including a thermomechanical-coupled welding simulation and dynamic elastic-plastic UIT simulation is developed, which has been validated by X-ray diffraction measurement and indentation strain method. The results show that longitudinal residual stresses basically turned into the small tensile stress state from the large tensile stress state, and transverse residual stresses have mainly turned into compressive stresses from large tensile stress after the UIT. In the thickness direction, the average decrease of longitudinal residual stress is 259.9 MPa, which is larger than the 149.1 MPa of transverse residual stress. The calculated residual stress distribution after the UIT of the thin plate is compared with that of the thick plate in the literature, with the results showing the stress accumulation layer inside the thick plate. The simulation results show that the elastic strains are decreased slightly and the equivalent plastic strain is increased markedly after UIT, which explains the mechanism of residual stress relaxation.

An experimental and theoretical investigation of thermo-mechanical issues in friction surfacing of Al–Mg aluminum alloys: material flow and residual stress

Material flow and residual stress distribution during friction surfacing of aluminum alloy AA5083 on aluminum alloy AA5052 substrate have been evaluated employing a three-dimensional model and the finite element software, ABAQUS, as well as experimental investigation. Based on the results, the nature of residual stress in the coating was tensile while getting compressive by straying away from the boundary of the coating. An increment in heat input per unit length of coating has caused a decrease in the maximum tensile residual stress albeit increasing the extent of the region with tensile residual stress. On the advancing side, the velocity vector was larger than the retreating side due to the larger velocity difference between rotating rod and substrate. Moreover, the velocity difference between advancing and retreating sides was much lower in sample with minimum heat input compared to a sample with maximum heat input.

The effect of microstructure parameters on the residual stresses in the ultrafine-grained sheets

In this research, the influence of microstructure parameters on the residual stresses of ultrafine-grained sheets was investigated. For this purpose, the constrained groove pressing (CGP) process was carried out on the copper sheets with 3 mm thickness, and residual stresses of the CGPed sheets was measured using the contour method. Microstructure of the CGPed specimens was evaluated by the optical microscopy, micro x-ray diffraction (micro-XRD), and transmission electron microscopy (TEM) experiments. Microstructure parameters including crystallites size, dislocations density, and lattice strain were calculated using Williamson-Hall and Williamson-Smallman equations, and the calculated results were validated by the TEM images. The influence of these parameters on the residual stresses was investigated by analysis of variance (ANOVA) method, and two approaches were considered in this way. According to the results, the CGP process can create nanostructures in the CGPed sheets, and with increasing number of CGP passes, grains size, crystallites size, lattice strain, and residual stresses decrease, and density of dislocations increases. Microstructure parameters have a significant effect on the macro-residual stresses, and strain is the most effective parameter. Also, in the ultrafine-grained sheets, micro-parameters have an undeniable contribution, which is the same as that of macro-parameters on the macro-residual stresses.

Theoretical calculation and experiment of the surface residual stress in the plane ultrasonic rolling

The service life of the workpiece is largely determined by residual stress on the workpiece surface, which is the most important parameter of anti-fatigue. In order to study the characteristics of residual stress on workpiece surface, the theoretical model of residual stress on the surface of the single impact workpiece is established based on the elastoplastic theory. Subsequently, the relationship between the rolling depth and the rolling force in the plane ultrasonic rolling is established based on the Hertz contact theory, and the contact area coefficient is established to correct the theoretical model. Then, the plane ultrasonic rolling experiments are carried out to validate the model. The results exhibit that the rolling force linearly increases with the increase of rolling depth. The effect of step has a highest relationship with the contact area coefficient, moderate with the feed rate, and minor with the static force. With the increase in static force, the residual compressive stress increased as a whole. The residual compressive stress decrease with the increase in step and the feed rate has little influence on the residual stress. The results reveal that the modified theoretical model can improve the prediction accuracy of residual stress.

In-plane stress development in sol–gel-derived titania and silica thin films on Si(100) substrates

In order to study (i) how the in-plane stress develops in alkoxide-derived oxide gel films on heating and (ii) how the residual stress changes with firing temperature, we prepared titania and silica gel films on Si(100) wafers from alkoxide solutions. The intrinsic stress was previously measured in situ during heating up to 500 °C for the gel films, where the stress was calculated from the radius of curvature of the substrate bending. Because the commercialized apparatus that measures the substrate bending has an upper limitation of temperature at 500 °C, we devised a method for estimating the intrinsic stress over 500 °C in the present work. The gel films were heated from 100 °C up to 900 or 1000 °C successively and cumulatively. Then we estimated the intrinsic stress over 500 °C by monitoring the changes in stress in situ during heating and cooling for the cumulatively fired films. Combining the estimated data over 500 °C with those measured below 500 °C, we found that the intrinsic stress increases and then decreases around to zero with temperature for both titania and silica gel films, which we recognized as a general trend in alkoxide-derived oxide thin films in conjunction with our previous work on yttria stabilized zirconia (YSZ) films. Regarding the residual stress, the titania and silica films exhibited different behaviors. The titania film showed an increase followed by a slight decrease, and finally a significant increase in residual tensile stress with increasing firing temperature. The silica films also exhibited an increase and a decrease in residual tensile stress with increasing firing temperature, but the stress continued to decrease and turned into compressive one at ca 800 °C. The last decrease in residual tensile stress that turned into compressive one resulted from the development of compressive thermal stress during cooling, which is due to the smaller thermal expansion coefficient of silica than silicon. It was thus clarified that the difference in thermal expansion coefficient between the film and the substrate becomes prominent in residual stress when the films are fired at high temperatures like 800 °C. Thus we could successfully obtain a general view on how the residual stress changes with firing temperature as well as on how the in-plane stress develops during heating thanks to the information on the stress development in the sol–gel-derived titania and silica films that was added to the information on the YSZ films.

Investigation of boring on gunmetal in dry, wet and cryogenic conditions

Secondary operation of boring is carried out to produce close geometric tolerance holes produced in drilling. In this work, an attempt has been made in producing a hole by dry boring, wet boring and cryogenic boring of gunmetal. Gunmetal finds its application in areas of casting, steam turbines and pressure valves, due to its high resistance to corrosion. Investigation of cutting temperature generated during machining, cutting force experienced by the tool and surface roughness of the machined workpiece was toted out with analogous to cutting speed and feed, by Taguchi, ANOVA and TOPSIS analyses. Surface morphology study, tool wear analysis, residual stress analysis were done in order to distinguish the modification in the bored surface and tool material after machining. Cryogenic boring of gunmetal reduced the cutting temperature by 63.43% and 53.85% over dry boring and wet boring, respectively. Furthermore, cutting force is reduced by 34.51% and 18.29% over dry boring and wet boring, respectively. Additionally, a decrease of 62.23% and 35.10% is observed in surface roughness on comparing dry boring and wet boring with respect to cryogenic boring of gunmetal. Taguchi and ANOVA arbitrated speed as an imperative parameter for cutting force and feed as a paramount parameter in cutting temperature. Furthermore, speed is a crucial parameter for arbitrating surface roughness in dry boring and wet boring, additionally feed for surface roughness in cryogenic boring condition. TOPSIS analysis illuminated speed of 1200 rpm and feed of 0.055 mm/min as the most closest to exemplar elucidation for all three cutting preconditions. Aggrandizement in compressive residual stress is discerned in cryogenic boring by 39.74% and 19.35% correlated with dry boring and wet boring, respectively, as the material undergoes work hardening. A decrease in residual tensile stress is espied in cryogenic boring when juxtaposed to wet boring, ensuring upsurge in tool life and better surface characteristics. Microhardness in cryogenic boring of gunmetal improves by 5.83–11.05% and 0.51–2.57% analogous to dry boring and wet boring, respectively. Corrosion resistance in cryogenic boring increases by 77.43% and 49.25% analogous to dry boring and wet boring of gunmetal, respectively. The circularity and cylindricity increase by 4.76–98.40%, 8.33–97.50% and 6.25–97.15%, 2.43–92.85% in cryogenic boring juxtaposed to dry boring and wet boring of gunmetal, respectively.

Laser beam welding of DP980 dual phase steel at high temperatures

Dual phase steels have been used in safety components for the automotive industry and represents a standard in terms of energy absorbing steel alloys. After welding, these components present a martensitic transformation in the fusion and heat-affected zones with an intrinsic brittleness. The current contribution presents a procedure where the DP980 steel sheet is kept at a given temperature during and after the laser weld in order to generate bainite instead of martensite. The results using an isothermal treatment at 527 °C shown a microstructure composed by grain boundary and bainitic ferrite and retained austenite with a constant hardness in the base material and heat-affected and fusion zones of 280 HV. The room temperature welds present hardness values between 320 and 500 HV. The high-temperature welds also shown a decrease in the maximum residual stress at the weld centerline by 1/3, with a consequential reduction in the warp of the joined component.

Viscoelastic finite element evaluation of transient and residual stresses in dental crowns: Design parametric study

Porcelain-veneered zirconia (PVZ) are one of the popular choice for crown restorations. Veneer layer of these dental restorations, however, is susceptible to chipping and delamination due to the development of transient and residual stresses during the cooling phase of veneer firing. The aim of this study is to elucidate the effect of material property mismatch, veneer to core thickness ratio, and cooling rate on these transient and residual stresses of PVZ restorations. Three-dimensional viscoelastic finite element modelling (VFEM) was performed. The VFEM model was developed using the UEXPAN subroutine in ABAQUS software and was validated for transient and residual stresses in a sandwich seal problem with experimental data available. A good agreement between the simulated VFEM results and experimental data was obtained. Using validated VFEM, two PVZ systems (PM9/zirconia and ZirPress/zirconia), three veneer to core thickness ratios (2:1, 1:1 and 1:2), and two cooling rates controlled slow cooling at 1.74E-5 W/mm2°C (i.e. ~30 °C/min) and fast bench cooling at 1.74E-4 W/mm2°C (i.e. ~300 °C/min) were used. The results showed that PM9/zirconia has smaller thermal contraction mismatch, resulting in lesser residual stress (33.36 MPa) as compared to ZirPress/zirconia (37.94 MPa) for controlled cooling and 2:1 veneer to core ratio. In addition, in both systems with the decrease in veneer thickness, we observed a decrease in residual stresses developed. We also observed some effect of cooling rate on residual stresses. The controlled cooling resulted in lower residual stress (24.35 MPa) for PM9/zirconia with a 1:1 veneer to core thickness ratio as compared to bench cooling (28.04 MPa). The effect of cooling rate was more evident on transient stresses. For instance, in the PM9/zirconia with 1:1 thickness ratio model, the difference in transient stresses was 9.93 MPa between controlled and bench cooling. Therefore, properties such as elastic modulus and coefficient of thermal contraction (CTC), as well as the thickness ratio and cooling rate all play an important role in transient and residual stresses developed in the studied ceramic systems.

Evolutions of microstructure, phase, microhardness, and residual stress of multiple laser shock peened Ni-based single crystal superalloy after short-term thermal exposure

In this work, evolutions of microstructure, phase, microhardness, and residual stress of multiple laser shock peened (LSP) Ni-based single crystal (SC) superalloy after short-term thermal exposure for 1 h at 950 °C and 1200 °C were investigated. The results showed that slipping systems of {1 1 1} 〈1 1 0〉 were activated by multiple LSP in [3 1 1] orientation, which resulted in the formation of dislocation slip bands along (1 1¯ 1) plane. The dislocation structures induced by LSP in γ and γ′ phases had a vital influence on the lattice misfits of two phases as compared to the composition changes of γ phase, which led to increased lattice misfits. Moreover, the decrease in microhardness and residual stress after thermal exposure was attributed to the decrease in dislocation density due to dislocation annihilation.

Stress relaxation through thermal crack formation in CVD TiCN coatings grown on WC-Co with different Co contents

TiCN coatings were grown by chemical vapor deposition (CVD) on WC-Co substrates with different Co contents, in order to control thermal stress. The driving force for the development of thermal stress is attributed to the difference between room and deposition temperature (ΔT ≈ −780 °C), and the mismatch of the coefficient of thermal expansion (CTE) between substrate and coating. Co contents of 6, 7.5, 10, 12.5, and 15 wt% were utilized to adjust the CTE of the substrate, and therefore tune the stress in TiCN coatings. Dilatometry of the substrates and high temperature X-ray diffraction of a powdered TiCN coating indicate a decreasing CTE-mismatch for increasing substrate Co contents. In consequence, residual stress in TiCN determined by X-ray diffraction increases up to 662 ± 8 MPa with decreasing Co contents down to 10 wt%. For Co contents below 10 wt%, the residual stress decreases. The formation of thermal crack networks in TiCN, analyzed by scanning electron microscopy, coincides with 10 wt% Co. Stress relaxation in TiCN coatings through the formation of thermal cracks becomes evident. A finite element simulation utilized for the calculation of residual stress distributions reveals shielding effects, which occur with the introduction of thermal cracks. Discrepancies between experimental and simulated thermo-elastic stresses imply the presence of secondary relaxation sources. High temperature residual stresses in TiCN, determined up to 1000 °C (i.e. above deposition temperature), suggest additional thermal crack formation for substrate Co contents of 6 wt%.

Experimental study on the influence of different carburized layer depth on gear contact fatigue strength

Contact fatigue is one of the main failure modes of gears. Gear contact fatigue reliability test is not only an important way to understand the gear capacity, but also the data foundation in product design. In this paper, the installation method of gear meshing staggered is used, and the two states of full tooth and staggered meshing are compared and analyzed by simulation software to verify the feasibility of the experimental design proposed in this paper. The gear contact fatigue test method combined with the up-down method and the grouping method is used to obtain test data with a minimum of sample gears. Under a certain degree of confidence interval, the logarithmic normal distribution is used to fit the C-R-S-N curve, and the fatigue limit stress of 20CrMnMo carburized gear under different reliability is obtained. The 20CrMnMo different carburized layer depth gears were tested. The results show that the carburized layer is not as thick as possible and has an optimum value. Too thick a layer depth usually causes deterioration of the surface layer structure or a decrease in residual stress, resulting in a decrease in contact fatigue limit. This provides basic test data for the finite life design and high reliability design of gear contact fatigue.