Residual Stresses In Surface Layer Research Articles

Effect of Residual Stress in Surface Layer on Plastic Yield Inception

This study aimed to acquire a comprehensive explanation on how the residual stress in the surface layer affects the contact behavior of solids. Plastic yield inception of residual stressed surface layer/substrate system during contact is simulated using the finite element method with the software ANSYS Workbench. The critical loads and locations for yield inception were acquired for contact systems with different residual stress levels and different surface layer thicknesses. Results show that the residual stress in the surface layer has little influence on the stress field in the substrate during contact. The influence of the residual stress on the critical yield load is mainly due to variations in the stress field in surface layer. A moderate compressive residual stress is preferable for increasing the critical yield load. An optimal value of compressive residual stress of 60% of the yield strength of surface layer was found to increase the critical yield load. The surface layer thickness and residual stress determine the yield inception location and the critical load of the contact system jointly.

Residual Stresses in Surface Layers with a Gradient Structure

Residual Stresses in Surface Layers with a Gradient Structure

Residual stresses in surface layers and coatings

Methods of measurement and mechanisms of formation of residual stresses in the surface layers of metal alloys after ion nitriding, as well as in heat-shielding and refractory coatings are considered. Examples of the application of a technique based on the peculiarities of elastic anisotropy for measuring residual stresses in heterogeneous surface layers, for which the standard technique of diffraction tensometry “sin2Ψ” is not applicable, are given.

Effects of laser shock peening on microstructural evolution and wear property of laser hybrid remanufactured Ni25/Fe104 coating on H13 tool steel

• LSP was combined with LC to realize the hybrid additive remanufacturing. • MLSPT generated compressive residual stress in surface layer of LCed coating. • The wear resistance of LCed coating was obviously improved by MLSPT. • MLSPT-induced wear mechanisms of LCed coating were proposed. H13 tool steel is often damaged by wear, erosion and thermal fatigue, and laser hybrid additive remanufacturing is an effective method to repair damaged locations to extend their service lives. In this study, the Fe-based layer with Ni-based transitional layer is fabricated in the surface layer of H13 tool steel by laser cladding (LC). Subsequently, massive laser shock peening treatment (MLSPT) is applied to improve the mechanical properties of the LCed coating. Meanwhile, the effects of MLSPT on the residual stress, micro-hardness, microstructure and wear performance are systematically investigated. Results indicate that after MLSPT, the residual stress is transformed from tensile to compressive state, and high-density dislocations and a large number of mechanical twins are generated in the coating. MLSPT-induced surface nanocrystallization contributes to the improvement of micro-hardness and wear resistance of the LCed Ni25/Fe104 coating, and the grain refinement and wear property enhancement mechanisms are also revealed.

Residual stresses in Ti6Al4V alloy after surface texturing by femtosecond laser pulses

Surface topography and residual stresses in surface layers of α + β titanium alloy Ti6Al4V textured by 1030-nm, 320-fs-laser pulses were studied by scanning electron microscopy and X-ray diffraction analysis. It was found that multipulse laser processing leads to the formation of laser-induced periodic surface structures (LIPSS) on the surface of Ti6Al4V alloy. XRD studies showed that depending on the laser pulse fluence, both tensile and compressive residual stresses are formed in thin near-surface layers.

Effect of shot peening on the fatigue properties of nickel-based superalloy GH4169 at high temperature

Abstract This study investigates the influence of shot peening on the fatigue properties of GH4169 alloy at 20 °C, 350 °C and 650 °C in air. Work hardened layer with nanocrystals and deformation twins was generated in GH4169 surface after shot peening. Nanocrystallization process of microstructures was deeply discussed. The effect of twin morphology and compressive residual stress on fatigue properties was then analyzed in detail. Also, the fatigue fracture mechanism was systematically investigated. Results show that the depth of work hardened layer is about 96 μm and the increment of microhardness for the topmost surface reaches approximately 34.6%. Grains are refined to about 9 nm in the topmost surface after shot peening. Original twins are roughened or even disappear as test temperature gradually increases. The fatigue properties of shot peening specimens can be greatly improved by shot peening, especially at low external stress and test temperature (20 °C and 350 °C). The improvement of fatigue properties is mainly attributed to the induced nanocrystals and deformation twins, as well as strain hardening and compressive residual stress in surface layer.

Triaxial analysis of residual stress in surface layers after high feed machining using X-ray diffractometer

Continuously increasing of productivity is main cause of finding of new ways and methods of machining. High feed machining (HFM) is one of methods of high-productivity machining developed to achieve higher metal removal rates and decrease machining time. Each machining or treatment operation introduces residual stress into the material and its surface layers. Roughing methods of machining generate tensile residual stress obviously. Tensile character of residual stress is not suitable for functional properties of produced parts. In some cases, finishing methods of machining can improve residual stress to suitable character. New detection method of residual stress by applying of x-ray diffraction allows to measure residual stress as triaxial tensor and distribution of residual stress. When we know analyse the residual stress thoroughly, we can design right finishing method and so improve the character of residual stress. This article is focused on analysing given measuring method of residual stress in triaxial direction and next possibilities of their eventual improvement.

Triaxial X-Ray Diffraction Method and its Application to Monitor Residual Stress in Surface Layers after High-Feed Milling

AbstractHigh-feed milling is a milling method characteristic with shallow depth of cut and high feed rate to maximize the amount of removed metal from a part, generating residual stresses in the surface and subsurface layers of the machined parts. The residual stress has a large influence on the functional properties of the components. The article is focused on the application of triaxial x-ray diffraction method to monitor residual stresses after high feed milling. Significance of triaxial measuring method is the capability of measuring in different angles so it is possible to acquire stress tensor containing normal and shear stress components.

Determination of Residual Stresses in Surface Layers Upon Ion Nitriding by Microhardness Values

We present the results of investigations on the value and distribution of residual stresses in surface layers of 20Kh13 steel upon ion nitriding in hydrogen-free media. The effect of nitriding parameters on the depth and hardness of the nitrided layer as well as on residual stresses in the surface layer is analyzed. The procedure for the determination of residual stresses at the arbitrary point of the nitrided layer depth by the microhardness values at the given point is developed.

Temperature modes and critical velocities when drawing the wire

When producing rod and wire wares, residual stresses are formed. This phenomenon is caused both by plastic deformation and by possible thermoplastic deformation, which appears due to contact heating the metal ware surface due to external friction forces. Undesirable residual stresses in surface layers affect the accuracy of metal wares and increase their failure probability, which is observed in the practice of drawing production. In this study, a procedure is proposed to determine the contact heating conditions from the formation prevention criteria of residual stresses. Based on thermoelasticity equations, temperature modes leading to the appearance of thermoplastic deformations are established. Critical values of the temperature difference between the drawing wire surface and the center, at which the wire surface layers transform into the plastic state with the subsequent formation of residual stresses, are determined. Limiting drawing velocities for a series of nonferrous metals (copper, zirconium, and titanium), which, if exceeded, will lead to undesirable residual stresses in the drawn wire, are determined. To increase the critical velocities, it is recommended to implement the hydrodynamic (fluid) friction mode conditions when producing metal wires.

Lubricating properties of oil cooling fluids with tribologically active additives in the metal cutting process

The tribological characteristics (roughness of the surface, properties of shaving, residual stress in surface layers, and resistance test of cutting tools) are studied in lubricating oils with various tribologically active additives during metals cutting. Molybdenum dialkyldithiocarbamate ((n-C4H9)4N2C2Mo2S8) at its content in oil of 1–2 wt % is shown to exhibit the best properties among the studied additives.

Structural transformation and residual stresses in surface layers of α + β titanium alloys nanotextured by femtosecond laser pulses

Surface topography, phase composition and compressive residual stresses were characterized in surface layers of α + β titanium alloys VT6 (Ti–6Al–4V) and VT16 (Ti–3Al–4.5V–5Mo) nanotextured by 744-nm, 120-fs-laser pulses. The relative content of β-phase, along with the residual compressive stresses, increases significantly in both these materials over the depth ~0.2 μ in the nanotextured surface layer comprised by nanograins and remains almost unchanged at higher depths of 1–2 μ in bulk. The laser-driven α → β phase transformation is related to the combined effect of ultrafast heating/cooling, strong (multi-GPa) shock waves, chemical segregation and nanograin formation induced during the ablative surface nanotexturing.

Application of multireflection grazing incidence method for stress measurements in polished Al–Mg alloy and CrN coating

Multi-reflection grazing incidence geometry, referred to as MGIXD, characterized by a small and constant incidence angle, was applied to measure low surface stresses in very thin layers of Al–Mg alloy and CrN coating. These two materials were selected in order to deal with the low and high levels of residual stress, respectively. The influence of different mechanical treatments on residual stresses was studied for Al–Mg samples. It was found that both rolling and mechanical polishing influence the distribution and amplitude of residual stress in surface layers. In the case of CrN coating, a very high compressive stress was generated during the deposition process. The stress distributions determined by the MGIXD method is in good agreement with the classic sin2ψ technique results for all studied samples. In performing stress measurements for a powder sample, it was found that the application of the Göbel mirror in the incident beam strongly reduces statistical and misalignment errors. Additionally, the root mean square values of the third order lattice strain within diffracting grains were determined.

Residual stresses in surface layer after dry and MQL turning of AISI 316L steel

Residual stresses in the surface layer exert a significant impact on functional aspects of machined parts. Their type and value depend on the workpiece and tool material properties, cutting parameters and cooling and lubrication conditions in the tool-chip-machined surface interface. As the effects of material properties and cutting parameters have been widely studied, the influence of cooling and lubrication conditions, especially minimum quantity lubrication (MQL) on the surface layer residual stresses and the relationships between them have not been investigated. In this paper the effects of dry, MQL cutting and cutting with emulsion conditions together with cutting parameters on residual stresses after turning AISI 316L steel were investigated. X-ray diffraction method was used for measuring superficial residual stresses in the cutting (hoop) and feed (axial) directions. Tensile residual stresses were detected in both directions and the values in the cutting direction turned out to be higher than in the feed direction. The effects of cooling and lubrication conditions largely depend on the selected cutting parameters, whose influence is linked to the cutting zone cooling and lubrication mode. Elaborated regression functions allow calculation and optimization of residual stresses in turning AISI 316L steel, depending on cooling and lubrication conditions as well as cutting parameters.

Investigation of laser shock peening effects on residual stress state and fatigue performance of titanium alloys

Abstract Laser shock peening can potentially enhance fatigue life of titanium components by inducing compressive residual stresses in surface layers much deeper than caused by traditional shot peening (SP). In the present study, the high cycle fatigue (HCF) performance of α Ti-alloy Ti–2.5Cu, (α + β) Ti-alloy TIMETAL 54M and the metastable β Ti-alloy TIMETAL LCB was investigated after laser shock peening without coating (LPwC). The fatigue results were interpreted by examining the changes of surface morphology, microhardness and residual stress generated in the surface layer. Furthermore, thermal stability of residual stresses in aged Ti–2.5Cu, as an example, was evaluated after annealing LPwC-treated material at various elevated temperatures and exposure times by applying a Zener–Wert–Avrami approach. The depth profiles of residual stresses were obtained by means of synchrotron X-ray diffraction or by incremental hole drilling method. Results revealed that the HCF performance of Ti–2.5Cu and TIMETAL LCB was markedly improved after LPwC, while it was deteriorated in TIMETAL 54M. Compared to LPwC, better 10 7 fatigue strength of Ti–2.5Cu was obtained after ball-burnishing (BB). Moreover, LPwC-induced residual stresses are thermally more stable than shot peening-induced ones.

The Residual Stress Research of Rolling Slab Based on the No-Linear Elastic and Plastic Analysis

The cold rolling of slab is analyzed by using elastic-plastic and heat-mechanic coupling FEM with the nonlinear method. The distribution of residual stress was analyzed mainly in this paper. It is indicated by the results that the residual stress in surface layer of slab material is the pressure stress and inside the plate is the tension stress under the smaller press quantity, the residual stress in surface layer is the tension stress and inside the slab is the pressure stress under bigger press quantity, the maximum residual tension stress in the slab becomes bigger with the increment of the reduction.

Fabrication and characterization of Sialon–Si3N4 graded nano-composite ceramic tool materials

Sialon–Si3N4 graded nano-composite ceramic tool materials with five-layered symmetrical distribution were fabricated by using hot pressing technique. Mechanical property tests have been conducted to determine the optimal structural parameters and sintering parameters. The residual stresses in the surface layer of the graded ceramic tool materials were calculated by the indentation method. The experiment results showed that Sialon–Si3N4 graded ceramic tool materials with a thickness ratio of 0.3, which were sintered under a pressure of 35MPa at a sintering temperature of 1700–1750°C for 60min, had optimum mechanical properties. And the graded structure can induce residual compressive stresses in the material surface layer. The characterization revealed a typical duplex distribution with small β-Si3N4 grains embedded in the matrix of large β-Si3N4 grains. This duplex microstructure can contribute to the improvement of flexural strength and fracture toughness. Additionally, a mix of intergranular and transgranular fracture, crack deflection and crack bridging in the material surface layer contributed to the strengthening and toughening mechanisms for Sialon–Si3N4 graded ceramic tool materials.

Use of nanoindentation to measure residual stresses in surface layers

Equal biaxial residual stresses (of up to about 175 MPa) have been generated in thin copper foils via differential thermal contraction. These foils were subsequently indented, under displacement control, and the load–displacement–time characteristics were measured. The applied load required for penetration to a given depth (in a given time) was found to decrease with increasing (tensile) residual stress, in accordance with predictions from a finite-element model (incorporating both plasticity and creep). The main thrust of this paper concerns sensitivities. Relatively small changes in residual stress (of the order of a few tens of MPa) were observed to generate effects that should be detectable via their influence on the nanoindentation response. This is encouraging in terms of the potential of the technique for characterizing (in-plane) residual stresses in surface layers, particularly for mapping of point-to-point variations (as opposed to obtaining accurate absolute values). In contrast to this, it is shown that changes in the hardness, as a consequence of changes in residual stress level, are smaller and more difficult to analyse.

Thermal healing of the sub-surface damage layer in sapphire

The sub-surface damage layer formed by mechanical polishing of sapphire is known to reduce the mechanical strength of the processed sapphire and to degrade the performance of sapphire based components. Thermal annealing is one of the methods to eliminate the sub-surface damage layer. This study focuses on the mechanism of thermal healing by studying its effect on surface topography of a- and c-plane surfaces, on the residual stresses in surface layers and on the thickness of the sub-surface damage layer. An atomically flat surface was developed on thermally annealed c-plane surfaces while a faceted roof-top topography was formed on a-plane surfaces. The annealing resulted in an improved crystallographic perfection close to the sample surface as was indicated by a noticeable decrease in X-ray rocking curve peak width. Etching experiments and surface roughness measurements using white light interferometry with sub-nanometer resolution on specimens annealed to different extents indicate that the sub-surface damage layer of the optically polished sapphire is less than 3 μm thick and it is totally healed after thermal treatment at 1450 °C for 72 h.

Microstructure and residual stresses in surface layer of simultaneously laser alloyed and burnished steel

The new hybrid method, which combines the laser alloying process with slide burnishing, was investigated and presented in the work. Both treatments were performed on the laser stage in one operation. The experiments were done on carbon steel alloyed with cobalt stellite. The alloying process was conducted with continuous laser CO 2, at different parameters. The single- and multiple-path processes were investigated. The microstructure, microhardness and residual stresses of surface layer after the laser alloying process and laser alloying combined with burnishing were presented. The results of the experimental studies have shown that the proposed new hybrid method allowed for the generation of compressive stresses in surface layer of the alloyed material. The structural analysis has proven that the burnishing process had caused deformation of grains in the 20–30 μm thick zone and increased microhardness of the surface zone material. The X–ray diffraction measurements of residual stresses in surface layer of the samples subjected to the alloying process and burnishing, both in cold and hot conditions, were performed. In the case of multiple-path laser alloying treatment the tensile stresses, approximately 500 MPa, were obtained at the surface. Multiple alloying combined with burnishing generated compressive stresses of about −600 MPa at the surface, substantially improving the surface layer.