High Compressive Residual Stress Research Articles

Temperature-Dependent Fatigue Strength of Diamond Coating-Substrate Interface Quantified via the Shear Failure Stress

A dynamic 3D-finite element method (FEM) thermomechanical model is employed for quantifying the temperature-dependent fatigue strength of nanocrystalline diamond (NCD) coating-substrate interface. This model simulates dynamically the inclined impact test on NCD-coated cemented carbide inserts considering the temperature-dependent residual stresses in the NCD coating structure. A fatigue damage of the NCD coating-substrate interface develops after a certain number of repetitive impacts depending on the applied impact load and temperature. After the interface fatigue failure, the high compressive residual stresses of the NCD coating structure are released, and the detached coating hikes up at a certain maximum height (bulge formation). The critical impact forces for avoiding the fatigue failure of the NCD coating-substrate interface, and the subsequent film detachment after 106 impacts at various temperatures were determined by conducting inclined impact tests up to 400 °C. Considering the critical impact forces, using the mentioned FEM model, the related shear failure stresses in the NCD coating-substrate interface at various temperatures were predicted.

Change in Residual Stress of TiN Coating Material during Heat Treatment in an Air Atmosphere

TiN films are widely used as strengthening coatings for cutting tools. In a previous study, the crystal structure of TiN films deposited by arc ion plating was found to be strongly influenced by the bias voltage during deposition. The TiN films deposited under a high bias voltage were found to have a high compressive residual stress of-9.5 GPa. The residual stresses of the TiN films relaxed to thermal stress levels upon annealing. In the present study, the authors investigate the relaxation of the residual stress during heat treatment in atmosphere for TiN films with different initial residual stress values. The surface layer of the TiN films is oxidized by heat treatment in an air atmosphere. However, the crystalline state of the TiN films is hardly affected. So far, the residual stress of the TiN film hardly changes in a temperature state lower than the heating temperature when it is relaxed by heat treatment.

Characterization of residual stresses in zirconia veneered bilayers assessed via sharp and blunt indentation

ObjectivesThe present study evaluated the effect of the coefficient of thermal expansion (CTE) mismatch and the cooling protocol on the distribution of residual stresses and crack propagation in veneered zirconia bilayers. MethodsCeramic discs with two different CTEs (Vita VM9 and Lava Ceram) were fired onto zirconia plates and cooled following a slow (0.5°C/s) or a fast (45°C/s) cooling protocol. The residual stress distribution throughout the veneer thickness was assessed by means of depth-wise Vickers indentation after sequentially sectioning the bilayers parallel compared to normal to the interface. A mathematical solution for the residual stress distribution was used as reference. Additionally, Hertzian cone crack propagation in the veneers was induced by cyclic contact loading and measured at different number of cycles to estimate the crack growth rate. ResultsThe higher CTE mismatch of the VM9 group generated an important stress gradient with high compressive residual stresses near the interface, hindering the crack propagation. The low CTE mismatch group (Lava Ceram) developed only a slight stress gradient and higher cone crack growth rates. No differences were observed between the two cooling protocols applied regarding stress magnitude and crack propagation behavior. SignificanceThe CTE mismatch has a predominant role in the generation of residual stress gradients within the veneer, which directly influences contact-induced crack propagation. Based on the results, the cooling protocol had no significant effect on the residual stress distribution in zirconia-veneer bilayers.

Laser Shock Processing with Different Conditions of Treatment on Duplex Stainless Steel

The laser shock processing (LSP) has been developed as an effective alternative to traditional methods for improvement of metallic materials properties and as surface treatment to metals. Duplex stainless steel is a material that has a microstructure formed by two phases, with approximately equal amounts of each one. This stainless steel has wide applications in different fields like shipping, petrochemical, and chemical industries. We present results of the LSP performance using two pulse density configurations of 2500 and 5000 pulses/cm2, both of them at laser irradiation of 532 and 1064 nm (keeping approximately constant power density), in order to treat in under water-jet the surface of 2205 duplex stainless steel samples without coating. A flat mirror and a converging lens is used to deliver 400 mJ/pulse, (5 ns FWHM, 1.1 mm spot diameter with 532 nm wavelength) and 850 mJ/pulse, (6 ns FWHM, 1.5 mm spot diameter with 1064 nm wavelength) laser pulse produced by 10 Hz Q-switched Nd:YAG laser. A motor-controlled x-y precision stage is used, for sweep the treated zone on sample. The use of two wavelengths with approximately the same power density is an effective way for obtaining high compressive residual stresses (~90% of the yield stress). An improvement of hardness (12-25%) at the surface of 2205 duplex stainless steel due to LSP is presented.

Effects of LSP on micro-structures and residual stresses in a 4 mm CLAM steel weld joints

The effects of laser shock processing (LSP) on the distribution of residual stress and micro-structure of China Low Activation Martensitic (CLAM) steel weldment were investigated via neutron diffraction and optical microscope (OM). A pair of 4mm CLAM steel plates joined by GTA welding. Special attention is paid to the generation of high level compressive residual stresses introduced by LSP. Residual stress in longitudinal, normal and transversal direction at weldment surface and longitudinal stress through thickness are evaluated via neutron diffraction. Compressive residual stress after LSP occurred at more than 90% areas within the weld joint, it is almost double the areas of compressive stress compare to weldment surface before LSP. The maximum compressive normal residual stress becomes to −183MPa after LSP from −63MPa before LSP. The Modification of surface micro-structures including weld zone (WZ), heat affected zone (HAZ) and base metal (BM) are also discussed. Results to date demonstrate that laser shock processing has been a great potential method for the improvement of mechanical performance of components.

An investigation of ultrasonic nanocrystal surface modification machining process by numerical simulation

As a method for surface severe plastic deformation (S2PD), ultrasonic nanocrystal surface modification (UNSM) enhances metal surface properties through striker peening, a metal dimpling process driven by ultrasonic vibration energy. UNSM treatment introduces residual stress, surface hardening, and nano-crystalline structures into metal surfaces which are beneficial for reducing wear, fatigue, and corrosion properties. In this paper, the process of UNSM is described and a simplified physical model created using the equivalent static loading method is presented. Along with the simplified physical model, a finite elements simulation model was developed. Effective plastic strain was considered as a parameter for evaluating the level of work hardening produced in the simulation. The dynamic processes and energy dissipation were also examined, and it was found that different kinds of energy dissipation occur during UNSM treatment. Comparisons between the processing parameters (processing velocity, static load, and feed rate) were performed using a simulated example of UNSM linear processing. The results show that the linear processing produces a uniform region containing identical distributions of residual stress and effective plastic strain. The effects of the parameters on the processing results (residual stress, plastic deformation and work hardening) were likewise studied using UNSM linear processing. Compared to processing velocity, a high static load produced more work hardening and higher compressive residual stress. Surface deformation and residual stress results were also more sensitive to static load than processing velocity. Feed rate was found to be an important parameter as well, greatly influencing both surface deformation and work hardening.

Mechanical Properties of Samurai Swords (Carbon Steel) Made using a Traditional Steelmaking Technology (tatara)

The material and mechanical properties of samurai swords (Japanese swords), made using a traditional steelmaking technology (tatara), are investigated experimentally. The quality of these swords appears to be low because of the presence of a large number of inclusions, including oxide- and phosphorus-based structures; however, their mechanical properties are relatively good because of their fine-grained structure and high residual stress. The swords consist of several carbon steels, with a fine microstructural formation being obtained in the sharp edge of the sword (knife) as a result of the forging process. There is high residual compressive stress in the thick edge of the sword (mandrel), caused by bending due to the martensitic phase transition in the sharp edge. The carbon content of the sword varies depending on region: the sharp edge is found to have 0.55% C, which is more than twice the amount in the thick edge. The Vickers hardness and tensile strength in the sharp edge region are about 6 and 1 GPa, respectively, which are about three times higher than the corresponding values in the other regions of the sword. The hardness in the sharp edge region is almost the same as in a conventional carbon steel (Fe-C0.55) produced by presentday steelmaking technology. The tensile strength of the sharp edge of the sword is relatively high, but is slightly lower than that of the conventional Fe-C0.55 steel, despite the fine-grained structure and high residual compressive stress in the sharp edge region. This is caused by the presence of various inclusions in the sword.

Ti-6Al-4V 合金の機能性および強度に及ぼす複合処理の効果

This study was conducted to comprehensively investigate the effect of combination treatment on the wear resistance, corrosion resistance, mechanical properties and fatigue strength of Ti-6Al-4V alloy. The combination treatment was composed of plasma nitriding, short-time heat treatment and fine-particle bombarding (hereafter, FPB). Plasma nitriding was performed at 1123 K. The obtained results were compared with those of the previous study concerning the combination treatment in which plasma nitriding was performed at 1023 K. A thick hardened layer (thickness: 200 μm) was formed by plasma nitriding. The substrate was strengthened by short-time heat treatment. The surface brittle compound layer was eliminated by FPB, and high compressive residual stress was introduced at the same time. The combination treatment improved wear resistance without the deterioration of corrosion resistance. Moreover, the combination treatment improved tensile strength and fatigue strength although it markedly reduced ductility. The comparison with the results obtained in the previous study showed that the combination treatment in which plasma nitriding was performed at 1023 K was more effective to improve the functionalities and strength of Ti-6Al-4V alloy.

二重らせん経路での摩擦攪拌形バニシングによる高硬度・圧縮残留応力を両立する表面強化層の創成

Frictional Stir Burnishing (FSB) is a surface enhancement method after machining without using additional device. The FSB process can be utilized on the machine tool which uses the rotation tools such as a machining center and a multi-tasking machine. Therefore, the FSB process can be applied just after the cutting process on the same machine tool. FSB was applied to the shaft materials of 0.45%C steel by using a multi-tasking machine in this paper. FSB is a process where the burnishing tool rotates at high revolution speed. Then the thin surface layer is rubbed and stirred with a temperature elevation and reduction. However it is difficult to achieve both high hardness and high compressive residual stress by FSB on 0.45%C steel shaft with helical path. In order to overcome this problem, FSB process with double helical path was proposed in this paper. As a result, both high hardness (600 HV) and compressive residual stress (-400 MPa) could be achieved.

Method of Welding and Spinning Combination for Complex Aluminium Alloys Lightweight Components

A technology for a fast, flexible and low cost production of aluminium parts was developed for small quantity down to prototypes. Those parts are pre-defined by measures and material properties. The first effects from the welding and flow forming were theoretical analysed by FEM-Simulations. The achieved surface compaction from the flow forming has a high residual compressive stress especially in weld seam area, which increases the durability for load cycles, corrosion and abrasion. It saves additional steps in the manufacturing of an aluminium precise pipe, like the pre-processing of the aluminium sheet, flattening and post-processing of the weld seam.

オートバイ用リアアームを想定したアルミニウム合金のフレッティング疲労強度改善のための表面処理に関する検討

Plain fatigue and fretting fatigue strength tests of aluminum alloy (JIS A7N01) specimens with surface treatments (fine particle peening, burnishing and solid lubricant film) were carried out using an electromagnetic fatigue testing machine. Fretting fatigue limit of untreated specimen was significantly low, which was about one fourth of the plain fatigue strength. Fretting fatigue strength of the specimen surface-treated with fine particle peening was slightly higher than that of the untreated specimen. The fretting fatigue strengths for solid lubricant film and burnishing have been remarkably increased compared to that of the untreated specimen. However, the fatigue limit for solid lubricant film was almost same as that of untreated specimen. From the in-situ SEM observation of fretting fatigue process, it was found that burnishing with smooth surface and high compressive residual stress effectively delayed the fretting fatigue crack nucleation and crack propagation. It was also found that solid lubricant film with low frictional coefficient effectively delayed them.

Investigations of Nucleate Boiling Processes During Quenching Based on Possibilities of Noise Control System

Abstract A new method for evaluating and control of the optimal concentration of water salt solutions is proposed which is based on the possibilities of sound control system. Water salt solutions as quenchants are used in the practice to intensify hardening processes. In this paper, it is shown that water salt solutions are used for low and medium carbon alloy steels to create high compressive residual stresses at the surface of steel parts and improve mechanical properties of steels. It is underlined that quenching in water salt solutions must be interrupted at the appropriate time to prevent crack formation during fast cooling. When interruption occurs at the surface of steel parts, compressive residual stresses are formed and self-tempering takes place. During this time, at the core, a bainitic structure is formed which has enough strength and high plastic properties to prevent crack formation at the core where tensile stresses could be. It is shown that salt solutions can be also used for quenching of big steel parts like rollers and rotors. The benefits from the technology proposed are discussed in this paper. In the future, organic salt solutions can be replaced by organic salt solutions which prevent corrosion completely.

Research on Laser Peening of TC21 Titanium Alloy with High Energy Laser

Abstract Laser peening (LP) also known as laser shock processing (LSP), is a surface enhancement technique that induces intensive plastic deformation, high dislocation density and deeper compressive residual stress to improve the surface performance of materials. The microhardness, surface profiles, roughness, and the residual stress of TC21 alloy were tested by LSP with high energy laser. The results show that the microhardness of the shocked area is improved apparently compared with that of unshocked area. The magnitude of dent is related with the diameter and the distribution of laser spot. The roughness Ra of shocked area is less than 0.8 μm. The compressive residual stress is enhanced greatly. The investigations show that the technology of LSP could further improve the performance of TC21 alloy.

Effect of ultrasonic nanocrystal surface modification on surface and fatigue properties of quenching and tempering S45C steel

Ultrasonic nanocrystal surface modification (USNM) utilizing ultrasonic vibration energy is a method which induces severe plastic deformation to a material's surface and an enhanced surface layer in order to produce a nano-structured surface. In this paper, USNM was performed to enhance the surface properties of quenched and tempered S45C steel by producing a nanostructured surface layer. Various processing parameters, such as static loading (50N, 60N and 70N) and processing density (34,000mm−2 and 68,000mm−2), were applied in the surface treatment. The microstructure, hardness and residual stress of the material were analyzed. A rotating bending fatigue test was used to investigate the fatigue properties of the enhanced surface layer. A maximum static load of about 50N was found for S45C steel process. As the strike number increased, a deeper refined grain layer and higher compressive residual stress was produced on the material's surface. The fatigue strength can be improved from 464Mpa to about 550Mpa through this process. Surface cracks, formed due to a heightened processing density of 68,000mm−2, were found on the top surface layer of the material and large processing density was the reason of the formation of cracks.

Effect of combination treatment on wear resistance and strength of Ti–6Al–4V alloy

Abstract This study was conducted to comprehensively investigate the effect of combination treatment on the wear resistance, mechanical properties, and fatigue strength of Ti–6Al–4V alloy. The combination treatment was composed of plasma nitriding, short-time duplex heat treatment (hereafter, duplex heat treatment), and fine-particle bombarding (FPB). A hardened layer was formed by plasma nitriding. The substrate was strengthened by duplex heat treatment. The brittle compound layer, formed by plasma nitriding, was eliminated by FPB, and also high compressive residual stress was introduced. Wear resistance was improved by combination treatment; however, hybrid surface treatment, composed of plasma nitriding and FPB, was more effective to improve wear resistance than combination treatment. The tensile strength was improved 30% by combination treatment. Fatigue crack initiation from the surface was strongly suppressed by the formed layer and introduced high compressive residual stress. Moreover, subsurface crack initiation was suppressed by the strengthened substrate. As a result, fatigue strength was greatly improved, by 59%, by the combination treatment.

Comparative study of the mechanical properties of nanostructured thin films on stretchable substrates

Comparative studies of the mechanical behavior between copper, tungsten, and W/Cu nanocomposite based on copper dispersoïd thin films were performed under in-situ controlled tensile equi-biaxial loadings using both synchrotron X-ray diffraction and digital image correlation techniques. The films first deform elastically with the lattice strain equal to the true strain given by digital image correlation measurements. The Cu single thin film intrinsic elastic limit of 0.27% is determined below the apparent elastic limit of W and W/Cu nanocomposite thin films, 0.30% and 0.49%, respectively. This difference is found to be driven by the existence of as-deposited residual stresses. Above the elastic limit on the lattice strain-true strain curves, we discriminate two different behaviors presumably footprints of plasticity and fracture. The Cu thin film shows a large transition domain (0.60% true strain range) to a plateau with a smooth evolution of the curve which is associated to peak broadening. In contrast, W and W/Cu nanocomposite thin films show a less smooth and reduced transition domain (0.30% true strain range) to a plateau with no peak broadening. These observations indicate that copper thin film shows some ductility while tungsten/copper nanocomposites thin films are brittle. Fracture resistance of W/Cu nanocomposite thin film is improved thanks to the high compressive residual stress and the elimination of the metastable β-W phase.

Fatigue strength of USP treated ASTM CA6NM for hydraulic turbine runner

In order to investigate the effect of an ultrasonic shot peening (USP) treatment on the fatigue characteristics of structural materials for hydroelectric facilities, plane bending fatigue tests were carried out using USP treated ASTM CA6NM stainless cast steel. The results showed that the fatigue limit of the USP material was approximately 60% higher than that of the untreated material. Haigh’s diagram evaluation suggested that an increase in crack initiation resistance associated with the high hardness and compressive residual stress by USP treatment was the main reason for the improvement in fatigue strength. Furthermore, the simulation of fatigue crack propagation implied that compressive residual stress leads to a low crack propagation rate compared with the untreated material. Consequently, it is clear that the USP treatment is an effective process for improving the fatigue properties of CA6NM.

Characterization of microstructure and residual stress in a 3D H13 tool steel component produced by additive manufacturing

Abstract

Analysis of Residual Stress in Stress Harps of Grey Iron by Experiment and Simulation

Stress harps with bars of different size were used to study residual stresses due to different cooling rate during casting of a grey iron. Finite element (FE) simulations were performed to predict residual stresses from the casting process and the effect of a stress relieving heat treatment. Intended for validating the simulations, neutron diffraction (ND) and hole drilling methods were used to measure the residual stress distribution through the thickness and in a thin surface layer, respectively. Good agreement between the FE simulations and ND measurements is observed for the annealed harp and the normal and transverse directions of the as cast harp. Discrepancy occurs in the axial direction and especially in the side bars of the as cast harp for which the simulation shows much higher compressive residual stresses. The observed difference between the different techniques was discussed with respect to the characteristics of the different methods.

Stress stabilization of a new ferroelectric phase incorporated into SrTaO2N thin films

Microstructural analyses of highly stressed SrTaO2N thin films deposited on SrTiO3 substrates by cathodoluminescence spectroscopy revealed coexistence of ferroelectric and relaxor-ferroelectric-like phases in the films. These two phases are, respectively, associated with “trans-type” and “cis-type” anion orders, as supported by the relative difference of the band gap energies calculated by first principles calculations based on the density functional theory. The formation of the new ferroelectric phase is considered to occur upon stabilization by the high compressive residual stress stored into the film structure, with the length/size of the “trans-type” region strongly depending upon the local stress state in the film.