High Compressive Residual Stress Research Articles

Upshift of phase transition temperature in nanostructured PbTiO3 thick film for high temperature applications.

Thick polycrystalline pure PbTiO3 films with nano size grains were synthesized for the first time by aerosol deposition. Annealed 7 μm thick films exhibit well-saturated ferroelectric hysteresis loops with a remanent polarization and coercive field of 35 μC/cm(2) and 94 kV/cm, respectively. A large-signal effective d33,eff value of >60 pm/V is achieved at room temperature. The measured ferroelectric transition temperature (Tc) of the films ∼550 °C is >50 °C higher than the reported values (∼490 °C) for PbTiO3 ceramics. First-principles calculations combined with electron energy loss spectroscopy (EELS) and structural analysis indicate that the film is composed of nano size grains with slightly decreased tetragonality. There is no severe off-stoichiometry, but a high compressive in-plane residual stress was observed in the film along with a high transition temperature and piezoelectric response. The ferroelectric characteristics were sustained until 200 °C, providing significant advancement toward realizing high temperature piezoelectric materials.

Fatigue Strength of Diamond Coating-Substrate Interface Quantified by a Dynamic Simulation of the Inclined Impact Test

Fatigue damage of the nanocrystalline diamond coating (NCD) bonding to the cemented carbide substrate develops when repetitive impact loads are applied onto the film. Thus, the highly compressive residual stresses of a NCD film are released leading to its lifting from the substrate (bulge formation). The present paper deals with the analytical description of the progressive failure of the NCD coating-substrate interface under repetitive impacts. In this context, an advanced 3D-finite element analysis model was developed for the dynamic simulation of the inclined impact test, using the LS-DYNA software. This model considers the high thermal compressive residual stresses developed in the NCD coating structure during cooling from chemical vapour deposition process temperature to ambient one. The fatigue failure of the NCD coating-substrate interface is associated with a critical shear failure stress (SFLS). The determined SFLS represents the maximum operational stress permitted in the NCD film-substrate interface in order to avoid the coating detachment initiation. According to the results obtained, the successive impacts lead to a progressive weakening of the initial film-substrate interface strength depending upon the pretreatments prior to the NCD coating deposition.

Transformation-induced plastic deformation in Ce-TZP/alumina nanocomposite generated during fatigue tests at room temperature

Abstract An approximate permanent strain of 0.3% was generated in Ce-TZP/alumina nanocomposite during static fatigue tests carried out at room temperature under ≈800 MPa for up to 10 6 s. For the deformed specimens, changes in the crystalline phase, ferroelastic domain orientation, and residual stresses were investigated. No evidence to support crystalline orientation due to ferroelasticity was observed. The monoclinic content of the deformed surface was determined to be 27 and 17 vol% by using small-area XRD and Raman spectroscopy, respectively. The estimated and experimental strains corresponding to the transformed monoclinic content were roughly in good agreement. A fairly high transformation zone and compressive residual stresses were observed up to 100 μm depth from the surface. Generated permanent strain and residual stresses disappeared completely upon annealing at 1100 °C. The obtained results revealed plastic deformation to be principally attributable to volume dilatation caused by t–m transformation and that it developed with residual strains.

Influence of the cutting edge preparation method on characteristics and performance of PVD coated carbide inserts in hard turning

The use of cemented tungsten carbide inserts in hard machining requires proper coatings and edge micro-geometries. A suitable choice of these factors enables the reduction of cutting forces, the increase of tool life and the improvement of workpiece surface quality. However, the effects of the edge preparation method and coating process on the substrate properties influence the performance of the insert during cutting. In this context, the influence of two different edge preparation methods (plunge-face grinding and brushing) on the performance of TiAlN-coated cemented tungsten carbide inserts during hard turning is investigated. In general, higher values of surface roughness (Rz≅0.3μm) and edge chipping (Rk≅4.5μm) were observed for brushed inserts in comparison to the ground tools (Rz≅0.2μm, Rk≅3.7μm). Moreover, higher compressive residual stresses are induced by brushing in comparison to grinding (≅500MPa against≅400MPa). In turning tests, cutting forces for the ground inserts are approximately 10% higher than for the brushed inserts. However, higher wear values are better related to lower compressive residual stresses in the substrate than to higher cutting forces.

Numerical Simulation of One Pulse Power Laser Shock Peening

Laser shock peening (LSP) is a novel technology of surface treatment. LSP utilizes a short laser pulse with high energy density, which induced a high pressure stress wave propagation and residual compressive stress on material surface. The effects of LSP of SAE9310 steel with a laser pulse of 14.2J at 2.9mm square beam have been studied by finite element method. The underlying formulation is based on Lagangian elastoplastic materials model. The propagation of shock wave, residual stress and plastic strain are simulated. The simulations show that the residual stress is mainly in the radial direction of the workpiece, and nearly zero in the longitudinal direction. The plastic strain remains on the processed surface dominantly. Divergences between theoretical and experimental residual stress occur due to the simplification of shock peening conditions.

Combination of Plastic Upsetting Joining and Plastic Serration Joining of Disk and Shaft

Cold joining method using plastic flow has been useful for production of joint parts. The high torsional strength of the joint of a disk and a shaft was obtained by plastic flow serration joining, but the axial strength of the joint was not so high. To improve the axial strength, the serration joining was combined with additional upsetting joining. After upsetting joining high residual compressive stresses were induced between the shaft and the disk by a level with the yield stress of the disk material. The initial axial strength of joining of the disk and the shaft increases by 2.5 times by using the combination of upsetting joining and serration joining under a well-rinsed condition.

Stress Measurements in Polished Al-Mg Alloy and CrN Coating Using Multireflection Grazing Incidence Method

The multi-reflection grazing incidence X-ray diffrection was used to determine residual stress gradient in the mechanically polished Al-Mg alloy and CrN coating. Also, the root mean square values of the third order lattice strain was determined using Wiliamson-Hall method. The results obtained for Al-Mg alloy show that the stress field in the surface layer as well as the microstructure (density of dislocation) depend strongly on the sample preparation. A very high residual compressive stress, which does not change significantly with depth, was measured in the CrN coating. Moreover, a large value of the measured third order strains in the coating was found.

Dressing of vitrified bonded CBN tools for continuous generating grinding

Profile accuracy, high surface quality and compressive residual stress in the tooth root and flank are necessary for a high durability of heavy stressed gears. This article shows the advantages of vitrified bonded cubic boron nitride (CBN) tools in comparison to corundum tools relating producible compressive residual stress. In this context, especially the relationship between the dressing strategy for vitrified CBN tools and the workpiece surface and subsurface was investigated in detail.

Effect of Ultrasonic Shot Peening on the Fatigue Strength of Stainless Cast Steel ASTM CA6NM for Hydraulic Turbine Runner

In this paper, in order to investigate the effect of the ultrasonic shot peening (USP) treatment on fatigue characteristics of the structural materials for hydroelectric facilities, plane bending fatigue tests were carried out using stainless cast steel ASTM CA6NM performed by USP treatment. The fatigue test results showed that the fatigue strength of the USP materials was approximately 60% higher than that of the untreated materials. In order to examine the reason for that, the effect of USP treatment on fatigue crack initiation behavior was evaluated based on the Haigh's diagram. This evaluation implied that increasing the crack initiation resistance associated with high hardness and high compressive residual stress at surface by USP treatment is the major cause for the improvement of fatigue strength. Furthermore, the effect of USP treatment on fatigue crack propagation behavior was also examined by simulating the crack growth rate considering the stress intensity factor at crack tip. Crack propagation simulation results suggested that compressive residual stress leads crack growth rate slow compared with untreated material.

Erosion mechanism of the boron-doped diamond films of different thicknesses

Chemical vapor deposition (CVD) diamond film has extensively applied as the protective coating under hostile and abrasive conditions, the erosion mechanism of which is significantly influenced by the composition and thickness of the film. This paper describes an erosion study, which examines the effects of the film thickness on the erosive wear behavior of the boron-doped diamond (BDD) films deposited on the SiC substrates by the hot filament CVD (HFCVD) method, with the undoped ones as comparisons. A laboratory designed air–sand erosion rig is used to conduct the erosion tests, with the velocities in the range of 100–140m/s and 90° nominal impact angle. The erodents are silica sands with an average diameter of 180μm. The diamond films are examined both pre- and post-test by the field emission scanning electron microscopy (FESEM) in order to determine the erosion mechanisms of the diamond films. Firstly, it is observed that the higher residual compressive stress and critical tensile strength can slow down the formation of the ring cracks. Moreover, the 12μm diamond film has the highest steady-state erosion rate because the depth of the maximum shear stress is much close to the film–substrate interface. Furthermore, the complicated effects of the film thickness on the film lives of both the BDD and undoped diamond films are also further studied, as well as the velocity exponents of the different diamond films. The research results in the present study are conductive to the widespread applications of BDD films on the erosion resistant components.

TRIP型ベイニティックフェライト鋼の表面残留応力に及ぼす微粒子ピーニングの影響

To apply a transformation-induced plasticity (TRIP)-aided steel consisting of bainitic ferrite structure matrix and metastable retained austenite of 10 vol% (TBF steel) to some precision gears, the effects of fine particle peening on the Vickers hardness and residual stress in a surface layer of the TBF steel were investigated. The peened surface layer showed much higher Vickers hardness and compressive residual stress than those of a quenched and tempered SNCM420 steel. The increased Vickers hardness was mainly caused by an increase in the strain-induced transformed martensite fraction. The compressive residual stress was increased by the increases in size and gravity of shot material and arc-height. The higher compressive residual stress was principally associated with (1) plastic strain due to severe plastic deformation and (2) expansion strain due to the strain-induced transformation of metastable retained austenite. Contribution of the (2) was approximately 30% of total residual stress.

Grinding Effects on Surface Integrity and Mechanical Strength of WC-Co Cemented Carbides

In this study, the correlation existing among grinding, surface integrity, and flexural strength is investigated for WC-Co cemented carbides (hardmetals). A fine-grained WC-13wt % Co grade and three different surface conditions: (1) ground, (2) mirror-like polished (reference), and (3) ground plus high-temperature annealed, are investigated. Surface integrity and mechanical characterization is complemented with fractography. The grinding strongly affects both surface integrity and flexural strength. During grinding, a damaged thin layer together with high compressive residual stresses is introduced. The layer results in considerable strength enhancement compared to the reference polished surface condition. Fractography reveals that the improved strength mainly stems from grinding-induced changes on effective location, from surface into subsurface levels, of the strength-controlling flaw.

Fatigue Strength of Laser Hardened 42CrMo4 Steel Considering Effects of Compressive Residual Stresses on Short Crack Growth

The paper contains results of a study aimed at an experimental evaluation of fatigue resistance and initiation mechanisms of heat treated and laser hardened 42CrMo4 steel. Experiments were performed using quite small specimens of 8 x 8mm cross section, under three point bend fatigue loading. Two different parameters of laser hardening were used, one of them resulted in considerable longitudinal residual stresses – surface speed of laser beam 4mm/s. Results of fatigue tests of basic reference material, just heat treated, were characteristic by a surprisingly high scatter, particularly in the region near fatigue limit. Fractographical analyses indicated that this scatter was connected with presence of surface or subsurface defects, mostly inclusions, even quite large, which in some cases caused fatigue crack initiation. Compressive residual stresses after the laser treatment, dependent on laser treatment parameters, improved fatigue strength and reduced the scatter, likely due to short crack retardation in the compressive residuals stress field. Further analyses were carried out using Murakami method of evaluation of fatigue life of materials containing defects. The Murakami model of fatigue limit evaluation of specimens containing defects was just slightly conservative, when applied to specimens just conventionally heat treated, but quite strongly conservative particularly in case of laser surface hardening with high longitudinal compressive residual stresses. The results indirectly confirm significant beneficial effects of compressive stresses induced by laser hardening on fatigue resistance caused by retardation or arrest of short fatigue cracks emanating from microstructure defects.

G0310601 超音波ショットピーニング処理による発電用水車ランナ材SCS6の疲労強度改善(材料力学部門一般セッション:表面処理・改質)

In this study, the effect of ultrasonic shot peening (USP) treatment on the fatigue strength of stainless cast steel SCS6 for hydraulic turbine runner was investigated carrying out plane bending fatigue tests for USP treated material and untreated material. According to the fatigue test results, it was clear that the fatigue strength of SCS6 was improved by USP treatment, especially, the fatigue limit was 60 % improved. The reasons of the fatigue strength enhancement are thought to be the effects of high hardness and compressive residual stress generated by USP treatment. In addition, the effectiveness of USP treatment on the fatigue strength of SCS6 having the fatigue crack was also examined, The specimen was made by performing USP treatment after creating the fatigue crack of about 1 mm by using the plane bending fatigue test machine. The results of the fatigue tests indicated that USP treatment delayed the fatigue crack propagation compared with the case of USP untreated, The main reason of above results was that the fatigue crack propagation resistance was increased by the compressive residual stress generated by USP treatment, in other words, the stress intensity factor K was decreased by that factor. According to these results, it can be said that USP treatment is very effective method to improve the fatigue strength of SCS6.

Effect of carbonitriding temperature process on the adhesion properties of diamond like-carbon coatings deposited by PECVD on austenitic stainless steel

Abstract The deposition of adherent coatings such as diamond-like carbon (DLC) on substrates of iron-based materials is difficult to obtain for two reasons: high residual compressive stress occurs in the inner film formation, and the mismatch of thermal expansion coefficient between steel and DLC film generates delamination effects. In order to determine the carbonitriding temperature prior to film deposition, the steel substrate and the DLC films were analyzed for their microstructure and mechanical properties of adhesion as a function of temperature. The technique used to deposit the coating was DC-pulsed plasma enhanced chemical vapor deposition. The delamination distances and the critical load of the film were obtained by scratch testing. The surface analysis by X-ray diffraction indicated the formation of nitride phases on the steel. Raman spectroscopy showed the fraction of sp3 carbon bonds in DLC films. Hardness profiling was used to verify the extent of the interface modified by carbonitriding along the cross section. For this, the steel sample with the appropriate surface modification to have high adhesion of the DLC film was used.

Investigation of microstructures and residual stresses in laser peened Incoloy 800H weldments

Laser Shock Peening (LSP) is an advanced surface enhancement technique to improve the mechanical properties of engineering materials. In the present study, LSP was performed on Incoloy 800H laser weldments . The microstructure and residual stress, two key factors for application of weldments, were investigated via optical and transmission electron microscopy and crystallographic and residual stress X-ray diffraction analysis. Micro-hardness tests were also used to evaluate mechanical properties. Results show that significant grain refinement occurs in the LSP-treated zone where original lath structures are refined to equiaxed grains, and dislocation density increases significantly. Because of the high strain rates produced by LSP, grain deformation by slip is limited, and therefore deformation by grain twinning occurs. The micro-hardness of weld joint increased after LSP with a hardened depth of about 1.2 mm. LSP processed welded joints exhibited high compressive residual stress , and the residual stress distribution was uniform. It is shown that LSP is an effective way to refine microstructure, increase strength and rebalance residual stress which will improve fatigue life and corrosion cracking resistance of Incoloy 800H weldments. • Dislocation slipping and twinning matrix are observed in peened 800H weldments. • The effect depth of LSP for 800H weldments is about 1.2 mm. • LSP is effective to refine grain and rebalance residual stress of 800H weldments.

Erosive wear performance of boron-doped diamond films on different substrates

Diamond films have been considered as good candidate protective coatings on varieties of substrates in order to improve their erosive wear performance. In the present study, boron-doped diamond films with thicknesses of about 6–7 µm are first deposited on five different substrates using the hot filament chemical vapor deposition method, including SiC, WC-Co, Ta, Ti, and Si substrates. The residual stress and adhesive strength of the five boron-doped diamond films are estimated, respectively, by means of material properties of substrates and the diamond, Raman spectra, and static indentation results. Erosion tests are conducted on all the boron-doped diamond coated samples in an air–sand erosion rig with angular SiC sands as erodents. The results exhibit that the formation of ring cracks on the boron-doped diamond film in the erosion process has a strong link to the total residual stress. The higher residual compressive stress in the Ti-based boron-doped diamond film can slow down the formation of ring cracks to some extent. Nevertheless, the erosive wear performance, which is mainly evaluated based on the erosion rate and film removal, is much related to the film–substrate adhesion. As a result, the Ti-based boron-doped diamond film is quickly worn and removed because of the poorest adhesion. On the contrary, both the SiC- and Si-based boron-doped diamond films with favorable adhesion perform much better erosion resistance. Moreover, comparative erosion tests on thicker SiC- and WC-Co-based boron-doped diamond films (21–23 µm) and their applications on nozzles can both further manifest the same kind of relationship, the SiC-based boron-doped diamond film presenting longer steady erosive stage and slower film removal than the WC-Co-based one.

Tribological behavior between micro- and nano-crystalline diamond films under dry sliding and water lubrication

The tribological behavior of micro- and nano-crystalline diamond films is evaluated in dry sliding and water lubricating condition. The main wear mechanism is found to be abrasive wear mode induced by self-polishing. Non-diamond components and higher compressive residual stresses are detected in flat MCD films after dry sliding, in comparison to NCD. Origin of decreased friction coefficient in CVD diamond tribosystems under water lubrication is attributed to the effect of water on the formed graphic material and the chemisorbing of diamond surface with H2O, hydrogen or hydroxyl ions. For the MCD/NCD or NCD/MCD contact, the surface roughness of ball largely determines the stable friction coefficient in dry sliding, where NCD film usually presents higher wear rate.

The influence of residual stress on incipient plasticity in single-crystal copper thin film under nanoindentation

The incipient plastic deformation of single-crystal copper thin film with in-plane residual stress under Hertzian nanoindentation is studied using molecular dynamics simulation. The result reveals that the residual stresses significantly influence the surface strength and dislocation nucleation behavior of material: (i) the indentation hardness decreases with tensile residual stress, while it increases with moderate compressive residual stress, but it may drop down under higher compressive residual stress; (ii) the dislocation nucleation depth and its slip direction also vary with different residual stress state. This demonstrates that residual stress may influence incipient plasticity not only on the threshold value but also on the initial dislocation nucleation behavior under indentation.

Non-Destructive Residual Stress Analysis of Induction Hardened Components by Neutron and X-Ray Diffraction

In this paper the microstructural and residual-stress analysis of an induction hardened plate of medium carbon steel is described. The stress gradient was determined using laboratory X-ray diffraction (IWT, Bremen, Germany) and neutron strain scanning (ILL, Grenoble, France). Due to slight variations of chemical composition in the depth, matchstick like (cross section 2×2mm²) d0-reference samples were prepared from a similarly treated sample. The d0shift induced by variation of chemical composition was measured by neutron and by X-ray diffraction along the strain free direction (sin²ψ*) and used for the evaluation of the neutron stress calculation. The d0distribution obtained from the neutron measurement did not appear reliable while the method using X-ray diffraction seems to be an efficient and reliable method to determine d0profiles in small samples. The evaluation of neutron measurements was then done using the X-ray diffraction d0distribution. High compressive residual stresses were measured in the hardened layer followed by high tensile residual stresses in the core. A comparison of the neutron measurements with X-ray diffraction (XRD) depth profiles obtained after successive layer removal showed that both methods give similar results. However, these investigations opened the question about the direct comparison of the residual stresses obtained by neutron and XRD. Indeed, a correction of the neutron data regarding the residual stresses in thickness direction might be necessary as these are released in the case of X-ray diffraction measurements after layer removal.