Showing papers on "Shot peening published in 1999"

Cyclic deformation and near surface microstructures of shot peened or deep rolled austenitic stainless steel AISI 304

Abstract: Cylindrical specimens of the austenitic stainless steel AISI 304 were shot peened or deep rolled with different peening intensities, and rolling pressures, respectively. The resulting near surface properties were characterized by cross sectioning transmission electron microscopy (TEM), residual stress and phase analysis as well as interference line half-width and microhardness measurements. Cyclic deformation curves were obtained by hysteresis measurements under stress control with zero mean stress. The microstructural alterations in the fatigued surface regions were again characterized by the above mentioned methods. The investigations revealed that both shot peening and deep rolling lead to a complex near surface microstructure, consisting of nanocrystalline regions, deformation bands and strain induced martensitic twin lamellae with high dislocation densities in the austenitic matrix. These microstructural changes severely influence the cyclic deformation behaviour: Plastic strain amplitudes and cyclic creep were drastically decreased by shot peening and especially by deep rolling. Both surface finishing methods were found to decrease crack initiation and propagation rate. Remarkably, the initial residual stress profile and surface strain hardening were not completely eliminated even by applying high cyclic stress amplitudes. This is due to the fact that during cyclic loading dislocation cell structures were only formed in greater depths whereas the nanocrystalline layer remained stable. In the case of deep rolled surfaces, the martensitic layer was even increased by fatigue-induced martensite formation.

Laser-shock processing effects on surface microstructure and mechanical properties of low carbon steel

Abstract: The effects of laser-shock processing (LSP) on the microstructure, microhardness, and residual stress of low carbon steel were studied. Laser-shock processing was performed using a Nd:glass phosphate laser with≈600 ps pulse width and up to 120 J pulse energy at power densities above 10 12 W cm −2 . The effects of shot peening were also studied for comparison. Laser-shock induced plastic deformation caused the surface to be recessed by≈1.5 μm and resulted in extensive formation of dislocations. Surface hardness increased by up to 80% after the LSP. The microstructure and mechanical properties were altered up to≈100 μm in depth. The LSP strengthening effect on low carbon steel was attributed to the presence of a high dislocation density. Shot peening resulted in a relatively higher compressive residual stress throughout the specimen than did LSP.

Carburizing: Microstructures and Properties

Abstract: Detailed discussions and over 250 graphs and charts describe the effects of microstructure on the properties of carburized stees. In-depth coverage clarifies the causes, interpretation, prevention, and consequences of various microstructural variations and defects in carburized parts. Also covered are the effects of post-hardening heat treatments, surface grinding, and shot peening. Contents: Internal Oxidation Decarburization Carbides Retained Austinite Grain size, Microsegregation, and Microcracking Core Properties and Case Depth Post Hardening Heat Treatments Post Carburizing Mechanical Treatments.

Improvement of the fretting fatigue and fretting wear of Ti6Al4V by duplex surface modification

Abstract: Ion-beam-enhanced deposition (IBED) was investigated as a way to increase the fretting fatigue resistance of Ti6Al4V. Both hard CrN coatings with good toughness and soft CuNiIn coatings of low friction have been applied on the base material, and shot peening combined with coatings has also been studied in order to improve the fretting fatigue (FF) resistance. Since these IBED coatings exhibit a good bonding strength even after shot peening, they do not spall off during fretting fatigue and fretting wear tests. When the contact stress is not severe and gross slip contact conditions are operative, both CrN and CuNiIn show a better fretting fatigue resistance than that of shot-peened Ti6Al4V. As the contact stress concentration of fretting fatigue is high, coatings combined with shot peening achieved high levels. The fretting fatigue lifetime is largely dependent on the sliding contact conditions such as contact geometry, sliding distance and contacting materials. Under partial slip, cracks initiate at an early stage limiting the fretting fatigue lifetime, while under gross slip, a much higher fretting fatigue limit is achieved. Compressive residual stresses are particularly important to improve the fretting fatigue lifetime, when crack propagation is predominant during the failure progress.

Characterization of a Water Peening Process

Abstract: A traversing water jet was used to impact the surface of 1100 series aluminum specimens in an effort to generate compressive residual stresses on the surface. Stresses induced by the water peening operation were measured using X-ray diffraction, and compressive stress increases as large as 60 percent of the monotonic yield strength resulted. Surface roughness and hardness were also measured. Finite element modeling of a stationary water jet impinging on an elastic-plastic half-space was performed to characterize the water peening process. Surface residual stresses were found to be a result of sub-surface plastic deformations.

Performance of a rotating gear pair coated with an amorphous carbon film under a loss-of-lubrication condition

Abstract: The ability of gear boxes to complete their missions following loss of lubrication is an important parameter in design criteria for various machines. This paper shows the results of the actual gear performance test conducted using a gear testing machine that was subjected to a loss-of-lubrication condition immediately after a short operating period under fully lubricated conditions. The result showed that a gear pair subjected to an initial shot peening process and a subsequent PVD process to deposit an amorphous carbon film (WC/C film) could endure the conditions for a very long time before it failed or seized even under a very severe loading condition, thus demonstrating the utility of gears coated with an amorphous carbon film.

Residual stress relaxation in shot peened Timetal 21s

Abstract: Selective surface aging treatments (mechanical surface treatment followed by aging) on β-titanium alloys can result in higher endurance limits than conventional mechanical surface treatments. An explanation of fatigue behaviour of selectively surface aged parts should not only consider preferential precipitation strengthening but also take into account the remaining residual stresses. The β-titanium alloy Timetal 21s with two oxygen contents (0.15 and 0.30 wt%), in two solution treated conditions (fully and partially recrystallized) was aged at temperatures between 350 and 500°C after shot peening. Microhardness and X-Ray measurements allowed the determination of the degree of precipitation strengthening and relaxation of residual stresses, respectively, in the near surface regions during aging.

Fatigue behavior of titanium alloys

Abstract: This symposium was international in nature, with leaders in the fields of fatigue technology and the metallurgy of titanium from the US, Europe and Asia. It covered basic research, development, applications and modeling--life predictions and design of both fatigue crack initiation and propagation of titanium alloys. There were presentations on the full range of titanium alloy systems, from commercially pure and {alpha}-alloys, {alpha}/{beta}- and {beta}-alloys to the gamma titanium aluminides. The effects of processing/heat treatment/microstructure on the fatigue properties were discussed, and models proposed to correlate the microstructures to the observed fatigue performance. Test environments reported on included hard vacuum (and the effect of vacuum level), vacuums with partial pressures of miscellaneous gases, lab air and aqueous media. A session was devoted to the effects of environment and fatigue enhancement via surface treatments using techniques such as shot peening and roller burnishing. The effects of dwell on both S-N and crack growth rate behavior were covered. It was a very comprehensive symposium with presentations from academia, government laboratories and industry, with industrial participants ranging from the petroleum industry to medical and aerospace interests. This book has been separated into four sections, representing the technology areas covered in various sessions, namelymore » Mechanisms of Fatigue crack Initiation and Propagation of Conventional Alloys, Fatigue in Intermetallics, Environmental and Surface Aspects of Fatigue, and Application, Life Prediction and Design. Separate abstracts were prepared for most papers in this volume.« less

Mechanical surface treatments of lightweight materials—Effects on fatigue strength and near-surface microstructures

Abstract: Mechanical surface treatments such as shot peening or deep rolling are well-known processes to improve the fatigue strength of metallic components. This is due to favorable microstructural alterations in relatively thin surface layers as a consequence of near-surface inhomogeneous plastic deformations. Typical examples demonstrate the fatigue-strength increase for mechanically surface-treated specimens. Existing possibilities to improve the fatigue strength of welded joints by mechanical surface treatments are also included. In the case of lightweight materials (e. g. magnesium- or aluminum-base alloys), process parameters must be well adapted in individual cases to achieve optimum near-surface material states, taking into account the wide range of mechanical properties attainable as a result of their specific material microstructure. The effects of process parameters and microstructures on near-surface materials properties resulting from mechanical surface treatments are demonstrated with examples. Depth distributions of macroresidual and microresidual stresses are analyzed together with microstructural observations. An important point for the effectiveness of mechanical surface treatments is the stability of the near-surface material states during loading history. This aspect is treated for the case of fatigue loading.

Eddy current offers a powerful tool for investigating residual stress and other metallurgical properties

Abstract: Residual stress alters the natural conductivity of a metal only slightly; typical values of {Delta}{sigma}/{sigma} range from 5 to 100 parts per million (ppm). To detect such small effects, an eddy current bridge must be extremely stable and free of thermal or noise effects. By analyzing the conductivity as a function of frequency the residual stress distribution in the surface layers can be compared to standard samples whose stress distribution is known from X-ray analysis. It is not yet determined what the relationship between conductivity and stress is, only that it is repeatable. Many different shot peened metals have been measured successfully. Changes in conductivity which produce changes in the eddy current signatures have also been observed in samples of welded aluminum, heat treated steel, and others.

Influence of surface finishing on residual stress depth profiles of a coarse-grained nickel-base superalloy

Abstract: Residual stress depth profiles of a cast nickel-base superalloy were measured by regarding the deflections occurring in plate-shaped specimens while successively removing layers from the machined or treated surface by electropolishing. The results are in good agreement with previous findings showing (i) the influence of grinding parameters on the width of so-called white layers, which correspond to steep gradients of residual tensile stress, and (ii) a broad zone of compressive residual stress in the case of shot peening.

Processing system for increasing the quality of a gear and a barreling apparatus usable in the same

Abstract: A processing system for increasing the quality of a gear comprises: a shot peening apparatus 1 for subjecting, to shot peening, a gear 5 after tooth-forming and surface hardening; a barreling apparatus 2 positioned adjacently to the shot peening apparatus, for subjecting, to barreling, the gear which has been subjected to the shot peening by the shot peening apparatus; and a gear feeding apparatus 3 positioned adjacently to the shot peening apparatus and the barreling apparatus, for feeding, to the barreling apparatus, the gear which has been subjected to the shot peening by the shot peening apparatus. Thus, the gear of high quality can be efficiently produced, and working environment can be cleaned at a low cost by a dust collecting apparatus.

High-strength valve spring and it's manufacturing method

Abstract: The high-strength valve spring uses, as the material, a steel containing 0.5-0.8% C, 1.2-2.5 wt % Si, 0.4-0.8 wt % Mn, 0.7-1.0 wt % Cr, balance Fe and inevitable impurities, where, in the inevitable impurities, Al is no more than 0.005 wt % and Ti is no more than 0.005 wt %, and the largest non-metallic inclusion is 15 μm. In the oil tempering treatment, the heating temperature at hardening is between 950-1100° C., and nitriding treatment is performed after coiling. It is preferable to nitride at a temperature no lower than 480° C. Since the material is a high-silicon steel, the tempering temperature can be set at a higher temperature, and the nitriding temperature can be so high. In another way, after coiling, the spring is subjected to shot peening at least twice with shot particles of hardness 720 Hv or higher to produce a compressive residual stress of 85 kgf/mm2 at around surface. These measures render high surface hardness, and produce high-strength valve springs having good fatigue strength, sag resistance and delayed fracture resistance.

Effects of post‐drawing treatments on the fatigue strength of eutectoid steel wires

Abstract: The effects of bluing and shot peening on the S-N curve of eutectoid steel wires, drawn up to a strain of 3.5, were studied. Vickers hardness tests and measurements of residual stresses in the direction of the wire axis using Heyn's method were also performed. The fatigue limit of the wires, together with the hardness and the residual stresses in the surface layer of the wires, increased with the drawing strain. The bluing increased the hardness at low temperatures up to 300 °C and then decreased at higher temperatures. The residual stress decreased monotonically to zero with the temperature rise up to 500°C. Bluing increased the fatigue limit, being highest at 400 °C, through competitive effects of strain ageing and recovery of the structure. Shot peening slightly increased the surface hardness and drastically changed the residual stress from 1000 MPa to -300 MPa, which resulted in the highest fatigue limit of 1200 MPa in the wire drawn to a strain of 3.55. It is concluded that both the hardness and the residual stress are the controlling factors for the fatigue limit of the wires examined, where the crack initiation is observed to occur from the surface flaw.

Advances in Neutron Diffraction for Engineering Residual Stress Measurements

Abstract: The increasing awareness amongst engineers and designers, of the significance of residual stresses in influencing the useful lifetimes of engineering components, has resulted in more demanding expectations being placed on the methods used to obtain these stresses. The neutron diffraction technique is emerging as the most attractive measuring method as the residual stresses can usually be obtained non-destructively to depths of up to 40 mm in some common engineering materials. Although it is a relatively new technique it has been used to measure the residual stresses in a range of engineering materials introduced by a wide variety of manufacturing processes such as welding, quenching, machining, shot peening, cold hole expansion and autofrettage.

Dual intensity peening and aluminum-bronze wear coating surface enhancement

Abstract: An article and a method for improving an article that results in a reduction or elimination of damage due to fretting from contact of similar metals. The invention specifically reduces wear-related fretting between titanium alloy parts by lowering the stresses between mating parts. An aluminum bronze coating is applied to one of the parts. The aluminum bronze coating provides an improvement over prior art coatings in reducing coefficient of friction between the parts. Additionally, the cumulative stresses at the surface of the parts is reduced by a dual intensity peening treatment. This involves a first peening operation using large peening media that provides a compressive stress to the required depth. This first peening operation is followed by a second peening operation that provides additional compressive stresses closer to the dovetail surface. The combined metallurgical and mechanical improvement results in a system with less susceptibility to fretting damage and corresponding improved fatigue resistance.

On The Effects Of A Machining-Like Scratch The Fatigue Life Of 4340 Steel

Abstract: The main objective of this study was to assess the effects of a machine-like scratch on the fatigue life of a high strength steel. The steel chosen for this study was 4340 steel heat treated to an ultimate strength of 210 ksi. To accomplish this, constant amplitude fatigue tests were conducted on unnotched specimens with and without a 0.002 inch deep machining scratch which was machined across the specimen’s surface. Specimens with scratches that had been shot peened were also tested to see if the compressive residual stresses from the shot peening would provide any relief from the stress concentration caused by a scratch. The specimen was shot peened after the scratch was machined on the specimen’s surface. Tests results showed about a 40 percent reduction in the material’s endurance limit due to the machine-like scratch. However, the tests on the specimens that were shot peened after a scratch was machined into the specimen’s surface showed that the shot peening almost eliminated the effects of the stress concentration caused by a scratch. In this study it was also shown that a small-crack fracture mechanics analysis can predict the total fatigue life of constant amplitude fatigue tests with and without machine-like scratches.

Improvement of fatigue properties of PM steels by shot peening

Abstract: Shot peening was used for improving the fatigue properties of Fe–2Cu–0·5C PM steel. The steel is generally used for production of high performance sintered parts such as small connecting rods for cooling system compressors. To distinguish the effects of each alloying element, Fe, Fe–2Cu, and Fe–0·5C were also investigated. Optimum shot peening intensities are: 25A for pure iron and Fe–2Cu, 30A for Fe–0·5C, and 35A for Fe–2Cu–0·5C. For these intensities, improvements of the fatigue strengths of the materials investigated are as follows: 31% for pure iron, 48% for Fe–0·5C, 46% for Fe–2Cu, and 38% for Fe–2Cu– 0·5C. From the experimental results it could be concluded that both of the alloying additions, carbon and copper, are contributing to the fatigue strength improvements by shot peening.

Laser shock processing of Al-SiC composite coatings

Abstract: Laser shock processing (LSP) is a technique of surface treatment (similar to shot peening) in which laser-induced mechanical shocks develop compressive stresses in the material. The stresses are of sufficient intensity to modify microstructure and properties of the coatings. In the present study, laser shocks of power density of 5 to 8 GW/cm2 power density, generated by means of a neodymium-glass laser, were used to treat Al + SiC composite coatings deposited by means of a HVOF spraying technique. The laser processed samples were metallographically prepared, and their microstructure was investigated by optical microscope and SEM. The latter was also used to investigate the surface morphology of the laser treated specimens. Finally, the microhardness and oscillating wear resistance of the coatings were tested and compared to data obtained for as-sprayed samples.

High-Throughput Laser Peening of Metals Using a High-Average-Power Nd: Glass Laser System

Abstract: Laser shot peening, a surface treatment for metals, is known to induce residual compressive stresses to depths of over 1 mm providing improved component resistance to various forms of failure. Recent information also suggests that thermal relaxation of the laser induced stress is significantly less than that experienced by other forms of surface stressing that involve significantly higher levels of cold work. We have developed a unique solid state laser technology employing Nd:glass amplifier slabs and SBS phase conjugation that enables this process to move into high throughput production processing.

Fretting fatigue analysis and palliatives

Abstract: : The deleterious effects of fretting on the fatigue properties of a material have been known since the work of Warlow-Davies in 1941. However, a widely accepted fretting fatigue life prediction method still does not exist and debates persist as to what the critical parameter(s) for fretting fatigue are. This work demonstrates that the surface stresses due to contact can be used to characterize the damaging effects of fretting on the fatigue properties of a material. The elastic stress analysis performed by Hamilton for a sphere on flat plane fretting geometry is used to determine the stresses due to contact for various experimental conditions provided in previous work. It is shown that the specimen fretting fatigue life is directly related to the surface stresses induced in the material by fretting. fretting fatigue life prediction methods are analyzed. The stress-life approach, which is widely used in industry, is examined for its applicability for fretting fatigue conditions. The damage tolerant approach is used to determine the relative magnitudes of the crack nucleation and long crack propagation stages of fretting fatigue life. An analysis of fretting fatigue palliatives, focusing on shot peening and coatings, is presented. A systematic method to determine the optimum shot peening depth for fretted components is proposed. The method uses the elastic stress field expressions derived by Hamilton for a sphere on flat surface contact geometry and is demonstrated for Ti-6Al-4V. However, the method is general and can be applied for any material and any contact geometry which allows analytic evaluation of the stress fields.

Superfinishing and shot peening of surfaces to optimise roughness and stress

Abstract: Residual stress and surface roughness significantly affect component performance. For many years, Engineers have designated roughness constraints on drawings with little heed to residual stress. Fortunately this is changing as industries become aware of the significance of each and both are designated in critical applications. Superfinishing is developing as a post Shot Peening treatment in situations where metal to metal contact occurs, high temperature or fluid flow and/or optimum performance is required. Consequently the combination of residual stress and roughness control are essential on certain applications.