Shaping of Ceramics Using Residual Stresses

2013 ◽  
Vol 768-769 ◽  
pp. 478-483
Author(s):  
Heiko Höpfel ◽  
Wulf Pfeiffer
Keyword(s):  
Shot Peening ◽  
Surface Region ◽  
Cyclic Strength ◽  
Common Procedure ◽  
Near Surface ◽  
Peen Forming ◽  
Deformation Work ◽  
Stress States ◽  
Underlying Mechanisms ◽  
Localized Plastic Deformation

Shot peening is a common procedure used to improve the static and cyclic strength of metal components and for forming of thin walled components. The underlying mechanisms are localized plastic deformation, work hardening and the introduction of compressive stresses into the near-surface region. During the last decade we have been establishing damage-free shot peening processes for brittle materials such as ceramics. Based on these results we are now developing processes for peen-forming of ceramic components. This paper describes the first successful experiments aimed at shaping ceramic specimens using shot peening. Strips of different thicknesses, made of silicon nitride ceramic, were shot-peened using different shot sizes, peening pressures and coverage. The residual stress-depth distributions were determined using X-ray diffraction. Based on the experimentally determined stress states, the curvatures of the strips were calculated analytically and using Finite Element calculations (FEM). The results of the curvature measurements and calculations agree well.

Shot Peening of Brittle Materials - Status and Outlook

2010 ◽  
Vol 638-642 ◽  
pp. 799-804 ◽  
Author(s):  
Wulf Pfeiffer ◽  
Johannes Wenzel
Keyword(s):  
Shot Peening ◽  
Surface Region ◽  
Strength Properties ◽  
Cyclic Strength ◽  
Cemented Carbides ◽  
Common Procedure ◽  
Surface Strength ◽  
Crack Network ◽  
Near Surface ◽  
Compressive Stresses

Shot peening is a common procedure to improve the static and cyclic strength of metal components by a combination of work hardening and the introduction of compressive stresses into the surface region. Our investigations through the last years showed that high compressive stresses of more than 1 GPa can also be introduced in brittle ceramics under specific shot peening conditions. These stresses significantly increase the near-surface strength. Based on the findings for ceramics, shot peening procedures have now been developed for cemented carbides and hard chromium platings. Recent investigations showed that, due to the higher fracture toughness of cemented carbides, shot peening could be performed using higher peening intensities leading to a higher gain in strength properties. Although chromium platings are less brittle than ceramics, shot peening of these layers are very challenging due to the formation of a micro-crack network being typically for these coatings. Nevertheless, first results indicate the possibility of a successfully shot peening of these coatings.

scholarly journals A Numerical Investigation of a Single-Shot in a DEM-FEM Approach to Shot Peening Simulation

Metals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 1183
Author(s):  
Aghogho Bright Edward ◽  
P. Stephan Heyns ◽  
Schalk Kok
Keyword(s):  
Shot Peening ◽  
Strain Energy ◽  
Equivalent Plastic Strain ◽  
Contact Forces ◽  
Metallic Surface ◽  
Single Shot ◽  
Near Surface ◽  
Controllable Process ◽  
Localized Plastic Deformation ◽  
The Impact

Shot peening (SP) is a controlled and systematic process of surface treatment that has a large number of controllable process parameters that make its application highly challenging. It involves the shooting of small and hard metallic balls at a targeted surface, with the aim of enhancing the fatigue strength of the workpiece under unfavorable service conditions. The compressive residual stress (CRS) induced by this application is expensive to evaluate experimentally. This paper presents a numerical model of the impact of a single-shot on a metallic surface, with the aim to set the stage for a realistic multiple shots peening simulation. The approach proposed herein is a sequential Discrete Element-Finite Element (DE-FE) coupled simulation, based on the use of different types of coefficients of restitution (CoRs) with emphasis on the energetic CoR. The energetic CoR relates the shot/target contact forces to the fractional strain energy needed for localized plastic deformation of the near-surface layer in the workpiece. The generated results of the induced compressive residual stresses (CRS) and equivalent plastic strain (PEEQ) from single-shot simulations are validated with similar results from the literature. Our study clarifies the strain energy aspects of a single-shot impact responsible for the desired effects of CRS and PEEQ, thereby laying the groundwork for accurate and realistic modeling of the SP process via the DEM-FEM approach.

Modification of Alumina Ceramics Properties by Stressonic® Shot Peening

2005 ◽  
Vol 490-491 ◽  
pp. 509-514 ◽  
Author(s):  
Henryk Tomaszewski ◽  
K. Godwod ◽  
Ryszard Diduszko ◽  
F. Carrois ◽  
J.M. Duchazeaubeneix
Keyword(s):  
Shot Peening ◽  
Treatment Time ◽  
Surface Region ◽  
Microplastic Deformation ◽  
Material Surface ◽  
Alumina Ceramics ◽  
X Ray Diffraction ◽  
Near Surface ◽  
Compressive Stresses ◽  
Ultrasonic Shot Peening

Modification of material surface layers by conventional shot peening is commonly used to improve the strength of metal components. As it occurred high compressive stresses up to 2.0 GPa may be introduced also to near surface region of alumina ceramics by this technique. Two alumina ceramics were given to ultrasonic shot peening which is a new, compact and small consuming of shot media method developed by Sonats company. This process is named Stressonic®. The dependence between diameter of tungsten balls, treatment time (at constant mass of balls in the housing and vibration amplitude) and level of compressive stresses introduced was determined. High microplastic deformation in shot peened surface layer of alumina was observed by X-ray diffraction. An increase of surface resistance to fracture of ceramics with increasing level of compressive stresses was also found.

Surface Effects on the Mechanical Properties of Gamma Titanium Aluminides

2012 ◽  
Vol 706-709 ◽  
pp. 1071-1076 ◽  
Author(s):  
Janny Lindemann ◽  
Maria Glavatskikh ◽  
Christoph Leyens
Keyword(s):  
Surface Roughness ◽  
Fatigue Strength ◽  
Shot Peening ◽  
Titanium Aluminides ◽  
Surface Region ◽  
Fatigue Performance ◽  
Near Surface ◽  
Gamma Titanium ◽  
Compressive Stresses ◽  
Gamma Titanium Aluminides

Surface conditions are of significant importance for the fatigue performance of rotating components for aircraft and automotive applications. Compared to the electropolished reference state the fatigue performance of gamma titanium aluminides at ambient temperature can be significantly improved by shot peening, while the fatigue strength after roller burnishing is hardly affected. Fatigue strength improvements after shot peening are mainly caused by cyclically stable residual compressive stresses in the near-surface region. Notably, also conventional turning operations generate high dislocation densities and residual compressive stresses in the near-surface region resulting in fatigue strength improvements similar to shot peening. Surface strengthening by shot peening or machining leads to subsurface fatigue crack nucleation and overcompensates the detrimental influence of the high surface roughness on fatigue. However, for temperatures above 650 °C, residual compressive stresses induced by shot peening and machining quickly relax. This indicates that, at elevated temperatures, surface roughness and dislocation strengthening become increasingly important for the fatigue performance of components.

Shot Peening - A New Method for Improving Mechanical Properties of Structural Ceramics

2006 ◽  
Vol 317-318 ◽  
pp. 277-280 ◽  
Author(s):  
Henryk Tomaszewski ◽  
K. Godwod ◽  
Ryszard Diduszko ◽  
F. Carrois ◽  
J.M. Duchazeaubeneix
Keyword(s):  
Compressive Stress ◽  
Shot Peening ◽  
Structural Changes ◽  
Treatment Time ◽  
Surface Region ◽  
Microplastic Deformation ◽  
Material Surface ◽  
Near Surface ◽  
Compressive Stresses ◽  
Ultrasonic Shot Peening

Shot peening is commonly used to modify material surface layers and improve the strength of metal components. As it occurred the same technique can be applied for brittle ceramics. High compressive stresses up to 2.4 GPa were introduced into near surface region of alumina and zirconia ceramics by ultrasonic shot peening maintaining its surface integrity. Dependence between diameter of tungsten balls, treatment time (at constant mass of balls in the housing and vibration amplitude) and level of compressive stress introduced was determined for both ceramics with nano and micrograins. Coarser grained ceramics was found to be more sensible to structural changes responsible for stress creation than the smaller one. High microplastic deformation in shot peened surface layer of ceramics was observed by X-ray diffraction. An increase of hardness and surface resistance to fracture with increasing level of compressive stress was found.

A self-consistent method for X-ray diffraction analysis of multiaxial residual-stress fields in the near-surface region of polycrystalline materials. II. Examples

1999 ◽  
Vol 32 (4) ◽  
pp. 779-787 ◽  
Author(s):  
Ch. Genzel ◽  
M. Broda ◽  
D. Dantz ◽  
W. Reimers
Keyword(s):  
Residual Stress ◽  
Stress Component ◽  
Stress Gradient ◽  
Surface Region ◽  
Evaluation Procedure ◽  
Polycrystalline Materials ◽  
Vector Method ◽  
Near Surface ◽  
X Ray ◽  
Stress States

The application of the formalism for residual-stress gradient evaluation based on the measuring principle of the scattering-vector method, which has been derived in the first paper of this series [Genzel (1999).J. Appl. Cryst.32, 770–778], is demonstrated by practical examples. Depending on the statistical scattering of the experimental data, either biaxial or even triaxial residual-stress states may be analysed; the latter case yields self-consistently the depth profiles of the in-plane stresses, σ11(τ) and σ22(τ), the normal stress component, σ33(τ), as well as the strain-free lattice spacing,d0(hkl). The results obtained by this new evaluation procedure are compared with those obtained by X-ray stress-gradient analysis performed on the basis of the sin2ψ method.

Preparation of cross-sectional samples for near-surface TEM studies

1987 ◽  
Vol 45 ◽  
pp. 380-381
Author(s):  
R.C. Dickenson ◽  
K.R. Lawless
Keyword(s):  
Standard Sample ◽  
Surface Region ◽  
Specimen Preparation ◽  
Thick Sheet ◽  
Drill Bit ◽  
Sample Holder ◽  
Metal Interface ◽  
Cross Sectional ◽  
Near Surface ◽  
Cold Worked

In thermal oxidation studies, the structure of the oxide-metal interface and the near-surface region is of great importance. A technique has been developed for constructing cross-sectional samples of oxidized aluminum alloys, which reveal these regions. The specimen preparation procedure is as follows: An ultra-sonic drill is used to cut a 3mm diameter disc from a 1.0mm thick sheet of the material. The disc is mounted on a brass block with low-melting wax, and a 1.0mm hole is drilled in the disc using a #60 drill bit. The drill is positioned so that the edge of the hole is tangent to the center of the disc (Fig. 1) . The disc is removed from the mount and cleaned with acetone to remove any traces of wax. To remove the cold-worked layer from the surface of the hole, the disc is placed in a standard sample holder for a Tenupol electropolisher so that the hole is in the center of the area to be polished.

The Effects of Ion Implantation on the Surface Features of Inconel 600

1985 ◽  
Vol 43 ◽  
pp. 288-289
Author(s):  
John D. Rubio
Keyword(s):  
Grain Boundary ◽  
Ion Implantation ◽  
Nuclear Power ◽  
Power Plants ◽  
Surface Region ◽  
Selective Dissolution ◽  
Boundary Region ◽  
Near Surface ◽  
Inconel 600 ◽  
Steam Generator Tubing

The degradation of steam generator tubing at nuclear power plants has become an important problem for the electric utilities generating nuclear power. The material used for the tubing, Inconel 600, has been found to be succeptible to intergranular attack (IGA). IGA is the selective dissolution of material along its grain boundaries. The author believes that the sensitivity of Inconel 600 to IGA can be minimized by homogenizing the near-surface region using ion implantation. The collisions between the implanted ions and the atoms in the grain boundary region would displace the atoms and thus effectively smear the grain boundary.To determine the validity of this hypothesis, an Inconel 600 sample was implanted with 100kV N2+ ions to a dose of 1x1016 ions/cm2 and electrolytically etched in a 5% Nital solution at 5V for 20 seconds. The etched sample was then examined using a JEOL JSM25S scanning electron microscope.

Microstructural changes of Aluminum Nitride after laser irradiation and electroless copper deposition

1994 ◽  
Vol 52 ◽  
pp. 636-637
Author(s):  
S. Cao ◽  
A. J. Pedraza ◽  
L. F. Allard
Keyword(s):  
Aluminum Nitride ◽  
Laser Irradiation ◽  
Electroless Deposition ◽  
Thermal Evaporation ◽  
Surface Region ◽  
Near Surface ◽  
Laser Patterning ◽  
Electroless Copper ◽  
Excimer Laser Irradiation ◽  
Laser Effect

Excimer-laser irradiation strongly modifies the near-surface region of aluminum nitride (AIN) substrates. The surface acquires a distinctive metallic appearance and the electrical resistivity of the near-surface region drastically decreases after laser irradiation. These results indicate that Al forms at the surface as a result of the decomposition of the Al (which has been confirmed by XPS). A computer model that incorporates two opposing phenomena, decomposition of the AIN that leaves a metallic Al film on the surface, and thermal evaporation of the Al, demonstrated that saturation of film thickness and, hence, of electrical resistance is reached when the rate of Al evaporation equals the rate of AIN decomposition. In an electroless copper bath, Cu is only deposited in laser-irradiated areas. This laser effect has been designated laser activation for electroless deposition. Laser activation eliminates the need of seeding for nucleating the initial layer of electroless Cu. Thus, AIN metallization can be achieved by laser patterning followed by electroless deposition.

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