Shot peening.pdf - Influence of Shot Peening on Material Properties and the Controlle Shot Peening of Turbine Blades C M Verpoort and C Gerdes Asea

Shot peening.pdf - Influence of Shot Peening on Material...

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Influence of Shot Peening on Material Properties and the Controlle Shot Peening of Turbine Blades. C. M. Verpoort and C. Gerdes Asea Brown Boveri Corporate Research, Baden, Switzerland First published in Metal Behaviour and Surface Engineering, IITT-International(1989) Abstract The change of surface properties and the metallurgical processes during shot peening treatment are studied in some detail. In addition, the influence of shot peening on the fatigue strength is explained using an austenitic steel and a ferritic 12% chromium steel as examples. The aim of the work was t o investigate shot peening parameters which influence the fatigue strength of components. The presented results should lead t o a better understanding of the metallurgical processes during shot peening and should thus allow the choice of the optimum peening parameters. I t will also be demonstrated, how shot peening can be integrated into the production process of components and which measures, concerning the peening parameters and the quality control, have t o be taken into account. New methods of quality assessment will be introduced.
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Highly stressed componcnts such as turbine bladcs demand, in the development and concept phase, an optimum judgement of material. production and design based on the actual loading conditions (Fig. 1). The material surface plays an important role in components with vibrating loads because fatigue cracks usually start in the surface a t notches, pores, fatigue slip steps and inclusions. In general, a turbine blade material has t o fulfil several requirements: - I t has t o satisfy the static and dynamic loading requirements. - I t has t o satisfy the requirements in respect t o wear. erosion and corrosion. - I t must allow easy manufacturing and processing. Such a material that has to fulfil all these demands can in most cases only be produced by material combination o r a composite design. In this respect, the various techniques for surface treatment are becoming more and more important. Three different procedures can be distinguished whereby the untreated substrate material can be improved (Fig. 2): 1 . mechanical surface treatments. 2. surface diffusion treatments. 3. surface overlay coatings. The shot peening treatment belongs t o the group of mechanical surface treatments as do hammering, surface rolling, polishing, milling, turning, lapping and vibration grinding. All mechanical surface treatments that should improve the fatigue strength of components are based on the principle of preventing dislocation movement in the surface layer either by a local increase of the yield strength in the outer surface (mechanical hardening), the introduction of favourable compressive residual stresses o r by reducing the surface roughness I l l .
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  • Spring '18
  • Ernesto Cordoba

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