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Title: Effect of Modified Surface Microstructures through Shot Peening and Subsequent Heat Treatment on the Elevated Temperature Fat
Author: Gray, Wagner, Lutjering,
Source: Conf Proc: ICSP-3, (p.467-476)
Publication year 1987
Document number: 1987018
Number of pages: 9
Abstract:
Shot peening is well recognized as a mechanical surface treatment which can significantly improve the fatigue resistance of high-strength materials. The potential
application of shot peening is often thought to be necessarily restricted to low temperatures since the residual compressive stresses which are known to be of most
importance in improving the fatigue strength at low temperatures can readily relax at elevated temperatures due to recovery of the material. However, previous work on
Ti-alloys has demonstrated that the 10(7) cycles fatigue strength at elevated temperatures can be significantly increased without the presence of residual compressive
stresses due to the thermal stability of the induced high dislocation density. To take advantage of the beneficial effect of high dislocation densities on fatigue crack
nucleation the rough as peened surface was smoothened by additional polishing treatments.
L
ately, it was observed that smaller grains or finer phase dimensions in
Ti-alloys besides the beneficial effect on fatigue crack nucleation can also improve the resistance to propagation of small surface cracks. In the recent past, developments
of high temperature titanium alloys have reflected the increased drive for optimizing their all-round capabilities. While it seems to be quite difficult to optimize a
microstructure with regard to the resistance against creep and fatigue shot peening may offer a method for combining excellent fatigue with superior creep properties in
engineering components, such as gas turbine blades. By shot peening of an engineering component with a coarse creep resistant microstructure and by subsequent annealing
that component at sufficiently high temperatures, very fine recrystallized (fatigue resistant) phase dimensions can be produced in near surface regions without changing the
coarse (creep resistant) microstructure in deeper regions.
I
n the present investigation, shot peening and subsequent
recrystallization was applied on fatigue specimens of Ti-alloys to modify the surface layer microstructures for an improved resistance to elevated temperature fatigue
behavior.
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