Modelling of Crack Growth in Single-Crystal Nickel-Base Superalloys

Abstract

No part of this publication may be reproduced, stored in a retrieval system, or be transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior permission of the author. Thank you! Linköping, December 2019 Christian Busse iii The nature of science is not that of a steady, linear progression toward the truth, but rather a tortuous road, often characterized by dead ends and U-turns, and yet ultimately inching toward a better, if tentative, understanding of the natural world.

Implications of ΔK‐Rratio in vacuum

“…Inserts in Figure 5A,B show the crack path profiles for the two alloys are taken from Petit 13 and Busse. 15 In spite of the linear crack path for 7075-T7351 alloy (wavy slip) and a deflected crack branching for PWA1480 (planar slip) both alloys display a weak dependence of ΔK with FCG rates for R > 0. For PWA1480 alloy the scatter in ΔK for a given (da/dN) is less than 2 MPa ffiffiffiffi m p , which may come from the experimental resolution of measurements of this very rough fracture surface.…”

“…F I G U R E 4 Independence of ΔK th threshold with R-ratio for several alloys in vacuum 12 F I G U R E 5 Fatigue crack growth data for (A) 7075-T7351 (wavy slip), 4,13 and (B) a single crystal PWA-1480 alloy (planar slip) in high vacuum, 14,15 showing small variation with R-ratio [Colour figure can be viewed at wileyonlinelibrary.com] The environmental threshold behavior with R is commonly explained using the "crack closure" concepts. Here we do understand that the crack flanks do come into contact but the disagree with the assumed relation to ΔK eff at the crack tip.…”

“…Fatigue crack growth data for (A) 7075‐T7351 (wavy slip), 4,13 and (B) a single crystal PWA‐1480 alloy (planar slip) in high vacuum, 14,15 showing small variation with R ‐ratio [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…For both alloys, the Δ K variation with FCG rates remained nearly independent of R ‐ratio (with some experimental scatter), over several orders of magnitude in FCG rate. Inserts in Figure 5A,B show the crack path profiles for the two alloys are taken from Petit 13 and Busse 15 …”

Crack growth in single crystal gas turbine blade alloys under service-like conditions

“…Several researchers propose crack driving force parameters based on shear stress intensity factors resolved onto the {111} planes [4][5][6][7][8][9] , but there is no general consensus regarding the precise definition. Within the present PhD thesis work, testing was done to investigate the crystallographic crack growth behaviour under different testing conditions and the results were used in the development of the crystallographic crack driving force parameter recently proposed by Busse et al [9][10][11][12] . While the complexity of localized inelastic deformation and crystallographic crack growth is mainly associated with lower temperatures, there are other challenges associated with fatigue crack growth in single crystal superalloys at higher temperatures.…”