ISSN: 1546-962X
CODEN: JAIOAD
Published Online: 1 May 2012
Page Count: 12

Fatigue Sensitivity to Small Defects of a Gamma–Titanium–Aluminide Alloy

Filippini, Mauro
Politecnico di Milano, Dipartimento di Meccanica, Via La Masa 1, Milano,

Beretta, Stefano
Politecnico di Milano, Dipartimento di Meccanica, Via La Masa 1, Milano,

Patriarca, Luca
Politecnico di Milano, Dipartimento di Meccanica, Via La Masa 1, Milano,

Pasquero, Giuseppe
Avio S.p.A., Via I Maggio 99, Rivalta di Torino,

Sabbadini, Silvia
Avio S.p.A., Via I Maggio 99, Rivalta di Torino,

(Received 26 August 2011; accepted 16 February 2012)

Abstract

The fatigue properties of a Ti-48Al-2Cr-2Nb alloy obtained by electron-beam melting (EBM) with a patented process has been examined by conducting high cycle fatigue tests performed at different R ratios at room temperature. Fatigue-crack propagation tests have been performed for the purpose of characterizing the fatigue-crack growth rate and threshold of the material. Additionally, specimens with artificially introduced defects have been fatigue tested with the objective of studying the growth behavior of small cracks. Artificial defects with different sizes have been generated in the gauge section of the specimens by electron-discharge machining (EDM). After EDM defects are produced, the specimens are pre-cracked in cyclic compression, so that small cracks can be generated at the root of the EDM starter defects. Fatigue tests are conducted by applying the staircase technique with the number of cycles of censored test (runout) fixed at 10⁷ cycles. By employing the Murakami model for the calculation of the range of stress intensity factor, the threshold stress intensity factor range dependence on the loading ratio R and on the defect size is evaluated, highlighting the relevant parameters that govern the specific mechanisms of failure of the novel γ–TiAl alloy studied in the present work.

Keywords:
gamma titanium aluminides, high-cycle fatigue, fatigue-crack propagation, compression pre-cracking, short-crack behavior

Paper ID: JAI104293
DOI: 10.1520/JAI104293
ASTM International is a member of CrossRef.