Identification of Relationships between Heat Treatment and Fatigue Crack Growth of αβ Titanium Alloys

Abstract

This study deals with the influence of microstructure on the fatigue crack growth resistance of αβ titanium alloys: Ti-6Al-4V ELI (Extra Low Interstitial) that may compete with the conventional Ti-6Al-4V alloy in the manufacture of high performance aircraft. Six different microstructures have been considered: the as-received bimodal microstructures and five distinct fully lamellar microstructures. The characteristic parameters of these microstructures were determined and crack growth tests were performed with crack closure measurements in order to evaluate the shielding effect induced by closure. A comparison of crack growth rates, fracture surfaces, and crack path was carried out for the different microstructures. The results outline a transition between two propagation regimes from a microstructure-sensitive to microstructure-insensitive propagation.

Interactions between microstructure and fatigue crack growth in αβ titanium alloy

“…The important crystallographic propaga on in the first regime, similar for the two load ra o values inves gated, induces important crack path devia ons along crystallographic planes, and subsequently significant crack closure effects at R = 0.1. These two shielding processes account for the higher performance of the lamellar microstructure, especially in the first propaga on regime in comparison with bimodal microstructures [1] However, above the transi on, the reduc on of "crystallographic" propaga on is significant. 23% of propaga on segments are related to basal or prisma c traces is the post-transi on regime,…”

“…Crack growth tests have been performed on CT specimens in ambient air, with a load ratio of 0.1, and for ΔK values ranging from 15 to 40 MPa√m [1]. The results outline a transition between two propagation regimes, at a value of the variation of stress intensity factor ΔK = 25 MPa√m, the first regime before transition presenting reduced crack growth rate (Figure 1).…”

Comparison of Repair Methods for Cracked Titanium Alloy Aircraft Structures with Single-Sided Adhesively Bonded Composite Patches

“…The usage of Ti-alloy components in high-speed airplanes can lighten the structural weight, improve the loading quantity, and enhance maneuverability [2]. However, as with other metallic materials, Ti-alloy airframes are prone to cracking under the extreme loading spectrum during their years of service life [3]. The crack damage in Ti-alloy structures is a critical problem to be solved for the structural integrity and performance recovery in the maintenance of aged aircrafts [4].…”

Titanium Alloys: Processing and Properties

“…At the opposite end of the fatigue process, the paper from Renon et al [14] concentrates upon the damage tolerant characteristics of conventional forms of Ti 6/4 and Ti 6/4 ELI (extra low interstitial variant) subjected to various heat treatments. A comprehensive database is presented to describe constitutive behaviour and continuum fatigue crack growth.…”