Towards Qualification in the Aviation Industry: Impact Toughness of Ti6Al4V(ELI) Specimens Produced through Laser Powder Bed Fusion Followed by Two-Stage Heat Treatment

Lehlohonolo Francis Monaheng,Claudia Polese,Willie Bouwer Du Preez

doi:10.3390/met11111736

Lehlohonolo Francis Monaheng, Claudia Polese + Show 1 more

Open Access

https://doi.org/10.3390/met11111736

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Abstract

Laser powder bed fusion (L-PBF) has the potential to be applied in the production of titanium aircraft components with good mechanical properties, provided the technology has been qualified and accepted in the aviation industry. To achieve acceptance of the L-PBF technology in the aircraft industry, mechanical property data needed for the qualification process must be generated according to accepted testing standards. The impact toughness of Ti6Al4V extra low interstitial (ELI) specimens, produced through L-PBF followed by annealing, was investigated in this study. Charpy impact testing complying with American Standard Test Method (ASTM) E23 was performed with specimens annealed and conditioned at low temperature. On average, the toughness recorded for the specimens with 3D-printed and machined V-notches was 28 J and 31 J, respectively. These results are higher than the 24 J required in the aerospace industry. Finally, fractographic analyses of the fracture surfaces of the specimens were performed to determine the fracture mechanism of the Ti6Al4V(ELI) impact specimens.

Highlights

The requirement of the aerospace industry for materials with exceptional strength to weight ratio and outstanding mechanical properties has justified the growing use of additively manufactured (AM) Ti6Al4V extra low interstitial (ELI), even for mission-critical components, such as a landing gear nose wheel fork [1,2]
The impact toughness of Ti6Al4V(ELI) specimens produced through Laser powder bed fusion (L-powder bed fusion (PBF)) followed by two-stage heat treatment, was investigated in this study
Charpy impact testing complying with American Standard Test Method (ASTM) E23 was performed with specimens annealed and conditioned at a low temperature of −50 ◦ C

Summary

Introduction

The requirement of the aerospace industry for materials with exceptional strength to weight ratio and outstanding mechanical properties has justified the growing use of additively manufactured (AM) Ti6Al4V extra low interstitial (ELI), even for mission-critical components, such as a landing gear nose wheel fork [1,2]. Due to the α to β transformation, the microstructure and mechanical properties, such as tensile strength and ductility, of this alloy can be tailored through heat treatment [3]. The as-built AM Ti6Al4V(ELI) components have ultimate tensile strength (UTS) of 1155 MPa with a low elongation of about 4.1%, which can be altered to 1230 MPa, 914 MPa, and 871 MPa after stress relief, recrystallisation annealing, and two-stage heat treatment, respectively [5]. These are done to optimize elongation to approximately 11.5% after two-stage heat treatment. Mill-annealed wrought Ti6Al4V(ELI) has the UTS of 930–970 MPa with an elongation of 17–19% [6]

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