Internal Crack Initiation and Growth Starting from Artificially Generated Defects in Additively Manufactured Ti6Al4V Specimen in the VHCF Regime

Abstract

The aim of the present work was to investigate the ‘fine granular area’ (FGA) formation based on artificially generated internal defects in additively manufactured Ti6Al4V specimens in the early stage of fatigue crack growth in the ‘very high cycle fatigue’ (VHCF) regime. Fatigue tests were performed with constant amplitude at pure tension-compression loading (R = −1) using an ultrasonic fatigue testing setup. Failed specimens were investigated using optical microscopy, high-resolution ‘scanning electron microscopy’ (SEM), and ‘focused ion beam’ (FIB) techniques. Further, the paper introduces alternative proposals to identify the FGA layer beneath the fracture surfaces in terms of the ‘cross section polishing’ (CSP) technique and metallic grindings with special attention paid to the crack origin, the surrounding microstructure, and the expansion of the nanograin layer beneath the fracture surface. Different existing fracture mechanical approaches were applied to evaluate if an FGA formation is possible. Moreover, the results were discussed in comparison to the experimental findings.

Titanium Alloy Implants with Lattice Structures for Mandibular Reconstruction

“…Internal defects, particularly lack-of-fusion defects, are known to affect the elastic modulus, strength, elongation, and fatigue resistance of SLM-built nonporous Ti6Al4V constructs [ 220 , 228 , 229 , 230 , 231 , 232 , 233 ]. In all the cited studies, the defect volume percentage had to be very high for an appreciable effect on material properties to occur.…”

Artificial Defects in 316L Stainless Steel Produced by Laser Powder Bed Fusion: Printability, Microstructure, and Effects on the Very‐High‐Cycle Fatigue Behavior

“…Although there are several works where artificial surface defects were used for VHCF studies, [ 12,32 ] there is only one very recent work in which it was used for AM materials. [ 33 ] The authors used spherical artificial defects of sizes in the range from 100 to 400 μm in Ti6Al4V. The defects were located in the center of the cylindrical specimen.…”