Additive Manufacturing Fatigue and Fracture: Developing Predictive Capabilities: Heat Treatment Development
Sponsored by: TMS Structural Materials Division, TMS: Additive Manufacturing Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Nik Hrabe, National Institute of Standards and Technology; John Lewandowski, Case Western Reserve University; Nima Shamsaei, Auburn University; Mohsen Seifi, ASTM International/Case Western Reserve University; Steve Daniewicz, University of Alabama

Thursday 8:30 AM
March 3, 2022
Room: 258B
Location: Anaheim Convention Center

Session Chair: Mohsen Seifi, ASTM International/Case Western Reserve University

8:30 AM  Invited
Mechanical Behaviour of Additively Manufactured Al-Alloys: Impact of Post-processing: Moataz Attallah1; 1University of Birmingham
    Additively Manufactured Al-Alloys are prone to the formation of gas porosity and oxide films. In addition, other process-induced defects (e.g. lack of fusion and keyholing) can further deteriorate the mechanical performance. A combination of heat treatment and hot isostatic pressing is usually required to improve the mechanical behaviour (tensile and fatigue properties). Nonetheless, the use of heat treatment usually results in grain coarsening, combined with the removal of the as-fabricated dislocation structure. The repeated high-temperature treatments can be counterproductive, as they may lead to the growth of the entrapped gas pores, resulting in a poorer mechanical behaviour than the as-fabricated structure. A full overview of the factors affecting the mechanical behaviour of AMed Al-alloys will be discussed.

9:00 AM  
Fatigue Resistance Improvement of Laser Powder Bed Fusion AlSi10Mg by Post-processing: Juan Guillermo Santos Macias1; Chola Elangeswaran2; Brecht Van Hooreweder2; Jean-Yves Buffière3; Brigitte Bacroix4; David Tingaud4; Grzegorz Pyka1; Lv Zhao1; Aude Simar1; 1UCLouvain; 2KU Leuven; 3Université de Lyon; 4Université Paris 13
    Additive manufacturing (AM) has a clear potential to induce a general leap in fabrication. However, it also presents specific challenges that have to be tackled to make it a success. Metal AM parts often present porosity and surface quality levels that influence fatigue resistance negatively. A way to deal with these shortcomings is to perform post-processing. Considering a surface finishing step is necessary to solve the surface roughness issue, in this work stress relieve heat treatment and hot isostatic pressing, which can be carried out before surface machining, were explored to gauge their fatigue life improvement potential on laser powder bed fusion AlSi10Mg, obtaining mitigated success. A third alternative post-treatment, friction stir processing, which can be implemented in a single step including surface finishing, proved to be very beneficial to improve fatigue resistance, mainly due to its porosity reduction effect.

9:20 AM  
The Study on Microstructural Evolution during Post-processing of Additively Manufactured Ti64: Bryan Naab1; Denis Dowling1; Mert Celikin1; 1University College Dublin
    The advent of additive manufacturing (AM) technologies such as selective laser melting (SLM) is creating a demand for new research into how AM post-processing, such as hot isostatic pressing (HIP) and heat treatment, influences the material properties and failure mechanisms of Ti-6Al-4V. The present study examines the relationships between microstructure, processing, static mechanical properties, impact toughness and fatigue crack growth behavior of Ti64 alloy produced by SLM. Furthermore, the effects of HIP and heat treatment on microstructural evolution on the fatigue crack growth behavior were investigated via interrupted fatigue tests and Transmission electron microscopy (TEM) analysis. A direct correlation between the tensile properties with microstructure was established, however the impact toughness was determined to be mainly controlled by the porosity content rather than the microstructure.

9:40 AM  
Tailoring Hot Isostatic Pressing Treatments to Homogenize Process-dependent Microstructures and Mechanical Properties of Electron Beam Melted Ti-6Al-4V Parts: Jake Benzing1; Nik Hrabe1; Enrico Lucon1; Tim Quinn1; Julius Bonini2; Chad Beamer3; Magnus Ahlfors3; 1National Institute of Standards and Technology; 2Lucideon Consulting; 3Quintus Technologies
    Materials of known, repeatable properties that are resistant to fracture are of prime importance for structural applications, but additively manufactured parts often contain internal porosity and heterogeneities in the grain structure which reduce strength and reliability. Post-manufacture, hot isostatic pressing (HIP) treatments are commonly employed to seal the internal porosity. In this work, Ti-6Al-4V parts were manufactured by electron beam melting powder bed fusion and subjected to a range of HIP treatments that were carried out at temperatures above and below the β transus for Ti-6Al-4V. Super-β transus HIP treatments eliminate microstructural heterogeneities, including unexpected fiber textures. This presentation will attempt to isolate variables of interest and establish relationships between post-processing strategies and the following variables: porosity, crystallographic texture, prior-β grain morphology, α-lath thickness, tensile and small-punch properties, J-type fracture toughness, and high-cycle fatigue life. Future goals include using these relationships to calibrate and validate crystal plasticity-based finite element models.

10:00 AM Break

10:20 AM  Invited
Cold Spray for Aircraft Structural Repair: Sarah Galyon Dorman1; Justin Rausch1; Moriah Ausherman1; Scott Fawaz1; 1SAFE Inc
    Cold spray (CS) is being use in both civil aviation and military aircraft fleets as a method for repairing obsolete or damaged parts. There is also ongoing research by the United States Navy examining the corrosion and mechanical property equivalency of CS repairs on aluminum alloys for structural applications on military aircraft. Recent fatigue testing has shown that CS repair of various fatigue sample geometries with blend outs ranging from 15-30% of the sample thickness are able to improve fatigue life at multiple stress ratios and static mechanical properties to near that of an undamaged sample. This proof of concept testing has allowed CS to move towards use for aircraft structural component repair. Variations in how the spray is applied, raster pattern and dwell time, have been shown to be critical to the fatigue performance of CS repairs in aluminum alloys.

10:50 AM  
Effects of Process Parameters, Post-processing, and Defects on Tension and Fatigue Properties of LPBF AlSi10Mg: Austin Ngo1; Collin Sharpe1; Varthula Jayasekera2; Brett Conner3; Holly Martin2; Christopher Tuma1; John Lewandowski1; 1Case Western Reserve University; 2Youngstown State University; 3Honeywell Federal Manufacturing & Technologies
    Mechanical testing specimens of AlSi10Mg were fabricated via LPBF. Specimens were built in XY and Z orientations using multiple parameter sets, including optimized parameter sets to establish the baseline material properties and sub-optimal parameter sets to systematically induce lack of fusion defects of varying sizes. Multiple types of post-processing heat treatments were applied to the baseline and defect-induced specimens to study the effects of T6 heat treatment and/or HIP on defect population and mechanical properties. Specimens were machined for tension testing, constant amplitude fatigue testing, and three-point bend fatigue crack growth testing. Defect characteristics collected by metallography and fractography are compared across build parameter sets. Crack front plastic zone size is calculated and discussed in terms of interactions with defects and microstructure. The effects of build parameters, build orientation, post-processing, and lack of fusion defects on the subsequent mechanical properties will be covered.

11:10 AM  
Effects of Processing Parameters and Heat Treatments on the Mechanical Properties of SS316L Parts Repaired by Laser Metal Deposition: Thomas Cailloux1; Wilfried Pacquentin1; Narasimalu Srikanth2; Hicham Maskrot1; Frédéric Schuster1; Kun Zhou2; Fanny Balbaud1; 1CEA; 2Nanyang Technological University
    With the development of additive manufacturing, new possibilities for the repair of damaged metal components are developing. Powder Laser Metal Deposition is one of these processes. In order to master and qualify this repair process, it must be characterized, controlled and optimized. The repair process consists of three main steps, consisting of removing the defect by machining, adding material by additive manufacturing and obtaining a good surface finish by finishing. During the repair process, the parts undergo thermal cycle control by preheating, inter-layers time or post-heat treatment, which will influence their mechanical properties. Repairs are performed by an OPTOMEC additive manufacturing machine according to a design of experiment that takes into account the substrate preheating temperature, the inter-layers time and the post-heat treatment. Characterizations will be undertaken to know the influence of the processing parameters and heat treatments on the mechanical properties, through microhardness mapping, tensile and Charpy impact tests.

11:30 AM  
Effects of Process Parameters, Defects, and HIP Processing on S-N Fatigue of LPBF AlSi10Mg: Collin Sharpe1; Austin Ngo1; Christopher Tuma1; Michael Shinohara1; Holly Martin1; John Lewandowski1; 1Case Western Reserve University
    The effects of changes in process parameters and resulting defects on tension and S-N fatigue behavior of additively manufactured AlSi10Mg have been determined through tensile and fatigue testing of cylindrical samples according to ASTM E8/E8M-16a and ASTM E466 respectively. Samples were prepared under distinct P-V parameters and heat treatments for the following classifications: nominal + HIP, large defects + HIP, small to medium defects + HIP, many defects + HIP, large defects without HIP, and small to medium defects without HIP. Scanning electron microscope (SEM) images of the fracture surfaces have been captured and used to quantify fatigue-initiating defects, including those that did not produce catastrophe. Box-and-whisker plots are used to demonstrate the distribution these defects’ square root area. By reviewing those distributions in conjunction with the tension and S-N data, average S-N fatigue performance can be compared between groups of different process parameters, heat treatments, or build orientations.