Advances in Titanium Technology: Session V
Sponsored by: TMS Structural Materials Division, TMS: Titanium Committee
Program Organizers: Yufeng Zheng, University of North Texas; Zachary Kloenne, Ohio State University; Fan Sun, Cnrs Umr 8247 - Chimie Paristech Psl; Stoichko Antonov, National Energy Technology Laboratory; Rongpei Shi, Harbin Institute of Technology (Shenzhen)

Wednesday 8:30 AM
March 22, 2023
Room: Cobalt 500
Location: Hilton

Session Chair: Sriram Vijayan, The Ohio State University

8:30 AM  Invited
Towards a Single Crack Nucleation Mechanism Involving Basal Twist Grain Boundaries in Ti Alloys: Cyril Lavogiez1; Clement Dureau1; Patrick Villechaise1; Yves Nadot1; Samuel Hemery1; 1Institut Pprime
    Titanium components employed in the aerospace industry generally experience fatigue loadings during in-service operation. Intense research efforts were put into the understanding of crack formation mechanisms to enable accurate prediction of the fatigue performance. However, literature review reveals an intricate situation owing to the competition between different mechanisms. In this presentation, a brief overview of microstructural features found at crack initiation sites in a variety of alloys with different microstructures and loading conditions will be reported first. Based on additional experimental data collected using a dedicated experimental campaign including low-cycle fatigue, high-cycle fatigue and low-cycle dwell-fatigue, the occurrence of a single crack nucleation mechanism involving (0001) twist grain boundaries will be demonstrated. In addition to loading conditions, the influence of composition and microstructural features will be discussed. Finally, a criterion to identify candidates for crack initiation and details of the elementary mechanisms governing fatigue crack formation will be presented.

9:00 AM  Invited
Reorientation Induced Plasticity (RIP) in High-strength Titanium Alloys: An Insight into Underlying Mechanisms and Resulting Mechanical Properties: Odeline Dumas1; Loic Malet1; Frederic Prima2; Stephane Godet1; 1Université Libre de Bruxelles; 2PSL Chimie ParisTech
    Titanium alloys for aerospace applications suffer from low work-hardening capabilities. Attempts to increase strain-hardening by combining non-conventional deformations mechanisms such as Transformation Induced Plasticity (TRIP) or Twinning Induced Plasticity (TWIP) often come with a drastic decrease in yield stress. In the present paper, we focus on Reorientation Induced Plasticity (RIP) within the martensite of alpha/alpha’ microstructures. They are shown to macroscopically exhibit very large hardening rates combined with large yield stress (typically over 800 MPa). The criteria triggering this new deformation mechanisms are scrutinized and analyzed by high resolution EBSD. It is shown that in order to enable reorientation, the martensite must exhibit (i) a critical amount of beta stabilizer elements, (ii) specific misorientation between neighbouring variants and (iii) a transformation strain that complies with the applied stress.

9:30 AM  Invited
Deformation Micromechanisms Observed in Binary Beta Ti Alloys Using TEM In Situ Tensile Tests: Nicolas Bello1; Florence Pettinari-Sturmel1; Joël Douin1; Frédéric Mompiou1; Fan Sun2; Frédéric Prima2; Philippe Vermaut2; Thierry Glorian3; Philippe Castany3; 1CEMES - Université de Toulouse; 2IRCP, Chimie ParisTech; 3ISCR Rennes
    Titanium alloys are mostly used in aeronautics, due to their high strength/density ratio and for biomedical applications because of their superior biocompatibility. While alloys with predominant beta phase (hcp) are the most common, metastable  Ti alloys, i.e. alloys composed of beta phase (stable phase at high temperature; bcc) are more and more used for structural parts in aeronautics and are becoming the most credible alternative to improve the lifespan of biomedical devices into the human body. The beta phase is then stabilized at room temperature by the addition of beta-stabilizing alloying elements such as Mo, Nb, Cr or Ta. Different mechanisms of deformation can be activated in  Ti alloys: dislocation slip, twinning and stress induced martensitic (SIM) transformation. This work is aimed to analyzed the deformation micromechanisms obtained in different binary  Ti alloys using TEM in situ tensile experiments.

10:00 AM Break

10:20 AM  
Additive Manufacturing of Titanium – Boron Carbide In situ Composites: Mohan Sai Kiran Nartu1; Srinivas Mantri1; Thomas Scharf1; Brandon Mcwilliams2; Kyu Cho2; Narendra Dahotre1; Rajarshi Banerjee1; 1University of North Texas; 2US Army Research Laboratory
    The present study will focus on detailed microstructural characterization and holistic understanding of the sequence of formation of ceramic phases in Laser engineered net shaping (LENS) processing of in situ Ti-B4C composites for high loading fractions, i.e., 25 wt.% and 35 wt.% B4C. Though, both in-situ composites, Ti-25wt.%B4C and Ti-35wt.%B4C were similarly processed via LENS, their as-processed microstructures were drastically different. Ti-25wt.%B4C exhibited nearly homogeneous microstructure, mainly dominated by TiB, TiC and α-Ti phases. Ti-35wt.% B4C exhibited alternatively-repeating layered microstructure with TiB2 and TiC phases in one layer, and TiB and TiC phases with a small fraction of retained-B4C and α-Ti in another layer. Heipel-Roper theory of weld pool dynamics has been employed to rationalize the mechanism underlying the evolution of these layered composites. Further, results from the hardness, wear and compression tests performed, indicate the potential for the AM processed Ti-B4C composites as wear and abrasion resistant materials.

10:40 AM  
Investigation to Density and Metallurgical Characteristics of Selective Laser Melted Ti-5Al-5V-5Mo-3Cr Vs. Ti-6Al-4V : David Yan1; Roman Bolzowski1; 1San Jose State University
    Ti-5Al-5V-5Mo-3Cr (Ti-5553) is a metastable near beta titanium alloy with excellent fatigue performance and corrosion resistance. Hence, it is of significant importance in several high-performance aerospace applications such as aircraft landing gear components. The selective laser melting (SLM) technique shows a great potential compared to subtractive methods in generating complex geometries. However, the poor surface finish of the SLMed Ti-5553 components means that post machining is required to achieve the desired surface quality and dimensional accuracy. Although there is a profound knowledge about the surface integrity of SLMed α + β Ti alloys (typically Ti-6Al-4V), there is a lack of understanding regarding the microstructure of internal subsurface layers of SLMed Ti-5553 components. In this paper, experimental studies were performed on SLM of Ti-5553 and Ti-64 to determine the effect of SLM parameters on the surface integrity of SLMed Ti components. The density and subsurface microstructure of printed Ti components were measured and evaluated in relation to the SLM conditions.

11:00 AM  
Titanium Metal Matrix Composite Formation in Ternary and Quaternary Compositions and Amenability to Laser Powder Bed Fusion Techniques: William Hixson1; Howard Stone2; Jonathan Poplawsky3; James Coakley1; 1University of Miami; 2University of Cambridge; 3Oak Ridge National Laboratory
    Ti-based metal matrix composites (MMCs) have highly desired qualities, but implementation has been hindered by poor processability. It is recognized that MMCs can be formed in-situ through exploiting the rapid cooling rates of laser powder bed fusion (LPBF). Ternary Ti-Si compositions plus C/Zr and quaternary Ti-Si-Zr plus Al/Sn, targeting invariant reactions to minimize solidification cracking, are examined to compare the effects of typical interstitial elements and substitutional elements, alpha and beta stabilizing elements on LPBF amenability, nanostructure and mechanical properties. In general, the MMCs are amenable to LPBF. Atom probe tomography was used to compare elemental partitioning to CALPHAD predictions. X-ray diffraction and scanning electron microscopy reveals a dependency of crystal structure and nanostructure with alloying addition. The beta matrix is retained on laser melting of Ti-Zr based compositions. Exceptional hardness values are obtained across the MMCs, highlighting very promising material systems that are processable via LPBF.

11:20 AM  
Understanding the Effect of Process Variables on Melt Pool Dynamics and Solidification Kinetics during Laser Spot Melting of Ti-6Al-4V Alloy Using In-situ Dynamic Synchrotron X-ray Radiography: Rakesh Kamath1; Raymond Wysmierski1; Ryan Heldt1; Logan White1; Gerald Knapp2; John Coleman2; Samuel Reeve2; Kamel Fezzaa3; Hahn Choo1; 1University of Tennessee Knoxville; 2Oak Ridge National Laboratory; 3Argonne National Laboratory
    Key determinants in establishing the process-structure correlations in fusion-based additive manufacturing (AM) processes are the solid-liquid and liquid-vapor phase transformations. In-situ dynamic synchrotron x-ray imaging technique was used in tandem with a laser-AM simulator (beamline 32-ID-B, APS) to investigate the dynamics of the melt pool and vapor cavity during laser spot melting (and subsequent solidification) of Ti-6Al-4V alloy. The dynamics were mapped as a function of laser power and spot dwell time, spanning both the conduction and keyhole melting regimes. The velocity of the liquid-solid interface (R), a key physical variable which determines the solidification microstructure, was obtained from the analysis. Further, the melt pool dynamics was used to inform and improve melt pool simulations performed using additiveFOAM and PicassoMPM (Material Point Method). Experimental findings are supplemented with thermal gradient (G) and fluid flow results extracted from the above simulations to better understand microstructure formation in Ti-6Al-4V laser spot melts.

11:40 AM  
Additive Manufacturing of Ti-Nb-Ta-Zr Beta Ti-Alloys: Peter Ibrahim1; Moataz Attallah1; 1University of Birmingham
    Ti-Nb-Ta-Zr beta alloys have lower elastic modulus, resulting into improved mechanical biocompatability with bone tissues than commercial Ti64 and CP-Ti. This study focuses on additive manufacturing of TNTZ alloy using Laser-Powder Bed Fusion, in particular process optimisation and mechanical behaviour. Laser energy density effect on the texture and the nature of the defects was studied. Moreover, the mechanical properties and microstructure of TNTZ with various thermal post-processing techniques such as HIP and heat treatments were evaluated using mechanical testing and electron microscopy. Findings indicate that TNTZ has high printability producing almost fully dense components with stable beta microstructure. The alloy is found to be very sensitive to thermal post-processing increasing its ultimate strength by 25% and introducing a stress-induced phase change effect when loaded.