CAMM presents at TMS 2022

Posted: February 1, 2022

Monday, February 28

Invited - Developing New Metastable Beta-titanium Alloys and Optimizing Their Properties through Heat-treatments

Speaker: Hamish L. Fraser

Brian Welk1; Nevin Taylor1; Mathew Cohen1; Zachary Kloenne1; Hamish Fraser1;  1Ohio State University

Room 252A

2:00 - 2:20 PM

Metastable beta-titanium alloys have exhibited attractive balances of properties for structural components. In this paper, the results of research aimed at developing new metastable beta-titanium alloys are presented, and the degree to which their properties may be optimized by heat-treatment is described. Regarding the development of new alloys, two methods have been employed. The first is based on the characterization of microstructure in existing alpha/beta alloys, and the second involves dilute alloying additions to existing alpha/beta alloys. Regarding the optimization of microstructure, structural and compositional instabilities have been exploited in order to produce refined microstructures using heat-treatments that do not make use of rapid quenching from a temperature above the beta transus. Hence, these heat-treated samples exhibit refined uniform microstructures and do not possess significant residual stresses. These uniform microstructures have been produced in large scale samples to demonstrate the degree of deep hardening that can be developed. 

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Posters

Room Exhibit Hall C

5:30 PM

Development of Equiaxed Titanium Alloys in Additive Manufacturing

Presenter: Nevin Taylor

Commercial titanium alloys such as Ti-64, which are widely used in additive manufacturing today, have anisotropic properties due to large prior beta grains that develop during additive manufacturing. This research investigates alloying elements that expand the freezing range and induce a columnar to equiaxed transition at rather low alloying content. It has been shown that beta-eutectoid elements including Iron, Nickel and Cobalt at ~3wt% will induce a fully equiaxed microstructure with grains an order of magnitude smaller than in their counterpart alloys. The mechanical properties or these newly developed alloys also shows significant promise, as they have increased strength, as well as similar ductility. Post-build heat treatments also introduce possibilities for different properties and microstructures depending on the desired application.

Prior Grain Boundary Alpha in BASCA Ti-17

Presenter: Mathew Cohen

Metastable beta titanium alloys offer attractive properties given their ability to form refined microstructures. However, allotriomorphic alpha at the grain boundaries often limits the ductility in these alloys. A beta anneal slow cool age (BASCA) heat treatment is often used with Ti-5553. Ti-5Al-2Sn-2Zr-4Cr-4Mo (Ti-17) is also an excellent material to undergo a BASCA heat treatment as it is beta rich and has a relatively low beta transus. In this study, Ti-17 underwent a variety of different whole and partial BASCA heat treatments, mainly resulting in basketweave microstructures. The grain size, as well as the ratio of grain boundaries with and without allotriomorphic alpha, were evaluated with different heat treatment parameters, and it was found that higher cooling rates resulted in less alpha lathes on the grain boundaries. Scanning electron microscopy (SEM) in conjunction with back scattered electron (BSE) imaging was used to study the material after heat treatment.


Tuesday, March 1

Prismatic Slip Induced Interface Sliding in a/b Titanium Alloys

Speaker: Zachary T. Kloenne

Zachary Kloenne1; Stoichko Antonov2; Gopal Viswanathan1; Michael Loretto3; Hamish Fraser1;  1Ohio State University; 2Max-Planck-Institut für Eisenforschung GmbH; 3University of Birmingham 

Room 207A

3:00 - 3:20

Titanium and its alloys have shown to deform through a combination of dislocation slip and deformation twinning. Grain boundary sliding has also been reported to contribute to the plasticity of CP titanium and Ti-6Al-4V, though these results have been reported far less frequently. More recently, Ti-1Al-4V-0.25Si-0.25Fe-0.15O has been shown to deform through sliding at the alpha/beta interface. Whilst interface sliding appears to be a slip-stimulated event, significant strain gradients were observed in response, thus speculating the presence of GNDs. The nature of these dislocations were studied using a split dislocation density analysis by HR-EBSD. Absolute character of the dislocations involved were confirmed by trace analysis in the TEM. Additionally, the sequence of events, and associated plastic strain, were studied via in-situ straining in the SEM coupled with HRDIC. Interestingly, APT results showed a Si enrichment at the alpha/beta interface. The effect of Si on sliding was studied further. 

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Wednesday, March 2

Anomalous <c+a> Dislocation Activity in an a/b Titanium Alloy

Speaker: Zachary T. Kloenne 

Zachary Kloenne1; Gopal Viswanathan1; Michael Loretto2; Hamish Fraser1;  1Ohio State University; 2University of Birmingham

Room 252A

8:30 - 8:50

Typically, two types of Burgers vectors are possible for glissile dislocations in Ti: b = [a] and b = [c+a], with the former gliding on the prismatic, basal, or first-order pyramidal planes. Previous studies have shown a large difference in CRSS between [a] slip and [c+a] slip, with the latter only being activated with close alignment of the c-axis and tensile direction. In this study, the dislocation behavior of Ti-1Al-4V-0.25Si-0.25Fe-0.15O (wt.%, Ti-407) was studied and compared with Ti-6Al-4V (wt.%). While Ti-64 was shown to deform by [c+a] dislocations in hard grains, Ti-407 exhibited [c+a] activity in both hard and soft grains. Initial CRSS measurements (micro-compression testing) show a similar trend in Ti-407 and Ti-64. FIB foils were extracted from said micropillars and studied further. It was determined that misfit dislocations at the alpha/beta interface were responsible for anomalous [c+a] activity in Ti-407, which were studied further via CTEM and HRSTEM. 

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Invited - Optimizing Composition and Microstructure in Compositionally Complex Alloys Possessing bcc and B2 Mixtures

Speaker: Hamish L. Fraser

Zachary Kloenne1; Brian Welk1; Kamalnath Kadirvel1; Gopal Viswanathan1; Jean-Philippe Cousinie1; Yunzhi Wang1; Hamish Fraser1;  1The Ohio State University

Room 254A

3:05 - 3:35 PM

In several compositionally complex alloys (CCA), a microstructure is exhibited that includes mixtures of a bcc phase and the ordered B2 compound, and which often resembles that of Ni-base superalloys. The present study has involved an assessment of whether these new alloys offer a promise for intermediate and high temperature applications. The research has involved three aspects. In the first, the transformation pathway responsible for the development of microstructures has been determined using a combination of phase field modeling and microstructural characterization. In the second, the nature of the B2 phase has been studied, involving a determination of the site occupancy in the sub-lattices of the B2 compound, using spatially-resolved energy dispersive spectroscopy (XEDS). In the third, the nature of the interfaces between the ordered and disordered phases has been fully characterized using aberration-corrected (S)TEM, and the nature of slip transmission through these interfaces has been studied.

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Invited - Evolution of Microstructure and Deformation Substructure in Al1 Mo0.5 Nb1Ta0.5Ti1Zr1, a Refractory HEA Alloy with Disordered BCC Precipitates Embedded in a Continuous Ordered B2 Matrix

Speaker: Gopal Viswanathan 

Gopal Viswanathan1; Jean-Philippe Couzinie2; Zachary Kloenne1; Brian Welk1; Oleg Senkov3; Hamish Fraser1;  1The Ohio State University; 2The Ohio State University; Université Paris Est ICMPE; 3UES Inc.

Room 251C

9:30 - 10:00 AM

The introduction of refractory elements in the high-entropy concept has led to the design of complex alloys with body centered cubic (BCC) microstructure with the aim to develop new materials with enhanced mechanical properties at high temperature. In particular, the ordered B2 phase in the BCC matrix has been highly sought in the case of refractory compositions with the aim to mimic the g-g’ type microstructure obtained in Ni-based superalloys. In alloy Al1 Mo0.5 Nb1Ta0.5Ti1Zr1 in this study the microstructure is however inverted compared to Ni-based superalloys with a B2 matrix and BCC precipitates embedded in it. To this end, the current study will focus on describing first the concomitant formation of fine scale microstructure leading to BCC+B2 microstructures with strong analogy to Ni-based superalloys and second, the characterization of defects in the plastic zone beneath the nano-indentation at RT.

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Understanding the Effect of Solute Elements on the Evolution of Equiaxed and Columnar Grains in AM Processed Beta Titanium Alloys

Speaker: Mohan Sai Kiran Nartu

Mohan Sai Kiran Nartu1; Srinivas Aditya Mantri1; Brian Welk2; Narendra Dahotre1; Hamish Fraser2; Rajarshi Banerjee1;  1University of North Texas; 2Ohio State University

Room 261A

10:25 - 10:45 AM

Virtually, all additive manufacturing (AM) processes involving complete melting of metal powders/wires produce significantly textured columnar grains along build direction, which are deleterious for mechanical properties. Therefore, understanding growth and texture of these columnar grains becomes crucial for AM alloys. Significant research in the last decade has been focused on extending the concept of growth restriction factor (GRF) (a classical theory originally developed for conventional casting) to AM. However, there are some critical concerns regarding the applicability of GRF model to AM and there is a need to understand and validate this model.Current work analyzes the evolution of grain morphology and texture in few commercial as well as model metastable beta titanium alloys processed via AM. Results indicate that the GRF model fails to interpret the grain growth behavior in these alloys. Alternatively, an approach based on solidification range has been proposed for the first time to rationalize the observations.

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