T. Neeraj

Bio: T. Neeraj is an academic researcher from Ohio State University. The author has contributed to research in topics: Creep & Titanium alloy. The author has an hindex of 4, co-authored 5 publications receiving 585 citations.

Short-range order (SRO) and its effect on the primary creep behavior of a Ti–6wt.%Al alloy

Abstract: Titanium alloys have been shown to exhibit significant levels of creep at room temperature at stresses well below the macroscopic yield strength. In this work, the effect of short-range order (SRO) on the room temperature creep behavior of Ti–6wt.%Al was studied. It was observed that SRO provides significant strengthening and that the creep transients are dramatically altered due to changes in the SRO state. Slip was observed to be planar in samples that were treated to have significant SRO and homogeneous in samples in which SRO was decreased by heat treatments.

Mechanisms of primary creep in α/β titanium alloys at lower temperatures

Abstract: Creep occurs in two phase α/β Ti alloys at room temperature and at stresses below the yield strength. In polycrystalline Ti alloys, creep strain exhibits two distinct power-law regimes, an initial higher exponent which exhausts to a constant value at longer times. However, the exhaustion is much more gradual than that for other metals at lower homologous temperatures. The deformation mode in creep involves heterogeneous planar dislocation arrays. This paper describes the details of the dislocation processes and the observations of dislocation interaction with α/β interface boundaries in lamellar colony structures.

Damage evolution during fracture by correlative microscopy with hyperspectral electron microscopy and laboratory-based microtomography

Abstract: Damage evolution during fracture of metals is a critical factor in determining the reliability and integrity of the infrastructure that the society relies upon. However, experimental techniques for directly observing these phenomena have remained challenged. We have addressed this gap by developing a correlative microscopy framework combining high-resolution hyperspectral electron microscopy with laboratory x-ray microtomography (XMT) and applied it to study fracture mechanisms in a steel inclusion system. We observed damage nucleation and growth to be inhomogeneous and anisotropic. Fracture resistance was observed to be controlled by inclusion distribution and the size scale of an inclusion-depleted zone. Furthermore, our studies demonstrate that laboratory XMT can characterize damage to the micrometer scale with a large field of view in dense metals like steel, offering a more accessible alternative to synchrotron-based tomography. The framework presented provides a means to broadly adopt correlative microscopy for studies of degradation phenomena and help accelerate discovery of new materials solutions.

Verification of Short-Range Order and Its Impact on the Properties of the CrCoNi Medium Entropy Alloy

Abstract: Traditional metallic alloys are mixtures of elements where the atoms of minority species tend to distribute randomly if they are below their solubility limit, or lead to the formation of secondary phases if they are above it. Recently, the concept of medium/high entropy alloys (MEA/HEA) has expanded this view, as these materials are single-phase solid solutions of generally equiatomic mixtures of metallic elements that have been shown to display enhanced mechanical properties. However, the question has remained as to how random these solid solutions actually are, with the influence of chemical short-range order (SRO) suggested in computational simulations but not seen experimentally. Here we report the first direct observation of SRO in the CrCoNi MEA using high resolution and energy-filtered transmission electron microscopy. Increasing amounts of SRO give rise to both higher stacking fault energy and hardness. These discoveries suggest that the degree of chemical ordering at the nanometer scale can be tailored through thermomechanical processing, providing a new avenue for tuning the mechanical properties of MEA/HEAs.

Microstructure and Mechanical Properties of Wire and Arc Additive Manufactured Ti-6Al-4V

Abstract: Wire and arc additive manufacturing (WAAM) is a novel manufacturing technique in which large metal components can be fabricated layer by layer. In this study, the macrostructure, microstructure, and mechanical properties of a Ti-6Al-4V alloy after WAAM deposition have been investigated. The macrostructure of the arc-deposited Ti-6Al-4V was characterized by epitaxial growth of large columnar prior-β grains up through the deposited layers, while the microstructure consisted of fine Widmanstatten α in the upper deposited layers and a banded coarsened Widmanstatten lamella α in the lower layers. This structure developed due to the repeated rapid heating and cooling thermal cycling that occurs during the WAAM process. The average yield and ultimate tensile strengths of the as-deposited material were found to be slightly lower than those for a forged Ti-6Al-4V bar (MIL-T 9047); however, the ductility was similar and, importantly, the mean fatigue life was significantly higher. A small number of WAAM specimens exhibited early fatigue failure, which can be attributed to the rare occurrence of gas pores formed during deposition.