Title: The effects of Ti content and quenching on phase transformations, microstructures, and mechanical properties in uranium-titanium alloys

Abstract

In this work, the effect of Ti content on phase transformations, microstructures, and mechanical properties of U-Ti alloys are described for alloys containing 0.3 wt.% to 2.0 wt.%Ti. Rapid cooling is required to overcome diffusional decomposition of γ-phase and facilitate diffusionless transformation to supersaturated variants of α-phase. Critical cooling rate increases with increasing Ti content, opposite to the trend observed in U-Mo and U-Nb alloys. This difference occurs because the martensite transformation temperatures in these relatively dilute U-Ti alloys are above the knee of the C-curve for diffusional decomposition, unlike those in the more concentrated U-Mo and U-Nb alloys. In these U-Ti alloys critical cooling rate depends on the amount of undercooling required to reach M_s, which increases with increasing Ti content, and the time for diffusional decomposition to occur just above M_s, which decreases with increasing Ti content. The net result is that higher cooling rates are required as Ti content increases. Full quenching results in diffusionless transformation of γ-phase to supersaturated variants of α-phase. Very dilute alloys transform via a γ → β → α_m sequence of massive transformations. Martensitic γ → α'_a transformation begins at ~0.4%Ti, and 100% α'_a microstructures are obtained from ~0.65% to ~1.4% Ti.more » A transition to banded α'b martensite occurs at ~1.5%Ti. Evidence suggests that the α'_a to α'_b transition may occur when the cubic γ-phase first transforms to tetragonal γ°, which in turn transforms to orthorhombic α'_b via the sequence γ → γ° → α'_b. Fully quenched alloys exhibit moderate strengths and ductilities, and their supersaturation with Ti makes them amenable to subsequent age hardening. Subcritical quenching typically results in two-phase microstructures with lower ductilities and near-zero Ti-supersaturation, eliminating the possibility of subsequent age hardening.« less

Authors:

Eckelmeyer, Kenneth H. ^[1]; Romig, A. D. ^[1]; Ludtka, Gerard M. ^[2]; Mackiewicz-Ludtka, Gail ^[2]; Chapman, Lloyd R. ^[2]

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+ Show Author Affiliations

1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2. Y-12 National Security Complex, Oak Ridge, TN (United States)

Publication Date:

Sat Nov 27 00:00:00 EST 2021

Research Org.:

Oak Ridge Y-12 Plant (Y-12), Oak Ridge, TN (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1880015

Alternate Identifier(s):

OSTI ID: 1862421

Grant/Contract Number:  

NA0001942; AC52-06NA25396; 89233218CNA000001

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Nuclear Materials

Additional Journal Information:

Journal Volume: 559; Journal ID: ISSN 0022-3115

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; Uranium alloys; Quenching; Phase transformations; Martensite; Microstructure