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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Precipitation of Carbides and Dissolution of Widmanstätten Structure for Enhanced Hardness in Ti{sub 2}AlNb-Based Alloys

Carbide-reinforced Ti{sub 2}AlNb matrix composites were spark plasma sintered at 1100 °C by incorporating CNTs into single-B2-phase Ti-22Al-25Nb powders. The as-SPSed alloys were solution treated and then aged in different phase regions. By kinetics analysis and energy-dispersive spectroscopy, it is found carbon will stabilize α{sub 2} phase during solution treatment, and the formation of carbide results in the Nb-depleted regions, which further induces the formation of curly B2 + O Widmanstätten structure during quenching. Different from the general Widmanstätten structure in the aged Ti{sub 2}AlNb alloy, the remained α{sub 2} will consume the B2 within the Widmanstätten structure, when the carbon-added alloy is aged in B2 + O phase region. Compared to the alloy without CNTs, the Vickers hardness of the aged carbon-added Ti{sub 2}AlNb alloy is increased significantly, which is related to the uniform and abundant columnar carbides within the O-phase matrix.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Intercritical Annealing Time at Pearlite Dissolution Finish Temperature (Ac{sub 1f}) on Mechanical Properties of Low-Carbon Dual-Phase Steel

The effect of intercritical annealing at Ac{sub 1}, Ac{sub 1f}, and Ac{sub 3} temperatures followed by water quenching was studied on the microstructure and mechanical properties of a 0.035C-0.27Mn low-carbon steel. During short-term holding at Ac{sub 1} and Ac{sub 1f}, some pearlite remained after quenching and the yield-point phenomenon was still detectable, which was related to the formation of small amount of martensite inside pearlite colonies and on ferrite grain boundaries with marginal effect on the surrounding ferrite phase. By increasing holding time at Ac{sub 1f}, pearlite disappeared and DP microstructures were achieved with the disappearance of the yield-point phenomenon and the enhancement of the work-hardening capacity. At long holding times, however, the mechanical properties deteriorated mainly due to the coarsening of martensitic islands and disappearance of dynamic strain aging (Portevin–Le Chatelier) effect at room temperature.

36 MATERIALS SCIENCE↗