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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Feature Based Qualification (FBQ) of Wire Arc Additively Manufactured (WAAM) 17-4PH Martensitic Stainless Steels

The Department of Defense (DOD) programs of records desire to reduce the time and cost of the development and delivery loop in metal additive manufacturing (AM), including establishing forwarded AM capabilities. The success of these efforts relies on a robust and qualified process. To achieve this, the United States Army Combat Capabilities Development Command Ground Vehicle Systems Center Materials Engineering (GVME) needs to be able to quickly evaluate, test, and develop feedstocks, processes, and parts. This report is directed towards demonstrating the need for a framework for metal AM processes, defining and exploring geometries for metal AM process qualification, testing resultant deposition, and delivering actionable data.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Temperature-Dependent Thermal and Mechanical Properties of a Wire Arc Additively Manufactured Low Transformation Temperature Steel

Recent research has studied the use of low transformation temperature (LTT) martensite steel as feedstock for wire arc additive manufacturing (WAAM) and low tensile residual stresses or compressive residual stresses were detected in the printed walls. These residual stress states help to improve printed product properties such as fatigue strength and corrosion resistance. However, the thermal and mechanical properties of WAAM printed LTT martensite steel walls are largely unknown. In this work, a printed LTT martensite steel was characterized for its thermal, metallurgical, and mechanical behavior at room and elevated temperatures. The temperature-dependent specific heat capacity, thermal expansion, atomic lattice spacing, and tensile properties were measured during both heating and cooling and related to observed microstructural features and computational thermodynamics predictions. These results revealed a large hysteresis in the martensitic transformation, with a martensite start temperature of 240 °C and austenite start temperature of 680 °C. Additional thermal cycles and specimen orientation did not affect the printed specimen austenite and martensite transformations. However, it was observed that the printed metal may exhibit tempering embrittlement at about 350 °C but further studies are needed to confirm that. Further, these results suggest that a temperature control of 250 °C to 350 °C during WAAM is needed to maximize the stress reduction potential of the LTT250 martensite steel. Opportunities for future implementation of LTT martensite steels and optimization of additive manufacturing process conditions are identified.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effects of magnetic and structural phase transitions on the normal and anomalous Hall effects in Ni-Mn-In-B Heusler alloys

In this work, magnetization, electrical resistivity, magnetoresistance, and Hall resistivity of Ni 50 Mn 35 In 14.25 B 0.75 and Ni 50 Mn 35 In 14.5 B 0.5 Heusler alloys were studied in a temperature range $\textit{T}$ = 80–400 K in magnetic fields up to 20 kOe. Both alloys exhibit a martensitic transformation from a high-temperature ferromagnetic austenite phase to a low-temperature, low-magnetization martensitic phase. The electrical resistivity nearly doubles as a result of the martensitic transformation, reaching 180 and 100 µΩ cm in the martensitic states of Ni 50 Mn 35 In 14.25 B 0.75 and Ni 50 Mn 35 In 14.5 B 0.5 , respectively. The temperature dependence of the electrical resistivity does not corresponded with the Mooij correlation. The magnetoresistance is negative with a narrow negative peak at the martensitic transition. Normal and anomalous Hall effect coefficients were determined by fitting the field dependences of the Hall resistivity using magnetization data. The coefficients of the normal Hall effect for both compositions were found to decrease with temperature from positive values in the austenite to negative values in the martensite phase. None of the known correlations between the anomalous Hall effect coefficient and resistivity were satisfied. Significant changes in the values of the anomalous Hall coefficients during the martensitic transformation are explained by the difference in spin-up and spin-down state occupations in the martensite and austenite phases. First-principles calculations of the electronic structures confirm this explanation.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Quench and Partitioning Steels

Quench and Partitioning (Q&P) steels are produced by implementing a unique thermal history designed to produce microstructures that contain martensite, and potentially ferrite, along with significant amounts of retained austenite stabilized by high carbon contents. Carbon-stabilized austenite is obtained by carbon transfer from martensite into austenite after a controlled amount of martensite is introduced by judicious selection of a so-called quench temperature at which quenching below the martensite start temperature is interrupted. Following the quench interruption, during the partitioning step, the steel is either held at the quench temperature or brought to a higher temperature and held for a specific time, to stimulate carbon transfer from martensite to austenite, to decrease the carbon supersaturation in martensite and correspondingly stabilize the austenite by carbon enrichment. A final quench to room temperature may be associated with the transformation of a certain fraction of austenite into secondary or “fresh” martensite, which is usually undesirable. A review of the Q&P process is presented, including prediction of austenite retention, alloying effects on its stabilization, a mechanical properties survey, including tensile and local formability relevant to sheet steels for automotive applications, along with perspectives on reactions competing with carbon partitioning that may operate during partitioning.

Kang, Singon↗
DOE OSTI2021

The effects of microstructures and radiation damage on the deformation behavior of a HT-9 alloy using microtensile testing

Understanding the influence of radiation damage on the mechanical properties of HT-9 and other tempered martensitic alloys is part of the mission in developing radiation-tolerant materials for the next generation of nuclear reactors. Although there has been extensive data on the macroscopic mechanical properties of the irradiated HT-9 alloys and microstructural changes, it is not well-understood how radiation damage and the resulting microstructural changes influence the local mechanical properties. In this study, we utilized in situ SEM microtensile testing to investigate the deformation behavior of specific martensitic boundaries in 1 dpa proton-irradiated HT-9 and answered the question of what is the weakest link. Additionally, we provided the direct observation of the failure modes of microtensiles containing high angle and low angle martensitic boundaries. In the unirradiated condition, the deformation is ductile and no martensitic boundary failure is observed. In the irradiated condition, the high angle martensitic boundaries are more susceptible to radiation-induced boundary failure as compared to the low angle martensitic boundaries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

In-situ synchrotron diffraction study of the localized phase transformation and deformation behavior in NiTi SMA

The accumulation of dislocation defect was generally recognized as the origin of residual strain and the pseudoelastic instability in NiTi shape memory alloys (SMAs). In the present work, the pseudoelastic instability was studied by comparing the characteristics of Luders-type and uniform transformation mechanism via in-situ synchrotron-based high-energy X-ray diffraction (XRD) characterization. The experimental results showed that the Liiders-type mechanism could result in an intense and sharp increase of stress-induced martensite at the expense of austenite. The residual austenite with high lattice strain within the Luders band might be fully martensitic beyond the stress plateau of the E-a curve. With the accumulation of dislocation defect, the uniform martensitic transformation took place by the progressively homogeneous nucleation and growth of martensite in a local region. While the residual martensite and dislocation density was stabilized during mechanical cycling, the deformation of NiTi SMA turned into a mixture of (i) a balanced forward and reverse phase transformation between austenite and martensite, as well as (ii) the elastic deformation of the aggregate. As a result, there was no apparent increase in dislocation density detected during further cycling.

36 MATERIALS SCIENCE↗