The effect of Chromium (Cr) on the dynamic transformation (DT) of austenite to ferrite at temperatures up to 430 °C above Ae
3
was studied in a medium-carbon low-alloy steel. Hot compression tests ...were performed using Gleeble 3800
®
thermomechanical simulator followed by microstructural examinations using electron microscopy (FESEM-EBSD). Driving force calculation using austenite flow stress and ferrite yield stress on an inverse absolute temperature graph indicated that Cr increases the driving force for the transformation of austenite to ferrite; however, when the influence of stress and thermodynamic analysis are taken into account, it was observed that Cr increases the barrier energy and therefore, emerges as a barrier to the transformation. An analysis, based on lattice and pipe diffusion theories is presented that quantifies the role of stress on the diffusivity of Cr and is compared with other the main alloying elements such as C, Si and Mn and its impact, positive or negative, on the DT barrier energy. Finally, a comparison is made on the differential effects of temperature and stress on the initiation of DT in medium-carbon low-alloy steels.
We investigate the complex band structure and forced response of flexural waves propagating in an elastic metamaterial thick plate. Mindlin-Reissner thick plate theory is considered. We study the ...influence of periodic arrays of spring-mass resonators attached to the surface of a homogeneous thick plate on the formation of Bragg-type and locally resonant band gaps. The plane wave expansion and extended plane wave expansion approaches are used to compute the complex band structure and wave shapes of the metamaterial thick plate with attached spring-mass resonators. An experimental analysis is conducted with a 3D-printed metamaterial plate with resonators. Modal shapes, forced response and band structure are computed by finite element and wave finite element methods. Analytical, numerical and experimental results present good agreement.
Double-hit hot compression tests were carried on medium-carbon low-alloy steels using Gleeble 3800
®
thermomechanical simulator. The experiments were performed at strain rates of 0.25 and 0.5 s
−1
...and temperatures of 1150 and 1200 °C with interpass times of 5, 15, and 25 s. The onset of critical stresses for dynamic transformation (DT) for both first and second hit were detected using the double-differentiation method. It was found that the critical stress for DT increased with a decrease in temperature and an increase in strain rate. The presence of dynamically transformed ferrite was observed and quantified using electron-backscatter diffraction, kernal average misorientation, and grain boundary maps. Then, a thermodynamic analysis was carried out using JmatPro software. A method of determining the change in Gibbs energy during DT phenomenon is proposed for double hit deformation.
Graphic Abstract
The manufacturability of equiatomic high-entropy alloy (HEA) particles with single- and dual-phase crystal structures using the high-energy mechanical alloying (HE-MA) method was explored in this ...study. Following a material design-of-experiment (DoE) curriculum, particles were synthesized in a planetary mill. Milling times varied while operating under two distinct HE-MA manufacturing regimes: the conventional approach (simultaneous milling of constituent elements) and the sequential method (progressive milling with the introduction of elements in a specific order). Within the conventional regime, equiatomic AlCoCrFe and AlCoCrFeNi blends were milled, focusing on the influence of incorporating nickel (Ni) as a transient element into the base composition. This led to an equivalent particle size distribution ranging from 5 to 100 μm. Notably, the presence of Ni resulted in an increased fraction of the face-centered cubic (FCC) phase, coupled with a simultaneous reduction in grain and crystallite sizes, thereby enhancing the overall material strength. This knowledge was applied to the design and synthesis of a target equiatomic FeNiCoCrAl HEA system. In this context, individual elements were added to the starting/milled Fe + Ni alloy at four-hour intervals, in line with the sequential milling regimen. The results showed an interesting evolution: the conventionally milled AlCoCrFeNi particles exhibited a dual-phase body-centered cubic (BCC) and FCC structure, with a composition of 55% BCC and 45% FCC phase fractions, while the sequentially milled FeNiCoCrAl particles demonstrated a single-phase BCC structure after 24 h of milling.
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•Detailed DoE varying composition and milling parameters for HEAs was performed.•Synthesis of HEAs with varying phases via sequential and conventional milling.•FeNiCoCrAl HEA alloy production in a shorter cycle using higher milling speed.•Ni addition increased plasticity in the HEA increasing the milling time requirement.•Increase in particle hardness of AlCoCrFeNi as a result of finer grain was observed.
Particulate feedstock constitutes the building block in modern day additive manufacturing (AM) era. Cold spray (CS) is a leading process technology to adhere to the AM principle. Therefore, meeting ...feedstock qualities is of utmost interest to ensure the conformability and competitiveness of the developed industrial modules, including coatings, architectured components, and additively repaired devices. This research advances the understanding of nanoscale hardness/strength properties of particulate matters, specifically of an emerging material class, - high-entropy alloys (HEAs). The feasibility of determining the hardness of mechanically alloyed AlCoCrFeNix (x = 0, 1, 2.1) HEA particles was studied employing the nanoindentation technique. Mechanical properties of milled AlCoCrFeNix particles with varying Ni atomic ratio (x = 0, 1, 2.1) were investigated over different milling times ranging between 4 and 24 h. The study analyzed the impact of mounting resin, pre-determined maximum load, and indentation depth on hardness/strength properties. Results reveal that the hot mounted samples yielded greater accuracy and higher hardness values than compared to those of the cold mounted samples. Additionally, although the low-load sensitivity of AlCoCrFeNix provided consistent nano-scale hardness values across selected loads, their hardness values were found to be depth-dependent. Overall, the study concludes with a methodology for the nano-scale hardness/strength measurement of HEA particles that must account for particle size, sample preparation technique, and nanoindentation test parameters.
This study conducts a comparative electrochemical evaluation of three types of pearlitic steels used in flexible pipelines for oil transport in marine environments. The steels have been manufactured ...with chemical composition and geometry variations to optimize operation performance under adverse conditions. Electrochemical tests were conducted using solutions simulating marine environments with NaCl and CO2, and at high temperatures. The results indicated that spheroidized (SC) steel demonstrated the best corrosion resistance under these specific conditions. Additionally, the Raman spectroscopy characterization technique was used to analyze the layers of corrosion products formed during the tests, identifying the presence of FeCO3 (siderite) and other corrosive oxides. These discoveries are valuable for selecting and improving materials in flexible pipelines used in oil production in marine waters. The study highlights the importance of the cementite morphology present in pearlite as a relevant factor in the corrosive behavior of steels, contributing to the development of more efficient and durable solutions for the offshore oil and gas industry.
•SiC incorporation in a Mg2Si matrix for improving wear resistance during additive manufacturing.•Localization of secondary phase along the edge of each melt pool of the primary phase.•Formation of a ...compositional gradient distribution from the center to the edge of each melt pool of the Mg2Si–SiC/nitride hybrid composite.•Yield strength of the aged Mg2Si–SiC/nitride hybrid composite after longitudinal additive manufacturing was 559.6 MPa.•Discovery of a new type of hybrid composite with a build-direction-dependent functionally graded structure.
The ex-situ incorporation of the secondary SiC reinforcement, along with the in-situ incorporation of the tertiary and quaternary Mg3N2 and Si3N4 phases, in the primary matrix of Mg2Si is employed in order to provide ultimate wear resistance based on the laser-irradiation-induced inclusion of N2 gas during laser powder bed fusion. This is substantialized based on both the thermal diffusion- and chemical reaction-based metallurgy of the Mg2Si–SiC/nitride hybrid composite. This study also proposes a functional platform for systematically modulating a functionally graded structure and modeling build-direction-dependent architectonics during additive manufacturing. This strategy enables the development of a compositional gradient from the center to the edge of each melt pool of the Mg2Si–SiC/nitride hybrid composite. Consequently, the coefficient of friction of the hybrid composite exhibits a 309.3% decrease to –1.67 compared to –0.54 for the conventional nonreinforced Mg2Si structure, while the tensile strength exhibits a 171.3% increase to 831.5 MPa compared to 485.3 MPa for the conventional structure. This outstanding mechanical behavior is due to the (1) the complementary and synergistic reinforcement effects of the SiC and nitride compounds, each of which possesses an intrinsically high hardness, and (2) the strong adhesion of these compounds to the Mg2Si matrix despite their small sizes and low concentrations.
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