Magnesium is a light metal, with a density two-thirds that of aluminium, is abundant on Earth and is biocompatible; it thus has the potential to improve energy efficiency and system performance in aerospace, automobile, defence, mobile electronics and biomedical applications. However, conventional synthesis and processing methods (alloying and thermomechanical processing) have reached certain limits in further improving the properties of magnesium and other metals. Ceramic particles have been introduced into metal matrices to improve the strength of the metals, but unfortunately, ceramic microparticles severely degrade the plasticity and machinability of metals, and nanoparticles, although they have the potential to improve strength while maintaining or even improving the plasticity of metals, are difficult to disperse uniformly in metal matrices. Here we show that a dense uniform dispersion of silicon carbide nanoparticles (14 per cent by volume) in magnesium can be achieved through a nanoparticle self-stabilization mechanism in molten metal. An enhancement of strength, stiffness, plasticity and high-temperature stability is simultaneously achieved, delivering a higher specific yield strength and higher specific modulus than almost all structural metals.

Processing and properties of magnesium containing a dense uniform dispersion of nanoparticles

Dual-phase (DP) steel is the flagship of advanced high-strength steels, which were the first among various candidate alloy systems to find application in weight-reduced automotive components. On the one hand, this is a metallurgical success story: Lean alloying and simple thermomechanical treatment enable use of less material to accomplish more performance while complying with demanding environmental and economic constraints. On the other hand, the enormous literature on DP steels demonstrates the immense complexity of microstructure physics in multiphase alloys: Roughly 50 years after the first reports on ferrite-martensite steels, there are still various open scientific questions. Fortunately, the last decades witnessed enormous advances in the development of enabling experimental and simulation techniques, significantly improving the understanding of DP steels. This review provides a detailed account of these improvements, focusing specifically on (a) microstructure evolution during processing, (b) exp...

An Overview of Dual-Phase Steels: Advances in Microstructure-Oriented Processing and Micromechanically Guided Design

https://pure.tue.nl/ws/files/3966928/686372654811463.pdf

Strain localization and damage in dual phase steels investigated by coupled in-situ deformation experiments and crystal plasticity simulations

Integrated experimental-simulation analysis of stress and strain partitioning in multiphase alloys

Deformation response of ferrite and martensite in a dual-phase steel

An investigation of a low-carbon, Fe-Cu–based steel, for Naval ship hull applications, with a yield strength of 965 MPa, Charpy V-notch absorbed impact-energy values as high as 74 J at –40 °C, and an elongation-to-failure greater than 15 pct, is presented. The increase in strength is derived from a large number density (approximately 1023 to 1024 m−3) of copper-iron-nickel-aluminum-manganese precipitates. The effect on the mechanical properties of varying the thermal treatment was studied. The nanostructure of the precipitates found within the steel was characterized by atom-probe tomography. Additionally, initial welding studies show that a brittle heat-affected zone is not formed adjacent to the welds.

/pdf/high-strength-low-carbon-ferritic-steel-containing-cu-fe-ni-4mxu254shz.pdf

High-Strength Low-Carbon Ferritic Steel Containing Cu-Fe-Ni-Al-Mn Precipitates

Microscale-calibrated modeling of the deformation response of dual-phase steels

Microscale-calibrated modeling of the deformation response of low-carbon martensite

The steels used for structural and other applications ideally should have both high strength and high toughness. Most high-strength steels contain substantial carbon content that gives poor weldability and toughness. A theoretical study is presented that was inspired by the early work of Weertman on the effect that single or clusters of solute atoms with slightly different atom sizes have on dislocation configurations in metals. This is of particular interest for metals with high Peierls stress. Misfit centers that are coherent and coplanar in body-centered cubic (bcc) metals can provide sufficient twisting of nearby screw dislocations to reduce the Peierls stress locally and to give improved dislocation mobility and hence better toughness at low temperatures. Therefore, the theory predicts that such nanoscale misfit centers in low-carbon steels can give both precipitation hardening and improved ductility and fracture toughness. To explore the validity of this theory, we measured the Charpy impact fracture energy as a function of temperature for a series of low-carbon Cu-precipitation-strengthened steels. Results show that an addition of 0.94 to 1.49 wt pct Cu and other accompanying elements results in steels with high Charpy impact energies down to cryogenic temperatures (198 K [–75 °C]) with no distinct ductile-to-brittle transition. The addition of 0.1 wt pct Ti results in an additional increase in impact toughness, with Charpy impact fracture energies ranging from 358 J (machine limit) at 248 K (–25 °C) to almost 200 J at 198 K (–75 °C). Extending this concept of using coherent and coplanar misfit centers to decrease the Peierls stress locally to other than bcc iron-based systems suggests an intriguing possibility of developing ductile hexagonal close-packed alloys and intermetallics.

/pdf/a-new-paradigm-for-designing-high-fracture-energy-steels-b2e3xoy685.pdf

Shrikant P. Bhat

Papers

Deformation response of ferrite and martensite in a dual-phase steel

High-Strength Low-Carbon Ferritic Steel Containing Cu-Fe-Ni-Al-Mn Precipitates

Microscale-calibrated modeling of the deformation response of dual-phase steels

Microscale-calibrated modeling of the deformation response of low-carbon martensite

A New Paradigm for Designing High-Fracture-Energy Steels