Metals have been mankind's most essential materials for thousands of years; however, their use is affected by ecological and economical concerns Alloys with higher strength and ductility could alleviate some of these concerns by reducing weight and improving energy efficiency However, most metallurgical mechanisms for increasing strength lead to ductility loss, an effect referred to as the strength-ductility trade-off Here we present a metastability-engineering strategy in which we design nanostructured, bulk high-entropy alloys with multiple compositionally equivalent high-entropy phases High-entropy alloys were originally proposed to benefit from phase stabilization through entropy maximization Yet here, motivated by recent work that relaxes the strict restrictions on high-entropy alloy compositions by demonstrating the weakness of this connection, the concept is overturned We decrease phase stability to achieve two key benefits: interface hardening due to a dual-phase microstructure (resulting from reduced thermal stability of the high-temperature phase); and transformation-induced hardening (resulting from the reduced mechanical stability of the room-temperature phase) This combines the best of two worlds: extensive hardening due to the decreased phase stability known from advanced steels and massive solid-solution strengthening of high-entropy alloys In our transformation-induced plasticity-assisted, dual-phase high-entropy alloy (TRIP-DP-HEA), these two contributions lead respectively to enhanced trans-grain and inter-grain slip resistance, and hence, increased strength Moreover, the increased strain hardening capacity that is enabled by dislocation hardening of the stable phase and transformation-induced hardening of the metastable phase produces increased ductility This combined increase in strength and ductility distinguishes the TRIP-DP-HEA alloy from other recently developed structural materials This metastability-engineering strategy should thus usefully guide design in the near-infinite compositional space of high-entropy alloys

Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off

Open literature publications, in the period from 2010 to the end of January 2018, on refractory high entropy alloys (RHEAs) and refractory complex concentrated alloys (RCCAs) are reviewed. While RHEAs, by original definition, are alloys consisting of five or more principal elements with the concentration of each of these elements between 5 and 35 at.%, RCCAs can contain three or more principal elements and the element concentration can be greater than 35%. The 151 reported RHEAs/RCCAs are analyzed based on their composition, processing methods, microstructures, and phases. Mechanical properties, strengthening and deformation mechanisms, oxidation, and corrosion behavior, as well as tribology, of RHEA/RCCAs are summarized. Unique properties of some of these alloys make them promising candidates for high temperature applications beyond Ni-based superalloys and/or conventional refractory alloys. Methods of development and exploration, future directions of research and development, and potential applications of RHEAs are discussed.

Development and exploration of refractory high entropy alloys—A review

A TRIP-assisted dual-phase high-entropy alloy: Grain size and phase fraction effects on deformation behavior

A review on fundamental of high entropy alloys with promising high–temperature properties

Revealing the strain-hardening behavior of twinning-induced plasticity steels: Theory, simulations, experiments

Design of a novel Mn-based 1 GPa duplex stainless TRIP steel with 60% ductility by a reduction of austenite stability

Wrought austenitic stainless steels are widely used in high temperature applications. This short review discusses initially the processing of this class of steels, with emphasis on solidification and hot working behavior. Following, a brief summary is made on the precipitation behavior and the numerous phases that may appear in their microstructures. Creep and oxidation resistance are, then, briefly discussed, and finalizing their performance is compared with other high temperature metallic materials.

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A Short review on wrought austenitic stainless steels at high temperatures: processing, microstructure, properties and performance

Duplex stainless steels (DSSs) are based on the Fe-Cr-Ni system and consist of ferrite (30-70%) and austenite. DSSs have shown an excellent combination of resistance to general and localized corrosion, stress corrosion cracking, high strength and low cost due to reduced contents of Ni and Mo [1-3]. DSSs are used in oil, gas, paper, desalination and petrochemical industries. The main process steps in the industrial manufacturing of duplex stainless steel sheets are continuous casting, slab reheating, hot rolling, coiling, hot band heat treatment, cold rolling and final recrystallization annealing. Particular attention during manufacturing of these steels has to be paid to the forming steps at high temperatures. Hot working of steels with two phases may cause complications for several reasons: the precipitation of detrimental phases [1,4], such as -phase and M23C6, the low hot ductility, and edge crack formation. The ductility depends on different factors like temperature, strain rate, microstructure and chemical composition. Moreover, it is affected by the different softening mechanisms in ferrite and austenite [5-9]. The formation of as-cast microstructures of duplex stainless steels depends on undercooling, cooling rates and subsequent solid state transformations which are influenced by the local chemical composition [1,10-12]. Duplex stainless steels solidify by forming primary ferrite with austenite precipitates either from the liquid or in the solid state during cooling. The amount of austenite and its morphology depend on the cooling rate. At increased cooling rate the amount of austenite is reduced [10-14]. The austenite can have a specific orientation relationship with the ferrite matrix. Grains that have been formed by a !-\" phase transformation should show a Bain, NishiyamaWassermann (N-W), or Kurdjumov-Sachs (K-S) orientation relationship. These orientation relationships can be described as a rotation of an angle # about a common crystallographic axis (axis of rotation), this angle and axis are known as angle/axis pair, Table 1. Owing to these aspects associated with the microstructural state of the two phases prior to hot working the present study investigates in detail the microstructure, the crystallographic microtexture, and the segregation of an as-cast duplex stainless steel slab produced by continuous casting (duplex stainless steel 1.4362).

Characterization of the microstrcture, crystallographic texture and segregation of an as-cast duplex stainless steel slab

https://www.ipen.br/biblioteca/2009/14889.pdf

Texture and mechanical properties evolution of a deep drawing medium carbon steel during cold rolling and subsequent recrystallization

Medium carbon steels are mostly used for simple applications; nevertheless new applications have been developed for which good sheet formability is required. This class of steels has an inherent low formability. A medium carbon hot rolled SAE 1050 steel has been selected for this study. It has been cold rolled with reductions in the 7–80% range. Samples have been used to assess the cold work hardening curve. For samples with a 50 and 80% thickness reduction, an annealing heat treatment has been performed to obtain recrystallization. The material has been characterized in the “as received”, cold rolled and annealed conditions, using several methods: optical microscopy, X-ray diffraction (texture), Vickers hardness and tensile testing. The 50% cold rolled and recrystallized material has been further studied in terms of sheet metal formability and texture evolution during the actual stamping of a steel toecap that has been used to validate the finite element simulations.

Clara Herrera

Papers

Design of a novel Mn-based 1 GPa duplex stainless TRIP steel with 60% ductility by a reduction of austenite stability

A Short review on wrought austenitic stainless steels at high temperatures: processing, microstructure, properties and performance

Characterization of the microstrcture, crystallographic texture and segregation of an as-cast duplex stainless steel slab

Texture and mechanical properties evolution of a deep drawing medium carbon steel during cold rolling and subsequent recrystallization

Medium carbon steel deep drawing: A study on the evolution of mechanical properties, texture and simulations, from cold rolling to the end product