High strength Fe–Mn–(Al, Si) TRIP/TWIP steels development — properties — application

Formation of Shear Bands and Strain-induced Martensite During Plastic Deformation of Metastable Austenitic Stainless Steels

Materials with low stacking fault energies have been long sought for their many desirable mechanical attributes. Although there have been many successful reports of low stacking fault alloys (for example Cu-based and Mg-based), many have lacked sufficient strength to be relevant for structural applications. The recent discovery and development of multicomponent equiatomic alloys (or high-entropy alloys) that form as simple solid solutions on ideal lattices has opened the door to investigate changes in stacking fault energy in materials that naturally exhibit high mechanical strength. We report in this article our efforts to determine the stacking fault energies of two- to five-component alloys. A range of methods that include ball milling, arc melting, and casting, is used to synthesize the alloys. The resulting structure of the alloys is determined from x-ray diffraction measurements. First-principles electronic structure calculations are employed to determine elastic constants, lattice parameters, and Poisson’s ratios for the same alloys. These values are then used in conjunction with x-ray diffraction measurements to quantify stacking fault energies as a function of the number of components in the equiatomic alloys. We show that the stacking fault energies decrease with the number of components. Nonequiatomic alloys are also explored as a means to further reduce stacking fault energy. We show that this strategy leads to a means to further reduce the stacking fault energy in this class of alloys.

Mechanical Properties and Stacking Fault Energies of NiFeCrCoMn High-Entropy Alloy

Alloys have evolved from simple to complex compositions depending on the ability of mankind to develop the materials. The resulting improved functions and performances of alloys enable advancements in civilizations. In the last century, significant evolution and progress have led to the invention of special alloys, such as stainless steels, high-speed steels, and superalloys. Although alloys composed of multiple elements have higher mixing entropy than pure metals, the improved properties are mostly due to mixing enthalpy that allows the addition of suitable alloying elements to increase the strength and improve physical and/or chemical properties. Since the turn of the century, more complex compositions with higher mixing entropies have been introduced. Such complex compositions do not necessarily guarantee a complex structure and microstructure, or the accompanied brittleness. Conversely, significantly higher mixing entropy from complex compositions could simplify the structure and microstructure and impart attractive properties to the alloys. Jien-Wei Yeh and Brian Cantor independently announced the feasibility of high-entropy alloys and equi-atomic multicomponent alloys in reports published in 2004. This breakthrough in alloying concepts has accelerated research on these new materials throughout the world over the last decade.

High-Entropy Alloys Fundamentals and Applications

Dependence of tensile deformation behavior of TWIP steels on stacking fault energy, temperature and strain rate

The stacking fault energies of seven commercial austenitic Fe-Cr-Ni, Fe-Cr-Ni-Mn and Fe-Mn-Ni alloys have been determined by X-ray diffraction line profile analysis. From comparison with existing data on laboratory alloys with similar compositions, it is concluded that both Ni and C increase γ while Cr, Si, Mn, and N decrease γ. Regression analysis of data produced in this study provides an expression relating γ to commercial alloy composition in terms of Ni, Cr, Mn, and Mo alloy concentrations.

R. E. Schramm

Papers

Stacking fault energies of seven commercial austenitic stainless steels