Derived crystal structure of martensitic materials by solid–solid phase transformation

A mathematical description of crystal structure is proposed consisting of two parts: the underlying translational periodicity and the distinct atomic positions up to the symmetry operations in the unit cell, consistent with the International Tables for Crystallography. By the Cauchy–Born hypothesis, such a description can be integrated with the theory of continuum mechanics to calculate a derived crystal structure produced by solid–solid phase transformation. In addition, the expressions for the orientation relationship between the parent lattice and the derived lattice are generalized. The derived structure rationalizes the lattice parameters and the general equivalent atomic positions that assist the indexing process of X-ray diffraction analysis for low-symmetry martensitic materials undergoing phase transformation. The analysis is demonstrated in a CuAlMn shape memory alloy. From its austenite phase (L21 face-centered cubic structure), it is identified that the derived martensitic structure has orthorhombic symmetry Pmmn with the derived lattice parameters a d = 4.36491, b d = 5.40865 and c d = 4.2402 Å, by which the complicated X-ray Laue diffraction pattern can be well indexed, and the orientation relationship can be verified.

Mechanical Properties of Ferritic Martenstic Steels: A Review

The word-wide demand for energy is constantly increasing, and therefore ideas around future energy-generation are also on the increase with the aim of meeting this demand. This includes designs for the next generation of nuclear power reactors, such as gas-cooled, liquid-metal-cooled and water-cooled reactors; the goal being to create smarter ways to produce more economical, environmentally-friendly energy. The conditions such reactors would need to meet, present significant design challenges for scientist and engineers, not least around the structural materials and components to use. Depending on the operational conditions, use of elevated- temperature ferritic/martensitic materials such as P91 and P92 steel are favoured by several of the designs for use with out-of-core and in-core applications. The main goal behind this review article is to explain mechanical properties of P91 and P92 steel; these are two types of ferritic/martensitic steels. This reviewer, highlight and discuss the development of ferritic/martenisitc steels for nuclear programmes and to explain the effect of irradiation on mechanical properties of P91 and P92.

Microstructures and Properties of Martensitic Materials

Martensite, initially named in honor of Adolph Martens and his pioneering work in metallography and microstructures at the end of the 19th century, has now a far broader meaning than previously used [...]

High Temperature Oxidation of 9-12% Cr Materials P91 and P92 in Supercritical Water

The article summarizes the results obtained within a project PRAMEK. The project is focused on corrosion behavior of structural materials in water environment with supercritical parameters. Ferritic - martensitic materials P91 and P92 was evaluated. Multi-layered oxide was created on materials sample surface after 1000 hours long exposures in Supercritical Water Loop (SCWL) and Supercritical Water Autoclave (SCWAc) under SCWR operational parameters (600 °C, 25 MPa). The outer layer consisted of magnetite was porous and may tend to exfoliate. The inner layer is formed by spinel with Cr and Fe oxides. Microstructure of materials P91 and P92 and surface oxidic scales were evaluated by means of light and scanning electron microscopy equipped with wave and energy spectroscopy.

The Self-Accommodation and Rearrangement of Martensite Multi-Variants under Cyclic Stress: Phase-Field Simulation

A twin boundary model was established to describe the multi-variant interface in the martensitic materials. The modified semi-implicit Fourier-spectral method was proposed to solve the 3-D phase-field equation. Self-accommodation plays an important role in the micro-structural evolution during the loading and unloading. The external compressive stress can cause the rearrangement of martensites from three variants to one variant. After releasing the loading, another variant can nucleate and grow in one variant at the twin boundary. Cyclic stress may lead to the redistribution of martensite variants besides the rearrangement.

Phase Transformations of Nanocrystalline Martensitic Materials

The physical phenomena and engineering applications of martensitic phase transformations are the focus of intense ongoing research. The martensitic phase transformation and functional properties such as the shape-memory effect and superelasticity are strongly affected by the crystal size at the nanoscale. The current state of research on the impact of crystal size on the phase stability of the martensite is reviewed summarizing experimental results of various nanostructured martensitic materials and discussing the corresponding theoretical approaches. The review outlines the effects of crystal size on the complex morphology of the martensite, leading to interface structures not encountered in coarse-grained bulk materials. The unique shape-memory properties of martensitic materials can persist even at the nanoscale. Nanocrystalline martensitic materials can be processed to obtain tailored functional properties in combination with enhanced strength. Structural changes of metallic nanowires are similar to those arising by martensitic phase transformations and also can lead to shape-memory effects, as predicted by atomistic simulations.

Jog my shape memory: dynamics as a challenge in mathematical materials science

Many complex phenomena in nature exhibit multiple scales. The challenge is to understand how the effects on one scale influence those on another. This review discusses some aspects of a multiscale analysis of martensitic materials as a prominent example of materials that exhibit nuanced structures and surprising implications on various scales. The emphasis is on dynamic issues. Some speculations are offered on future research directions.