Perspectives on Titanium Science and Technology

This article presents an overview of the developments in stainless steels made since the 1990s. Some of the new applications that involve the use of stainless steel are also introduced. A brief introduction to the various classes of stainless steels, their precipitate phases and the status quo of their production around the globe is given first. The advances in a variety of subject areas that have been made recently will then be presented. These recent advances include (1) new findings on the various precipitate phases (the new J phase, new orientation relationships, new phase diagram for the Fe–Cr system, etc.); (2) new suggestions for the prevention/mitigation of the different problems and new methods for their detection/measurement and (3) new techniques for surface/bulk property enhancement (such as laser shot peening, grain boundary engineering and grain refinement). Recent developments in topics like phase prediction, stacking fault energy, superplasticity, metadynamic recrystallisation and the calculation of mechanical properties are introduced, too. In the end of this article, several new applications that involve the use of stainless steels are presented. Some of these are the use of austenitic stainless steels for signature authentication (magnetic recording), the utilisation of the cryogenic magnetic transition of the sigma phase for hot spot detection (the Sigmaplugs), the new Pt-enhanced radiopaque stainless steel (PERSS) coronary stents and stainless steel stents that may be used for magnetic drug targeting. Besides recent developments in conventional stainless steels, those in the high-nitrogen, low-Ni (or Ni-free) varieties are also introduced. These recent developments include new methods for attaining very high nitrogen contents, new guidelines for alloy design, the merits/demerits associated with high nitrogen contents, etc.

Recent developments in stainless steels

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1037&context=mepubs

Additive manufacturing of Ti6Al4V alloy: A review

Wire and arc additive manufacturing (WAAM) is a novel manufacturing technique in which large metal components can be fabricated layer by layer. In this study, the macrostructure, microstructure, and mechanical properties of a Ti-6Al-4V alloy after WAAM deposition have been investigated. The macrostructure of the arc-deposited Ti-6Al-4V was characterized by epitaxial growth of large columnar prior-β grains up through the deposited layers, while the microstructure consisted of fine Widmanstatten α in the upper deposited layers and a banded coarsened Widmanstatten lamella α in the lower layers. This structure developed due to the repeated rapid heating and cooling thermal cycling that occurs during the WAAM process. The average yield and ultimate tensile strengths of the as-deposited material were found to be slightly lower than those for a forged Ti-6Al-4V bar (MIL-T 9047); however, the ductility was similar and, importantly, the mean fatigue life was significantly higher. A small number of WAAM specimens exhibited early fatigue failure, which can be attributed to the rare occurrence of gas pores formed during deposition.

Microstructure and Mechanical Properties of Wire and Arc Additive Manufactured Ti-6Al-4V

The physics of fatigue crack initiation

Analysis of the different slip systems activated by tension in a α/β titanium alloy in relation with local crystallographic orientation

Slip and fatigue crack formation processes in an α/β titanium alloy in relation to crystallographic texture on different scales

Crystal plasticity modeling of slip activity in Ti–6Al–4V under high cycle fatigue loading

A microstructure-sensitive constitutive modeling of the inelastic behavior of single crystal nickel-based superalloys at very high temperature

The dependence of cyclic behavior, fatigue crack initiation and fatigue life, on crystallographic texture was investigated for a 316L austenitic stainless steel in the low cycle fatigue range. Specimens of five different orientations of the rolled sheet were compared to study different textures. It is shown that, texture influences the stress–strain response of the material and the fatigue damage (crack density). Moreover, to study the influence of the environment on the fatigue behavior and the coupling effects with crystallographic aspects, fatigue tests were performed in air and in vacuum. It is shown that the environment modifies both the total crack density and the ratio of transgranular to intergranular cracks. All results are discussed with regard to the relative fraction of 〈111〉 and 〈100〉 grains oriented for multiple slip or to the fraction of grains favoring single slip behavior.

José Mendez

Papers

Analysis of the different slip systems activated by tension in a α/β titanium alloy in relation with local crystallographic orientation

Slip and fatigue crack formation processes in an α/β titanium alloy in relation to crystallographic texture on different scales

Crystal plasticity modeling of slip activity in Ti–6Al–4V under high cycle fatigue loading

A microstructure-sensitive constitutive modeling of the inelastic behavior of single crystal nickel-based superalloys at very high temperature

Influence of the crystalline texture on the fatigue behavior of a 316L austenitic stainless steel