Recent advances in friction-stir welding : Process, weldment structure and properties

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

Superplasticity—Recent advances and future directions

The relationship between stress and strain rate is often sigmoidal in superplastic materials, with a low strain rate sensitivity at low and high strain rates (regions I and III, respectively) and a high strain rate sensitivity at intermediate strain rates (region II) where the material exhibits optimal superplasticity This relationship is examined in detail, with reference both to the conflicting results reported for the Zn-22 pct Al eutectoid alloy and to the significance of the three regions of flow

The mechanical properties of superplastic materials

Grain boundary sliding is an important mode of deformation in superplasticity. Measurements of the contribution of sliding to the total strain generally give values of about 50–70% so that there is an apparent “missing strain” of about 30–50%. It is demonstrated that the experimental method used to measure the sliding contribution will lead to estimates in the range of about 45–90% even when all the deformation is by grain boundary sliding and the associated accommodation process. Since the problem of accommodation is less severe at the specimen surface, it is shown that estimates of the sliding contribution from surface marker lines will tend to lie at the lower end of this predicted range. It is concluded that grain boundary sliding accounts for essentially all the deformation under optimum superplastic conditions and there is no “missing strain” of about 30–50%.

An evaluation of the strain contributed by grain boundary sliding in superplasticity

A method has been proposed to estimate the grain size, which is defined as the grain size distribution in three dimensions, from the measured distribution of linear intercept length. The method is developed on the assumption that the grain size distribution is log normal in three dimensions. The three-dimensional grain size distribution is expressed as that of the «grain diameter» D defined as the equivalent volume diameter; the distribution of D is estimated from In D g and In σ g , (where D g is the geometric mean of D and σ g is the geometric standard deviation for D)

A Significant Method for Estimation of the Grain Size of Polycrystalline Materials

The origin of high strain rate sensitivity of flow stresses in superplastic AlCu alloys

Direct determination of the strain rate sensitivity of flow stresses based on grain boundary sliding in a SnPb eutectic during superplastic and non-superplastic deformation

Norio Furushiro

Papers

A Significant Method for Estimation of the Grain Size of Polycrystalline Materials

The origin of high strain rate sensitivity of flow stresses in superplastic AlCu alloys

Direct determination of the strain rate sensitivity of flow stresses based on grain boundary sliding in a SnPb eutectic during superplastic and non-superplastic deformation

Ultra Grain Refinement of Aluminium 1100 by ARB with Cross Rolling

Strain rate dependence of internal and effective stresses in superplastic deformation