This paper discusses the use of laser-ultrasonics to monitor the metallurgical transformations of advanced high-strength steels. In this technique, acoustic waves are generated and detected in the material by use of lasers. The ultrasonic velocity can sense the austenite formation/decomposition in real time. Unlike dilatometric measurements the ultrasonic velocity measurements show little influ...

The reverse martensitic (“austenitic”) transformation upon heating of equiatomic nickeltitanium nanoparticles with diameters between 4 and 17 nm is analyzed by means of molecular-dynamics simulations with a semi-empirical model potential. After constructing an appropriate order parameter to distinguish locally between the monoclinic B19′ at low and the cubic B2 structure at high temperatures, t...

T his is the fourth paper in our series, identifying unusual phenomena and providing recommendations for the thermo-mechanical characterization of shape memory alloy (SMA) wire. Part 11 provided basic background of the martensitic transformations between austenite (A) and martensite (M) which are responsible for the shape memory (SM) effect and superelasticity (SE). Two typical NiTi SMA alloys ...

transformation induced plasticity (trip) steels have a vast application in automotive industry because of theirhigh strength, high ductility and hence excellent energy absorption capacity. these characteristics of tripsteels are due to the existence of retained austenite in their microstructures in the ambient temperature, whichtransforms to the martensite phase during deformation. the microstr...

High silicon (>1.5%) steels with different compositions were isothermally transformed to bainite at 220 and 250 ◦C to produce what is often referred to as nanostructured bainite. Interrupted tensile tests were carried out and the retained austenite was measured as a function of strain. Results were correlated with tensile ductility. The role of retained austenite stability is remarkably underli...

The response of a strong bainitic–steel to tempering at high temperatures is investigated, because a softened state is sometimes necessary during the manufacture of engineering components, prior to the final heat–treatment which hardens the material. Thermodynamic calculations conducted to determine the maximum temperature at which the steel could be annealed without forming austenite were foun...

Ferromagnetic shape memory alloys are characterized by strong magneto-mechanical coupling occurring at the atomic scale causing large magnetically inducible strains at the macroscopic level. Employing combined atomic and magnetic force microscopy studies at variable temperature, we systematically explore the relation between the magnetic domain pattern and the underlying structure for as-deposi...

The orientation of crystals of allotriomorphic ferrite in austenite has been investigated in order to understand the mechanism by which particular relationships are favoured over others via a process known as “variant selection”. This kind of selection in the context of diffusional transformations contrasts with displacive products where the interaction of transformation plasticity with an exte...

Thermodynamically consistent, three-dimensional (3D) phase field approach (PFA) for coupled multivariant martensitic transformations (PTs), including cyclic PTs, variant– variant transformations (i.e., twinning), and dislocation evolution is developed at large strains. One of our key points is in the justification of the multiplicative decomposition of the deformation gradient into elastic, tra...

The solidification process in a weld pool has been shown to have a considerable influence upon the properties of the resultant weld. It influences the development of microstructure (Edvardsson et al., 1976), and determines the distribution of alloying elements, and hence the homogeneity of the weld. Previous work on the cooling behaviour of welds (Garland and Kirkwood, 1974; Svensson et al., 19...