The most efficient way to tune microstructures and mechanical properties of metallic alloys lies in designing and using athermal phase transformations. Examples are shape memory alloys and high strength steels, which together stand for 1,500 million tons annual production. In these materials, martensite formation and mechanical twinning are tuned via composition adjustment for realizing complex...

The stabilization of retained austenite was studied via a two-step cooling procedure. Alloys with M , temperatures below 0 OC were used. It was found that the martensitic transformation starting temperature, M,, was lowered to M,' during the second step of cooling. With increasing the amount of previously formed martensite, the difference in the transformation starting temperatures, AM, (= M,M,...

Ti-Nb-based Gum Metals exhibit extraordinary superelasticity with ultralow elastic modulus, superior strength and ductility, and a peculiar dislocation-free deformation behavior, most of which challenge existing theories of crystal strength. Additionally, this kind of alloys actually displays even more anomalous mechanical properties, such as the non-linear superelastic behavior, accompanied by...

Flash processing is a new heat treatment process being developed to produce steel with relatively high strength and ductility. It involves rapidly heating steel sheet or strip to a temperature in the austenite range and quenching; the entire thermal cycle takes place within 15 seconds. The resulting microstructure is fine and difficult to resolve using standard metallographic techniques. In thi...

Plastic deformations, such as those obtained by shot peening on specimen surface, are an efficient way to improve the mechanical behavior of metals. Generally, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) are commonly used to observe the complex microstructural evolutions, such as grain refinement and phase transformation, induced by the surface treatment. In...

The structural relationship between the parent and product phases in martensitic transformation from ? phase is described. atomic movements leading to martensite are accomplished by a long-range shear {112} < 111 > that transforms lattice short-wavelength displacement or shuffle {110} 110 induces correct stacking. microstructures arising out of these paths depend on which modes initiates transf...

We report results on a nite element simulation of a needle-like martensitic microstructure observed in biaxial loading experiments conducted by Chu and James on single crystals of the shape-memory alloy Cu-14at.%Al-3:9at.%Ni. This microstructure was observed near an interface between twinned layers of two variants and a pure variant of martensite. We used a geometrically nonlinear theory of mar...

Based on the experimental results and the finite element analysis, a constitutive model is proposed for two phase shape memory alloys by introducing a compensative volumetric strain into a constrained relationship between the two phases, accounting for the reduced constraint due to the growth of martensite band. The pseudoelasticity of NiTi shape memory alloy micro-tube, subjected to pure tensi...

Investigations into the possibility of improving the strength-ductility relation in a metastable β-titanium alloy (Ti-10V-2Fe-3Al) through plasticity induced transformation (PiTTi) have been carried out. Various heat treatments in the β and/or α+β condition were performed to study their influence on both the microstructure and solute partitioning, which eventually control the PiTTi effect. Stre...