A constitutive model of the deformation behaviour of twinning induced plasticity (TWIP) steel at different temperatures

The mechanical behaviour of Fe-18Mn-0.6C-1Al (wt%) TWIP steel was modelled in the temperature range from room temperature to 400°C. The proposed constitutive model was based on the Kocks-Mecking-Estrin (KME) model. The model parameters were determined using extensive experimental measurements of the physical parameters such as the dislocation mean free path and the volume fraction of twinned grains. More than 100 grains with a total area of ~300μm2 were examined at different strain levels over the entire stress-strain curve. Uniaxial tensile deformation of the TWIP steel was modelled for different deformation temperatures using a modelling approach which considers two distinct populations of grains: twinned and twin-free ones. A key point of the work was a meticulous experimental determination of the evolution of the volume fraction of twinned grains during uniaxial tensile deformation. This information was implemented in a phase-mixture model that yielded a very good agreement with the experimental tensile behaviour for the tested range of deformation temperatures. © 2014 Elsevier B.V.

Microstructure development and solute behaviour in Fe-C and Fe-C-V alloys during strip casting and secondary processing

 Strip casting is a rapid, environment friendly technology for manufacturing thin sheets of steel directly from molten metal. Research presented in this thesis examines the effect of atomic location, cluster size and composition on internal microstructure development during strip casting. Current research potentially leads to green manufacturing of steel.

Method for determining reaction rate of mild steel containers during melting of magnesium-aluminium alloys and effect of aluminium content on directionally solidified microstructures

A magnesium alloy of eutectic composition (33 wt-'%Al) was directionally solidified in mild steel tubes at two growth rates, 32 and 580 mum s(-1,) in a temperature gradient between 10 and 20 K mm(-1). After directional solidification, the composition of each specimen varied dramatically, from 32'%Al in the region that had remained solid to 18%Al (32 mum s(-1) specimen) and 13%Al (580 mum s(-1) specimen) at the plane that had been quenched from the eutectic temperature. As the aluminium content decreased, the microstructure contained an increasing volume fraction of primary magnesium dendrites and the eutectic morphology gradually changed from lamellar to partially divorced. The reduction in aluminium content was caused by the growth of an Al-Fe phase ahead of the Mg-Al growth front. Most of the growth of the Al-Fe phase occurred during the remelting period before directional solidification. The thickness of the Al-Fe phase increased with increased temperature and time of contact with the molten Mg-Al alloy. (C) 2003 Maney Publishing.

Twinning and the ductility of magnesium alloys Part II. “Contraction” twins

Magnesium and its alloys do not in general undergo the same extended range of plasticity as their competitor structural metals. The present work presents part II of a study that examines some of the roles deformation twinning might play in the phenomenon. A series of tensile and compression tests results are reported for common wrought alloys: AZ31, ZK60 and ZM20. These data are combined with EBSD analysis and simple flow stress models to argue the following: (i) that “contraction” double twinning (which enables contraction along the c axis) can decrease the uniform elongation, and (ii) that compression double twinning can also account for shear failure at low strains. The last of these is described as a combined consequence of strain softening of the continuum and the local generation of twin sized voids.

Twinning and the ductility of magnesium alloys Part I: “Tension” twins

Magnesium and its alloys do not in general undergo the same extended range of plasticity as their competitor structural metals. The present work is part I of a study that examines some of the roles deformation twinning might play in the phenomenon. A series of tensile test results are reported for the common wrought alloy AZ31. These data are employed in conjunction with a simple constitutive model to argue that View the MathML source twinning (which gives extension along the c-axis) can increase the uniform elongation in tensile tests. This effect appears to be similar to that seen in Ti, Zr and Cu–Si and in the so called TWIP phenomenon in steel.

Effect of microalloying with rare-earth elements on the texture of extruded magnesium-based alloys

A series of alloys have been produced with microalloying additions of rare-earth (RE) elements in the range of 0.1–0.4 wt.%. The alloys have been extruded to produce grain sizes of 23 ± 5 μm. The texture of the extruded alloys was measured, and it was found that the extrusion texture was weakened by the addition of RE elements. The samples with weakened extrusion textures exhibited an increase in the tensile elongation.

The microstructure evolution and mechanical properties of cryorolled Al alloys

A solutionized Al2024 alloy was subjected to rolling at liquid nitrogen temperature (cryorolling) resulting in an ultra-fine stmcture. The material was also subjected to recovery annealing at 160°C. The ultrafine structured material demonstrated increased strength but very low ductility. The uniform elongation of the material after recovery annealing increased without any sacrifice of strength.

Austenite stability in Fe-Mn-Si-based shape memory alloys

The stability of austenite in a number of Fe–Mn–Si-based shape memory alloys has been investigated. It was found that a grain boundary precipitate of BCC structure is formed over a wide range of alloy compositions and heat treatment temperatures. This grain boundary phase has been identified as the chi (χ) phase. Although up to 3 vol.% of the grain boundary precipitate was generated by isothermal aging in the range 500–800 °C, it was found not to markedly affect the mechanical properties or the shape memory effect. Nano-indentation indicated that the hardness and strength of the parent and precipitate phase are very similar, as are their compositions.

Processing and mechanical properties of open-cell Mg alloys

Mechanical properties of open-cellular magnesium alloys with three types of
geometric cell-structures, that is, a random round cell-structure (type A). a controlled diamond cell-structure for which the angle between the struts and the load direction is 45 degree (type B) and a controlled square cell-structure for which the angle between the struts and the loading direction is 0 degree (90 degree) (type C), are investigated by compressive tests. Results indicate that type C showed a higher collapse stress than the other two types. The collapse mechanism and the effects of the loading direction on collapse stress for the three types of magnesium alloys arc discussed from the viewpoint of bending, buckling and yielding of the struts. It is suggested that collapse for the open-cellular magnesium aHoys is associated with yielding of struts

Role of grain boundary sliding in the anisotropy of magnesium alloys

The plastic anisotropy of magnesium alloy sheet drops rapidly with test temperature. It has previously been suggested that this may be due to an increase in the activity of (c+a) dislocations. The present note points out that the phenomenon may result, instead, from the action of grain boundary sliding. This can explain the strong effect of grain size on anisotropy. Furthermore, it points to a new avenue for alloy development.

Synthesis and physical property characterisation of phosphonium ionic liquids based on P(O)2(OR)2− and P(O)2(R)2− anions with potential application for corrosion mitigation of magnesium alloys

Phosphonium cation based ionic liquids (ILs) have become of interest due to their unique chemical and electrochemical stability as well as their promising tribological properties. At the same time, interest has also grown in the use of phosphate and phosphinate based ionic liquids for corrosion protection of reactive metals. In this work we describe the synthesis and characterization of six novel ionic liquids based on the tetraalkylphosponium cation coupled with organophosphate and organophosphinate anions and their sulfur analogues. The conductivity and viscosity of these ILs has been measured and discussed in terms of the nature of the interactions, effect of anion basicity and the extent of ionic character. The reaction of the IL with a ZE41 magnesium aerospace alloy surface is also demonstrated.