The effect of thermomechanical controlled processing on recrystallisation and subsequent deformation-induced ferrite transformation textures in microalloyed steels

The evolution of texture components for two experimental 0.06 wt% C steels, one containing 0.03 wt% Nb (Nb steel) and the second containing both 0.03 wt% Nb and 0.02 wt% Ti (Nb–Ti steel), was investigated following a new thermomechanical controlled process route, comprising first deformation, rapid reheat to 1200 °C and final deformation to various strains. Typical deformation textures were observed after first deformation for both steels. Following subsequent reheating to 1200 °C for various times, the recrystallisation textures consisted primarily of the α-(Formula presented.)//RD texture fibre with a weak γ-{111}//ND texture fibre, similar to deformation textures, indicative of the dominance of a strain-induced boundary migration mechanism. The texture components after finish deformation were different from the rough deformation textures, with a strong α-(Formula presented.)//RD texture fibre at the beginning, and then the strong peaks move to (111)(Formula presented.) and (111)(Formula presented.) textures due to the deformation-induced ferrite (DIF) transformation. The effect of Ti on the recrystallisation textures and deformation textures has also been analysed in this study. The results illustrate that Ti significantly influences the γ-{111}//ND texture fibre. Finally, the textures after deformation and recrystallisation in the austenite were calculated based on the K–S orientation relationship between the austenite and ferrite. This allowed the understanding of the mechanism of recrystallisation between first and final deformation and the DIF textures during phase transformation

A phase quantification method based on EBSD data for a continuously cooled microalloyed steel

Mechanical properties of steels depend on the phase constitutions of the final microstructures which can be related to the processing parameters. Therefore, accurate quantification of different phases is necessary to investigate the relationships between processing parameters, final microstructures and mechanical properties. Point counting on micrographs observed by optical or scanning electron microscopy is widely used as a phase quantification method, and different phases are discriminated according to their morphological characteristics. However, it is difficult to differentiate some of the phase constituents with similar morphology. Differently, for EBSD based phase quantification methods, besides morphological characteristics, other parameters derived from the orientation information can also be used for discrimination. In this research, a phase quantification method based on EBSD data in the unit of grains was proposed to identify and quantify the complex phase constitutions of a microalloyed steel subjected to accelerated coolings. Characteristics of polygonal ferrite/quasi-polygonal ferrite, acicular ferrite and bainitic ferrite on grain averaged misorientation angles, aspect ratios, high angle grain boundary fractions and grain sizes were analysed and used to develop the identification criteria for each phase. Comparing the results obtained by this EBSD based method and point counting, it was found that this EBSD based method can provide accurate and reliable phase quantification results for microstructures with relatively slow cooling rates

1,8-Naphthalimide based fluorescent sensors for enzymes

Fluorescent probes have long been valuable tools in the study of biological systems. With the ever-expanding range of known enzymatic biomarkers for disease, it has never been more important to develop synthetically facile, sensitive, selective, and robust methods for the detection of these analytes. The 1,8-naphthalimide fluorophore presents an ideal scaffold on which to design a range of fluorescent probes for an unknowable diversity of biomarkers. With tuneable photophysical properties, synthetic versatility, photostability and a large Stokes shift, the 1,8-naphthalimide has, and continues to be, exploited for the detection of a wide range of enzymatic conversions. This review will outline the recent progress towards the design and synthesis of 1,8-naphthalimide fluorophores for the detection of selected enzymatic conversions

ANALISI DEL COMPORTAMENTO PLASTICO DI UN ACCIAIO AUSTENITICO DEFORMATO IN TORSIONE AD ALTA TEMPERATURA

Il comportamento meccanico dell’acciaio austenitico AISI 316L deformato in torsione nell’intervallo di temperature 850-1100°C con velocità di deformazione equivalente 0,0001-0,006 s-1 è stato analizzato ed un modello che lega il comportamento meccanico con l’evoluzione microstrutturale è proposto. Il materiale a temperature superiori a 900°C ha presentato un comportamento meccanico anomalo, mostrando una significativa riduzione dello sforzo di flusso plastico fino a circa 40 % in seguito alla riduzione della dimensione media del grano da 100 a 30 ?m. Congiuntamente all’anomalo comportamento meccanico, il materiale ha esibito un’evoluzione della struttura del grano inusuale durante la deformazione: la forma dei grani è evoluta da quella equiassica precedente alla deformazione a quella romboidale (con bordi di grano allineati con le direzioni degli sforzi principali di taglio in torsione), formando bordi di grano con punti tripli aventi angoli di 90° e 180°, e bordi di grano con gomiti di 90°, configurazioni che sono in disaccordo con la minimizzazione dell’energia superficiale dei bordi di grano. Le evidenze sperimentali dell’evoluzione microstrutturale, razionalizzata in [1], hanno portato a concludere che la formazione della struttura romboidale è avvenuta in seguito alla migrazione dei bordi di grano indotta dalla deformazione in accordo con la configurazione degli sforzi principali per la torsione. Secondo il modello qualitativo proposto nella presente memoria, il flusso plastico è stato affetto dalla migrazione dei bordi di grano, la quale, avvenendo, ha causato la riduzione della densità dislocativa. Tale riduzione ha determinato per la lega con dimensione media del grano di 30 ?m una diminuzione significativa dello sforzo di flusso plastico rispetto alla lega con grano dalla dimensione media di 100 ?m, dove la diminuzione non si è manifestata a causa dell’inferiore valore del rapporto fra la superficie dei bordi di grano ed il volume del materiale

Influence of strain reversal on dynamic transformation in microalloyed steels deformed above the Ae₃ temperature

In the present work, the effect of strain path reversals on dynamic transformation (DT) above Ae3 temperature was studied using an API grade X-70 microalloyed steel deformed by torsion with single and multiple strain path reversals. The results revealed the important role played by strain path reversals on influencing the evolution of austenite grain boundaries through inhomogeneous deformation, therefore, affecting DT behaviours. In addition to flow stress–strain analysis and microstructure investigation, finite element method combined with 3D digital materials representation approach was used to gain insights into the effects of deformation with strain path reversals on the development of microstructural features in the prior-austenite grains

Titanium alloy microstructure fingerprint plots from in-process machining

Titanium alloy components require several machining stages of forged billets which are supplied in a range of annealing conditions. Generally, the machining performance is influenced by the heat treatment and changes in billet microstructures are often overlooked by tool manufacturers and machinists. Due to the non-linear strain path during primary forging, titanium alloy billets are anisotropic in nature and require ex-situ non-destructive evaluation (NDE) during the manufacturing stages to ensure excellent service performance, particularly in safety-critical aerospace components. In this study, the local analysis of the fluctuations presented in the force response during face-turning operations is directly linked to the billet heat treatment condition and presented as microstructure fingerprint plots. The evolution of cutting forces in four different billet conditions of the alpha + beta titanium alloy Ti–6Al–2Sn–4Zr–6Mo (Ti-6246) was measured. The magnitude and fluctuations in force were directly correlated to microstructural features derived from the heat treatments. In addition, local spatial high-resolution synchronization of the cutting forces was used to determine the effects of microstructure from the heterogeneous upstream forging process and subsequent heat treatment. These rapidly produced microstructure fingerprint plots are an important development step for providing manufacturers with an in-process machining NDE method: this will help to qualify material upstream prior to expensive secondary forging or finish machining stages

Tool for automatic macrozone characterization from EBSD data sets of titanium alloys

Microtexture heterogeneities are commonly found in titanium forgings because of the thermomechanical processing. Also known as macrozones, these regions can reach millimetres in length, with grains sharing a similar crystallographic orientation leading to less resistance to crack propagation. Since the link between macrozones and the reduction of cold-dwell-fatigue performance on rotative components in gas turbine engines was established, efforts have been put into macrozone definition and characterization. The electron backscatter diffraction (EBSD) technique, widely used for texture analysis, allows for a qualitative macrozone characterization; however, further processing is required to define the boundaries and disorientation spread of each macrozone. Current approaches often use c-axis misorientation criteria, but this can sometimes lead to a large disorientation spread within a macrozone. This article describes the development and application of a computational tool implemented in MATLAB for automatic macrozone identification from EBSD data sets on the basis of a more conservative approach where both the c-axis tilting and rotation are considered. The tool allows for detection of macrozones according to the disorientation angle and density-fraction criteria. The clustering efficiency is validated by pole-figure plots, and the effects of the key parameters defining the macrozone clustering (disorientation and fraction) are discussed. In addition, this tool was successfully applied to both fully equiaxed and bimodal microstructures of titanium forgings

The effect of forging texture and machining parameters on the fatigue performance of titanium alloy disc components

The Mechanisms of fatigue failure in Ti-6Al-2Sn-4Zr-6Mo forged discs are investigated: the effects of forging and machining operations on fatigue are decoupled. A four-point bend fatigue testing approach enabled the crack initiation and propagation characteristics to be studied at multiple locations around the disc periphery. Fatigue performance variation (of ~60%) at different positions, and crack initiation and propagation behaviour were linked to the heterogeneous crystallographic texture - developed during upstream forging. Downstream machining processes were found to increase fatigue life, regardless of the cutting speed. However, circumferential fatigue heterogeneity, inherent from the forging stage was still evident even after machining

Exploring the mechanism of “Rare Earth” texture evolution in a lean Mg–Zn–Ca alloy

The entire recrystallisation sequence and associated crystallographic texture evolution of Mg-0.8Zn-0.2Ca (wt.%) alloy was tracked using a quasi-in-situ electron backscatter diffraction (EBSD) method. Characteristic “Rare Earth” (RE) texture was formed, originating mainly from double twins and twinning-related shear bands consisting of compression and double twins. The RE textures appeared during the nucleation stage and were preserved during the relative uniform grain growth period because of solute segregation and concurrent precipitation although the alloying element content was very low. Ca and Zn co-segregated along grain boundaries with no evidence that segregation was preferred along special types of grain boundaries. The interactions between deformation microstructures, concurrent precipitation, solute drag, grain growth and texture evolution are discussed in detail. All the results indicate that Ca performs a similar role to that of RE elements in forming RE texture

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results