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This research focusses on a complex precipitation (Ni3(Ti,Al)) hardenable metastable stainless steel. Dual phase (austenite, γ/martensite, α′) and ultrafine grained austenitic microstructures obtained after applying isochronal heat treatments (0.1–10 ℃/s) to a cold-rolled (CR) metastable stainless steel have been microstructurally and mechanically characterized using different experimental techniques (optical microscopy, SEM, TEM, magnetic measurements, tensile tests). A wide range of strength (2.1–1.1 GPa) and elongation (3–25%) values have been obtained using sub-size samples (7 mm in gauge length). The scientific aim is the understanding of those microstructural parameters and mechanisms that influence the achievement of ultra-fine grained microstructures and control or the mechanical behaviour of different complex microstructures in this type of steels. Whereas the industrial aim would be to expand the applicability of this steel and use this scientific knowledge to design steels with optimized microstructures and mechanical properties.

The effects of heat treatment on the hardness and electrochemical behavior of the Ti6Al4V alloy were studied. Two heat treatments were performed: one below (800 °C) and the other above (1050 °C) its beta transformation temperature (T= 980 ± 20 °C) and cooled using three conditions: water quenching, normalizing, and furnace. A microstructure observed using Optical Microscopy showed dependence on the heat treatment temperature applied; mainly three microstructures were obtained: martensitic, globular, and lamellar. Besides, alpha and beta phases were characterized by X-ray diffraction (XRD) technique. The Berkovich tests were performed to measure the hardness and reduced modulus (E). The Ti6Al4V alloy treated at 1050 °C and air-cooled exhibited hardness values closer to those of the Ti6Al4V as-received alloy. Electrochemical tests were carried out to analyze the electrochemical behavior after 7-day immersion in Hank’s solution at 37 °C and pH 7.40. Open Circuit Potentials (E) showed less negative values for Ti6Al4V and Ti6Al4V alloys, suggesting ennoblement of these materials. Furthermore, these alloys exhibited an outstanding electrochemical behavior compared to the Ti6Al4V as-received alloy by Electrochemical Impedance Spectroscopy (EIS) technique., The authors thank David Pérez-Risco for sharing his experience and useful advice on Berkovich Nano-indenter at the National Metallurgical Research Center (CENIM-CSIC Madrid, Spain), allowing this work to be carried out. Mercedes Paulina Chávez-Díaz thanks the National Science and Technology Council (CONACyT) for a doctoral fellowship to hold a research stay at CENIM-CSIC. This work was supported by the Government of Spain, through the Ministry of Economy and Competitiveness [MAT2015-67750-C3-1]. Elsa Miriam Arce-Estrada and Román Cabrera-Sierra wish to thank the National Research System (SNI) for the distinction of its members and the stipend received.

The directionality of the ductile-brittle transition behavior of two oxide-dispersion-strengthened (ODS) FeCrAl steels with similar chemical compositions, tensile properties, and sub-micrometric grain sizes but different processing routes, and a Zr-particle strengthened FeCrAl steel manufactured by high vacuum melting is discussed. Despite the similarities of the ODS FeCrAl steels, strong differences in the lower and upper shelf energy and the ductile to brittle transition temperature were observed for longitudinal through thickness notched specimens. Although the lower and upper shelf energies of longitudinal surface-notched specimens of ODS FeCrAl steels are similar, a strong difference in the ductile-to-brittle transition temperature is observed. For through-thickness notched and surface-notched specimens taken transversely, the analyzed ODS FeCrAl steels show a similar ductile-to-brittle behavior. In general, the FeCrAl alloy strengthened with Zr-particles presents a more isotropic behavior and a higher ductile-to-brittle transition temperature than the ODS FeCrAl steels. In addition, the upper shelf energy of the FeCrAl steel strengthened with Zr-particles is significantly higher than that of the ODS FeCrAl steels., The authors acknowledge financial support to Spanish Ministerio de Economia y Competitividad (MINECO) in the form of a Coordinate Project (MAT2016-80875-C3-1-R). The authors are grateful for the dilatometer tests by Phase Transformation laboratory. This work contributes to the Joint Programme on Nuclear Materials (JPNM) of the European Energy Research Alliance (EERA).

The isothermal aging behavior of a cold-rolled precipitation hardening stainless steel has been studied at 723 K (450 °C) for holding times up to 72 hours. The precipitation hardening has been investigated using microhardness Vickers (Hv), thermoelectric power (TEP) measurements, and tensile testing. Microhardness compared to TEP measurements is more sensitive to detect the initial stages of aging. Two precipitation regimes have been observed: the first one related to the formation of Cu-clusters for aging times below 1 hour and a second one associated with formation of Ni-rich precipitates. The results show that the material exhibits an outstanding continuous age strengthening response over the aging time investigated, reaching a hardness of 710 ± 4 HV1 and an ultimate tensile strength (σ UTS) of 2.65 ± 0.02 GPa after 72 hours. Engineering stress-plastic strain curves reveal that the strength increases and the ductility decreases as the aging time increases. However, after prolonged holding times (24–72 hours) and, although small, a rise in both the strength and the total elongation is observed. The precipitation kinetics can be well predicted over the entire range of aging times by the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation. Finally, a reliable linear hardness-yield strength correlation has been found, which enables a rapid evaluation of the strength from bulk hardness measurements.

The strengthening mechanism observed during ageing at temperatures of 435 and 475 °C in the oxide dispersion strengthened (ODS) Fe-Cr-Al-Ti system has been investigated. Atom probe tomography (APT) and high-resolution transmission electron microscopy (HRTEM) analyses determined that the alloy undergoes simultaneous precipitation of Cr-rich (α′ phase) and nanoscale precipitation of TiAl-rich intermetallic particles (β′ phase). APT indicated that the composition of the intermetallic β′ phase is FeAlTiCr, and the evolving composition of α′ phase with ageing time was also determined. The results obtained from HRTEM analyses allow us to confirm that the β′ precipitates exhibit a cubic structure and hence their crystallography is related to the Heusler-type FeAlTi (L2) structure. The strengthening could be explained on the basis of two hardening effects that occur simultaneously: the first is due to the α-α′ phase separation through the modulus effect, and the second mechanism is due to the interaction of nanoscale β′ particles with dislocations., PM 2000™ is a trademark of Plansee GmbH. LEAP® is a registered trademark of CAMECA Instruments Inc. CC and JC acknowledge financial support to Spanish Ministerio de Economia y Competitividad (MINECO) through in the form of a Coordinate Project (MAT2013-47460-C5-1-P). Atom probe tomography (MKM) was supported through a user project supported by ORNL's Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

© 2015, The Minerals, Metals & Materials Society. The first part of this two-part study reported the possibility of simultaneously generating a dense, self-healing α-alumina layer by thermal oxidation and a coarse-grained microstructure with a potential goodness for high-temperature creep resistance in a FeCrAl oxide dispersion-strengthened ferritic alloy that was cold deformed after hot rolling and extrusion. In this second part, the factors affecting the formation of the coarse-grained microstructure such as strain gradients induced during the rolling process are analyzed. It is concluded that larger strain gradients lead to more refined and more isotropic grain structures., G. Pimentel acknowledges the Spanish Ministerio de Ciencia e Innovación for financial support in the form of PhD research grant (FPI). The authors acknowledge financial support to Ministerio de Economia (MINECO) and Fondo Europeo de Desarrollo Regional (FEDER) in the form of ENE2009-13766-C04-01 project and MAT2013-47460-C5-2-P project.

In this paper tensile tests and LS and LT notched Charpy impact tests were performed at the temperature range between -196 and 200 °C on an oxide dispersion strengthened (ODS) Fe20Cr6Al0.5Y2O3 hot-rolled tube. The absorbed energy values in the range of high-temperatures of LS notched specimens is considerably higher than those of LT notched specimens; however such values tend to converge as temperature increases. Ductile fracture on the normal planes to RD with delaminations parallel to the tube surface were observed in the temperature range between RT and 200 °C. Delaminations of crack divider type were observed in LT specimens, whereas delaminations of crack arrester type were observed in LS specimens. The yttria particles in the grain boundaries and the transverse plastic anisotropy are the possible causes of that the delaminations were parallel to the tube surface, PM 2000 is a trademark of Plansee GmbH. The authors acknowledge the financial support of the Spanish Ministerio de Economia e Innovacio´ n (MINECO) in the form of a Coordinate Project in the Energy Area of Plan Nacional 2009 (ENE2009-13766-C04-01). G.P. acknowledges MINECO for financial support in the form of PhD Research Grant (FPI). This research was supported by ORNL’s Shared Research Equipment (SHaRE) User Facility, which is sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy

The ferritic oxide dispersion strengthened alloys (ODS) are manufactured using the mechanical alloying process. The development of a coarse grained microstructure during recrystallization has been noted and discussed by a number of authors, but the mechanism of grain control remains uncertain. Recent work has emphasized the large influence of non-uniformities on the development of the recrystallized microstructure. The purpose of the present work was to study, with the help of finite element modeling techniques, the effect of non-uniform plastic strain on recrystallization of Fe-base ODS alloy named MA 957.

The acicular ferrite formation as decomposition product of S-lean V-alloyed austenite with high N content is studied in this article. A combination of thermodynamic models as well as some physical metallurgical principles was used to analyze the intragranular nucleation potency of V(C,N) precipitates. The designed thermomechanical and heat treatments ensure an almost homogeneous microstructure consisting of acicular ferrite for this N-rich laboratory cast steel. The results presented in this work demonstrate that, in the absence of sulfide inclusions, acicular ferrite is nucleated on V(C,N) precipitates.

Ferritic oxide dispersion-strengthened alloys (ODS) are manufactured using a mechanical alloying process. The development of a coarse-grained microstructure during recrystallization has been detected and discussed by several authors, but the mechanism of grain growth remains uncertain. Recent work has emphasized the large influence of non-uniformities on the development of the recrystallized microstructure. The purpose of the present work is to study the effect of both slight heterogeneous plastic strains and strong directional deformation on recrystallization of a ferritic Fe-base ODS alloy., The authors acknowledge financial support from the Spanish Ministerio de Economia y Competitividad (MINECO) in the form of a Coordinate Project (MAT2016-80875-C3-1-R). The work presented here is done within the Joint Programme on Nuclear Materials of the European Energy Research Alliance Pilot Project CREMAR. The authors would also like to acknowledge financial support from Comunidad de Madrid through DIMMAT-CM_S2013/MIT-2775 project. J. Vivas acknowledges financial support in the form of a FPI Grant BES-2014-069863.

This paper presents a finite element modeling analysis of deformation on iron-base mechanically alloyed oxide dispersion strengthened alloy by spherical indentations (Brinell test). Results of the model are used to interpret the role of residual shear stresses on the development of recrystallized grain structure and the temperature at which recrystallization occurs., I. Toda Caraballo acknowledges the Spanish Ministerio de Ciencia e Inovacio´n for financial support in the form of Ph.D. research grant (FPI). The authors acknowledge financial support for this investigation from the Spanish Ministerio de Educacio´n y Ciencia through the Plan Nacional 2006 ENE2006-15170-C02- 01/ALT.

Carbide free bainite has achieved the highest strength and toughness combinations to date for bainitic steels in as-rolled conditions. By alloying designing and with the help of phase transformation theory, it was possible to improve simultaneously the strength and toughness because of the ultra-fine grain size of the bainitic ferrite plates. Ultimate tensile strengths ranging from 1600 MPa to 1800 MPa were achieved while keeping a total elongation higher than 10 %. Their toughness at room temperature matches tempered martensitic steels, known to be the best-in-class regarding this property. However, it has been observed that the presence of coalesced bainite leads to a dramatic deterioration in toughness in these novel high strength bainitic steels.

Tensile specimens have been tested at room temperature, finding clear delamination in the rolling direction but only incipient delamination in the transverse direction. Delamination is found to be a strain rate-controlled process whose morphology depends on the material’s processing history, suggesting that its cause may be embrittlement induced by hydrogen occluded during processing. Delamination has only a small influence on mechanical properties in the rolling direction, but in the transverse direction a loss of ductility is detected particularly for aged specimens., The authors acknowledge financial support from the Spanish Ministerio de Educación y Ciencia in the form of a Coordinated Project in the Energy Area of Plan Nacional 2006 (ENE2006-15170- C02). Moreover, one of the authors (J. Ch) gratefully acknowledges the contribution of Ms. C. Pe˜na for her help with the fractographic work.

In this work we characterize the microstructural changes induced by grit blasting of the Ti6Al4V alloy and their effect on the sub-surface mechanical properties by means of micro- and ultramicro indentations techniques. It has been observed that the severe plastic deformation at the surface produces an increase in roughness. Such deformation, however, does not cause any evident hardening at the sub-surface zone, which contrast with the work hardening observed on blasted cp Ti and austenitic stainless steel 316 L. It is proposed that the different behaviour of the Ti-base alloy is related to its lower strain hardening exponent. The implications of the absence of subsurface hardening on the loss of fatigue strength observed by other authors are analysed. © 2009 Elsevier B.V. All rights reserved.

This article deals with the mechanical properties achieved in two S-lean laboratory-cast V steels with two different N content levels, as compared with commercial acicular ferrite steel. The designed heat treatments ensure an almost homogeneous microstructure consisting of acicular ferrite for N-rich and commercial steels and consisting of bainite for the N-lean steel. The results presented in this work demonstrate that, in the absence of sul.de inclusions, acicular ferrite is nucleated on V(C,N) precipitates. The mechanical tests indicate that N-rich acicular ferrite steel achieves the same toughness values as N-lean bainitic steel but with a substantial improvement in strength properties. The S-lean steels present better toughness properties than commercial acicular ferrite steel, which is consistent with the detrimental e.ect of inclusions on toughness. © The Minerals, Metals & Materials Society and ASM International 2009.

Zinc-plated AISI C1022 steel self-drilling screws, used to fasten steel frames containing grille panels to I-shaped beams on a building facade, fractured after a just few months in service. Metallographic techniques and scanning electron microscopy were used to analyse the microstructure and the fracture surface of the screws. Tensile, torsion, shear and hardness tests were performed to verify compliance with the manufacturer’s specifications. The stress on the screws in the considered service conditions was estimated. The mechanical properties of the screws were found to be in agreement with the manufacturer’s specifications. Fractographic analysis of the fracture surfaces revealed no fatigue features, but indicated intergranular fracture on the periphery and ductile features (microvoid coalescence) with some patches of transgranular cleavage in the core. Intergranular fracture was found to be hydrogen embrittlement (HE) induced. However, HE was not the only cause of screw failure, which was also partly due to in-service overloading.

In order to improve the ductility of carbide free bainitic microstructures, consisting of a bainitic ferrite matrix and a mixture of austenite and martensite, the TRIP effect i.e. the strain induced transformation of retained austenite to martensite, should be controlled. In this sense, the effect of the chemical composition on the mechanical stability of the retained austenite and the morphology, size, and distribution of this phase has been studied to determine the role that plays on the ductility behaviour of advanced bainitic steels. Results suggest that apart of the retained austenite, the morphology of the bainitic matrix is an important factor controlling ductility. Bainitic microstructures formed by coiling with coarse and blocky bainite morphology have shown higher uniform deformation values than those obtained by air cooling with the typical thin bainite platelets. © 2008 ISIJ.

PM 2000 offers an excellent oxidation resistance that relies on the capability to develop during service an α-alumina scale, fine, but tightly adhered to the substrate. Advantages of the scale protection at low temperatures are obtained by performing a pre-oxidation treatment prior to operation. Due to the high temperatures involved in the preoxidation treatment microstructural stability of the alloy could be affected. The aim of this study is to characterise the microstructural changes during oxidation (1100ºC /120 h) of the alloy in a fine grained state that is more suitable for room temperature applications. Special emphasis is devoted to the analysis of zones beneath the scale where tensile and fatigue fractures are usually initiated. It is interesting to remark that beneath the oxide scale grain growth occurs forming a shell of about 10 microns of coarse grains. Microtexture analysis performed at these zones reveals that population of grains with a {111} texture decreases towards the centre of the sample. The results presented in this work clearly confirms that recrystallization is not related to oxidation-induced effects but to the heterogeneous deformation produced during machining, that stimulate recrystallization to occur at much lower temperatures., The authors thank financial support to CICYT (Spain) under Project ENE2006-15170-C02-01/ALT.

In the last few years the Fe-base oxide dispersion strengthened (ODS) PM 2000 alloy has been shown to be a biomaterial for its outstanding combination of mechanical properties and corrosion resistance. In this work, we are describing the effect of high temperature annealing at 1100°C (pre-oxidation) and low temperature annealing at 475°C on the main mechanical properties at room temperature, with particular emphasis on tensile and fatigue properties, which are suitable for achieving the required biofunctionality of load bearing implants. It has been shown that annealing at 475°C is responsible for an increase in the YS and UTS with the subsequent decrease in ductility. However, despite of the loss of ductility, the material shows ductile behaviour as is observed in the necked zone of tensile specimens, which contrasts with the so-called >475°C embrittlement> observed for another ferritic alloys. Moreover, aged material at 475°C exhibits a better fatigue limit than that non aged pre-oxidised material. © 2007 ISIJ.

© 2015, The Minerals, Metals & Materials Society. Coarse-grained Fe-based oxide dispersion-strengthened (ODS) steels are a class of advanced materials for combined cycle gas turbine systems to deal with operating temperatures and pressures of around 1100°C and 15–30 bar in aggressive environments, which would increase biomass energy conversion efficiencies up to 45% and above. This two-part paper reports the possibility of the development of simultaneous corrosion barrier and optimized microstructure in a FeCrAl heat-resistant alloy for energy applications. The first part reports the mechanism of generating a dense, self-healing α-alumina layer by thermal oxidation, during a heat treatment that leads to a coarse-grained microstructure with a potential value for high-temperature creep resistance in a FeCrAl ODS ferritic alloy, which will be described in more detail in the second part., G. Pimentel acknowledges the Spanish Ministerio de Ciencia e Inovación for financial support in the form of PhD research grant (FPI). The authors acknowledge financial support to Ministerio de Economia (MINECO) and Fondo Europeo de Desarrollo Regional (FEDER) in the form of ENE2009-13766-C04-01 project and MAT2013-47460-C5-2-P project.

Iron aluminides have been examined over many years, especially since the 1960s with renewed attention since the 1980s. Several clear characteristics of these materials have been demonstrated, some good and some less attractive. Properties seen are those such as reasonable strength from room temperature to about 500 °C; acceptable but not good ductility at room temperature dependent in part on environmental sensitivity; poor creep and high temperature strength above 500 °C; excellent oxidation and corrosion resistance; cheap constituent elements but difficult thermomechanical forming. This article reviews advances in strengthening and improving ductility of FeAl over the last decade or so, concentrating especially on activities of the authors' groups, and reviews also possibilities for exploiting the excellent oxidation/corrosion resistance at high temperatures by improving the high temperature creep behaviour.

The influence of a variety of machining conditions on the tensile behaviour of a mechanically alloyed FeAl intermetallic has been examined. Yield behaviour is hardly affected by machining conditions, and ductility is only weakly sensitive to machining speed or cutting depth. This behaviour seems to be related more with the extent of subsurface damage or work hardening than with the roughness of the machined samples. © 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Fe-based oxide dispersion strengthened (ODS) steels are oriented to applications where high operating temperatures and good corrosion resistance is paramount. However, their use is compromised by their fracture toughness, which is lower than other competing ferritic-martenstic steels. In addition, the route required in manufacturing these alloys generates texture in the material, which induces a strong anisotropy in properties. The V-notched Charpy tests carried out on these alloys, to evaluate their impact toughness, reveal that delaminations do not follow the path that would be expected. There are many hypotheses about what triggers these delaminations, but the most accepted is that the joint action of particles in the grain boundaries, texture induced in the manufacturing process, and the actual microstructure of these alloys are responsible. In this paper we focused on the actual role of crystallographic texture on impact toughness in these materials. A finite elements simulation is carried out to solely analyze the role of texture and eliminate other factors, such as grain boundaries and the dispersed particles. The work allows us to conclude that crystallographic texture plays an important role in the distribution of stresses in the Charpy specimens. The observed delaminations might be explained on the basis that the crack in the grain, causing the delamination, is directly related to the shear stresses τ on both sides of the grain boundary, while the main crack propagation is a consequence of the normal stress to the crack., The authors acknowledge financial support from Spanish Ministerio de Economia y Competitividad (MINECO) in the form of a Coordinate Project (MAT2016-80875-C3-1-R). Authors also acknowledge financial support to Comunidad de Madrid through the DIMMAT-CM_S2013/MIT-2775 project.

© 2014 Elsevier B.V. Blasting of 316 LVM steel was performed by using alumina and zirconia particles that yield rough (up to Ra ~. 8. μm) and nearly smooth (up to Ra ~. 1. μm) surfaces, respectively. Besides roughening, the severe plastic deformation imposed during blasting yields subtle sub-surface microstructural changes such as grain size refinement, α'-martensite formation, and work hardening. In this work we investigate the thermal treatment at 700. °C of the blasted steel, aimed to reverse the strain induced α'-martensite to austenite, with special emphasis in the correlation of the microstructural changes with the fatigue resistance. Blasting with rounded zirconia particles increases the fatigue resistance whereas the opposite effect is observed using alumina ones, which are more abrasive and cause a huge amount of embedded particles acting as stress raisers. It is shown that thermal treatment at 700. °C is very effective in the reversion of martensite, even after 2. min of annealing. Interestingly, the short thermal treatment of the alumina blasted steel increases the fatigue strength to values close to non-blasted material (400. MPa). Prolonged exposures, however, contribute to a full relaxation of the beneficial compressive residual stresses, being the net effect a decrease in the fatigue limit (340. MPa)., The authors are thankful for financial support from the MICINN (MAT2009-14695-C04) and the MINECO (MAT 2012-37736-C05-01). S. Barriuso thanks to JAE predoc grant of CSIC. Technicians of Laboratories of X-Ray Diffraction, Mechanical Testing, and Microscopy (CENIM) and the SPM-Service of the ICMM-CSIC are specially acknowledged.

Mechanically alloyed iron-base oxide dispersion-strengthened (ODS) alloys are the class of advanced materials for application in heat exchangers tubing in which creep and oxidation resistance are paramount. The yttria dispersion in such alloys improves the high-temperature creep and stress rupture life. The strength is further enhanced by the development of a coarse-grained microstructure during recrystallization. Factors controlling the evolution of this desirable microstructure are explored in this work, focusing specifically on PM 2000. The results presented in terms of orientation imaging, transmission electron microscopy, and scanning electron microscopy indicate that the recrystallization process consists of two different stages. Before the coarse grain takes place, the alloy undergoes an extended recovery process followed by abnormal grain growth. The initial microstructure consisted of subgrains (submicrometer sizes) with a strong 〈110〉RD fiber texture (α fiber), which are transformed into coarse grains (mm sizes) with orientations 〈112〉RD. The aim of this study is to describe the mechanisms involved in the intermediate stages of recrystallization process from the submicrometer grain size to the abnormal grain size. © 2014 The Minerals, Metals & Materials Society.

Grit blasting is used as a cost-effective method to increase the surface roughness of metallic biomaterials, as Ti. 6Al. 4V and 316 LVM, to enhance the osteointegration, fixation and stability of implants. Samples of these two alloys were blasted by using alumina and zirconia particles, yielding rough (up to Ra~8. μm) and nearly smooth (up to Ra~1. μm) surfaces, respectively. In this work, we investigate the sub-surface induced microstructural effects and its correlation with the mechanical properties, with special emphasis in the fatigue behavior. Blasting with zirconia particles increases the fatigue resistance whereas the opposite effect is observed using alumina ones. As in a conventional shot penning process, the use of rounded zirconia particles for blasting led to the development of residual compressive stresses at the surface layer, without zones of stress concentrators. Alumina particles are harder and have an angular shape, which confers a higher capability to abrade the surface, but also a high rate of breaking down on impact. The higher roughness and the presence of a high amount of embedded alumina particles make the blasted alloy prone to crack nucleation. Interestingly, the beneficial or detrimental role of blasting is more intense for the Ti. 6Al. 4V alloy than for the 316 steel. It is proposed that this behavior is related to their different strain hardening exponents and the higher mass fraction of particles contaminating the surface. The low value of this exponent for the Ti. 6Al. 4V alloy justifies the expected low sub-surface hardening during the severe plastic deformation, enhancing its capability to soft during cyclic loading. © 2013 Elsevier Ltd.

The corrosion behaviour of MA 956 in the Hank's solution has been investigated after three different thermal cycles, which lead to hardness values of 250, 289, and 330 HV. The electrochemical tests have shown that the uniform corrosion resistance is independent of the material state. The alloy develops a passive layer on the surface, which provides it with low corrosion rates. The pitting corrosion resistance, however, was seriously affected by the degree of precipitation. Specimens with the lowest and intermediate hardness were able to withstand polarization above 1000 mV, whereas specimens with the higher hardness had a value of 250 mV. We believe that the local differences in Cr concentration associated with the spinodal decomposition, which increase with increasing annealing time at 475°C, could have influenced the characteristics of the passive layer. © 2001 Elsevier Science Ltd. All rights reserved.

The present study examines the influence of a wide range of microstructural parameters and tensile test conditions on the tensile behaviour of a mechanically-alloyed, fine grained Fe-40Al intermetallic. Major changes of tensile strength and ductility are obtained by reducing the grain size (with the ductility increasing from 1 to 10% for grain sizes of 100 and 1 μm), by avoiding environmental attack during the test, and by avoiding premature stress/strain concentrators (with the ductility increasing from 5 to 10% as imperfectly machined samples have their sample surfaces polished). Ductility variations are interpreted using a model based on the slow propagation of an initial crack which eventually reaches a condition of instability, and where the respective roles of environment, plastic deformation processes, and fracture mechanisms can be distinguished. The tensile ductility is highly sensitive to the surface state, meaning the degree of exposure to the environment, the extent of geometrical stress raisers, and the microstructure made up of the grain and particle size and distribution. © 2001 Elsevier Science Ltd.

In the present work attention is paid on the composition, structure and protective properties of alumina layer produced by high temperature oxidation on MA 956 superalloy (Fe-20Cr-4.5Al-0.5Ti-0.5Y(2)O(3) (wt %)). The combination of good mechanical properties of this material and the excellent biocompatibility, the good wear and corrosion behavior of an outer alpha-alumina layer, limiting the release of ionic species and wear debris from the bulk material into the body-fluid environment, can make this material a candidate alloy for medical applications. Isothermal oxidation at 1100 degrees C in air of the alloy has led to the formation of a fine-grained, compact and adherent alpha-alumina scale. Oxide nodules rich in Ti, Y, Cr, and Fe were found on the top of the surface. In vitro electrochemical corrosion experiments showed good protective properties of the oxide scale. Moreover, no spallation of the alumina layer was observed. This feature is significant considering that the alumina layer has to withstand very high compressive stresses resulting from both growth and thermal stresses incorporated during cooling.

The present work analyzes the oxidation kinetics of MA 956 and PM 2000 alloys at 900 and 1100°C for exposure times up to 1000 hr. Special emphasis was placed on a comparison of the alumina-scale integrity formed at 1100°C by means of electrochemical tests at room temperature, which have been shown to be very reliable methods to detect the presence of microdefects within oxide scales. To check whether a preoxidation treatment makes these materials corrosion resistant against aggressive fluids, an electrolyte containing chloride ions was chosen. The mass gain of MA 956 was found to be slightly lower than that of PM 2000 up to 200 hr exposure at 1100°C and for the whole exposure range at 900°C. A subparabolic time dependence (n=0.3) of the oxide growth rate was determined for both alloys at both temperatures. On the other hand, the electrochemical-impedance spectroscopy (EIS) and anodic-polarization tests performed on preoxidized alloys (1100°C/100 hr) revealed good room-temperature corrosion behavior for both alloys, the corrosion resistance and polarization values being somewhat higher for preoxidized PM 2000. Consideration of these results and those of both surface and cross-section examinations of the scale, the better room-temperature corrosion behavior of preoxidized PM 2000 denotes the formation of a denser and mechanically more stable alumina scale containing a lower number of microdefects. This could result from the higher aluminum content of this alloy and the lower density of chemical heterogeneities within the scale. The higher mass gain of PM 2000 could be related to the higher concentration of oxide nodules on top of the alumina scale, as deduced from SEM examination.

This investigation was undertaken in an attempt to gain a fundamentalunder-standing of the oxidation behavior of a fine-grain MA 956 in thetemperature range 800 to 1200°C, with emphasis placed on the scalemorphology and oxidation kinetics. Oxidation reaction led to the formationof a thin and dense alumina scale, irrespective of the oxidationtemperature. At intermediate temperatures plateletlike oxides of alumina,probably θ-Al2O3, covered the surface, whereas at othertemperatures small nodules of Fe-, Cr-, Ti or Y-rich oxides were observed inthe outer part of the alumina scale. The temperature dependence of theparabolic rate constant revealed a change in the oxidation mechanism with atransition at about 1000°C. The high-temperature mechanism is controlled bythe formation of α-alumina, whereas the low-temperature oxidationmechanism is controlled by formation of metastable alumina. Comparison withthe reported oxidation kinetics for coarse-grain MA 956 is inconclusive,since microstructure (grain size, texture) of the substrate changed duringoxidation in the high-temperature range.

The oxidation behaviour of an oxide dispersion-strengthened (ODS) NiAl intermetallic, microalloyed with Ti and Mo and strengthened by a fine dispersion of Y2O3, is investigated in the temperature range of 900-1200°C for up to 200h exposure. The results have shown that a nearly pure alumina scale is formed irrespective of the exposure time, which is consistent with previous results on oxidation of NiAl or doped NiAl alloys. From the analysis of the kinetics results and the surface scale morphology it follows that below 1100°C metastable alumina control the oxidation kinetics, even after long exposure times. The presence of yttria seems to account for this increase in the transient oxidation period. Preoxidation of the alloy (1200°C/3 h) leads to a substantial reduction of the oxidation rate and precludes void formation at the scale/gas interface. Furthermore, formation of uniform scale, which would diminish the probability of failure of the scale due to thermal stresses, is favoured. © 1998 Elsevier Science Ltd. All rights reserved.

Microstructure and mechanical properties of Fe-xMn-3,2Al-0,23C alloys with 12 ≤ x ≤ 43 (mass %) at 77 and 290 K have been studied to determine the mechanisms controlling plastic deformation. Austenitic alloys (Mn ≥ 22) show an increase of elongation to failure with decreasing temperature of testing (inverse ductility). This behavior has been related to formation of deformation twins, which is favored at 77 K. Alloys with manganese content lower than 17 % present a two-phase microstructure (α' + γ). The martensite volume fraction increases as the manganese content decreases. These alloys show a loss of ductility, especially at 77 K. In contrast to asutenitic alloys, this different mechanical behavior has been associated with a TRIP mechanism (transformationinduced plasticity).Se han estudiado la microestructura y las propiedades mecánicas a 77 y 290 K de una serie de aleaciones Fe-xMn-3,2Al-0,23C con 12 ≤ x ≤ 43 (% en masa) con objeto de determinar los mecanismos que controlan la deformación plástica. Se ha comprobado que, en las aleaciones con estructura austenítica (Mn ≥ 22), el alargamiento a rotura aumenta al disminuir la temperatura de ensayo (ductilidad inversa). Este comportamiento se ha relacionado con un proceso de deformación por maclaje favorecido a 77 K. Las aleaciones con contenidos de manganeso < 17 % presentan una estructura bifásica (α' + γ), siendo mayor la fracción de volumen de martensita a medida que disminuye la concentración de manganeso. Estas aleaciones presentan una disminución del alargamiento a rotura especialmente a 77 K. El diferente comportamiento mecánico con respecto al de las aleaciones austeníticas se asocia a un proceso de transformación a martensita inducida por deformación (TRIP).

Se describen las características microestructurales y la textura de la aleación MA956 en las etapas intermedias de su procesado termomecánico para obtener el producto en forma de barras. Se partió de un material procesado en INCO Alloys International de tres formas: compactado isostáticamente, eximido en caliente + 1.330°C/1 h y laminado en caliente. Los materiales procesados mediante compactación isostática y laminación en caliente, se sometieron, además, a dos tipos de recocido, uno a 1.100ºC/100 h y otro a 1.330ºC/1 h. En el caso del material procesado mediante extrusión en caliente, la textura inicial de fibra del tipo evoluciona hacia una del tipo cuando se la somete al tratamiento de 1.330ºC/1 h, mientras que en el caso del material procesado mediante laminación en caliente, la textura inicial, con componentes y , cambia hacia una del tipo después del mismo tratamiento. La razón de la diferencia en la textura final del material procesado por ambos métodos se atribuye a las diferencias en la fracción en volumen de granos primarios con orientaciones y .

The temperature dependence of the stress-induced martensite (SIM) formation in a Ti-10V-2Fe- 3Al (Ti-1023) alloy under compressive loading has been studied. At low temperatures, the stress level at which martensite starts to form increases linearly with the deformation temperature, while the stress at which the deformation switches to regular plastic deformation is roughly temperature independent. A thermostatistical model for dislocation evolution is employed to describe deformation twinning in martensite. Combined effects of twinning induced plasticity and solid solution strengthening are considered in terms of temperature variations. The SIM effect disappears on deformation at temperatures beyond s233 C, which is close to the predicted Ms temperature of 240 C. The thermostatistical model predicts a transition from twinned martensite to pure slip at 250 C. By providing a model to predict stress induced martensite formation, and by describing deformation twinning, the present work provides a number of tools that may be employed to conceive new titanium alloys combining improved strength and ductility, (Project number:MC5.05206)of the Materials Innovation Institute (www.m2i.nl) in The Netherlands. Ministerio de Economia y Competitividad(Project no.MAT2010-19522).Spain

The kinetics of Fe rich α and Cr rich α′ phase separation during aging of Fe-Cr-Al oxide dispersion strengthened alloys have been analysed with a combination of atom probe tomography and thermoelectric power measurements. The slight lattice parameter decrease measured by X-ray diffraction after thermal aging was associated with a lattice misfit between the emerging α and α′ domains. The elastic strain associated with this misfit and the different elastic moduli for the α and α′ phases would produce an increase in internal stresses that would retard the motion of dislocations and thus would be the main cause for the strengthening. © 2013 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute.

Similarly to aluminium alloys, interrupted ageing in steels may increase hardness by 10%. By adding an intermediate stage between quenching and tempering, where quenched martensite is left to age at room temperature, carbon forms finer precipitate microstructures, which become more stable at room temperature. Using thermoelectric power to model carbon segregation to dislocations, it appears that room temperature ageing increases the number of effective nucleation sites for the subsequent tempering stage, as reflected in the microstructure and hardness, ASCOMETAL for financial support. DSM acknowledges financial support from Ministerio de Economía y Competitividad (Project No. MAT2010-19522

The effects of Fe-rich (α) and Cr-enriched (α′) phase separation, occurring during aging at 475 °C on the microstructure and mechanical properties of Fe–20Cr–6Al ODS alloy (PM2000™) hot-rolled tube, were investigated by means of atom probe tomography, microhardness, tensile and V-notched Charpy impact tests. Disregarding of the aging treatment, this material presents splitting of crack-divider type in longitudinal-transverse (LT) specimens, whereas crack-arrester type is observed in longitudinal-short transverse (LS) specimens, which induces significant differences in ductile-to-brittle transition temperature (DBTT) and upper shelf energy (USE). Additionally, a significant increase in DBTT and decrease in USE were recorded during aging at 475 °C as a function of aging time. The main cause of embrittlement is the α–α′ phase separation with an apparent activation energy measured in the range of 214–240 kJ/mol, which is consistent with the activation energy for Cr diffusion in this type of alloy, financial support of the Spanish Ministerio de Economia e Innovación in the form of a Coordinate Project in the Energy Area of Plan Nacional 2009 (ENE2009-13766-C04-01). This research was supported by ORNL’s Shared Research Equipment (ShaRE) User

The ductile-to-brittle transition (DBT) behavior of two similar Fe-Cr-Al oxide dispersion strengthened (ODS) stainless steels was analyzed following the Cottrell–Petch model. Both alloys were manufactured by mechanical alloying (MA) but by different forming routes. One was manufactured as hot rolled tube, and the other in the form of hot extruded bar. The two hot forming routes considered do not significantly influence the microstructure, but cause differences in the texture and the distribution of oxide particles. These have little influence on tensile properties; however, the DBT temperature and the upper shelf energy (USE) are significantly affected because of delamination orientation with regard to the notch plane. Whereas in hot rolled material the delaminations are parallel to the rolling surface, in the hot extruded material, they are randomly oriented because the material is transversally isotropic., Financial support of the Spanish Ministerio de Economia e Innovación (MINECO) through a Coordinated Project in the Materials Area of Plan Nacional 2013 (MAT2013-47460-C5-1) is gratefully acknowledged. We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)

Mechanically alloyed iron-based oxide dispersion-strengthened alloys have the potential for application in heat exchangers for biomass power plants, with operating temperature and pressure at entry of the gas turbine working fluid being around 1,100 °C and 15-30 bar, respectively. The yttria dispersion in such alloys improves the high-temperature creep and stress rupture life. The strength is further enhanced by the development of a coarse-grained microstructure during recrystallization. Factors controlling the evolution of this desirable microstructure are explored in this study, focusing specifically on PM 2000. The results can be interpreted if it is assumed that anything which makes the microstructure heterogeneous stimulates recrystallization. The combination of these results with finite element modelling is used to interpret the role of strain heterogeneity on the development of recrystallized grain structure. In this sense, larger strain gradients lead to more refined and more isotropic grain structures. © 2012 Springer Science+Business Media, LLC.

The effect of different starting microstructures on the kinetics of Fe-rich (a) and Cr-rich (a0) phase separation during aging of Fe– Cr–Al oxide dispersion strengthened (ODS) alloys has been analyzed with a combination of atom probe tomography and thermoelectric power measurements. The results revealed that the high recrystallization temperature necessary to produce a coarse grained microstructure in Fe-base ODS alloys affects the randomness of Cr-atom distributions and defect density, which consequently affect the phase separation kinetics at low annealing temperatures.

The influence of bainite morphology on the impact toughness behaviour of continuously cooled cementite-free low carbon bainitic steels has been examined. In these steels, bainitic microstructures formed mainly by lath-like upper bainite, consisting of thin and long parallel ferrite laths, were shown to exhibit higher impact toughness values than those with a granular bainite, consisting of equiaxed ferrite structure and discrete island of marteniste/austenite (M/A) constituent. Results suggest that the mechanism of brittle fracture of cementite-free bainitic steels involves nucleation of microcracks in M/A islands but is controlled by the bainite packet size, Spanish Ministry of Science and Innovation for financial support in the form of a PhD research grant (FPI grant under the project no. MAT2007-63873)

The α–α′ phase separation kinetics in a commercial Fe–20 wt.% Cr–6 wt.% Al oxide dispersion-strengthened PM 2000™ steel have been characterized with the complementary techniques atom probe tomography and thermoelectric power measurements during isothermal aging at 673, 708, and 748 K for times up to 3600 h. A progressive decrease in the Al content of the Cr-rich α′ phase was observed at 708 and 748 K with increasing time, but no partitioning was observed at 673 K. The variation in the volume fraction of the α′ phase well inside the coarsening regime, along with the Avrami exponent 1.2 and activation energy 264 kJ mol−1, obtained after fitting the experimental results to an Austin–Rickett type equation, indicates that phase separation in PM 2000™ is a transient coarsening process with overlapping nucleation, growth, and coarsening stages, PM 2000™ is a trademark of Plansee GmbH. LEAP® is a registered trademark of Cameca Instruments. C.C. and J.C. acknowledge financial support by the Spanish Ministerio de Ciencia e Innovación in the form of a Coordinate Project in the Energy Area of Plan Nacional 2009 (ENE2009-13766-C04-01

Technologies and means for developing biomass plant with higher energy conversion efficiencies are essential in order to implement the commitment to renewable biomass energy generation. Advanced, indirect Combined Cycle Gas Turbine (CCGT) systems offer overall biomass energy conversion efficiencies of 45 % and above, compared with the 35 % efficiency of conventional biomass steam plant. However to attain this efficiency in CCGT operation it will be necessary to develop a heat exchanger capable of gas operating temperatures and pressures of around 1100 °C and 15-30 bar, respectively, for entry heating the gas turbine working fluid. ODS ferritic steels is the kind of advance material to deal with this challenge, however work to optimize the coarse grain microstructure to improve creep hoop strength needs to be done. In this sense, this paper reports the recrystallisation behaviour of PM 2000 oxide dispersion strengthened ferritic alloy which was cold deformed after hot-rolling and extrusion. The results can be interpreted if it is assumed that anything which makes the microstructure heterogeneous, stimulates recrystallisation. In this sense, larger strain gradients lead to more refined and more isotropic grain structures. The combination of these results with finite element modeling are used to interpret the role of residual shear stresses on the development of recrystallized grain structure.

Carbide free bainitic steels alloyed with manganese have achieved the highest strength and toughness combinations to date for bainitic steels. Ultimate tensile strengths ranging from 1600 to 1800MPa were achieved while keeping a total elongation higher than 10%. Their toughness at room temperature matches tempered martensitic steels, known to be the best-in-class regarding this property. This improvement in toughness is achieved suppressing the precipitation of cementite during bainite formation by alloying the steel with about 1.5 wt% of silicon. However, it has been observed that strongly orientated martensite bands, associated to inhomogeneous manganese redistribution during solidification, lead to a remarkable deterioration in toughness in these advanced bainitic steels. The stress concentration associated with highly heterogeneous hardness distribution in the microstructure contributes to the premature crack nucleation., The authors gratefully acknowledge the support of the Research Fund for Coal and Steel and the Spanish Ministry of Science and Innovation for funding this research under the contracts RFSR-CT- 2008-00021 and MAT2007–63873, respectively. All of us want to thank T. Iung and S. Allain from ArcelorMittal (Maizières les Metz- France) for manufacturing the studied steels.

The present paper deals with a new vanadium and nitrogen alloyed steel for heavy products applications, which offer improved toughness and strength properties as compare with a commercial heavy product steel. A strong structural refinement, by introducing acicular ferrite microstructure, combined with an optimum cooling process can be utilised to develop tough, high strength thick products. © 2009 Institute of Materials, Minerals and Mining.

New carbide free bainitic microstructures are gaining an increasing interest on behalf the scientific and industrial community. The excellent combination of mechanical properties achieved in those microstructures with no need of complex heat treatments or thermomechanical processes represents their main advantage. The strength is mainly achieved by means of the very fine bainitic ferrite plates, consequence of the transformation mechanism, but the parameters contributing to the ductility of those microstructures are still unclear in this type of microstructures, where a soft phase, retained austenite, is imbibed in a very strong matrix of bainitic ferrite. A priori is reasonable to assume that retained austenite will control the levels of ductility achieved. Further enhancement of ductility can be achieved by the transformation of retained austenite into martensite (strain or stress assisted), thus its mechanical stability plays an important role in the final ductility. In this study, by means of X-ray analysis of interrupted compression tests, it is studied the influence that different microstructural aspects of retained austenite may have on its mechanical stability. © 2009 Springer Science+Business Media, LLC.

A theoretical design procedure based on phase transformation theory alone has been successfully applied to design steels with a microstructure consisting of a mixture of bainitic ferrite and retained austenite. Using thermodynamics and kinetics models, a set of four carbide free bainitic steels with a 0.3 wt-% carbon content were designed and manufactured following a thermo-mechanical treatment consisting of hot rolling and two-step cooling. The designed steels present significant combinations of strength and ductility, with tensile strengths ranging from 1500 to 1800 MPa and total elongations over 15%. However, a carbon content of 0.3 wt% is still high for in-use properties such as weldability. In this sense, a reduction in the average carbon content of advanced bainitic steels was proposed. Improved bainitic steels with a carbon content of 0.2 wt% reached combinations of strength and ductility comparable to those in TRIP assisted steels., The authors gratefully acknowledge the support of Spanish Ministerio de Ciencia y Tecnología Plan Nacional de I + D + I (2004–2007) funding this research under the Contract MAT2007- 63873. All of us want to thank to T. Iung and S. Allain (ARCELOR RESEARCH) for manufacturing the designed alloys.

The coarsening of the three-dimensional microstructure resulting from phase separation during ageing at 748K of a Fe-based PM 2000TM oxide dispersion strengthened (ODS) steel has been investigated by atom probe tomography and hardness measurements. Phase separation resulted in the formation of isolated particles of the chromium-enriched phase. The aluminum and titanium were found to preferential partition to the iron-rich phase. The partitioning of aluminum is consistent with theoretical calculations. The change in the scale of the chromium-enriched phase was found to fit a power law with a time exponent of 0.32 in accordance with that predicted by the classical Lifshitz, Slyozov and Wagner (LSW) theory. The solute concentrations of the coexisting and phases were estimated from concentration frequency distributions with the Langer–Bar-on–Miller (LBM) method and proximity histograms. The hardness was linearly related to the chromium content of the phase. © 2008 Elsevier B.V. All rights reserved., The authors acknowledge financial support from the Spanish Ministerio de Educaci´on y Ciencia in the form of a Coordinate Project in the Energy Area of Plan Nacional 2006 (ENE2006- 15170-C02). Research at the Oak Ridge National Laboratory SHaRE User Facility was sponsored by Basic Energy Sciences, US Department of Energy. PM2000TM is a trademark of Plansee SE. and LEAP® is a registered trademark of Imago Scientific Instruments.

PM 2000 is a Ni-free oxide dispersion strengthened Fe-20Cr-5Al alloy able to develop a fine, dense and tightly adherent α-alumina scale during high-temperature oxidation. Despite the high temperature involved during thermal oxidation (1100°C), microstructural changes in the candidate material, a hot rolled product, hardly occurs. Consequently, the good mechanical properties of the as-received material are not significantly affected. Moreover, due to the high compressive residual stresses at the alumina scale, an increase in the fatigue limit from 500 to 530 MPa is observed. Such stresses also account for the high capability of the coating/metal system to withstand more than 1% tensile deformation without cracking. The biocompatibility of the alloy was assessed in comparison to commercial alumina. Saos-2 osteoblast-like cells were either challenged with PM 2000 particles, or seeded onto PM 2000 (with and without scale) solid samples. Viability, growth, and ALP release from cells were assessed after 3 or 7 days, while mineralization was checked at 18 days. This study has demonstrated that PM 2000 with and without scale are capable of supporting in vitro growth and function of osteoblast-like cells over a period of 18 days. Results from this study suggest that the resulting alumina/alloy system combines the good mechanical properties of the alloy with the superior biocompatibility of the α-alumina, for which there is very good clinical experience. © 2004 Elsevier Ltd. All rights reserved.