Search

An in-situ analysis of local strain accommodation on transformation induced plasticity (TRIP) aided multi-phase steel was performed with a correlative application of characterization techniques such as digital image correlation (DIC), electron backscatter diffraction (EBSD), and micro-mechanical testing. The local strain on the complex microstructure of the multi-phase steel was measured during a tensile test using an innovative DIC method (which does not employ artificial patterns), in conjunction with a scanning electron microscope. The constituent phases of the examined surface were identified by postprocessing implemented on the EBSD maps. This was further verified by nano-indentation, consequently enabling systematic and quantitative analyses of the strain partitioning between the phases. Soft acicular ferrite accommodated the largest strain with sites of intense strain localization around the hard, neighboring martensite. The retained austenite transformed gradually into martensite because of the applied strain and caused strain localization in the neighboring acicular ferrite. This verified that DIC method proposed in this study enables precise and effective data collection at the interfaces between different phases that could have certainly been blocked by the DIC patterns in the conventional method.

High-temperature oxidation behaviour of an alumina-forming austenitic (AFA, Febalance–20Ni–14Cr–2.5Al–0.15Si–2Mn–2.5Mo–0.9Nb, in wt%) steel and W-substituted AFA steel was examined. The isothermal ...

Competing magnetic interactions in low-dimensional quantum magnets can lead to the exotic ground state with fractionalized excitations. Herein, we present our results on an $S=\frac{5}{2}$ quasi-one-dimensional spin system ${\mathrm{Bi}}_{3}{\mathrm{FeMo}}_{2}{\mathrm{O}}_{12}$. The structure of ${\mathrm{Bi}}_{3}{\mathrm{FeMo}}_{2}{\mathrm{O}}_{12}$ consists of very well separated, infinite zigzag $S=\frac{5}{2}$ spin chains. The observation of a broad maximum around 10 K in the magnetic susceptibility $\ensuremath{\chi}(T)$ suggests the presence of short-range spin correlations. $\ensuremath{\chi}(T)$ data do not fit the $S=\frac{5}{2}$ uniform spin chain model due to the presence of second-nearest-neighbor coupling (${J}_{2}$) along with the first-nearest-neighbor coupling (${J}_{1}$) of the zigzag chain. The electronic structure calculations infer that the value of ${J}_{1}$ is comparable with ${J}_{2}$ (${J}_{2}/{J}_{1}\ensuremath{\approx}1.1$) with a negligible interchain interaction (${J}^{\ensuremath{'}}/J\ensuremath{\approx}0.01$) implying that ${\mathrm{Bi}}_{3}{\mathrm{FeMo}}_{2}{\mathrm{O}}_{12}$ is a highly frustrated triangular chain system. The absence of magnetic long-range ordering down to 0.2 K is seen in the heat-capacity data, despite a relatively large antiferromagnetic Curie-Weiss temperature ${\ensuremath{\theta}}_{CW}\ensuremath{\approx}--\phantom{\rule{0.16em}{0ex}}40$ K. The magnetic heat capacity follows nearly a linear behavior at low temperatures indicating that the $S=\frac{5}{2}$ anisotropic triangular chain exhibits the gapless excitations.

To gain the fundamental understanding of deformation mechanisms in an aluminum-containing austenitic high-Mn steel (Fe-32Mn-8.9Al-0.78 C (wt.%)), in-situ straining transmission electron microscopy (TEM) analysis is conducted. The in-situ observation during the deformation demonstrates that the plastic deformation is accommodated by the pronounced planar dislocation gliding followed by the formation of slip bands (SBs) and highly dense dislocation walls (HDDWs). Experimental evidences of the glide plane softening can be obtained from the interaction between the gliding perfect dislocations and the L’12 ordered precipitates in the austenite matrix. Furthermore, the observation of the localized cross-slip of dislocations at the slip band intersections enables to understand why slip bands are extensively developed without mutual obstructions between the slip bands. The enhanced strain hardening rate of the aluminum-containing austenitic high-Mn steels can be attributed to the pronounced planar dislocation glides followed by formation of extensive slip band which prevent premature failure by suppressing strain localization.

Martensitic transformation (MT), constituting an essential part of deformation scenario, plays a key role in plasticity and thermoelasticity of face-centered cubic (fcc) materials. Despite being an area of intense research, discrepancies remain about the essential parameter dictating nucleation of hexagonal close-packed (hcp) martensite and about the dislocation activities governing plasticity. Here, we show that screw dislocation induces the torsional flow of close-packed atomic planes of fcc matrix, characterized by Eshelby twist, and its dissociation provides a self-perpetuating step to bring forth Frank partial dislocation acting as a critical component to accomplish the atomic periodicity for fcc-to-hcp MT. The critical condition to initiate fcc-to-hcp MT was estimated from the Eshelby twist angle measured from high-angle annular dark field scanning transmission electron microscopy (HAADF STEM). Once the critical condition is satisfied, the trajectory of screw dislocation can span two atomic planes, its dissociation proceeds by forming both Frank partial sessile to {111} and Shockley partial glissile along {111} plane. Based on our dislocation model for MT, we demonstrate how dissociation route of perfect dislocation can be exploited to determine deformation mechanism (MT, twinning, slip). By incorporating dislocation dissociation model into the concept of stacking fault energy, we suggest a synthesized concept of deformation scenario that can provide fundamental and predictive insight into plasticity and transformability of fcc material.

A borated stainless steel based on the composition of type 304 stainless steel containing different amount of boron was fabricated through a conventional ingot metallurgy-hot working process, and the relationship between the microstructure and mechanical properties was investigated. As the content of boron increases, the volume fraction of (Fe,Cr)2B increases, as predicted by thermodynamic equilibrium calculations. As the annealing proceeds at 1180°C, the plate-like shape of (Fe,Cr)2B turned into a spherical shape. In addition, brittle fracture of the boride was dominant before the heat-treatment, but ductile mode due to the formation of dimples in the austenite was dominant after heat-treatment. In the specimen containing 1.78 wt% of boron, the Cr and Ni contents of the austenite matrix were homogenized after annealing at 1180 °C for 192 h, and the strength and ductility were simultaneously improved.

Background Clinical benefits of complete revascularization (CR) in acute myocardial infarction (AMI) patients are unclear. Moreover, the benefit of CR is unknown in AMI with Diabetes Mellitus (DM) patient. Objectives We sought to compare prognosis of CR and incomplete revascularization (IR) in patients with AMI and multivessel disease, according to the presence of DM. Methods A total of 2,150 AMI patients with multivessel coronary artery disease were analyzed. CR was defined based on angiographic image. The primary endpoints of this study was patient oriented composite outcome (POCO) defined as a composite of all cause death, any myocardial infarction, and any revascularization within 3 years. Results Overall, 3-year POCO were significantly lower in patients receiving angiographic CR (985 patients, 45.8%) compared with IR (1165 patients, 54.2%). When divided into subgroups according to the presence of DM, CR reduced 3-year clinical outcomes in the non-DM group but not in the DM group (POCO: 11.7% vs. 23.2%, p Conclusion In AMI patients with multivessel disease, CR may be ineffective in improving clinical outcomes in patients with DM. Funding Acknowledgement Type of funding source: None

Background Venoarterial extracorporeal membrane oxygenation (VA-ECMO) support is a lifesaving tool used in the treatment of cardiogenic shock, acute heart failure, or extracorporeal cardiopulmonary resuscitation (CPR). We report on a single center experience with ECMO and aim to identify the prognostic markers for in-hospital mortality and death at 72 hours after ECMO. Methods Between 2011 and 2019 we evaluated 131 patients, who received ECMO. Collected data was analyzed to identify baseline characteristic, outcomes including clinical variables predictive of poor outcome. Results The mean age was 62.5 years, 67.2% were male patients, with prior CPR in 61.8%. The annual number of VA-ECMO procedures steadily increased, whereas in-hospital mortality is decreasing. Within the total cohort, the indication for VA-ECMO was cardiac arrest in 19.1%, acute coronary syndrome in 41.2%, acute heart failure in 23.7%, and myocarditis in 10.7%. Overall in-hospital mortality was 58.8%. Multivariate logistic regression model revealed presence of malignancy, history of revascularization, duration of cardiac arrest, and low BMI as independent predictors for mortality in 72 hours after ECMO (table). On the other hand, predictors of in-hospital mortality were prior congestive heart failure, male, and history of malignancy. The C-statistic for discriminating mortality in 72 hours after ECMO with the duration of cardiac arrest was 0.67 (figure). Conclusions Although the use of ECMO as a last line in the treatment of critical patients measures constitutes an important improvement in their care; with 41.2% overall survival; patient selection and timing of ECMO initiation remains challenging. The importance of consideration for ECMO use earlier in course of illness rather than later. Funding Acknowledgement Type of funding source: None

The cornerstone of materials design is solving materials-related optimization problems to obtain microstructural or processing variables that lead to the most desirable material properties. Because the objective of materials design is to maximize their performance, the related optimization problems often require a global solution. This type of unconstrained optimization overlooks the feasibility of the solution, which is a key engineering issue. For any practical application, feasibility should be reflected in the constraints included in the optimization problems. Nevertheless, the constraints related to feasibility are considerably complex due to the high dimensionality of the design space and non-physical aspects of the constraints, such as machine specifications, material dimensions, and available initial microstructure. In this work, we propose the use of a simple support vector machine (SVM) trained with information in an existing database to model complex feasibility constraints for material optimization. We present a problem involving optimization of the initial texture of a body-centered cubic (BCC) polycrystalline material to obtain specific target textures after cold-rolling. Both unconstrained and constrained optimizations are conducted for comparison, and the results demonstrate that constrained optimizations yield viable solutions while unconstrained optimizations do not.

The effects of Mn on oxidation resistance of Fe-18Cr-8.5Ni-3.5Cu-0.5Nb-0.1C-0.1 N-(0.08–2.05 wt%)Mn alloys were investigated by isothermal oxidation in ambient air at 700 °C for up to 8 weeks. The Mn addition up to 0.44 wt% increased the oxidation resistance, but further addition decreased it, thus the best oxidation resistance was obtained in the alloy with 0.44 wt% Mn. Mn promoted the internal oxidation and changed the Mn and Cr concentrations of the inner oxide layer. The best oxidation resistance of the alloy with 0.44 wt% Mn was attributed to the improved protectiveness of the inner oxide layer having the highest Cr content.

Small objects of an alloy tool steel were built by selective laser melting at different scan speeds, and their microstructures were analyzed using electron backscatter diffraction (EBSD). To present an explicit correlation with the local thermal cycles in the objects, prior austenite grains were reconstructed using the EBSD mapping data. Extensive growth of austenitic grains after solidification could be detected by the disagreement between the networks of carbides and austenite grain boundaries. A rapid laser scan at 2000 mm/s led to less growth, but retained a larger amount of austenite than a slow one at 50 mm/s. The rapid scan also exhibited definite evolution of Goss-type textures in austenite, which could be attributed to the growth of austenitic grains under a steep temperature gradient. The local variations in the microstructures and the textures enabled us to speculate the locally different thermal cycles determined by the different process conditions, that is, scan speeds.

At 700 °C and 200 MPa, the creep rupture time of W-containing alumina-forming austenitic heat-resistant (WAFA) steel increases from 1044 to 3119 h by pre-strain. Pre-strain introduces a lot of dislocation into the matrix and most of the dislocations remain stable to the end of creep without recovery and recrystallization. In addition, the dislocations have enabled secondary NbC and Laves phase to be uniformly distributed and refined. However, the dislocations lower grain boundary strength due to the coarsening of precipitates along grain boundaries Therefore, the increase in the creep rupture time in spite of deterioration of grain boundary strength is attributed to the dislocation strengthening and enhanced precipitation hardening within grains.

The hot workability of two cold-work tool steels were evaluated and compared. A D2 and an advanced alloy based on 8% Cr steels (TDx) were deformed at high temperatures between 900 and 1100 °C with strain rates 0.001–10 s− 1 via hot compression test. From the flow curves, processing maps were constructed based on the dynamic material model. The deformed microstructures were observed and compared in various scales with respect to the deformation conditions. Although the two alloys exhibited a large similarity in the flow instability consideration of the processing map, their behavior in microstructure evolution was different. While both alloys exhibited a tendency of strain localization in the conditions of instability, the efficiency of power dissipation in the processing maps showed an intricate correlation with the progress of dynamic recrystallization and carbide precipitation. TDx showed a distinctive behavior of carbide precipitation and a larger resistance to dynamic recrystallization, which implied a requirement on more delicate control of hot working conditions.

The aging behavior and orientation relationships in Fe–31.4Mn–11.4Al–0.89C low-density steel were investigated with respect to constituent phases and precipitates, including γ-austenite matrix, β-Mn, and α-precipitate. After aging treatment at 550 °C for various periods of time, the microstructural changes and corresponding mechanical response were characterized by Vickers hardness measurement combined with EBSD and TEM observations. The precipitation sequence during the aging treatment showed that nano-sized κ-carbides firstly precipitated within the γ-austenite matrix at the incipient stage of aging, and induced the primary age hardening. After aging for 300 min, the lath-type β-Mn phase was formed, leading to the dramatic secondary hardening response. The α-precipitates with partial D0 3 order were subsequently produced at the β-Mn interior, grain/phase boundary region, and the γ-austenite interior after further aging over 10,000 min. The misorientation-angle distribution, Rodrigues–Frank vector space, and orientation relationship stereogram (OR stereogram) from EBSD measurements were employed for analyzing γ-matrix/β-Mn and β-Mn/α-precipitate interphase boundaries, respectively. The OR stereograms showed that the preferred orientation relationships were represented as ( 111 ) γ / / ( 221 ) β − M n , ( 01 1 ¯ ) γ / / ( 01 2 ¯ ) β − M n , ( 2 ¯ 11 ) γ / / ( 5 ¯ 42 ) β − M n for γ-matrix/β-Mn interface, and ( 012 ) β − M n / / ( 001 ) α , ( 02 1 ¯ ) β − M n / / ( 010 ) α , ( 100 ) β − M n / / ( 100 ) α for β-Mn/α-precipitate interface, respectively. The orientation relationships obtained from the OR stereograms were clarified by checking the deviation angle distributions of interface segments from the ideal orientation relationships, as well as the TEM diffraction patterns at the interface boundaries. In addition, the misorientation distribution between γ-matrix and α-precipitate was examined and compared to conventional fcc/bcc orientation relationships.

A cold-work tool steel powder is used to fabricate 3-dimensional objects by selective laser melting using a high-pressure gas atomization process. The spherical powder particles form continuous carbide networks among the austenite matrix and its decomposition products. The carbides comprise Nb-rich ...

We investigated the effect of W addition on the creep and precipitation behavior of alumina-forming austenitic (AFA) heat-resistant steels at 700 °C and 160 MPa. Our results showed that the creep rupture time of the W containing AFA (WAFA) increased more than that of the AFA due to enhanced precipitation hardening of Laves phase and suppression of sigma phase formation. W increased the volume fraction of Laves phase and enhanced precipitation hardening by higher driving force for the precipitation and affinity of the Laves phase. Therefore most W were consumed for the precipitation of the Laves phase, however Mo content contributed to the precipitation of M 23 C 6 as well as precipitation of Laves phase due to the lower affinity of Laves phase. The M 23 C 6 in AFA contained enough Mo to form the sigma phase, which served as an initiation site for cavitation and crack propagation. The sigma phase grew and coarsened at the expense of M 23 C 6 and Mo-rich Laves phase to match the stoichiometric composition of the sigma phase, and finally creep strength of AFA was greatly reduced.

The combined effects of ultrasonic melt treatment (UST) with the cooling rate on the microstructural evolution in a multicomponent Al-14Si-CuNiMg casting alloy was investigated. UST was applied to a melt at 800°C, followed by casting into a steel step mold at cooling rates in the range of 4-32 K/s. UST in the fully liquid state significantly reduced the sizes of the primary phases (the phases formed before Al) crystallized in the initial stage of solidification, and the structural refinement by UST became more pronounced for a faster cooling. With trace additions of Ti, V and Zr, the primary phase is most likely (Al,Si)3(Zr,Ni,Fe), and primary Si and then Al3Ni are sequentially formed upon solidification. AlP particles, well-known nucleants for primary Si, were also found to exist inside the (Al,Si)3(Zr,Ni,Fe) and Al3Ni which exhibited a very low lattice misfit with AlP (~0.7 and 4.7%, respectively). This importantly suggests that AlP can nucleate all the primary phases while it has the highest efficiency of structural refinement by UST for (Al,Si)3(Zr,Ni,Fe) phase that first nucleated in the molten metal. The nucleation of the primary phases was quantified using an analytical model based on exponential statistics. The hierarchical refinement operated by UST is further discussed.

In this work, high-cycle fatigue property of high nitrogen steels which have different deformation modes was explored. The samples, Fe-18Cr-10Mn-0.4N (0.4N) and Fe-18Cr-10Mn-0.6N (0.6N), were fabricated under different nitrogen partial pressures in order to obtain the different deformation modes by controlling stacking fault energy: Deformation-Induced Martensite Transformation (DIMT) in 0.4N and deformation twins in 0.6N. Owing to solid solution strengthening of nitrogen, the fatigue limit of 0.6N is higher than that of 0.4N. However, a ratio of the fatigue limit to the yield strength of 0.6N is lower than that of 0.4N. This result is ascribed to the different influence of the deformation modes on fatigue damages. The DIMT formed in 0.4N could restrict the path of moving dislocations, and thus the fatigue property was relatively improved with the decrease of the fatigue damages by the DIMT. The deformation twins, on the other hand, were not clearly activated during fatigue of 0.6N, and therefore did not affect the fatigue damages.

Damages on shear cutting blades were analyzed after 50,000 strokes of trimming on an ultra high-strength steel sheet. Traditional D2 alloy and an advanced one (Cr08H) based on the composition of 1C-8Cr were quenched from 1030 °C, tempered at 180 °C and submitted to the shear cutting test. Cr08H had lower hardness, a smaller volume fraction of M 7 C 3 carbides while it contained a larger volume fraction of retained austenite. And these resulted in more scratches and rounded edges because of degraded resistance to wear and local plastic deformation. In spite of higher impact toughness, Cr08H exhibited inferior resistance to chipping which was the consequence of localized brittle fracture. It could be concluded that this was caused by more transformation of austenite as well as by insufficiently hardened matrix, both of which were attributed to inappropriate conditions of the heat treatment.

Twinning in face-centered cubic materials has received increasing attention owing to its favorable contributions to materials properties. While the models designed to account for twin nucleation have been mainly concerned with deformation twinning under external stress, addressing autocatalytic nucleation of twin (self-twinning) remains a challenge. Here, we report experimental evidences and a dislocation-based model demonstrating that a new source for twinning (self-twinning) operatives during solid-state decomposition. The initial stage of self-twinning is a stress relaxation process to relieve the local stress concentration caused by pile-up of interfacial dislocations at the precipitate-matrix interface. Dynamical two-beam analyses on dislocations configurations showed that three types of partial dislocations were involved in self-twinning: two Shockley partials, 1 6 [ 112 ] on primary ( 11 1 ¯ ) plane and 1 6 [ 11 2 ¯ ] on conjugate (111) plane; a stair-rod dislocation of 1 6 [ 110 ] connecting primary and conjugate planes. We further show that the thermally-activated cross-slip of Shockley partials with aid of stair-rod dislocation plays a crucial role in self-twinning process.

Mechanically induced martensitic transformation (MIMT) and consequent plastic flow behavior with respect to austenitic texture were investigated in a lean duplex stainless steel. Different grain sizes and textures with fixed phase fractions were obtained via varying the thermomechanical processes. Nearly random distribution of austenitic orientation exhibited a distinguished flow curve from the others with a major D {4 4 11}〈11 11 8〉 component due to more gradual enhancement of hardening by less martensitic transformation. In order to compare the susceptibility to the transformation with respect to individual austenitic orientations and the experimental textures, interaction energy between the imposed stress and transformation strain was calculated by a classical transformation and a crystal plasticity model. The results indicated that a larger stress imposed on the D component led to higher interaction energy and a steeper progress of MIMT observed in the textured materials.

The deformation behavior of alumina-forming austenitic heat-resistant steels at high temperatures was studied to elucidate their hot workability using two types of alloys, i.e. AFA and MAFA. Uniaxial compression tests were performed between the temperature range of 800–1100 °C with strain rates of 0.005–5.0 s− 1. From the constitutive relationship between flow stress, temperature and strain rate, the activation energies for hot deformation were estimated. Both of the investigated alloys exhibited higher activation energies (AFA: 618.8 and MAFA: 711.1 kJ/mol) than other conventional alloys under similar conditions. Processing maps based on dynamic material model and microstructures after the tests indicated that the hot working of both alloys became more efficient and stable with increasing temperature and decreasing strain rate, which was attributed to more active operation of restoration processes such as dynamic recovery and recrystallization. In both alloys, secondary NbCs were precipitated during the test. Due to their pinning effect on dislocations, grain and sub-grain boundaries, the progress of restoration processes was hindered, which contributed to their high activation energy. In spite of the common types of restoration processes, MAFA with increased Nb and C content exhibited degraded hot workability due to more extensive precipitation of NbC.

The precipitation behavior and creep properties of lower phosphorus (P) alumina-forming austenitic (AFA LP ) heat-resistant steel were investigated and compared to those of AFA. The creep rupture time and hardness of the investigated steels were improved with the decrease of the P content. The TEM and EELS analyses confirmed an enhanced P concentration in the M 23 C 6 precipitates along the grain boundaries. The P promoted the precipitation of M 23 C 6 and also suppressed the precipitation of secondary NbC in the earlier stage of aging. The creep rupture time of AFA became shorter compared to AFA LP due to the reduction in the fraction of secondary NbC which acts as a dominant strengthening phase during creep. The suppression of secondary NbC precipitation by P increased the Nb content in the austenite matrix and accelerated the precipitation of the Laves phase in the intermediate stage. However, the difference in Vickers hardness caused by Laves phase was not large in both alloys because the volume fraction of Laves phase strongly depended on the nominal content of Mo rather than Nb. The Vickers hardness at the earlier stage is determined by the precipitation of secondary NbC and the difference of the hardness maintained at the final stage. Thus, it is found that P degrades the creep rupture time and P is a detrimental element in terms of creep and precipitation hardening in AFA steels.

The β-Mn formation behavior of high-Mn low-density steels was investigated in terms of the morphological characteristics and alloying element distribution after aging treatments. A dramatic difference in the formation kinetics and morphology of β-Mn was observed depending on the addition of Al, which may increase the driving force for β-Mn formation. In addition, the effects of the aging process on the fracture behavior were examined in uniaxial tensile tests combined with microstructural observations. A severe loss of ductility resulted from the β-Mn formation and ordering of ferrite into the D03 phase, which was transformed before the β-Mn formation process.

The feasibility controlling the morphology of retained austenite in TRIP steel was investigated utilizing double bainitic transformation which is two-step isothermal heat treatment. The change in morphology of the retained austenite from a blocky to film type improved the tensile properties owing to higher mechanical stability of film-like retained austenite.

A trace addition of Zr to a multicomponent Al-14Si-3Cu-4.5Ni casting alloy has often been found to form a coarse plate-like Zr-rich intermetallic compound with a size of a few tens of μm at the beginning of solidification. Evaluation of the phase composition has confirmed that the Zr-rich intermetallic phase consists of multicomponent constituent elements, mainly Al, Si, Ni and Fe, and is present in a form of (Al,Si)3(Zr,Ni,Fe). The existence of such a complex (Al,Si)3(Zr,Ni,Fe) phase has not yet been predicted by phase equilibria calculation of the multicomponent Al-14Si-CuNiMg systems. In this paper, transmission electron microscopy studies combined with electron backscattered diffraction pattern analysis reveals the crystallography information of the (Al,Si)3(Zr,Ni,Fe) phase for the first time and identifies it as a modified Al3Zr-D023 crystal (tetragonal, I4/mmm(139)) with slightly changed lattice parameters of a = b = 3.275 A and c = 15.475 A. The primary (Al,Si)3(Zr,Ni,Fe) phase is found to nucleate directly onto AlP particles. The mechanical properties of the Zr-rich intermetallics were also investigated using nanoindentation at both room and elevated temperatures and were compared to those of the Si phase.

The microstructure and the intrinsic mechanical behavior of an austenite-based lightweight steel containing 11.4 wt.% Al under aging heat treatment were investigated with respect to β-Mn precipitation. The solution-treated lightweight steel samples were aged at 550 °C for various periods of time. The β-Mn phase nucleated at both ferrite/austenite phase boundaries and austenite/austenite grain boundaries after aging for 300 min, and grew extensively into the austenite matrix with lath-type morphology by further aging treatment. Lattice expansion of austenite and κ-carbide after β-Mn precipitation was observed by X-ray diffractometry (XRD) peak shift. This result suggested that the β-Mn phase expelled carbon to the austenite matrix during formation of β-Mn, which increased the lattice parameter of the austenite and κ-carbide. The Vickers hardness increased dramatically after an aging time of 1000 min. The singular aging behavior also proceeded from precipitation of the β-Mn phase. The intrinsic mechanical property of austenite phase, which was obtained by nanoindentation, was correlated with the increase and inhomogeneous distribution of carbon in the austenite matrix.

Hot ductility of medium carbon steel containing 0.52 wt% of carbon and 0.11 wt% of vanadium was investigated using a hot tensile test performed up to fracture. The hot ductility was evaluated by measuring the reduction of area of the fractured specimens, which were strained at a variety of test temperatures in a range of 600–1100 °C at a strain rate of 2×10 −3 /s. The hot ductility was excellent in a temperature range of 950–1100 °C, followed by a decrease of the hot ductility below 950 °C. The hot ductility continued to drop as the temperature was lowered to 600 °C. The loss of hot ductility in a temperature range of 800–950 °C, which is above the Ae 3 temperature, was due to V(C,N) precipitation at austenite grain boundaries. The further decline of hot ductility between 700 °C and 750 °C resulted from the transformation of ferrite films decorating austenite grain boundaries. The hot ductility continued to decrease at 650 °C or less, owing to ferrite films and the pearlite matrix, which is harder than ferrite. The pearlite was transformed from austenite due to relatively high carbon content.

Corrosion behavior of extruded Mg and Mg5Sn (in wt%) alloy was investigated, and a passivated surface of the Mg5Sn was examined. Immersion test in a 0.6 M NaCl solution revealed that corrosion of the Mg was significantly faster than the Mg5Sn alloy, and vigorous H2 evolution was accompanied with the severe corrosion of Mg. Polarization tests confirmed that cathodic reaction was inhibited in the Mg5Sn alloy. It was considered that the decreased H2 evolution of the Mg5Sn alloy was attributed to the formation of Sn-accumulated layer between the passive film and matrix, which was examined by an XPS analysis.

High-temperature tensile and creep properties of W-added Alumina-Forming austenitic (AFA W ) heat-resistant steel were investigated as compared with AFA steel without W. High-temperature tensile properties of two steels were similar to each other, but creep lifetime of AFA W steel was increased. Microstructural examination using SEM and TEM revealed that creep rate rapidly decreased when Laves phase initially precipitated. This indicated that the precipitation of Laves phase played an important role in hardening of AFA steel. It is also found that AFA W steel exhibited finer and denser Laves phase compared with AFA steel, which is due to partial substitution of W for Mo. The finer and denser distribution of Laves phase contributed to improved creep properties of AFA W steel by enhancement in precipitation hardening.

The precipitation sequence during ageing of Fe–14Cr–20Ni–0.9Nb–2.5Al based alumina-forming austenitic (AFA) steel was explored through a transmission electron microscopy analysis and a small angle neutron scattering experiment. The samples were aged at 700 °C for up to 504 h. Particles of NbC, M 23 C 6 and Ni 3 Al-type L1 2 were observed in the early stage of ageing. Metastable L1 2 particles were formed both in grain interior and along grain boundary. M 23 C 6 carbides precipitated along grain boundary accompanied with precipitation of L1 2 particles. After ageing for longer than 48 h, particles of B2-NiAl and Laves-Fe 2 Nb were newly formed. We suggest the possibility of phase transition from L1 2 to B2 with increase in ageing time. Finally, this study examined the change of mechanical properties during ageing through a Gleeble hot tension test and a Vickers hardness test, and then the relationship between precipitation behavior and mechanical properties was carefully investigated and discussed in terms of precipitation behavior.

We grew Pt films on TiO2-terminated SrTiO3 (001) by atomic layer deposition, using trimethyl(methylcyclopentadienyl)-platinum(IV) as the Pt source and O2 and O3 as the oxidants. The orientation of the Pt films grown with O2 varied from (111) to (001) as the growth temperature was increased from 220 to 350 °C, while the Pt films grown with O3 have a strong preference for the (111) orientation even at a high growth temperature of 350 °C. The difference in the orientation of the Pt films on SrTiO3 (001) was attributed to changes in the degree of chemical bonding across the Pt/SrTiO3 interface with respect to the oxidant. We observed an increase in Pt–O bonding at the interface between the Pt grown with O3 and the SrTiO3 substrate. The interfacial energy of Pt (111)∥SrTiO3 (001) may have been significantly decreased by the increase in Pt–O bonding at the interface, which eventually led to the strong (111) preference of the Pt grown with O3. The findings provide the possibility of controlling the orientation o...

This study aimed to present the complete history of carbide evolution in a cold-work tool steel along its full processing route for fabrication and application. A sequence of processes from cast to final hardening heat treatment was conducted on an 8% Cr-steel to reproduce a typical commercial processing route in a small scale. The carbides found at each process step were then identified by electron diffraction with energy dispersive spectroscopy in a scanning or transmission electron microscope. After solidification, MC, M 7 C 3 and M 2 C carbides were identified and the last one dissolved during hot compression at 1180 °C. In a subsequent annealing at 870 °C followed by slow cooling, M 6 C and M 23 C 6 were added, while they were dissolved in the following austenitization at 1030 °C. After the final tempering at 520 °C, fine M 23 C 6 precipitated again, thus the final microstructure was the tempered martensite with MC, M 7 C 3 and M 23 C 6 carbide. The transient M 2 C and M 6 C originated from the segregation of Mo and finally disappeared due to attenuated segregation and the consequent thermodynamic instability.

Two types of advanced cold-work tool steels were characterized and compared. A higher-alloyed ledeburitic steel with primary carbides (denoted as 9Cr) and a lower-alloyed steel without primary carbides (5Cr) were fabricated by vacuum induction melting and subsequent hot forging. They were spheroidizing-annealed at , quenched at and tempered at 180 or . Their machinability after annealing and hardness, impact toughness, wear resistance after tempering were compared and interpreted in association with their characteristic microstructures. After annealing, 5Cr showed higher resistance to machining due to higher ductility and toughness in spite of lower strength and smaller carbide volume. Owing to smaller carbide volume fraction and the absence of coarse primary carbides, 5Cr showed even better impact toughness although the hardness was lower. The improved toughness of 5Cr resulted in excellent wear resistance, while smaller volume fraction of retained austenite also contributed to it.

The bulky oxide nodule and its underlying structure were investigated in an alumina-forming austenitic steel exposed to dry air at 1053 K for 336 h. Some bulky oxide nodules were found to be attached on globular phases in the matrix. By combined application of electron backscattering diffraction and energy dispersive X-ray spectroscopy, the bulky nodule was identified as Cr-rich M3O4 underlying which was Nb-rich MO2. Thermodynamic calculation suggested that the MO2 was transformed from the primary NbC near surface.

The relationships between the martensitic phase transformation kinetics, texture evolution, and the microstructure development in the parent austenite phase were studied for a 304L stainless steel that exhibits the transformation-induced plasticity effect under biaxial loading conditions at ambient temperature. The applied loading paths included: pure torsion, simultaneous biaxial torsion/tension, simultaneous biaxial torsion/compression, and stepwise loading of tension followed by torsion (i.e., first loading by uniaxial tension and then by pure torsion in sequence). Synchrotron X-ray and electron backscatter diffraction techniques were used to measure the evolution of the phase fractions, textures, and microstructures as a function of the applied strains. The influence of loading character and path on the changes in martensitic phase transformation kinetics is discussed in the context of (1) texture-transformation relationship and the preferred transformation of grains belonging to certain texture components over the others, (2) effects of axial strains on shear band evolutions, and (3) volume changes associated with martensitic transformation.