Pct Cr Research Articles

Identification of Precipitate Phases in an 11 Pct Cr Ferritic and Martensitic Steel after Thermomechanical Treatment

Identification of Precipitate Phases in an 11 Pct Cr Ferritic and Martensitic Steel after Thermomechanical Treatment

Influence of Cooling Rate After Destabilization on Microstructure and Hardness of a High-Cr Cast Iron

AbstractThis study investigates the impact of cooling rate after destabilization at 980 °C on the microstructure of 23 wt pct Cr–2.7wt pct C hypoeutectic high-Cr cast iron. Lowering cooling rate intensifies the secondary carbides formation, depleting carbon in austenite. This raises the martensite start temperature and lowers the bulk hardness. We thereby provide evidence explaining the origin of the sensitivity to cooling rate in high-Cr cast irons.

Potentials of surface modified biochar for removal of Cr from tannery effluent and its regeneration to ensure circular economy

Industries play a substantial role in contaminating the freshwater sources. This study was performed to appraise the potential of biochar activated with 85% phosphoric acid was used as chemisorbent for the removal of Chromium III and VI (Cr III and VI)) and desorbed chromium was utilized for replacing the conventional basic chromium sulfate to ensure circular economy. In our previous studies, the factors for biosorption of Cr were optimized through Box–Behnken model under Response Surface Methodology. Batch adsorption studies revealed that the optimum conditions for maximum Cr (VI) biosorption by activated biochar is pH = 2, biosorbent dose: 1%, biosorbent size: 1 mm, solute concentration: 985 mg L−1 and reaction time 35 h. Based on these results a column experiments were carried out and flow rate was optimized as 0.5 ml m−1 where prominent “S” shaped breakthrough curves were noticed. The predicted values under Thomas model for the adsorption of Cr was 3827.2 µg g−1, which was in close agreement with experimental value of 3566.1 µg g−1. The percent Cr sorption varied from 70.05 to 88.75% in first cycle and showed decreasing trend in the subsequent cycles. The elutant 0.5 M H2SO4 desorbed 89.56% of chromium furthermore eluted chromium was utilized for leather tanning. Reusing of recovered chromium for tanning experiments does not alter the leather Tensile (240.82 kg cm−2) and tear strengths (32.41 kg mm−1). This study suggested that recovered chromium from biosorbent can be well utilized for leather tanning to attain the leather of equivalent qualities as that of conventional methods which could save 20–22% of the production cost besides defending the environment from Cr contamination.

Destabilization Treatment and Its Influence on Microstructure and Matrix Hardness of High-Cr Cast Iron

AbstractHigh-chromium cast irons are an essential class of wear-resistant materials commonly used for wear-resistant applications in the mining and steel industries. There is ongoing debate on the secondary carbide types and their formation sequences during heat treatment. This work examines the microstructural evolution during destabilization treatment of a hypoeutectic high-chromium cast iron containing 2.2 wt pct C and 16.5 wt pct Cr. Starting from an inhomogeneous as-cast microstructure consisting of ~ 28 pct M7C3 eutectic carbide and a mixed matrix of martensite and retained austenite, destabilization treatments resulted in the establishment of near homogeneous structure with a near equilibrium level of carbon concentration in the matrix, which fully transformed to martensite upon cooling. Homogeneously distributed M23C6 secondary carbides with a square-shaped morphology and 100 to 500 nm in size precipitated during heating up to the destabilization temperature. For higher destabilization temperatures (1000 °C), M7C3 secondary carbides formed together with M23C6 and were identifiable by a distinctly different morphology (elongated). It was found that the carbon content of the matrix, a function of the destabilization temperature and subsequent eutectic carbide dissolution, controls the martensite start temperature and has a dominating influence on bulk-hardness.

Microstructural Evolution of a Re-Containing 10% Cr-3Co-3W Steel during Creep at Elevated Temperature

Ten percent Cr steels are considered to be prospective materials for the production of pipes, tubes, and blades in coal-fired power plants, which are able to operate within ultra-supercritical steam parameters. The microstructural evolution of a Re-containing 10% Cr-3Co-3W steel with low N and high B content during creep was investigated at different strains at 923 K and under an applied stress of 120 MPa using TEM and EBSD analyses. The studied steel had been previously normalized at 1323 K and tempered at 1043 K for 3 h. In the initial state, the tempered martensite lath structure with high dislocation density was stabilized by M23C6 carbides, NbX carbonitrides, and M6C carbides. At the end of the primary creep stage, the main microstructural change was found to be the precipitation of the fine Laves phase particles along the boundaries of the prior austenite grains, packets, blocks, and martensitic laths. The remarkable microstructural degradation processes, such as the significant growth of martensitic laths, the reduction in dislocation density within the lath interiors, and the growth of the grain boundary Laves phase particles, occurred during the steady-state and tertiary creep stages. Moreover, during the steady-state creep stage, the precipitation of the V-rich phase was revealed. Softening was in accordance with the dramatic reduction in hardness during the transition from the primary creep stage to the steady-state creep stage. The reasons for the softening were considered to be due to the change in the strengthening mechanisms and the interactions of the grain boundary M23C6 carbides and Laves phase with the low-angle boundaries of the martensitic laths and free dislocations.

Kinetics of Transformation, Border of Metastable Miscibility Gap in Fe–Cr Alloy and Limit of Cr Solubility in Iron at 858 K

The study was aimed at determination of the position of the Fe-rich border of the metastable miscibility gap (MMG) and of the solubility limit of Cr in iron at 858 K. Towards this end, a Fe73.7Cr26.3 alloy was isothermally annealed at 858 K in vacuum up to 8144 hours and Mössbauer spectra were recorded at room temperature after every step of the annealing. Three spectral parameters viz. the average hyperfine field, 〈B〉, the average isomer shift, 〈IS〉, and the probability of the atomic configuration with no Cr atoms in the two-shell vicinity of the probe Fe atoms, P(0,0), gave evidence that the transformation process took place in two stages. All three parameters could have been well described in terms of the Johnson–Mehl–Avrami–Kolmogorov equation, yielding kinetics parameters. The first stage, associated with the phase decomposition, proceeded much faster than the second stage, associated with the alpha-to-sigma phase transformation. The most reliable estimation of the position of the MMG and that of the value of the Cr solubility limit was obtained from the annealing time dependence of 〈B〉, namely 24.5 at. pct Cr for the former and 20.3 at. pct Cr for the latter. A comparison of these figures with the recent phase diagrams pertinent to Fe–Cr system was done.

Compaction Effort Evaluation of Crumb Rubber Modified Hot Mix Asphalt

The primary goal of this study was to obtain the same performance from an asphalt mixture made using a Marshall impact hammer (MIH) as from asphalt made using a Superpave gyratory compactor (SGC). This was due to the expense of Superpave equipment compared with Marshall equipment. A wet process was used to blend the CR with PG 70-16 asphalt. A crushed stone aggregate was used with a 19 mm nominal maximum aggregate size, and the samples were prepared using an SGC and an MIH. The results show that nine percent CR was determined to be the optimum crumb-rubber content (OCRC). In addition, the SGC provided excellent performance in Marshall stability, density, tensile strength, and compressive strength at different numbers of blows and gyrations compared with the MIH. Moreover, the MIH required approximately 21, 21, 18, and 24 extra blows to obtain the same stability, density, tensile strength, and compressive strength, respectively, as the SGC at the design number of gyrations (Ndesign). Furthermore, modified mixtures at the OCRC increased the compressive strength in the range from 16 to 48 percent and had higher values on the index of retained strength than unmodified mixtures. As a result, they provided mixtures with less susceptibility to moisture damage. The significance of this study is that asphalt that performed the same as Superpave samples was obtained using only Marshall equipment.

Investigation on Corrosion Behavior of Simulated Welding HAZ for 22 pct Cr Lean Duplex Stainless Steel With Different Mn/N Ratio Addition

Investigation on Corrosion Behavior of Simulated Welding HAZ for 22 pct Cr Lean Duplex Stainless Steel With Different Mn/N Ratio Addition

Adsorption of Cr(V) from aqueous solution using eggshell-based cobalt oxide- zinc oxide nano-composite

In the present work, eggshell-based zinc oxide-cobalt oxide (ES-ZC) nanocomposite was synthesized and used for removal of Cr(VI) from an aqueous solution. The synthesized nanocomposite was characterized using SEM, FTIR, and XRD. The specific surface area of the nanocomposite was also measured using BET and its point of zero charge was determined using a standard method. The effects of adsorption process parameters (adsorption time, pH of solution, adsorbent dose, and initial Cr(VI) concentration) on the response (percent Cr(VI) removal) were investigated using a batch adsorption system. The Cr(VI) adsorption percentage increases with adsorbent dosage. The Cr(VI) adsorption percentage rapidly increases as adsorption time increases from 30 to 90 minutes, however, further increases in adsorption time does not significantly affect the Cr(VI) removal performance. The optimum pH for Cr(VI) adsorption was observed at 2.0, however, a further increase in pH results in a reduction of Cr(VI) removal. Similarly, the initial Cr(VI) concentration negatively affects its removal percentages. The effects of the adsorption process parameters were investigated and optimum Cr(VI) adsorptions were obtained using Response Surface Methodology (RSM) applying Central Composted Design (CCD). The optimum Cr(VI) percent removal obtained by RSM was 94.8% at adsorption time of 90 minutes, pH of 2, adsorbent dose of 1.5 g/L, and initial concentration Cr(VI) of 45 mg/L. The experimental Cr(VI) percent removal at this condition was 93.5 % showing its agreement with the predicted value. . This shows the model can sufficiently estimate the percent of Cr(VI) removal. Moreover, the adsorption kinetics was correlated with pseudo-second-order with R2 value of 0.989. Further, Langmuir isotherm model better fits the current adsorption process with R2 value of 0.999.

To Investigate Mechanical Properties of Al-based Composite Reinforced with Waste Product

The most common use for aluminium metal matrix composite, or AMMC, is variety of industrial submissions, including those in aerospace, automotive, marine, and sports industries, amongst many others. The most important reinforcing components for manufacturing AMMC are SiC, aluminium oxides, MnO, graphene, and carbon nano tubes, since these components are often used in practice. This article’s goal is to build AMMCs that are reinforced with Silicon carbide (SiC) and Alumina (Al2O3). In order to make AMMC, a procedure known as stir casting is used. Since the last several years, increased attention has been placed on the preparation of AMMCs employing agro waste as reinforcing materials. Examples of such waste are rice husk and/or SiC. As soon as the Al-matrix material has been melted using this method and churned violently, reinforcing material is added to one side of this vortex, creating a spherical structure. The AMMCs may be prepared via a procedure called stir casting, which involves a violent and whirling motion. In the beginning, the furnace is used to melt the aluminium alloy (AA3105) when the metal is in a semisolid state. The reinforcing materials, also known as SiC and Alumina (Al2O3), are warmed to temperatures of 260 and 220 degrees Celsius, respectively. According to the findings of AMMC, tensile strength and hardness of material both rose by 22.41 percent and 45.5 percent, respectively, when they were reinforced with 4.75 weight percent of each kind of reinforcement (SiC, Al2O3, and 1 percent Cr). When 1 percent Cr, 4.75 weight percent SiC, and 4.75 weight percent Al2O3 of composite material are used.

Significance of nutrition in hemodialysis patients with peripheral arterial disease evaluated by skin perfusion pressure

BackgroundPeripheral artery disease (PAD) is a serious complication in hemodialysis (HD) patients. Low skin perfusion pressure (SPP) is a useful marker for detecting PAD. Malnutrition is an important cause of intractable complications. We examined the relationship between low SPP and various indicators of nutritional status.MethodsA total of 120 patients on maintenance HD were enrolled for SPP measurement. SPP was measured at the soles of both feet during HD, and patients were divided into low SPP (L-SPP) and normal SPP (N-SPP) groups by 50 mmHg. The following values were determined by averaging four blood samples taken before SPP measurements every 3 months for one year: hemoglobin, total protein, albumin (Alb), total cholesterol, urea nitrogen, creatinine (Cr), potassium, calcium, phosphate, intact parathyroid hormone, iron (Fe), transferrin saturation (T-SAT), and C-reactive protein (CRP). We calculated the percent Cr production rate, dialysis index (Kt/V), normalized protein catabolic rate (nPCR), geriatric nutritional risk index (GNRI), and estimated salt intake using the required formulas. In addition, the age, body mass index, and presence of diabetes mellitus (DM) were compared between both groups along with all other measurements. Data were expressed as the mean ± standard deviation or median with interquartile range as appropriate. Differences in continuous variables between the two groups were analyzed by Student’s t-test or Wilcoxon’s rank-sum test, as appropriate. Multivariate logistic analysis and receiver operating curve (ROC) analysis were performed for significant variables. The results were expressed as odds ratios with respective 95% confidence intervals (CIs).ResultsThe enrolled patients were 82 men and 38 women, with a mean age of 66.9 ± 13.3 years and HD duration of 4.76 (2.13–12.28) years (median interquartile range). Twenty patients belonged to the L-SPP group, suggesting PAD. Comparison between the L-SPP and N-SPP groups showed significant differences in age, Cr, Fe, T-SAT, CRP, nPCR, GNRI, DM, and estimated salt intake. When the GNRI, estimated salt intake, CRP, and DM were applied as independent variables for multiple logistic regression analysis, the GNRI (odds ratio: 0.857, 95% CI 0.781–0.941, p = 0.001), CRP (2.406, 1.051–3.980, p = 0.035), and DM (9.194, 2.497–33.853, p = 0.001) were found to be significant for L-SPP, and a cutoff level of 92.1 (sensitivity 80%, specificity 72%, AUC: 0.742, 95% CI 0.626–0.858, p = 0.001) in the GNRI obtained by ROC was consistent with the risk index in the elderly presented previously.ConclusionsSPP measurement is an essential tool for detecting high-risk PAD in maintenance HD, which is affected by malnutrition, DM, and inflammation. The GNRI is important for the determination of malnutrition.

Effect of Stress on Spinodal Decomposition in Binary Alloys: Atomistic Modeling and Atom Probe Tomography

Self-organizing nanostructure evolution through spinodal decomposition is a critical phenomenon determining the properties of many materials. Here, we study the influence of stress on the morphology of the nanostructure in binary alloys using atomistic modeling and atom probe tomography. The atomistic modeling is based on the quasi-particle approach, and it is compared to quantitative three-dimensional (3-D) atom mapping results. It is found that the magnitude of the stress and the crystallographic direction of the applied stress directly affect the development of spinodal decomposition and the nanostructure morphology. The modulated nanostructure of the binary bcc alloy system is quantified by a characteristic wavelength, lambda . From modeling the tensile stress effect on the A-35 at. pct B system, we find that lambda _{001}< , lambda _{111}< , lambda _{101}< , lambda _{112} and the same trend are observed in the experimental measurements on an Fe-35 at. pct Cr alloy. Furthermore, the effect of applied compressive and shear stress states differs from the effect of the applied tensile stress regarding morphological anisotropy.

Evolution of the Non-metallic Inclusions Influenced by Slag-Metal Reactions in Ti-Containing Ferritic Stainless Steel

Laboratory experiment and thermodynamic calculation for the Ti-containing 24 mass pct Cr ferritic stainless steel with a CaO-SiO2-Al2O3-MgO system slag were performed to investigate the effect of slag addition on the inclusion characteristics in molten steel. The morphology, composition, and size evolution of inclusions in steel samples were analyzed in three-dimensional by the electrolytic extraction method and in two-dimensional by the automatic analysis method. The results showed that the Ti content significantly decreased after the slag addition. However, the change of the Si content showed an opposite tendency. The decrease of the Ti content in steel was due to the reduction of SiO2 and Al2O3 in the slag by dissolved Ti in steel. An increase of the TiO2 content in the slag can decrease the Ti loss in steel based on the slag-steel kinetic analysis. The total O content in the steel melt decreased from 62 to 26 ppm, and the steel cleanliness was improved, since the number density of inclusions decreased after the slag refining. The results of a kinetic analysis showed that the rate-determining step of the oxidation of Ti in the steel and the reduction of SiO2 in the slag were the mass transfer on the slag side. In addition, high Ti2O3-containing inclusions were found to be transformed to Cr2O3-Ti2O3-Al2O3 and Cr2O3-Ti2O3-SiO2 system inclusions after the slag addition. The Al2O3 contents in inclusions increased while the Ti2O3 contents decreased with time. However, there were some amount of high melting point inclusions with high Al2O3 content, which were not what we expected. When plotted on logarcxithmic scales, the mole ratio X_{{{text{Al}}_{2} {text{O}}_{3} }} /(X_{{{text{Ti}}_2 {text{O}}_{3} }} cdot X_{{{text{Cr}}_{2} {text{O}}_{3} }} ) values of the inclusions were expressed as a linear function of the a_{text{Al}}^{2} /(a_{Ti}^{2} cdot a_{text{Cr}}^{2} cdot a_{text{O}}^{3} ) values of the steel melts with a slope of unity, which was theoretically expected.

Mechanical Properties of Ausformed Carbide-Free Bainite

In this study, the effect of ausforming temperature and strain on the bainite transformation in a model alloy containing 0.39 pct C, 2.0 pct Mn, 1.9 pct Si, and 0.5 pct Cr (mass percent) was investigated. Samples were deformed at 300 °C, followed by isothermal holding to monitor the phase transformation kinetics. Dilatometry results confirm the acceleration of transformation kinetics when the material is deformed to small strains (0.05 to 0.20). Tensile testing results show that, for long isothermal holding times, no improvement in strength or ductility is achieved as a result of ausforming in comparison with the non-deformed state. However, the benefit of ausforming lies in its ability to accelerate the bainite transformation kinetics and to reduce the isothermal holding time needed to avoid premature fracture due to the presence of a high volume-fracture of fresh martensite. Fracture analysis reveals ductile fracture, with cracks along martensitic regions within the microstructure. The distribution of martensite in the final microstructure was associated with bands of Mn segregation. This banding effect was less visible within the ausformed microstructure because bainite was able to nucleate within both the high- and low-Mn regions. A second advantage of ausforming is, therefore, to reduce the microstructure heterogeneity associated with compositional banding within the steel sheets and, by so doing, eliminate crack propagation within the bands. In spite of the fact that ausforming accelerates the bainite transformation kinetics, the required transformation times for the present steel are still too long for use within industrial continuous annealing lines.

Effect of Prior Plastic Deformation on the α-Cr Precipitation in a Binary Ni-Cr Alloy

The effect of prior plastic deformation on the discontinuous precipitation in a supersaturated binary Ni-Cr alloy (42 wt pct Cr) was investigated. Solutionised samples were cold rolled to different extents of reduction (20, 50 and 70 pct) and then subjected to aging heat treatments in the temperature range of 923 K to 1123 K (650 °C to 850 °C) for different time periods, resulting in the precipitation of α-Cr in various morphologies. The α-Cr precipitates were in the form of lamellar discontinuous precipitation, acicular continuous precipitation along the deformation bands, globularization and equiaxed precipitation concurrently with matrix recrystallization. The volume fraction of each morphology varied according to the heat treatments. Overall, the prior plastic deformation had a retarding effect on the kinetics of discontinuous precipitation and accelerated the kinetics of continuous precipitation. The retardation of discontinuous precipitation was attributed to the loss of supersaturation of the matrix due to the other competing modes of precipitation supported by deformation. Plastic deformation prior to aging is shown to be a possible route for engineering the microstructure in this alloy.

Prevention of High-Temperature Surface Degradation in SiMo Cast Irons by Cr and Al Alloying

High silicon molybdenum-alloyed cast irons (SiMo) with spherical graphite are widely used for cast thin-wall exhaust manifolds, worked in high-temperature oxidation environment; therefore, prevention of surface degradation during service is important for such common application. The base SiMo and two alloyed by 1 pct Cr and 3 pct Al cast irons were tested at high temperatures in air and a combustion atmosphere to study the microstructural processes of surface degradation. It was shown that surface degradation of SiMo cast irons involves several microstructural processes, including the formation of multilayered oxide scale and development of internal porosity, resulting in decarburization of graphite nodules. Monitoring weight change of the specimens and Leco C analysis were used for decoupling the rates of surface oxidation and metal matrix decarburization. SEM/EDX analysis was used to study the phase composition of scale and high-resolution TEM analysis was performed to determine the detailed information about the atomic structure of protection layers formed on scale/metal matrix interface. The results were used to qualify and link different surface degradation mechanisms. In the base SiMo cast iron, the protection efficiency of formed amorphous silica layers is limited by intensive decarburization at temperatures above 700 °C. It was shown that Cr and Al alloying prevents surface degradation and suppresses decarburization by developing thermally stable oxide films on metal-scale interface, thus allowed to increase a safe working temperature up to 800 °C in air and the combustion atmosphere.

Magnetic-Field-Induced Liquid–Solid Interface Transformation and Its Effect on Microsegregation in Directionally Solidified Ni-Cr Alloy

The transformation of liquid–solid interface induced by the steady magnetic field (SMF) in the directionally solidified Ni-10 wt pct Cr alloy was studied experimentally. At the moderate pulling rate (50 μm s−1), it could be observed that the interface morphology gradually transformed from planar to cellular shape with increasing the SMF intensity (0 T, 3 T, 6 T). However, the cellular interface at the high pulling rate (100 μm s−1) was not influenced by the SMF. 3D numerical simulations suggested that the transformation of interface morphology originated from the thermoelectric magnetic convection near the wavelike interface at the early stage of solidification. From the composition measurement, it was found that the formation of microsegregation at the moderate pulling rate was associated with the interface morphology. Under the 3 T SMF, the liquid–solid interface remained planar and the microsegregation level increased in comparison with that without the SMF. Under the 6 T SMF, the liquid–solid interface became cellular and the microsegregation level was reduced. The factors affecting microsegregation were evaluated. The effective partition coefficient was estimated based on composition data. It was revealed that the effective partition coefficient increased with the 6 T SMF due to the thermoelectric magnetic and magnetic damping effects within the cellular structure. Additionally, the solid diffusivity was measured using the diffusion couple technique. It was found that the interdiffusion coefficient of Cr decreased with increasing the SMF intensity. The modified Brody model was used to predict the microsegregation behavior in the SMF. The predicted results were in agreement with experimental observation. It could be concluded that the decrease in solid diffusivity enhanced the formation of microsegregation for the planar interface, whereas the increase in effective partition coefficient in the SMF was beneficial for alleviating the extent of microsegregation for the cellular interface.

Microstructural Evolution of Dissimilar Metal Welds Involving Grade 91

Dissimilar metal weld failures between low alloy Cr-Mo ferritic steels and austenitic stainless steels made with Ni-base filler metals are typically observed along the fusion line. Such DMW failures often exhibit the onset of damage well before their expected service life. Failure is typically associated with a carbon-depleted region in the ferritic steel and formation of creep voids along a row of so-called Type I carbides. More recently, the formation of Type I carbides adjacent to a carbide-free ferrite band has also been observed in DMWs where the ferritic steel was a 9 pct Cr creep strength-enhanced ferritic steel. However, it has not been completely clarified whether these microstructural features formed during welding, post-weld heat treatment or service. In this study, single pass bead-on-plate welds were prepared on a Grade 91 steel substrate using commonly specified Ni-base weld metals; ENiCrCoMo-1, ENiCrMo-3, ENiCrFe-3, ENiCrFe-2 and EPRI P87 (ENiFeCr-4) and were characterized in the as-welded, post-weld heat treatment (PWHT) and aged conditions. The evolution of the ferrite band was found to form by a diffusion-controlled process and was observed after PWHT and aging associated with regions exhibiting steep concentration gradients in the partially mixed zone (PMZ). In this study, steep concentration gradients were observed along the toe of the weld whereas relatively shallow gradients were observed at the weld bottom-center, resulting in a discontinuous ferrite band along the fusion line during PWHT and aging. The variation in chemical gradients in the PMZ corresponded to different chemical potential gradients, which lead to differences in carbon diffusion during high-temperature PWHT and aging. The results of this study provide insight into potential solutions for minimizing the risk of failure in future applications.

Computational modeling of the effect of B and W in the phase transformation of M23C6 carbides in 9 to 12 pct Cr martensitic/ferritic steels

The effect of B and W in the precipitation kinetic of M23C6 carbides in martensitic/ferritic steels were studied assisted by ThermoCalc and TC-PRISMA. The simulation predicts that B has low solubility in the austenitic and ferritic matrix, thus promoting the formation of M2B borides and (Cr, Fe)23(C, B)6 carbides. Furthermore, calculation carried out in ThermoCalc shown that M2B borides are stable even at austenization temperature (1100 °C). This suggests that in martensitic/ferritic steels M2B precipitates first, hence consuming most of available B. Additionally, the precipitation kinetics of (Cr, Fe)23C6, (Cr, Fe, W)23C6 and (Cr, Fe)23(C, B)6 were simulated in TC-PRISMA, results obtained predict a higher steady nucleation rate for the latter. When B atoms incorporate to (Cr, Fe)23C6 reduces the interfacial energy from 0.26 J/m2 to 0.17 J m−2, which indicates a smaller misfit between (Cr, Fe)23(C, B)6 carbides and matrix. On the other hand, B and W reduce the coarsening rate of M23C6 carbides by decreasing the interfacial energy and reducing diffusivities, respectively. Theoretical results compared with experimental data of the coarsening rate of (Cr, Fe, W)23(C, B)6 shown that it is one order of magnitude lower than the predicted by TC-PRISMA. This suggests that B can be the rate-controlling element of the coarsening of (Cr, Fe, W)23(C, B)6 carbides instead of W.

Influence of Minor Cr-Additions to the Growth of Columnar Dendrites in Al-Zn Alloys: Influence of Icosahedral Short Range Order in the Liquid

The effect of minute Cr additions on dendritic growth directions in Al-20 wt pct Zn alloy has been investigated. As first evidenced by Gonzales and Rappaz (Metall Mater Trans A 37:2797–2806, 2006) Al-Zn alloys exhibit a Dendrite Orientation Transition (DOT), from 〈100〉 below 25 wt pct Zn to 〈110〉 above 60 wt pct, regardless of the solidification speed. The DOT has been interpreted as a modification of the solid–liquid interfacial energy anisotropy (Gonzales and Rappaz, 2006; Haxhimali et al. in Nat Mater 5:660–664, 2006). However, 0.02 to 0.1 wt pct addition of Cr in Al-20 wt pct Zn drastically modifies the dendrite trunk direction from 〈100〉 to 〈110〉 at low solidification speed, typically 200 μm/s. Even more surprising, 〈100〉 dendrite trunks are retrieved in Al-20 wt pct Zn-0.1 wt pct Cr when the speed is increased to 1000 μm/s, but with the concurrent formation of twinned dendrites. Minute additions of Cr have been reported recently to promote icosahedral short range order (ISRO) in liquid Al-Zn, thus reducing the atomic mobility (Kurtuldu et al. in Acta Mater 115:423–433, 2016) and modifying the nucleation kinetics (Kurtuldu et al. in Acta Mater 61:7098–7108, 2013). The present results indicate that ISRO also modifies the attachment kinetics of icosahedral clusters rather than individual atoms, and is most likely responsible of growth direction change in Al-Zn-Cr alloy and of twinned dendrites formation.