Dendrite Cell Size Research Articles

Multi-physics simulation of non-equilibrium solidification in Ti-Nb alloy during selective laser melting

This paper underscores the critical role of temperature distribution in the molten pool on the resulting solidification microstructure during selective laser melting (SLM) process. A powder-resolved computational fluid dynamics (CFD) model of Ti-Nb alloy is established to investigate heat transfer and fluid flow in the molten pool. When comparing the bulk model to the powder bed model, discrepancies in temperature gradient and cooling rate can reach up to 26.29 % and 18.32 %, respectively. Utilizing the powder bed CFD model, temperature gradient and cooling rate data at the molten pool boundary are integrated into the finite interface dissipation phase-field model. The simulation results illuminate the non-equilibrium solidification microstructure in the SLMed Ti-Nb alloy. Results indicate that the rapid solidification fosters a pronounced solute trapping effect, mitigating solute microsegregation. The microstructure manifests as cellular and dendritic structures, with Nb concentration in cellular cores and depletion in intercellular region. Predicted primary dendrite arm spacing (PDAS) or cell size range between 0.4 to 0.6 μm, consistent with experimental observations. In particular, the study reveals a transition from dendritic to cellular and from cellular to planar structures, with an accompanying analysis of the underlying mechanisms.

Evaluation of aqueous-deficient and evaporative dry eye cases with confocal microscopy

Dry eye disease (DED) is an important health problem affecting hundreds of millions of people worldwide. In vivo confocal microscopy (IVCM) is a non-invasive imaging tool that can visualize ocular surface diseases. In this study, we aimed to evaluate corneal structures and inflammatory cells with IVCM in DED patients. The patients were divided into three subgroups: group 1, consisting of 22 patients with aqueous tear insufficiency; group 2, consisting of 21 patients with evaporative type DED; and group 3, consisting of 20 healthy patients. Imaging was performed with IVCM. The corneal epithelium, nerves, stroma, endothelial and inflammatory cells were compared between groups. There was a significant decrease in corneal epithelial cell density in cases with DED, and there was a significant increase in corneal basal epithelial cell density in the aqueous-deficient type. Keratocyte density was significantly increased in the aqueous-deficient type. A significant decrease in the number and density of sub-basal nerves was found in aqueous-deficient cases, and an increase was found in neural pilling and folding. Dendritic cell density, size, number and area were significantly increased in the aqueous-deficient type. There was also decreased corneal endothelial cell density in DED. We evaluated pathological changes in DED on the corneal surface by IVCM. This methodology is valuable in terms of objectively evaluating how the corneal surface is affected in accordance with disease severity and in predicting poor response to treatment.

Investigations of the processing–structure–performance relationships of an additively manufactured AlSi10Mg alloy via directed energy deposition

In this paper, the microstructure formation mechanism of an AlSi10Mg alloy prepared by laser directed energy deposition (DED-LB) and its influence on the mechanical properties was fully studied. The relationships between the microstructure characteristic scale, the molten pool solidification/thermal cycle conditions, and the tensile mechanical properties were established by combining the numerical simulation, theoretical calculation, and experimental validation. The as-deposited microstructure consists of the columnar α-Al dendritic array growing epitaxially along the building direction with the primary dendritic arm spacing of 18 ± 4.5 µm, the dendritic arm cell of 3 ± 1 µm surrounded by the refined eutectic network, and the Si precipitation of 17.7 ± 0.8 nm dispersed in the α-Al dendritic trunk. The feature size of the primary dendritic arm spacing and the dendritic arm cell size can be well predicted using the Kurz-Fisher and KGT dendritic growth models. The formation and size evolution of the Si precipitation was well described by the non-isothermal aging KWN model for the first time. The as-DED-LB-processed AlSi10Mg alloy exhibits a good comprehensive mechanical property with a yield strength of 187 ± 1.5 MPa and elongation to fracture of 7.4 ± 0.5%. The boundary strengthening from the eutectic phase network, the load-bearing capacity for dislocations caused by refined dendritic arms, and the precipitation strengthening of nano-Si particles play a major role in the improvement of the tensile strength and hardening ability. As a result, a quantitative relationship of the processing–microstructure–performance has been systematically investigated and established, which explores a method for the precision control and large-scale application of DED-AlSi10Mg alloys.

Conceptual principles of roll casting-rolling of high-strength aluminum alloys

This paper presents the results showing the possibility of obtaining thin-sheet billets from a wide range of aluminum alloys by the method of two-roll casting. In the course of the research, an analysis of the technological solutions of the currently known methods of continuous casting and rolling of sheet metal products was performed. At the laboratory installation of two-roll casting of metals, physical and technological parameters (temperature and speed of casting, intensity of heat removal, etc.) have been worked out, which ensure a stable process of obtaining a sheet billet of small thickness (1-5 mm) from the investigated aluminum alloys. For the first time in metallurgical practice, cast sheet billets from wide-interval aluminum alloys EN2024 (Д16) (≥130 °С) and EN7075 (В95) (≥160 °С) were obtained by the roll casting method In the course of research to determine the evolution of the structures of test samples from the studied alloys, their metallographic studies were carried out at all stages of the technological chain "roll casting + hot rolling + heat treatment". Taking into account that there is a hereditary relationship between the primary structure of the cast billets and the quality of the final metal product, it was established that for all studied aluminum alloys, the basis of the structures at the "roll casting" stage is the a-phase. It was established that at the cooling rate characteristic of roll casting, the a-phase in the cast billets has a homogeneous fine-grained structure. At the same time, small inclusions of dispersed intermetallic and eutectic phases, which are present in the structure of cast billets, are evenly distributed along their cross-sections. In order to evaluate the processes occurring in the billets at the "hot rolling" stage, the patterns of changes in the quantitative characteristics of the structures depending on the degree of their deformation were determined, namely: E is the proportion of intermetallic phases; D is the size of intermetallic crystals; A is shape parameter of intermetallics; R is the size of dendritic cells; Ar is a shape parameter of dendritic cells. It was also established that at the stage of "heat treatment" of the test samples after their hot rolling, partial recrystallization of the a-Al solid solution occurs, as well as a decrease in the content of intermetallics and spheroidization of the remaining intermetallic phases. Ultimately, the changes occurring in the structures of the experimental samples had a positive effect on the quality of the final tape, which was confirmed by a relatively higher level of their mechanical characteristics.

Influence of High-Pressure Die Casting Parameters on the Cooling Rate and the Structure of EN-AC 46000 Alloy.

The paper presents the results of the research on the impact of process parameters of high-pressure, cold-chamber die casting of an industrial casting made of aluminium alloy on the casting properties assessed macroscopically by measuring the casting average density and microscopically through the characteristics of the casting microstructure. The analysis covers the influence of three selected velocity settings of the pressing plunger, which determine the filling time, and three values of the compression pressure setting characteristic of the third phase of the casting process. The cooling and solidification simulations of the casting were performed using the ProCAST software. During the simulation tests, the impact of the filling rate of the alloy into the die cavity on the cooling rate and the alloy solidification path at selected points were determined. The conducted research allowed linking the process parameters with the parameters of the casting structure with different wall thicknesses. Metallographic examinations of the castings were carried out using a light microscopy, SEM, and EDS analysis. The fraction of the phases α(Al), the size of dendritic cells, and the size of silicon particles, in the cross-sections of the castings with wall thickness of 3, 6, and 11 mm, respectively, were determined.

Effect of Melt Overheating on Structure and Mechanical Properties of Al-Mg-Si Cast Alloy

The paper discusses the complex effect of melt overheating with subsequent fast cooling down to the pouring temperature on the crystallization process, microstructure and mechanical properties of Al-Mg-Si aluminum alloy. The results obtained facilitated the establishment of rational modes of melt overheating, leading to a significant change in the dispersion and morphology of structural components. In particular, with an increase in the melt overheating temperature to 900 °C with holding and subsequent rapid cooling to the casting temperature, a decrease in the average size of dendritic cells of the aluminum solid solution from 39 μm to 13 μm was observed. We also noticed the refinement of eutectic inclusions of the Mg2Si phase with compact morphology. An increased level of mechanical properties was noted; the maximum values of tensile strength and elongation reached 228 MPa and 5.24%, respectively, which exceeded the initial values by 22.5% and 52.3%, correspondingly. The microhardness of the aluminum solid solution sequentially increased from 38.21 to 56.5 HV with an increase in the temperature during melt overheating. According to the EDS linear scanning, an increase in the superheat temperature of the melt is accompanied by an increase in the degree of saturation of the solid solution with magnesium.

Novel alterations in corneal neuroimmune phenotypes in mice with central nervous system tauopathy

BackgroundTauopathy in the central nervous system (CNS) is a histopathological hallmark of frontotemporal dementia (FTD) and Alzheimer’s disease (AD). Although AD is accompanied by various ocular changes, the effects of tauopathy on the integrity of the cornea, which is densely innervated by the peripheral nervous system and is populated by resident dendritic cells, is still unknown. The aim of this study was to investigate if neuroimmune interactions in the cornea are affected by CNS tauopathy.MethodsCorneas from wild type (WT) and transgenic rTg4510 mice that express the P301L tau mutation were examined at 2, 6, 8, and 11 months. Clinical assessment of the anterior segment of the eye was performed using spectral domain optical coherence tomography. The density of the corneal epithelial sensory nerves and the number and field area of resident epithelial dendritic cells were assessed using immunofluorescence. The immunological activation state of corneal and splenic dendritic cells was examined using flow cytometry and compared between the two genotypes at 9 months of age.ResultsCompared to age-matched WT mice, rTg4510 mice had a significantly lower density of corneal nerve axons at both 8 and 11 months of age. Corneal nerves in rTg4510 mice also displayed a higher percentage of beaded nerve axons and a lower density of epithelial dendritic cells compared to WT mice. From 6 months of age, the size of the corneal dendritic cells was significantly smaller in rTg4510 compared to WT mice. Phenotypic characterization by flow cytometry demonstrated an activated state of dendritic cells (CD86+ and CD45+ CD11b+CD11c+) in the corneas of rTg4510 compared to WT mice, with no distinct changes in the spleen monocytes/dendritic cells. At 2 months of age, there were no significant differences in the neural or immune structures between the two genotypes.ConclusionsCorneal sensory nerves and epithelial dendritic cells were altered in the rTg4510 mouse model of tauopathy, with temporal changes observed with aging. The activation of corneal dendritic cells prior to the gradual loss of neighboring sensory nerves suggests an early involvement of corneal immune cells in tau-associated pathology originating in the CNS.

The Effects of Aging on Corneal and Ocular Surface Homeostasis in Mice.

Aging is a risk factor for dry eye disease. The aim of this study was to investigate if aging is associated with a range of signs of dry eye disease, including tear hyperosmolarity, reduced nerve density, and increased dendritic cell number, in mice. Healthy C57BL/6 female mice, aged 2 months (young, n = 10) and 22 months (aged, n = 11) were used. Clinical assessments included corneal sensitivity (Cochet-Bonnet esthesiometry), tear secretion (Phenol red thread test), tear film osmolarity (TearLab osmometer), and corneal thickness (optical coherence tomography). The sum length of the corneal superficial terminals and sub-basal nerves, density of vertical nerve projections, and density and tree area of resident epithelial dendritic cells, were assessed using immunofluorescence and confocal microscopy. Aged mice had significantly higher tear secretion, lower corneal sensitivity, and a thicker corneal stroma but thinner epithelium. There was no significant intergroup difference for tear osmolarity. Aged mice showed a significantly lower sum length of nerves in the superficial terminals and sub-basal plexus, relative to young mice. Dendritic cell density and morphology were similar in both groups. In mice, aging is associated with higher tear secretion and corneal epithelial thinning, together with lower corneal nerve density and sensitivity. However, aging was not significantly associated with changes to tear osmolarity or dendritic cell density or size, despite a significant reduction in total nerve length. These findings demonstrate that aged mice exhibit some changes to ocular surface parameters that parallel the anomalies evident in dry eye disease.

Microstructural refinement of 355 aluminium alloys by ultrasonic melt treatment (UST)

Chemical grain refining of high-silicon-content aluminium alloys, such as 355 alloy, is impaired by the high silicon content. One solution is the use of ultrasonic melt treatment (UST). This study sought to determine the duration of UST and type of horn (steel or Ti) required to achieve optimal grain refining in these alloys. Samples produced by conventional casting underwent UST for different times with steel and Ti horns and were compared with as-cast samples. For all the conditions studied, analysis of the samples showed that UST is an effective grain refining technique and yields satisfactory values of average grain size and primary and secondary dendrite arm spacing (λ1, λ2) as well as low porosity. The chemical composition of the samples was analysed by SEM–EDS mapping and point analysis to identify the intermetallic phases before and after UST. Best results were achieved after only 20 s of UST with a steel horn. UST for this length of time with a steel horn produced a homogeneous microstructure and possible homogeneous mechanical properties. Grain size was 160 µm; primary dendrite arm spacing, or dendrite cell size, was 130 µm; secondary arm spacing was approximately 18 µm; and Vickers hardness was approximately 95 HV.

INFLUENCE OF CONSUMABLE ELECTRODE ROTATION ON ANISOTROPY OF PROPERTIES OF THE BILLET OBTAINED BY ELECTROSLAG REMELTING

The article presents theoretical substantiation of the influence of electroslag remelting technology with rotation of consumable electrode on physicomechanical properties of the formed casting (billet). The technology of electroslag remelting with rotation of consumable electrode around its own axis leads to formation of upward flow of heat in the slag bath, making hydrodynamic environment in mold more rational from the point of using generated heat. During rotation of consumable electrode, centrifugal forces act on liquid metal film formed at the end of the electrode, providing radial flow of molten metal droplets. Subsequent separation occurs from the outer perimeter of electrode. Thus, drops of electrode metal fall into the metal bath closer to the wall of the mold, aligning temperature front of the bath. Decrease in temperature gradient of bath over the cross section leads to a flatter crystallization front. Studied technology of electroslag remelting with rotation of consumable electrode should have an impact on physical and mechanical properties of resulting casting (billet). In order to establish effect of rotation of consumable electrode during electroslag remelting on properties of metal obtained, experimental remelting was carried out. The article presents data on experimental electroslag remelting of electrodes of 20Kh13 grade steel using various technologies at A-550 unit. In course of experiment, influence of rotation technology of consumable electrode on conditions of remelting process, billet crystallization, changes in mechanical and physical properties was established. The influence of remelting method on complex properties of resulting billet was analyzed. As the main research tool, processing of the obtained data on microhardness, density, dendritic cell size of experimental samples was used. Analysis of the research results of billets in transverse direction showed an increase in microhardness uniformity in implementation of electroslag remelting technology with rotation of consumable electrode along the course of smelting. It is also shown that use of the rotation technology reduces size of dendritic cell of billet and increases density of the ingot formed in comparison with traditional technology without rotating electrode.

CSF1R regulates the dendritic cell pool size in adult mice via embryo-derived tissue-resident macrophages

Regulatory mechanisms controlling the pool size of spleen dendritic cells (DC) remain incompletely understood. DCs are continuously replenished from hematopoietic stem cells, and FLT3-mediated signals cell-intrinsically regulate homeostatic expansion of spleen DCs. Here we show that combining FLT3 and CSF1R-deficiencies results in specific and complete abrogation of spleen DCs in vivo. Spatiotemporally controlled CSF1R depletion reveals a cell-extrinsic and non-hematopoietic mechanism for DC pool size regulation. Lack of CSF1R-mediated signals impedes the differentiation of spleen macrophages of embryonic origin, and the resulted macrophage depletion during development or in adult mice results in loss of DCs. Moreover, embryo-derived macrophages are important for the physiologic regeneration of DC after activation-induced depletion in situ. In summary, we show that the differentiation of DC and their regeneration relies on ontogenetically distinct spleen macrophages, thereby providing a novel regulatory principle that may also be important for the differentiation of other hematopoietic cell types.

Analysis of properties for in situ Al2O3p/A356 composites synthesised from the Al-SiO2 system

ABSTRACTIn situ Al2O3p/A356 composites with different particle volume fractions were successfully synthesised from the Al-SiO2 system by a direct-melt reaction. γ-Al2O3 was first produced during the reaction between Al and SiO2, and the phase transformation from γ-Al2O3 to α-Al2O3 then occurred at higher temperatures (1050°C), resulting in a volume contraction. The α-Al2O3p/A356 composite exhibited a reduction in dendrite cell size that was 1.5–2 greater than for the matrix alloy cast using the same conditions. A 10% particle volume fraction yielded optimum mechanical properties, with values for the yield stress, tensile strength, elongation and microhardness of 132 MPa, 268 MPa, 5.1% and 107.2 HV, respectively. These corresponded to increases 50, 31, 19 and 47%, respectively, when compared to the matrix.This paper is part of a thematic issue on Light Alloys.

Simulation of Centrifugal Casting and Structure of Fe-Ni-Co Super-Invar Alloy

This paper is focused on multi-scale modeling of solidification and alloy microstructure evolution through computer-aided simulation of the technological processes. Microstructure characterization of cast alloy after centrifugal casting including grain size, dendrite cell size and porosity is of interest in this paper. The centrifugal technological process was simulated using special LVMFlow program for computer-aided analysis of casting technologies to predict shrinkage porosity in axi-symmetric part blanks. The cast blanks were made of Fe-Ni-Co alloy with low thermal expansion and after turning could be used as bearing parts in contact with glass or ceramics. A method of combined simulation of technological processes and operating regimes of cast components was developed. The proposed method of simulating the complicated model allows separating the component from casting geometry in CAE postprocessor and the plot distribution of calculated parameters over the component. Also, this method allows varying diameters of hollow cylindrical casting and choosing the best location of components relative to the predicted porosity in the blank for high quality turning. The distribution of temperature and porosity could be used for more precise calculation of internal stresses in cast component under loading conditions with respect to the structural factors. The structural parameter was stated on a base of the calculated temperature fields to associate grain structure of cast alloy with solidification conditions. The austenitic microstructure of Fe-Ni-Co super-invar alloy was studied on the samples, which were cut from the axi-symmetric part after turning the blank. The calculated structural parameter was assigned with the types of grain structure.

Investigation of the microstructure and properties of Al–Si–Mg/SiC composite materials produced by solidification under pressure

Composite materials based on alloys of the Al–Si–Mg system have been obtained via the introduction of 5, 10, and 15 wt % of SiC particles into the alloy melt and the solidification under a pressure. As a result of solidification under pressure, the porosity of the composite materials decreased substantially. An increase in the content of SiC particles in the composites enabled a smaller size of dendritic cells to be obtained. It has been shown by the X-ray diffraction method that, in the process of solidification under pressure, an interaction occurred between the matrix and reinforcing SiC particles. The presence of SiC particles in the structure of composites led to the acceleration of the aging process and to an increase in the peak hardness in comparison with the matrix alloy.

Effect of Ultrasonic Treatment in the Static and Dynamic Mechanical Behavior of AZ91D Mg Alloy

The present study evaluates the effect of high-intensity ultrasound (US) in the static and dynamic mechanical behavior of AZ91D by microstructural modification. The characterization of samples revealed that US treatment promoted the refinement of dendrite cell size, reduced the thickness, and changed the β-Mg17Al12 intermetallic phase to a globular shape, promoted its uniform distribution along the grain boundaries and reduced the level of porosity. In addition to microstructure refinement, US treatment improved the alloy mechanical properties, namely the ultimate tensile strength (40.7%) and extension (150%) by comparison with values obtained for castings produced without US vibration. Moreover, it is suggested that the internal friction, enhanced by the reduction of grain size, is compensated by the homogenization of the secondary phase and reduction of porosity. It seems that by the use of US treatment, it is possible to enhance static mechanical properties without compromising the damping properties in AZ91D alloys.

용체화처리한 AZ91-X%Sn 마그네슘 합금의 부식 저항성 변화

The effects of Sn addition and solution treatment on corrosion behavior were studied in AZ91 magnesium casting alloy. The addition of 5%Sn contributed to the introduction of phase, to the reduction in dendritic cell size and to the increase in the amount of secondary phases. After the solution treatment, trace amount of particles were observed in the -(Mg) matrix for the AZ91 alloy, while phase with high thermal stability was additionally found in the AZ91-5%Sn alloy. Before the solution treatment, the AZ91-5%Sn alloy had better corrosion resistance than the Sn-free alloy, which is caused by the enhanced barrier effect of the () phases formed more continuously along the dendritic cell boundaries. It is interesting to note that after the solution treatment, the corrosion rate of both alloys became increased, but the Sn-added alloy showed higher corrosion rate than the Sn-free alloy. The microstructural examination on the corroded surfaces revealed that the remaining particles in the solution-treated AZ91-5%Sn alloy play a role in accelerating corrosion by galvanic coupling with the -(Mg) matrix.

The Crystal Segregation During Casting of the Alloy AlZn5.5Mg2.5Cu1.5

Abstract In the course of homogenizing annealing of aluminium alloys being cast continually or semi-continually it appears that chemical inhomogenity takes off within separate dendritic cells (crystal segregation). It is about a diffusion process that takes place at the temperature which approaches the liquid temperature of the material. In that process the transition of soluble intermetallic compounds and eutectic to solid solution occurs and it suppresses crystal segregation significantly [1]. The temperature, homogenization time, the size of dendritic cells and diffusion length influences homogenizing process. The article explores the optimization of homogenizing process in terms of its time and homogenizing annealing temperature which influence mechanical properties of AlZn5,5Mg2,5Cu1,5 alloy.

Microstructural Origins of Variability in the Tensile Ductility of Tilt-Pour Permanent Mold Cast Al Alloy at a Warm Temperature

Abstract Light-alloy castings often exhibit variability in the fracture sensitive properties such as ductility that does not necessarily correlate to the global average microstructural parameters such as dendrite cell size and porosity volume fraction in the three-dimensional microstructure. Nonetheless, in numerous such cases, the variability in the fracture sensitive properties does correlate to the variability in the local distributions of microstructural features and processing defects because the fracture path preferentially goes through the regions containing large concentrations of the defects and/or microstructural extrema. This paper presents the results of a detailed quantitative metallography and quantitative fractography based investigation of the relationships between microstructure and variability in uniaxial tensile ductility of the tensile test specimens drawn from very large size Al alloy automotive component castings fabricated using tilt-pour permanent-mold casting process. The percent tensile ductility e shows strong quantitative correlation with the area fraction of the porosity f in the corresponding fracture surfaces, which can be represented by the following power-law relationship, where e0 and n are empirical constants.

Influence of the homogenization annealing on microstructure and mechanical properties of AlZn5,5Mg2,5Cu1,5 alloy

In the course of homogenizing annealing of aluminium alloys being cast continually or semi-continually it appears that chemical in homogeneity takes off within separate dendritic cells (crystal segregation). It is about a diffusional process that takes place at the temperature which approaches the liquid temperature of the material. In that process the transition of soluble intermetallic compounds and eutectic to solid solution occurs and it suppresses crystal segregation significantly. Temperature, homogenization time, the size of dendritic cells and diffusion length influence homogenizing process. The article explores the optimization of homogenizing process in terms of its time and homogenizing annealing temperature which influence mechanical properties of AlZn5,5Mg2,5Cu1,5 alloy.

Microstructure and Mechanical Properties at Room and Elevated Temperatures in AM50-0.3 wt%CaO Alloy

The present study is intended to comparatively investigate the changes in microstructure and tensile properties at room and elevated temperatures in commercial AM50(Mg-5%Al-0.3%Mn) and 0.3 wt%CaO added ECO-AM50 alloys produced by permanent mould casting. The typical microstructure of AM50 alloy was distinctively characterized using two intermetallic compounds, <TEX>${\beta}(Mg_{17}Al_{12})$</TEX> and <TEX>$Al_8Mn_5$</TEX>, along with <TEX>${\alpha}$</TEX>-(Mg) matrix in an as-cast state. The addition of a small amount of CaO played a role in reducing dendrite cell size and quantity of the <TEX>${\beta}$</TEX> phase in the AM50 alloy. It is interesting to note that the added CaO introduced a small amount of <TEX>$Al_2Ca$</TEX> adjacent to the <TEX>${\beta}$</TEX> compounds, and that inhomogeneous enrichment of elemental Ca was observed within the <TEX>${\beta}$</TEX> phase. The ECO-AM50 alloy showed higher hardness and better YS and UTS at room temperature than did the AM50 alloy, which characteristics can be mainly ascribed to the finer-grained microstructure that originated from the CaO addition. At <TEX>$175^{\circ}C$</TEX>, higher levels of YS and UTS and higher elongation were obtained for the ECO-AM50 alloy, demonstrating that even 0.3 wt%CaO addition can be beneficial in promoting the heat resistance of the AM50 alloy. The combinational contributions of enhanced thermal stability of the Ca-containing <TEX>${\beta}$</TEX> phase and the introduction of a stable <TEX>$Al_2Ca$</TEX> phase with high melting point are thought to be responsible for the improvement of the high temperature tensile properties in the ECO-AM50 alloy.