Residual Stress Measurement of Laser-Engineered Net Shaping AISI 410 Thin Plates Using Neutron Diffraction

In an attempt to relate the laser-engineered net shaping (LENS) process parameters, laser power and laser travel speed, to the quality of LENS-produced parts, strain measurements were taken at several predetermined points within seven LENS AISI 410 thin plates using the neutron diffraction method. The residual stresses at these points were then calculated using the measured strain values to ascertain how the internal stress varies as a function of the input parameters and location. It is found that the component of the stress in the vertical direction (i.e., perpendicular to the raster direction of the laser/powder nozzle) is dominant, in agreement with previous reports, and relatively insensitive to variations in process parameters. This was confirmed with numerical simulations performed with a thermomechanical model developed using the commercial program SYSWELD. The simulations also showed a good qualitative agreement with the measured simulated stresses. This article is based on a presentation given in the symposium entitled “Neutron and X-Ray Studies for Probing Materials Behavior,” which occurred during the TMS Spring Meeting in New Orleans, LA, March 9–13, 2008, under the auspices of the National Science Foundation, TMS, the TMS Structural Materials Division, and the TMS Advanced Characterization, Testing, and Simulation Committee.     

Examination of Galvanic Action between Fe-Based Bulk Metallic Glass and Crystalline Alloys

Fe-based bulk metallic glasses (amorphous metals) have been developed, and several compositions are shown to have excellent corrosion resistance in chloride solutions. Further, thermal-spray amorphous metals are being developed for use as a barrier coating layer, to protect substrate materials from corrosion. Galvanic action between dissimilar metals and the coating/substrate for the amorphous-alloy coatings is of practical interest for a number of applications. The mixed-potential theory provides a useful approach for examining the corrosion behavior of the component materials in the galvanic couple and is applied in this study. Galvanic action was studied for an Fe-based structurally amorphous metal (SAM) 1651 and several crystalline alloys that included 1018 C-steel, stainless steel (SS) 316L, and alloy 22. Anodic and cathodic polarization curves of each of the metals were measured by potentiodynamic polarization. Based on the mixed-potential theory, the behavior of the component materials in a galvanic cell was predicted. The predictions are compared to the measured behavior of galvanic couples with the crystalline alloys. This article is based on a presentation given in the symposium entitled “Iron-Based Amorphous Metals: An Important Family of High-Performance Corrosion-Resistant Materials,” which occurred during the MSandT meeting, September 16–20, 2007, in Detroit, Michigan, under the auspices of The American Ceramics Society (ACerS), The Association for Iron and Steel Technology (AIST), ASM International, and TMS.     

Indentation Behavior of Zr-Based Metallic-Glass Films via Molecular-Dynamics Simulations

Molecular dynamics (MD) models of the Zr-based metallic-glass film (Zr₄₇Cu₃₁Al₁₃Ni₉, in atomic percent) were constructed by simulating sputter depositions on the titanium substrate. The as-deposited films were used as initial structures for subsequent nanoindentation simulations. For the deposition simulations, a many-body, tight-binding (TB) potential was adopted for interatomic interactions among the multiple species of atoms. The interactions between the metallic atoms and working gas (Ar⁺) were modeled with the pairwise Moliere potential. The TB potential parameters for unlike atoms were chosen to be the algebraic average of those for like ones, and hence, the MD simulations provide qualitative information. The deposition simulations revealed an amorphous morphology in the as-deposited films. Indentation simulations with a right-angle conical indenter tip showed a homogeneous flow to form pileups on the surface of the metallic glass around the indent. The pileup index calculated from MD is consistent with that obtained from the experiment. Moreover, our MD results show that the pileup index exhibits anomalies, which are defined as unusual changes in the values of the pileup index, around the experimentally found glass-transformation temperature through in situ indentation simulations at elevated temperatures. From indentation load-displacement curves at various temperatures, indentation modulus and hardness obtained from MD simulations were in qualitative agreement with experimental findings in terms of their decreasing rates with respect to the temperature. Three-dimensional atomic-strain calculations revealed strain localization and propagation of shear bands under the indenter tip at their initial evolution stages after the formation of shear transformation zones. In addition, higher loading rates decrease hardness, cause larger disturbed regions under the indent, and enlarge shear-banding patterns.     

铁基块体金属玻璃软磁合金近期研发进展概况

 总结了1995年首次报道铁基块体金属玻璃(BMG)软磁合金研发成功以来该类合金的研发进展概况;阐述了BMG形成条件,BMG合金系及制备方法,各种类型铁基BMG合金的成分、制备要点及磁性,初步探索了双相BMG合金,简要介绍了铁基块体纳米晶合金,并评价了铁基BMG软磁合金的优势、不足及应用前景。     

Corrosion Behavior of Fe-based Bulk Metallic Glass and In-situ Dendrite-reinforced Metallic Glass Matrix Composites in Acid Solution

The corrosion behavior study was conducted on a novel Fe_(77)Mo_5P_9C_(7.5)B_(1.5)in-situ metallic glass matrix composite(MGMC).This composite sample was developed by introduction of bccα-Fe dendrites as reinforcing phase.The corrosion behavior of this composite was compared to its monolithic counterpart and other Fe-based alloys such as 304 Land 2304Lstainless steels.The corrosion resistance of MGMCs in H_2SO_4 solution shows inferior to that of other Fe-based alloys.Experiments suggest that Fe-BMGs samples possess better corrosion resistance property than that of Fe-MGMCs.The possible underlying reasons can be the inhomogeneity induced by the precipitation ofα-Fe dendrites in the MGMCs.     

微量掺杂铜元素提高铁基非晶合金降解偶氮染料稳定性

非晶合金具有优异的催化性能,但失去亚稳态,催化性能通常显著下降,因此如何获得稳定的催化性能是一大难题。以降解偶氮染料为污染物模型,研究了掺杂微量铜元素对铁基非晶合金(Fe-Si-B-Cu非晶合金)降解性能受退火温度(T_a)的影响规律。结果表明：Fe-Si-B-Cu非晶合金微观结构为纳米铜团簇分布在非晶基底的不均匀结构;在300～800℃的温度范围内对其进行等温退火处理,Fe-Si-B-Cu非晶合金在高于380℃退火处理后开始发生晶化现象,得到纳米晶合金样品。将铸态和退火非晶态及退火纳米晶化态样品用于降解偶氮染料,研究铸态和退火温度对降解性能影响。结果表明：随着退火温度的升高,Fe-Si-B-Cu对偶氮染料降解性能不但没有明显下降,反而略微有所提高。其中,450℃退火处理的样品表现出了最优异的降解性能,降解速率高达0.164 min^-1;40 min时的降解效率达到100%。由此可见,引入纳米异质结构,为稳定非晶合金催化性能受退火引起的结构变化影响提供了一种有效途径。     

A Study on Synthesis, Crystallization, and Magnetic Behavior of Nanocrystalline Fe-Based Metallic Glasses

In the present work, structure of the as-cast melt-spun ribbons, nonisothermal crystallization kinetics, and the effect of heat treatment on the magnetic properties have been studied. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses have revealed the presence of amorphous and partly crystalline structures in the as-cast Fe₆₇Co₁₈Si₁B₁₄ and Fe₅₇Co₂₆Cr₃B₁₄C_0.2 metallic-glass ribbons, respectively. The crystalline phase present in the as-cast Fe₅₇Co₂₆Cr₃B₁₄C_0.2 metallic-glass was identified as α-Fe. Direct transformation from liquid to α-Fe has been analyzed from a thermodynamic and kinetics point of view. The differential scanning calorimetry (DSC) studies have shown two-stage crystallization behavior. The primary and secondary crystallization phases were identified as bcc-Fe(Co) and bct-(Fe,Co)₃(Si,B), respectively. Kissinger and Gao et al. methods were employed for nonisothermal crystallization kinetic studies. The activation-energy values obtained by the two models were in good agreement. The nucleation and growth morphologies of crystalline phases have been explained on the basis of the Avrami exponent, which were found to be consistent with the observed microstructures. The magnetic properties of as-cast amorphous ribbons showed low coercivity, and this has been attributed to averaging of magnetocrystalline anisotropy over grains coupled within an exchange length, i.e., based on a random anisotropy model. The influence of microstructure on magnetic properties was studied by crystallizing the amorphous phase at 400 °C for 3 hours. The saturation magnetization and coercivity had increased after crystallization for both alloys. This article is based on a presentation given in the symposium entitled “Materials Behavior: Far from Equilibrium” as part of the Golden Jubilee Celebration of Bhabha Atomic Research Centre, which occurred December 15–16, 2006 in Mumbai, India.

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On the Prospects of Using Nanoindentation and Wear Test to Study the Mechanical Behavior of Fe-Based Metallic Glass Coating Reinforced by B4C Nanoparticles

In this study, Fe-based metallic glass was served as the matrix in which various ratios of hard B₄C nanoparticles as reinforcing agents were prepared using a high-energy mechanical milling. The feedstock nanocomposite powders were transferred to the coatings using a high-velocity oxygen fuel process. The results showed that the microstructure of the nanocomposite coating was divided into two regions, namely a full amorphous phase region and homogeneous dispersion of B₄C nanoparticles with a scale of 10 to 50 nm in a residual amorphous matrix. As the B₄C content is increased, the hardness of the composite coatings is increased too, but the fracture toughness begins to be decreased at the B₄C content higher than 20 vol pct. The optimal mechanical properties are obtained with 15 vol pct B₄C due to the suitable content and uniform distribution of nanoparticles. The addition of 15 vol pct B₄C to the Fe-based metallic glass matrix reduced the friction coefficient from 0.49 to 0.28. The average specific wear rate of the nanocomposite coating (0.48 × 10⁻⁵ mm³ Nm⁻¹) was much less than that for the single-phase amorphous coating (1.23 × 10⁻⁵ mm³Nm⁻¹). Consequently, the changes in wear resistance between both coatings were attributed to the changes in the brittle to ductile transition by adding B₄C reinforcing nanoparticles.

     

Estimation of Melt Pool Dimensions, Thermal Cycle, and Hardness Distribution in the Laser-Engineered Net Shaping Process of Austenitic Stainless Steel

Laser engineered net shaping (LENS) and other similar processes facilitate building of parts with freeform shapes by melting and deposition of metallic powders layer by layer. A-priori estimation of the layerwise variations in peak temperature, build dimension, cooling rate, and mechanical property is requisite for successful application of these processes. We present here an integrated approach to estimate these build attributes. A three-dimensional (3-D) heat transfer analysis based on the finite element method is developed to compute the layerwise variation in thermal cycles and melt pool dimensions in the single-line multilayer wall structure of austenitic stainless steel. The computed values of cooling rates during solidification are used to estimate the layerwise variation in cell spacing of the solidified structure. A Hall–Petch like relation using cell size as the structural parameter is used next to estimate the layerwise hardness distribution. The predicted values of layer widths and build heights have depicted fair agreement with the corresponding measured values in actual deposits. The estimated values of layerwise cell spacing and hardness remain underpredicted and overpredicted, respectively. The slight underprediction of the cell spacing is attributed to the possible overestimation of the cooling rates that may have resulted due to the neglect of convective heat transport within the melt pool. The overprediction of the layerwise hardness is certainly due to the underprediction of corresponding cell spacing. The application of Hall–Petch coefficients, which is strictly valid for wrought and annealed grain structures, to estimate the hardness of as-solidified cellular structures may have also contributed to the overprediction of the layerwise hardness.     

High-Temperature Deformation Behavior and Formability of a Zr-Cu-Al-Ni Bulk Metallic Glass

The deformation behavior of a monolithic Zr₅₅Cu₃₀Al₁₀Ni₅ (at. pct) bulk metallic glass (BMG) fabricated by suction casting has been investigated at elevated temperatures in this study. A series of compression tests has been performed in the supercooled liquid temperature region. In the homogeneous flow regime, this alloy exhibited a transition from the Newtonian to non-Newtonian flow depending upon both the strain rate and the temperature. These two flow modes were then described by applying the Newtonian viscous flow theory and the transition state theory, respectively. On the basis of a dynamic materials model (DMM), a processing map could successfully be constructed to estimate the feasible forming conditions for this BMG alloy. Imaginary laboratory-scale extrusion tests were also performed to determine solid-to-solid formability, and the results from both the finite element method (FEM)-based simulation and processing map were then compared and discussed. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

Processing Ti-25Ta-5Zr Bioalloy via Anodic Oxidation Procedure at High Voltage

The current paper reports the processing of Ti-25Ta-5Zr bioalloy via anodic oxidation in NH4BF4 solution under constant potentiostatic conditions at high voltage to obtain more suitable properties for biomedical application. The maximum efficiency of the procedure is reached at highest applied voltage, when the corrosion rate in Hank’s solution is decreased approxomately six times. The topography of the anodic layer has been studied using atomic force microscopy (AFM), and the results indicated that the anodic oxidation process increases the surface roughness. The AFM images indicated a different porosity for the anodized surfaces as well. After anodizing, the hydrophilic character of Ti-25Ta-5Zr samples has increased. A good correlation between corrosion rate obtained from potentiodynamic curves and corrosion rate from ions release analysis was obtained.     

Al-Co-Y合金系非晶的形成及其晶化过程

利用熔体快淬法制备出了Al92-xCo8Yx（x=4,6,8,9,10）薄带,采用X射线衍射（XRD）和扫描电镜（SEM）进行结构分析,示差扫描量热仪（DSC）进行热稳定性分析。研究了Y的加入对合金的非晶形成能力的影响以及Al84Co8Y8合金薄带等温退火的晶化过程。结果表明：当Y的原子分数为8%时,合金系的非晶形成能力最好;非晶态Al84Co8Y8合金的晶化过程分为3个阶段进行,退火过程中的组织结构转变为：非晶合金→非晶基体＋初晶α-Al＋少量未知亚稳相→α-Al相＋未知亚稳相＋Al9Co2→α-Al相＋Al9Co2相＋Al3Y相。     

块状金属玻璃研究进展与应用

综述了块状金属玻璃的研究进展，介绍了块状金属玻璃的应用及几种制备方法，阐明了块状金属玻     

Corrosion and Oxidation Behavior of Zr58Cu22Fe4Co4Al12 Metallic Glass

The pitting corrosion behavior of melt spun ribbon made at a wheel speed of 20 ms in 3.5 wt% NaCl solution and nonisothermal and isothermal oxidation behavior of 2 mm diameter rod samples of newly developed Zr₅₈Cu₂₂Fe₄Co₄Al₁₂ bulk metallic glass have been studied. The pitting corrosion is more on the air side as compared to the wheel side mainly due to the presence of air pockets. The pitted regions are enriched with copper suggesting dealloying effect due to its noble nature. The alloy shows very good oxidation resistance compared to some of the exiting bulk metallic glass forming alloys. The oxidation leads to the formation of mainly tetragonal ZrO₂ with the presence of monoclinic ZrO₂, mixture of CuO and Cu₂O and Al₂O₃. Copper in the alloy oxidized progressively with the appearance of white flowery globule shape which later forms interconnected faceted CuO network.     

Ti基大块金属玻璃的研究与应用

阐述了Ti基大块金属玻璃(BMG)的成分设计原则及制备方法，并对Ti基非晶合金及其部分晶化复合材料的力学性能及断裂机理进行了评述。结果表明：Ti基大块金属玻璃具有较高的断裂强度、弹性延伸率及一定的塑性延伸率，而经过部分晶化获得的非晶合金基纳米颗粒复合材料，其室温塑性获得很大的改善。在此基础上探讨了该合金目前所存在的问题、研究热点以及其应用前景。