Metallurgical Considerations Research Articles

The Advanced Assessment of Nanoindentation-Based Mechanical Properties of a Refractory MoTaNbWV High-Entropy Alloy: Metallurgical Considerations and Extensive Variable Correlation Analysis

In the present study, a thorough examination of nanoindentation-based mechanical properties of a refractory MoTaNbVW high-entropy alloy (RHEA) was conducted. Basic mechanical properties, such as the indentation modulus of elasticity, indentation hardness, and indentation-absorbed elastic energy, were assessed by means of different input testing variables, such as the loading speed and indentation depth. The obtained results were discussed in terms of the elasto-plastic behavior of the affected material by the indentation process and material volume. Detailed analysis of the RHEA alloy’s nanoindentation creep behavior was also assessed. The effect of testing parameters such as preset indentation depth, loading speed, and holding—at the creep stage—time were selected for their impact. The results were explained in terms of the availability of mobile dislocations to accommodate creep deformation. Crucial parameters, such as maximum shear stress developed during testing (τmax), critical volume for dislocation nucleation (Vcr), and creep deformation stress exponent n, were taken into consideration to explain the observed behavior. Additionally, in all cases of mechanical property examination and in order to identify those input testing parameters—in case—that have the most severe effect, an extensive statistical analysis was conducted using four different methods, namely ANOVA, correlation matrix analysis, Random Forest analysis, and Partial Dependence Plots. It was observed that in most of the cases, the statistical treatment of the obtained testing data was in agreement with the microstructural and metallurgical observations and postulates.

The Degradation in Creep Strength of ASME Grade 122 Steel

The degradation of the long-term rupture strength of ASME Grade 122 steel occurs earlier than that of Grade 92 steel. To investigate the reasons for this phenomenon, the long-term creep curves of Grade 122 steel pipe, plate, and tube product forms were analyzed by applying an exponential law to the temperature, stress, and time parameters. The activation energy (Q), activation volume (V), and Larson–Miller constant (C) were obtained as functions of creep strain. All Q, V, and C (QVC) decreased simultaneously with an increase in creep strain during the transient creep in a data group (Gr.IIIa), where an unexpected drop in the long-term rupture strength was experienced. Metallurgical considerations of the variations in QVC meant that “heterogeneous recovery and heterogeneous deformation” (HRHD) should occur during the simultaneous decreases in QVC. The Z-phase is easily formed by the consumption of the strengthening particles of MX in the HRHD zone, which causes the degradation of the long-term strength of Grade 122 steel. The higher hardness of Grade 122 steels promotes the coarsening of the Laves phase particles and, in addition to this, the amount of MX inside the subgrains is estimated to be less than Grade 92 steel, which cause severe HRHD and the resultant degradation in rupture strength compared to Grade 92 steel. In a data group subjected to lower stresses than those of Gr.IIIa, the degradation rate is mitigated, and a deformation mechanism was proposed. The improvement in the long-term rupture strength of Grade 122 steel was also discussed.

State of the art of fatigue strength of materials & structures from additive manufacturing – The pivot, A CETIM development.

Additive manufacturing is a subject at the heart of innovation in many fields of mechanics. It allows, through different techniques, to produce increasingly complex parts. It also offers greater design freedom, often with shorter times than conventional manufacturing. These techniques having a multitude of parameters and finishing methods, Cetim wishes to study their influence on fatigue resistance through tests on standardized samples and on mechanical parts.The pivot is an example of study part developed at CETIM. It is at the crossroads of technical art and technological developments. This part, resulting from a mechanical assembly of cable reels for industry, has been specially developed for additive manufacturing. It incorporates all the constraints and advantages of current technology. This part is stressed in fatigue during operation in combined rotations. It is subjected to alternating loads linked to centrifugal forces.The design optimizes the constraints and design opportunities linked to additive manufacturing (topological optimization, supports optimizations). It also integrates metallurgical considerations and geometric constraints necessary for the finish. A specific range of surface finishes was produced for this part, driven by the reduction of two key roughness values, the Ra and Rz of the surfaces.The validation of the mechanical properties was carried out on several production batches characterize the alloy behavior (metallurgically, mechanically and in fatigue). The parameters obtained during the first test phase (static and Manson-coffin) were incorporated into the simulations and dimensioning of the fatigue tests of the part. The pivot had several metrological checks with no-contact methods (tomography, scan, CMM, etc.) to check the dimensions and whether any defect was present. Then, the part was placed under a test bench to validate its mechanical performance and industrial expectations.This study therefore proposes a direct correlation between the difficulties linked to the development of parts of additivemanufacturing structures. The various technical problems from the microstructure to the structure of the part were removed step by step.

Electron Diffraction Study of the Space Group Variation in the Al–Mn–Pt T-Phase

Binary high temperature “Al3Mn” (T-phase) and its extensions in ternary systems were the subjects of numerous crystallographic investigations. The results were ambiguous regarding the existence or lack of the center of symmetry: both Pna21 and Pnam space groups were reported. Our research on the Al–Mn–Pt T-phase allowed concluding that inside a continuous homogeneity region, the structure of the Al-rich T-phase (e.g., Al78Mn17.5Pt4.5) belongs to the non-centrosymmetric Pna21 space group, while the structure of the Al-poor T-phase (such as Al71.3Mn25.1Pt3.6) is centrosymmetric, i.e., Pnam. Following metallurgical and crystallographic considerations, the change in the symmetry was explained.

A review of high energy density beam processes for welding and additive manufacturing applications

High-energy density beam processes for welding, including laser beam welding and electron beam welding, are essential processes in many industries and provide unique characteristics that are not available with other processes used for welding. More recently, these high-energy density beams have been used to great advantage for additive manufacturing. This review of the literature serves to provide an overview of the evolution of the laser and electron beam processes including the fundamental nature of the beam itself and how such a high-energy density beam has been applied for welding. The unique nature of each process regarding weld bead formation and penetration, and metallurgical considerations are covered in detail. In addition, the evolution of monitoring systems for both characterization and control of these beam processes is reviewed. Over 500 references have been cited in this comprehensive review that will allow the reader to both understand the current state-of-the-art and explore in more detail the fundamental concepts and practical applications of these processes.

Compositionally graded SS316 to C300 Maraging steel using additive manufacturing

Joining of dissimilar metals is required for numerous applications in industries such as chemical, energy and automotive. It is challenging due to differences in melting point, density, and thermal expansion of the metals being joined. Common welding techniques involve limiting melting and solidification to a narrow area leading to high thermal stresses and potentially brittle intermetallic phases. Furthermore, the geometric complexity of these welded joints can be rather limited. Additive Manufacturing (AM) presents new techniques for joining of dissimilar metals. One of the emerging methods is the building of functionally graded parts using Directed Energy Deposition (DED) to spatially vary composition. In this paper, a SS316 L and C300 maraging steel couple were joined by DED and heat treated. 13 discrete composition layers were selected using metallurgical considerations, in order to ensure a smooth transition in properties and microstructure. The mechanical properties of the as-built joints were found to be similar to the SS part and no intermetallic phases were found in the interface.

Mechanical and metallurgical considerations on the effects of ppb-level chloride on stress corrosion cracking of low alloy steels in high-temperature water

This paper studies the effects of very low-level chloride (< 5 ppb) on the stress corrosion cracking (SCC) growth of low-alloy pressure vessel steel in oxygenated high-temperature water. Chloride levels as low as 3 ppb increase SCC susceptibility. Besides the chemical reason, this paper provides perspectives on the underlying mechanical and metallurgical contributions. A substantial variation was observed from three high-sulphur steels. Sulphur is not the only contributor to SCC. The synergy of material, environmental, and mechanical parameters controlled the crack-tip strain rate and crevice chemistry that govern the SCC response in the high-purity high-temperature water environments at intermediate K.

Experimental-based methodology for the double ellipsoidal heat source parameters in welding simulations

The welding numerical simulation involves thermal and mechanical analyses and metallurgical consideration. The thermal analysis determines the transient temperature distribution on the welded part, and its accuracy is relevant for the following analyses on structural integrity, in particular buckling and fatigue failure modes of steel-plated structures. The temperature distribution is strongly influenced by the size and shape of the heat source, which can be represented as a double ellipsoid and defined by Goldak’s parameters. The main difficulty is that the adjustment of these parameters to obtain a suitable temperature distribution is usually determined by trial and error. In this paper, a parametric study is performed to analyze the influence of Goldak’s parameters on the weld bead size for 2D and 3D numerical welding simulations. A method to estimate the parameters of a double ellipsoidal heat source in motion is proposed. An algorithm has been implemented based on the combination of analytical formulation, experimental data, and numerical simulation. As an analytical formulation, the Fachinotti’s solution is used to determine the isotherms. The weld bead dimensions are defined from the melting temperature isotherm of the material. Experimental data, such as the welding process parameters and the weld bead dimensions are input to the algorithm. Numerical simulations of the welding process have been developed to calibrate and validate the method. The numerical simulation results from the obtained Goldak’s parameters by the proposed method are correlated with the experimental results of fillet-welded specimens.

Corrosion Performance and Surface Analyses of Laser Cladded Zn-Ni-Fe Coatings on ASTM A29 Steel.

The corrosion behaviour of the laser coatings was investigated in 3.65 % sodium chloride solutions at 30°C via potentiodynamic polarization technique. The composition of Zn-50Ni-5Fe at parameters 900 W and 1.2 m/min exhibited enhanced electrochemical performance in 3.65wt.% NaCl solution. Microstructures with unique characteristics and refinement of grain size were observed. The fast solidification of the coating is accounted for this unique features. In terms of corrosion performance, results revealed that increasing the laser scanning speed was beneficial to the property, showing that the corrosion performance became better at higher scanning speeds. At the set laser intensity of 900 W and increased laser velocity, Zn-50Ni-5Fe coatings showed enhanced microstructure. The multiple tracks applied in the direct laser metal deposition (DLMD) process had resulting fields of residual stresses which attributed to the solid-state phase transformation that was a repeated process. The study validated the reliability of optimizing DMLD set parameters for metallurgical and mechanical considerations. These bring improvements in coatings which were laser cladded in terms of their corrosion performance and the dimensional accuracy, by optimizing the processing parameters. The only processing parameters which were varied was the laser intensity and the scanning speed, which were employed to numerically design the DLMD experiment. An empirical method was also developed and was used to validate the results achieved experimentally. The Grey relational model (GRM) used in this research described vividly the influence of optimized factors on the improved corrosion resistance and compared reasonably with the experimental results. In addition, the proposed model has the potential to provide induced corrosion rate predictions of coatings fabrication that are additively manufactured.

Atmospheric corrosion of weathering steels. Overview for engineers. Part I: Basic concepts

Abstract The atmospheric corrosion of weathering steel (WS) has been extensively discussed in the scientific literature, but a comprehensive overview of this topic from an engineering viewpoint is currently lacking. The present publication seeks to fill this gap, providing engineers, designers and steel manufacturers with an insight into the current state of knowledge on this important structural material and presenting key research findings in a way that promotes their practical application. The Part I of this review is addressed to various aspects of WS atmospheric corrosion, such as corrosion mechanisms, corrosion products and layers, effect of exposure environment conditions and long term performance. A number of design and metallurgical considerations is also focused.

Effect of Microadditives on Center Segregation and Mechanical Properties of High-Strength Low-Alloy Steels

One of the main tasks of steelmaking is to obtain the necessary thermodynamic conditions that ensure fine and homogeneous solidified microstructure. The relatively economical solution is to feed microadditives into liquid steel. The metallurgical considerations and techniques on the feeding of microadditives are described in the present work. The effect of small addition of reactive fine particles and ultra-high melting point powders on the control of non-metallic inclusions, slab center segregation, and mechanical properties, especially the Z-direction properties, was investigated. The results showed that the microadditives had composite effects on microalloying and modification of inclusions. The segregation of elements in the slab center of high strength steels was remarkably reduced. The mechanical property along the Z-direction of steel plates was greatly improved.

Criteria for extending the operation periods of thermoelectric converters based on IV-VI compounds

The recent energy demands affected by the dilution of conventional energy resources and the growing awareness of environmental considerations, had positioned the research of renewable energy conversion methods in general and of thermoelectric direct conversion of thermal into electrical energies in particular, in the forefront of the currently active applicative sciences. IV-VI thermoelectric compounds (e.g. GeTe, PbTe and SnTe) and their alloys comprise some of the most efficient thermoelectric compositions ever reported. Yet a proper utilization of such materials in practical thermoelectric devices, still requires an overcoming the so-called technological “valley of death”, including among others, transport properties' degradation, due to sublimation of volatile Te rich species, while being subjected to elevated temperatures for long periods of time. In an attempt to establish practical operation criteria for extending the operation periods of such thermoelectric converters, it is currently shown based on thermal gravimetric and metallurgical considerations that such harmful sublimation can be practically bridged over by limiting the maximal operating temperatures to the 410–430°C range for GeTe rich alloys and to 510–530°C for PbTe and SnTe rich alloys, depending of the thermoelectric leg's diameter.

Numerical Analysis to Investigate the Effects of Thermal-Hydraulic Instabilities on Deterioration Heat Transfer and Wall Temperature in the CANDU Supercritical Water Reactor

The present work analyzes the thermal-hydraulic behavior of the CANDU supercritical water reactor (SCWR) using a 1-D numerical model. The possibility of a static instability, the Ledinegg excursion, is investigated, which reveals it can occur only in a hypothetical condition, far from the proposed operating regime of the CANDU SCWR. The investigation demonstrates the possibility of density wave oscillations (DWOs), a dynamic instability, in the operating regime of the CANDU SCWR and its marginal stability boundary (MSB) is obtained. The phenomenon of the deterioration in heat transfer is observed, and the related investigation shows that the strong buoyancy effect is responsible for its appearance inside the heating section of the channel of the CANDU SCWR core. The MSB is found to be inadequate in determining the safe operating zone of the reactor because the wall temperature can exceed the allowable limit from metallurgical consideration. The investigations also determine the safe as well as stable zone where the CANDU SCWR should operate in order to avoid the maximum temperature limit and DWOs.

Method of Estimating the Long-term Rupture Strength of 11Cr-2W-0.4Mo-1Cu-Nb-V Steel

Long-term rupture data of 11Cr-2W-0.4Mo-1Cu-Nb-V steel were analyzed using an exponential equation for stress regarding time to rupture as a thermal activation process. The fitness was compared with the usually employed method assuming power-law creep. In the exponential method, rupture data are classified into several groups according to the thermal activation process; the activation energy, Q; the activation volume, V; then, the Larson–Miller constant, C, values are calculated, and a regression equation is obtained for each data group. The fitness level of the equation was satisfactorily high for each group. The values of Q, V, and C were unusually small for a data group where an unexpected drop in rupture strength was observed. The critical issue is how to comprehend signs of degradation within the short term. We can observe several signs at a creep time of approximately one-tenth of the times of the degradation events. The small values of Q and V indicate that completely softened regions form and creep locally, which is consistent with previous observations. From both metallurgical considerations and the variations of Q and V, it is suggested that the rate of the unexpected drop in strength is mitigated after further long-term creep.

Metallurgical considerations for the fabrication of low-enriched uranium dispersion targets with a high density for 99Mo production

It is necessary to develop high-uranium-density targets with low enriched uranium in order to improve 99Mo production efficiency. In order to investigate the use of high density low enriched uranium (LEU) dispersion targets using atomized U–Al alloy powder, U–10 wt% Al and U–20 wt% Al powders were fabricated by centrifugal atomization. Metallurgical reactions between uranium and aluminum during the hot working were investigated in order to minimize changes in the established chemical processes for 99Mo extraction. It is concluded that LEU based dispersion target plates with increased uranium density can be fabricated by controlling the chemical reactions between U and Al in atomized U–Al alloy powders.

Impact of Metallurgical Size Effects on Plasticity of Thin Metallic Materials

Three examples involving size effects are presented with implications concerning the formability: small Ni-20wt.%Cr resistive bridges, magnetic micro-sensors performed with (Ni, Co, Fe) based alloys and copper clad aluminum thin wires. The mechanical properties are directly linked to the ratio thickness over grain size (t/d ratio) of the parts. These metallurgical considerations must be taken into account when we are concerned by the numerical simulation of the process of such components. It is shown that the simulations can correctly reproduce the softening effect linked to a decrease in thickness and in number of grains across the thickness: the quality of the final shape strongly depends on the number of grains across the thickness. Finally the effect of a moderate increase in temperature on these results will be briefly reported.

Progress in Surface Treatment and Processing of Coatings

The surface treatments of materials and processing of coatings are becoming increasingly important for imparting functional properties, repairing the surfaces, and protecting the surfaces from conditions of stress, temperature, and corrosive media. The processing approaches involving surface cleaning and finishing, plating and electroplating, dip and conversion coatings, vacuum and controlled atmosphere coatings, surface modification using high-energy and particle beams (laser surface processing and ion implantation), and heat treatments (flame, induction, and high-energy beams) have all been successfully implemented to improve the surface properties and functionalities of materials. The advancements in the surface treatments and coatings processing have kept pace with the advances in the materials development. Novel processes have been regularly introduced and the existing processes have been continuously adapted for surface engineering of materials that are becoming increasingly important in new design considerations. The surface engineering of light alloys, ceramics, and amorphous/nanostructured materials is gaining unprecedented momentum. Metallurgical (interfacial bonding, elemental redistribution, and defects/porosity/cracking), manufacturing (noncontact, rapid, and flexible processing), environmental (eco-friendly and benign processing), and health (nontoxic materials and processing) considerations are becoming increasingly important in the surface treatments and processing of coatings. The TMS Surface Engineering Committee regularly organizes symposia in TMS/Materials Science & Technology (MST 16–20 March 2014), the committee organized a symposium titled Advances in Surface Engineering: Alloyed and Composite Coatings III. The symposium featured 49 presentations including nine invited talks in the areas of processing (thermal spray, laser, and friction stir, and electrochemical processing) and properties (wear, oxidation/corrosion, mechanical, and high-temperature properties) of alloy and composite coatings. The Surface Engineering Committee also organized two joint sessions titled ‘‘Recent Developments in Biological, Electronic, and Functional Thin Films and Coatings’’ with the TMS Thin Films and Interfaces Committee. The joint sessions featured an additional 23 presentations including four invited talks on the topics coatings for biomedical applications, multilayer coatings, anticorrosive coatings, and thin films. The committee encourages the participation of industry in its programming. In addition to the presentations by university researchers and students, the symposium also featured several talks by researchers working in industry and government research laboratories. The committee recognizes the importance of partnership between the universities and industries in advancing the state-of-the-art in the areas of surface engineering. The committee is committed to organizing regular symposia and publishing feature issues to provide a platform for useful discussions on evolving topics in surface engineering. This issue of JOM presents five articles, including four articles based on presentations made at the TMS 2014 Annual Meeting on the topics of surface treatment and processing of coatings. In the article titled ‘‘Aqueous Corrosion Behavior of Micro Arc Oxidation (MAO)-Coated Magnesium Alloys: A Critical Review,’’ L. Rama Krishna and G. Sundararajan examine the prospects of the relatively novel and eco-friendly micro-arc oxidation (MAO) process in aqueous corrosion protection of Mg and its alloys. The authors present a critical review of the influence of MAO processing parameters such as electrolytic composition, presence of insoluble additives in the electrolytes, electrical parameters, and substrate composition on the corrosion resistance of Mg alloys. The authors conclude that the MAO process offers distinct advantages such as complete crystalline structure, good coating-substrate bonding, and the ability to tailor Sandip P. Harimkar is the guest editor for the Surface Engineering Committee of the TMS Materials Processing & Manufacturing Division, and coordinator of the topic Surface Engineering of Materials in this issue. JOM, Vol. 66, No. 6, 2014

Simple Heat Treatment for Production of Hot-Dip Galvanized Dual Phase Steel Using Si-Al Steels

This work presents relevant metallurgical considerations to produce galvanized dual phase steels from low cost aluminum-silicon steels which are produced by continuous strip processing. Two steels with different contents of Si and Al were austenized in the two-phase field ferrite + austenite (α + γ) in a fast manner to obtain dual phase steels, suitable for hot-dip galvanizing process, under typical parameters of continuous annealing processing line. Tensile dual phase properties were obtained from specimens cooled from temperature below Ar3, held during 3 min, intermediate cooling at temperature above Ar1 and quenching in Zn bath at 465 °C. The results have shown typical microstructure and tensile properties of galvanized dual phase steels. Finally, the synergistic effect of aluminum, silicon, and residual chromium on martensite start temperature (Ms), critical cooling rate (CR), volume fraction of martensite, and tensile properties has been studied.

Metallurgical Consideration about Abnormal Events during Slab Continuous Casting Process in the Quality Diagnosis Model

Some kinds of abnormal events occurred possibly during casting process have been taken into full consideration in the slab quality online diagnosis &amp; analysis mathematic model, CISDI_SQDS ONLINE R2011, the effects of which on relevant crack formation index have been introduced into the model in terms of the event level. As for the capture modes of event status, there are two styles, one is manual set mode, the other one is automatic judgment mode. And also, the effect ranges of all the events in the casting strand have been discussed respectively. The mathematic model has been put into industrial application successfully in Xinjiang Bayi Steel, which shows obviously that, the capture method of event status is accurate and reliable, the influence factors of events to quality defects are reasonable and can reflect the effect degree normally.

Metallurgical Considerations in Shape‐Memory Nitinol Middle Ear Prosthetics

Objectives: At the conclusion of this presentation, the participants should be able to 1) describe how the metallurgical phenomenon of creep may be involved in the failure of nitinol middle ear devices, and 2) describe how other metallurgical phenomena such as microfractures can also be involved. Methods: Retrospective literature review of nitinol middle ear device failure; retrospective literature review of known metallurgical properties of nitinol such as creep and microfractures; and prospective survey of otologic surgeons. Study period: January 2001 to present (literature review), and 2011 to present (survey). Condition studied: Delayed conductive hearing loss after stapes surgery. Subjects studied: Patients with otosclerosis described in previous studies who underwent surgery with nitinol shape-memory devices. Surgeons who implanted such devices. Interventions: Analysis of known metallurgical properties of nitinol applied to results obtained with such devices. Results: A comprehensive literature review revealed many instances of delayed conductive hearing loss after middle ear surgery with nitinol shape-memory devices. A survey of otologic surgeons by the author revealed 50% of surgeons reporting “loose-wire” syndrome as a delayed complication of such surgeries, signifcant to P &lt; 0.05 confidence level (94 surgeons). Conclusions: 1) “Loose-wire” syndrome is a frequent complication encountered by surgeons performing middle-ear surgery with nitinol shape-memory devices. 2) Metallurgical properties of nitinol such as creep (deformation over time as a result of stress) and microfractures may theoretically be responsible. 3) Additional metallurgical laboratory analysis of nitinol is indicated in order to explain and prevent such complications.