Metallurgical Microstructure Research Articles

Laser beam welding of steel plates using consumable inserts

Summary The aim of this study was to identify the appropriate parameters for laser welding of steel plates. The mechanical characteristics and metallurgical microstructures of the joints were analysed experimentally. Welded joints were made using two different types of steel (Cr–Mo low-alloy steel and austenitic stainless steel). Samples were cut from the welds and examined macrographically and micrographically; tensile and microhardness tests were also performed. Observation of these samples showed the beneficial effects of narrower molten and heat-affected zones and the consequent advantageous reductions in distortions and residual stresses. On the basis of these experimental results we conclude that both ferritic and austenitic steels can be properly welded, with good mechanical and metallurgical results, using consumable inserts pre-fitted to the edges before welding, provided that suitable welding parameters are chosen.

Steel making in the ancient Korean Kingdom of Koguryo

Five iron artifacts excavated from the same spot in a military fortress of the former Korean kingdom, Koguryo (37 BCE–668 CE), have been metallographically examined. The result shows that they comprise two pieces of white cast iron, one piece of wrought iron and two pieces with microstructures consisting of high C steel buried in white cast iron or white cast iron buried in high C steel. This provides direct material evidence of both white cast iron and wrought iron being combined to form steel. This article is to present the detailed account of metallurgical microstructures observed in the rare archaeological evidence of the unique ancient steel making process involving liquid cast iron.

Magnetostriction of Polycrystalline Strong-Textured Fe–17 at%Ga Laminates

Magnetostrictive bulk Fe–17 at%Ga alloy was fabricated by combining laminates of rapid-solidified ribbons (80 μm in thickness) using the spark plasma sintering/joining (SPSJ). The SPSJ is characterized by a short time, low temperature heating and sintering process. The laminated sample made by the SPSJ maintained a unique metallurgical microstructure of polycrystalline texture of columnar grains, as well as the almost non-equilibrium metastable phase with little evidence of the precipitates of the ordered phases as found in the as-spun ribbons. An excellent sintered sample exhibiting large magnetostriction was obtained under a condition of compressive stress of 100 MPa at a temperature of 973 K. The magnetostriction depended on compressive pre-stress level for each specimen and reached about 100 ppm, which was half the value obtained for the ribbon sample. Furthermore, by subjecting this specimen to a short annealing process, the magnetostriction increased to 170 ppm, comparable to the value for the ribbon.

Improved thermal stability of exchange bias of Mn–Ir/Co–Fe bilayers by novel in situ thermal annealing procedure

The effect of in situ thermal annealing of Mn–Ir films under ultra-high vacuum on the metallurgical microstructure and on the thermal stability of the unidirectional anisotropy constant, JK, was investigated for Mn73Ir27/Co70Fe30 bilayers. As a result, we found that the average lateral grain size of Mn–Ir increases with increasing the in situ annealing temperature, TIR and that the shape of JK–T curve changes to convex with increasing the TIR, implying a narrowing distribution of local blocking temperature. We conclude that ultra-high vacuum annealing is effective in improving the thermal stability of the exchange anisotropy of Mn–Ir/Co–Fe bilayers through the change of lateral grain size distribution of the Mn–Ir layer.

Thermal Plastic-Elastic Analysis in Consideration of Metallurgical Microstructure

Depending on casting methods, aluminum alloy cylinder heads differ greatly in quality and local strength as well as overall strength. Obviously, casting methods largely affect the durability of a cylinder head. Therefore, in order to precisely evaluate the durability of a newly-designed cylinder head by CAE, it is necessary to introduce a new method with the effects of a casting method taken into account. In our research, a method has been devised to be used in CAE in such processes from engineering to manufacturing for evaluation. More specifically, by using the method, metallurgical microstructure of cast aluminum alloy is analyzed by dividing cylinder head into such domains as lower deck, middle and upper deck parts for mechanical properties and a casting defect of porosity. The domain profile information on mechanical properties and porosity has helped us improve accuracy in the structural analysis.

超高真空中加熱処理による金属薄膜の粒成長と平坦化

The effect of thermal annealing under ultra-high vacuum on the metallurgical microstructure of (111) -textured face-centered cubic (FCC) metal thin films was investigated. The surface morphology of 500-A-thick metal films drastically changes with increasing annealing temperature. Regardless of the kind of metal, the morphological changes can be classified into four stages, when the annealing temperature, TIR, is normalized by the respective melting point of the metals, TM. In stage I , 0.15 ≤ TIR/TM < 0.3, the surface roughness, Ra, of metal films decreases to ∼ 3 A. In stage II, 0.3 ≤ TIR/TM ≤ 0.35, remarkable grain growth occurs, and the lateral grain diameter exceeds 1000 A. Small (∼ 200 A) crystals appear on the large grains in the stage II’, 0.35 < TIR/TM ≤ 0.45, and they grow large and coarsen the Ra in stage III, 0.45 < TIR/TM. We conclude that ultra-high vacuum annealing in stage II is effective in realizing large lateral grain size with small surface roughness in FCC metal films.

An investigation of tearing failure in fine-blanking process using coupled thermo-mechanical method

In fine-blanking processes, localized deformation is prone to cause tearing failure at the surface of shearing edges, which can influence the quality and functionality of the blanked part. In this paper, a numerical simulation of a fine-blanking process has been conducted by using a coupled thermo-mechanical finite element method. The thermal effect on the material properties has been taken into account in the simulation. On the basis of the results of the simulation, the distributions of equivalent plastic strain and stresses in a fine-blanking process have been analyzed. Moreover, examinations of metallurgical microstructure by means of optical and scanning electron microscopy have been performed. It has been observed that the grains near the shearing edge were highly distorted within a narrow shearing zone. The formation of microvoids under large shear deformation supports the argument that material damage initiates and develops around this local area during the fine-blanking process. It is suggested that tearing failure could initiate from the damaged area of the workpiece adjacent to the tool tips where cracking occurs due to excessive local tensile stress produced by fine blanking attributes and interfacial friction.

Body centered cubic buffer layers for enhanced lateral grain growth of Co/Cu multilayers

The effect of buffer layers (BLs) on metallurgical microstructure and giant magnetoresistance of Co/Cu multilayers fabricated on them is discussed. The lateral grain size and the magnetoresistance (MR) ratio of multilayers are generally enlarged with changing the chemical composition of BLs toward a limiting concentration, within the range where the solid solution of body-centered-cubic (bcc) structure is formed. A guiding principle for material research for the BLs, which realize flat interfaces with large lateral grain size in the multilayers, is deduced from the correlation between the MR ratio of the multilayers and the surface energy of bcc BLs: the difference between the surface energy of BL (γS) and the interfacial energy (γSL) in Young–Dupré’s equation (cos θ=(γS−γSL)/γL) should agree with the surface energy of Co layer (γL), which is deposited first on the BL.

Effect of rare earth elements on the erosion resistance of nitrided 40Cr steel

An investigation of the effect of rare earth elements (RE) on erosion resistance of nitrided 40Cr steel is carried out using an erosion test rig in a water-based slurry with quartz particles. Results indicate that a significant improvement occurs in erosion resistance of nitrided 40Cr steel by introducing RE in nitriding processes comparing conventional nitriding processes. Measurement of physical properties exhibits that both hardness and toughness of nitrided 40Cr steel increase in the case using RE-nitriding processes comparing the conventional. Metallurgical microscopy reveals that there is a transformation from a coarse to a fine metallurgical microstructure in the case and an increase in the thickness of white layer on the top of case attributed to an introduction of RE in nitriding, which attributed to an improvement in erosion resistance and physical properties. EDX analysis shows that RE diffuse into the case of 40Cr steel in nitriding process as a result of appearance of micro-alloy. Microscopy revealed that the furrow-like peeling from plastic deformation of material is predominant erosion mechanism of RE nitrided 40Cr steel while the furrow-like peeling with initial cross crack and large grinding peelings takes place predominantly in tests of conventionally-nitrided ones, which results in a significant difference in erosion resistance.

Research and Progress in Laser Welding of Wrought Aluminum Alloys. II. Metallurgical Microstructures, Defects, and Mechanical Properties

With the wide application of aluminum alloys in automotive, aerospace, and other industries, laser welding has become a critical joining technique for aluminum alloys. In this review, the research and progress in laser welding of wrought aluminum alloys are critically discussed from different perspectives. The primary objective of the review is to understand the influence of welding processes on joint quality and to build up the science base of laser welding for the reliable production of aluminum alloy joints. Two main types of industrial lasers, carbon dioxide (CO2), and neodymium-doped yttrium aluminum garnet (Nd:YAG), are currently applied but special attention is paid to Nd:YAG laser welding of 5000 and 6000 series alloys in the keyhole (deep penetration) mode. In the preceding article of this review (part I), the laser welding processing parameters, including the laser-, process-, and material-related variables and their effects on welding quality, have been examined. In this part of the review, the metallurgical microstructures and main defects encountered in laser welding of aluminum alloys such as porosity, cracking, oxide inclusions, and loss of alloying elements are discussed from the point of view of mechanism of their formation, main influencing factors, and remedy measures. The main mechanical properties such as hardness, tensile and fatigue strength, and formability are also evaluated.

Research and Progress in Laser Welding of Wrought Aluminum Alloys. I. Laser Welding Processes

With the wide application of Al alloys in automotive, aerospace and other industries, laser welding has become a critical joining technique for aluminum alloys. In this review, the research and progress in laser welding of wrought Al alloys have been critically discussed from different perspectives. The primary objective of this review is to understand the influence of welding processes on joint quality and to build up the science base of laser welding for the reliable production of Al alloy joints. Two main types of industrial lasers, carbon dioxide (CO2) and neodymium-doped yttrium aluminum garnet (Nd:YAG), are currently applied but special attention is paid to Nd:YAG laser welding of 5000 and 6000 series alloys in the keyhole (deep penetration) mode. In this part of the review, the main laser welding processing parameters including the laser-, process-, and material-related variables and their effects on weld quality are examined. In part II of this article in this journal, the metallurgical microstructures and main defects encountered in laser welding of Al alloys such as porosity, cracking, oxide inclusions, and loss of alloying elements are discussed from the point of view of mechanism of their formation, main influencing factors, and remedy measures. In part II, the main mechanical properties such as hardness, tensile, and fatigue strength and formability are also discussed.

Variation of structure with input energy during laser surface engineering of ceramic coatings on aluminum alloys

Surface modification of metal alloys using laser has become a unique tool to reduce surface related failure mechanisms such as wear, corrosion, erosion or high temperature oxidation. Laser surface engineered (LSE) ceramic coatings have been proved to enhance surface properties of Al alloys such as hardness and wear resistance. This technique has been shown to be capable of producing a wide variety of interesting metallurgical microstructure in the coating as well as in the adjoining substrate. These microstructures provide novel properties, which cannot be produced by any conventional processing technique. In addition, these coatings are metallurgically bonded, thus providing a sound and adherent interface between the coating and the substrate. In this present investigation, laser surface engineering technique has been employed to deposit ceramic (TiC) coating on aluminum alloy substrate. TiC coating was deposited on two types of aluminum substrates, alloy 2024 and 6061 using an Nd-YAG laser beam. The effect of laser processing parameters, such as power intensity and speed on the thickness, microstructure and morphology of both the coating and the heat-affected zone have been evaluated using a scanning electron microscope (SEM). Results of experiments in this study show that by controlling the process parameters it is possible to produce varied microstructures according to the surface requirement of the application.

Visualization of the hydrogen desorption process from ferrite, pearlite, and graphite by secondary ion mass spectrometry

The distribution and desorption processes of hydrogen and deuterium have been visualized by secondary ion mass spectrometry (SIMS). The present article deals with four principal points: (1) visualizing the hydrogen distribution, (2) visualizing the hydrogen desorption process from each metallurgical microstructure under various holding times at 25 °C, (3) visualizing the hydrogen desorption process during heating, and (4) determining the correspondence between desorption profiles and desorption sites. A spheroidal graphite cast iron specimen was prepared for visualizing hydrogen, since it consists of basic microstructures of steels such as ferrite and pearlite. Hydrogen and deuterium were occluded into the cast iron. The amount of hydrogen and the existing states of hydrogen in the cast iron were analyzed by thermal desorption spectrometry (TDS). The TDS analyses show that the hydrogen desorption has two peaks, namely, the low- and high-temperature peaks corresponding to trap activation energies of 21.6 and 105.8 kJ/mol, respectively. The SIMS analyses of the specimen cooled after heating to 100 °C, 200 °C, and 300 °C reveal that the hydrogen desorbs from the ferrite after heating to 100 °C, from the pearlite and the interfaces between the ferrite and the graphite after heating to 200 °C, and from the pearlite after heating to 300 °C. The graphite remains, trapping hydrogen after heating to 300 °C. On the basis of TDS and SIMS results, the relationship between the desorption profile and desorption sites was identified; that is, the low-temperature peak corresponds to ferrite, pearlite, and graphite/ferrite interfaces, while the high-temperature peak corresponds to graphite.

Concurrent CAE Method to Develop Aluminum Cylinder Head. Thermal Plastic-Elastic Analysis in Consideration of Metallurgical Microstructure.

Depending on casting methods, aluminum alloy cylinder heads differ greatly in quality and local strength as well as overall strength. Obviously, casting methods largely affect the durability of a cylinder head. Therefore, in order to precisely evaluate the durability of a newly-designed cylinder head by CAE, it is necessary to introduce a new method with the effects of a casting method taken into account. In our research, a method has been devised to be used in CAE in such processes from engineering to manufacturing for evaluation, More specifically, by using the method, metallurgical microstructure of cast aluminum alloy is analyzed by dividing cylinder head into such domains as lower deck, middle and upper deck parts for mechanical properties and a casting defect of porosity. The domain profile information on mechanical properties and porosity has helped us improve accuracy in the structural analysis.

503 アルミシリンダーヘッド開発におけるコンカレント CAE 手法の構築 : 鋳造組織状態を考慮した熱弾塑性構造解析手法の開発

503 アルミシリンダーヘッド開発におけるコンカレント CAE 手法の構築 : 鋳造組織状態を考慮した熱弾塑性構造解析手法の開発

Advanced nanocrystalline Zr-based AB2 hydrogen storage electrode materials for NiMH EV batteries

Abstract The metallurgical microstructure, crystal-structure and electrochemical properties of Laves phase Zr–V–Mn–Ni system alloys (modified with Ti, Co, Sn, etc.) were investigated systematically in the present paper. Conventional polycrystalline Zr-based alloys, which consist of cubic C15 Laves phase, hexagonal C14 Laves phase and non-Laves phase (such as Zr7Ni10, Zr9Ni11, Zr(NiMn)Sn0.35), show the highest discharge capacity of 342 mAh g−1 (at 60 mA g−1 charge–discharge current), which decreases by 7.8% after 300 cycles. Amorphous phase alloys in melt-spun alloys exhibit poor electrochemical properties. Advanced nanocrystalline C15-Laves single-phase alloys were prepared by completely crystallizing the melt-spun amorphous Zr1−xTix[(NiVMnCo)1−ySny]2+α alloys. These alloys have a special microstructure composed of high-density interface phase and random-oriented grains varying from several nanometres to several dozens of nanometres. It was found that these materials had high discharge capacity (the maximum capacity is up to 379 mAh g−1) and long cycle life (the capacity only decreases 3% after 300 cycles). The maximum discharge capacities were found in the metallurgical microstructure and crystal-structure in Zr-based AB2 alloys. The maximum discharge capacity increases in regular nanocrystalline/C15-Laves single-phase>polycrystalline/multi-phase (Laves and non-Laves)>comorphous state/C15-Laves single-phase. It was shown that the complete crystallization method from amorphous solids is an effective way to greatly improve the electrochemical performance of Zr-based AB2 hydrogen storage electrode materials, which is not only significant for academic research but also valuable for practical applications in the NiMH battery system for pure electric vehicles (PEV) and hybrid electric vehicles (HEV).

Fatigue Properties of Reinforcing Steel Produced by TEMPCORE Process

TEMPCORE is a patented mill process that produces high-strength reinforcing steel bars via in-line quenching and self-tempering. This paper reports on the fatigue performance of 400 MPa-grade reinforcing steel produced by TEMPCORE process, called TEMPCORE steel in this paper. Seven bar diameters were axially fatigue-tested in air, and the results in terms of S-N curves and failure features are presented, and compared with test data for other types of reinforcing steels from the literature. Comparisons indicate that this type of reinforcing steel has higher fatigue resistance. Although the general geometrical features are similar to those of other types of reinforcing steels, existing models fail to predict its fatigue properties. It is suggested that the metallurgical microstructure and residual stresses developed during the TEMPCORE process contribute to the superior fatigue properties and must therefore be considered in the models.

Rapid-Solidified Metallic Actuator Materials Developed by Electromagnetic Nozzleless Melt Spinning Method

AbstractElectro-magnetic nozzleless melt-spinning method was developed by combining the control of the flow down of the molten metals after electromagnetic float-melting(i.e. levitation) with rapid solidification by rotating roll. The metallurgical grain microstructures can be changed by rotating roll speed. It was confinned that the produced, intermetallic TiNi and NiAl system alloy thin plates showed the strong crystal anisotropy, higher shape memory functional properties than those of the conventionally processed melt-worked samples having its same origin. As new SMAs by using this method, ferromagnetic shape memory, FePd alloy having very large magnetostriction and super high temperature shape memory, RuTa alloy having the transformation over 1000°C were developed. Moreover, our recent study on the advanced rapid-solidification machine to produce many kinds of short fibers as well as ribbons is introduced. Finally, harmonic material design for sensor/actuator stacking composite system, namely “Smart Board” for aircraft structures will be introduced.

Development and performance of aluminum nitride insulating coatings for application in a lithium environment

The blanket system is one of the most important components in a fusion reactor because it has a major impact on both the economics and safety of fusion energy. Based on the requirement that an electrically insulating coating on the inner wall of cooling tubing must minimize the magnetohydrodynamic pressure drop that occurs during the flow of liquid metal in a magnetic field, aluminum nitride (AlN) is considered a candidate coating material for the lithium self-cooled blanket concept. Detailed investigations were conducted on the fabrication, metallurgical microstructure, compatibility with liquid Li, and electrical characteristics of AlN as a coating material. Lithium compatibility studies were conducted in static systems by exposure of AlN-coated specimens for several time periods, at various temperatures, and in various lithium chemistries. Electrical resistance of the specimens was measured at room temperature before and after exposure to liquid Li. The paper discusses the results from ongoing activities on the development of AlN coatings.

Corrosion behaviour of Zr1−xTixV0.6Ni1.2M0.2 (M=Ni, Cr, Mn) AB2-type metal hydride alloys in alkaline solution

Abstract An examination is made of the discharge and cycle life of Zr 0.5 Ti 0.5 V 0.6 Ni 1.4 alloys when a fraction (0.2 at.%) of the Ni-component is substituted by Cr or Mn. In addition, the Zr:Ti component ratios are varied to extend the cycle life of high capacity, Mn-substituted Zr 1− x Ti x V 0.6 Ni 1.2 Mn 0.2 ( x =0.0, 0.25, 0.5, 0.75) alloys. The metallurgical microstructure is observed by X-ray diffraction analysis, scanning electron microscopy, and energy dispersive X-ray analysis. Active–passive potentiodynamic behaviour, as well as charge–discharge cycle characteristics, is evaluated, and dissolved V-species in the electrolytic solution is analyzed by inductively coupled plasma spectroscopy. The corrosion behaviour of the V–Cr or the V–Mn phase in the alkaline electrolyte solution is found to determine the cycle life of an AB 2 alloy. Cr-substituted (Zr 0.5 Ti 0.5 Ni 1.2 Cr 0.2 ) alloy, containing a V–Cr phase, is estimated to involve a dissolution rate of 0.028 wt.% vanadium per cycle in an alkaline electrolytic solution, while Mn-substituted (Zr 0.5 Ti 0.5 V 0.6 Ni 1.2 Mn 0.2 ) alloy, containing a V–Mn phase, is estimated to have a dissolution rate of 0.138 wt.% vanadium per cycle. For Mn-substituted alloys, an optimum Zr:Ti ratio of 3:1, i.e., Zr 0.75 Ti 0.25 V 0.6 Ni 1.2 Mn 0.2 , is found to have the most stable cycle life. The improvement in cycle life caused by increasing the Zr content in the alloy is attributed to increase in the corrosion resistance of the alloy due to less formation of the corrosive V–Mn phase.