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The deformation mechanism of the fine structure composed of primary α phase (αp) and acicular secondary α phase (αs) on quasi-static mechanical properties is still not very clear. The main controversy is focused on the role of αp in the mechanical behavior. In this paper, the microstructure of the heat-treated near β-type Ti-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr-2.9Zn alloy after tensile tests was observed by transmission electron microscopy (TEM). And the results showed that in the slight deformation region the dislocations were accumulated at the intersection of αp and β matrix separated by αs, while only a few dislocations nucleated in β matrix. In the severe deformation region, a large quantity of dislocations in both αp and β matrix were observed. It can be inferred that αp deformed firstly and then activated the deformation of β matrix, that is, the thickness of αp and the inter-particle spacing of αs played a dominant role in the deformation process. The quantitative relationship between the yield strength and the microstructure parameters is consistent with this inference. By adjusting the solution treatment parameters and the subsequent aging treatment, three fine structures were obtained, and the corresponding mechanical properties were determined. Furthermore, the yield strength can be described by the mathematical model σy ​= ​756.4 ​+ ​135.6/hp1/2 +32.2/ds1/2, where hp and ds are the thickness of αp and the inter-particle spacing of αs, respectively.

Commercially pure titanium (CP-Ti) has seen major applications in biomedical equipment. The use of selective laser melting (SLM) has become more common concerning the fabrication of CP-Ti components with a complicated shape in biomedical implants, where high strength and ductility are required. However, SLM manufactured CP-Ti often exhibits high strength and low ductility, as well as mechanical anisotropy because SLM process typically results in the formation of long columnar grains comprising of fine acicular α′ martensite. Heat treatment must be preceded to transform the acicular α′ to equiaxed α grain. This study demonstrated that annealing at 650 °C of SLM CP-Ti can create an equiaxed structure, resulting in a weakened texture. The formation of equiaxed grains occurred at two types of microstructural features, acicular α′ and irregular massive (α′m) martensite, which exhibited different sizes, morphologies, and contained different types of substructures under SLM as-fabricated condition. The formation mechanism of equiaxed grains in the α′ region is dominated by the coalescence of acicular α′ of the same variant and the dissolution of α′ into the matrix, whereas the formation mechanism in the α′m region is primarily dominated by the growth of the preexisting subgrains. A small number of equiaxed grains with new orientations were formed in the α′m region. The majority of equiaxed grains were formed in the acicular α′ region and inherited the grain orientations of the preexisting α′ or matrix. Therefore, a similar but weakened texture was inherited from the microstructure of the SLM CP-Ti after annealing.

A wide range of post process hot isostatic pressing (HIP) studies of electron beam additively manufactured Ti-6Al-4V in this research program have shown that cooling rates of 103 °C/min from temperatures above and below the beta transus produced acicular alpha-prime martensite characteristic elongations < 10%. Optimum yield strength (0.9 GPa), UTS (1.0 GPa), and elongation (∼14%) were achieved for slow cooling (at 102 °C/min) from 850 °C HIP which produced a dense, Widmanstatten alpha structure within the retained, as-fabricated columnar grains by alpha-prime decomposition. These results suggest that manipulation of AM process parameters to produce a small-grain, equiaxed microstructure, HIPed below the beta transus and slow cooled, will have a wide range of superior, isotropic mechanical properties corresponding to a Widmanstatten alpha microstructure within the equiaxed grains.

Large size sandwich structure is involved in a wide range of applications, such as aerospace and ship. However, the weak connection between panel and lattice is the bottleneck problem restricting their application. To solve this problem, this work demonstrates a novel circular scanning connection method based on pulse hot-wire arc additive manufacturing (PHWAAM) to connect the centimeter-scale and meter-scale panel. This method exhibits great connection quality (without unmelted holes) and high efficiency (about 60s for each connection). The optimized process is studied, based on systematical analysis of the microstructure, the macro defects, and the compression testing results. By comparing and analyzing three different connection modes, the optimized circular scanning process has the advantages of low heat input and high deposition efficiency. It can be observed from the microstructure that there are equiaxed crystals and short columnar crystals in the connection area. The width of acicular α phase is finer than that of other processes, which is conducive to improving the mechanical properties. The connection area of the circular scanning process has a better matching of strength and plasticity through the compression test. Finally, the proposed connection method is also applicable to fabricate multi-cell lattice sandwich structure.

In order to overcome weld joint softening of aluminum alloy, laser melting injection (LMI) methodology with 6H-SiC particles (SiCp) and 6061 aluminum alloy was introduced. In this manufacturing, the molten pool morphology and temperature were gained by high speed camera and thermal imager. After LMI, a graded distribution of SiCp with 4.6%–4.8% volume fraction was obtained along the depth direction of weld. The aluminum grain under LMI (12.80 μm) was much finer than that under single laser welding (SLW) (40.94 μm). It was novel that the in-situ reactant Al4C3 platelets would mainly locate discontinuously on the SiC/Al interface whereas acicular Al4SiC4 was found primarily in the aluminum matrix. In addition, the nano-spherical simple substance carbon was precipitated around the surface of SiCp. Eventually, due to these particular in-situ reactions during laser welding with SiCp injection, the Vickers hardness of weld with SiCp was larger than that under SLW; a gradual hardness distribution in the depth direction of PRW was also observed; the tensile strength of weld with SiCp (192 MPa ~ 243 MPa) became much higher without sacrificing ductility than SLW (165 MPa); the failure mechanism of weld with SiCp would change from SiCp cracking to the SiCp decohesion with the increasing welding speed.

As a commonly used engineering material, the mechanical properties of titanium alloy under dynamic loads are closely related to their microstructure. In this work, the effects of solution treatment (ST) and solution and aging treatment (SAT) on the microstructure and dynamic compressive properties of Ti–6Al–4V alloy manufactured by selective laser melting were studied. The results showed that the microstructure of selective laser melted Ti–6Al–4V consisted of nearly full acicular α′ martensite, then the acicular α′ martensite was decomposed into α+β phase with basket-weave morphology with solution treatment. Clusters of α2 particles with size of several hundred nanometers were precipitated in the α plates further with solution and aging treatment. The ultimate compressive strength (UCS) of selective laser melted TC4 alloy was increased with the increasing strain rate, showing strong strain rate hardening effect. Stress collapse happened once the strain exceeded 1500/s, which is the dominant failure model of selective laser melted TC4 under impacting load. As expected, the UCS of the ST sample decreased, but the ductility increased compared with the as-built sample; however, both the UCS and ductility of the SAT samples were enhanced synergistically due to the widely distributed α2 precipitates. Besides, the SAT samples had the highest energy absorption compared with the as-built and ST counterparts under the same conditions, indicating that the SAT samples had better load-bearing capacities.

In this paper, Ti6Al4V octahedron lattice structures with top cap and bottom base were fabricated through selective laser melting (SLM). The structural integrity, microstructural evolution, compressive properties and failure mechanism of as-fabricated (AF) and vacuum annealing treated (VAT) samples were studied through both experiments and numerical modeling. The X-ray computed tomography analysis revealed that vacuum annealing had an insignificant effect on internal pore elimination and porosity reduction. For both the AF and VAT samples, larger pores exhibited more irregular shape than smaller pores. The microstructural analysis suggested that vacuum annealing was able to transform acicular α/α` martensites into uniformly distributed lamellar α + β phases and also to cause the formation of nano-particle precipitation and dislocation. The compressive test indicted that the lattice structure with confined top and bottom had much better compressive properties than those without. Also, vacuum annealing significantly improved the compressive strength by 26% due to the synergistic effect of residual stress relief, nano-particle precipitation and dislocation strengthening. The ductility of the VAT sample was also improved as compared to the AF sample, which was mainly attributed to the formation of α + β phases.

No underwater laser additive manufacturing technology has been reported. In this paper, the underwater thin-walled Ti-6Al-4V part was built firstly by underwater laser metal deposition (ULMD), and the formability, grain growth and microstructure transformation were investigated. The stable local dry cavity and the shielding-gas flow layer surrounding the deposited layer formed during the ULMD process utilizing an improved ULMD nozzle, generating the uniform thin-walled part without cracks and pores. Columnar β-grains, growing epitaxially opposite to the heat flow direction, were observed in the whole ULMD part, and the grain size increased firstly and then reduced with increasing the deposition layer, attributed to the comparative growth and decreasing cooling rate. The water cooling effect suppressed the formation of equiaxed β grains that only formed in the top region of ULMD part. For the microstructures of ULMD sample, only acicular martensites α' with different size scales formed in the bottom region, and martensites α' were replaced gradually by α phase with lamellar, lathy and blocky shapes with increasing the building height, except the top region because the absence of multiple thermal cycles. The larger cooling rate promoted the formation of α' martensite and decreased the width of α lath of ULMD part.

Additive manufacturing has emerged as a promising route to fabricate complex-shaped Ti-6Al-4V parts. The microstructural evolution and variant selection across builds in response to different printing strategies processed by electron beam powder bed fusion has been previously clarified. However, a detailed knowledge of the grain boundary plane characteristics of the α-α intervariant interfaces is still missing. The aim of this study was to reveal the full ‘five-parameter’ crystallographic characteristics of the intervariant boundaries. The most common α-α intervariant for colony and basketweave microstructures was 60°/[1 1 2 ¯ 0], while in the acicular microstructure, the maximum was at 63.26°/[ 10 ¯ 5 5 3 ¯ ]. This is discussed in terms of self-accommodation during the β to α phase transformation, and the degree of coherence of the α laths in the as-deposited condition and during further growth. The grain boundary plane distributions reveal a high tendency for intervariant boundaries to terminate on prismatic and pyramidal planes rather than on low-energy basal planes. This suggests that, during additive manufacturing of Ti-6Al-4V and irrespective of the α morphology, the crystallographic constraints imposed by the Burgers orientation relationship determine the boundary plane distribution characteristics.

Microstructural features of austenite formation, including the growth morphologies and partitioning of alloying elements, during reverse transformation in a Fe-9.6Ni-7.1Mn (at.%) martensitic steel have been studied by phase field modelling with a coupled diffusional/displacive mechanism. Typical morphological patterns of reversed austenite transformed from lath martensite are revealed by the simulation results, containing acicular austenite (γA) formed along the martensite lath boundaries and globular austenite (γG) formed along the high angle prior austenite grain boundaries. It is also shown that the growth of γA, as governed by a combined displacive and diffusional mechanism, is accompanied by a higher enrichment of alloying elements (Mn and Ni) compared with γG, which is governed by a diffusional mechanism. Meanwhile, γG tends to grow preferentially to one side of the prior austenite grain boundaries, due to the presence of partial non-orientation relationship with adjacent martensite laths during the transformation. At the later stage of the reverse transformation, invasive growth behavior of γG to γA after impingement is found due to the minimization of gradient energy in the system and the concentration difference of alloying elements within the two types of reversed austenite. A possible mechanism for grain refinement during intercritical annealing process is finally proposed. Keywords: Phase field modelling, Morphological patterns, Acicular austenite, Globular austenite, Reverse transformation

Based on cold metal transfer (CMT) welding, wire-arc additive manufacturing (WAAM) technology was adopted to manufacture 2Cr13 part. The spatial periodicity of the microstructural evolution and the anti-indentation properties was explored. The results show that the as-deposited part was featured by periodic martensite laths within the block-shaped ferrite matrix in the inner layers, followed by epitaxial ferrite grains containing ultra-fine acicular martensite in the top layer only. A slightly decreased Fe intensity was caused by local elemental segregation during the re-melting process; the homogeneity of Fe and Cr was attributed to similar cooling conditions in the top layer. The martensite size gradually coarsened from the fine grain zone to the coarse grain zone and the shape transformed correspondingly from irregularly short bar-like to orderly long rod-like due to the location-related thermal history. Elongated ferrite grains exhibited a slight fiber texture in the top layer and a random crystallographic orientation in the middle region. The anti-indentation properties evolved periodically due to the periodic microstructural characteristics. The obtained experimental results confirmed higher anti-indentation properties of the as-deposited part following comparison with the as-annealed base metal, while the elastic moduli of samples were not significantly different. Keywords: 2Cr13 thin-wall part, Wire-arc additive manufacturing, Cold metal transfer welding, Periodic structure, Anti-indentation properties

Antibacterial Fe-Cr alloy is emerging in biomaterials. To study the influence of plastic strain on the copper precipitations in this material, a series of experiments were performed in this paper. A commonly used Fe-17wt%Cr alloy with 1.5wt%Cu was cold rolled with a reduction from 12.5% to 75%. It was found that the rod-shaped copper precipitations transformed to acicular or equiaxed and the lattice constant of the matrix became larger after cold rolling which demonstrated that the copper precipitations dissolved into the matrix. The antibacterial tests indicated that the material will lose its antibacterial effectiveness after cold rolling. These phenomena are because that the copper precipitation is softer than the matrix and the plastic deformation more easily occurs in copper precipitation, which significantly improves the gibbs free energy of copper precipitation resulting in a bigger copper solubility and critical precipitation radius. Therefore, the copper precipitation dissolves into the matrix during the cold rolling process and the antibacterial function deteriorates. These results will provide fundamental guidelines for the optimal design of antibacterial Fe-17wt%Cr alloy production process. Keywords: Copper precipitation, Deformation, Dissolution, Antibacterial Fe-17wt%Cr alloy

The synthesis and characterization of thin M-type barium hexaferrite (BaFe12O19 or BaM) films on silicon are reported. Multilayer in situ technique was employed to anneal the films at 850–900 °C for 10 min. The thickness dependence of the magnetic properties of the BaM films has been investigated using VSM. For the BaM 150 nm thickness film, acicular BaM grains were present having their c-axis randomly oriented. For the BaM films thicker than 150 nm, lattice relaxation favors the c-axis to be aligned in the film plane. The micromagnetic simulation was used to model the out-of-plane and the in-plane hysteresis loops. We have achieved good matching between the experimental data and the model. Using the micromagnetic model, we have estimated the deflection angle of c-axis from the normal plane θ = 25° for the 150 nm thick film. Keywords: Barium hexaferrite, Magnetic properties, Hysteresis loop, Micromagnetic modeling, VSM

The composition, phase transitions and isothermal oxidation dynamics of a new polycrystalline Ni-Cr-Co-W base superalloy are investigated using CALculation of PHAse Diagrams (CALPHAD), Differential Scanning Calorimetry (DSC), ThermoGravimetric analysis (TG/dTG), Scanning Electron Microscope and Energy Dispersion Spectrum (SEM/EDS) methods. The microstructure of the designed alloy shows a uniform γ matrix with the precipitates of rich-Ti cellular η and rich-Nb acicular platelet δ phase, and no Topologically Close-packed Phases (TCPs) observed, and the oxide behavior obeys a parabolic law with a parabolic constant (kp) 2.945mg2/(cm4·h) at isothermal 1300°C for 30 hours. The oxide scales are composed of an outer loose oxide mixture containing Cr, Ni, Ti and Nb/Ta and generous pores presented for a volatilization of Cr2O3, and a dense aluminum-rich oxide layer. Keywords: Nickel base superalloy, Composition design, Phase transition, Isothermal oxidation dynamics

A novel beta titanium alloy Ti-4Al-7Mo-3Cr-3V (Ti-4733) was developed and the effect of its microstructure on the tensile properties was investigated and compared with the one of the commercial titanium alloy Ti-5553. Various alpha phase morphologies, namely globular, lamellar, acicular and a combination of them, were obtained as a result of the various heat treatments to which both the alloys were subjected. Although the alpha phase morphology for a given heat treatment was similar in both the alloys, the obtained microstructure was generally finer in the Ti-4733 alloy than in the Ti-5553 alloy, leading to enhanced tensile properties. The results showed that the microstructures with solely fine acicular alpha precipitates exhibited the highest tensile strength. While the highest reduction of area was derived in case of globular-acicular morphology, the maximum elongation was observed in microstructures containing lamellar-acicular alpha phase. Furthermore, for both the alloys the best balance between strength and ductility occurred in microstructures with a combination of globular and acicular alpha phase. The fractography analysis carried out on the tensile tested specimens showed a completely ductile fracture in case of globular-acicular morphology, ductile-transgranular brittle for lamellar-acicular morphology, and ductile-intergranular brittle for fully acicular α phase morphology. Keywords: Beta titanium alloys, Alpha phase morphology, Tensile properties, Fracture

Ti6Al4V alloy exhibits an excellent potential for biomechanical applications as well as structural engineering applications, especially in the aerospace industry and marine applications. In this study, the effect of laser welding (LW) on grain structure and the mechanical properties in a selective laser melted (SLM) Ti6Al4V is reported. The studied material was SLMed at two different layer thicknesses t, 30 and 50 µm, and respective energy densities 69.4 and 60.3 J/mm3. Post-annealing treatment at 940 °C for 4 h was carried out to relieve stress, induce the β-phase and reduce the acicular ά martensite content, thereby helping to enhance its mechanical properties. Subsequently, LW was employed to join SLMed Ti6Al4V plates using a 2.4 kW laser travelling at 60 mm/s. The microstructures were studied as-built by SLM and after LW, followed by an evaluation of the mechanical properties. X-ray diffraction (XRD) and optical microscopy were applied for phase analysis and uniaxial tensile tests were conducted to study the joint strength. The most relevant results of the present work are that the layer thickness plays a key role on tensile properties of the SLMed Ti6Al4V. The SLMed material with t = 50 µm showed higher strength with yield strength 940 MP and ultimate strength 1130 MPa, while the corresponding properties of t = 30 µm were 910 MPa and 1080 MPa, respectively. However, the fracture elongation of the as-built materials with t = 30 µm was 15% as compared to 9% in the higher t. The tensile results of the laser welded materials did not reveal loss in the mechanical properties at both t.

A novel titanium alloy (Ti–5.5Al–3.4Sn–3.0Zr–0.7Mo–0.3Si–0.4Nb–0.35Ta) with a relative density of 99.34% was produced by selective laser melting (SLM) under the condition of 140 W laser power and 400 mm/s scanning speed. The microstructure, high temperature oxidation resistance and micro-hardness were studied. The results showed that the acicular martensitic α′ phase was about 0.5 μm in width due to the high cooling rate during the SLM process. The comparative measurements showed that the as-SLMed sample had higher oxidation resistance and micro-hardness than those of the as-casted one. And the oxidation mechanism was proposed. Keywords: Selective laser melting, Titanium alloys, Microstructure, High temperature oxidation resistance

Laser additive manufacturing (LAM) is a novel manufacturing technique in which metal components can be fabricated layer by layer. In this study, a recently developed damage tolerance titanium alloy TC21 (Ti–6Al–2Zr–2Sn–3Mo–1.5Cr–2Nb) was deposited by LAM process. Texture and microstructure characterization have been investigated by XRD, SEM and EBSD. Prior β grains texture analysis indicates that the (100) poles concentrate in build direction with a texture intensity about 18.7. During cooling down from β phase field, the β to α phase transformation follows the Burger orientation relationship and a pronounced variant selection occurred. Besides, morphology and scale of α phase are quite different along the build direction due to different thermal history. Very fine rib-like α phase with the length less than 2 μm and acicular martensite α' can be obtained at the bottom and the top of the sample, respectively. In the middle position, distribution and morphology of α phase is quite uneven and the precipitation sequence of α phase is αGB → αWGB → αWM → αS. The reasons by which they formed are discussed. Keywords: Texture, Microstructure characterization, Thermal history, Laser additive manufacturing

Mullite based ceramics were prepared by reaction sintering of mixtures containing kaolin clay and kaolin waste. Phase composition, apparent density, apparent porosity, and modulus of rupture were investigated as a function of sintering temperature and kaolin waste content (varied from zero to 50 wt%). The sintering shrinkage behavior was monitored by dilatometry. The results showed that samples derived from formulations containing kaolin waste were composed of acicular mullite and glass phases at 1500 °C. Ceramic bodies prepared with kaolin waste (25 or 50 wt%) showed better physico-mechanical properties (for sintering up to 1400 °C) than the ones of pure kaolin clay. The evidence seems to suggest that this behavior can be due to a liquid phase assisted sintering mechanism associated with a content of mica ranging from 13.3 to 22.4 wt%.

The scientific literature contains very little knowledge on the morphology of the different rust phases formed upon exposure of carbon steel to the atmosphere. In recent years this topic has attracted the attention of many researchers working on atmospheric corrosion, but the various morphologies seen in microscopic observations and reported in many publications lack a rigorous characterisation and identification in terms of the rust phases that give rise to them. The aim of this paper is to advance in this respect with a dual purpose: firstly to try to make a classification of the numerous different types of morphologies seen in the microscopic observation of rusts formed on carbon steel exposed to marine atmospheres, and secondly to identify some of these morphologies, perhaps the most common, using the powerful SEM/Micro-Raman spectroscopic technique. This work distinguishes several main types of morphology: globular, acicular, laminar, tubular and toroidal, and the variants existing within each group. The rust phases most commonly found are the oxyhydroxides lepidocrocite, goethite and akaganeite and the iron oxide magnetite., The authors gratefully acknowledge the financial support for this study from the Ministry of Science and Innovation of Spain (CICYT-MAT2008-06649). The authors would like to express their gratitude to the companies ENEL and GAS NATURAL-FENOSA for the facilities provided and for allowing the location of the corrosion stations at Cabo Vilano wind farm (Camariñas, Spain).

Welding is an important technology for using titanium alloy plates in aerospace applications. However, pores (welding defects) are introduced into the welded zone during welding, including during the melting process, leading to a decrease in the fatigue strength of the welded titanium alloy joint. Friction stir welding (FSW) seems to be effective for avoiding the deterioration of fatigue strength because it is difficult for pores to form in the welded zone during FSW, which does not include a melting process. Therefore, the microstructure and mechanical properties, including the fatigue properties, of an (α + β)-type titanium alloy, Ti-4.5Al-2.5Cr-1.2Fe-0.1C alloy (Ti-531C), subjected to FSW were investigated. In this study, FSW was conducted from both sides of the plates (double-sided FSW) to ensure that the samples were subjected to the same experimental conditions (plate thickness, specimen geometry, etc.) used in our previous study on laser-welded Ti-531C plates for comparison. No pores are observed on the fractured surfaces of Ti-531C subjected to double-sided FSW. Consequently, higher fatigue strength is obtained for Ti-531C subjected to double-sided FSW compared with the samples subjected to double-sided laser welding. However, an acicular secondary α phase and a grain-boundary α phase in the first welded zone are coarsened by heating in the second welded zone, leading to a difference in hardness in the direction of the loading axis for the fatigue test. As a result, the boundary between these two regions became a stress-concentration site that deteriorates the fatigue strength of Ti-531C subjected to double-sided FSW.

We often notice that we are always surrounded by various colors, and our usual life would be satisfied with colors. Appropriate colorant particles are used in many applications such as foods, cosmetics, papers, walls, toys, and others. Colorant particles have a wide variety of size and shape. Particle sizes are from a few nm to several mm, and there are many kinds of particle shapes such as spherical, acicular, spindle, and granular, according to their manufacturing process (Ito, 2000). It is very important that the suitable colorant particle should be selected for each specific application.

A series of anisothermal hot torsion tests were carried out to simulate hot rolling on a high-strength low-carbon CMnNbMoTi microalloyed steel corresponding to an industrial X80 grade for pipeline construction. Mean Flow Stress was graphically represented against the inverse of temperature to characterize the evolution of austenite microstructure during rolling, which was also studied by optical microscopy and SEM on samples quenched from several temperatures. On the other hand, particles precipitated at different temperatures during rolling were analyzed by means of TEM using the carbon extraction replica technique and their size distribution and mean size were determined, as well as their morphology, nature and chemical composition. The effect of rolling temperature and austenite strengthening obtained at the end of thermomechanicalprocessing on final microstructure and precipitationstate was studied. Austenite strengthening was characterized by means of the parameter known as accumulated stress (Δσ). It was found that ferrite grains are finer and more equiaxed when the austenite is more severely deformed during finishing (higher values of Δσ) but lower values of Δσ generate a higher density of acicular structures after cooling, which should improve the balance of mechanical properties. The increase in strength associated to acicular ferrite compared to polygonal ferrite is revealed by the higher values of Vickers microhardness measured on samples corresponding to low Δσ. On the other hand, (Ti, Nb)-rich carbonitrides can be found from reheating and their size keeps a constant value near 20–30 nm during thermomechanicalprocessing. A second population of much finer (Nb, Mo)-rich carbonitrides whose size is close to 5 nm forms from lower temperatures, near 1000 °C. The accomplishment of two different levels of Δσ at the end of hot rolling schedule does not seem to introduce major differences in precipitationstate before final cooling.

Lime-based mortars modified with admixtures were prepared and subjected to different environments such as outdoor and indoor exposures, climatic chamber, SO2-chamber, and freezing–thawing cycles. The influence that the different admixtures (water repellents, water retainers, polypropylene fibre and a viscosity modifier) had on the pore size distribution of the hardened specimens was assessed and related to the water absorption capacity, and hence to the durability. Ageing resistance and mechanical strengths improved when additives reduced the water intake and increased the air-content. High dosages of water repellents were necessary to enhance the durability, sodium oleate being the most effective additive to endure freezing processes. Also the low tested dosage of fibre, a water retainer (guar gum derivative), and a starch proved to be useful. SO2 deposition caused the formation of calcium sulphite hemihydrate as the main degradation product. A very small amount of calcium sulphate dihydrate was observed. A crystal habit composed of acicular agglomerates of calcium sulphite hemihydrate was detected in SO2 deposition on calcareous materials.

International audience; With the aim of preparing mullite, reactions between aluminum sulfate and silica in appropriate proportions and molten sulfate media M2SO4 (M=Na and/or K) were performed at different temperatures. The powders obtained were characterized by XRD, FT-IR, SEM and TEM. The reactivity was the same in Na2SO4 and (K,Na)2SO4 media. The best results in terms of yield (98.3%) and weight of mullite produced (95%) were obtained in Na2SO4 at 950 °C. The mullite phase exhibits an acicular morphology (75×0.75 μm) and a specific surface area close to 20 m2/g. In K2SO4 medium, a potassium alumino silicate is formed as well as mullite.

In this study, the compression deformation behavior of a Ti6Al4V powder compact, prepared by the sintering of cold compacted atomized spherical particles (100–200 Am) and containing 36–38% porosity, was investigated at quasi-static (1.6 10 3–1.6 10 1 s 1) and high strain rates (300 and 900 s 1) using, respectively, conventional mechanical testing and Split Hopkinson Pressure Bar techniques. Microscopic studies of as-received powder and sintered powder compact showed that sintering at high temperature (1200 8C) and subsequent slow rate of cooling in the furnace changed the microstructure of powder from the acicular alpha (a) to the Widmanst7tten (a+h) microstructure. In compression testing, at both quasi-static and high strain rates, the compact failed via shear bands formed along the diagonal axis, 458 to the loading direction. Increasing the strain rate was found to increase both the flow stress and compressive strength of the compact but it did not affect the critical strain for shear localization. Microscopic analyses of failed samples and deformed but not failed samples of the compact further showed that fracture occurred in a ductile (dimpled) mode consisting of void initiation and growth in a phase and/or at the a/h interface and macrocracking by void coalescence in the interparticle bond region., Technology Development Foundation of Turkey #TTGV-102/T13

Nano-sized BaAl12O19 particles with different morphologies, i.e. spherical, cylindrical, spindly, and acicular, were prepared in the reverse microemulsion. The effects of microemulsion composition and drying method on the particle morphology were investigated. It was found that the acicular BaAl12O19 catalyst has higher thermal stability and catalytic activity for methane combustion than the spherical one.

A small specimen impact test using miniaturized specimens with 1.5, 1.0 and 0.7 mm square and 20 mm length has been demonstrated for evaluating the strength-toughness balance along a cross section of Japanese sword and the ductile-brittle transition properties of three different kinds of weld metals. The traditional empirical processing of Japanese sword gave the excellent gradated balance of strength-toughness. The edge side consisting of the hard structure of martensite showed low absorbed impact energies. On the other hand, the back side of the ferrite/pearlite coexisting structure exhibited higher values. In the case of weld meals, the statistically reliable ductile-brittle transition curves and the values of DBTT and FATT were obtained by using the miniaturized specimens sampled from the different weld metals. They were correlated to those of the conventional Charpy-V specimens. Consequently, the laser welded steel metal composed of an extremely fine acicular ferritic structure has a superior toughness and was estimated to exhibit a DBTT as large as 168 K when converted to the value estimated for standard size specimen.

Publisher Summary This chapter deals with the application of monodispersed particles to industrial applications. Monodispersed silver halide particles are widely used in the photographic industry. They are used in the forms of mixed silver halides, such as AgBrI, AgBrCl, and AgClBrI, nearly pure AgBr and AgCl, or core/shell particles consisting of a core and shell different in composition. Doping a host powder with a small amount of different metal ions is a useful technique for the modification of the physical or chemical properties of original ceramic powders. In addition, it is of great importance to develop new productive methods, such as the gel–sol method, or to extend conventional productive methods, such as the controlled double-jet (CDJ) method. Also, except for barium ferrite, almost all of the monodispersed particles are used in the form of acicular particles in order to achieve a high coercive force by shape anisotropy, because of their relatively low magnetocrystalline anisotropy. For this use, monodispersed particles with a sharp distribution in size and shape are the ideal materials.

Acicular ferrite formation was achieved in medium carbon microalloyed forging steel by both isothermal treatments and continuous cooling. Inhibition of grain boundary nucleation of bainite was observed, which enabled the formation of fully acicular microstructures. High cooling rates were needed to completely avoid the formation of allotriomorphic ferrite. Lower cooling rates caused other phases to develop, but a high volume fraction of acicular ferrite could be obtained using two stage continuous cooling cycles.

Publisher Summary This chapter focuses on silicate structures, which can be considered inorganic polymers based on two basic “monomer” structures: the tetrahedron and the octahedron. Many of the silicates can be pictured as configurations made by the joining of such tetrahedra and octahedra to themselves and to each other in three dimensions. These involve the sharing of corners, edges, and faces in numerous conformations. The possible geometric permutations are further modified by chemical substitutions within the structure, which usually depend on how well a metal ion will fit among close-packed oxygen ions. The fundamental structural unit of industrial silicate minerals is silica tetrahedron. Extended in three dimensions, this structure provides the characteristic hardness and inertness of quartz. The various forms of crystalline silica—most commonly quartz, cristobalite, and tridymite—differ mainly in the relative orientation of adjacent tetrahedra and the shape of voids created within a given plane. Among the industrial minerals, high terahedra density and consequent hardness are also found in chain silicates. Wollastonite is characterized by a repeating, twisted, three-tetrahedra unit, where the chains formed by these silica tetrahedra are connected by calcium in octahedral coordination. Because of this chain structure, wollastonite can occur as acicular crystals in some cases of macroscopic dimensions. Phyllosilicates are characterized in part by an indefinitely extended sheet of rings, with three of the tetrahedral oxygens shared and the fourth (apical) oxygen, in each case pointing in the same direction. Phyllosilicates are often differentiated as dioctahedral or trioctahedral based on octahedral occupancy.

Publisher Summary This chapter develops a science-based methodology for analyzing, optimizing, and designing metal forming processes to control the microstructure and properties in a finite shape. The isothermal forging of a titanium alloys disk is analyzed by the rigid-viscoplastic finite element method (FEM). The nominal composition of titanium alloy TC11l that belongs to two-phase titanium alloy is Ti-6Al-3.5Mo-2Zr-0. 3Si. It has two kinds of microstructure under normal temperature: one is the acicular Weisz structure with good elevated temperature creep property obtained by heat treatment heating above the phase transition temperature (990°C) and the other is the equiaxed α + β structure with good elevated temperature fatigue property obtained by large deformation and heat treatment under phase transition temperature. The acicular β structure can be translated into the stable equiaxed α + β structure with the alloy's being heated and deformed under the phasetransus temperature. The property and extent of this transus depends on the heating temperature and strain. According to this, it is practicable to control the final structure and distribution by controlling blocking shape and forging parameters.

Al ions ranging from 0 to 24 wt% were introduced in α-FeOOH when α-Fe particles were produced through the neutralization of FeCl2 to Fe(OH)2, air oxidation of Fe(OH)2 to α-FeOOH, dehydration of α-FeOOH to α-Fe2O3, and finally reduction of α-Fe2O3 to α-Fe. The effects of Al ion on α-Fe particle are as follows: (1) it increases the dehyration temperature of α-FeOOH particle; (2) it effectively prevents the acicular particles from inter-particle sintering and spherization; (3) it impedes the hydrogen reduction reaction of Fe2O3; (4) it reduces the σ value of Fe particles; (5) it increases the 1Hc and squareness of Fe particles; and (6) it increase the stability of α-Fe toward environmental resistance.

Effect of pretreatment with Ca(II) or Mg(II) ions on the room-temperature coercivity and emission Mossbauer spectrum was studied for acicular γ-F2O3 particles having cobalt ions adsorbed in 3M NaOH solution range from 303 to 375K. When Ca(II)(or Mg(II)) ions particles prior to Co(II) ions adsorption above 341K(or Co-modified γ-F2O3 particles pretreated by Ca(I higher(or lower) than that without pretreatment. Emissi showed that the average internal magnetic field of tides pretreated with Ca(II) ions was larger than that ions. Effect of pretreatment with Ca(II) or Mg(II) ion ions on the surface of γ-F2O3 particles was discussed site preference of cations in ferrite and distribution ion in the temperature were adsorbed on γ-F2O3 303K), the coercivity of I)(or Mg(II)) ions was on Mossbauer spectroscopy Co-modified γ-F2O3 with Mg(II) s on adsorption of cobalt from the view point of ratio of each cation.

After a brief description of the forces encountered between particles in liquids, three different suspensions of magnetic particles are discussed. (1) The lacquers used to make magnetic recording media. In spite of very strong aggregation, magnetization measurements under simultaneous application of shear can discriminate between loosely aggregated particles and permanent clusters. (2) Suspensions of very small acicular particles that repel one another. With these, magnetic parameters of isolated particles were obtained from magneto-optical experiments. (3) Bitter fluids, in which small, permanent aggregates are shown to be the active component.

In this study we present an analysis of the behaviour of low Ms iron-nickel alloys containing different amounts of carbon. Influence of parameters like carbon content, test frequency, cycling rate and strain amplitude are analysed during cooling (austenite to martensite transformation) and heating (first stages of rearrangement). Results are discussed in comparison with phase transformation models on one hand and with carbon-dislocation interaction on the other hand.

Halloysite derived from weathered plagioclase in volcanic ash soils in the San-in district, Japan, exhibits various micromorphological forms, namely, of spherical, walnut-meat-shaped, acicular, crinkly, platy, tubular and square-tube types. Spherical, walnut-meat-shaped and crinkly ones are allophane-halloysite aggregates, whereas the ones of other types are normal halloysite with no allophane. The crinkly type ones consist of rolling spheroidal particles of halloysite and fine allophane granules. The weathering process can be traced morphologically from fresh plagioclase to various types of halloysite. The possible mechanisms of the crystal growth are discussed.

Boron is a powerful, low-cost hardenability promoter; however, its use in HSLA steels has been rather limited due to incomplete understanding of the influence of austenite processing and other microalloying elements on the boron hardenability effect. This study deals with the influence of austenite processing and the effects of microalloy additions and residual elements (namely sulphur and nitrogen) on boron hardenability. Deformation dilatometry coupled with boron autoradiography and transmission electron microscopy has been used to study the effects of processing, in particular, the amount of reduction, the temperature of deformation, and the cooling rate on the transformation kinetics and the final microstructure. Dilatometry results show that air cooling is sufficient to obtain a completely acicular ferritic microstructure. A homogeneous distribution of boron in solution prior to controlled rolling appears to be the most important factor for obtaining a uniform fine-grained acicular ferrite microstructure. Results for plates subjected to accelerated cooling after controlled rolling in a laboratory rolling mill are presented and compared with dilatometry results.

Publisher Summary This chapter discusses the temperature field around a spheroidal, cylindrical, and acicular crystal growing in a supercooled melt. The problem that is formulated is to find all surfaces of the crystallization front and the corresponding temperature fields in the liquid phase satisfying the presented differential equations and the boundary-value conditions. The sequence for solving the problem presented is to find integrals of the nonlinear first-order equation in which arbitrary functions appear and determine the form of the latter. In some cases, it proved to be possible to find the form of the arbitrary function and, thus, solve the formulated problem.