Variety Of Different Microstructures Research Articles

Influence of Local Microstructure on Stresses, Durability and Fracture Mechanics of Cast Iron Components

Cast iron components show a large variety of different microstructures in dependence on chemical composition, inoculation and cooling conditions. In conventional static and dynamic calculations as well as in fracture mechanics assessment of cast iron components, the influence of local microstructure on the overall behavior of the component is not considered. Usually one material dataset is applied for the whole material. The paper describes recent developments in the field of the prediction of local microstructure and its correlation to local stress-strain, fatigue durability as well as fracture toughness. The benefit of combining casting process simulation with lifetime predictions and fracture mechanics assessment is shown for selected examples. By integrating casting process simulation, microstructure modelling, local material characterization and load analysis, a simulation based approach for predicting the behavior and performance of cast iron components already during the design stage is enabled. Thus, the local assessment helps designers to assess risks and strive for light weight designs before the casting is made.

Improved Mechanical Properties by Control of Bainite Transformation

The term bainite describes a variety of different microstructures that can be generated by continuous cooling or isothermal heat treatments. Based on systematic microstructural investigations, a bainite characterization scheme has been developed that distinguishes between different basic structures and substructures, the latter being described by location, type, and form. According to this detailed description, microstructures have been quantitatively analyzed using light optical microscope (LOM), scanning electron microscope (SEM), and electron beam backscatter diffraction (EBSD)-techniques. Some of the microstructural features can be further characterized by nano-hardness measurements. The transformation kinetics of different bainite forms has been determined by dilatometer studies. The kinetics differs significantly depending on the amount of diffusion involved during the phase transformation. Several numerical approaches have been tested and critically evaluated in order to describe the kinetics. Furthermore, for various steel groups, microstructure-property relations have been investigated with a focus on the development of cracks. By this, recommendations for optimized bainitic steels with improved balance of strength and ductility as wells as improved toughness can be deduced.

Controlling the colloidal behavior of styrene–isoprene diblock copolymers by selective end functionalization

ω-Lithium poly(styrene- b-isoprene) sulfonates were synthesized by anionic polymerization. The copolymers carrying the lithium sulfonate (SuLi) end group at either the soluble or the insoluble block form a variety of different microstructures in n-decane. In the case where the SuLi group is located at the PS insoluble end block, micellar aggregates with larger aggregation number, hydrodynamic radius and thermal stability are formed, compared to the non-functionalized diblock precursor case. When the polar group is located in the soluble PI block end, the solubility of the system depends on temperature. At high temperatures where end group association primarily exists, star-like aggregates are formed. At lower temperatures PS block association also takes place, resulting in a system of highly polydisperse and interconnected aggregates. The latter materials can be considered as ABC heterotelechelic associating macromolecules presenting new ways of controlling the colloidal behavior of block copolymer systems by selective end functionalization.

Dynamics of microstructure formation in the two-phase region of peritectic systems

Directional solidification experiments have been carried out in the two-phase region of the Sn–Cd peritectic system. A variety of different microstructures have been shown to form under intrinsically non-steady-state growth conditions in both the hyperperitectic and hypoperitectic compositions. The selection of microstructure is shown to be governed by the relative effects of convection, nucleation undercooling, nucleation rate and the growth competition between the two phases. Convection effects have been found to give significantly different microstructures than those predicted by the diffusive growth models. Experiments are thus carried out in samples of different diameters in which convection effects are shown to be reduced as the diameter of the sample is decreased. It is shown that diffusive growth condition is achieved in this alloy system when the sample diameter is <1.0 mm. Experimental studies are then carried out in hypoperitectic alloys in a composition range for which banded microstructures have been predicted by the diffusive growth model. This composition window is established experimentally, and the values of nucleation undercoolings of the primary and peritectic phase have been obtained. The experiments also confirmed the prediction of the model that the banding cycle occurs above and below the peritectic temperature and bands of primary and peritectic phases form by the alternate nucleation and lateral spreading of one phase onto the other. It is also found that when the sample diameter is reduced further, or growth conditions changed, several new dynamical oscillatory microstructures evolve and the formation of these microstructures is shown to be controlled by the competitive growth processes between the nuclei and the parent phase. This competitive growth is shown to be influenced by the distance between the nuclei or the nucleation rate. It is shown that the directional solidification of peritectic alloys provides a means to quantitatively study the complex process of dynamical evolution of two-phase microstructures in which fluid flow, nucleation undercoolings, nucleation rates of the two phases and the competitive growth of the two phases control the evolution of complex two-phase microstructures.

Compaction of bulk ferromagnetic Fe80P13C7amorphous alloys

When bulk ferromagnetic Fe80P13C7 amorphous rods of approximately 2-mm diameter are compacted together in a hot press, a variety of different microstructures, depending on the experimental conditions, are produced. The most intriguing microstructure is that two different bulk amorphous rods can be fused together perfectly at a temperature of 683 K and under a pressure of 2.5 to 4 GPa for a period of 5 min.

Deformation Microstructure of Cold Gas Sprayed Coatings

ABSTRACTCold Gas Spraying is a new coating technique, in which the formation of dense, tightly bonded coatings occurs only due to the kinetic energy of high velocity particles of the spray powder. These particles are still in the solid state as they impinge on the substrate. Adiabatic heating after impingement can cause local shear instabilities and jet formation. The local microstructure is strongly dependant on local stress state and temperature rise. A variety of different microstructures is observed by TEM. The results are compared with modelling of the spray process.

Modification of the Microstructure in Poloxamer Block Copolymer−Water−“Oil” Systems by Varying the “Oil” Type

Amphiphilic block copolymers can self-assemble in the presence of selective solvents (“water” and “oil”) into a variety of different microstructures. The role that “oil” plays in the phase behavior and structure of copolymer−oil−water systems is the focus of the present investigation. We examined a poloxamer-type poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) triblock copolymer (Pluronic F127: E100P70E100) in ternary isothermal systems with water and each of three “oils” (of varying polarity), p-xylene, n-butyl acetate and butan-1-ol. A total of six phases with different microstructures have been identified in the ternary systems studied here: normal (oil-in-water) micellar cubic (I1), normal hexagonal (H1), lamellar (Lα), and reverse (water-in-oil) hexagonal (H2) lyotropic liquid crystals, and normal micellar (L1) and reverse micellar (L2) solutions. The number and types of phases, as well as the composition range of their stability, are different for each ternary system, reflecting the effects of oil. Systematic small-angle X-ray scattering (SAXS) measurements have been performed in order to establish the structure of the phases and determine their characteristic length-scales. The location of the “oils” in the different self-assembled microstructures has been deduced from the structural dimensions obtained from SAXS and the constraints imposed by the copolymer total volume fraction and interfacial area: all xylene is present in the interior (apolar core) of the oil-in-water microdomains and butanol is located at the interfacial region between poly(propylene oxide) and poly(ethylene oxide), while butyl acetate contributes to both the core and the interfacial domains.

Ion beam analysis of diamond-like carbon films

Diamond-like carbon films are deposited with a number of different methods. This results in a wide variety of different microstructures and even compositions of the films, which challenges characterization capabilities. Ion beam analysis can be used in many ways to probe the properties of the films. A classic application is the determination of hydrogen concentrations in hydrogenated amorphous carbon films, a-H : C. This is performed by using either a resonance of the nuclear reaction 1H( 15N, αγ) 12C or a forward recoiling technique. Diamond-like films have been doped with metals, Si, F, etc. in order to modify mechanical, tribological, or optical properties. Dopand concentrations can be qualitatively measured using either a backscattering or nuclear reaction analysis (NRA) method. A fairly trivial application is the utilization of either Rutherford or non-Rutherford backscattering to obtain the number of carbon atoms per square centimetre. Combined with other information on the chemical composition of the film and with the thickness obtained with a profilometer, for example, the density of the very thin films can be calculated. The density is an interesting parameter of the films and may vary considerably, depending on the hydrogen concentration and the structure of chemical bonding. If the thickness of the films is not constant or if a diamond-like material is just a deposition with an irregular shape, the above method cannot be utilized. The ion beam technique may still be useful and the Doppler shift attenuation of the resonance can be used. Resonance techniques are useful in analysing some other carbon related films, for example in analysing nitrogen in CN x films. In this paper, the most useful ion beam techniques for analysing diamond-like materials are given with examples.

Polymer-derived Si-based bulk ceramics, part II: Microstructural characterisation by electron spectroscopic imaging

The microstructure of polymer-derived Si-based ceramic materials was characterised with elemental distribution images produced by electron spectroscopic imaging. Depending on the processing conditions, a variety of different microstructures were obtained from the same precursor: without sintering additives, amorphous silicon carbonitride which is stable against crystallisation up to 1400 °C is formed. In the presence of Al 2O 3 and Y 2O 3 as sintering additives, Si 3N 4/SiC-composite materials and Si 2N 2O ceramics are produced. Sintering a mixture of Si 3N 4 powder with additional polysilane leads to a Si 3N 4/SiC-composite comprising nano-sized SiC inclusions in the Si 3N 4 grains. The development of the microstructure of the Si 3N 4/SiC composite materials was investigated as a function of the sintering temperature and of the concentration of the sintering additives. The observed microstructural changes lead to conclusions on the processes which occur during the sintering of the materials.

Catalytic hydrosilation of polybutadienes as a route to functional polymers

Polybutadienes having a variety of different microstructures have been hydrosilated using HSiMexCl3 –x, x= 0–2 in the presence of H2[PtCl6]. High conversions of double bonds pendant from the main chain are observed but hydrosilation also occurs on the backbone of the polymer especially if there is a high percentage of backbone double bonds. This backbone hydrosilation is accompanied by double-bond migration along the polymer backbone to give conjugated diene units within the polymer backbone. These polymers have been further functionalised by reactions with alcohols [EtOH, EtO(CH2CH2O)2H, 4-hydroxybiphenyl or MeO(CH2CH2O)nH (Mn= 500 or 750)] in the presence of Et3N or by alkylation, e.g. with 2-lithiomethylpyridine or with 6-lithio-2,2′-bipyridine. Polymers containing —SiMex(OR)3 –xx= 2 or 0, R = EtO(CH2CH2O)2H or MeO(CH2CH2O)nH (Mn= 500 or 750) have been shown to form polymer electrolytes, in some cases with room-temperature conductivities as high as 2.5 × 10–5S cm–1. Sequential hydrosilation and epoxidation reactions have been carried out to give polymers in which the pendant double bonds have been hydrosiiated and the backbone double bonds have been epoxidised.

Heat treatment of a melt spun Fe 70Cr 18Mo 2B 10 alloy

Microstructural changes during annealing of melt spun Fe 70Cr 18Mo 2B 10 ribbons have been studied by a combination of differential scanning calorimetry, X-ray diffractometry, transmission electron microscopy, and energy dispersive X-ray microanalysis. The as-melt spun microstructure consists of bcc ferrite primary crystals embedded in an amorphous matrix. The crystallization onset, peak and finish temperatures of the amorphous phase are 533, 552 and 573°C, respectively, during continuous heating at 10°C/min. Isothermal annealing of the as-solidified amorphous ribbons for 2 h at different temperatures in the range 500–1000°C leads to a variety of different microstructures depending on the annealing temperature. At 500 and 600°C, the amorphous alloy crystallizes to form a fine scale mixture of bcc ferrite grains and Cr rich primitive tetragonal M 3B boride particles. At 700 and 800°C, the alloy microstructure transforms into a mixture of faulted Cr rich orthorhombic M 2B and Mo rich fcc M 23B 6 boride particles embedded in a matrix of bcc ferrite. At 900°C, the bcc ferrite matrix is replaced by fcc austenite, which transforms to dislocated lath martensite on cooling to room temperature. At 950 and 1000°C, the Mo rich fcc M 23B 6 boride particles are replaced by Mo rich primitive tetragonal M 3B 2 boride particles.

Polycarboxylic acids via catalytic hydrocarboxylation of polybutadienes

Polycarboxylic acids with a variety of different micro-structures have been prepared by homogeneous catalytic hydrocarboxylation of polybutadienes using palladium based catalysts; the microstructure of the product polymers depends upon that of the starting material as well as on the nature of the catalyst system, since selectivity between functionalisation at the backbone double bonds or at the terminal or internal carbon atom of the pendant double bonds can to some extent be engineered.

Low-shrinkage reaction-bonded alumina

A novel method of manufacturing strong Al2O3 bodies with low (<1%) shrinkage is presented. Compacts of attrition-milled Al/Al2O3 powder mixtures are heat treated at temperatures between 1200 and 1550°C such that the expansion due to the Al→Al2O3 reaction and the shrinkage on sintering of Al2O3 is nearly balanced. Depending on processing parameters such as Al/Al2O3 ratio, compaction pressure and heating cycle, a variety of different microstructures can be developed. In spite of some residual porosity, strengths of ∼300 MPa are attained.

The use of mixed alloy contacts to engineer the interfaces and electrical characteristics of metal-InP contacts

The present study has examined the relationship between the I-V electrical characteristics and the interfacial microstructure present in Ag/In-(100)InP metal-semiconductor contacts. By depositing mixed alloy contacts of silver and indium on to (100)InP surfaces and then using thermal treatments to activate the interface, a variety of different microstructures has been generated within the interface of the contact. The different microstructures have then been related to the electrical characteristics of the contact. It has proved possible to engineer the contact's interface into differing states that reproducibly generate Schottky or truly Ohmic-like behaviour. The alloy contacts have been deposited with precise compositions by making use of separate Knudsden sources operating within an MBE system. The contact's interface has been characterised with Auger profiling and by direct observation with scanning electron microscopy.