Effect Of Material Microstructure Research Articles

Microstructure characterization and crystal plastic finite element simulation of additive manufacturing 316 L stainless steel

Due to the layer-by-layer molding mode of additive manufacturing (AM) technology, the mechanical properties of additive manufacturing structural parts are very different from those of traditional structural parts. The macroscopic mechanical properties of additive structural parts show obvious anisotropy; thus, the macroscopic model is not suitable to describe the effect of material microstructure (grain distribution, initial grain orientation, etc.) on the macroscopic mechanical behavior. Setting up a simplified structure microstructure of representative volume element (RVE), and the mechanical behavior response of AM 316 L stainless steel is simulated based on the finite element method for crystal plasticity. While uniaxial tension was regarded as a typical loading, the effect of microstructure on macroscopic mechanical properties is analyzed in combination with grain distribution and grain orientation. The results show that the numerical model not only reflects the impact of microstructure on macroscopic mechanical behavior but also suggests theoretical advice for practical production.

Microstructural effects on the response of a multi-layered elastic substrate

The size dependent response of a multi-layered elastic substrate under surface loading is investigated in the present work. The effect of material microstructure is modeled using the generalized continuum theory of couple stress elasticity. In the formulation, the displacement field is chosen as a primary unknown and the generalized Navier’s equation is established for a generic material layer. The Fourier integral transform method is directly applied to derive the general solution of the elastic field for the generic layer, and such solution is subsequently utilized to form the layer stiffness equation in the transform space. Boundary conditions together with the field continuity across the material interfaces are enforced, via the standard assembly procedure, to obtain a system of linear algebraic equations governing all unknowns of the multi-layered system. An efficient quadrature is adopted to carry out all involved integrals arising from the integral transform inversion. Detailed results are reported that confirm the validity of our results through the comparison with well-known solutions and demonstrate the capability of the proposed model to simulate various scenarios of layered media including those made of functionally graded materials. The important role of the material length scale effect on the predicted response is also elucidated.

Influence of batch-to-batch material variations on grindability of a medium‑carbon steel

This study addresses the influence of material variations on the grindability of crankshaft steel. Most previous studies on the effect of material microstructure on grindability involve comparisons of significantly different steel grades. This study, in contrast, is focused on batch-to-batch grindability variations for one steel grade, a scenario frequently occurring in industry where batches from different steel makers are fed into a production line. For this purpose, a batch made of recycled steel and a batch made of ore-based steel were compared with regards to microstructure and grindability under identical grinding and dressing conditions. Although both batches met the same material specifications, microstructural variations were identified in terms of grain size and micro-constituents (inclusions, carbonitrides). While specific grinding energy, residual stress and full-width at half-maximum profiles of ground surfaces were the same for both batches, the recycled batch showed different and unfavorable variation in wheel wear and Barkhausen noise (BN) response. Larger fractions of oxide inclusions and larger grain sizes (affected by carbonitrides) were present in the recycled batch, which were the likely reasons for the differences in wheel wear and BN response, respectively. These findings may aid grindability improvement by steel-grade adjustments, e.g. modification of the distribution and type of inclusions and/or amount of elements forming carbonitrides. Furthermore, the results highlight the importance of understanding and controlling material microstructure, as existing in-line quality by BN control may not always be able to correctly indicate surface integrity, which could lead to misinterpretations (e.g. false part-rejection on the assumption of grinding burn).

Electromechanical fields in a hollow piezoelectric cylinder under non-uniform load: flexoelectric effect

The relations of a local gradient non-ferromagnetic electroelastic continuum are used to solve the problem of an axisymmetrical loaded hollow cylinder. Analytical solutions are obtained for tetragonal piezoelectric materials of point group 4 mm for two cases of external loads applied to the body surfaces. Namely, the hollow pressurized cylinder and a cylinder subjected to an electrical voltage V across its thickness are considered. The derived solutions demonstrate that the non-uniform electric load causes a mechanical deformation of piezoelectric body, and vice versa, the inhomogeneous radial pressure of the cylinder induces its polarization. Such a result is obtained due to coupling between the electromechanical fields and a local mass displacement being considered. In the local gradient theory, the local mass displacement is associated with the changes to a material’s microstructure. The classical theory does not consider the effect of material microstructure on the behavior of solid bodies and is incapable of explaining the mentioned phenomena. It is also shown that the local gradient theory describes the size-dependent properties of piezoelectric nanocylinders. Analytical solutions to the formulated boundary-value problems can be used in conjunction with experimental data to estimate some higher-order material constants of the local gradient piezoelectricity. The obtained results may be useful for a wide range of appliances that utilize small-scale piezoelectric elements as constituting blocks.

Multiscale Modeling of the Effect of Membrane Thickness on the Performance of Proton-Exchange Membranes Based on Multiblock Copolymers of Sulfonated PSU/Ppsu Poly(Ether Sulfone)s: Towards High-Performance Fuel Cells

Polymer electrolyte fuel cells (PEFCs) are promising power sources for stationary, portable and vehicular applications due to its key advantages, including quiet operation, quick start-up and load response, and high efficiency. In the last decades, several fuel cell vehicles have been developed by automakers, such as General Motors, Hyundai and Toyota. However, the widespread commercialization of PEFCs for vehicular applications is still limited by their cost, performance and durability, among which durability is the most challenging aspect. The target lifetimes for PEFCs set by the U.S. Department of Energy (DOE) are 5,000 h for passenger cars, 25,000 h for transit buses and 40,000 h for stationary applications. Therefore, currently there is a need to demonstrate the above lifetimes, while decreasing capital and operating costs. In this context, mathematical modeling is an indispensable tool to examine the effect of material microstructure on PEFC performance and degradation. This task requires the development of multiscale models that incorporate key information from the microscale into the macroscale, while keeping computational cost moderate for engineering applications.In this work, multiblock copolymer membranes composed of sulfonated Polysulfone and Polyphenylsulfone poly(ether sulfone) (SPSU/SPPSU) were synthetized by polycondensation using a “one-pot two-step” route [1]. The performance of membranes with different thicknesses at different temperatures (T) and relative humidities (RH) was examined experimentally (see Figure 1). The data were compared with the predictions of a multiscale, non-isothermal, two-phase model of a PEFC accounting for non-equilibrium water sorption/desorption in the catalyst layers, as well as non-equilibrium water evaporation/condensation in the porous media of the MEA (GDLs, MPLs and CLs) and in the channels. The dominant transport mechanisms of dissolved water in the electrolyte were assumed to be diffusion and electro-osmotic drag. Double-trap kinetics was considered to model the oxygen reduction reaction, while Butler-Volmer kinetics was used to model the hydrogen oxidation reaction [2-5].The combined experimental and numerical work has revealed key information on the interplay between membrane thickness, performance and water management for the design of high-performance, durable PEFCs. Currently, work is underway to develop thin multiblock copolymer membranes with power densities above 1 W cm-2 and extended durability within DOE targets.[1] N. Ureña, M.T. Pérez-Prior, C. del Río, A. Várez, J.Y. Sánchez, C. Iojoiu, B. Levenfeld, Multiblock copolymers of sulfonated PSU/PPSU Poly(ether sulfone)s as solid electrolytes for proton exchange membrane fuel cells, Electrochim. Acta 302 (2019) 428–440.[2] P.A. García-Salaberri, D.G. Sánchez, P. Boillat, M. Vera, K.A. Friedrich, Hydration and dehydration cycles in polymer electrolyte fuel cells operated with wet anode and dry cathode feed: A neutron imaging and modeling study, J. Power Sources 359 (2017) 634–655.[3] A. Goshtasbi, P.A. García-Salaberri, J. Chen, K. Talukdar, D. García-Sánchez, T. Ersal, Through-the-Membrane Transient Phenomena in PEM Fuel Cells: A Modeling Study, J. Electrochem. Soc. 166 (2019) F3154–F3179.[4] P.A. García-Salaberri, I.V. Zenyuk, G. Hwang, M. Vera, A.Z. Weber, J.T. Gostick, Implications of inherent inhomogeneities in thin carbon fiber-based gas diffusion layers: A comparative modeling study, Electrochim. Acta 295 (2019) 861–874.[5] J. Liu, P.A. García-Salaberri, I.V. Zenyuk, Bridging Scales to Model Reactive Diffusive Transport in Porous Media, J. Electrochem. Soc. 167 (2020) 013524.. Figure 1. (left) Polarization curves and (right) power density curves corresponding to multiblock copolymer membranes with different dry thicknesses and RHs. The operating temperature of the pure oxygen feed PEFC is T=60 oC.. Figure 1

Size effects in two-dimensional layered materials modeled by couple stress elasticity

In the present study, the effect of material microstructure on the mechanical response of a two-dimensional elastic layer perfectly bonded to a substrate is examined under surface loadings. In the current model, the substrate is treated as an elastic half plane as opposed to a rigid base, and this enables its applications in practical cases when the modulus of the layer (e.g., the coating material) and substrate (e.g., the coated surface) are comparable. The material microstructure is modeled using the generalized continuum theory of couple stress elasticity. The boundary value problems are formulated in terms of the displacement field and solved in an analytical manner via the Fourier transform and stiffness matrix method. The results demonstrate the capability of the present continuum theory to efficiently model the size-dependency of the response of the material when the external and internal length scales are comparable. Furthermore, the results indicated that the material mismatch and substrate stiffness play a crucial role in the predicted elastic field. Specifically, the study also addresses significant discrepancy of the response for the case of a layer resting on a rigid substrate.

Effect of microstructure on high-speed cutting modified anti-fatigue performance of Incoloy A286 and titanium alloy TC17

Anti-fatigue performance is vital for components used in aerospace industry, and cutting processes were widely considered to modify the workpiece anti-fatigue performance. However, most of the existing researches only associated the anti-fatigue performance to the cutting condition and surface integrity, without revealing the effect of material microstructure. In this work, the Incoloy A286 and titanium alloy TC17, two kinds of commonly used material in aerospace industry, were adopted as samples to reveal the influence mechanism of material microstructure on the high-speed cutting modified anti-fatigue performance. It was found that, due to the different microstructure, especially the grain structure and size, the effects of cutting process on the machined surface integrity and anti-fatigue performance of these two materials were different. For Incoloy A286, the large size and cubic structure increased the difficulty in deformation and breaking of grains, making the cutting parameters have limited effect on grain refinement. Hence, the fracture toughness of machined surfaces decreased on the whole with an increased feed rate and depth of cut, which reduced the fatigue life. For titanium alloy TC17, the small lath-shaped grains were easy to deform and break, resulting in the notably grain refinement of machined surfaces, which contributed to the prolonged fatigue life when the feed rate and depth of cut increased. All in all, the material microstructure may change the effect rule of cutting process on the machined workpiece anti-fatigue performance, and thus the cutting condition should be designed by considering the material microstructure.

Effect of crystallographic orientation on residual stress induced in micro-grinding

In micro-grinding, the effect of material microstructure on residual stress is significant since the depth of cut is usually smaller than the average grain size. In this paper, the effect of crystallographic orientation (CO) on the distribution of residual stress induced by micro-grinding is investigated. The COs and their volume fractions of workpiece material are quantified by Taylor factor, based on which the models of flow stress and plastic modulus of polycrystalline materials are proposed. Then, the residual stress is calculated based on the micro-grinding force and temperature derived from the flow stress, after the mechanical and thermal loading followed by relaxation process, which are analyzed with the developed plastic modulus. Thereby, the compressive analytical model of micro-grinding-induced residual stress is proposed considering the grinding parameters, wheel topography, and material microstructure. In addition, micro-grinding experiments and residual stress measurements are conducted to verify the models. The prediction of residual stress agrees well with the experimental result. Residual stresses are measured by X-ray techniques, and the results illustrate that the COs of material would influence the state of stress. Finally, the sensitivity analysis is carried out, with the result showing that the effect of CO on residual stress is significant.

Effect of material microstructure on tool wear behavior during machining additively manufactured Ti6Al4V

Additive Manufacturing (AM) technologies are increasingly applied in various industries since they provide the possibility to manufacture the components with high geometrical complexity easier and faster than traditional processes. However, the subsequent semi-finish/finish machining operations such as drilling, turning and/or milling are still necessary for AM parts to obtain the required surface textures and meet the practical requirements. As such, the AM parts usually indicate different machinability compared with conventionally produced ones in view of the different material microstructures. A comprehensive understanding of this machining effort is of great importance for similar engineering applications but not widely reported. Thus, an attempt was made in this work to address the effect of the material microstructure on the machining stability and tool wear behavior in dry drilling of the hard titanium alloys. The experimental results highlight a correlation between the tool wear behavior and material microstructures. A great number of micro-pits appeared on the tool flank face and the abrasive marks, coating delamination, as well as catastrophic failure of the cutting edge were found to be more obvious during machining the DMLS alloy. In contrast, adhesion wear followed by micro chipping and build-up edge were distinguished when machining the wrought Ti6Al4V. Meanwhile, heat treatment can improve the flow plasticity and reduce the brittleness of the AM material since catastrophic failure disappeared and chip adhesion becomes more predominant when machining the HTDMLS Ti6Al4V.

Coated conductor technology for the beamscreen chamber of future high energy circular colliders

The surface resistance of state-of-the-art REBa2Cu3O7−x coated conductors has been measured at 8 GHz versus temperature and magnetic field. We show that the surface resistance of REBa2Cu3O7−x strongly depends on the microstructure of the material. We have compared our results to those determined by the rigid fluxon model. The model gives a very good qualitative description of our data, opening the door to unravel the effect of material microstructure and vortex interactions on the surface resistance of high temperature superconductors. Moreover, it provides a powerful tool to design the best coated conductor architecture that minimizes the in-field surface resistance. We have found that the surface resistance of REBa2Cu3O7−x at 50 K and up to 9 T is lower than that of copper. This fact poses coated conductors as strong candidate to substitute copper as a beamscreen coating in CERN’s future circular collider. To this end we have also analyzed the secondary electron yield (SEY) of REBa2Cu3O7−x and found a compatible coating made of sputtered Ti and amorphous carbon that decreases the SEY close to unity, a mandatory requirement for the beamscreen chamber of a circular collider in order to prevent the electron-cloud phenomenon.

Investigating the effect of material microstructure and irradiation temperature on the radiation tolerance of yttria stabilized zirconia against high energy heavy ions

Yttria stabilized zirconia pellets with different crystallite sizes were irradiated with 80 MeV Ag6+ ions at room temperature and 1000 K to understand the effect of crystallite size/material microstructure and irradiation temperature on the radiation tolerance against high energy heavy ions [where electronic energy loss (Se) dominates]. XRD and Raman spectroscopy measurements reveal that, irrespective of the irradiation temperature, the nano-crystalline samples suffered more damage when compared with the bulk-like sample. A reduction in the irradiation damage, i.e., improvement in the radiation tolerance, was observed for all the samples irradiated at 1000 K. The reduction in the damage, however, was remarkably higher for the nano-crystalline samples compared with the bulk-like sample, and hence the difference in the damage between the bulk-like and nano-crystalline samples was also significantly lower at 1000 K than that at room temperature. The irradiation damage, against Se, was thus found to be critically dependent on the interplay between the irradiation temperature and the crystallite size. These results are explained on the basis of the “in-elastic thermal spike” model by taking into consideration the combined effects of crystallite size and environmental (irradiation) temperature on the electron-phonon coupling strength and the lattice thermal conductivity and hence on the resulting thermal spike. These results, besides being crucial from the fundamental prospect of comprehending the size and temperature dependent radiation damage against Se, may also be important from the perspective of designing highly nano-crystalline materials for applications in various radiation environments.

The effect of material microstructure on the built-up layer formation in dry cutting of Inconel 718

The effect of material microstructure on the built-up layer formation in dry cutting of Inconel 718

Effects of material microstructure and surface microscopic geometry on the performance of ceramic cutting tools in intermittent turning

The present work was performed to reveal the integrated effects of material microstructure and surface microscopic geometry on the performance of Al2O3-based composite ceramic cutting tools in intermittent turning. Influences of material microstructure on the initial elastic modulus and material damage of ceramic cutting tools were evaluated on the basis of the established microstructure models and damage mechanics. The effects induced by tool surface microscopic geometry on cutting forces and tool temperatures were revealed based on finite element simulation. Taking the cutting condition into account, a new indicator was used to reflect the integrated effects of material microstructure and surface microscopic geometry on tool performance. A theoretical method was proposed to acquire the optimal combination of tool material microstructure and tool surface microscopic geometry in terms of too life. When material porosity increased from 0.5% to 2.5%, elastic modulus and tool damage decreased and increased, respectively. Compared to ceramic tool material (A) reinforced only by micro (W, Ti)C particles, the variation of material porosity had less effects on the damage within the tool material (B) which contained both micro (W, Ti)C and nano Al2O3 particles. Designing micro-texture pattern (pattern d) on the tool rake face with both the solid-like and liquid-like properties of the chip considered was most efficient for the reduction of cutting forces and tool temperatures. The optimum combination of tool material microstructure and tool surface microscopic geometry can be achieved by using ceramic tool material B and micro-texture pattern d. The experimental tool lives demonstrated the correctness of the tool performance indicator and the theoretical method for acquiring the optimum combination of tool material microstructure and tool surface microscopic geometry.

Lamb wave extraction of dispersion curves in micro/nano-plates using couple stress theories

In this paper, Lamb wave propagation in a homogeneous and isotropic non-classical micro/nano-plates is investigated. To consider the effect of material microstructure on the wave propagation, three size-dependent models namely indeterminate-, modified- and consistent couple stress theories are used to extract the dispersion equations. In the mentioned theories, a parameter called ‘characteristic length’ is used to consider the size of material microstructure in the governing equations. To generalize the parametric studies and examine the effect of thickness, propagation wavelength, and characteristic length on the behavior of miniature plate structures, the governing equations are nondimensionalized by defining appropriate dimensionless parameters. Then the dispersion curves for phase and group velocities are plotted in terms of a wide frequency-thickness range to study the lamb waves propagation considering microstructure effects in very high frequencies. According to the illustrated results, it was observed that the couple stress theories in the Cosserat type material predict more rigidity than the classical theory; so that in a plate with constant thickness, by increasing the thickness to characteristic length ratio, the results approach to the classical theory, and by reducing this ratio, wave propagation speed in the plate is significantly increased. In addition, it is demonstrated that for high-frequency Lamb waves, it converges to dispersive Rayleigh wave velocity.

Investigation on the influence of material crystallographic orientation on grinding force in the micro-grinding of single-crystal copper with single grit

In the micro-grinding process, owing to the size effect, the effects of material microstructure on the grinding force are more significant through the variation of material flow stress. Currently, the variation of material flow stress resulting from the change of crystallographic orientation during the micro-grinding has not been well examined. In this paper, a new predictive model for the variation of flow stress due to the process-induced change of crystallographic orientation is developed, which is based on the Taylor factor as determined by calculating the activated slip systems, thus quantifying the way crystallographic orientation affects both the number and the style of activated slip systems. Moreover, the predicted force is compared with previous reported experimental data on monocrystalline copper. As a result, the following findings are obtained from the comparison between the predicted result and the experimental data: (1) The predicted microgrinding force agrees well in trend with the experimental force, suggesting that the approach for predicting the grinding force based on the Taylor factor is feasible; (2) In the microgrinding of single-crystal materials, the feed rate direction relative to the crystallographic orientation has great effects on the flow stress and hence on the grinding force.

Material microstructure effects in micro-endmilling of Cu99.9E

This article presents an investigation of the machining response of metallurgically and mechanically modified materials at the micro-scale. Tests were conducted that involved micro-milling slots in coarse-grained Cu99.9E with an average grain size of 30 µm and ultrafine-grained Cu99.9E with an average grain size of 200 nm, produced by equal channel angular pressing. A new method based on atomic force microscope measurements is proposed for assessing the effects of material homogeneity changes on the minimum chip thickness required for a robust micro-cutting process with a minimum surface roughness. The investigation has shown that by refining the material microstructure the minimum chip thickness can be reduced and a high surface finish can be obtained. Also, it was concluded that material homogeneity improvements lead to a reduction in surface roughness and surface defects in micro-cutting.

Effects of grain size of AISI 304 on the machining performances in micro electrical discharge machining

The material removal process of micro electrical discharge machining is based on the instantaneous ultra-high temperature generated by a series of repetitive discharge pulses. Due to the size effects, the polycrystal cannot be considered as continuous and homogeneous material when machining is in micron scale, and the effects of material microstructure should not be neglected. In this article, the thermoelectric characteristics of grain and grain boundary are discussed, and the influence of grain size on the machining performances in micro electrical discharge machining is researched. Two kinds of austenitic stainless steels (AISI 304) which are different in grain size are chosen as the workpieces in experiments. It is verified by both theory models and experimental results that the smaller the grain size, the higher the material removal rate, under the same discharge conditions. Both thermal conductivity and melting point of the grain boundary are lower than those of the grain because of the grain boundary segregation. The effective thermal conductivity and local effective melting point of polycrystalline materials vary with their grain sizes since the grain boundary volume fractions change. As a consequence, the material removal rate of micro electrical discharge machining has direct relationship with grain size of the workpiece.

A novel discrete computational tool for microstructure-sensitive mechanical analysis of composite materials

In this article, we present a novel pixel-based nonlocal discrete computational tool for the modeling and simulation of mechanical behaviors of composite materials with isotropic phases based on their photographic microstructural information. First, formulation of the proposed model is presented and interface modeling is discussed. Following this, a procedure on quantifying materials effective elastic properties is provided. Details on a spring-based failure criterion for modeling of fracture events are discussed. After that, investigations on effects of material microstructure, interface properties and inclusion characteristics on effective elastic and fracture properties of bi-phase composites reinforced by various inclusions are performed. Based on current study, conclusions are drawn at the end.

Deformation behavior and microstructure evolution in thermal-aided mesoforming of titanium dental abutment

With the increasing demand for meso/micro-scaled medical products made of biocompatible materials, thermal-aided mesoforming is proposed to improve material formability and homogenize flow behavior of materials that are difficult to deform at room temperature. However, the unique material deformation behavior and the interactive effects of material microstructure and deformation temperature on forming quality of the fabricated micropart remain unknown. This study thus aims at addressing this issue in thermal mesoforming in terms of deformation load, material flow, microstructural evolution, dimensional accuracy, and defect formation. Accordingly, the fabrication of a titanium dental abutment by one-stroke mesoforming at elevated temperature is conducted and explored. The characteristic and quality of the mesoformed part are extensively examined. The surface grains on the square extrudate undergo severe deformation and generate an equiaxed structure, reflecting that mesoforming at elevated temperature facilitates the homogenization of material flow without coarsening grain size. In addition, the dimensional accuracy, surface quality and the sizes of burr and flash are associated with the initial grain size of pure titanium, and the surface finish is improved by using fine-grained titanium. The fine-grained material is thus desirable for achieving the optimal surface quality in the thermal-aided mesoformed parts.

Ductile fracture and deformation behavior in progressive microforming

Abstract With the increasing demand for the quality and quantity of miniaturized parts, fabrication of microparts directly using sheet metals is proven to be promising and efficient for mass production. In this process, however, there are many unknowns in terms of size effect and its affected fracture and deformation behavior. This study is thus aimed at investigating the micromechanical damage and deformation behavior in progressive microforming and establishing a systematic knowledge to support the microformed part design, process configuration and tooling design. In detail, a micro cylindrical part is fabricated via shearing process and a multi-level flanged part is produced via progressive micro extrusion and blanking. To explore the effect of material microstructure on the deformation behavior, ductile fracture and the product quality of microformed part, the original sheet metals are annealed under different temperatures. To realize the microforming process, a progressive microforming system is developed and its characteristics are investigated. The effect of grain size on dimensional accuracy, microstructure evolution and fracture behavior in microforming is also studied. The ductile fracture and its induced defects are identified and the damage accumulation is predicted. In the end, the validity and applicability of different fracture criteria in microforming is discussed.