Presence Of Second Phase Particles Research Articles

Intelligent optimization of non-rigidly supported stationary shoulder friction stir welding parameters

During the online welding of railway aluminum alloy trucks using fixed shoulder stirring friction welding technology, defects such as flying edges, cracks, and tunnels may occasionally occur due to poor coordination of the welding process parameters. This inconsistency can compromise the success rate of the welding. To enhance the quality and efficiency of the welding repairs, an optimization of the welding process parameters of the developed equipment was undertaken. An intelligent prediction model for welding parameters was established based on the BSO-BP neural network. The model was trained with 17 sets of authentic welding data, and its accuracy was validated through a comparison of predictive outputs with actual welding outcomes. The BSO-BP neural network demonstrated a maximum error of 1.85% and a relative error of 1.27%, showing a marked improvement over traditional BP neural network predictions. Utilize the optimized welding process parameters obtained from a trained predictive model to conduct welding experiments under actual working conditions. During the experiment, the deformation of the test plates was minimal. The resulting welds were smooth, free of defects such as flash and grooves, and the overall welding quality was good. The tensile strength of the welds, at 262.95 MPa, was close to the predicted results and reached 78.49% of the base material’s tensile strength. In the microstructure of the weld, sporadically distributed dimples of varying sizes can be observed, indicating the presence of second phase particles which contribute to enhancing the tensile strength of the weld, thereby meeting the strength requirements of the aluminum alloy car body. The parameter optimization method used has certain reference value and can provide guidance for similar research.

A computational approach to restoration phenomena during annealing of rolled Cu-2Be: recrystallization, grain growth and abnormal grain growth

In this study, an integrated paradigm was developed for the simulation of static recrystallization (SRX) after cold rolling of a Cu-2Be alloy. The proposed framework also models with the normal and abnormal grain growth (AGG) of the after transient recrystallization through post-rolling annealing when stored and interfacial energies are varying. The simulation of AGG was done to study the influence of precipitates and sub-boundaries. The initial stored energy as a result of deformation was calculated. The finite element analysis was used to compute the heterogeneous distribution of stored energy due to heterogeneous deformation and is then incorporated to Monte Carlo (MC) algorithm to attain SRX grain size and kinetics. The stored energy assigned to the as-rolled grain micrograph is introduced to the MC simulation as the initial condition considering the size-scale of the calculation domain. The effects of the Zener drag pressure stemming from the presence of second phase particles on the recrystallization progress was also incorporated into the MC model. To evaluate the simulation predictions, the numerical results of the SRX fractions and grain sizes after cold rolling was studied and compared to the experimental ones, and a reasonable accordance is achieved. The numerical results presented that precipitates and sub-boundaries in cooperation take a significant role in persuading AGG by wetting alongside triple junctions. To validate the quantitative results, SRX transformation kinetics has been investigated using the differential scanning calorimetry.

Synergistic effect of grain size and second-phase particle on the oxidation behaviour of a high-manganese austenitic heat-resistant steel

The effect of grain size and second-phase particles on the oxidation behaviour of a high-manganese austenitic (HMA) heat-resistant steel are investigated. Four HMA steels with controlled grain size and volume fraction of second-phase particles are prepared and then exposed at 1023 K in air for 400 h. The results show that the particle-reinforced HMA heat-resistant steels exhibit excellent oxidation resistance. A physical model was proposed to investigate the synergistic effect of grain size and second-phase particle on the oxide scale evolution in HMA steels. The presence of second-phase particles can significantly reduce the effective grain size for the oxide scale formation by providing diffusion channels. Therefore, the formation of nodular oxide and the occurrence of internal oxidation are effectively inhibited in the particle-reinforced heat-resistant steels.

Void-Induced Ductile Fracture of Metals: Experimental Observations

The paper presents a literature review on the development of microvoids in metals, leading to ductile fracture associated with plastic deformation, without taking into account the cleavage mechanism. Particular emphasis was placed on the results of observations and experimental studies of the characteristics of the phenomenon itself, without in-depth analysis in the field of widely used FEM modelling. The mechanism of void development as a fracture mechanism is presented. Observations of the nucleation of voids in metals from the turn of the 1950s and 1960s to the present day were described. The nucleation mechanisms related to the defects of the crystal lattice as well as those resulting from the presence of second-phase particles were characterised. Observations of the growth and coalescence of voids were presented, along with the basic models of both phenomena. The modern research methods used to analyse changes in the microstructure of the material during plastic deformation are discussed. In summary, it was indicated that understanding the microstructural phenomena occurring in deformed material enables the engineering of the modelling of plastic fracture in metals.

Effect of second phase particles on the microstructure and texture of rare earth elements containing magnesium matrix surface-composite produced by friction stir processing

The present research clarifies the texture and microstructure evolution of a rare earth (RE) containing magnesium composite reinforced by SiC particles (Mg-RE/SiC) during friction stir processing. Rotating tool induced mechanical stirring and frictional heat lead to occurrence of dynamic recrystallization (DRX) and development of the strong basal texture component. The presence of second phase particles in the matrix could stimulate the occurrence of continuous dynamic recrystallization (CDRX) and particle stimulated nucleation (PSN) and postpone discontinuous dynamic recrystallization (DDRX). The presentation of crystallographic orientations in an appropriate reference frame indicated formation of a new rare earth texture (RE-texture) component, near the <11-24>//shear plane normal (SPN) and <20-21>-<11-21>//shear direction (SD) orientations. This texture component was developed through simultaneous activity of basal and non-basal slip systems during dynamic recrystallization.

Biodegradable properties of AZ31-0.5Ca magnesium alloy

ABSTRACT In this work, the effect of Ca addition on the microstructure, mechanical properties, electrochemical corrosion and biocompatibility of AZ31 Mg alloy was investigated. Scanning electron microscopy and electron probe microanalyzer were used to analyse microstructural characteristics of both alloys. Open circuit potential , potentiodynamic polarisation and electrochemical impedance spectroscopy techniques were carried out in Ringer lactate solution at 37 ± 1°C to determine the mechanism of corrosion and rate of deterioration of AZ31 and AZ31-0.5Ca. The results revealed that addition of Ca significantly enhanced the corrosion resistance of AZ31 (20.21 mpy and 10.08 mpy for AZ31 and AZ31-0.5Ca, respectively), which was attributed to the presence of second phase particles. the cell viability and biocompatibility of the both alloys were determined by performing the cytotoxicity test after 24 h, 48 h and 72 h incubation in L929 and MC3T3-E1 cell extract. Both the alloys demonstrated adequate cell viability and biocompatibility.

Microstructural Evolution and High-Performance Giant Dielectric Properties of Lu3+/Nb5+ Co-Doped TiO2 Ceramics.

Giant dielectric (GD) oxides exhibiting extremely large dielectric permittivities (ε’ > 104) have been extensively studied because of their potential for use in passive electronic devices. However, the unacceptable loss tangents (tanδ) and temperature instability with respect to ε’ continue to be a significant hindrance to their development. In this study, a novel GD oxide, exhibiting an extremely large ε’ value of approximately 7.55 × 104 and an extremely low tanδ value of approximately 0.007 at 103 Hz, has been reported. These remarkable properties were attributed to the synthesis of a Lu3+/Nb5+ co-doped TiO2 (LuNTO) ceramic containing an appropriate co-dopant concentration. Furthermore, the variation in the ε’ values between the temperatures of −60 °C and 210 °C did not exceed ±15% of the reference value obtained at 25 °C. The effects of the grains, grain boundaries, and second phase particles on the dielectric properties were evaluated to determine the dielectric properties exhibited by LuNTO ceramics. A highly dense microstructure was obtained in the as-sintered ceramics. The existence of a LuNbTiO6 microwave-dielectric phase was confirmed when the co-dopant concentration was increased to 1%, thereby affecting the dielectric behavior of the LuNTO ceramics. The excellent dielectric properties exhibited by the LuNTO ceramics were attributed to their inhomogeneous microstructure. The microstructure was composed of semiconducting grains, consisting of Ti3+ ions formed by Nb5+ dopant ions, alongside ultra-high-resistance grain boundaries. The effects of the semiconducting grains, insulating grain boundaries (GBs), and secondary microwave phase particles on the dielectric relaxations are explained based on their interfacial polarizations. The results suggest that a significant enhancement of the GB properties is the key toward improvement of the GD properties, while the presence of second phase particles may not always be effective.

Appearance of textures with a c-axis parallel to the extrusion direction in Mg alloys

The appearance of an unusual texture with the crystallographic c-axis parallel to the extrusion direction (‘C-texture’) occurs in bands in extruded and fully recrystallized Mg-6.5Zn alloy. This texture was previously only reported in rare-earth-containing Mg alloys. Based on our results and the available literature, it seems that this texture requires heavy alloying, and it is not linked exclusively to the presence of second phase particles. Moreover, it appears to be associated with higher extrusion ratios. Also, the starting texture seems not essential for its formation. The most likely mechanism would be the promoted pyramidal <c+a> slip stimulated by high solute levels that provides the necessary lattice rotation, along with the easy activation of prismatic <a> slip.

Investigation on the Strengthening Mechanisms of Nickel Matrix Nanocomposites.

The strengthening effect of carbon nanotubes (CNTs) in metal matrix nanocomposites occurs due to several mechanisms that act simultaneously. The possible strengthening mechanisms for metal matrix nanocomposites reinforced with CNTs consist of: (1) load transfer, (2) grain refinement and texture strengthening, (3) second phase strengthening, and (4) strain hardening. The main focus of this work is to identify the strengthening mechanisms that play a role in the case of the Ni-CNT nanocomposite produced by powder metallurgy. For the dispersion and mixing of the metallic powders with CNTs, two different routes were performed by ultrasonication and ball milling. The results indicated that four different strengthening mechanisms are present in the nanocomposites and had a different contribution to the final mechanical properties. The load transfer and the increase in dislocation density seem to strongly affect the properties and microstructure of the nanocomposite. The grain refinement and the presence of second phase particles have a small contribution in the strengthening of this nanocomposite, since the introduction of CNTs in the Ni matrix slightly affects the size and orientation of the grains in the matrix and a few nanometric particles of Ni3C were identified.

Role of recrystallization and second phases on mechanical properties of (CoCrFeMnNi)95.2Al3.2Ti1.6 high entropy alloy

The present work reports microstructures and mechanical properties of the homogenized and cold-rolled (CoCrFeMnNi) 95.2 Al 3.2 Ti 1.6 (at. %) high entropy alloy annealed at various temperatures. The material was cold-rolled and annealed in the temperature range from 600 °C to 1000 °C for 1 h. The σ phase was observed in the annealing temperature range from 600 °C to 800 °C while the B2 phase was observed in the annealing temperature range from 700 °C to 900 °C. The fully recrystallized material annealed at 900 °C shows a considerably lower grain size compared to the reported grain size of the CoCrFeMnNi alloy, due to the presence of second phase particles. With increasing annealing temperature, a fraction of fully-recrystallized grains increases, leading to an increase in ductility and a decrease in strength. The material annealed at 900 °C and 1000 °C shows a low strength but large ductility due to fully recrystallized microstructures. Grain size strengthening and precipitation strengthening by B2 particles play a major role in the yield strength of the fully-recrystallized material annealed at 900 °C. The deformation mechanism of the material annealed at 900 °C is mainly dislocation slip with the minor occurrence of deformation twinning. A high density of dislocations near the B2/FCC matrix suggests the strengthening effect of the B2 phase. The material annealed at 800 °C shows ultimate tensile strength exceeding 1 GPa due to the combined effect of partially recrystallized microstructure and precipitation hardening and shows moderate ductility due to the less brittle character of the B2 phase by Ti alloying.

Effect of second-phase particles on the oxidation behaviour of a high-manganese austenitic heat-resistant steel

In this work, the presence of second-phase particles was found can significantly improve the oxidation and spallation resistances of a high-manganese austenitic heat-resistant steel. We show this unexpected improvement is originated from three correlated phenomena caused by the second-phase particles. First, the stratified growth of scale is avoided due to the chemical inhomogeneity of the novel steel. Further, the selective oxidation of second-phase particles provides a pinning effect for the scale. Last but not least, the accelerated outward diffusion of Mn reduces the critical Cr concentration for the formation of a stable protective Cr2O3 layer.

A Potts Model parameter study of particle size, Monte Carlo temperature, and “Particle-Assisted Abnormal Grain Growth”

Grain growth kinetics are known to deviate from the classical n = 2 behavior when particles in the microstructure impede grain boundary motion, and eventually halt as the driving force of grain boundary curvature approaches the pinning force exerted by the particles. Potts Model simulations were evaluated with respect to the non-physical Monte Carlo simulation temperature and theoretical predictions of grain growth behavior in the presence of second-phase particles. These simulations demonstrate that by modifying the simulation temperature, the pinned grain size will follow a selected inverse-linear relationship with respect to particle volume fraction. From these results, we suggest an approach for selecting Potts Model simulation temperature. Additionally, parameterizations of particle size, volume fraction, and simulation temperature in which the previously observed simulation phenomenon “Particle-Assisted Abnormal Grain Growth” (PA-AGG) occurred were recorded and discussed. The majority of this grain growth behavior occurred for simulation temperatures TS ≥ 1.5, particle diameters of less than six cells, and particle volume fractions smaller than 10%. However, PA-AGG was also observed in simulation for particle diameters of up to ten cells, particle volume fractions of twenty percent, and simulation temperatures as small as TS = 0.5. An analysis of the simulated grain size distributions showed that the occurrence of PA-AGG was not dependent on the abnormal grain reaching a critical relative grain size. The simulation domain size does not appear to have an influence on this effect.

Phase-Field Simulation of Grain Boundary Evolution In Microstructures Containing Second-Phase Particles with Heterogeneous Thermal Properties

Understanding the interaction between complex thermal fields and metallic structures at the meso-scale is crucial for the prediction of microstructural evolution during thermomechanical processing. The competitive growth of crystal grains, driven by thermodynamic forces at the grain boundaries, is one of the most fundamental phenomena in metallurgy and solid state physics. The presence of second phase particles, which act as pinning sites for boundaries, drastically alters the coarsening behaviour of the system; particularly when considering that these particles have different thermal properties to the primary phase. In this work a multi-phase field model, incorporating thermal gradient and curvature driving forces, is used to predict grain growth in a Ti6Al4V alloy system with second phase particle inclusions representative of oxide and carbide precipitates. The multi-phase field framework is fully coupled to the heat equation. The incorporation of the thermal gradient driving force enables the detailed behaviour of the grain boundaries around the particles to be predicted. It is shown that the inclusion of particles with a lower thermal conductivity has a significant influence on the coarsening behaviour of various systems of grains, due to the combined effects of thermal shielding and the generation of thermal gradient driving forces between the boundaries and pinning particles.

Molten salt corrosion of Ni-Mo-Cr candidate structural materials for Molten Salt Reactor (MSR) systems

In the present study, the corrosion performance of three candidate Ni-Mo-Cr alloys (HASTELLOY-N®, GH3535®, and MONICR®) for Molten Salt Reactor (MSR) systems have been investigated. It is shown that the molten salt corrosion performance of these alloys is not only dependent on their chemical composition, but also on their microstructural characteristics (grain size, grain boundary length, and the presence of second-phase particles). Obtained results suggest that MONICR® alloy is the least affected by the exposure to the FLiNaK molten salt. This is attributed to its chemical composition, high-angle grain boundary length (grain size) and virtually no presence of large (M6C) carbides.

The influence of strain rate and presence of dispersed second phases on the deformation behaviour of polycrystalline D2O ice

ABSTRACTThis contribution discusses results obtained from 3-D neutron diffraction and 2-D fabric analyser in situ deformation experiments on laboratory-prepared polycrystalline deuterated ice and ice containing a second phase. The two-phase samples used in the experiments are composed of an ice matrix with (1) air bubbles, (2) rigid, rhombohedral-shaped calcite and (3) rheologically soft, platy graphite. Samples were tested at 10°C below the melting point of deuterated ice at ambient pressures, and two strain rates of 1 × 10−5 s−1 (fast) and 2.5 × 10−6 s−1 (medium). Nature and distribution of the second phase controlled the rheological behaviour of the ice by pinning grain boundary migration. Peak stresses increased with the presence of second-phase particles and during fast strain rate cycles. Ice-only samples exhibit well-developed crystallographic preferred orientations (CPOs) and dynamically recrystallized microstructures, typifying deformation via dislocation creep, where the CPO intensity is influenced in part by the strain rate. CPOs are accompanied by a concentration of [c]-axes in cones about the compression axis, coinciding with increasing activity of prismatic-&lt;a&gt; slip activity. Ice with second phases, deformed in a relatively slower strain rate regime, exhibit greater grain boundary migration and stronger CPO intensities than samples deformed at higher strain rates or strain rate cycles.

Determination of the Root Causes for Cracking in a Large-Size Cast Ingot of AISI 4317 Steel Using Microstructural Analysis

The objective of the present work is to study the root causes for the cracking and material detachment from the external surface of a 10 metric tons high-strength low-alloy steel ingot after solidification and annealing processes. Failure analysis investigations were conducted on different samples from the cracked areas as well as from non-cracked ones. A combination of optical and electron microscopies, x-ray diffraction, and microhardness techniques were used to study and analyze the nature, morphology, and composition of the different microstructural components in the cracked regions. Thermodynamic software, Thermo-Calc® was used to corroborate and interpret the experimental findings with the existing theories. The results indicated a strong intergranular character of the cracks accompanied by the presence of second-phase particles at prior austenite grain boundaries. Segregation of chromium and manganese was demonstrated through local chemical analysis of the grain boundaries. It was concluded that a rapid cooling rate combined with the weakening of grain boundaries was at the origin of crack initiation.

Estimation of C∗ including the effect of threshold stress

In some alloys such as 9%Cr heat resistant steels and magnesium alloys, the creep constitutive equation of the power-law requires a term of threshold stress due to the presence of second phase particles. It is necessary to establish an estimation method of C∗ for such alloys to predict the life of their components. In this paper, the General Electric/Electric Power Research Institute (GE/EPRI) method and the reference stress method were modified to estimate C∗ for power-law creep materials with threshold stress. The finite element method was used to verify the accuracy of the modified methods. The accuracy of the calculation equation of C∗ in the American Society for Testing Materials (ASTM) E 1457 was also assessed. The results indicated that the modified GE/EPRI method was sufficiently exact as an engineering method. h1 was slightly affected by the applied load and significantly affected by the threshold stress. The accuracy of the modified reference stress method increased with increased applied load and was within ±40%. The accuracy of the calculation equation of C∗ in ASTM E 1457 was not affected by the threshold stress and the equation could be directly used for power-law creep materials with threshold stress.

Structure and Properties of CuCr0.6 Alloy after Severe Plastic Deformation

This paper focuses on the effect of rolling with cyclic movement of rolls (RCMR) on microstructure refinement, mechanical properties and electrical conductivity of CuCr0.6 alloy after applying different heat treatments (quenching and aging). It was found that the presence of second phase particles obtained during aging treatment has a significant effect on the formation of ultrafine grain (UFG) structure during the RCMR processing. The presence of high dislocation density inside subgrains and presence microshear bands are the marked features of the microstructure after aging at 500°C/2h and RCMR deformation. Whereas after aging at 700°C/24h and RCMR processing, fine precipitates were effective in inhibiting the grain/subgrain boundary motion. The RCMR processed alloy after aging at 500°C/2h shows high mechanical strength attributed to the high density of coherent precipitates and ultrafine grained structure. The RCMR processing induces a significant reduction of the electrical conductivity for samples at quenching state but for samples at aging state electrical conductivity was restored thanks to precipitation process.

Corrosion pathways in aluminium alloys

The corrosion pathways in AA2024-T3, AA5083-O and AA6082-T6 alloys have been investigated. The objective of the investigation is to further the understanding of the complex localised corrosion mechanism in aluminium alloys. The investigation was carried out by examining the corroded surfaces of the alloys after potentiodynamic polarization tests in a 3.5% NaCl solution with the aid of a scanning electron microscope, and by analysing the flow of anolyte solution using the scanning vibrating electrode technique. The results revealed that the overall corrosion pathways in the alloys are distinctively different and are influenced by the flow of anolyte solution. Also revealed, was the fact that corrosion propagates in two ways (particularly in the AA5083-O and AA6082-T6 alloys): an overall pathway in the corrosion front (filiform-like pathway in the AA5083 alloy and organized linear pathways in AA6082 alloy); and the crystallographic channelling along the 〈100〉 directions. These are dependent on the grain distinct features of the AA5083-O and AA6082-T6 alloys and are not influenced by the presence of coarse second phase particles in these alloys, compared with the AA2024-T3 alloy, where the corrosion pathways are more dependent on the presence of second phase particles and grain boundary character.

Synthesis & Characterization of Al-Ti-Cr MMC as friction material for disc brakes application

A stir die casting coupled with chill casting technique was used to prepare the Al-Ti-Cr composite with variable percentage of SiC and B4C particles. The electrolytic grade of 300 mesh powder was added in the molten of commercially master alloy of Al-Ti-Cr by the simultaneously addition of SiC and B4C. The SiC and B4C in the composite are varied from 0 to 10wt%.The developed composite were characterized using a Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). F.T.I.R. in corroboration with X.R.D,which confirms the crystallization of corundum (α-Al2O3) as one of the alumina phases.The presence of hard phase in the composite not only improved the ultimate tensile strength, 0.2% proof stress and the hardness of AMC composite. The ductility showed the adverse effect with increase of the SiC and B4Cin the matrix. The results from microstructure confirms the presence of second phase particles at the grain boundaries of aluminium-rich phase as well as within the grain itself which was confirmed by EDAX as well as XRD analysis. These composite have also been subjected to wear and frictiontesting at different operating parameters. Result shows that with increase in wt% of SiC and B4C from 2-10%, the ultimate strength and elongation percent of the Al-Ti-Cr alloy are still higher than that of monolithic alloys. Micro-structural characterization by using SEM depicted that the particles tend to be more agglomerated along with Al2O3 content, confirmed with FTIR analysis. The AFM results revealed that the surface roughness value of the composite is reduced by a factor of ∼3 μm. The results from microstructure showed the presence of second phase particles at the grain boundaries of aluminium-rich phase as well as within the grain itself which was confirmed by FTIR, XRD, AFM and EDAX.