Effect Of Different Microstructures Research Articles

Effect of microstructure refinement on hydrogen-induced damage behavior of low alloy high strength steel for flexible riser

The effect of different microstructures on hydrogen-induced damage behavior of low alloy high strength steel for flexible riser was studied by hydrogen permeation test and electrochemical hydrogen charging test. The mechanism of hydrogen-induced damage behavior in tested steel was elucidated in terms of microstructure characterization, calculation of hydrogen permeation parameters and sensitivity analysis of hydrogen-induced cracking of tested steel. The results indicated that the microstructure of the tested steel was tempered martensite with precipitated phase, and the microstructure was finer and contained more proportions high angle grain boundaries after multi-stage heat treatment. After multi-stage heat treatment, the irreversible hydrogen traps and total number of hydrogen traps in the microstructure increased significantly, resulting in a significant decrease in hydrogen effective diffusion coefficient (Deff). Compared with quenched and tempered heat treatment, the crack sensitivity of hydrogen-induced cracking in microstructure obtained by multi-stage heat treatment decreased greatly, and the crack mainly presented transgranular propagation and more tortuous.

Effect of a Zinc Interlayer on a Cu/Al Lap Joint in Ultrasound-Assisted Friction Stir Welding

This study proposes a welding process, ultrasound-assisted friction stir welding of dissimilar Al/Cu metals. Zinc foil is melted using the heat generated by a pinless stirring tool, and the molten intermediate layer is stirred by ultrasonic cavitation to achieve an effective connection. The metallurgical reaction behavior of the joint under the action of the sound field was studied, and the effects of different microstructures on the joint performance were analyzed. Specifically, the following observations were reported in this study: (1) When ultrasound assistance was used, the cavitation effect changed the brittle intermetallic compounds of Al2Cu from a continuous distribution to a block distribution, and the mechanical properties of the joint were greatly improved; (2) the effects of the thickness of the zinc were also determined. The results showed that the highest shear tensile force was obtained when the thickness of the zinc foil was 0.2 mm. When the thickness was 0.3 mm, the ultrasound effect was weakened. The copper-side interface generated a zigzag-shaped Al4.2Cu3.2Zn0.7 layer with a thickness of 3.4 μm and had a continuous distribution. Increasing the thickness of the zinc to 0.5 mm, however, drastically decreased the mechanical properties of the joint due to incomplete melting of the zinc layer.

Cold-working mediated converse age hardening responses in extruded Mg-14Gd-2Ag-0.5Zr alloy with different microstructure

Figuring out the influencing factors is important to explore the potential of age hardening response for Mg alloys. Here the effect of different microstructure on age hardening response in extruded Mg-14Gd-2Ag-0.5Zr alloy is investigated. The age hardening response is weakened by cold-rolling for the extruded sample with large grain size due to the solute atom segregation to form bulk particles in twin boundaries during aging. Conversely, the age hardening response is enhanced by cold-rolling for the extruded sample with fine grain size and dynamical precipitates along grain boundaries, which is attributed to the segregation of solute atoms into the nano subgrain boundaries within grains during aging.

Effect of Different Microstructures on the Performance of Air-Cooled Forging Steel 46MnVS5 Fracture Splitting Connecting Rod

This paper analyzed mechanical properties and splitting fracture performance of 46MnVS5 with different microstructures. It will provide support of date for new type of splitting fracture connecting rod materials. The results show that bainite has good strength and ductility, but its high ductility is bad for splitting fracture. Martensite and tempered martensite have high strength and low ductility, which is bad for using performance. Ductility of tempered sorbite is too high to meet splitting fracture performance. Tensile and yield strength, impact toughness of tempered troostite is 1569MPa, 1407MPa and 17.5J/cm2, respectively. Tempered troostite has high strength and good splitting fracture performance. Bainite+martensite and tempered troostite maybe two good choices for better splitting fracture and using performance.

Measurements of sound speed in two types of ice with different microstructure

Measurements of sound speed were made on laboratory-grown ice samples serving as proxies for two types of sea ice with different microstructure. The first one, congelation ice, has relatively homogeneous structure typical for first-year sea ice. The second one, granular ice, with a more heterogeneous microstructure, was prepared as a proxy for retextured multi-year sea ice. Both samples had approximately equal bulk salinity (12 ppt) to isolate effects of different microstructure. Sound speed was estimated by measuring time of flight of 400 kHz pulses and was found in congelation ice to be about 10% higher than in granular ice. Error bounds were estimated to be within 1% based on same measurements made for plastic material with known sound speed. Therefore, the results confirm sensitivity of sound speed in ice to its internal microstructure and heterogeneity which are known to affect large-scale ice properties, such as strength, elasticity, permeability, air-sea exchange, habitability, and partitioning of shortwave solar radiation. This motivates future work that would include modeling and measurement of sound speed, attenuation and scattering in natural sea ice, with a goal to develop a remote acoustic sensing technique for sea-ice characterization and, in particular, discrimination between first-year and multi-year ice types. Measurements of sound speed were made on laboratory-grown ice samples serving as proxies for two types of sea ice with different microstructure. The first one, congelation ice, has relatively homogeneous structure typical for first-year sea ice. The second one, granular ice, with a more heterogeneous microstructure, was prepared as a proxy for retextured multi-year sea ice. Both samples had approximately equal bulk salinity (12 ppt) to isolate effects of different microstructure. Sound speed was estimated by measuring time of flight of 400 kHz pulses and was found in congelation ice to be about 10% higher than in granular ice. Error bounds were estimated to be within 1% based on same measurements made for plastic material with known sound speed. Therefore, the results confirm sensitivity of sound speed in ice to its internal microstructure and heterogeneity which are known to affect large-scale ice properties, such as strength, elasticity, permeability, air-sea exchange, habitability, and partitioning of ...

Experimental Research on Hydrogen Resistance Performance of Different Microstructure

The paper studies the effects of different microstructures on the hydrogen resistance properties. Four kinds of microstructures were obtained by using four kinds of heat treatment processes for 45 steel materials. The mechanical properties of different microstructure materials were obtained by Vickers hardness test and internal residual stress test. The relationships between hardness and depth of four kinds of microstructures were obtained by stratified microhardness test. Static hydrogen resistance property of different microstructures was obtained by using the stripping method. Results show that the H2S corrosion layer of different microstructures is basically the same, and the depth and hardness distribution of the hydrogen embrittlement layer are quite different. More pearlite, lead to the weakness of hydrogen resistance property; quenched and tempered sorbite after the hydrogen corrosion is better than ferrite + pearlite structure, martensite has a good resistance to hydrogen permeability. Finally, the relationships between microhardness and depth of the hydrogen embrittlement layer with different microstructures were fitted.

A novel structure of YSZ coatings by atmospheric laminar plasma spraying technology

A novel structure of yttria stabilized zirconia coatings was developed in this study by a newly laminar plasma spraying technology in atmospheric environment. The unique microstructures of coatings showed the multi-island protrusions feature at the top surface, quasi-columnar structures along the cross-section distributed as a certain interval and hybrid droplet/vapor deposited structures at the fracture surface. The distributions of particle velocity and surface temperature along the axial direction of long laminar plasma jet were investigated and compared with other plasma spraying methods. The effects of different microstructures to thermal conductivities comparing with other current plasma spray methods were also demonstrated.

Effect of thermomechanical parameters on mechanical properties of base metal and heat affected zone of X65 pipeline steel weld in the presence of hydrogen

In this study, the effect of different microstructures resulting from thermochemical processes of X65 pipeline steel on mechanical properties of welding in the presence of hydrogen was investigated. According to studies conducted, due to the charge of hydrogen, the hardness of base metal (BM) increased by 10%, the hardness of heat affected zone (HAZ) samples increased by about 13%, the yield strength of base metal increased by an average of 5% and the yield strength of HAZ increased by about 7%, indicating hardening. Elongation was reduced by 32–70% and the percentage of ductile fracture decreased by an average 46% which shows that the fracture of samples in the presence of hydrogen is brittle. In the study of hydrogen defect and concentration of hydrogen permeated to the material it was determined that, the ferrite-pearlite banded microstructure of base metal has a higher hydrogen defect sensitivity than HAZ with an acicular ferrite microstructure and hard phase. In base metal samples under various rolling conditions, the two-pass rolled and the final rolling temperature of 800 °C sample (2BM800), with a smaller grain microstructure and higher interface, had the most diffusive hydrogen content and therefore had the highest hydrogen defects. In the case of HAZ samples, the effect of hydrogen on the increase in hardness and strength properties is greater than that of the base metal samples due to the different microstructure (of the acicular ferrite) and the variable grain size (i.e. the presence of two coarse-grained and fine grained areas). Overall, the results of this study showed that the microstructure has a significant effect on mechanical properties, the amount of diffusive hydrogen and hydrogen defects in welds.

Microstructural Aspects of Bifocal Laser Welding of Trip Steels

AbstractThis work is concerned with comparative tests involving single-spot and twin-spot laser welding of thermomechanically rolled TRIP steel. The welding tests were carried out using keyhole welding and a solid state laser. In the case of twin-spot laser beam welding, the power distribution of beams was 50%:50%. The changes in macro- and microstructures were investigated using light and scanning electron microscopy. Three main zones subjected to the tests included the fusion zone, the heat affected zone and the intercritical heat affected zone (transition zone between the base material and the HAZ). Special attention was paid to the effect of various thermal cycles on the microstructure of each zone and on martensite morphology. The tests involved hardness measurements carried out in order to investigate the effect of different microstructures on mechanical properties of welds.

Ameliorated longitudinal critically refracted—Attenuation velocity method for welding residual stress measurement

This work aims at quantitative analysing the effect of different microstructures on the velocity at stress-free and stress coefficient (K) of longitudinal critical refraction (LCR) wave in measuring welding residual stress process, ameliorating the traditional LCR wave method for improving its’ effectiveness and accuracy. The longitudinal critically refracted wave attenuation velocity (LCR-AV) method was proposed in the evaluation of residual stresses in A7N01 welded joints. The same initial status base materials samples are used to produce different levels of grain size and precipitation by heat treatment technology, obtained the velocity at stress-free and attenuation of LCR wave. As expected, the voltage amplitude changes linearly with velocity and stress coefficient, and the precipitation effect can be ignored. The LCR-AV method based on the liner relationship between velocity, attenuation and grain size are efficient to decrease the errors resulting from the different microstructure (base metals, heat-affected zones, and welded zones). Differ with the traditional LCR waves method, the LCR-AV method also measures the voltage amplitude, and the measured results of LCR-AV method compared with those obtained by the hole-drilling reference method shows more sufficient measurement reliability and precision. It shows that LCR-AV method is a valuable quantitative technology to estimate the residual stress of welded joints.

Electrodeposition of Dendritic Ni-Co Onto High-Voltage Electrodes of Electrostatic Particulate Matter (PM) Sensors

Particulate matter (PM) or soot sensing technologies are needed for feedback and control of exhaust after-treatment systems to meet increasingly stringent environmental regulations. A novel low-cost electrostatic PM sensing approach has recently been developed based on a concentric electrode design with a central cylindrical high-voltage electrode surrounded by an inner baffle that serves as the ground/negative terminal. The sensing principle is not completely understood, but seems to rely on capturing naturally combustion charged particles on electrode surfaces where a delay in sensor startup time occurs during initial testing. The influence of three-dimensional dendritic Ni-Co coatings on PM sensor performance was examined. Nickel and cobalt were co-electrodeposited on cylindrical stainless steel substrates from an electrolytic bath using a square waveform cathodic current. The effect of altering the applied current density and the number of current cycles on the height and spacing of dendritic features was monitored in attempts to correlate surface morphology to the performance of the materials as PM sensors. Coatings were characterized using scanning electron microscopy and confocal laser microscopy, and Ni-Co coated cylinders were used as the central high-voltage electrodes of electrostatic PM sensors to determine the effect of different microstructures on sensor performance. The coated electrodes demonstrated an improvement in startup time for an optimized coating morphology when compared to bare control electrodes. The surface features of the dendritic Ni-Co coatings are believed to alter the interaction of PM with the high-voltage electrode and can induce a faster response of the sensor when optimal electrodeposition conditions are employed.

Pore-scale modeling and simulation of flow, transport, and adsorptive or osmotic effects in membranes: the influence of membrane microstructure

The selection of an appropriate membrane for a particular application is a complex and expensive process. Computational modeling can significantly aid membrane researchers and manufacturers in this process. The membrane morphology is highly influential on its efficiency within several applications, but is often overlooked in simulation. Two such applications which are very important in the provision of clean water are forward osmosis and filtration using functionalized micro/ultra/nano-filtration membranes. Herein, we investigate the effect of the membrane morphology in these two applications. First we present results of the separation process using resolved finger- and sponge-like support layers. Second, we represent the functionalization of a typical microfiltration membrane using absorptive pore walls, and illustrate the effect of different microstructures on the reactive process. Such numerical modeling will aid manufacturers in optimizing operating conditions and designing efficient membranes.

Effect of the Microstructure on the Fatigue Strength of a TiAl Intermetallic Alloy Produced by Additive Manufacturing

ABSTRACTIn this work we examine a Ti-48Al-2Cr-2Nb alloy obtained with an additive manufacturing technique by Electron Beam Melting (EBM) by conducting monotonic and cyclic loading experiments both on tension and compression samples for investigating the influence of the microstructure in strain accumulation process by fatigue loading. The residual strain maps corresponding to different applied stress levels, number of cycles and microstructures are obtained through the use of high-resolution Digital Image Correlation (DIC). The strain maps were overlaid with the images of the microstructure and detailed analyses were performed to investigate the features of the microstructure where high local strain heterogeneities arise. Such experiments, conducted ex-situ at room temperature, allow to characterize the effect of different microstructures on the strain accumulation process, and to clearly identify the role of the microstructural features of this TiAl intermetallic alloy on the fatigue initiation process.

Nondestructive characterization of microstructure and mechanical properties of intercritically annealed dual-phase steel by magnetic Barkhausen noise technique

Detection of microstructural changes is a great importance matter in production line of steel parts. To implement such a task, many destructive tests are involved in industries. Current work examines the effects of different microstructures and mechanical properties on the magnetic Barkhausen noise technique as a suitable alternative testing method. In this study, different dual-phase steels with different martensite percentages were manufactured using various intercritical annealing temperatures from 750 to 850°C. The results concerning magnetic Barkhausen noise were discussed in terms of position, height and shape of Barkhausen noise profiles, taking into account the effect of different percentages of martensite. Since this method is nondestructive after calibration, some beneficial relations for nondestructive characterization of microstructure as well as mechanical properties of any unknown dual-phase steel sample were achieved. Additionally, the feasibility of using the magnetic Barkhausen noise to detect microstructural changes during tempering of dual-phase steels was evaluated. The results revealed this magnetic method had a high potential to be used as a reliable nondestructive tool to detect microstructural changes occurring during manufacturing of dual-phase steels.

Influence of adiabatic shear bands intersection on the ballistic impact of Ti–6Al–4V alloys with three microstructures

The intersection of adiabatic shear band (ASB) and its effect on the ballistic performance of the Ti–6Al–4V plates with equiaxed, bimodal, and lamellar microstructures were studied using transmission electron microscopy (TEM). Focused ion beam (FIB) technology was used to accurately prepare TEM samples at specific locations around the ASB intersections. The effect of different microstructures on the number and morphology of subgrains in ASB intersections was investigated.Multiple ASBs and their interactions were observed in the Ti–6Al–4V plates with equiaxed, bimodal, and lamellar microstructures impacted by armor-piercing projectiles. The ASBs mainly expanded along two directions, which were top-to-down and left-to-right. All the ASBs comprised dynamically recrystallized equiaxed grains and some partial dynamically recrystallized strip subgrains. The arrangement directions of these subgrains were different between the top-to-bottom and left-to-right ASBs. The expansion range of the left-to-right ASBs was the largest in the bimodal microstructure and the smallest in the equiaxed microstructure. The existing subgrains in the previously formed ASBs were elongated and fragmented during the intersection process, and decreased with the expansion of later-formed ASBs. Some of the subgrains were sheared again, which probably inhibited the expansion of the later-formed ASBs. The least amount of fragments and the smallest craters were observed in the Ti–6Al–4V plates with the equiaxed microstructure because of the lowest amount of ASB intersections and cracks, as well as the smallest expansion range of sideward ASBs. More and larger fragments and the largest craters were observed in the bimodal and lamellar microstructures because of more intersections, cracks and the largest expansion range of sideward ASBs.

Strain Accumulation in TiAl Intermetallics via High-resolution Digital Image Correlation (DIC)

Novel manufacturing process are more and more used to produce advanced structural materials such as the gamma titanium aluminide alloys (γ-TiAl). In this work we examine a Ti-48Al-2Cr-2Nb alloy obtained with an additive manufacturing technique by Electron Beam Melting (EBM) by conducting monotonic and cyclic loading experiments both on tension and compression samples to investigate the influence of the microstructure in strain accumulation process by fatigue loading. The residual strain maps corresponding to different applied stress levels, number of cycles and microstructures are obtained through the use of high- resolution Digital Image Correlation (DIC). The strain maps were overlaid with the images of the microstructure and detailed analyses were performed to investigate the features of the microstructure where high local strain heterogeneities arise. Such experiments, conducted ex-situ at room temperature, allow to characterize the effect of different microstructures on the strain accumulation process, providing additional information into the effect of the lamellar and equiaxed grains and also to capture the evolution of the local deformation process for TiAl. The measure of the residual strains provides further information on the role of the intermetallic phases on the fatigue behavior of γ-TiAl alloys. The comparison with the strain accumulation in fully lamellar microstructure with larger grain size permits to highlight the influence of the position of grain boundaries and the orientation of the lamellae for the onset of fatigue cracking. The analysis and comparison of the strain maps provide information for the selection of the microstructural parameters during material design (i.e. grain size and lamellar grains volume fraction).

A Combined Experimental and Numerical Approach to the Laser Joining of Hybrid Polymer – Metal Parts

A two-step method for the joining of opaque polymer to metal is presented. Firstly, the metal is structured locally on a micro-scale level, to ensure adhesion with the polymeric counterpart. In a second step, the opposite side of the micro-structured metal is irradiated by means of a laser source. The heat thereby created is conducted by the metal and results in the melting of the polymer at the interface. The polymer thereby adheres to the metal and flows into the previously engraved structures, creating an additional mechanical interlock between the two materials. The welding parameters are fine-tuned with the assistance of a finite element model, to ensure the required interface temperature. The method is illustrated using a dual phase steel joined to a fiber-reinforced polyamide. The effect of different microstructures, in particular geometry and cavity aspect ratio, on the joint's tensile-shear mechanical performance is discussed.

Corrosion of Zinc and Zn-Mg Alloys with Varying Microstructures and Magnesium Contents

This work addresses the effect of the Mg-content on the corrosion performance of Zn-Mg alloys. Since only low Mg-contents are used in modern Zn-Mg-X coatings, the magnesium in the investigated Zn-Mg alloys was varied in the low content range from 0 wt% to 3 wt%. In addition pure, intermetallic MgZn2 was investigated for comparison. Furthermore, for the case of the alloy with 2 wt% magnesium, the effect of different microstructure at same composition was investigated, which was adjusted by applying different cooling rates during solidification from the melt. The alloys can be ranked in order of the fineness of their microstructure. With increasing magnesium content the lamellar eutectic becomes finer and more evenly distributed. The slowly cooled specimen exhibits coarser microstructure than the quenched alloy. The corrosion of the investigated alloys can be described in three stages, i.e. activation, active corrosion and formation of a protective layer. While the development of the corrosion resistance in the first two stages is very similar for all investigated alloys, in the last stage distinct differences were found for the different samples. It was observed that an increase of the fineness of the microstructure leads to an improved corrosion performance.

Microstructural Effects on Fatigue Behaviour of a Forged Medium Carbon Microalloyed Steel

Abstract The effect of different microstructures on the fatigue behaviour of a medium carbon vanadium microalloyed steel has been studied. Specimens were subjected to a controlled closed die forging followed by cooling in sand, air or oil, respectively. The hardness and fatigue properties of the microalloyed steel are determined and compared with those of ferrite-pearlite and martensite microstructures obtained by cooling with different mediums after forging. Relatively fine ferrite and pearlite increase the fatigue strength of the steel, while the martensite structure reduces the fatigue strength. Characteristics of fatigue fracture surface morphology are summarized and related to fatigue crack initiation and propagation mechanisms in the forged medium carbon microalloyed steel. The cooling rate has a remarkable effect on the microstructure, hardness, and fatigue behaviour at room temperature.

Effects of Different Microstructure on Resistance of EA4T Railway Axle Steel of Equal Strength to Fatigue Crack Growth

Fatigue crack growth (FCG) rates in an EA4T railway axle steel heat treated by two different methods in near threshold and stable regions of growth were evaluated. Quite significant differences were observed, when the obtained results were compared with those published in the literature. Participation of the laboratory in an Exova (GE Aviation) FCG measurement qualification round robin programme with very good results practically excluded errors in the experimental methodology used. Strength of the two different evaluated series of the experimental material was equivalent. Nevertheless, there were substantial differences in fatigue crack growth rates, about 5-times in stable FCG region and even more than 10-times in the near threshold region, when oil quenching and air hardening treatments were compared. The differences were explained by different microstructures of the two groups of materials. Some minor differences between the character of the FCG curve in the threshold region evaluated using SEN(B) and M(T) specimens, published in the literature, are discussed considering crack closure phenomenon.