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At least 1,405 records · Page 78
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DOE OSTI2019

Influence of Substrate Bias Voltage on Corrosion and Wear Behavior of Physical Vapor Deposition CrN Coatings

The objective of the present paper is to study the influence of the substrate bias voltage on the microstructure, composition, deposition rate, tribological and corrosion properties of CrN coatings obtained by DC magnetron sputtering on 90CrMoV8 steel and Si (100) substrates. The substrate bias voltage varied from 0 to − 700 V. The deposited films were characterized by SEM, XRD and potentiodynamic polarization. The wear behavior and coefficient of friction were determined and investigated after rotative tribometer tests. The results indicated that the substrate bias voltage considerably affected the intrinsic properties of the CrN films. Indeed, it significantly influenced the grain size and the root-mean-squared roughness which varied from 20 to 29 nm, and from 9 to 19 nm, respectively, when polarization changed from 0 to − 700 V. All the CrN coatings have a dense columnar structure and are well crystallized according to the XRD analyses. Nevertheless, it has been shown that the peaks intensity decreased by increasing the substrate bias voltage. By applying a substrate bias voltage, it was obvious that the friction behavior was enhanced, and the wear volume was decreased. Finally, the CrN coating obtained under a substrate bias voltage of − 500 V presented the best corrosion resistance and wear resistance probably due to its dense microstructure.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Ce Addition on Grain Boundary Character Distribution, Corrosion Behavior and Impact Toughness of AISI 204Cu Stainless Steel

In this study, the effects of Ce addition on grain boundary character distribution, corrosion behavior and impact toughness of AISI 204Cu stainless steel were investigated. The results revealed that rare earth Ce affected the characteristics and size of inclusions, and the change in the austenite grain size was attributable to Ce multi-phase inclusions as the core of heterogeneous nucleation in stainless steel. The high adjacent probability of γ-fiber textures comprising {111} 〈110〉 and {111} 〈112〉 components was available for more ∑3{sup n} boundaries with increasing Ce contents, which was believed to have a contribution to the enhancement of corrosion resistance. Meanwhile, the austenite grain refinement and ∑3{sup n} boundaries increment were beneficial for the impact toughness improvement of Ce-added steel by increasing the difficulty of crack initiation and propagation. Adding excessive Ce caused a decline in the corrosion behavior and impact toughness of 204Cu stainless steel.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Parametric Study of Cyclic Plasticity Behavior in a Directionally Solidified Superalloy with Partial Recrystallization by Crystal Plasticity Finite Element Simulation

To understand the influence of recrystallization on the low-cycle fatigue behavior of directionally solidified nickel-based DZ4 superalloy, crystal plasticity-based finite element (CPFE) analysis was carried out to study the cyclic plastic behaviors. Using the design of experiments (DOE) technique, a series of CPFE simulations were designed and performed for DZ4 superalloy with recrystallized grains to examine the cyclic plastic shear deformation at the carbide/matrix interface, at the recrystallized grain boundary/matrix, and in the matrix. Seven influence factors, i.e., applied strain, strain ratio, carbide modulus, dwell time, misorientation angle, carbide aspect ratio, and carbide size, were considered, and the effects of which were quantitatively evaluated by the maximum accumulated plastic shear strains via CPFE-based DOE analysis. The results showed that carbide and recrystallized grain boundary had competitively significant effects on fatigue crack initiation. Applied strain was the most influential parameter among all the studied parameters.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Corrosion Behavior of Annealed Steels with Different Carbon Contents (0.002, 0.17, 0.43 and 0.7% C) in Freely Aerated 3.5% NaCl Solution

Four annealed carbon steels with different carbon contents (0.002, 0.17, 0.43, and 0.7% C), consisting of ferrite, ferrite-pearlite and fully pearlite microstructures, were selected to understand the corrosion behavior of carbon steel as a function of carbon content in freely aerated 3.5% NaCl solution. Dynamic polarization, electrochemical impedance and linear polarization methods were used. The corrosion rate obtained from the different carbon steels was found to increase greatly from ultra-low carbon steel (0.002%) to low carbon steel (0.17%) due to the presence of pearlite in the low carbon steel. However, the increase in corrosion rate was marginal with the increase in carbon content from low carbon (0.17%) to medium (0.43% C) and high carbon steels (0.7% C). The mirostrucural evolution of the steels before and after polarization test without etching as observed by scanning electron microscopy could show that the corrosion behavior of the steels with the presence of pearlite was due to the combined effect from % pearlite, interlamellar spacing and cementite/ferrite area ratio in pearlite. Pearlite morphology also led to the differential corrosion within the pearlite colony in all the steels except the steel with 0.002% C. Catalytic activity of cementite on enhancing oxygen reduction reaction attributes to the higher corrosion rates in case of the steels with the presence of pearlite.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure and Corrosion Behavior of Cr Coating on M50 Steel Fabricated by Electrospark Deposition

Cr coatings are deposited on M50 steel by electrospark deposition with different parameters (100 V-60 μF, 100 V-90 μF, 100 V-120 μF, 150 V-60 μF, 150 V-90 μF and 150 V-120 μF). Influences of the depositing parameters on the microstructure and the corrosion behavior of the coatings were experimentally investigated. There is a linear trend of growth between the mass gain per area and the deposition cycles before reaching the maximum values. The voltage has more influence on the mass gain per area than the capacitance. The coatings display a splash-like pattern decorated with a few of micro-cracks. The micro-cracks are more sensitive to the voltage than the capacitance. The anti-corrosion ability of the coating is significantly better than the M50 steel. Local corrosion occurs in the coating when there are through-coating cracks. The coating deposited under 150 V-60 μF has the minimum defect density and the best anti-corrosion behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Deformation Behavior and Microstructure Evolution of Powder Metallurgy Ti6Al4V Alloy During Hot Compression

In order to determine appropriate workability parameters for cross-wedge rolling products of powder metallurgy (PM) Ti6Al4V alloys, thermal compression experiments were carried out within the temperature range of 850-1050 °C, the strain rate range of 0.1-10 s{sup −1}, and with a height decrease of 60%. The compression deformation behavior was investigated. A strain-compensated constitutive model was established based on the flow stress curves corrected by the friction, which can predict the flow behaviors under the entirety of the experimental deformation conditions. Moreover, the processing map was developed, and stable and unstable deformation regimes were established. The microstructure analysis illustrated that globularization and dynamic recrystallization were the main deformation mechanisms. The porosity of the compressed samples was greatly reduced and influenced by the temperature and strain rate. Considering the material flow stress, hot processing map, microstructure and porosity, the appropriate hot deformation parameters for PM Ti6Al4V alloy preforms are suggested.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Cobalt on the Microstructure and Corrosion Behavior of Martensitic Age-Hardened Stainless Steel

To evaluate the influence of cobalt on the microstructure and pitting behavior of martensitic age-hardened stainless steel (MASS), the microstructures and electrochemical behaviors were characterized by optical microscopy, scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy, potentiodynamic curve, electrochemical impedance spectroscopy, and Mott–Schottky analysis. Results indicated that adding cobalt reduced the grain size of the original austenite, refined the lath martensite, inhibited the precipitation of Cu-rich phases, and increased the content of reversed austenite. Compared with the cobalt-free steel, the cobalt-containing steel has a higher pitting potential, lower corrosion current density, and higher pitting resistance. The primary components of the passive film grown on the cobalt-free steel included (Cr, Fe) oxides, such as Cr{sub 2}O{sub 3}, Cr(OH){sub 3}, FeOOH, and Fe{sub 2}O{sub 3}. The cobalt-containing steel included the aforementioned components as well as Co, which was attributed to the formation of the passive film in the forms of CoFe{sub 2}O{sub 4}, Co(OH){sub 2}, and CoO. In addition, the synergy of the refined lath martensite and the precipitation of the Cu-rich phase induced an increase in corrosion resistance in MASS containing cobalt.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Welding Parameters on Junction Structure and Fracture Behavior of Friction-Stir-Welded Joints of 2024 Aluminum Alloys

In this paper, the effect of welding speed and tool rotation speed on the junction structure and fracture behavior of friction-stir-welded joints was investigated with use of 2024 aluminum alloys of 3.2 mm thick. Results show that the formation of junction structure is more affected by tool rotation speed than by welding speed due to the differences of heat input levels. When welding speed is at 100 mm/min and tool rotation speed is in the range of 400-600 r/min, the joint junction structure causes complete bonding with no welding defects. While under improper welding parameters, the junction structure causes the precipitate aggregation on the bonding line and the partial bonding with the appearance of both tunnel defects and kissing bond defects. Meanwhile, the results of tensile tests show that the tensile fracture of all FSW joints occur at the weld center. The failure mode of joints with defects-free junction structure characterized by shear fracture is ductile. While the failure mode of joints with defects-existent junction structure characterized by layered fracture surface is brittle. Furthermore, that heterogeneous microstructure, precipitate aggregation and welding defects converge inside the junction structure is the main factor affecting the tensile properties and fracture behavior of the friction-stir-welded joint.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Test Temperature and Strain Rate on Dynamic Mechanical Behavior of Aluminum Alloy 2519A

The dynamic mechanical behavior of aluminum alloy 2519A-T9I6 has been investigated by a split Hopkinson bar at temperature range from 298 to 523 K and at strain rates of from 10{sup 3} to 5 × 10{sup 3} s{sup −1} in this study. The results show that both the strain rate and test temperature have a significant effect on the dynamic behavior and microstructure evolution of aluminum alloy 2519A-T9I6. Under similar strain rate, the strengthening effect of strain rate decreases with the increase in the test temperature. Moreover, the dynamic yield strength at above 423 K drops sharply at the strain rate of about 5000 s{sup −1}, which is attributed to the flow softening caused by decomposition of θ′ precipitates at high strain rate and high temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A Comparative Study of Deformation Behaviors Between Laser-Welded Joints and Base Metal of Ti-22Al-24.5Nb-0.5Mo Alloy

The tensile deformation behaviors of laser-welded Ti-22Al-24.5Nb-0.5Mo alloy joints have been investigated at room temperature and 650 °C using in situ tensile analysis methods. The α{sub 2} phase had a significant influence on deformation behaviors of base metal at room temperature and 650 °C. The microcracks mainly nucleated in B2/α{sub 2} phase boundaries or within α{sub 2} phase and then propagated along B2/α{sub 2} phase boundaries subsequently. Compared with the plastic fracture of base metal, the fracture modes of the fully B2-phase fusion zone at room temperature and 650 °C were quasi-cleavage and intergranular fracture, respectively. While dislocation slips became foremost deformation mode in the fusion zone at room temperature, there were a great amount of slip bands on the surface of grains caused by the slip systems. The microcracks of fusion zone at 650 °C nucleated and propagated along the grain boundaries of B2 phase. Owing to the lack of grain deformation, the cross-slip bands were in small quantities on the surface of B2 phase grains.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Hot Deformation Behavior and Processing Maps of As-Cast Hypoeutectic Al-Si-Mg Alloy

The hot deformation behavior of as-cast hypoeutectic Al-Si-Mg alloy has been investigated through hot compression tests at temperatures between 573 and 773 K and the strain rate of 0.001-1 s{sup −1}. A modified Hansel-Spittel constitutive model is proposed, which takes the effect of strain rate on strain hardening into account. The processing maps are established based on the dynamic material model and the Murty criterion. Microstructure observations show that dynamic recovery dominates the dynamic softening behavior, and recrystallized grains are found in the sample tested at 773 K with strain rate of 0.01 and 0.001 s{sup −1}. The size of Si particles decreases by about 64.73% with the effective strain increasing from 0 to 1.2. The optimal hot processing parameters of as-cast hypoeutectic Al-Si-Mg alloy are established based on the processing maps.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Hot Deformation Behavior of Aluminum Alloys AA7010 and AA7075

The hot deformation behavior of high-strength aluminum alloys AA7010 and 5 was studied through hot isothermal compression testing in the temperature regime of 623-723 K (at an interval of 25 K) and at varying strain rates (0.001 to 10 s{sup −1}). The safe zone of hot workability of both the alloys was determined using the instability criteria and correlating with the microstructure evolution. Zener–Hollomon parameters were calculated, and constitutive equations were also derived. Common characteristics observed in both the alloys were adiabatic shear band formation at a temperature of 623 K and strain rate of 10 s{sup −1} and flow localization at combination of all temperatures and high strain rate of 10 s{sup −1} with evolution of very fine recrystallized (DRX) grains. High-temperature resistance to deformation, large extent of recrystallization and relatively larger zone of stable deformation and higher activation energy in Al alloy AA7010 were observed as compared to AA7075. Considering the role of precipitates, dynamic recrystallization was found to have significant role in governing the hot deformation behavior of the alloys. Prediction of constitutive equations was found to be more accurate at higher temperatures and at moderate-to-high strain rates with relatively less error in AA7075 alloy as compared to AA7010 alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Y{sub 2}O{sub 3} Addition on the Microstructure, Wear Resistance, and Corrosion Behavior of W-4.9Ni-2.1Fe Heavy Alloy

Binding and particle phases are the two important parameters influencing materials properties. In this study, a series of novel W-4.9Ni-2.1Fe-xY{sub 2}O{sub 3} (in weight%) alloys with different Y{sub 2}O{sub 3} contents are prepared by secondary ball milling and spark plasma sintering (SPS) techniques to obtain uniformly distributed γ-(Ni, Fe) binding phases and finer grains. The microstructure, mechanical, wear resistance, and corrosion behavior of the sintered bodies with different Y{sub 2}O{sub 3} were obtained by x-ray diffraction, scanning electron microscopy, Rockwell hardness tester, friction wear tester, and three-dimensional profile instruments. The results showed that a certain addition of Y{sub 2}O{sub 3} led to refined grains and uniformed microstructures; but, if excessive, a weak grain refinement would be appeared. Moreover, the grain size tends to be stable with enhancing of the Y{sub 2}O{sub 3} content. Considering properties such as density, hardness, compression yield strength, grain size, and uniform distribution of tungsten hard phase and γ-(Ni, Fe) binding phase, the comprehensive optimal amount of 0.7 wt.% of Y{sub 2}O{sub 3} was attained for the alloy. Meanwhile, the SPS sintered body also exhibited the best friction, wear behavior, and corrosion resistance in 3.5% of NaCl solution.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Stress States on Twinning Behavior in Twinning-Induced Plasticity Steel

The effects of stress state on the twin structures and kinetics in twinning-induced plasticity (TWIP) steel have been investigated to understand the twinning behaviors in more detail. Twinning behaviors of tension, compression, wire drawing, and caliber rolling were evaluated and compared using the EBSD technique, TEM measurement, and Schmid factor analysis. Twin structures, such as twin thickness, twin variant, twin shape, and twin kinetics were different with stress states. The specimen under compressive stress had wavy-shaped twins, less twin variant, lower twin thickness, and more twin volume fraction in comparison with the specimen under tensile stress. The different structures and kinetics of deformation twin with stress state were highly related to the grain rotation during plastic deformation. Under tensile stress, the grain rotation to <111> orientation, twinning-favored regions by Schmid factor analysis, encouraged the lateral growth of twins, more twin variants, and straight-type twins, while the grain rotation to <110> orientation under compressive stress suppressed the twin growth and twin variant and developed wavy-shaped twins. Drawn wire and caliber-rolled wire had both twin features under tensile and compressive stress states and higher twin volume fraction since complex stress state that combined tension and compression was applied in these processes. The hardness values were strongly related to the twin volume fraction with strain and stress state.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Friction Stir Processing on the Microhardness, Wear and Corrosion Behavior of Al6061 and Al6061/SiO{sub 2} Nanocomposites

An effect of the friction stir processing (FSP), its pass numbers and addition of the SiO{sub 2} nanoparticles on microhardness, wear behavior and corrosion performance of the Al6061 aluminum alloy was investigated. Scanning electron microscopy (SEM) and optical microscopy were utilized to characterize the microstructure of the alloy, FSPed and composite samples. SEM observations revealed that the SiO{sub 2} particles were not uniformly dispersed in the matrix after two passes of FSP. However, increasing the pass number more than two passes resulted in a great improvement in the distribution of the SiO{sub 2} particles. The application of FSP led to overall softening compared to the base metal. Softening of the Al6061 alloy was probably attributed to the coarsening of Mg{sub 2}Si. Corrosion resistance of the FSPed samples found a significant reduction compared to the base metal. Applying higher pass number of the process and also addition of the SiO{sub 2} nanoparticles improved the wear behavior of the samples.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Electrochemical Corrosion Behavior of 5083 Aluminum Alloy Subjected to Laser Shock Peening

This paper investigates the effect of ablative coating used during laser shock peening (LSP) on corrosion behavior of 5083 aluminum alloy in artificial seawater. Micro-hardness, residual stress, and surface morphology of the specimens were measured. The corrosion behavior was investigated by electrochemical test. Surface corrosion morphologies after electrochemical tests were examined by SEM and EDS. The results show that surface roughness and surface compressive residual stress of the specimen treated by LSP without ablative coating (LSPwC) are lower than that of the specimen treated by LSP with ablative coating under the same laser energy. The open-circuit potentials and self-corrosion potentials of the specimens treated by LSP and LSPwC both shift positively, and the diameters of the capacitor arcs were larger after LSP and LSPwC. The corrosion resistance of 5083 aluminum alloy is improved by LSP and LSPwC. Moreover, superior corrosion resistance is achieved without using the ablative coating during LSP.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Corrosion Behavior of AZ31 Magnesium Alloy Produced by Continuous Variable Cross Section Direct Extrusion

In order to study the corrosion behavior of magnesium alloys of high performance in the simulated seawater by continuous variable cross section direct extrusion (CVCDE), an electrochemical method and weight loss method were used to study the difference between AZ31 magnesium alloys produced by CVCDE with different numbers of interim dies to examine the electrochemical corrosion behavior and corrosion rate at 3.5 wt.% NaCl solution in this paper. Scanning electron microscopy and x-ray diffraction were used to analyze the morphology of corrosion surfaces and the composition of the corrosion products of samples soaked for different times. The results show that after CVCDE with different numbers of interim dies, the size of the microstructure is refined gradually, and the grain orientation is also different; with the increase in the number of interim dies, the thermodynamic corrosion tendencies are different, and the corrosion resistance of samples extruded by conventional extrusion is relatively good; the charge transfer and material transfer process are the two main factors affecting the corrosion rate, which determines the direction of the electrochemical reaction; the corrosion form of the sample extruded by CVCDE is the local corrosion which is the filiform corrosion and pitting corrosion, and the corrosion product is mainly water-insoluble Mg(OH){sub 2}.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Mechanical Behavior of Lead at High Strain Rates

This paper presents a study on the material behaviors and constitutive models of lead at high strain rates. Quasi-static compressive tests and split Hopkinson pressure bar (SHPB) tests were conducted at room temperature. The results of the SHPB tests were verified by high-speed photography, and the error of strain is less than 3% at high strain rate (5000/s). Our results show that the yield stress and flow stress increase at high strain rates. This result indicates that lead is sensitive to the strain rate at high strain rates, but the dependence is not linear during 3000-5000/s. The strain-rate dependence of lead was fitted by a quadratic polynomial curve. To describe the nonlinear strain-rate relationship of lead, modified Johnson–Cook and Cowper–Symonds material models were used to fit the experimental stress–strain curves. The modified Cowper–Symonds model agrees better with the experimental results and can better describe the dynamic mechanical behavior of lead under high strain rates.

36 MATERIALS SCIENCE↗