Mechanical Strength and Surface Roughness of Magnesium-Based Metallic Glasses

This work evaluated the mechanical strength and surface roughness of MgZn₃₀Ca₅ ribbon manufactured via a melt spinning technique for applications in the biomedical field. Annealing was performed at 280°C. The inner side (in contact with the wheel) and the outer side (not in contact with the wheel) of the ribbons were mechanically evaluated using nanoindentation, and its surfaces were analyzed by an optical profilometer. Differential scanning calorimeter (DSC) and X-ray diffraction (XRD) analyses were also performed to identify the structure and devitrification of the magnesium metallic glass (MgMG). The nanohardness and elastic modulus increased after annealing (p < 0.0001). No differences were seen in the strength between the two sides of the ribbons (p > 0.05). Although both sides of the ribbons showed different surface profiles (p < 0.0001), no statistical difference was detected in roughness parameters on either ribbon side before (p = 0.3094) and after (p = 0.8742) annealing. DSC curves showed disturbances in enthalpy attributed to a relaxation in the MgMG structure and free volume annihilation. The DRX diffractogram showed sharp peaks after annealing, with MgZn and Ca₂Mg₅Zn₁₃ phases being identified. Although the use of MgMG in biomedical applications is promising, the ribbons displayed limited ductility, toughness, and a relevant embrittlement after the annealing procedure. There were significant changes in the surface profile of both sides of the ribbons. Nevertheless, neither annealing nor the ribbon side had influenced surface roughness parameters.     

Mechanical Behavior of a Magnesium Alloy Nanocomposite Under Conditions of Static Tension and Dynamic Fatigue

In this paper, the intrinsic influence of nano-alumina particulate (Al₂O_3p) reinforcements on microstructure, microhardness, tensile properties, tensile fracture, cyclic stress-controlled fatigue, and final fracture behavior of a magnesium alloy is presented and discussed. The unreinforced magnesium alloy (AZ31) and the reinforced composite counterpart (AZ31/1.5 vol.% Al₂O₃) were manufactured by solidification processing followed by hot extrusion. The elastic modulus, yield strength, and tensile strength of the nanoparticle-reinforced magnesium alloy were noticeably higher than the unreinforced counterpart. The ductility, quantified by elongation-to-failure, of the composite was observably lower than the unreinforced monolithic counterpart (AZ31). The nanoparticle-reinforced composite revealed improved cyclic fatigue resistance over the entire range of maximum stress at both the tested load ratios. Under conditions of fully reversed loading (R = ?1) both materials showed observable degradation in behavior quantified in terms of cyclic fatigue life. The conjoint influence of reinforcement, processing, intrinsic microstructural features and loading condition on final fracture behavior is presented and discussed.     

Experimental Investigation of the Al-Fe-Nd System at 773 K

The phase diagram of Al-Fe-Nd is helpful for development of the magnetic and amorphous materials based on this system. The entire isothermal section of Al-Fe-Nd at 773 K was determined by means of x-ray powder diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive analysis (EDX) and optical microscopy (OM). The existences of 12 binary compounds of the Al-Fe, Al-Nd and Fe-Nd systems were confirmed, and binary phases Al₂Nd and Fe₁₇Nd₂ demonstrated appreciable ternary solubility. The ternary compounds: τ₁-Al₁₀Fe₂Nd, τ₂-Al_8+x Fe_4?x Nd (0 < x < 0.7) and λ-Nd₃₀Fe_62?x Al_8+x (0 < x < 17) were confirmed in the present work. The isothermal section consists of 18 single-phase regions, 36 two-phase regions and 19 three-phase regions.     

Nanocrystalline Surface Layer on AISI 52100 Steel Induced by Supersonic Fine Particles Bombarding

Surface treatment of AISI 52100 steel by supersonic fine particles bombarding (SFPB) was studied in this article. The surface topography, morphology of the surface layer, and microhardness distribution of the surface layer have been investigated using a surface profiler system, a scanning electron microscopy (SEM), and a microvickers hardness tester. The microstructure, phase composition, and residual stress distribution of the surface layer in AISI 52100 steel after the SFBP treatment have been characterized by means of x-ray diffraction, SEM, and transmission electron microscopy. The results showed that a nanocrystalline surface (NS) layer was formed on the top surface of the SFBP-treated AISI 52100 steel samples. The NS layer is about 2 μm in thickness with a surface roughness of R _a = 1.2 μm, R _y = 6.7 μm, R _z = 6.0 μm. Phase transitions occurred in the surface of the SFBP-treated samples. Residual compressive stress is obtained at the surface of the SFBP-treated samples. The maximum value of compressive stress appears at the outermost of the surface, and the affection region of the whole surface is about 60 μm in thickness. A hardened surface layer has been fabricated in the AISI 52100 steel. The thickness of the hardened surface layer is about 70 μm. The maximum value of hardness occurs at the depth of 20 μm from the outermost surface.     

Preliminary Investigation of the Corrosion Behavior of Proprietary Micro-alloyed Steels in Aerated and Deaerated Brine Solutions

The corrosion performance of fairly new generation of micro-alloyed steels was compared in different concentrations of aerated and deaerated brines. Electrochemical polarization, weight loss and surface analyses techniques were employed. The results showed a threshold of corrosion rate at 3.5 wt.% NaCl in both aerated and deaerated solutions. The average corrosion current density for steel B, for example, increased from 1.3 µA cm^?2 in 1 wt.% NaCl to 1.5 µA cm^?2 in 3.5 wt.% NaCl, but decreased to 1.4 µA cm^?2 in 10 wt.% deaerated NaCl solutions. The aerated solutions exhibited an average of over 80% increase in corrosion current density in the respective concentrations when compared with the deaerated solution. These results can be attributed to the effects of dissolved oxygen (DO) which has a maximum solubility in 3.5 wt.% NaCl. DO as a depolarizer and electron acceptor in cathodic reactions accelerates anodic metal dissolution. The difference in carbon content and microstructures occasioned by thermo-mechanical treatment contributed to the witnessed variation in corrosion performance of the steels. Specifically, the results of the various corrosion techniques corroborated each other and showed that the corrosion rate of the micro-alloyed steels can be ranked as CR_{Steel A} < CR_X65 < CR_{Steel B} < CR_{Steel C}.     

Thermal Oxidation of Cold Sprayed Titanium-Based Coating Deposited on Co-Cr Alloy

This study focuses on the surface modification of a medical grade Co-Cr alloy via combining cold spray and thermal oxidation processes. After deposition of a Ti96-Al4 (wt.%) coating, samples were oxidized at 600 °C for 60 h in air. Oxidation transformed the coating into a dual-layered structure comprising an outer oxide layer (mainly rutile) with a diffusion layer (mainly oxygen enriched titanium and Ti-Al intermetallics) beneath it. Formation of new phases made the diffusion layer brittle and prone to fracture during pull out tests. Scratch and Rockwell-C tests confirmed good adhesion between the oxide and underlying diffusion layers, having average hardness as 1297 HV and 387 HV, respectively. The dual-layer coating exhibited excellent wear performance in a 0.9 wt.% NaCl solution against sliding action of alumina ball as compared to Co-Cr substrate, especially at contact pressures?<?1200 MPa, while the maximum in vivo contact pressure is?<?15 MPa for load-bearing orthopedic implants. Furthermore, the release of the aluminum from the dual-layer coating into 0.9 wt.% NaCl solution is lower than the permissible limit stated by the International Agency for Research on Cancer.     

Influence of Al Contents on the Microstructure, Mechanical, and Wear properties of Magnetron Sputtered CrAlN Coatings

CrAlN (0 < x < 0.1) coatings were deposited on SA304 substrate by a reactive magnetron sputtering. The microstructure and composition of the as-deposited coatings were systematically characterized by field emission scanning electron microscopy/EDS and atomic force microscopy, and the phase formation by x-ray diffraction (XRD). The hardness of the coatings was investigated using nanoindentation, while wear properties were investigated using pin-on-disk tribometer. XRD study reveals that the deposited CrAlN coatings crystallized in the cubic B1 NaCl structure. The minimum and maximum hardness of the coatings are found to be 15.28 and 18.81 GPa, respectively. The COF and wear rate are found to be 0.48 and 2.25 × 10^?5 mm³/N · m, which is lower than the CrN coatings deposited and characterized under the same environment (0.63 and 2.25 × 10^?5 mm³/Nm).     

Effect of inclination of weld faying surface on joint strength of friction welded joint and its allowable limit for austenitic stainless steel solid bar similar diameter combination

This paper describes the effect of the inclination of the weld faying surface on joint strength of friction welded joint and its allowable limit for austenitic stainless steel (SUS304) solid bar similar diameter combination. In this case, the specimen was prepared with the inclination of the weld faying surface pursuant to the JIS Z 3607, and the joint was made with that diameter of 12 mm, a friction speed of 27.5 s^?1, and a friction pressure of 30 MPa. The initial peak torque decreased with increasing inclination of the weld faying surface, and then the elapsed time for the initial peak increased with increasing that inclination. However, the steady torque was kept constant in spite of the inclination of the weld faying surface increasing. The joints without the inclination of the weld faying surface, which were made with friction times of 1.5 and 2.0 s with a forge pressure of 270 MPa, had achieved 100% joint efficiency with the base metal fracture. Those joints had 90° bend ductility with no crack at the weld interface. The joints with the inclination of the weld faying surface of 0.3 mm (gap length of 0.6 mm), which were allowable distance, was also obtained the same result with this condition. Furthermore, those joints with a friction time of 2.5 s obtained the same result. On the other hand, the joints with the inclination of the weld faying surface of 0.6 mm (gap length of 1.2 mm), which were twice inclination of the allowable distance, also obtained the same result in a friction time of 2.5 s. However, the joints without the inclination of the weld faying surface at this friction time did not obtain the base metal fracture, although those achieved 100% joint efficiency. In conclusion, to obtain 100% joint efficiency and the base metal fracture with no cracking at the weld interface, the joint must be made with the inclination of the weld faying surface, with allowable distance pursuant to the JIS Z 3607.     

Effect of Hydrogen on Mechanical Properties of 23Co14Ni12Cr3Mo Ultrahigh Strength Steel

In order to evaluate the effect of hydrogen on mechanical properties of 23Co14Ni12Cr3Mo ultrahigh strength steel, the specimens were electrochemically hydrogen charged for different times. The tensile property, fatigue fracture behavior, fatigue crack growth (FCG) behavior, and threshold stress intensity (ΔK _th) of the samples were studied. The fracture morphology was characterized by scanning electron microscopy. It was shown that tensile strength decreases from 2300 to 2000 MPa, critical fatigue stress from 577 to 482 MPa, and ΔK _th from 27.4 to 14.3 MPam^0.5 with the increasing hydrogen contents from 0.0001 to 0.0008 wt.%. Hydrogen enhances the FCG rate from 2.4 × 10^?3 to 3.6 × 10^?3 mm/cycle at ΔK = 80 MPam^0.5 in the hydrogen-charging range. Microscopic observation showed that the tensile fracture is a combination of overload microvoids and some intergranular regions for 0 h, and isolated areas of transgranular (TG) fracture are observed with brittle cleavage for 24-72 h. The fatigue fracture is ductile for the uncharged specimens, while the hydrogen-charged specimens show mainly brittle TG fracture. These results suggest that hydrogen degrades the fracture behavior of 23Co14Ni12Cr3Mo ultrahigh strength steel.     

Influence of Microstructural Inhomogeneity and Residual Stress on Very High Cycle Fatigue Property of Clean Spring Steel

The present study investigated the very high cycle fatigue (VHCF) properties of a spring steel SUP7-T386 under the conditions of surface grinding and electro-polishing by performing the axial loading test at a stress ratio of ?1. The influence of the microstructural inhomogeneity (MI) generated in the process of heat treatment and the residual stress induced by surface grinding on the VHCF properties was discussed. This steel with surface grinding exhibits the continuously descending S-N characteristics, corresponding to the surface flaw-induced failure at high stress level and the interior flaw-induced failure at low stress level. Otherwise, with surface electro-polishing, it exhibits continuously descending S-N characteristics with lower fatigue strength, but only corresponding to the surface flaw-induced failure even at low stress level. Compared with the evaluated maximum inclusion size of about 11.5 μm, the larger MI size and the compressive residual stress play a key role in determining fatigue failure mechanism of this steel under axial loading in the VHCF regime. From the viewpoint of fracture mechanics, MI-induced crack growth behavior belongs to the category of small crack growth, and threshold stress intensity factors controlling surface and interior crack growth are evaluated to be 2.85 and 2.51 MPa m^1/2, respectively. The predicted maximum MI size of about 27.6 μm can be well used to evaluate surface and interior fatigue limit of this steel under axial loading in the VHCF regime, combined with the correction of residual stress.     

Effect of Induced Magnetic Field on Electrocrystallization of Zn-Ni Alloy and Their Corrosion Study

Zn-Ni alloy coatings have been deposited galvanostatically on mild steel under the effect of induced magnetic field (B), using gelatin and glycerol as additives. The effect of field intensity (from 0.05 to 0.4 T) and direction (both parallel and perpendicular) on electrocrystallization process has been studied considering the magnetohydrodynamic effect. The corrosion behaviors of coatings, deposited under different conditions of B, were evaluated by electrochemical AC and DC methods. Under optimal condition of B (perpendicular), Zn-Ni coatings showed about 3 times less corrosion rate (CR) than the one developed under natural convection (B = 0 T), deposited from same bath for same duration. The significant decrease of CR was attributed to unique electrocrystallization process during deposition, favoring increased γ-Ni₅Zn₂₁ (321) and decreased γ-Ni₅Zn₂₁ (330) phase. Progressive decrease of CR with increase of B showed that corrosion protection efficacy of the coatings bears close relation with their crystallographic orientations and surface topography, evidenced by XRD study and SEM analysis. The effect of B on thickness, microhardness, surface morphology, phase structure, and the corrosion resistance of coatings was analyzed and results were discussed.     

High-Frequency Absorption Properties of Three Kinds of Hollow Multiphase Ceramic Microspheres

Al-TiO₂-Fe₂O₃-MnO₂-Fe-Sucrose-Epoxy Resin as reaction system and self-reactive quenching technology which combines flame thermal spraying, self-propagating high-temperature synthesis and rapid solidification, were used to prepare three kinds of hollow multiphase ceramic microspheres (HMCMs) in different feeding gas (N₂, O₂) and dimension (coarse, fine). The characteristic results of three kinds of HMCMs indicated that various process parameters containing feeding gas and initial agglomerate size in this study can result in the change of surface organization, composition, morphology, and dimension. Investigation of microwave electromagnetic (EM) characteristics of three kinds of HMCMs showed that intrinsic characteristics play an important role in the determining the resulting properties. At 10-14.5 GHz, No. 3 HMCMs possess weak absorption intensity and narrow effective bandwidth (<?10 dB) owing to smaller dimension, but in higher-frequency band (14.5-17 GHz), an obvious absorption peak appears due to good EM match and nano-effects. Compared with No. 1 (O₂ coarse) and No. 3 (O₂ fine) HMCMs, enhanced absorption intensity and effective bandwidth (<?10 dB) were observed in No. 2 (N₂ coarse) HMCMs. Enhancements of absorption intensity and effective bandwidth are associated with extra nitride (AlN, FeN), partial open microspheres, M-hexagonal crystal and micro-nano thick dendrite. No. 2 HMCMs presented excellent microwave-absorption property, with the minimum reflectivity (R _L) of ?27.7 dB at 12.9 GHz. The effective bandwidth (<?10 dB) could reach to 4.1 GHz (10.9-15 GHz). This may be ascribed to the increased conductance loss, multiple scattering, magnetocrystalline anisotropy, and shape anisotropy.     

Comparison of Optical and SEM-BEI Inclusion Analyses of VIM-VAR Nickel-Titanium Alloy

The ASTM Standard for NiTi alloys does not specify the method to be used for the analysis of inclusions. Quantitative analysis is generally done by optical metallography with a computer program to measure size and area fraction. This study gives a comparison of quantitative analyses of inclusions by scanning electron microscopy using backscattered electron imaging (SEM-BEI) and quantitative analyses by optical metallography. Seven samples of 6.3-mm hot-rolled NiTi were evaluated. The coil samples were selected to exhibit a wide range of inclusion content. Each sample had a different Ni to Ti ratio corresponding to a different transformation temperature range (TTR) from A _s = ?25 °C (Ni = 50.79 a/o) to A _s = +95 °C (Ni = 49.63 a/o). Quantitative analyses by optical and by SEM-BEI are in reasonable good agreement for maximum particle size and maximum area fraction. Both methods of analysis show that carbide and intermetallic oxide inclusion populations in VIM-VAR hot-rolled coil vary significantly in the amount and size of inclusions with the alloy transformation temperature. Therefore, an analysis of a larger number of samples at each TTR is needed to develop statistically precise data. All carbide inclusions were less than 12.5 ??m and less than 1.0% area fraction in all the samples. Maximum size and area fraction of carbides decreased as TTR increased. Intermetallic oxide size and area fraction increased with increasing TTR Intermetallic oxides are fractured and separated from the matrix during hot working. However, stringering is very limited. The fracturing appears to happen in high TTR alloys but not in low TTR alloys. This dependence on TTR suggests that chemistry in or around the oxides affects their fracture behavior.     

Microstructure and Room-Temperature Mechanical Properties of FeCrMoVTi<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> High-Entropy Alloys

FeCrMoVTi _x (x values represent the molar ratio, where x = 0, 0.5, 1.0, 1.5, and 2.0) high-entropy alloys were prepared by a vacuum arc melting method. The effects of Ti element on the microstructure and room-temperature mechanical properties of the as-cast FeCrMoVTi _x alloys were investigated. The results show that the prepared alloys exhibited typical dendritic microstructure and the size of the microstructure became fine with increasing Ti content. The FeCrMoV alloy exhibited a single body-centered cubic structure (BCC1) and the alloys prepared with Ti element exhibited BCC1 + BCC2 mixed structure. The new BCC2 phase is considered as (Fe, Ti)-rich phase and was distributed in the dendrite region. With the increase of Ti content, the volume fraction of the BCC2 phase increased and its shape changed from a long strip to a network. For the FeCrMoV alloy, the fracture strength, plastic strain, and hardness reached as high as 2231 MPa, 28.2%, and 720 HV, respectively. The maximum hardness of 887 HV was obtained in the FeCrMoVTi alloy. However, the fracture strength, yield stress, and plastic strain of the alloys decreased continuously as Ti content increased. In the room-temperature compressive test, the alloys showed typical brittle fracture characteristics.     

Effects of AlN hydrolysis on fractal geometry characteristics of residue from secondary aluminium dross using response surface methodology

The effects of aluminium nitride (AlN) hydrolysis on fractal geometry characteristics of residue from secondary aluminium dross were studied using response surface methodology. The results show that the fractal dimensions of the residue can be significantly influenced by the AlN hydrolysis from secondary aluminium dross. The hydrolysis of AlN in the dross was spontaneous under temperatures of 303–373 K. The actual fractal dimensions of residue were significantly affected by the liquid–solid ratio (p<0.05) and changed from 1.16 to 1.80, which accurately aligned with those from the calculations. Moreover, the fractal dimensions of residue were significantly affected by the interactions between hydrolysis temperature and hydrolysis time, liquid–solid ratio and hydrolysis time, respectively (p<0.01). The minimum fractal dimensions of the residue reached 1.15 under the optimized conditions, which included a hydrolysis temperature of 30 °C, liquid–solid ratio of 5 mL/g and hydrolysis time of 10 min. The results suggest that response surface methodology can guide in optimizing the conditions of AlN hydrolysis in order to obtain the minimum fractal dimensions of residue for improving the reutilization of the dross.     

p-substituted phenols as corrosion inhibitors for aluminium-copper alloy in sodium hydroxide

The inhibition of corrosion of B26S aluminium (Al-4% Cu alloy) in solutions of sodium hydroxide has been studied by weight loss and galvanostatic methods. At constant alkali concentration the inhibitor efficiency increases with increase in the concentration of the inhibitor (except hydroquinone), and at constant inhibitor concentration the efficiency decreases with increase in alkali concentration. At 2.0% inhibitor concentration in 0.1 M NaOH, the efficiency of the inhibitors increases in the order: p-hydroxydiphenyl (65.3%) < p-aminophenol < p-bromophenol < hydroquinone < p-chlorophenol < p-cresol < p-hydroxyacetophenone < p-nitrophenol < phenol (～ 100%).An increase in exposure period or temperature does not appear to have any marked effect on percentage inhibition which, in most of the cases, remains constant or shows a slight tendency to decrease. The average activation energy in inhibited NaOH in the temperature range 20–50°C is found to be 55 kJ/mole, which is almost the same as that in uninhibited alkali. Polarization data indicate that the inhibitors act as mixed inhibitors with greater effect on the anode reaction.     

Microstructure and Mechanical Properties of Cr2Nb-Based Laves Phase Alloys Prepared by Laser Surface Remelting

The microstructure and mechanical properties of Cr₂Nb-based intermetallic matrix composites fabricated by laser surface remelting were investigated at hypoeutectic and hypereutectic compositions. In the hypoeutectic composition, the molten zones under different laser scanning velocities consist of fully α-Cr dendrites, whereas a series of morphology evolutions perpendicular to the scanning direction occurred in the hypereutectic composition: Cr₂Nb primary phase + Cr/Cr₂Nb eutectic → Cr/Cr₂Nb eutectic → α-Cr primary phase + Cr/Cr₂Nb eutectic → fully α-Cr dendrite. Based on the maximum growth rate criterion, the microstructure evolutions of the molten zones were analyzed by considering the competitive growth among the α-Cr phase, Cr₂Nb Laves phase, and the Cr/Cr₂Nb eutectic, which are in agreement with the experimental results. More importantly, the room-temperature fracture toughness values of the hypoeutectic and hypereutectic alloys attain 11.2 MPa m^1/2 and 7.9 MPa m^1/2, respectively, which increase by eight and six times over the as-cast Cr₂Nb Laves phase (1.2 MPa m^1/2), respectively. The remarkable enhancements in room-temperature fracture toughness were explained in terms of fine-grain toughening, second Cr phase toughening, and point defects toughening.     

Effect of Graphite Addition on Structure and Properties of Ti(CN) Coatings Deposited by Reactive Plasma Spraying

Ti(CN) coatings with graphite addition ranging from 0 to 50 wt.% were prepared using reactive plasma spraying technology and their microstructure, mechanical, and tribological properties were investigated using scanning and transmission electron microscopy, x-ray diffraction analysis, x-ray photoelectron spectroscopy, Vickers microhardness testing, and block-on-ring wear testing. The results showed that graphite addition resulted in crystallite size refinement and an increase in the amount of amorphous phase. The Ti(CN) coatings consisted of a mixture of Ti(CN), graphite, CN _x , and amorphous phases. The hardness first increased then decreased as the graphite content was increased, with a maximum of 1450 HV_0.2 for 30 wt.% graphite addition. The fracture toughness decreased from 4.38 MPa m^1/2 to 2.76 MPa m^1/2 with increasing graphite content. The friction coefficient decreased due to unreacted graphite embedded in the matrix. Also, the wear rate first decreased then increased, with a minimum value of 2.65 × 10^?6 mm³ N^?1 m^?1 for 30 wt.% graphite addition. The wear mechanisms of the Ti(CN) coatings included abrasive, adhesive, and oxidation wear.     

Fe-MCM-41 from Coal-Series Kaolin as Catalysts for the Selective Catalytic Reduction of NO with Ammonia

Fe-MCM-41, one kind of high-ordered mesoporous materials catalysts, with molar ratio of Fe/Si = 0.01-0.1, was synthesized by hydrothermal method from coal-series kaolin. Fe-MCM-41 catalysts were characterized by Fourier transform infrared spectroscopy, high resolution transmission electron microscopy, N₂ adsorption-desorption, x-ray photoelectron spectroscopy, and UV-vis spectroscopy. The results clearly indicated that: (1) all the samples exhibited typical hexagonal arrangement of mesoporous structure; (2) the incorporation of tiny amount of Fe³⁺ onto the surface and pore channel of MCM-41 mesoporous materials could efficiently promote the deNO _x activity of these catalysts. Moreover, the Fe-MCM-41 mesoporous materials were evaluated in the selective catalytic reduction of NO with NH₃. The results showed that Fe-MCM-41 catalyst with Fe/Si = 0.05 showed the highest catalytic activity at 350 °C, a gas hourly space velocity of 5000 h^?1, n(NH₃)/n(NO) = 1.1, and O₂% = 2.5%.