Microstructural control by spray forming and wear characteristics of a Babbit alloy

The effect of process variables during spray forming of a commercial Babbit alloy containing Pb74–Sn12–Sb11.5–Cu1.25–NiO.75–Cd0.3–As0.2 on its microstructure and wear characteristics were investigated. Variation in atomization gas pressure from 0.6 to 1.2 MPa and nozzle to substrate distance from 0.2 to 0.4 m revealed considerable change in the nature of porosity and microstructural features of the spray deposits. The process variables during spray deposition were optimized to achieve microstructural homogeneity and refinement in second phase particles of this alloy. The wear study of both the spray formed and as-cast alloy under an applied load of 10 to 70 N and sliding velocity of 0.2 to 1.5 ms-1 indicated two distinct regimes of mild and severe wear. In both the regimes, the spray-formed alloy consistently indicated a low wear rate compared to that of the as-cast alloy. In addition, the mild wear regime of the spray-formed alloy was extended to higher load and sliding velocity. Wear characteristics of the spray formed alloy is discussed in light of its microstructural features induced during spray deposition processing.     

Microstructural Features of Spray-Deposited Immiscible Bearing Alloys Al-43Sn and Al-7Sn-1.3Cu-1.3Ni

Two commercial grade aluminum based immiscible bearing alloys were spray-deposited using convergent-divergent type of nozzle. The processing parameters for spray-deposition were adjusted in such a way that most of the droplets arrived on the deposition substrate in either liquid or semi-liquid state. The microstructural features of spray-formed and as-cast alloys are compared. In spray-formed alloys equiaxed grains were observed. The cell boundaries and intercellular regions were observed to be decorated with sub-micron sized particles whereas in normal casting the second phase was observed to be segregated along grain boundaries. The morphology and distribution of second phase were observed to have similarity with those in over-spread and atomized powders produced under similar processing conditions. The microstructural features observed with variation in spray conditions are discussed in detail.     

Ultrafine grain structure features in spray-formed AZ31 magnesium alloy

The ultrafine grain structure was developed in spray-formed AZ31 magnesium alloy by optimizing delivery tube orifice diameter. A significant refinement of grain size ∼1 μm in ultrafine level was achieved by using 2.25 mm delivery tube orifice diameter. The tensile strength value was increased from 145 MPa of as-cast alloy to 250 MPa of spray-formed alloy, registering an enhancement of ∼72%. On the other hand, elongation was increased from 6% to 13% using 2.25 mm orifice, registering more than onefold increase in elongation. Also, hardness enhancement of ∼49% was observed in spray-formed AZ31 alloy compared to as-cast alloy. The fracture surface of spray-formed AZ31 Mg alloy evidences the mixed type of ductile and brittle fracture.     

Analytical electron microscopy techniques for track-plated Au-Cu alloy

Track-plated material offers improved mechanical properties over conventional plating. Track plating consists of burnishing the deposit during the plating process. The burnishing process, i.e. the mechanical rubbing of the deposit during electrodeposition, produces continuous nucleation of new grains during deposition, which effectively prevents large columnar grains and macroporosity. The unusual property improvement is associated with several significant microstructural features. These include periodic variations in the deposition chemistry, and an extremely fine grain-subgrain size and concomitant deformation.     

Development of a new integrated severe plastic deformation method

ABSTRACT

A novel one-pass integrated severe plastic deformation method, entitled extrusion compression angular pressing forward extrusion (ECAP-FE), was designed and used for fabricating a fine-grained as-cast AZ31 Mg alloy. Subsequently, mechanical (room temperature compression, tensile and microhardness) and microstructural properties of the processed sample were investigated in detail. In addition, a finite element simulation of the proposed method was carried out for evaluating the equivalent plastic strain and strain rate distribution. The results showed that the ECAP-FE method is a powerful method for processing the ultrafine-grained as-cast AZ31 Mg alloy in a single pass to achieve a uniform and fine microstructure with enhanced mechanical properties. Therefore, it appears that the proposed method has a great potential to a wide range of industrial applications.     

Compressive behaviour of SiC/ncsc reinforced Mg composite processed through powder metallurgy route

In this present work nano coconut shell charcoal (ncsc) and silicon carbide (SiC) particulates were reinforced with AZ31B Mg alloy and suitable magnesium composite was developed by using the powder metallurgy technique followed by hot extrusion. Density measurement of the Mg composites revealed that the addition of ncsc significantly improved the density of the composites and porosity measurement showed minimal porosity. The microstructure of the composites showed even distribution of the ncsc in the AZ31B/3SiC Mg composite. The compressive and impact behaviour of the samples were characterized, the results showed that on increasing the weight percentage of ncsc in AZ31B/3SiC/0.5ncsc Mg composites the mechanical properties such as ultimate compressive strength, 0.2% yield strength, ductility and impact strength decreased. The scanning electron microscope (SEM) analysis of fractured surface of AZ31B Mg alloy and AZ31B/3SiC/0.5ncsc Mg composites showed quasi-cleavage fracture. The presence of ncsc above 0.5 wt% composites revealed mixture of quasi cleavage planes and some dimples.     

High shear dispersion technology prior to twin roll casting for high performance magnesium/SiCp metal matrix composite strip fabrication

SiC particulate (SiC_p) reinforced AZ31 magnesium alloy composite strips were produced by a novel process. In the process, a high shear technique was utilised to disperse the reinforcing particles uniformly into the matrix alloy, and AZ31/5 vol%SiC_p slurry was solidified into thin strip by a horizontal twin roll caster. The experimental results showed that the AZ31/5 vol%SiC_p strip obtained with high shear treatment exhibited a significantly refined microstructure and uniform distribution of reinforcing SiC particles. High cooling rate in the TRC process was also considered to contribute to the grain refinement of the matrix alloy, together with the possible heterogeneous nucleation effect of the reinforcing particles. The mechanical properties of the high shear treated composites strips showed enhanced modulus, yield strength and ductility by hardness and tensile tests. The experimental results were discussed in terms of the microstructural features and the macroscopic reliability, where necessary, analytical and statistical analyses were conducted.     

Enhancing strength and hardness of AZ31B through simultaneous addition of nickel and nano-Al2O3 particulates

In the present study, AZ31B-Al₂O₃-Ni composites are developed by the addition of different amounts of Ni particulates into AZ31B-1.5Al₂O₃ using disintegrated melt deposition technique followed by hot extrusion. The AZ31B-1.5Al₂O₃ nano-composite is known to exhibit excellent ductility (∼30%) matching with that of pure aluminum but its strength levels are compromised. The composites developed in the current study show a homogeneous microstructure and significant improvement in mechanical characteristics. The results of mechanical properties characterization reveal that addition of Ni led to a simultaneous improvement in 0.2% YS (up to 25%), UTS (up to 13%) and hardness (up to 62%). The ductility, however, stayed almost similar to the ductility of monolithic AZ31B in the case of AZ31B-1.5Al₂O₃-1.5Ni composite while it was compromised for AZ31B-1.5Al₂O₃-3.19Ni. The results clearly reveal the superior capability of AZ31B-Al₂O₃-Ni formulations in terms of overall mechanical response when compared to monolithic AZ31B.     

Ultrasonic vibration assisted tungsten inert gas welding of dissimilar magnesium alloys

The effects of ultrasonic vibration assisted (UVA) treatment on the microstructures and mechanical properties of MB3/AZ31 dissimilar magnesium (Mg) alloy joints were studied by microstructural characterization, micro-hardness testing and tensile testing. Results indicate that the welding pores are eliminated and coarse ??-Mg grains of fusion zone are refined to 26 ??m, owing to the acoustic streaming effect and cavitation effect induced by the UVA treatment with an optimal ultrasonic power of 1.0 kW. In addition, Mg₁₇Al₁₂ precipitation phases are fine and uniformly distributed in the whole fusion zone of weldment. Micro-hardness of fusion zone of the Mg alloy joints increases to 53.5 HV after UVA process, and the maximum tensile strength with optimized UVA treatment increases to 263 MPa, which leads to fracture occurrence in the Mg alloy base plate. Eventually, it is experimentally demonstrated that robust MB3/AZ31 Mg alloy joints can be obtained by UVA process.     

Enhancing tensile/compressive response of magnesium alloy AZ31 by integrating with Al2O3 nanoparticles

AZ31 nanocomposite containing Al₂O₃ nanoparticle reinforcement was fabricated using solidification processing followed by hot extrusion. The Al₂O₃ nanoparticle reinforcement was isolated prior to melting by wrapping in Al foil of minimal weight (<0.50 wt% with respect to AZ31 matrix weight). The AZ31 nanocomposite exhibited slightly smaller grain and intermetallic particle sizes than monolithic AZ31, reasonable Al₂O₃ nanoparticle distribution, non-dominant (0 0 0 2) texture in the longitudinal direction unlike monolithic AZ31, and 30% higher hardness than monolithic AZ31. Compared to monolithic AZ31, the AZ31 nanocomposite exhibited higher 0.2%TYS, UTS, failure strain and work of fracture (WOF) (+19%, +21%, +113% and +162%, respectively). Also, compared to monolithic AZ31, the AZ31 nanocomposite exhibited higher 0.2%CYS and UCS, similar failure strain, and higher WOF (+5%, +5%, −4% and +11%, respectively). Inclusive of crystallographic texture changes, the effect of Al₂O₃ nanoparticle integration on the enhancement of tensile and compressive properties of AZ31 is investigated in this paper.     

Microstructural features induced by spray forming of a ternary Pb-Sn-Sb alloy

An alloy containing Pb-12% Sn-12% Sb with small addition of copper and arsenic was spray deposited employing two different atomization gas pressure and nozzle to substrate distances. The temperature of the spray-deposit was measured during deposition at a distance of 2 and 10 mm above the substrate-deposit interface. Thermal profile data indicated small variation in temperature with time during deposition stage whereas during post deposition stage an exponential decrease in temperature was recorded. Second phase particle size along the thickness of the deposit varied from 4 to 8 μm compared to 70 to 80 μm size of these particles in the as cast alloy. Maximum porosity occurred in the section of the deposit near the contact surface of the substrate and also in its peripheral regions. X-ray diffraction analysis exhibited the formation of additional Cu₂Sb phase in the spray-deposit and CuSn and Cu_3.3Sb phases in atomized powders compared to that of the as cast alloy. The microstructural evolution during spray deposition of this alloy is discussed.     

Corrosion resistance of biodegradable polymeric layer-by-layer coatings on magnesium alloy AZ31

Biocompatible polyelectrolyte multilayers (PEMs) and polysiloxane hybrid coatings were prepared to improve the corrosion resistance of biodegradable Mg alloy AZ31. The PEMs, which contained alternating poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), were first self-assembled on the surface of the AZ31 alloy substrate via electrostatic interactions, designated as (PAH/PSS)₅/AZ31. Then, the (PAH/PSS)₅/AZ31 samples were dipped into a methyltrimethoxysilane (MTMS) solution to fabricate the PMTMS films, designated as PMTMS/(PAH/PSS)₅/AZ31. The surface morphologies, microstructures and chemical compositions of the films were investigated by FE-SEM, FTIR, XRD and XPS. Potentiodynamic polarization, electrochemical impedance spectroscopy and hydrogen evolution measurements demonstrated that the PMTMS/(PAH/PSS)₅/AZ31 composite film significantly enhanced the corrosion resistance of the AZ31 alloy in Hank’s balanced salt solution (HBSS). The PAH and PSS films effectively improved the deposition of Ca-P compounds including Ca₃(PO₄)₂ and hydroxyapatite (HA). Moreover, the corrosion mechanism of the composite coating was discussed. These coatings could be an alternative candidate coating for biodegradable Mg alloys.     

Reactive sputter deposition of alumina films on magnesium alloy by double cathode glow-discharge plasma technique

In order to overcome the problem of the corrosion resistance of AZ31 magnesium alloy, the nanocrystalline Al₂O₃ film was deposited on AZ31 magnesium alloy by double cathode glow-discharge plasma technique. The microstructure, chemical composition and elemental chemical state of the sputter-deposited nanocrystalline Al₂O₃ film were analyzed by means of scanning electron microscopy equipped with an energy dispersive spectroscope, X-ray diffraction), transmission electron microscope and X-ray photoelectron spectroscopy. The results indicated that the sputter-deposited nanocrystalline Al₂O₃ film consisted of single θ-Al₂O₃ phase with average grain size about 60 nm. The hardness and the elastic modulus of the as-deposited nanocrystalline Al₂O₃ film were about 17.21 GPa and 217 GPa measured by nanoindentation instrument, respectively. The corrosion behavior of the sputter-deposited nanocrystalline Al₂O₃ film in 3.5%NaCl solution was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. The amount of porosity for the sputter-deposited nanocrystalline Al₂O₃ film calculated by two electrochemical methods was equal to 0.0086% and 0.168%, respectively. The sputter-deposited nanocrystalline Al₂O₃ film exhibited excellent corrosion resistance, which was attributed to its dense enough structure to prevent magnesium alloy from corrosion in aggressive solutions.     

Microstructure and mechanical properties of an indirect-extruded Mg-8Sn-1Al-1Zn alloy

The microstructure and mechanical properties of an indirect-extruded Mg-8Sn-1Al-1Zn (TAZ811) alloy were investigated and compared with those of a commercial Mg-3Al-1Zn (AZ31) alloy. In the extruded condition, the TAZ811 alloy shows a much smaller grain size but a stronger basal texture than the AZ31 alloy. In addition, the TAZ811 alloy contains fine Mg₂Sn particles in the microstructure, whereas the AZ31 alloy reveals relatively coarse and sparse Al-Mn particles. The TAZ811 alloy showed tensile and compressive strengthening as well as a reduction in yield asymmetry between tension and compression, which is mainly due to grain refinement and the presence of fine Mg₂Sn particles.     

蝶翅构型TiO2/等离子体纳米金复合体系全光谱二氧化碳光还原特性研究

以红珠灰蝶为生物模板,使用原子层沉积法构筑三维构型TiO_2光催化材料以增强其光捕获能力;使用种子生长法制备具有宽幅可见光波段吸收能力的等离子体共振金纳米棱结构,并将其负载于蝶翅构型TiO_2上以得到全光谱响应的复合光催化体系;采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、紫外-可见分光光度计、X射线衍射仪(XRD)等表征了所制备的样品;对样品进行了二氧化碳还原性能测试,结果表明在全光谱照射下,负载有金纳米棱的蝶翅构型TiO_2的二氧化碳光还原性能比无结构的提升了54%。     

Simultaneously enhanced tensile and compressive response of AZ31–NanoAl<Subscript>2</Subscript>O<Subscript>3</Subscript>–AA5052 macrocomposite

New bimetal AZ31–Al₂O₃/AA5052 macrocomposite comprising (a) Al₂O₃ nanoparticle-reinforced magnesium alloy AZ31 shell and (b) aluminum alloy AA5052 millimeter-scale core reinforcement was fabricated using solidification processing followed by hot coextrusion. Microstructural characterization revealed more rounded intermetallic particle of decreased size, reasonable Al₂O₃ nanoparticle distribution, and non-dominant (0 0 0 2) texture in the longitudinal and transverse directions in the AZ31–Al₂O₃ nanocomposite shell. Interdiffusion of Mg and Al across the core–shell macrointerface into each other was also significant. Compared to monolithic AZ31, the AZ31–Al₂O₃ shell exhibited significantly higher hardness (+33%). In tension, the presence of Al₂O₃ nanoparticles (in the AZ31 shell) and AA5052 core significantly increased stiffness (+39%), yield strength (0.2% TYS) (+9%), ultimate strength (UTS) (+19%), average failure strain (+7%), and work of fracture (WOF) (+27%) of AZ31. In compression, the presence of Al₂O₃ nanoparticles (in the AZ31 shell) and AA5052 core significantly increased yield strength (0.2% CYS) (+58%), ultimate strength (UCS) (+4%), average failure strain (+11%), and WOF (+49%) of AZ31. The effect of joint presence of (a) Al₂O₃ nanoparticles (in the AZ31 shell) and (b) AA5052 millimeter-scale core on tensile and compressive properties of AZ31 is investigated in this article.     

Microstructure and mechanical properties of spray-formed AZ91 magnesium alloy

The AZ91 magnesium alloy, preformed with complete shape, has been prepared using spray forming technology under a protective atmosphere. The microstructure and mechanical properties have been investigated. Initially, a homogeneous and equiaxed-grain structure with average grain size of 20 μm was obtained. The tendency for segregation of the divorced eutectic β(Mg₁₇Al₁₂) phase towards the grain boundary was greatly reduced. Further grain refinement was attributed to dynamic recrystallization during extrusion processing. When solution treated at 415 °C and aged at 175 °C, two kinds of β(Mg₁₇Al₁₂) precipitates are formed: the majority are lamellar discontinuous precipitates, in addition to a small amount of dispersed continuous precipitates. The average tensile ultimate and yield strength of the spray-formed and extruded AZ91 magnesium alloy samples were 435 MPa and 360 MPa with a room temperature elongation of 9.2%, indicating an enhanced combination of toughness and strength.     

Effect of bonding temperature on microstructure and intermetallic compound formation of diffusion bonded magnesium/aluminum joints

The diffusion bonding of two dissimilar alloys Aluminum 5083 and Magnesium AZ31 was carried out at 420 °C, 430 °C,440 °C and 450 °C for bonding time of 60 min. In order to characterize the microstructure evolution in the joint zone, scanning electron microscopy, energy dispersive spectroscopy and x-ray diffraction were applied. The results show that joint formation is attributed to the solid-state diffusion of magnesium and aluminum into Aluminum 5083 and Magnesium AZ31 alloys followed by eutectic formation and constitutional liquation along the interface. At bonding temperature of 430 °C diffusion induced grain coarsening was observed at the interface. With increase in bonding temperature, the atomic diffusivity increases, results in easier and speeder chemical bonding. In bonding temperature of 440 °C the weld had an irregular shaped region in the weld center, having a different microstructure from the two base materials. The irregular shaped region contained a large volume of intermetallic compound Al₁₂Mg₁₇ and showed significantly higher hardness in the weld center. The present study suggests that constitutional liquation resulted in the intermetallic compound Al₁₂Mg₁₇ in the weld center.     

Effects of TiO2 coating on the microstructures and mechanical properties of tungsten inert gas welded AZ31 magnesium alloy joints

The effects of TiO₂ coating on the macro-morphologies, microstructures and mechanical properties of tungsten inert gas (TIG) welded AZ31 magnesium alloy joints were investigated by microstructural observations, microhardness tests and tensile tests. The results showed that an increase in the amount of the TiO₂ coating resulted in an increase in the weld penetration and the depth/width (D/W) ratio of the TIG welded AZ31 magnesium alloy seams. Moreover, the average grain size of the α-Mg grains increased and the β-Mg₁₇Al₁₂ intermetallic compound (IMC) was coarser in the case of higher amount of the TiO₂ coating. With an increase in the amount of the TiO₂ coating, the microhardness of the fusion zone (FZ) of the AZ31 magnesium alloy welded joints decreased slightly initially and then decreased sharply. In addition, with an increase in the amount of the TiO₂ coating, the ultimate tensile strength (UTS) value and elongation of the welded joints increased at first and then decreased sharply.     

Surface mechanical attrition treatment-induced dissolution of Cu4Ti precipitates in Cu–4wt-%Ti alloy

ABSTRACT

The microstructural evolution of an overaged Cu-4wt-%Ti alloy associated with surface mechanical attrition treatment (SMAT) has been studied by X-ray diffraction, scanning electron microscope and transmission electron microscopy. The results show that β-Cu₄Ti precipitates in the topmost surface layer were dissolved after SMAT, and Cu solid solution phase with a fine grain size of approximately 25?nm was observed. Dislocation activities were the main deformation mechanism of lamellar structure in the overaged Cu–4wt-%Ti alloy. The twinning in lamellar Cu phase was inhibited by the β-Cu₄Ti precipitates.