Effect of silicon on microstructure and stress rupture properties at 1100°C of yttrium modified Ni-Al-Mo-B alloy IC6

The effect of adding 0.10–0.30 wt%Si on microstructure of the yttrium modified alloy IC6 was examined by scanning electron microscope (SEM), energy dispersive spectrum(EDS) technique of electron probe micro-analyzer (EPMA) and transmission electron microscope (TEM). The results show that two bulk shape phases, Mo_1.24Ni_0.76 and Mo₆(Ni_0.75Si_0.25)₇ are formed in the interdendritic area in the alloy with addition of 0.10–0.20 Siwt% and 0.12 wt%Y, and that a needle like phase named Y-NiMo precipitates in the interdendritic area in the alloy with addition of 0.30 wt% silicon and 0.12 wt% yttrium besides the formation of the bulk shape phases mentioned above. The stress rupture properties under 1100°C/80 MPa were improved by adding 0.12 wt%Y but decreased by adding 0.10–1.30 wt%Si and 0.12 wt%Y.     

Influence of heat treatment parameters on the microstructure and properties of some zinc-based alloys

The present investigation deals with microstructure and property related changes in a zinc-based alloy induced by varying solutionizing and ageing durations and (solutionizing) temperatures. The influence of partially replacing copper by nickel and silicon in the alloy composition has also been studied on similar lines. The microstructure of the as cast, nickel/silicon-free alloy revealed primary dendrites surrounded by eutectoid and eutectic + in the interdendritic regions along with the metastable phase. The addition of nickel and silicon partially altered the basic microstructure of the alloy by forming primary silicon particles and intermetallic compounds. Solutionizing led to the breaking of the dendritic structure and redistribution of the alloying elements whilst ageing formed the T phase. The morphology of silicon particles and the (nickel containing) intermetallic compound was noted to be unaltered in the nickel and silicon containing alloy during the heat treatment. The hardness of the alloys increased during solutionizing whilst it reduced after ageing when compared with that of the as cast sample value. The presence of silicon and nickel led to an increase in the hardness of the alloy. It also enabled the alloy to retain a higher hardness during the heat treatment. An increased solutionizing duration led to an initial increase in the hardness with a peak value being obtained which was followed by a reduction in the hardness. The presence of nickel and silicon in the alloy reduced the tendency of a reduction in hardness beyond the peak hardness. The microconstituents also lowered the detrimental influence of the coarsening of the T phase. The density of the nickel/silicon-free alloy varied in a narrow range. However within this range, solutionizing caused an increase in the density with duration followed by a reduction and finally a steady state value. The addition of silicon and nickel did not affect the density of the alloy to any great extent. The trend followed by the electrical resistivity was identical to that of hardness. Furthermore, the presence of silicon and nickel increased the resistivity of the alloy. Changes in the properties of the alloys during the heat treatment have been explained on the basis of microstructural alterations caused by the heat treatment.     

The effect of boron on the microstructure and physical properties of chemically vapour deposited nickel films

The solid solution addition of boron greatly enhances the strength and hardness of chemically vapour deposited (CVD) nickel while dramatically changing the microstructure. The solid solubility of boron in nickel is limited, and single-phase alloys containing in excess of 0.3 at% B are supersaturated with respect to the formation of one or more intermetallic boride phases. Single-phase Ni-B alloys containing 0 to 13.0 at% B were produced by CVD on polycrystalline copper substrates at 155° C in an atmospheric pressure process. The microstructure, mechanical and physical properties were characterized for the alloys both as-deposited and after various thermal treatments by using optical microscopy, transmission electron microscopy, X-ray diffraction and micro-indentation hardness testing with a diamond pyramid indentor. The grain size of the alloy was found to decrease sharply with rising boron content. Concomitantly, the defect density of the material rose significantly, the microhardness increased and the ductility decreased. With annealing at a temperature of 300° C or greater, precipitation of the Ni₃B intermetallic phase, recovery and grain growth occurred.     

Microstructural and mechanical properties evolutions of plasma transferred arc deposited Norem02 hardfacing alloy at high temperature

Plasma-transferred-arc welded Norem02, an iron-based hard-facing alloy, was characterised. Its microstructure and chemical composition were investigated using optical microscopy, scanning electron microscopy (with electron probe microanalysis), electron backscattering diffraction, and X-ray diffraction. The microstructure of the as-deposit alloy consists of a dendritic austenite structure with ferrite islets at dendrites centres, with an interdendritic eutectic region containing austenite, M₇C₃ and M₂₃C₆ carbides and zones containing Mo-rich precipitates. Tensile behaviour of Norem02 was characterised and completed by dilatometry tests in welding process temperature range. No significant phase transformation was detectable during mechanical testing. Different heat treatment cycles of ageing at high temperatures (until 1100 °C) were carried out for different durations. The microstructure of Norem02 heated at 1100 °C was not significantly affected by a short time (15 s) treatment whereas changes were observed for longer durations (2 h), although hardness remains almost unchanged.This work tends to demonstrate that for this alloy metallurgical evolution during the welding process has very little influence on mechanical properties.     

Structure-property relations in a hypereutectic aluminium-silicon alloy dispersed with graphite particles

Changes in the microstructure and properties of an Al-Si (BS LM30) alloy dispersed with graphite particles brought about by T6 (solutionizing followed by artificial ageing) treatment were investigated. A range of ageing temperatures such as 165, 180, 215 and 240 °C were selected while the soaking time was varied from 1–24 h with a view to optimize the parameters. The base alloy processed under identical conditions was also heat treated, together with the composite to understand the role of the dispersoid in the alloy. Their properties, such as hardness, density and electrical resistivity were determined. Corresponding microstructural changes as a function of ageing temperature and duration were also observed. Observations made in this study indicate that the hardness peak shifted towards shorter soaking periods with temperature. The base alloy and the composite were found to follow a similar trend. However, the former possessed higher hardness and density and lower electrical resistivity. The changes in properties of the specimens were supplemented with considerable morphological modification of the matrix, the latter included the spheoridization of eutectic silicon particles and complex intermetallic compounds together with reduction in the size of the primary silicon phase due to fragmentation and dissolution. The study suggests that the heat treatment has tremendous potential to produce a desired combination of matrix microstructure and properties in graphitic Al-Si alloys by varying the treatment parameters, e.g. temperature and duration.     

Plasma Sprayed NiAl Intermetallic Coating Produced with Mechanically Alloyed Powder

In the present research, mechanically alloyed Ni-Al powder was utilized to develop plasma sprayed coatings, and the effect of the spray distance and heat treatment on the phases, microstructure, and hardness of the coat- ings were examined. Coatings were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and through microhardness measurements. Although mechanically al- loyed Ni-Al powder showed no intermetallic phases, the coatings did. Different spray distances from 5 to 19 cm were employed for plasma spray and the specimens were heat treated at different temperatures, then the amount of oxides, porosity and hardness of the coatings were changed according to the spray condition. The thermal energy of the plasma spray caused the formation of NiAl phases while particles flew to the substrate or after that. Extreme increase in heat treatment temperature and spray distance resulted in oxidation and reduction in the quality of the coating. Furthermore, the best spray distance and heat treatment temperature to gain the NiAl intermetallic coating were established.     

Microstructural Stability of a Multiphase Ni-25Al-15Cr (at. pct) Intermetallic Alloy

1.IntroductionAlthoughtherehasbeenconsiderableworkontheeffectofsuchfactorsasalloycomposition,deviationfromstoichiometryandternaryalloyadditionsontheductilityandfracturebehaviorofsinglephaseNiAlalloyslll2l,therecenttrendhasbeentowardsthestudyofmultiphaseintermetallicalloywithcon-trolledmicrostructuresandphase.onstitu.nt[3ro5].Atypicalexampleofachievinghighroomtemperatureductilitybymicrostructurecontrolisthewell-knowncaseofNi-2OAl-3OFe(at.pct)multiphaseNiAl-basedalloyI4'5].ThemultiphaseNiAl…     

热输入对脉冲等离子弧增材制造Inconel 718合金组织与性能的影响

采用基于脉冲等离子弧的增材制造技术在Q235基板上加工了Inconel 718合金试样,通过改变功率和焊接速度研究了不同热输入对试样组织与性能演变规律的影响。借助光学显微镜、扫描电镜、能谱分析、维氏硬度仪等手段对试样晶粒形态、枝晶间距、元素偏析、析出相成分及分布、显微硬度等进行表征,结果表明随着热输入从1.08×106 J/m增大至1.76×106 J/m,晶粒形态从细长的柱状枝晶逐渐转变为粗大的胞状枝晶,枝晶间距从6.34μm增大至9.09μm,Nb、Mo等元素在枝晶间偏析加剧,Laves相由颗粒状、块状逐渐变为长链状,显微硬度不断下降。     

Effect of silicon content on microstructure and electrochemical behavior of hypoeutectic Al-Si alloys

The correlation of mechanical properties and corrosion behavior with microstructure parameters can be very useful for planning solidification conditions in order to achieve a desired level of final properties. The present study aims to investigate the influence of silicon content on the microstructural pattern, i.e., dendrite spacings and distribution of interdendritic phases on the corrosion behavior of Al-Si alloys castings. The corrosion resistance was analyzed by both the electrochemical impedance spectroscopy (EIS) technique and Tafel's plots carried out in a 0.5 M NaCl test solution at 25 °C. The increase on silicon content has provided a dendritic refinement and a more extensive redistribution of the eutectic mixture which has provoked a decrease on the corrosion resistance.     

Effect of heat treatment on interface microstructure and bond strength in explosively welded Ti/304L stainless steel clad

Abstract

The effects of heat treatment on the microstructure and bond strength at the interface of explosively welded titanium/304L stainless steel clad have been investigated. The microstructure of the clad interface were examined using optical and scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) techniques. At 700°C, the formation of intermetallic phases σ and Fe₂Ti besides β-Ti were confirmed, while in samples, heat treated at 800°C and 900°C, other intermetallic phases such as λ and FeTi, NiTi, NiTi₂ phases were detected in addition to σ and Fe₂Ti phases. The shear test results show that the shear strengths of heat treated samples are overall significantly lower than that of stress relieved samples. This could be due to the formation of brittle intermetallic phases at the interface. Despite of formation of the intermetallic phase at 700°C, the shear strength of the sample is still more than the minimum standard amount of 137·9 MPa. It is also observed that the higher the heat treatment temperature, the lower the interface shear strength, which can be explained by the fact that the volume fraction of intermetallics increases with increasing temperature. The shear strength values of heat treated samples are lower than those of diffusion bonded clads. This could be attributed to the fact that the total widths of intermetallic layers achieved in heat treated samples are larger than those of for diffusion bonded ones.     

Effect of temperature and reactivity of molten 55Al–Zn alloy on Co based alloy coatings

Abstract

The short service life of bearings in galvanising industry is a result of a complex set of deterioration mechanisms. This work addressed the effect of temperature and molten bath reactivity on the material of the bearings respectively. Three commercial alloys, the Co–Cr–W Stellite 6 and Co–Cr–Mo–Si Tribaloy (T400 and T800) alloy systems, were deposited by plasma transferred arc on AISI 316L plates. Coatings were evaluated for the effect of temperature exposure on hardness, microstructure and sliding abrasive wear. The reactivity with the molten 55Al–Zn alloy was assessed by immersion tests in an industrial bath. Results showed that exposure at 600°C for 168 h resulted in an increase in hardness, microstructure changes and loss of wear resistance for the Stellite 6 coatings. A superior performance to temperature was shown by Tribaloy T800 with a stable abrasive wear resistance. The three alloys exhibited a strong reactivity with the 55Al–Zn molten bath. An intermetallic layer formed on the coatings as the Al from the bath reacted with elements from the Co based alloys. This reactivity consumed the coatings, causing a reduction on thickness particularly on those processed with the T800 alloy.     

The effect of cooling rate on the dendritic spacing and morphology of Ag3Sn intermetallic particles of a SnAg solder alloy

The size and morphology of intermetallic compounds of Sn–Ag solder alloys can have a significant influence on the mechanical strength of solder joints. The aim of the present study is to characterize the as-cast microstructure of a Sn–2 wt.% Ag solder alloy, and to correlate the resulting scale of the dendritic matrix and the morphology of the Ag₃Sn intermetallic compound (IMC) with the corresponding solidification cooling rate. Pre-heated low-carbon steel molds and a water-cooled solidification apparatus were used permitting a significant range of solidification cooling rates to be experimentally examined. It is shown that under very slow cooling conditions (0.02 °C/s) the microstructure of the sample is formed by a coarse dendritic matrix and a mixture of fiber and plate-like Ag₃Sn IMC in the interdendritic region with the fibers located along the board line separating the matrix. For cooling rates from 0.15 to 1.15 °C/s a mixture of spheroid and fiber-like IMC and secondary dendrite arm spacings between 15 and 40 μm, with the spheroids located in the center of the interdendritic region. At higher cooling rates, of about 8 °C/s only Ag₃Sn spheroids (of about 0.5 μm in diameter) prevail in the eutectic mixture.     

Nanoindentation behavior of bulk metastable Al65Cu20Ti15 alloy prepared by consolidation of the ball milled powder

Present study concerns assessment of nanomechanical property in the bulk Al₆₅Cu₂₀Ti₁₅ alloy with varying microstructure synthesized by consolidation of mechanically alloyed powder at different temperature. The microstructure after consolidation at room temperature and 500 °C exhibits completely amorphous and nanocrystalline states respectively. Nanoindentation experiments suggest that the maximum strength and hardness values are achieved in the sample sintered at 450 °C. The corresponding microstructure revealed dispersion of nanocrystalline intermetallic phase (<50 nm) in the amorphous matrix.     

TEM analysis of diffusion brazement microstructure in a Ni<Subscript>3</Subscript>Al-based intermetallic alloy

Transmission electron microscopy study of brazed joint microstructure in a Ni₃Al-based intermetallic alloy IC 6 was performed. A continuously distributed microconstituents consisting of γ solid-solution, M₃B₂-type and M₂₃B₆-type borides, which were likely formed by eutectic-type reaction(s) from residual liquated insert during cooling from brazing temperature, were observed along the joint centreline. Consideration of possible incipient melting due to eutectic-type transformation reaction of these phases is pertinent to development of post braze heat treatment for modifying the brazement microstructure.     

Fabrication of multilayered titanium aluminide sheets by self-propagating high-temperature synthesis reaction using hot rolling and heat treatment

This study is concerned with the fabrication of multilayered and bulk Ti aluminide sheets by self-propagating high-temperature synthesis (SHS) reaction using hot rolling and heat treatment. A multilayered Ti/Al sheet was prepared by stacking thin Ti and Al sheets alternatively. When this sheet was hot-rolled and heat-treated at 1000°C, a multilayered sheet composed of Ti₃Al and TiAl was made through the process of formation and growth of intermetallic phases at Ti/Al interfaces and porosity reduction. A bulk Ti aluminide sheet having a lamellar structure of TiAl and Ti₃Al was also fabricated successfully by heat treatment at 1400°C.     

Failure Analysis Case Study on a Fractured Tailwheel Fork

A failure analysis investigation was conducted on a fractured aluminum tailwheel fork which failed moments after landing of a privately owned, 1955 twin-engine airplane. Non-destructive evaluation via dye-penetrant inspection revealed no discernible surface cracks. The chemical composition of the sand-cast component was identified via optical emission spectroscopy and is comparable to an aluminum sand-cast alloy, AA 712.0. Metallographic evaluation via optical microscopy and scanning electron microscopy revealed a high degree of porosity in the microstructure as well as the presence of deleterious intermetallic compounds within interdendritic regions. Macro-hardness testing produced hardness values which are noticeably higher than standard hardness values for 712.0. The primary fracture surfaces indicate evidence of mixed mode fracture, via intergranular cracking, cleaved intermetallic particles, and dimpled cellular regions in the matrix. The secondary fracture surface demonstrates similar features of intergranular fracture.     

The affect of densification and dehydroxylation on the mechanical properties of stoichiometric hydroxyapatite bioceramics

This paper reports the effects of processing densification on the mechanical properties of hydroxyapatite bioceramics. Densification of synthetic hydroxyapatite is conducted in the range 1000-1300 °C. X-ray diffraction and SEM microscopy are used to check the microstructure transformations. Vickers hardness, toughness and Young's modulus are analyzed versus the density and grain size. The sintering temperature and the particle size influence strongly the densification and the resulting mechanical properties. In addition, the critical sintering temperature appears around 1200 °C and the declined strength at the temperature up to 1200 °C is found sensitive to the dehydroxylation process of hydroxyapatite.     

Study on Al-Cu-Si braze containing small amount of rare earth erbium

In the present work, the effect of a small amount of rare earth Er addition on the microstructure of Al-Cu-Si brazing alloy has been investigated. In the study, the Al-20Cu-7Si brazing alloys with various Er contents were prepared. 3003 aluminum alloy was chosen as a substrate. The microstructure of the brazed alloys was carefully observed. In addition, melting temperature, wettability and hardness of the brazing alloys were measured. The results indicate that the constituent of the microstructure of Al-20Cu-7Si-Er brazed alloy is similar to the Al-20Cu-7Si, which is mainly comprised of solid solutions of aluminum, silicon and the intermetallic compounds CuAl₂. When the Er content increases, the size of Al phases is decreased, and the filament-like or needle-like Si phase is thickened. The Si phases dominating in the shape of a filament or needle are transformed to those in the shape of a block when Er content is increased. Moreover, adding a small amount of Er can improve the wettability and hardness of the Al-20Cu-7Si brazing alloy. However, the melting temperature of the Al-20Cu-7Si alloy is almost unchanged when a small amount of Er is added.     

Developing extreme hardness (>15 GPa) in iron based nanocomposites

Through a unique methodology, novel nanocomposite microstructures were created in a bulk iron based alloy by first processing into a glass condition followed by devitrifying the glass through heat treating above the crystallization temperature. The as-crystallized microstructure was made up of three nanoscale phases; α-Fe, Fe₂₃C₆, and Fe₃B phases. Vickers hardness testing revealed a maximum hardness of 16.2 GPa which is significantly harder than existing commercial steel alloys and hardmetals. Detailed structural studies uncovered two important factors which contribute to the development of this extreme hardness; reductions in microstructure scale to the nanometer regime and supersaturation of transition metal alloying elements significantly above their equilibrium solubility limits.     

The effects of Mg amount on the microstructure and mechanical properties of Al–Si–Mg alloys

In this study, the effects of magnesium (Mg) addition to A356 aluminum alloy at different amounts on the microstructure and mechanical properties of this alloy were examined. For the experimental studies, three different alloys (0.43, 0.67 and 0.86 wt%) having various amounts of Mg were prepared through casting process in the form of plates. The plates were homogenized and cooled in the furnace. All the samples were treated with aging process (T6) and then tensile samples were prepared from the homogenized samples. The samples treated with T6 process were characterized by optical microscopy, laser confocal microscopy, Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS) and X-Ray Diffraction (XRD) examinations as well as hardness measurements and tensile tests. The phases which were formed in the microstructures for different amounts of Mg were examined. It was observed that iron-rich intermetallic compounds were also formed in addition to the phases resulting from the aging process. Fe-rich intermetallic compounds, observed from the fracture surfaces, were found to reduce the tensile strength the alloy. The results also indicate that the tensile strength and hardness of the alloy increase with increasing Mg amount.