Effect of hot isostatic pressure on the microstructure and tensile properties of γ'-strengthened superalloy fabricated through induction-assisted directed energy deposition

The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples subjected to IDED under 1050℃ preheating with and without hot isostatic pressing(HIP,1190℃,105 MPa,and 3 h).Results show that the as-deposited sample mainly consisted of epitaxial columnar crystals and inhomogeneously distributed γ’ phases in interdendritic and dendritic core regions.After HIP,grain morphology changed negligibly,whereas the size of the γ’ phase became increasingly even.After further heat treatment(HT,1070℃,2 h + 845℃,24 h),the γ’ phase in the as-deposited and HIPed samples presented a bimodal size distribution,whereas that in the as-deposited sample showed a size that remained uneven.The comparison of tensile properties revealed that the tensile strength and uniform elongation of the HIP + HTed sample increased by 5% and 46%,respectively,due to the synergistic deformation of bimodal γ’phases,especially large cubic γ’ phases.Finally,the relationship between phase transformations and plastic deformations in the IDEDed sample was discussed on the basis of generalized stability theory in terms of the trade-off between thermodynamics and kinetics.

Effect of melt-to-solid volume ratio and preheating temperature on Mg/Al bimetals interface by centrifugal casting

Compound casting is an efficient method for bonding dissimilar metals,in which a dramatic reaction can occur between the melt and solid.The centrifugal casting process,a type of compound casting,was applied to cast Al/Mg dissimilar bimetals.Magnesium melt was poured at 700 °C,with melt-to-solid volume ratios(Vm/Vs) of 1.5 and 3,into a preheated hollow aluminum cylinder.The preheating temperatures of the solid part were 320,400,and 450 °C,and the constant rotational speed was 1,600 rpm.The cast parts were kept inside the casting machine until reaching the cooling temperature of 150 °C.The result showed that an increase in preheating temperature from 320 to 450 °C led to an enhanced reaction layer thickness.In addition,an increase in the Vm/Vs from 1.5 to 3 resulted in raising the interface thickness from 1.2 to 1.8 mm.Moreover,the interface was not continuously formed when a Vm/Vs of 3 was selected.In this case,the force of contraction overcame the resultant acting force on the interface.An interface formed at the volume ratio of 1.5 was examined using scanning electron microscopy(SEM) equipped with energy-dispersive X-ray spectroscopy(EDS),and the results demonstrated the formation of Al_(3)Mg_(2),Al_(12)Mg_(17) and(δ+Al_(12)Mg_(17)) eutectic structures in the interface.

Exploring Inflation Options for Warm Dark Matter Coupled to the Higgs Boson

We extend the Standard Model with a scalar warm dark matter field S with an interaction with the Higgs boson ∅. This warm dark matter scenario is in agreement with cosmological observations if S and ∅ come into thermal and diffusive equilibrium before the temperature drops below the Higgs boson mass mH. We study inflation driven by the fields ∅ or S, and also study preheating and reheating, in order to constrain the parameters of this extension of the Standard Model. It is remarkable that, with the current data, these models pass a closure test with no free parameters.

The Numerical Simulation of the Flow Field in a Cold Model of Five-stage Cyclone Preheater and Precalciner System

The flow field in a cold model of 2500 t/d five-stage cyclone preheater and precalciner system was numerically simulated. Renault stress model (RSM) turbulent model was adopted to simulate the flow field, and a hybrid mesh scheme was selected to generate calculation mesh. With the first order upwind difference, finite-volume method was used to convert turbulent equations into difference equations pressure-velocity coupling which were solved by the classic simple algorithm, and during the course of numerical solution, mesh self-adapting technology was applied. The main flow field structures of the whole system and each part of the cold model were studied by analyzing the simulation results.

Numerical Investigation of Fuel Dilution Effects on the Performance of the Conventional and the Highly Preheated and Diluted Air Combustion Furnaces

This numerical study investigates the effects of using a diluted fuel （50% natural gas and 50% N2） in an industrial furnace under several cases of conventional combustion （air with 21% O2 at 300 and 1273 K） and the highly preheated and diluted air （1273 K with 10% O2 and 90% N2） combustion （HPDAC） conditions using an in-house computer program. It was found that by applying a combined diluted fuel and oxidant instead of their uncombined and/or undiluted states, the best condition is obtained for the establishment of HPDAC＇s main unique features. These features are low mean and maximum gas temperature and high radiation/total heat transfer to gas and tubes; as well as more uniformity of theirs distributions which results in decrease in NOx pollutant formation and increase in furnace efficiency or energy saving. Moreover, a variety of chemical flame shape, the process fluid and tubes walls temperatures profiles, the required regenerator efficiency and finally the concentration and velocity patterns have been also qualitatively/quantitatively studied.

Effect of preheat on TIG welding of AZ61 magnesium alloy

The effects of preheat treatments on the microstructures and mechanical properties of tungsten inert gas （TIG）-welded AZ61 magnesium alloy joints were studied by microstructural observations, microhardness tests and tensile tests. The results showed that the vol- ume fraction of the lamellar β-Mg17（Al,Zn）12 intermetallic compound of in fusion zone （FZ） increased from 15% to 66% with an increase in preheat temperature. Moreover, the microhardness of the FZ and the ultimate tensile strength of the welded joints reached their maximum values when the preheat temperature was 300℃ because more lamellar β-Mg17（Al,Zn）12 intermetallic compounds were distributed at the α-Mg grain boundaries and no cracks and pores formed in the FZ of the welded joint.

Preparation and performance of a cold gas dynamic sprayed high-aluminum bronze coating

By mixing preheated high-aluminum bronze powders with different amounts of Al_2O_3 powder, a low-pressure cold-sprayed coating was prepared and sprayed onto a Cr12MoV steel substrate. The hardness of the coating and the bonding strength between the coating and the substrate were tested with a HV-1000 microhardness tester and a mechanical universal testing machine. The surface microstructure, cross-section and tensile fracture surface of the coating were observed with a scanning electron microscope(SEM). Correspondingly, the influences of the preheat treatment temperature of the bronze powder and the Al_2O_3 content on the coating performance were investigated. The results indicate that the hardness of bronze powders decreased and the coating deposition rate increased after the preheating treatment of the bronze powder. The Al_2O_3 content in the mixed powders contributed to the deformation of bronze powders during the spraying process. This trend resulted in varied performance of the coating.

Research on prediction model of formation temperature of ammonium bisulfate in air preheater of coal-fired power plant

Ammonium bisulfate(ABS)is a viscous compound produced by the escape NH_(3) in the NO reduction process and SO_(3) in the flue gas at a certain temperature,which can cause the ash corrosion of the air preheater in coal-fired power plants.Therefore,it is essential to study the formation temperature of ABS to prevent the deposition of ABS in air preheaters.In this paper,the SO_(3) reaction kinetic model is used to analyze the SO_(3) generation process from coal combustion to the selective catalytic reduction(SCR)exit stage,and the kinetic model of NO reduction is used to analyze the NH_(3) escape process.A prediction model for calculating the ABS formation temperature based on the S content in coal and NO reduction parameters of the SCR is proposed,solving the difficulty of measuring SO_(3) concentration and NH_(3) concentration in the previous calculation equation of ABS formation temperature.And the reliability of the model is verified by the actual data of the power plant.Then the influence of S content in coal,NH_(3)/NO_(x) molar ratio,different NO_(x) concentrations at SCR inlet,and NO removal efficiency on the formation temperature of ABS are analyzed.

Drying and preheating processes of iron ore pellets in a traveling grate

A mathematical model of drying and preheating processes in a traveling grate was presented based on the laws of mass, momen- tum, heat transfer, and drying semiempirical relations. A field test was systematically carried out in a traveling grate. The effects of pellet diameter, moisture, grate velocity, and inlet gas temperature on the pellet bed temperature were studied. The average relative error between actual measurements and simulations is less than 7.97%, indicating the validity of the model.

Effects of pin angle and preheating on temperature distribution during friction stir welding operation

Friction stir welding （FSW） is applied extensively in industry for joining of nonferrous metals especially aluminum. A three-dimensional model based on finite element analysis was used to study the thermal characteristic of copper C I 1000 during the FSW process. The model incorporates the mechanical reaction of the tool and thermo-mechanieal characteristics of the weld material, while the friction between the material and the probe and the shoulder serves as the heat source. It was observed that the predicted results about the temperature were in good compatibility with the experimental results. Additionally, it was concluded that the numerical method can be simply applied to measuring the temperature of workpiece just beneath the tool. The effects of preheating temperature and pin angle on temperature distribution were also studied numerically. The increase of pin angle enhances the temperature around the weld line, but preheating does not affect temperature distribution along the weld line considerably.

Experimental Study on Emission Control of Premixed Catalytic Combustion of Natural Gas Using Preheated Air

In this paper the premixed catalytic combustion emissions such as CO, unburned hydrocarbon (UHC), NOx and the temperature distribution in the catalytic monolith with ultra low concentration of Pd were studied. Three types of monoliths were used for experiments and the temperature of preheated air was respectively 50℃ , 100℃ and 200℃ . The results showed that preheated air made radial temperature in the catalytic monolith uniform which helped to avoid local hot spots so as to decrease NOx emission. The experiment also proved that the shorter monolith showed much better catalytic combustion performance than longer one and the temperature at the exit of the shorter monolith was relatively lower. On the contrary, the temperature was higher in the longer monolith and the lethal NOx emission was slightly increased.

Metallurgical behavior and variation of vibro-acoustic signal during preheating assisted friction stir welding between AA6061-T6 and AA7075-T651 alloys

The present work investigated the effects of pin profiles(cylindrical and square),pin eccentricity(0.5 mm and 1 mm)in cylindrical tool and preheating(secondary heating)on metallurgical behavior,variation of vibro-acoustic signal pattern and joint strength during friction stir welding(FSW)between AA6061-T6 and AA7075-T651 alloys.The eccentric tool pins were observed to provide good flowability and intermixing between dissimilar metals,increased the size of stir zone,and the grains in stir zone were sufficiently finer with eccentric tool pin than concentric pin.The magnitude of vibro-acoustic signal increased when shoulder plunging started and drop in signal was noted when the tool shoulder reached its desired depth.The signal magnitude was noted to be higher in welding stage compared to tool plunging stage as the tool took in fresh material during tool movement along the weld path.Preheating the workpiece prior to pin plunging and during welding notably influenced the flow behavior and mixing pattern,and the grains in stir zone were slightly coarser than those in specimen without preheating.Significant reduction in the magnitude of the signal was also observed after preheating.Tensile and flexural strength of joints were also improved slightly when additional heating was employed.

Estimation of deformed laser heat sources and thermal analysis on laser assisted turning of square member

Laser assisted machining （LAM） has difficulties in estimating temperature after applying a LAM process due to its very small heat input area, large energy and movement. In particular, in the case of laser assisted turning （LAT） process, it is more difficult to estimate the temperature after preheating because it has a shape of ellipse when a laser heat source is rotated. A prediction method and thermal analysis method for heat source shapes were proposed as a square shaped member was preheated. The temperature distribution was calculated according to the rotation of the member. Compared with the results of the former study, the maximum temperature of the calculation results, 1 407.1 ℃, is 8.5 ℃ higher than that of the square member, which is 1 398.6 ℃. In a LAT process for a square member, the maximum temperature is 1 850.8 ℃. It is recognized that a laser power control process is required because square members show a maximum temperature that exceeds a melting temperature at around a vertex of the member according to the rotation.

Electronically Controlling the System of Preheating Intake Air by Flame for Diesel Engine Cold-Start

In order to improve the cold start performance of heavy duty diesel engine, electronically controlling the preheating of intake air by flame was researched. According to simulation and thermodynamic analysis about the partial working processes of the diesel engine, the amount of heat energy, enough to make the fuel self ignite at the end of compression process at different temperatures of coolant and intake air, was calculated. Several HY20 preheating plugs were used to heat up the intake air. Meanwhile, an electronic control system based on 8 bit micro controller unit (MCS 8031) was designed to automatically control the process of heating intake air. According to the various temperatures of coolant and ambient air, one plug or two plugs can automatically be selected to heat intake air. The demo experiment validated that the total system could operate successfully and achieve the scheduled function.

THE DEVELOPMENT OF MINOR-CALIBER COMPOSITE PIPES ON CORROSIVE WEAR-RESISTANT

The ceramic lined pipes had been produced by gravitational separation SHS method and influential factors on combustion synthesis was investigated.The experimental results showed that the ceramic lined pipes had been produced easily under condition that selecting pipes well distributed on the wall thickness ,proper preheating temperature and appropriate additive.

Study on microstructures and properties of preheated flash butt welded SW400 steel joints

Under the spirit of sustainable development, ‘lightweight’ has been gradually included into the vehicle design criterion by many manufacturers and used in automobile production. Following this trend, domestic wheel suppliers also begin to study the technology of lightweight wheel. One way to achieve this goal is improving strength grade of the steel and optimizing the structure design in the field of steel wheels. But there are a few problems in flash butt welding process in the application of high strength steel, leading to high rejection rates. SW400 steel is a special high strength wheel steel developed by Benxi Steel. Taking SW400 steel as the research material, this article studys the feasibility of improving the properties of rim flash butt welded joints by adding preheating process.

Heat transfer characteristics of air cross-flow for in-line arrangement of spirally corrugated tube and smooth tube bundles

An experimental study on heat transfer and resistance coefficients of linearly arranged smooth and spirally corrugated tube bundles in cross-flow was performed. The heat transfer and resistance coefficients are presented in this paper with transverse and longitudinal tube-pitch and tube geometries taken into account. The experiment's results can provide technical guidelines for application to horizontal air preheater with arranged in-line spirally corrugated tube bundles, especially to the air preheater for CFBCBs (Circulating Fluidized Bed Combustion Boilers).

Improvement of fuel consumption and maintenance of heating furnaces using a modified heating pattern

This article studies the transient heat conduction in a slab when passing through various sections of the furnace, and focuses on the thickness of the scale layer formed on the slab. The transient heat conduction behavior of a slab in various sections of the heating furnace is analyzed using the Laplace transformation method, including the pre-heating zone, the first heating zone, the second heating zone, and the soaking zone. The heating pattern of the furnace is then modified to reduce fuel consumption. The simulation results show that the scale layer formed on the slab significantly influences the quality of the hot rolled coil formed, and how the furnace parameters affect the efficiency of the furnace and the quality of the coil.

Performance of Ti6Al4V fabricated by electron beam and laser hybrid preheating and selective melting strategy

Electron beam selective melting(EBM)and selective laser melting(SLM)are regarded as significant manufacturing processes for near-net-shaped Ti6Al4V components.Generally,in the conventional EBM process,preheating is necessitated to avoid"smoke"caused by the charging of electrons.In the conventional SLM process,laser as an energy source without the risk of"smoke"can be employed to melt metal powder at low temperatures.However,because of the low absorption rate of laser,the powder bed temperature cannot reach a high level.It is difficult to obtain as-built TiAl4V with favorable comprehensive properties via conventional EBM or SLM.Hence,two types of electron beam and laser hybrid preheating(EB-LHP)combined with selective melting strategies are proposed.Using laser to preheat powder allows EBM to be performed at a low powder bed temperature(EBM-LT),whereas using an electron beam to preheat powder allows SLM to be performed at a high powder bed temperature(SLM-HT).Ti6Al4V samples are fabricated using two different manufacturing strategies(i.e.,EBM-LT and SLM-HT)and two conventional processes,i.e.,EBM at a high powder bed temperature(EBM-HT)and SLM at a low powder bed temperature(SLM-LT).The temperature-dependent surface quality,microstructure,density,and mechanical properties of the as-built Ti6Al4V samples are characterized and compared.Results show that EBM-LT Ti6Al4V exhibits a higher ultimate tensile strength(981±43 MPa)and a lower elongation(12.2%±2.3%)than EBM-HT Ti6Al4V owing to the presence ofα′martensite.The SLM-HT Ti6Al4V possesses the highest ultimate tensile strength(1,059±62 MPa)and an elongation(14.8%±4.0%)comparable to that of the EBM-HT Ti6Al4V(16.6%±1.2%).

Formation of X-120 M Line Pipe through J-C-O-E Technique

The line pipe forming operation can be divided into two parts, first is to achieve the required shape in terms of curvature and ovality after formation of the line pipe. The curvature and ovality ultimately effects the final dimensional controls at the later stage i.e. after mechanical expansion of the line pipe. The second part is to make right welding joint geometry to make the final long seam weld of line pipe. The welding joint geometry ultimately controls soundness of final seam weld at later stage i.e. during submerged arc welding of the line pipe. As far as curvature or shape of line pipe is concerned, important operation is making the required curvature along the edges of TMCP and ACC (Thermo mechanical controlled processing and accelerated cooling process) plate for line pipe (Plate Edge Crimping press) up to the 150 mm in width minimum and forming of the line pipe at J-C-O press. The selection of dies with proper hardness and curvature in both the operation plays a vital role in the formation of line pipes. The main parameters of selection dies (Tools) are size of line pipe for which dies/tools are to be made i.e. the diameter of line pipe, thickness of line pipe and most important is grade of line pipe (Strength level). The grade or strength level decides amount of spring back behavior of the steel Plate. The spring back behavior again varies from steel mill to steel mill in the same grade of HR plate. This is because the each steel mill has its own manufacturing procedures to produce the TMCP and ACC plate. The plate for line pipe is produced through TMCP (Thermo mechanical controlled processing) and accelerated cooling process. In this process the strength level is achieved by the chemical composition of the slab, thickness of the slab, reheating temperature, roughing temperature at which reduction in the thickness, finish rolling temperature and finally the accelerated cooling temperature rate.