Precipitation Heat Treatment Research Articles

Role of Niobium Oxides on the Strength of Plain Carbon Steels

In this paper, the authors electrolytically extracted niobium inclusions from heats of 1030 steel with FeNb, NbO2, and NbO additions. From energy-dispersive spectroscopy, the inclusion chemistry of these additions was found to be similar. Pure niobium oxide inclusions were never found in the steel. Inclusion size was measured using polished samples and electrolytically extracted samples. Statistical analysis found that the average inclusion size was larger on filtered samples compared to the polished samples. Since pure NbO inclusions were not found, it was thought that the niobium strengthening reported in the earlier literature might be actually due to a precipitation hardening effect. Precipitation heat treatments were done at 600, 625, and 650 °C (1112, 1157, and 1202 °F) after solutionizing at 1100 °C (2012 °F). The hardness was measured at aging times of 30, 45, 60, 75, and 90 min. The observed relation between hardness and aging time matched that expected for a precipitation hardening mechanism. It was therefore theorized that the NbO and NbO2 additions dissolved in the melt and form precipitates.

Electrochemical characteristics of pyrrhotine as anode material for lithium-ion batteries

Micron-sized pyrrhotine particles with a standard hexagonal structure were prepared by simple precipitation and subsequent heat treatment and were investigated as anode material for lithium-ion batteries. The as-prepared Fe7S8 electrode delivered a highly reversible capacity of 604.1 mAh/g with a voltage range of 2.5–0.05 V. X-ray diffraction, scanning electronic microscopy and X-ray photoelectron spectroscopy were employed to characterize the reaction products at different stages, and a possible two-step reaction mechanism was proposed. The electrochemical test results demonstrated that the discharge/charge voltage range had a remarkable influence on the capacity retention and coulombic efficiency, which could be associated with the decomposability of lithiation products and volume change. Additionally, the dissolution of Li2Sx (2 < x < 8) in electrolyte was found to cause severe capacity loss as well. Thus a proper coating layer and cycling voltage range were essential for this kind of electrode material to achieve practical application in lithium-ion batteries.

A Study on Machinability Performance of Silicon Carbide Paticulate Reinforced Metal Matrix Composite

This paper aims to understand the influence of sintering temperature on the drilling performance of Al 2219 – SiCp composite. This type of composite is currently used in aerospace and transportation industries. Drilling is the most frequently employed operation of secondary machining owing to the need for fabrication. This composite is usually subjected to precipitation heat treatment and needs the study of influence of sintering temperature on machining performance. The composite is fabricated through powder metallurgy route. The drilling tests are conducted with PCD drill of 5 mm diameter and 118° point angle. The experiments are conducted under conditions of different spindle speeds of 500, 1000 and 1500 rpm and feed rates of 10, 15 and 20 mm/min. Specific cutting pressure and surface roughness of the hole are considered as performance indicators during the study. Weight fraction of the reinforcement and sintering temperature are found to have significant influence on the drilling performance of the composites.

Superelastic response of a single crystalline FeMnAlNi shape memory alloy under tension and compression

Polycrystalline FeMnAlNi shape memory alloys were recently shown to possess a small temperature dependence of the stress for the onset of martensitic transformation (σSIM). In this work, the superelastic behavior of single crystalline Fe43.5Mn34Al15Ni7.5 samples oriented along the [100] direction was investigated under tension and compression after a precipitation heat treatment at 200°C. In constant strain, multi-temperature experiments, the single crystals showed a σSIM vs. temperature slope of 0.54MPa°C−1 in tension and 0.41MPa°C−1 in compression, and superelasticity over a wide temperature range from −80°C to 160°C. The irrecoverable strains in both tension and compression samples detected during the superelastic experiments were found to be due to retained martensite in detailed transmission electron microscopy investigations. The volume fraction of the retained martensite in the samples tested under tension was considerably larger than those for the samples tested in compression showing that the transformation is less recoverable in tension. The differences in the volume fraction of retained martensite and reversibility in both tension and compression are attributed to high density of dislocations in the tension samples as compared to the compression samples. The differences between the shape of the stress–strain curves under tension and compression are attributed to the lower number of martensite variants activated under tension as compared to compression, which were clearly verified with the transmission electron microscopy examinations.

Effect of Deformation Process on Superplasticity of Inconel 718 Alloy

Abstract After grain refinement through hot-forging and δ-phase precipitation and recrystallization heat-treatment processes, the high temperature tensile experiments were carried out to investigate the effect of heat treatment and deformation process on the superplasticity of Inconel 718 alloy. Two tensile processes were used as follows: the maximum m value superplastic deformation method and the strain-reduced superplasticity deformation process based maximum m value method. The results indicate the fine and homogeneous grain structure of Inconel alloy is obtained by hot forging, δ phase precipitation and recrystallization heat treatment processes, and the δ phase can play a role in controlling grain size during recrystallization annealing and hot deformation. Upon stretching by the above two processes at 950°C, the percentage elongations of Inconel 718 alloy are improved from 340% and 566%, respectively. The results show that the higher value of percentage elongation can be obtained by the strain-induced superplastic deformation process based maximum m value method.

Aluminium AA6061 Matrix Composite Reinforced with Spherical Alumina Particles Produced by Infiltration: Perspective on Aerospace Applications

Metal matrix composites, based on AA6061 reinforced with 60 vol% Al2O3 spherical particles, were produced by gas pressure infiltration and characterized for hardness, impulse excitation modulus, tensile properties (at room temperature and at 250°C), and machining. It was experimentally demonstrated that the novel alumina powder used in the present work does not react with the liquid Mg-containing matrix during the infiltration process. The AA6061 matrix therefore retains its ability to be strengthened by precipitation heat treatment. The latter behaviour combined with the spherical particle shape confers the studied material higher strength and better machinability in comparison with similar composites produced using standard angular alumina particles. The overall features are promising for applications in the aerospace industry, where light and strong materials are required.

Influence of temperature and hydrogen content on stress-induced radial hydride precipitation in Zircaloy-4 cladding

Radial hydride precipitation in stress relieved Zircaloy-4 fuel claddings is studied using a new thermal–mechanical test. Two maximum temperatures for radial hydride precipitation heat treatment are studied, 350 and 450°C with hydrogen contents ranging between 50 and 600wppm. The new test provides two main results of interest: the minimum hoop stress required to precipitate radial hydrides and a maximum stress above which, all hydrides precipitate in the radial direction. Based on these two extreme stress conditions, a model is derived to determine the stress level required to obtain a given fraction of radial hydrides after high temperature thermal–mechanical heat treatment. The proposed model is validated using metallographic observation data on pressurized tubes cooled down under constant pressure. Most of the samples with reoriented hydrides are further subjected to a ductility test. Using finite element modeling, the test results are analyzed in terms of crack nucleation within radial hydrides at the outer diameter and crack growth through the thickness of the tubular samples. The combination of test results shows that samples with hydrogen contents of about 100wppm had the lowest ductility.

Synthesis and Characterization of a Novel Silver-Substituted Calcium Phosphate Cement

Antibacterial materials play an important role in clinical application, and silver has been known to exhibit strong cytotoxicity towards a broad range of micro-organisms. In this work, the amorphous calcium phosphate with silver substitution (Ag-ACP) was synthesized by chemical precipitation method, and the valence of silver in ACP was adjusted by temperature. The processed Ag-ACP was combined with slightly acidic compounds to form new calcium phosphate cement (CPC). Our results indicate that the valence of silver in CPC was adjusted successfully by chemical precipitation method and heat treatment. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results demonstrated that silver ion in CPC-1 and CPC-2 existed in Ag3PO4; after heat treatment of 460 °C, silver became more stable in CPC-3 and CPC-4. Silver in CPC-1 and CPC-2 exhibited better releasing property. After heat treatment at 460 °C, the amount of silver ion released from CPC decreased significantly. Besides, the antibacterial ability of Ag-CPC was adjusted by changing the valence of silver in Ag-CPC. Depending on the low valence of silver and good silver release, CPC-1 and CPC-2 exhibited better antibacterial activity. We believe that this study will motivate the development and applications of antibacterial CPC in bone tissue regeneration.

Numerical simulation of AM1 microstructure

A modelling approach is developed for the description of microstructure formation in the industrial AM1 Ni-base superalloy. Solidification and homogenization simulations are first carried out using a microsegregation model, before using the local compositions as an input for precipitation calculations, in order to characterize the influence of segregation on precipitation. First, the precipitation model was validated by comparing simulated and measured evolutions of the average precipitate radius during isothermal heat treatments at 1100 ∘ C and 1210 ∘ C. The chained microsegregation and precipitation simulations indicate that the global sequences of precipitation events remains are qualitatively the same at the different locations in the microstructure, but the growth and dissolution kinetics are strongly influenced by the local compositions. Local supersaturations have a larger effect on the average radius of the precipitates than certain stages of the precipitation heat treatment.

Superplasticity of Inconel 718 Alloy by Strain-Reduced Superplasticity Deformation Process

The high temperature tensile experiments were carried out to investigate the superplasticity of Inconel 718 alloy by using the strain-reduced superplasticity deformation process based maximum m value method. The results indicate the fine and homogeneous grain structure of Inconel 718 alloy is obtained by hot forging, δ phase precipitation and recrystallization heat treatment process. The Inconel 718 alloy exhibits good superplasticity at a wide range of temperature from 950°C to 1020°C, and the best elongation of 566% appears at 950°C. It shows the excellent superplasticity of Inconel 718 alloy can be obtained with the strain-reduced superplasticity deformation process based maximum m value method.

ChemInform Abstract: Preparation of Yttrium Barium Copper Oxide by Polymeric Precursor Technique.

AbstractYBa2Cu4O8 containing BaO impurities is prepared by heat treatment (air, 1000 °C, 1 h) of precipitates obtained from mixtures of aqueous solutions of sodium polyacrylate, Y(NO3)3, Cu(NO3)2, Ba(NO3)2, NaOH, and MeOH (20 °C, several days).

Heat Treating of a 718Plus Superalloy

Abstract Hot rolled rings made from nickel-based superalloys are used for the manufacture of rotating components in jet engines and land-based turbines. Contoured rings are attractive to manufacturers because they can simplify and improve manufacturing operations by reducing machining times and, in some cases, eliminating welding operations. ATI 718Plus is a nickel-based superalloy designed to achieve high strength and thermal stability at elevated temperatures while exhibiting good formability during forging operations, characteristics that making it a suitable alloy for the manufacture of contoured rings. This work presents the results of a series of solution and precipitation heat treatments of rings made from ATI 718Plus with the goal of optimizing their processing and mechanical behavior. Microstructural characteristics and mechanical properties are reported, including the results of tensile tests conducted at room temperature and at high temperature and of hardness and stress-rupture testing. The results of this work were implemented at a local factory to ensure the required mechanical properties of heat-treated parts.

Microstructure and Properties of Heat-Treated 440C Martensitic Stainless Steel

440C martensitic stainless steels are widely used because of their good mechanical properties. The mechanical properties of 440C martensitic stainless steel were evaluated after heat treatment of these materials at various types of heat treatment processes. The initial part of this investigation focused on the microstructures of these 440C steels. Microstructure evaluations from the as-received to the as-tempered condition were described. In the as-received condition, the formations of ferrite matrix and carbide particles were observed in this steel. In contrast, the precipitation of M7C3 carbides and martensitic structures were present in this steel due to the rapid quenching process from the high temperature condition. After precipitation heat treatment, the Cr-rich M23C6 carbides were identified within the structures. Moreover, a 30 minutes heat-treated sample shows the highest value of hardness compared to the others holding time. Finally, the tempering process had been carried out to complete the whole heat treatment process in addition to construct the secondary hardening phenomenon. It is believed that this phenomenon influenced the value of hardness of the 440C steel.

Effects of pre-precipitation of Cr2N on microstructures and properties of high nitrogen stainless steel

Aging precipitation and solid solution heat treatment were carried out on three steels which have chromium content of 18%, manganese content of 12%, 15%, 18%, and nitrogen content of 0.43%, 0.53%, 0.67%, respectively. The mechanisms of precipitation and solid solution of high nitrogen austenitic stainless steel were studied using the scanning electron microscopy, transmission electron microscopy, electron probe micro analysis and mechanical testing. The results show that, Cr2N is the primary precipitate in the tested stainless steels instead of Cr23C6. Cr2N nucleates at austenitic grain boundaries and grows towards inner grains with a lamellar morphology. By means of pre-precipitation of Cr2N at 800 °C, the microstructure of the steels at solid solution state can be refined, thus improving the strength and plasticity. After the proposed treatment, the tensile strength, the proof strength and the elongation of the tested steel reach 881 MPa, 542 MPa and 54%, respectively.

Microstructural and Mechanical Effects of Thermo-Mechanical Processing on ATI 718Plus® Contoured Rings

ATI 718Plus® is a nickel-base superalloy designed to promote resistance and thermal stability at elevated temperatures. Beside these properties, this material presents superior formability during forging operations, making ATI 718Plus® a suitable material for the manufacture of non-rotating and rotating components for jet engine and land-based turbines. Present contribution summarizes main results when several contoured rings were produced by ring-rolling processes considering selected parameters as temperature and deformation ratio. Effect of solution and precipitation heat treatments on ATI 718Plus® microstructure and mechanical properties are also reported. These results include tensile testing at elevated temperature and stress-rupture testing. Microstructural evaluations performed by optical microscopy and electronic microscopy, complement reported results.

Optimización de las propiedades mecánicas de las aleaciones AlSi7Mg moldeadas en arena

In the present work the mechanical properties of the alloy AlSi7Mg were studied in order to choose a suitable composition and heat treatment for sand castings. The mechanical properties have been evaluated varying the content of Mg, covering the alloys A356 and A357. The effect of heat treatment has been studied in alloy A356 varying the emperature and time of the precipitation heat treatment, while the dissolution treatment was kept constant. Several quality indexes have been defined which combine tensile strength, yield strength, tensile strength and elongation in order to select an adequate chemical composition and heat treatment for each application.

Precipitation Effect on Work Hardening Behavior of ECAP-Deformed Al-4%Cu Alloy

It is well known that severe plastic deformation techniques, while giving substantial strength benefits, produce low ductility material. The aim of the present work is to analyze whether second phase precipitates obtained by post-deformation heat treatment, have a positive effect on the W-H behavior. On this sense, the typical precipitation hardening Al-4%Cu alloy is subjected to one and four ECAP passes, followed by low temperature precipitation heat treatment. The W-H behavior and the mechanical stability were determined for two levels of ECAP - deformation, different precipitates average size and distribution, and presence/absence of solute in solid solution. It was concluded that Al2Cu precipitates increased both W-H rate and uniform elongation of the alloy and the best strength - ductility combination was obtained by a post-deformation, 100oC precipitation heat treatment of a sample which was ECAP-deformed in the solid solution condition.

Behaviour of Artificial Aging in 6066 Alloy Using Microhardness and Nuclear Techniques

Many Aluminum-based alloys are strengthened by using a heat-treatment process known as age-hardening. The aim of this work was to produce a high-strength 6xxx-series Aluminum alloy by adjusting the processing conditions, namely solutionizing and artificial aging. It consists of heating the alloy to a temperature at which the soluble constituents will form an homogeneous mass via solid diffusion, holding the mass at that temperature until diffusion takes place, then quenching the alloy rapidly to retain the homogeneous condition. In the quenched condition, heat-treated alloys are supersaturated solid solutions that are comparatively soft and workable, and unstable, depending upon the composition. After solution treatment and quenching, hardening is achieved either at room temperature (natural aging) or via a precipitation heat treatment at a suitable temperature (artificial aging). Precipitation heat treatments are generally low-temperature, long-term processes. Temperatures range from 115 to 190C; times vary from 5 to 48 h. The choice of time-temperature cycles for precipitation heat treatment should receive careful consideration. The objective is to select the cycle that produces an optimum precipitate size and distribution pattern. The mechanical characterization of heat-treatable 6xxx (Al-Mg-Si-Cu based) 6066 wrought aluminum alloys was studied. Their effects were investigated in terms of microstructure using positron annihilation lifetime techniques and monitoring the mechanical properties by mean of Vickers hardness measurements. The hardness is the resistance of a material to plastic deformation, and gives it the ability to resist deformation when a load is applied. The greater the hardness of the material, the greater resistance it has to deformation. The Vickers hardness of 6066 alloy has its maximum value (98) when aged for (10) hours at (175C) after quenching at 530C; so this temperature is the solution temperature of this alloy .The hardness conformed to reference values.

Artificial Aging Behavior of 6063 Alloy Studied Using Vickers Hardness and Positron Annihilation Lifetime Techniques

Many aluminum-based alloys are strengthened by a heat treatment process known as age hardening. The aim of this work was to produce a high-strength 6xxx series aluminum alloy by adjusting the processing conditions, namely solutionizing and artificial aging. It consists of heating the alloy to a temperature at which the soluble constituents will form an homogeneous mass by solid diffusion, holding the mass at that temperature until diffusion takes place, then quenching the alloy rapidly to retain the homogeneous condition. In the quenched condition, heat-treated alloys are supersaturated solid solutions that are comparatively soft and workable, and unstable; depending upon the composition. After solution treatment and quenching, hardening is achieved either at room temperature (natural aging) or by precipitation heat treatment at a suitable temperature (artificial aging). Precipitation heat treatments are generally low-temperature long-term processes. Temperatures range from 115 to 190°C and times vary from 5 to 48 h. Choice of time-temperature cycles for precipitation heat treatment should receive careful consideration. The objective is to select the cycle that produces the optimum precipitate size and distribution pattern. The mechanical characterization of heat-treatable 6xxx (Al-Mg-Si-Cu based) 6063 wrought aluminum alloys was studied. Their effects were investigated in terms of the microstructure, using positron annihilation lifetime techniques and mechanical properties monitoring via Vickers hardness measurements. The hardness is the resistance of a material to plastic deformation, which gives it the ability to resist deformation when a load is applied. The greater the hardness of the material, the greater the resistance it has to deformation. The hardness of 6063 alloy has its maximum value (58) when aged for 8 hours at 175oC after quenching from 520oC; which is the solution temperature of this alloy. The hardness conformed to the literature. We also test the aging ability of the 1xxx aluminum alloy: 1050.

Synthesis and catalytic performances of a novel photocatalyst BiOF

A novel oxyhalide photocatalyst BiOF was prepared by precipitation and subsequent heat treatment. The influence of calcination temperature on the synthesis of BiOF was investigated. Interestingly, the as-prepared BiOF exhibits high photocatalytic performance in the degradation of universal organic pollutants. The high photocatalytic activity is closely related to the internal electric fields between [Bi 2 O 2 ] slabs and fluorine anionic slabs.