Study of microstructural evolution and mechanical properties exhibited by non alloyed ductile iron during conventional and stepped austempering heat treatment

It was evaluated the microstructural and mechanical response that a non alloyed ductile iron (DI) presented when was subjected to Conventional Austempering (CA) and Stepped Austempering (SA) heat treatments. X-ray Diffraction (XRD) quantification techniques demonstrated to be the more reliable method for monitoring phase transformations taking place during both CA and SA. When CA was applied some intercellular areas remain untransformed even for long time, however when samples were subjected to SA those untransformed areas disappeared and instead finer ausferrite was found. Additionally mechanical properties values obtained from tensile and impact tests confirmed that for all times used, SA was superior to the CA.     

Nanometer-scale electronic and microstructural properties of grain boundaries in Cu(In,Ga)Se2

Despite many recent research efforts, the influence of grain boundaries (GBs) on device properties of CuIn_1−xGa_xSe₂ solar cells is still not fully understood Here, we present a microscopic approach to characterizing GBs in polycrystalline CuIn_1−xGa_xSe₂ films with x = 0.33. On samples from the same deposition process we applied methods giving complementary information, i.e., electron backscatter diffraction (EBSD), electron-beam induced current measurements (EBIC), conductive atomic force microscopy (c-AFM), variable-temperature Kelvin probe force microscopy (KPFM), and scanning capacitance microscopy (SCM). By combining EBIC with EBSD, we find a decrease in charge-carrier collection for non-∑3 GBs, while ∑ 3 GBs exhibit no variation with respect to grain interiors. In contrast, a higher conductance of GBs compared to grain interiors was found by c-AFM at low bias and under illumination. By KPFM, we directly measured the band bending at GBs, finding a variation from − 80 up to + 115 mV. Depletion and even inversion at GBs was confirmed by SCM. We comparatively discuss the apparent differences between the results obtained by various microscopic techniques.     

Effects of heat treatment on the microstructure and mechanical properties of AA2618 DC cast alloy

Direct chill (DC) cast ingot plates of AA2618 alloy have been increasingly used for large-mold applications in the plastics and automotive industries. The effects of different heat treatments on the microstructure and mechanical properties of AA2618 DC cast alloy were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and hardness and tensile testing. The as-cast microstructure contained a considerable amount of coarse intermetallic phases, including Al₂CuMg, Al₂Cu, Al₇Cu₄Ni, Al₇Cu₂(Fe,Ni) and Al₉FeNi, resulting in poor mechanical properties. Solution treatment at 530 °C for 5 h dissolved the first three phases into the solid solution and consequently improved the mechanical properties of the alloy. By utilizing the appropriate aging temperature and time, different combinations of strength and ductility could be obtained to fulfill the design requirements of large-mold applications. The strengthening of AA2618 DC cast alloy under the aging conditions studied was caused by GPB zones and S′ precipitates. The evolution of both precipitates in terms of their size and density was observed to have a significant effect on the mechanical properties of the alloy.     

Effect of Ru on microstructural evolution during heat treatment in single crystal superalloys

Abstract

The effect of Ru addition on the as cast microstructure, structural evolution during heat treatment and long term aging was employed in single crystal superalloys with different contents of Ru addition (0, 1·5 and 3·0 wt-%). The results show that NiAl based β phase can occur in the interdendritic region in 3Ru alloy. With increasing Ru content in the alloys, the incipient melting temperature of alloy decreases gradually, while the liquidus and solidus changed slightly. After solution treatment and the same aging treatment, the γ′ phase size decreased with increasing Ru addition. An remarkable inverse partition of alloying elements, i.e. more matrix forming elements Re and Mo distribute to the γ′ phase and more Ni element distribute to the matrix, was observed in the alloys with more Ru content after aging treatment. Ru addition can accelerate the rafting of γ′ phase and suppress the precipitation of topologically close packed (TCP) phases effectively.     

Effect of heat treatment on ultrasonic velocity in ductile cast iron

Abstract

The measurement of the ultrasonic velocity is a common method in the foundry industry for the evaluation of the nodularity in ductile iron castings. Practical experience has shown that heat treatment can reduce the ultrasonic velocity compared to the as cast condition. Using ductile iron samples with different heat treatments in order to vary the ferrite and pearlite content respectively confirmed this decrease in the ultrasonic velocity compared to the as cast state. Further investigations showed that with all the heat treatments applied, irrespective of their effect on the microstructure, the density was decreased. The decrease in density correlated with the decrease in ultrasonic velocity for all heat treatments. The mechanisms involved in the reduction in the density are discussed.     

Influence of electrodeposition potential and heat treatment on structural properties of CdTe films

A modified Butler-Volmer model is developed to predict the potential of perfect stoichiometry (PPS) for electrodeposition. CdTe thin films are deposited in an acidic solution; their electrodeposition mechanism is investigated using cyclic voltammetry. Calculated and experimental PPS values exhibit good agreement. At PPS, well-connected granular CdTe thin films can be deposited; these are predicted to be intrinsic, and slightly p-type due to cadmium vacancies. Type conversion occurs only because of defect redistribution and local defect reactions after annealing; the converted n-type layer exhibits lower resistivity and higher mobility. A film annealed at 350 °C exhibits excellent crystallization.     

In situ observation on microstructural development of high-speed steel during carbon partitioning process

Quenching–partitioning–tempering (Q–P–T) process was applied to treat high-speed steel. Microstructural development and properties were studied using high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy, X-ray diffraction and a drop hammer impact toughness tester. The results of impact toughness test showed that the impact absorption energy increased to 16.2–20.1?J along the Q–P–T process, namely 56–93% higher than that of traditional Q–T approach (10.4?J). The results of in situ HRTEM showed that the interface of martensite/austenite (α/γ) migrated from martensite towards austenite with the increase of holding time, which led to a reduction of retained austenite. One of the migration planes was (110)_α/(111)_γ. The cementite precipitation and slight decomposition of retained austenite were observed during carbon partitioning process.     

Modelling microstructural and mechanical properties of ferritic ductile cast iron

Abstract

It is well known that the mechanical properties of ductile cast iron (DCI) depend on its microstructure, and that the microstructure depends on the properties of the melt and the cooling conditions during casting. There have been many studies of the individual elements of the process of casting DCI, but as yet there have been very few examples of modelling the entire process to predict cooling rates, microstructure, and mechanical properties, particularly for large castings. The present paper describes a method of modelling the microstructural and mechanical properties of ferritic DCI, and applies the methods to the case of a large (13 t) thick walled (300 mm thickness) casting. The microstructure calculated includes nodule count, nodularity, ferrite grain size, and percentage ferrite. The mechanical properties calculated include yield stress, tensile strength, elongation, and static upper shelf fracture toughness (J _1C and K _JC). The calculated results compare well with those of a test casting.     

Modelling microstructural evolution and mechanical properties of austempered ductile iron

Abstract

Austempered ductile iron (ADI) is finding an ever increasing worldwide market in the automotive and other sectors. It offers a range of mechanical properties superior to those of other cast irons, and shows excellent economic competitiveness with steels and aluminium alloys. The aim of the present research is to develop a generic model that will enable the producers of ADI to optimise their product in terms of microstructure and mechanical properties, hence minimising the need for expensive and exhaustive experimental trials and reducing alloy development lead times.     

Improvement of physico-mechanical properties of coir-polypropylene biocomposites by fiber chemical treatment

In preparing polymer–matrix composites, natural fibers are widely used as “reinforcing agents” because of their biodegradable characteristic. In present research, coir fiber reinforced polypropylene biocomposites were manufactured using hot press method. In order to increase the compatibility between the coir fiber and polypropylene matrix, raw coir fiber was chemically treated with basic chromium sulfate and sodium bicarbonate salt in acidic media. Both raw and treated coir at different fiber loading (10, 15 and 20 wt%) were utilized during composite manufacturing. During chemical treatment, hydrophilic –OH groups in the raw coir cellulose were converted to hydrophobic –OH−Cr groups. Microstructural analysis and mechanical tests were conducted. Scanning electron microscopic analysis indicates improvement in interfacial adhesion between the coir and polypropylene matrix upon treatment. Chemically treated specimens yielded the best set of mechanical properties. On the basis of fiber loading, 20% fiber reinforced composites had the optimum set of mechanical properties among all composites manufactured.     

Microstructure,precipitates and mechanical properties of powder bed fused inconel 718 before and after heat treatment

IN718 alloy was fabricated by laser powder bed fusion (PBF) for examination of microstructure, precipitates and mechanical properties in the as-built state and after different heat treatments. The as-built alloy had a characteristic fine cellular-dendritic microstructure with Nb, Mo and Ti segregated along the interdendritic region and cellular boundary. The as-built alloys were then subjected to solution heat treatment (SHT) at 980 °C or 1065 °C for 1 h. SHT at 980 °C led to the formation of δ-phase in the interdendritic region or cellular boundary. The segregation was completely removed by the SHT at 1065 °C, but recrystallization was observed, and the carbides decorated along the grain boundaries. The as-built alloy and alloys with SHT at 980 °C and 1065 °C were two-step aged, which consisted of annealing at 720 °C for 8 h followed by annealing at 620 °C for 8 h. Transmission electron microscopy revealed the precipitation of γ' and γ” in all alloys after two-step aging, but the amount and uniformity of distribution varied. The Vickers hardness of the PBF IN718 alloy increased from 296 HV to 467 HV after direct aging. The hardness decreased to 267 HV and 235 HV after SHT at 980 °C and 1065 °C, respectively, but increased to 458 HV and 477 HV followed by aging. The evolution of Young’s modulus after heat treatment exhibited similar trend to that of hardness. The highest hardness was observed for IN718 after SHT at 1065 °C and two-step aging due to precipitation with greater amount and uniform distribution.     

Investigating microstructural evolution during homogenization of the equiatomic NiTi shape memory alloy produced by vacuum arc remelting

The vacuum arc remelting process is widely used for the commercial production of NiTi shape memory alloys. Due to the absence of electromagnetic forces in this method, several remelting and long-time homogenizing are required. In this work, a Ti-50 at.% Ni alloy was prepared using the non-consumable vacuum arc melting technique in a water-cooled copper crucible. After four times of remelting process, specimens were subjected to homogenization at 1000 °C. Micro/macrostructural changes during homogenization were investigated by optical microscope and SEM equipped with EDS analyzer. The results showed that the as-cast specimen consisted of mostly Ni₃Ti, Ti₂Ni and monoclinic (B1^9′) phases with high segregation. By increasing the holding time during the homogenization process at 1000 °C, the amount of austenite (B₂) phase was increased, while segregation and unfavorable phases, and accordingly, hardness were decreased. After 4 h of homogenization, austenite (B₂) was the only phase maintained in the microstructure of Ti-50 at.% Ni. In addition, macrostructure of the alloy was turned into polygonal structure after such a homogenization treatment.     

Surface reactivity of thin wall ferritic ductile iron. The effect of nodule count and grinding variables

Thin wall ductile iron (TWDI) castings constitute an attractive alternative to several applications in which the strength to weight ratio becomes a key design variable. In TWDI, the nodule count for a given chemical composition is highly dependent on cooling rate during solidification, and hence on thickness.For mechanical parts, where accurate dimensional tolerance is mandatory, the most common machining process applied is grinding. This process induces significant temperature gradients and surface plastic deformations which could affect service performance, particularly in corrosion environments.In TWDI, surface properties become more relevant due to the high surface area to volume ratio. Therefore, the aim of this paper is to determine the effect of nodular count and grinding conditions on surface reactivity of ferritic TWDI. Electrochemical assays were carried out in a three-electrode cell in a 3.5 wt.% NaCl solution on both polished and ground samples. The results obtained indicate that surface reactivity increases with higher nodular counts and residual plastic strain.     

The effect of deposition parameters on the properties of yttria-stabilized zirconia thin films

Yttria-stabilized zirconia (YSZ) films were deposited by RF magnetron sputtering in order to examine the effects of sputtering conditions on the properties of the resulting thin-films. X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS) and scanning electron microscopy (SEM) were used to characterize the films. Additionally, films were deposited on alumina bars to examine the effect of the coatings on the strength of a brittle substrate. RBS analysis indicated that the ratio of oxygen to zirconium in the films varied from 1.84 to 2.10. XRD showed that there was a wide variation in the amount of monoclinic and tetragonal phases that appeared to be related to the O:Zr ratio. Despite these variations, there was no significant difference found in flexural strength found among the groups of alumina bars that were coated with YSZ. The likely cause is the columnar grain morphology of the deposited thin-films, which does not allow strengthening mechanisms to become operative.     

Microstructural study and wear behavior of ductile iron surface alloyed by Inconel 617

In this research, microstructure and wear behavior of Ni-based alloy is discussed in detail. Using tungsten inert gas welding process, coating of nearly 1–2 mm thickness was deposited on ductile iron. Optical and scanning electron microscopy, as well as X-ray diffraction analysis and electron probe microanalysis were used to characterize the microstructure of the surface alloyed layer. Micro-hardness and wear resistance of the alloyed layer was also studied. Results showed that the microstructure of the alloyed layer consisted of M₂₃C₆ carbides embedded in Ni-rich solid solution dendrites. The partial melted zone (PMZ) had eutectic ledeburit plus martensite microstructure, while the heat affected zone (HAZ) had only a martensite structure. It was also noticed that hardness and wear resistance of the alloyed layer was considerably higher than that of the substrate. Improvement of wear resistance is attributed to the solution strengthening effect of alloying elements and also the presence of hard carbides such as M₂₃C₆. Based on worn surface analysis, the dominant wear mechanisms of alloyed layer were found to be oxidation and delamination.     

Effect of heat treatment on microstructural and optical properties of CBD grown Al-doped ZnO thin films

Investigations on the effect of annealing temperature on the structural, optical properties and morphology of Al-doped ZnO thin films deposited on glass substrate by chemical bath deposition have been carried out. X-ray diffraction studies revealed that deposited films are in polycrystalline nature with hexagonal structure along the (0 0 2) crystallographic plane. Microstructural properties of films such as crystallite size, texture coefficient, stacking fault probability and microstrain were calculated from predominant (0 0 2) diffraction lines. The UV-Vis-NIR spectroscopy studies revealed that all the films have high optical transmittance (>60%) in the visible range. The optical band gap values are found to be in the range of 3.25-3.31 eV. Optical constants have been estimated and the values of n and k are found to increase with increase of heat treatment. The films have increased transmittance with increase of heat treatment. Al-doped ZnO thin films fabricated by this simple and economic chemical bath deposition technique without using any carrier gas are found to be good in structural and optical properties which are desirable for photovoltaic applications. Scanning electron microscopic images revealed that the hexagonal shaped grains that occupy the entire surface of the film with its near stoichiometric composition.     

热处理对Ti-2.5 Cu合金组织和性能的影响

Ti-2.5Cu合金是含有(w(B))2.5%Cu β共析型元素的近α型二元合金,具有可与纯钛相媲美的成型性和可焊性,有一定的热强性,使用温度可达到350℃.通过对Ti-2.5Cu合金板材进行不同退火和固溶时效制度处理后,测试其室温拉伸性能和HV值,并利用光学显微镜和透射电镜观察其组织形貌,对该合金热处理制度与组织、性能关系进行了深入、系统地研究.结果表明,Ti-2.5Cu合金最佳退火温度为(790±10)℃.为了缩短时效时间,可采用双重时效制度,一次时效400℃,8 h,空冷,二次时效475℃,8 h,达到最佳的强化效果,此时Ti2Cu粒子析出并长大到最佳尺寸100nm.     

Effect of sonication parameters on the mechanical properties of multi-walled carbon nanotube/epoxy composites

In this study, the effects of duration and output power of sonication on the dispersion state of 0.5 wt.% multi-walled carbon nanotube (MWNT) in epoxy matrix were investigated. To disperse the MWNT in the polymer matrix, sonication powers of 25, 50 and 100 W and sonication times of 15, 45 and 135 min were used. Dynamic mechanical thermal analysis (DMTA) and tensile test were performed under different dispersion states of MWNT. The results indicated that with increase in the sonication time, there was an initial increase in Young’s modulus values followed by a drop in values at longer sonication times. The highest Young modulus was gained for the sonication power of 50 W and sonication times of 45 min. Also the highest tensile strength was obtained for the sonication power of 25 W and sonication time of 45 min. Also sonication at 50 W for 15 min was the most effective dispersion for achieving the highest glass transition temperature (T_g). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the dispersion state of MWNT. Well dispersion was observed as the power and duration of sonication were increased.     

热处理对各向同性热解炭材料微观结构和力学性能的影响

对化学气相沉积法（CVD）制备的各向同性热解炭材料在不同温度下进行热处理，利用金相显微镜、扫描电镜、透射电镜、X射线衍射和显微激光喇曼光谱等表征手段及显微硬度实验、三点弯曲实验，研究了材料的微观结构和力学性能与热处理温度之间的关系。结果表明，随着热处理温度的提高，各向同性热解炭材料的石墨片层间距缩小，石墨化程度增加，晶粒尺寸增大，同时材料中的孔隙结构也发生了较大的变化。材料的显微硬度和弹性模量随热处理温度的升高而降低，抗弯强度在1750℃和2400℃之间没有变化，在2600℃时有显著的增加。     

Effects of applied pressure on microstructure and mechanical properties of squeeze cast ductile iron

In this study, the effects of applied pressure during solidification on the microstructure and mechanical properties of cylindrical shaped ductile iron castings were investigated. Magnesium treated cast iron melts were solidified under atmospheric pressure as well as 25, 50 and 75 MPa external pressures. Microstructure features of the castings were characterized using image analysis, optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques. Tensile properties, toughness and hardness of the castings were also measured. The results showed that average graphite nodule size, free graphite content and ferrite content of the castings decreased and pearlite and eutectic cementite contents increased as the applied pressure was raised from 0 to 75 Mpa. Graphite nodule count was first increased by raising the applied pressure up to 50 MPa and then decreased. The highest graphite nodule count was obtained at 50 MPa applied pressure. The microstructural changes were associated with the improved cooling rate and the expected changes in the corresponding phase diagram of the alloy under pressure. The ultimate tensile strength (UTS), yield point strength (0.2% offset) and fracture toughness of the castings were improved when the applied pressure was raised from 0 to 50 MPa. Further increase of the applied pressure resulted in slight decrease of these properties due to the formation of more cementite phase in structures as well as reduced graphite nodule count. Hardness of the castings continuously increased with increasing the applied pressure.