Nital Solution Research Articles

(Invited) Mixing Elements in 2D Nanostructures Grown by Discharges in Liquids

The synthesis of nanosheets through discharges in liquid nitrogen is observed for certain metals when employed as electrodes [1,2]. Various metals have been examined, with bismuth, lead, or zinc showing a propensity to form nanosheets. Other metals, such as silver or indium, also exhibit sheet formation but with smaller aspect ratios (width/thickness). Mixing metals is not only interesting to create alloys with new properties but also to understand how discharges work to enable the synthesis of these objects.Recently, we demonstrated that these structures can be grown not only in liquid nitrogen but also in water. This is attributed to the discharge primarily originating from the metallic vapor emitted by the electrodes, a consistent process in both liquids, as confirmed by time-resolved optical emission spectroscopy.We showcased that a pre-treatment, involving chemical etching by a Nital solution, significantly enhances the efficiency of nanosheet production, increasing it from almost zero to nearly 100%. We successfully identified the growth mechanism of nanosheets in the case of bismuth electrodes. These structures grow on the cathode with ion assistance, collecting in the bubble formed during the discharge. Upon the collapse of the bubble, they transfer into the liquid phase. Interestingly, the number density of nanoparticles produced under these conditions is either null or too weak to be evaluated.It is feasible to incorporate two different elements into 2D nanostructures by utilizing two electrodes. We achieved a mixture of lead and bismuth oxide by using electrodes composed of the respective elements. This capability is likely associated with the similar melting points and miscibility of both elements. Nanosheets exhibit thicknesses around 5-10 nm for widths ranging in the tens of micrometers.We anticipate that a more comprehensive understanding of the synthesis of these alloys will pave the way for the production of alloyed nanosheets incorporating other elements.[1] A. Hamdan, H. Kabbara, C. Noël, J. Ghanbaja, A. Redjaimia, T. Belmonte, “Synthesis of two-dimensional lead sheets by spark discharge in liquid nitrogen”, Particuology 40 (2018) 152–159[2] H. Kabbara, J. Ghanbaja, C. Noël, T. Belmonte, “Nano-objects synthesized from Cu, Ag and Cu28Ag72 electrodes by submerged discharges in liquid nitrogen”, Materials Chemistry and Physics 217 (2018) 371–378

Metallographic characterization of a gold-steel composite

Abstract A gold-steel composite material for decorative applications was manufactured by forging. This procedure can be referred to as modified damascene technique. Sheets made of steel K110 (C-rich cold work steel) and gold sheets were assembled and forged together at approx. 800 °C. The bar was subsequently twisted to obtain the typical torsion pattern. The end portions of this bar were subjected to a metallographic examination. The steel K110 shows broken carbides which were formed during the forging process. The carbides can be etched using Murakami’s reagent, whereas a 3 % Nital solution can be used to etch the steel matrix. Gold etching was challenging because many etchants suitable to etch gold preferentially attack the steel. In reference to gold extraction by cyanide leaching, a KCN solution was used as etchant. It could be shown that atmospheric oxygen acting as an oxidant is already sufficient to etch gold. However, using a KCN-H2O2 mixture provides a more efficient etching effect. Gold grains in the gold layers can reach a size of up to 1 mm. A diffusion zone with a thickness of approx. 10 μm can be observed at the steelgold interfaces.

The Influence of Holding Time to Mechanical Properties of Steel Processed with Powder Metallurgy

Steel with very small grain has high strength but still have ductility. Heating the steel until reach to austenite temperature can make the grain of the steel will growth and reduce the hardness of the steel, to prevent this it is necessary to know the effect of holding time on steel hardness. The hardness is indicating of grain growth of the steel. In this research, we investigated the effect of holding time to the hardness of very small-grained steel. Heat treatment was done at 1100 °C using an electric furnace. Micro-hardness testing used a micro-Vickers method using 300 gram forces and indentation time 10 minutes. Microstructure observation was done with metallurgical microstructure. The etching solution for microstructure observation was nital solution. The heat treatment process of steel powder metallurgy with a holding time of 60 minutes will cause hardness to decrease from 245 in holding 15 minutes to 207 and grain size grow from 1 µm to 4 µm.

Effect of Niobium and Titanium Addition on Formation of Second Phase Particles in CHQ Steel Using Transmission Electron Microscope

It is common practice that formation of second phase particles such as nitrides or carbides in the steel matrix has significant role to control the grain size of steel. An attempt is made in the present research work to find out the role of nitrogen to form the nitride particles either with Al, Ti, B, Cr or Si. Two steel samples Steel-A and Steel-B with same titanium and aluminum weight percent in the chemical composition were obtained in hot rolled conditions from international market with only the difference of presence of Niobium in Steel-A. Solution heat treatment was performed at 1350°C with 60 minutes holding time in protherm heat treatment furnace available locally was used to dissolve the particles and then steel samples were reheat treated at 800°C with holding time of 60 minutes and water quenched and microstructure was revealed. Transmission electron microscope connected with Ehlers-Danlos Syndrome (EDS) was used to reveal the morphology of second phase particles. Both samples for a high resolution power Transmission Electron Microscopy (TEM) (Jeol JEM 3010) analysis were prepared by using carbon extraction replica method in 5% Nital solution as an etching technique. Both samples were then caught in copper grid of 3mm for using TEM analysis. TEM micrographs clearly revealed the second phase particles in the matrix of steel. The EDS peaks were studied and it was found that the peaks showed the titanium peaks in both the samples A and B and surprisingly there was no any peak found for aluminum. Stoichiometric calculations were carried out and it was found that weight percent nitrogen required for forming TiN is 0.0073, however the total nitrogen present in both the steels A and B is 0.0058 and 0.0061 respectively. That means that all the nitrogen present in the steel matrix was consumed by titanium to form the Titanium Nitride (TiN) so there was no nitrogen remain to fulfil the requirement of aluminum to form the Aluminum Nitride (AlN) particles.

Understanding the Effect of Aluminum Addition on the Forming of Second Phase Particles on Grain Growth of Micro-Alloyed Steel

The formation of second phase particles in the steel matrix during melting and casting plays an important role in controlling the grain size of steel. An attempt is made in the present work to find the role of nitrogen on forming nitride particles either with aluminum or titanium. Two steel samples with the same titanium and aluminum weight percent in their chemical composition were collected after the hot rolling process. Solution heat treatment at 1350°C for 60min holding time was used to dissolve the particles and then the steel samples were reheated at 800°C for 60min, water quenched and their microstructure was revealed by usual grinding and polishing process using 2% Nital. A transmission electron microscope connected with EDS was used to reveal the morphology of the second phase particles. The samples for TEM analysis were prepared by the replica extraction method in 5% Nital solution. The samples were then caught in 3mm copper grid for TEM analysis. TEM micrographs revealed the second phase particles in the matrix of steel. EDS peaks were studied and titanium peaks were found in both samples and surprisingly there was not any peak found for aluminum.

Grain growth of powder metallurgy steel after heat treatment

Steel with very small grain has high strength but still have ductility. When the steel is heated to austenitic temperatures it can make the steel grains grow and reduce the hardness of the steel. To prevent this, it is necessary to know the effect of holding time on steel hardness. The hardness is indicating of grain growth of the steel. In this study, we examined the effect of holding time on hardness of very small grained steel. The heat treatment is carried out at 1100 degrees Celsius using an electric furnace. Micro hardness testing using the micro-Vickers method uses 300 grams of force and an indentation time of 10 minutes. Observation of microstructure is carried out with metallurgical microstructure. The etching solution for microstructure observation was nital solution. Heat treatment of steel powder mettallurgy with holding time of 60 minutes will cause a decrease in hardness from 261 to 207 and grain size growing from 3.2 μm to 6.3 μm.

Phase transformation in white etching area in rolling contact fatigue

Rolling contact fatigue (RCF) involves microstructural change in the subsurface of contact. The changed microstructure is generally termed as white etching area (WEA) as it appears white under optical microscope when etching in nital solution. WEA has been acknowledged as one of the primary failure modes in RCF since it causes severe local inhomogeneity of microstructure. It was reported that WEA consists of nano ferrites as martensite grains and carbides are significantly refined in the WEA. Some carbides are dissolved. In some cases, an amorphous-like structure was occasionally observed in the WEA, indicating that phase transformation may possibly occur. The WEAs were studied by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Electron back scattered diffraction (EBSD). The result showed that WEA is dominated with an amorphous phase with martensite, austenite and carbides embedded interior. A distinct interface between the matrix and the WEA was present. In addition to grain refinement down to nanometers, phase transformation including amorphization and austenitization happened in WEAs. The content of austenite was increased from 2% in the matrix to 20% in the WEA. The analysis showed that phase transformation is controlled by plastic deformation mechanism.

Modeling the Effect of Plate Thickness on Dilution and Bead Height in SAW Process

Objectives: Dilution and bead height model generation for submerged arc welding and variable plate thickness Methods/Statistical Analysis: Central composite design (rotatable) technique used with Design Expert® software. 32 beads on plate specimen welded with submerged arc welding process. Current, voltage, plate thickness, travel speed and nozzle to plate distance taken as variable to identify the direct and interaction effects of these parameters on dilution and bead height. All weld samples cut from the specimen, polished and etched with 2% Nital solution to observe bead profile on high resolution microscope with 10 X image enhancement for quality measurement of bead parameters. Findings: Plate thickness along with other welding parameters affects the bead profile due to change in heat flow conditions. Variable plate thickness model for bead parameters help us to understand that how the changed heat flow conditions affects bead profile when plate thickness changes. Bead height increase with current and reduce with travel speed. The maximum bead height has been observed with 14 mm plate where bead height is observed 2.94 mm at 325 amperes current and 21.25 m/hr of travel speed while minimum is 1.79 mm for 12 mm plate at 250 Ampere current and 22.50 m/hr travel speed. Higher bead height is observed with thicker plate due heat sinking effect in thickness direction. Percentage dilution is affected by plate thickness along with other parameters, especially when we work with faster travel speed. Application/Improvements: Variable plate thickness model for bead height and dilution for Submerged arc welding represented which can be helpful to identify bead characteristics over a wide range of thicknesses for SAW welded carbon steels.

Hydrogen Entry into Pure Iron Treated By Plasma Nitriding

In order to prevent hydrogen embrittlement of steels, it is effective to decrease the amount of hydrogen entry into steel matrix under atmospheric corrosion environments. In this study, the nitrided layer was formed in the surface of pure iron by plasma nitriding to inhibit the hydrogen entry, and the hydrogen permeation tests were conducted to clarify the barrier effect of nitrided layer on the hydrogen entry into pure iron. Pure iron sheets of 1 mm thickness with 99.99 mass% purity were used as the specimens. The specimens were heat-treated at 1173 K for 18 ks and then furnace-cooled. The surfaces of the specimens were polished with diamond paste down to 1 μm. Plasma nitriding was performed in a nitrogen-hydrogen atmosphere composed of 75 % N2 and 25 % H2 for 3.6 ks at 673 K and at 600 Pa. The one side of the specimens was nitrided by masking another side. Figure 1a shows the cross-sectional image of the specimen etched with 3 % nital solution after the plasma nitriding. The layer with a different etching behavior from the matrix was observed in the surface region. The thickness of the surface layer was ca. 2.8 μm. Figure 1b shows the XRD patterns of the plasma-nitrided specimen. The peaks assigned to ε-Fe2-3N and γ ’-Fe4N were detected. The peaks of ε-Fe2-3N were larger than that of γ ’-Fe4N, suggesting that the surface layer was mainly composed of ε-Fe2-3N phase. In order to investigate the property of hydrogen entry in the surface of the nitrided specimen, the hydrogen permeation tests using the Devanathan-Stachurski cell1 were carried out. The hydrogen entry was conducted by galvanostatic polarization at −100 μA (i c) in deaerated boric-borate buffer solution with 0.01 M NaCl (pH 8.45) for 10.8 ks. The Pd-coated surface of the specimens in the hydrogen detection side was polarized at 0.2 V vs. SHE in deaerated 0.1 M NaOH solution. Figure 1c and 1d show time variation of the potential on the hydrogen entry side and the hydrogen permeation current density (i p), respectively. In the initial 30 s, the potential of both the untreated and the nitrided specimen drastically decreased to approximately the same value (ca. −0.75 V vs. SHE). In the case of the untreated specimen, the permeation current drastically increased to ca. 300 nAcm-2 in the period from 0.5 to 1.0 ks. After that, it gradually increased and reached to 450 nAcm-2 at 10.8 ks. On the other hand, the permeation current of the nitrided specimen slightly increased to 10 nAcm-2 in the period from 1.6 to 4.0 ks and stayed at ca. 10 nAcm-2 from 4.0 to 10.8 ks. The hydrogen permeation test revealed that the plasma nitriding treatment strongly inhibited the hydrogen entry into pure iron under the cathodic polarization. 1. M. A. V. Devanathan, and A. Stachurski, Proc. Roy. Soc. A, 270, 90 (1962). Figure 1

Influence of the initial surface state of bodies in contact on the formation of white etching layers under dry sliding conditions

The white etching layer (WEL) is a bright layer formed on the surface of steel and revealed when the latter is etched with Nital solution (a solution of nitric acid and ethanol). WELs have been observed on rail running bands for more than half a century. They are brittle, about 3 times harder than the traditional rail steel used. Two mechanisms of white etching layer formation are known such as thermal mechanism: temperature increase and quick cooling, or mechanical formation. The main purpose of this work, is to study the influence of the initial state of the sample surfaces on WEL mechanical formation. The samples were either oxidized or run-in before testing on a twin-disc machine under 1GPa contact pressure and 0.5% sliding ratio. The results presented incomplete WELs to fully formed WELs at the surface of the disks. The initial run-in or oxidized surface facilitated the birth of WEL and reduced wear.

Metallographic Characterization of a Ti-Containing Low-Density Fe-Mn-Al-C Steel in As-Cast Condition

ABSTRACTLow-density steels, with an excellent combination of outstanding mechanical properties, ultimate tensile strength and specific weight reduction, have been attracting great attention as a new group of materials in many industrial applications, particularly in the automotive industry. The aim of this work was to characterize the microstructure of a Ti-containing low-density Fe-Mn-Al-C steel in the as-cast condition. For this purpose, Ti-containing low-density steel was melted in an induction furnace using high purity raw materials and cast into a metal ingot mold. Chemical composition of the studied steel was Fe-32Mn-7.0Al-2.2C-0.5Ti (wt%). Samples were prepared by standard metallographic technique (grinding and polishing) and chemically etched with 2% nital solution, in order to reveal the dendritic microstructure. Microstructure observations were performed by scanning electron microscopy and the chemical nature of the present phases was determined by energy-dispersive X-ray. X-ray diffraction was performed at room temperature using a diffractometer with Cu Kα radiation. Phase equilibria by thermodynamic calculations for the studied steel were performed using JMatPro® software package. In general, results revealed a finer dendritic microstructure composed of ferritic matrix and austenite islands. The presence of ferrite and austenite in the steel was also confirmed by X-ray diffraction.

Fabrication of superhydrophobic textured steel surface for anti-corrosion and tribological properties

We describe a simple and rapid method to fabricate superhydrophobic textured steel surface with excellent anti-corrosion and tribological properties on S45C steel substrate. The steel substrate was firstly ground using SiC sandpapers, and then polished using diamond paste to remove scratches. The polished steel was subsequently etched in a mixture of HF and H2O2 solution for 30s at room temperature to obtain the textured steel surface with island-like protrusions, micro-pits, and nano-flakes. Meanwhile, to investigate the formation mechanism of the multiscale structures, the polished steel was immersed in a 3wt% Nital solution for 5s to observe the metallographic structures. The multiscale structures, along with low-surface-energy molecules, led to the steel surface that displayed superhydrophobicity with the contact angle of 158±2° and the sliding angle of 3±1°. The chemical stability and potentiodynamic polarization test indicated that the as-prepared superhydrophobic surface had excellent corrosion resistance that can provide effective protection for the steel substrate. The tribological test showed that the friction coefficient of the superhydrophobic surface maintained 0.11 within 6000s and its superhydrophobicity had no obvious decrease after the abrasion test. The theoretical mechanism for the excellent anti-corrosion and tribological properties on the superhydrophobic surface were also analyzed respectively. The advantages of facile production, anti-corrosion, and tribological properties for the superhydrophobic steel surface make it to be a good candidate in practical applications.

Rapid synthesis of ZnO nano-corncobs from Nital solution and its application in the photodegradation of methyl orange

Abstract This paper reports the synthesis of ZnO with nano-corncobs morphology; this method consists of two stages of reaction: the first is the formation of ZnO precursor at 70 °C by a mixture formed from a Nital solution (ethanol + nitric acid) and zinc acetate; the second stage occurs at 180 °C, where the combustion process occurs to obtain the ZnO nanoparticles. XRD data showed the presence of hexagonal single-phase ZnO with the wurtzite crystal structure. FE-SEM images indicated that the synthesized ZnO presents nano-corncobs morphology. The analysis of photoluminescence spectra shows the presence of oxygen vacancies in the synthesized ZnO, which are related to the ratio of polar and non-polar planes. The commercial and synthesized ZnO were used as catalysts for degradation of methyl orange under simulated sun-light. Results showed that synthesized ZnO is more catalytically active for photodegradation under simulated sun-light than commercial ZnO. Photocatalytic activity tests showed that best activity was obtained with uncalcined ZnO powders and this enhanced activity was attributed to the synergistic effect found between the material polar plane and oxygen vacancies. Additionally, electrochemical experiments shown that synthesized ZnO by Nital solution are free of photocorrosion.

Microstructure Refinement of Medium Carbon Steel through Ti Deoxidation

The medium carbon steel (C: 0.26%, mass percentage) was deoxidized by Ti alloys, and its features of inclusion and microstructure were systemically studied through the scanning electron microscope (SEM) and Energy Dispersive Spectrometer (EDS). The results show that the element of titanium in inclusions coexists with manganese, and no single-phase oxides of titanium are observed. Through the statistical analysis, it can be seen that the average size of Ti-contained inclusions is similar to the inclusions without the Ti, and the percentage of large inclusions (>5μm) is smaller in Ti-contained inclusions, which may reduce the harmful effect of inclusions. After etching in 3Vol% Nital solution, it’s found that the Ti-contained inclusions can act as nucleation sits for the intragranular acicular ferrite.

Microstructures of Electro-Carburized Mild Steels

The molten carbonate salts based electro-carburisation process, as reported here, is non-toxic, environment friendly, cheaper than the cyanide based techniques and highly effective in turning mild steels into a more valuable metal. The effectiveness of the electro-carburisation process was investigated by microstructure analysis. The sample was ground, polished and then etched in a 2 % nital solution. Examinations of the microstructural changes in the etched samples by SEM-BSE and microscope (500X magnification) revealed the distribution of carbon throughout the electro-carburised mild steel. The changes were typically represented by two phases, namely, the brighter areas resulting from the ferrite phase (iron rich), and the darker areas indicating the presence of carbon in the pearlite phase which were consisted of alternate stripes of ferrite and cementite (carbon rich). These microstructural features, particularly the ferrite and pearlite regions, were found to be affected by the cell voltages applied during electro-carburisation and the type of molten salts.

DETERMINING THE AMOUNT OF RETAINED IN AISI 52100 STEEL USING X-RAY DIFFRACTION

งานวิจัยนี้หาปริมาณออสเทนไนต์เหลือค้างในชิ้นงานเหล็กกล้า AISI52100 ที่ชุบแข็งและอบคืนตัวด้วยเครื่องรังสีเอ็กซ์แบบเลี้ยวเบน โดยอบเหล็กให้เป็นออส เทนไนต์ในช่วงอุณหภูมิ 800-900°C แล้วชุบแข็งในน้ำมันและอบคืนตัว โครงสร้างจุลภาคของชิ้นงานประกอบด้วยมาร์เทนไซต์ ซีเมนไตต์กลมและออส เทนไนต์เหลือค้าง แต่โครงสร้างจุลภาคเกิดลักษณะ Ghost line เมื่อกัดผิวด้วยสารละลาย nital จึงต้องใช้สารละลายที่แสดงซีเมนไตต์ให้เด่นชัดสำหรับหาปริมาณสัดส่วนเชิงปริมาตรของซีเมนไตต์ การใช้เครื่องรังสีเอ็กซ์แบบเลี้ยวเบนที่มีโครเมียมเป็นเป้า ทำให้หาอัตราส่วนของสัดส่วนเชิงปริมาตรของมาร์เทนไซต์และของออสเทนไนต์ได้ เมื่อรู้สัดส่วนเชิงปริมาตรของซีเมนไตต์ จึงคำนวณหาปริมาณออสเทนไนต์ได้ . This research is to determine retained austenite content in AISI 52100 steel specimens which were hardened and tempered, by X-ray diffractometer. Steels were austenitized in temperature range of 800°C to 900°C, then quenched in oil and tempered. Microstructure of specimens comprises martensite, spheroidized cementite and retained austenite. However, microstructure showed Ghost line when etched with nital solution. The etchant which showed cementite clearly was used to determine volume fraction of cementite. X-ray diffractometer with chromium target provides the ratio of volume fraction martensite and austenite. When volume fraction of cementite is known, the amount of retained austenite can be calculated. Austenitizing temperatures of 800, 815, 845, 860 and 900°C result in the amounts of retained austenite of 5.3, 6.3, 9.9, 13.3 and 20.1% respectively.

Nanoscale brass/steel multilayer composites produced by cold rolling

Metallic multilayer composites are of interest due to their attractive combination of strength and fracture resistance, tq These composites have been produced by a number of techniques including coextrusion and wire drawing,t2] vapor deposition,t3] and electrodepositionJ 4] On the other hand, cold rolling is a potential method for continuous mass production of microlaminate sheets, since the technology to cold roll strips of various metals already exists. In spite of this potential, application of cold rolling to produce nanoscale multilayer composites is yet to be performed. The primary objective of the present study was to explore the feasibility of fabricating nanolaminate composites, having different layer thicknesses, by cold rolling. The brass/steel system was selected, due to the limited mutual solid solubility, ease of deformability, and material availability at low cost. The deformation behavior during rolling and the evolution of microstructure and texture were studied. It is to be noted that this is the first attempt toward the fabrication of nanoscale multilayer composites by cold rolling. The starting materials for the fabrication of laminate composites were 25.4-/xm-thick sheets of AISI 1010 steel and CDA 260 cartridge brass (70 pct Cu-30 pct Zn). These sheets were degreased with acetone, sliced into 40 x 40mm pieces, and stacked alternately to form a multilayer composite. To reduce the friction as well as to prevent the bonding between the stack and the platen, top and bottom surfaces of the stack were sprayed with graphite lubricating powder. Diffusion bonding of the stack was done at 510 ~ for 4 hours with a pressure of 16 MPa, followed by air cooling to room temperature. Typically, there was a reduction of 30 to 35 pct in the thickness during the diffusion bonding process. The bonded composites were sliced into blanks of size 40 x 20 mm and polished by SiC abrasive papers. They were then cold rolled in a two-high rolling mill, with a roll diameter of 150 mm. The specimens were given an intermediate annealing treatment at 400 ~ for 15 minutes, after a level of reduction ranging from 30 to 60 pct. Specimens were cut at different rolling stages to obtain specimens with different percentage reductions and, hence, different layer thicknesses. The rolled specimens were sectioned and metallographically polished. The steel layers were preferentially etched with a 2 pct nital solution to enhance the contrast between layers for observation in the light microscope. Microstructural examinations and chemical analyses were performed

Effect of second phase on the fatigue crack growth in AlSl 4340 steel

Increasing applications of AISI 4340 steel necessitate more precise characterization of its mechanical properties so that designers can better ensure failsafe behaviour in service. The fatigue fracture process of a component includes crack initiation and crack propagation. C r a c k initiation behaviour can be evaluated by studying low cycle fatigue and high cycle fatigue. The crack propagation life depends on fatigue crack growth rate and fracture toughness. Many researchers have conducted fracture toughness measurement [1-3], dynamic fracture propagation [4-6] and bending and torsion fatigue tests [7] in 4340 steel. It has been shown that the fracture toughness can be improved by using higher austenitizing temperature (1100-1200 °C) or through high temperature thermomechanical treatment [3]. However, little work has been done on the fatigue crack growth rate of 4340 steel [8]. The second phase plays an important role in determining the mechanical properties. The second phase hard carbide particles in a tool steel will develop stresses at the boundary of the matrix and the inclusion during external cycling loading [9] and reduce the low cycle fatigue properties. Zaczyk et al. [10] indicate that the absorbed energy during stable crack growth depends upon the amount the morphology of second phase particles in ductile steels. The resistance to shear instability and fracture toughness also relies on second phase particle dispersions [11]. Tomita and Okabayashi have proposed two heat treatments that can produce a dutile second phase in the martensitic matrix of 4340 steel [12-15]. The first process is isothermal heat treatment (IHT), which produces a lower bainite second phase, and the second is interrupt quench treatment (IQT), which produces a highly tempered martensite second phase. The existence of the ductile second phase can significantly improve the mechanical behaviour such as tensile properties, impact energy [12-14] and plane strain fracture toughness [15]. However, Tomita and Okabayashi did not address the fatigue properties. In the study reported here we investigated the effect of types and volume fraction of the second phase on the fatigue crack growth rate in AISI 4340 steel. The results are compared to those of conventional quenched and tempered 4340 steel. A commercial AISI 4340 steel was used in this study. The chemical composition was (wt%: C 0.39, Si 0.24, Mn 0.61, P 0.02, S 0.01, Ni 1.46, Cr 0.67, Mo 0.17). The martensitic transformation temperature Ms determined by a dilatometer was 330 °C. Based on the Ms temperature, three different heat treatments were carried out to produce ductile second phase in the matrix: isothermal heat treatment, interrupt quench treatment and direct quench treatment (DQT). Table I lists these heat treatment processes and specimen identification. The microstructures of specimens etched with a 3% nital solution were observed by optical microscopy. Fatigue crack growth tests in accordance with the ASTM E647 standard [16] were performed in a computerized MTS servo-controlled testing system. Compact tension specimens of thickness 5.4 mm and width 43.2 mm were used. A sinusoidal load with frequency 40 Hz and load ratio R = 0.1 was applied throughout the test. A crack opening displacement gauge was attached close to the notch of the specimen, and the growi~ag crack length was measured by the compliance method. Fatigue cycles and cyclic stress intensity factor at every moment of stressing could be recorded automatically. Two duplicate fatigue tests were performed for each specimen. The broken surfaces were studied by scanning electron microscopy (SEM) to understand

A study of the effects of heat treatment on the microstructures and magnetic properties of Cu-added NdFeB type sintered magnets

High temperature (1100 °C) and low temperature (600 °C) heat treatments have been applied to sintered magnets of the composition Nd 17Fe 76.5B 5Cu 1.5. The magnets were observed microstructurally in order to explain their magnetic properties. The magnet which was quenched from 1100 °C showed no specific phases in its grain boundaries. In this magnet, clustering of the grains occurred and it was found that Vilella's reagent showed all of its grain boundaries while Nital solution did not. A high proportion of Nd 2Fe 17, was noted in this sample. The remaining Cu-containing samples had δ-phase (Nd 6Fe 13Cu) and NdCu/Nd-rich regions in their grain boundaries with very small amounts of Nd 2Fe 17 present. Their grains were well separated and their grain boundaries could be exposed with Nital solution. The sample which was slowly cooled from 1100 °C showed the best magnetic properties and was found to contain a lot of the NdCu/Nd-rich eutectic regions and a lesser amount of the δ-phase regions. Quenching after the 600 °C anneal was found to give better magnetic properties than furnace cooling from this temperature. The same heat treatments were applied to magnets of the composition Nd 16Fe 76B 8 for comparison. Marked differences in behaviour to the copper-containing magnets were observed.

Simplified method for elasto-plastic analysis of structures under variable cyclic loading: Wang, X., Lei, Y. and Chang, L. Int. J. Pressure Vessels Piping49 1 (1992) 97–108

We describe a simple and rapid method to fabricate superhydrophobic textured steel surface with excellent anti-corrosion and tribological properties on S45C steel substrate. The steel substrate was firstly ground using SiC sandpapers, and then polished using diamond paste to remove scratches. The polished steel was subsequently etched in a mixture of HF and H2O2 solution for 30 s at room temperature to obtain the textured steel surface with island-like protrusions, micro-pits, and nano-flakes. Meanwhile, to investigate the formation mechanism of the multiscale structures, the polished steel was immersed in a 3 wt% Nital solution for 5 s to observe the metallographic structures. The multiscale structures, along with low-surface-energy molecules, led to the steel surface that displayed superhydrophobicity with the contact angle of 158 ± 2° and the sliding angle of 3 ± 1°. The chemical stability and potentiodynamic polarization test indicated that the as-prepared superhydrophobic surface had excellent corrosion resistance that can provide effective protection for the steel substrate. The tribological test showed that the friction coefficient of the superhydrophobic surface maintained 0.11 within 6000 s and its superhydrophobicity had no obvious decrease after the abrasion test. The theoretical mechanism for the excellent anti-corrosion and tribological properties on the superhydrophobic surface were also analyzed respectively. The advantages of facile production, anti-corrosion, and tribological properties for the superhydrophobic steel surface make it to be a good candidate in practical applications.