Electroprobe Microanalysis Research Articles

High-throughput determination of interdiffusivity and atomic mobilities in bcc Ti–Cr–Mo alloys

A comprehensive understanding of the diffusion coefficients and atomic mobilities in the Ti–Cr–Mo system is crucial for establishing an atomic mobility database for titanium-based high-strength titanium alloys. In the present work, nine sets of solid/solid diffusion couples were prepared and measured in bcc Ti–Cr–Mo alloys, with the temperatures ranging from 1373 to 1473 K. Scanning electron microscopy (SEM), and Electro Probe Micro-Analysis (EPMA) techniques were used to respectively test its microstructure and composition distance. The diffusion coefficients in bcc Ti–Cr–Mo alloys were determined using the Matano-Kirkaldy method and numerical inverse method respectively. The diffusion coefficients obtained from the above two methods exhibit good consistency. The atomic mobility parameters for the Ti–Cr–Mo systems were provided with the assistance of HitDIC software. A three-dimensional plot of interdiffusivities was generated for chromium and molybdenum contents ranging from 0 to 20 mol % and 0–14 mol %. Moreover, the application of the Arrhenius equation enabled the determination of changes in frequency factors and activation energies concerning temperature and composition.

Growth kinetics of intermetallic compounds in Cu–Ti diffusion couples

Cu–Ti diffusion couples have been designed in the temperature range from 1013 K to 1163 K. Ensuing intermetallic compounds, including Cu4Ti, Cu4Ti3, CuTi, and the elusive CuTi2, have been identified in the diffusion zone. Growth kinetics and interdiffusion coefficients of involved Cu–Ti intermetallics have been quantified based on the measured compositional profiles using electro-probe microanalyzer. Moreover, activation energies required for the growth of these intermetallics have been confirmed to be 85.9 kJ mol−1 atom (Cu4Ti), 101.0 kJ mol−1 atom (Cu4Ti3), 70.0 kJ mol−1 atom (CuTi), and 64.9 kJ mol−1 atom (CuTi2), respectively. Our current findings could enable a rational design towards fully utilizing encrypted phases which are otherwise difficult to obtain.

Evolution of primary carbides during accelerated solidification process of high-carbon martensitic stainless steels

In order to evaluate the potential application advantage for development of sub-rapid cooling strip casting of high-carbon martensitic stainless steels, the effects of cooling rate on the solidification microstructure, solute element segregation, and primary carbide precipitation in high-carbon martensitic stainless steels were investigated using an association of high-temperature confocal laser scanning microscopy (HT-CLSM), optical microscopy (OM), scanning electron microscopy (SEM) and electro-probe microanalysis (EPMA). As a result, the microstructure becomes more refined and the secondary dendrite arm spacing (SDAS) decreases greatly by 51 μm from 65.9 μm as the increase of cooling rate from 30 to 6000 °C·min−1. The equation of SDAS versus cooling rate was formulated as λ2 = 191.62·RC−0.317. Solute elements are enriched in the inter-dendritic region, leading to the precipitation of primary carbides. The elemental segregation ratio reduces by more than 20 % for all elements, meanwhile, the size of primary carbides decreases significantly and the mean area fraction of the primary carbides decreases from 4.77 % to 0.82 % with increase of cooling rate from 30 to 6000 °C·min−1. Moreover, the reticulated carbides gradually become less continuous. Despite the type of carbide is not sensitive to the cooling rate, the content of Cr and Fe in the primary carbide is sensitive to cooling rate. Compared to the reported methods, sub-rapid cooling of strip casting shows great advantage in control of primary carbides of high-carbon martensitic stainless steels.

Sintering behavior of WC-10Co-V(C, N) nanocrystalline gradient cemented carbide

In the present study, nanocrystalline gradient cemented carbide with an average grain size of only 155 nm in tungsten carbide (WC) was prepared using V(C, N), and its sintering behavior was investigated. Scanning electron microscopy (SEM) and electro probe micro-analysis (EPMA) revealed that V(C, N) promotes the formation of a cubic carbide free layer (CCFL) and effectively suppresses the WC grains in the nanocrystal range at different sintering temperatures and holding times compared with Ti(C, N). The gradient cemented carbide had the highest hardness (2169 kg/mm2), the highest fracture toughness (11.94 MPa/m2), and the lowest friction coefficient (0.22) and wear resistance when the sintering temperature was 1400 °C and the holding time was 60 min. In addition, the cobalt (Co)-poor phenomenon occurred in the CCFL of the gradient cemented carbide, which was mainly related to the small radius of the capillaries in the nanocrystals.

Effects of Y addition on the microstructures and mechanical behavior of ZrOxNy/V2O3-Y nano-multilayered films

ZrOxNy/V2O3-Y nano-multilayered films with various yttrium additions were deposited on a Si substrate by reactive magnetron sputtering technique. The influences of yttrium addition on the microstructures, strengthening, and toughening characteristics of the nano-multilayered films were examined by the X-Ray diffraction, X-ray photoelectron spectroscopy, electro-probe microanalyzer, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and nanoindentation instrument. The experimental results showed that the template and modulation layers of the ZrOxNy/V2O3-Y nano-multilayered films consisted of ZrO2, ZrON, ZrN, and V2O3, Y2O3, respectively. Under the role of the template layer, the modulation layer maintained the epitaxial growth, which formed a coherent interface structure between the two sublayers as a function of the yttrium addition. When the Y/VO2 ratio was 1/2, the hardness, elastic modulus, and fracture toughness value could reach 15.1 GPa, 182.2 GPa, and 1.23 MPa m1/2, respectively. The incorporation of yttrium atoms gave rise to the phase transition, and the coherent interface inhibited the dislocation movement during nanoindentation loading, thus contributing to the optimal mechanical behavior of the ZrOxNy/V2O3-Y nano-multilayered films.

The role of Sc on the microstructures and mechanical properties of the Ni-rich NiTi alloy

The microstructure and mechanical properties of Ni-rich alloys with the addition of Sc range from 0.15 at% to 0.5 at% were investigated by X-ray diffractometer(XRD), electro-probe microanalyzer(EPMA), transmission electron microscopy(TEM), microhardness, room-temperature tensile properties, and room-temperature fracture toughness in this paper. The as-cast binary alloy and Sc modified ternary alloy are mainly composed of NiTi matrix phase, Ni4Ti3, and Ni3Ti2 phases. After solution treatment, the Ni3Ti2 phase is dissolved back into the matrix, and the alloy mainly consists of NiTi matrix phase and nanoscale Ni4Ti3 phases. The addition of Sc inhibits the precipitation of brittle Ti2Ni phases because O is prone to combine with Sc to form Sc2O3. Trace Sc addition has a weak effect on the microhardness, and it can improve the room-temperature tensile properties and fracture toughness of the alloy. Trace Sc addition moderately reduce the size of the Ni4Ti3 phases and change the aspect ratio of the Ni4Ti3 phases. The reduced precipitate size is responsible for the improvement of alloy mechanical properties.

Investigation on Optimal Ta/Cr Ratio of a Single Crystal Ni-Base Superalloy in View of the Isothermal Oxidation Behavior

The relative content of strengthening element tantalum (Ta) and oxidation-resistant element chromium (Cr) is an essential value for superalloys to obtain an excellent combination of oxidation resistance and mechanical properties. In the present paper, the isothermal oxidation behavior of several single crystal Ni-base superalloys with different Ta/Cr (wt. %, similarly hereinafter) ratios at 1000 °C in static air has been systematically investigated to explore the optimal Ta/Cr for excellent oxidation resistance. A detailed microstructure study using X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and an electro-probe microanalyzer (EPMA) was performed to reveal the oxidation products and mechanisms. For all alloys, a three-layer structured scale consisting of an outer (Cr, Al, Ti, Ni, Ta)-O layer, an inner Al2O3 layer and an inner nitride layer was formed. As Ta/Cr increased, the amounts of Ta-containing products, cracks, holes and inner nitride increased. Meanwhile, the completeness of the Al2O3 layer got worse. It was shown that if Ta/Cr ≤ 0.5, Ta increased the growth rate of Cr2O3 via the doping effect induced by Ta cations. If Ta/Cr > 0.5, Ta reduced the completeness of Cr2O3 through competitive growth of Ta2O5 and Cr2O3. A good oxidation performance can be expected with the value Ta/Cr ≤ 0.5.

Spheroidization of borosilicate glass powder by RF induction coupled plasma

The International Simple Glass (ISG) spherical particles were prepared by Ar–H2 radio-frequency (RF) plasma, the effect of experimental parameters on the volatilization and size distribution of spherical particles was studied. The results show that the spherical powders can be obtained by RF plasma. The spheroidized powders (112 μm) have a smaller diameter than starting particles (124 μm). The high spheroidization (98%) was achieved under low flow rate of carry gas and low feed rate. In addition, the volatilization of B2O3 and Na2O are 23.48% and 56.36%, respectively. The higher feed rate and flow rate of carry gas, the lower volatilization of B2O3 and Na2O and well-spheroidization rate. Meanwhile, the particle surface is not completely smooth at low flow rate of carry gas. The distribution of elements was studied by Electro-probe Microanalyzer (EPMA), which shows the distribution of element is nearly homogeneous that provides a possibility for subsequent research.

Investigation of nitrogen ionization state and its effect on the nitride layer during fiber laser gas nitriding of Ti-6Al-4V alloy

A nitride layer can be formed on the surface of a titanium alloy during laser gas nitriding, to improve the surface hardness and wear resistance of the titanium alloy. Importantly, the nitride layer is influenced by the nitrogen ionization state (nitrogen molecules or nitrogen atoms and ions). No research reports exist on the nitrogen ionization state or the effect on the nitride layer during fiber laser nitriding of titanium alloys. Radiation images that were taken with a high-speed camera and emission spectra that were collected with a fiber spectrometer were used to study the nitrogen ionization state. To study the effect of nitrogen ionization state on the nitride layer, the surface nitrogen and oxygen content were measured with an electro-probe microanalyzer, and the surface morphology of the nitride layer was studied by optical and scanning electron microscopy. The experimental results showed that the laser power density was too low to induce nitrogen ionization during fiber laser gas nitriding of the Ti-6Al-4V alloy. The nitrogen molecules had a lower energy than the nitrogen plasma (nitrogen atoms and ions) and a slower reaction rate with the titanium alloy, which resulted in a low nitrogen content and a few defects in the nitride layer. The relationship between the oxidation and nitriding was competitive; that is, nitrogen and oxygen competed to react with the titanium alloy. As such, a low nitrogen content led to a high oxygen content, and the nitride surface was golden-yellow in color with black markings. • Nitrogen did not ionize during fiber laser gas nitriding of Ti-6Al-4V alloy. • Molecular nitrogen is transferred into the molten pool. • Molecular nitrogen reduces the nitrogen content and minimizes nitride-layer defects. • A low nitrogen content led to a high oxygen content in the nitride layer.

The role of liquid feeding in nugget-edge cracking in resistance spot welding of dissimilar magnesium alloys

In fusion welding, cast magnesium alloys typically present higher sensitivity to liquation cracking than wrought alloys. In this study, a fluid-mechanics-based analytical model was established to investigate an unusual phenomenon: a lack of cracking in cast magnesium alloy while cracking took place in wrought magnesium alloy. This was observed in resistance spot welding, in which the pressure within the molten nugget allows the liquid to feed through the interface between the fusion zone and the partial melting zone, an aspect which is not generally considered in the typical criteria for liquation cracking. The analytical model shows that the liquid is easy to feed into the inter-grain zone of a cast coarse-grained metal but difficult to feed into wrought metal. The liquid feeding effect changes the composition of the inter-grain region, causing the semi-solid grains to bond to each other tightly in the cast magnesium alloy. Electro-probe microanalysis illustrates the mass transfer pattern of liquid feeding at the interface between the fusion zone and the partial melting zone. Magnesium alloys AZ31, AZ91, and ZK61 were selected to carry out resistance spot welding tests of which results match the theory raised in this work well.

Influence of CeO2 addition on forming quality and microstructure of TiCx-reinforced CrTi4-based laser cladding composite coating

TiCx-reinforced CrTi4-based composite coatings were successfully fabricated on a Ti6Al4V titanium alloy surface via laser cladding technology by using coaxial Ti6Al4V/NiCr-Cr3C2 mixed powders with different CeO2 contents (0, 1, 2, 3, and 4 wt%). The influence of CeO2 addition on the forming quality, phase composition, microstructure, and elemental distribution of the laser cladded coatings was investigated via penetrant flaw detection, optical microscopy, X-ray diffraction, scanning electron microscopy, energy spectrum analysis, electro-probe microanalysis, and transmission electron microscopy. The results showed that CeO2 addition can inhibit the formation of cracks and pores. The least number of cracks and pores were observed upon the addition of 2 wt% and 3 wt% of CeO2, respectively. The phases in the coatings consisted of vacant titanium carbide (TiCx) and β solid solution (CrTi4). The morphologies of TiCx in the transition, cladding, and bonding zones exhibited distinct granular, dendritic, and short needle-like differences, respectively. Notably, the addition of CeO2 did not affect the phase composition, but it significantly influenced the content of dendritic TiCx. The dendritic TiCx content was minimum (35%) for a CeO2 content of 3 wt%. The dendritic TiCx was mainly enriched by Ti and C, and the content of C in primary dendrites was higher than that in secondary dendrites. The Ce and O atoms from CeO2 decomposition were recrystallised as CeO2 and Ce2O3, and distributed in the interphase boundary between TiCx and CrTi4, within the TiCx and CrTi4 grains, and at their grain boundaries. The Al, V, and Cr elements were uniformly distributed in the matrix phase (CrTi4), while elements Ni and Cr appeared segregated.

Kinetics of Slag Reduction in Silicomanganese Production

In this study, the reduction of three silicomanganese charges prepared from industrial raw materials was investigated under isothermal conditions between 1783 K and 1933 K (1510 °C and 1660 °C). The main reactions examined are MnO and SiO2 slag reduction following the chemical equations MnO(l) + C = Mn(l) + CO(g) and SiO2(l) + 2C = Si(l) + 2CO(g). The charges containing a combination of Assmang ore, Comilog ore, high-carbon FeMn slag with quartz were pre-reduced, melted to a MnO-SiO2-Al2O3-MgO-CaO quinary slag and reduced in presence of coke using a thermogravimetric set-up. The reduced slags were further analyzed using electro-probe micro-analysis to evaluate their MnO and SiO2 contents. It is observed that the reduction pathway occurred in two stages: a first slow and stable stage was followed by a rapid rate increase during the second stage. The rate change shift between the two stages was found to depend on the initial charge’s composition and the extent of reduction, but not on the temperature. Using an established rate equation, the kinetics of MnO and SiO2 reduction were modeled over the first stage. A good fit was obtained between simulated and experimental data.

Interfacial microstructure and mechanical properties of dissimilar aluminum/steel joint fabricated via refilled friction stir spot welding

Aluminum alloy and steel hybrid structures offer clear advantages in weight reduction and energy conservation for the automotive industry. This paper exhibits sound refilled friction stir spot welded joints between the aluminum alloy and ST16 steel sheets with the maximum tensile/shear and cross-tension fracture loads of 3745 N and 1073 N, respectively. All samples failed through the interface of aluminum alloy/steel joints during tensile/shear test and cross-tension test. The microstructure and fracture mode of the joints were studied with the scanning electron microscope, electro-probe microanalyzer and X-ray diffraction. For the joints where the sleeve had not plunged into the ST16 steel, the effect of the sleeve plunging depth and rotation speed on the tensile/shear fracture load cannot be identified, as an intermetallic compounds layer formed between Al and Fe, which was almost uniform across the interface. The mechanical performance of joints increased dramatically when the sleeve plunged into the ST16 steel because of metallurgical bonding and mechanical interlocking in the sleeve-affected zone. However, this process caused considerable wear to the tool and shortened its service life. The bonding mechanism was investigated by studying joints between the aluminum alloy and galvanized steel for the same welding parameters.

Creep rupture properties of dissimilar metal weld between Inconel 617B and modified 9%Cr martensitic steel

In this study, creep rupture behaviors and rupture mechanism of dissimilar metal weld (DMW) between Inconel 617B and modified 9%Cr martensitic heat-resistant steel (hereinafter referred to 9Cr steel) with Inconel 617 filler metal were investigated. Creep tests were carried out at 600 °C and 620 °C in the stress range 130–240 MPa. Optical microscopy (OM), scanning electron microscopy (SEM), Electro-Probe Microanalyzer (EPMA) and micro-hardness test were used to examine the creep rupture behaviors and microstructure characteristics of the DMW. The results indicated that under different creep conditions, the rupture locations varied, including 9Cr base metal (BM), the intercritical heat affected zone (ICHAZ) of 9Cr steel, and the interface between weld metal (WM) and 9Cr steel. The rupture behavior occurring in the 9Cr BM was mainly controlled by plastic deformation, and the growth and coalescence of dimples eventually led to transgranular fracture. The rupture behavior occurring in the ICHAZ was caused by type IV crack due to matrix softening and lack of sufficient precipitates pinning the grain boundaries (GBs). The rupture behavior occurring at the interface was mainly related to the oxide notch forming at the interface. The formation and propagation of the oxide notch resulted in the interfacial failure.

Corrosion Performance of TRIP Steels under Atmospheric Environment

Atmospheric corrosion test of TRIP steels was conducted in laboratory. The surface morphologies of the specimens were analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD) and electro-probe microanalysis (EPMA). Corrosion performance of TRIP steels under atmospheric environment was investigated by discussing the protective mechanism. The corrosion rates of steel A are significantly greater than steel B in atmospheric environment tests. The enhancement of corrosion performance of TRIP steel is attributed to the additions of alloying elements, such as P, Cr, Cu, and Ni etc.. The alloying elements increase the compactness and densification of rust layers. Electrochemical characteristic of TRIP steel is improved by means of the enhancement of the thermodynamic stability.

Effects of Boron Content on microstructure and mechanical properties of AlFeCoNiBx High Entropy Alloy Prepared by vacuum arc melting

The AlFeCoNiBx (x = 0, 0.05, 0.10, 0.15, 0.2) high entropy alloys are prepared by vacuum arc melting. The effect of B on the microstructure and mechanical behaviors of the alloys are systematically investigated. X-Ray Diffraction results and Electro-Probe Microanalyzer results show that small amount of B atoms are dissolved into B2 matrix and the other B atoms result in the formation of FCC phase. The addition of B content leads to transformation of microstructure from pure B2 phase to “B2 phase + particle FCC structure” and then to “B2 phase + eutectic structure”. Eutectic structure consists of FCC1 phase and FCC2 phase. FCC1 phase is rich in Co and Ni and FCC2 phase is rich in B, Fe and Co. With the increase of B content, grain size of B2 phase firstly reduce and then increase. By increasing the B content from 0 to 0.2, fracture strength and plastic strain increase from 850 MPa to 2293 MPa and 0.07 to 0.27 respectively. The increase of yield strength is due to the solid solution strengthening and fine grain strengthening of boron atom. While, the increase of plasticity is due to the formation of FCC eutectic structure.

Dendritic branching patterns in platforms of complex Ni-based single crystal castings

Dendritic branching patterns at variable cross-sections in Ni-based single crystal (SX) castings of different generations were investigated using optical microscope (OM), electro probe microanalyzer (EPMA), differential scanning calorimeter (DSC), Thermo-Cal software and Pro-CAST software. Results show that the dendritic branching patterns are similar in outward platform in SXs of different generations. That is, the primary dendrites (PDs) are introduced into the platform by developing a series of secondary dendrites (SDs) to occupy the bottom of the platform, and the ternary dendrites (TDs) originating from these SDs grow upward to fill up the platform. With the SX generation increasing, the undercooling of melts in the inward platform increases significantly due to the increasing alloying elements and the segregation in the directional solidification (DS) process, and the growth velocity of the dendrite tip increases according to the dynamic model of dendrite growth, which is beneficial for the high-order dendrite development. The stronger dendritic branching ability is shown in the inward platform of the higher generation Ni-based SX.

Abnormal elemental redistribution in oxyfluoride glasses induced by high repetition rate femtosecond laser

We report on the elemental redistribution behavior in oxyfluoride glasses with a high repetition rate near-infrared femtosecond laser. Elemental analysis by an electro-probe microanalyzer demonstrates that the redistributions of Ca2+ and Yb3+ ions change dramatically with pulse energy, which are quite different compared with previous reported results. Confocal fluorescence spectra of Yb3+ ions demonstrate that the luminescence intensity changes obviously with the elemental redistribution. The mechanism of the observed phenomenon is discussed. This observation may have potential applications in the fabrication of micro-optical devices.

Cr or C controlled formation of transition martensite in dissimilar metal weld

In this study, Ta and Y, were added as inducing elements into low-alloy steel and Ni-based alloy dissimilar metal weld (DMW), to separately promote the interfacial diffusion of C and Cr, such that the formation of transition martensites was affected as well. The results show that the samples with inducing elements have broad transition zones compared with the control sample, and the C-rich and Cr-rich transition martensite layers can be distinguished by scanning electron microscopy. Energy-dispersive spectroscopic analysis and electro-probe microanalyzer indicates that the width of the transition martensite in the DMW is determined by the content and diffusion range of Cr rather than those of C. The C-rich martensite laths grow in various directions, whereas the Cr-rich martensite laths are at an angle of ~45° with respect to the fusion line. Kernel average misorientation maps demonstrate that when the C-rich martensite layer appears alone in the transition zone, the stress of the weld interface is high. When the C-rich and Cr-rich martensite layers appear together, the interfacial stress significantly decreases. X-ray diffraction spectra show that (110)α is the main peak of Cr-rich martensite, (111)γ is the main peak of the unconverted face-centered-cubic phase, and these two directions can fit each other well. The formation of the C-rich martensite layer is primarily driven by the chemical potential, whereas the formation of the Cr-rich martensite layer is primarily driven by the welding stress.

Effect of trace Ce and B additions on the microstructure of Nb-3Si-22Ti alloys

The effects of trace Ce and B additions on the microstructure Nb-22Ti-3Si alloys were studied. The microstructure of the alloys was observed by scanning electron microscope (SEM), and their phase compositions were analyzed with X-ray diffraction (XRD) and Electro-Probe micro-analyzer (EPMA). The distributions of the elements were detected by Spectrum analyzer. The interface of the phases in the alloys was investigated by transmission electron microscopy (TEM). The results indicated that two phases of Nbss and Nb3Si presented in Nb-22Ti-3Si, Nb-22Ti-3Si-0.2Ce and Nb-22Ti-3Si-0.2B alloys. The segregation of Ti at the interface between Nbss and Nb3Si was promoted and the volume fraction of silicides in the alloy increased with the trace B and Ce addition to the Nb-22Ti-3Si alloy respectively. And there was no single and definite orientation relationship between Nb3Si and Nbss in Nb-22Ti-3Si, Nb-22Ti-3Si-0.2Ce and Nb-22Ti-3Si-0.2B alloys. Compared with the Nb-22Ti-3Si alloy, the Nbss superlattice structure was found in Nb-22Ti-3Si-0.2Ce and Nb-22Ti-3Si-0.2B alloys.