Hybrid Laser-GMAW Welding of High Strength Quenched-Tempered Steels

High-strength quenched and tempered (HSQT) steels have been widely used in structural applications where light weight is of primary design interest.Gas metal arc welding is a common way to join QT steels.When GMAW is used to join the HSQT steel,multi-pass is usually required to achieve full penetration.In addition,weld crack is often observed because of HSQT steel’s high susceptibility to hydrogen embrittlement.In addition,due to the large amount of heat input from the arc,the heat affected zone is often softened.This reduces the ductility and strength of welds and makes the weld weaker than the base metal.In this study,a hybrid laser/GMAW process is proposed to produce butt joint for 6.5mm thick HSQT A514 steel plate.Hydrogen diffusion mechanism is first discusses for GMAW and hybrid laser-GMAW welding processes.Metal transfer mode during the hybrid laser/GMAW welding process is also analyzed.A high speed CCD camera with 4000 frame/second is used to monitor the welding process in real time.Welds obtained by GMAW and hybrid laser/GMAW techniques are compared and tested by static lap shear and dynamic impact.Effects of gap between two metal plates and laser beam/GMAW torch spacing on weld property are studied.By appropriately choosing these two parameters,crack-free butt joints with full penetration can be successfully obtained by the hybrid laser/GMAW welding process for HSQT A514 steel plate.     

Everything is Ready for AFC-11

The 11th Asian Foundry Congress (AFC-11) is to be held in Guangzhou China, from November 12 to 15, 2011. Foundry Institution of Chinese Mechanical Engineering Society (FICMES) will be the host of the event. The congress will be an opportunity for the international community to exchange ideas and develop a common vision for the future of world foundry industry. It will also offer a better chance for all participants to have a deeper understanding of the traditional Chinese culture. As the host of AFC-11, we will do our best to provide professional service for all participants, and make the AFC-11 a full success. After several months’careful preparation we are now ready for your coming and joining. The AFC-11 draws much attention of not only the Asian but also the global foundrymen. By August 10, 2011 totally 85 abstracts of technical papers from 15 countries and regions were received, which include the following titles list by country’s name:     

MICROMECHANICS OF THE DAMAGE-INDUCED CELLULAR MICROSTRUCTURE IN SINGLE CRYSTAL Ni-BASED SUPERALLOYS

An analytical method to investigate the morphological evolution of the cellular microstructure is explored and proposed. The method is essentially based on the Eshelby‘s micromechanics theory, and it is extended so as to be applied for a material system containing inclusions with high volume fraction, by employing the average stress field approximation by Mori and Tanaka. The proposed method enables us to discuss a stable shape of precipitate in the material system, which must be influenced by many factors: e.g., volume fraction of precipitate; Young‘s modulus ratio and lattice misfit between matrix and precipitate; external stress field in multiaxial state; and heterogeneity of plastic strain between matrix and precipitate. A series of numerical calculations were summarized on stable shape maps. The application of the method to predict the γ‘ rafting in superaUoys during creep showed that the heterogeneity of plastic strain between matrix and precipitates may play a significant role in the shape stability of the precipitate. Furthermore, it was shown that the method was successfully applied to estimate the morphology of the cellular microstructure formed in CMSX-4 single crystal Ni-based superaUoy.     

The Work of NAHE on Promotion of Achievements in Hydrogen Energy in Russia and of Advantages of Using Platinoids in the Energy Sector

National Association for Hydrogen Energy (NAHE) was established in 2003 to facilitate the effective integration of the Russian Federation into the world hydrogen economy. The priority for the Association is to create legislation and basic standards which necessary for the successful development of hydrogen energy, promote this sector to a large public and to support the development of those priority areas, where Russia has the best prospects to take a rightful place in the international division of labour (atomic hydrogen energy, fuel cells, hydrogen vehicles). Hydrogen Energy, National Association for Hydrogen Energy By now the Association has developed a draft technical regulation on security devices and systems for     

Critical Cooling Rate for the Glass Formation of Ferromagnetic Fe80P13C7 Alloy

In this paper the critical cooling rate, Rc, for the glass formation of Fe80P13C7 alloy has been determined using both Uhlmann’s and Barandiaran-Colmenero’s method. In Uhlmann’s method, all kinds of the expressions of △Gl-s (T) and η (T) determined using the different modes and methods had been investigated. It is indicated that the R c for the glass formation of Fe80P13C7 alloy can be estimated to be 349 K/s by Uhlmann’s method based on the appropriate expressions of △Gl-s (T) and η (T). The calculated result accords with our experimental result. The R c for the glass formation of Fe80P13C7 alloy has also been determined to be 0.49 K/s using Barandiaran-Colmenero’s method. This resultant R c is unreasonable low and it indicates that Barandiaran-Colmenero’s method does not suit to Fe-based alloy.     

Phase transformations and mechanical properties of a Ti36Nb5Zr alloy subjected to thermomechanical treatments

Various solid state phase transformations exist in metastable β-type Ti alloys,which can be employed to optimize the mechanical properties.In this paper,synchrotron X-ray diffraction(SXRD)experiments were carried out to study the phase transformations of a Ti36Nb5Zr alloy subjected to different thermomechanical treatments.Furthermore,the correlation between the phase constitutions and the mechanical properties was discussed.The a" texture formed,and high-density defects were introduced after cold rolling of the solution treated specimen,leading to the decrease in Young’s modulus and the increase in strength.The cold-rolled specimens were then annealed at temperatures from 423 to 773 K for 30 min.Both the Young’s modulus and strength increased with annealing temperatures increasing up to 673 K,which resulted from the precipitation of the ω and/or α phases.With further increase in annealing temperatures to 773 K,the β→α precipitation replaced the β→ω_iso phase transformation,and the density of defects decreased,leading to the decrease in both the Young’s modulus and strength.These results provide theoretical basis for the design biomedical Ti alloys with both low Young’s modulus and high strength.     

Micro-scale Abrasion and Medium Load Multiple Scratch Tests of PVD Coatings.

Micro-scale abrasion testing is widely used to determine the abrasion resistance of thin film coatings; it is a simple technique that can easily be used as part of a quality control procedure, but it has got the disadvantage of not allowing an easy study of the wear mechanisms involved: it is difficult to estimate the load applied on each abrasive particles in the contact between the loaded ball and the specimen. The possibility of using progressive loading scratch testing, a method widely used to assess the adhesion of thin film coatings, to model the abrasive wear of coatings has been studied in the past; the use of multiple scratch tests to study the wear mechanisms corresponding to a single abrasion scratch event has also been studied in the case of bulk materials (ceramics and hard metals). Two coatings, deposited by Closed Field Unbalanced Magnetron Sputter Ion Plating (CFUBMSIP) on ASP23 powder metallurgy steel substrate are chosen to be representative of the use of protective coatings in industry: titanium nitride, which is widely used to prevent tool wear, and TCL Graphit-iC^TM, which is widely used as a wear resistant solid lubricant coating. The two coatings are first characterised by using a standard quality control procedure: their thickness is determined by the cap grinding method, their adhesion by progressive loading scratch. Then micro-scale abrasion tests performed with a slurry at a concentration which promotes grooving wear, and medium load multiple scratch tests performed with diamond indenters are completed; the results of these tests are analysed and compared to determine if there is any correlation between the two sets of results; the multiple scratch tests wear tracks are also observed to determine the wear mechanisms involved.     

Differences of transformation behavior between Ni-rich TiNi shape memory films and alloys

The differences of transformation behavior between Ni-rich TiNi shape memory film (SMF) and shape memory alloy (SMA) age-treated at 773K after solution-treatment at 973K have been investigated, using Ti-51.5Ni thin film and Ti-51.5Ni bulk alloy as examples, by differential scanning calorimetry (DSC), SEM and EDX. It is found that the age-treated Ni-rich TiNi SMF and SMA are of the same types of transformation, i.e., A→R→M (during cooling), and M→A (during heating) (A: parent phase; R: R-phase; M: martensite); the transformation temperature of the TiNi SMF is lower than that of the SMA, but the SMFs hysteresis is larger. The transformation heat of the TiNi SMF and SMA is nearly the same. The reason that TiNi SMFs strain is sensitive to temperature is not hysteresis, but its thickness is thinner, and the temperature is easy to distribute homogeneously.     

Microstructure Evolution and Mechanical Hardening of Hypereutectoid Pearlitic Steel During Cold Rolling

The microstructure evolution of different cold rolling reductions (from 0 to 81.6%) was studied by SEM (scanning electron microscopy) and TEM (transmission electron microscope). The study showed that the orientation multiplicity of pearlitic lamellas resulted in inhomogeneous deformation of different pearlitic lamellas, and with the increase of reduction, the microstructure underwent a course of "homogeneity → inhomogeneity → homogeneity". The result of XRD (X-ray diffraction) analysis indicated that cementite did not decompose and dissolve into ferrite; the results of the mechanical property test suggested that the relationship between Rp0.2 (yield strength) and ε (true strain) was in good agreement with Hollomon relationship. With the equation Rp0.2 = 1465ε0.18, the yield strength of the steel in different reductions could be well predicted.     

A new dynamic method for measuring hydrogen partial pressure in molten aluminum alloy

Hydrogen partial pressure is an important parameter to calculate hydrogen concentration levels in molten aluminum alloy. A new dynamic method for measuring hydrogen partial pressure in molten aluminum alloy is studied. Dynamic and rapid measurement is realized through changing the volume of the vacuum chamber and calculating the pressure difference ΔP between the theoretical and measured pressures in the vacuum chamber. Positive ΔP indicates hydrogen transmits from melt to vacuum chamber and negative ΔP means the reverse. When ΔP is equal to zero, hydrogen transmitted from both sides reached a state of dynamical equilibrium and the pressure in the vacuum chamber is equal to the hydrogen partial pressure in the molten aluminum alloy. Compared with other existing measuring methods, the new method can significantly shorten the testing time and reduce measuring cost.     

Local Strain Energy Density Applied to Bainitic Functionally Graded Steels Plates Under Mixed-Mode(Ⅰ+Ⅱ) Loading

In this paper, the averaged value of the strain energy density(SED) over a control volume is used to predict the critical load of V-notched specimens made of functionally graded steels(FGSs) under mixed-mode loading. The studied FGSs contain ferritic and austenite phases in addition to bainitic layer produced by electroslag remelting. The mechanismbased strain gradient plasticity theory is used to determine the flow stress(yield stress or ultimate stress) of each layer. The Young’s modulus and the Poisson’s ratio have been assumed to be constant, while other mechanical properties vary exponentially along the specimen width. The control volume is centered in relation to the maximum principal stress present on the notch edge and assumes a crescent shape. The points belonging to the volume perimeter are obtained numerically. In the present contribution, the effects of notch radius and notch depth on the SED and the critical load are studied. The notch radius varies from 0.2 to 2.0 mm, and the notch depth varies from 5 to 7 mm. By using the SED approach and finite element simulations, the critical load is determined, and the obtained results show a sound agreement with the experimental results.     

Influence of thermo hydrogen treatment on microstructure and mechanical properties of Ti-5Al-2.5Sn ELI alloy

Thermo hydrogen treatment(THT) of titanium is a process in which hydrogen is used as a temporary alloying element in titanium alloys. It is an attractive approach for controlling the microstructure and thereby improving the final mechanical properties. In the present study, the microstructure of the original(non-hydrogenated) sample has only α phase and the grains is coarse with an average size of ~ 650 μm. While the grain size of thermo hydrogen treated Ti-5Al-2.5Sn ELI alloy became finer and the mechanical properties were improved significantly. When the hydrogen content of the hydrogenated Ti-5Al-2.5Sn ELI alloy is 0.321 wt.%, β phase and δ titanium hydride appear. Also the average grain size decreases to 450 μm. When the hydrogen content is 0.515 wt.%, the grain size decreases to 220 μm. The mechanical properties were tested after dehydrogenation, and the mechanical properties improved significantly compared to the unhydrogenated specimens. The tensile strength of the Ti-5Al-2.5Sn ELI alloy improved by 17.7% when the hydrogen content increased to 0.920 wt.%, at the same time the percentage reduction of area(Z) increased by 33% and the impact toughness increased by 37%.     

Effects of cooling rate on solidification behavior of dilute Al-Sc and Al-Sc-Zr solid solution

Six alloys with different compositions of Al-0.1%Sc, Al-0.3%Sc, Al-0.3%Zr, Al-0.1%Sc-0.1%Zr,Al-0.3%Sc-0.1%Zr and Al-0.3%Sc-0.3%Zr were prepared by casting in a wedge shaped copper mould. The hardness test, microstructure observation, and DSC thermal analysis were applied to fully investigate the solidification behavior of the wedge tip (whose cooling rate is 1000 K/s) and the top surface (cooling rate 100 K/s) of each casting. The results show that the cast structures in the hypoeutectic region of AI-Sc alloys are slightly affected by cooling rates during the solidification. In the case of hypereutectic alloy of Al-0.3%Sc-0.3%Zr, the cast grains were remarkably refined under the condition of a 100 K/s cooling rate, however, under a 1000 K/s cooling rate condition,solute atoms contribute nothing to the grain-refinement, due to the eutectic concentration becomes higher. The hardness can be improved to a greater degree by Sc single addition, compared to single Zr addition, but it can be improved even greater when Sc added together with Zr. It is sensitive to cooling rate, the higher the cooling rate, thegreater the hardness. By combining the results of TEM examination and DSC analysis, it can be seen that a supersaturated Al solid solution forms during the solidification, and the solubility of Sc in Al solution can be improved by increasing the cooling rate.     

Transformation Mechanism of (γ+γ') and the Effect of Cooling Rate on the Final Solidification of U720Li Alloy

The transformation mechanism of(γ+γ') was studied by analyzing the microstructure and elemental distribution of the U720 Li samples heated at 1250℃ and cooled at the rates in the range of 1–100℃/s. Although the(γ+γ') is deemed to be formed by a eutectic reaction and has been called eutectic(γ+γ'), it was found in the present study that the(γ+γ') precipitation begins with a peritectic reaction of(L+γ) ? γ', and develops by the eutectic reaction of L ?(γ+γ'). The energy for the γ' nucleation is low because the interfacial energy for the γ/γ' interface is about one-tenth of the solid/liquid interface, and hence, the nucleation rate is high and the fine structure of(γ+γ') is formed at the initial precipitation stage. The γ and γ'in(γ+γ') tend to grow into a lamellar structure because it is difficult for them to nucleate directly from the residual liquids, and hence, the γ' precipitates naturally tend to grow divergently direction of the regions rich in Al and Ti, forming a fan-like structure of the(γ+γ'). As a result, the γ' precipitates will coarsen finally because the space between them is enlarged. The solidification of the final residual liquids is a diffusion dependent process. When cooled at a higher rate, a higher degree of super cooling is reached and finally the solidification is finished by the pseudoeutectic reaction of L ?(γ+ boride) and L ?(γ+η), which can absorb Zr and B. When cooled at a rate low enough,most of the residual liquids are consumed by the(γ+γ') growth due to the sufficient diffusion, and the boride and Zrbearing phase are precipitated at a quasi-equilibrium state. Under this condition, Ti is depleted at the(γ+γ') growth front.However, the g-Ni_3 Ti phase is formed there occasionally due to the boride precipitation, because the compositions of the two phases are complementary.     

DFT research on activation of sphalerite

Activation of sphalerite ZnS, (Zn, Fe)S, (Zn, Cu)S were carried out using the density functional theory (DFT) method. The electronic structures and related properties of three kind of zinc sulfide compounds were investigated. In addition, the relation between electronic structure and flotation behavior was discussed. The results show that, ZnS has a broader band gap than (Zn,Cu)S and (Zn,Fe)S do, and it has low electrochemistry activity to react with flotation collectors to render the surface hydrophobic. When the Zn atom in ZnS is replaced by Cu atom,the band gap will be reduced, and the top valence band will be occupied by Cu 3d orbit, thus it is beneficial to the interaction between mineral surface and collector.     

NUMERICAL SIMULATION OF ULTRASONIC NONDESTRUCTIVE TESTING FOR WELDS

A computer simulation technique for ultrasonic propagation is utilized for the simulation of ultrasonic nondestructive testing (NDT).In this paper,one goal of the simulation is to compute ultrasonic field radiated by arbitrary transducers into pieces under examination.The other simulates a testing experiment.The simulation approach is based on the model for the computation of the ultrasonic field in isotropic media radiated from actual NDT transducers.After the field is known, remaining to be modeled is the interaction between this field and the scatters (defect) and the echo structure. The model of beam-defect interaction is based on the Kirchhoff‘s diffraction approximations theory applied to elastodynamics.We assumed that the incident wave fronts on the defect are plane in the case of a focused immersed transducer and material is isotropic and homogeneous.The simulating results demonstrate that the model in ultrasonic NDT of welds is practical in further research and useful in optimizing testing configurations.     

Precise point positioning and its application in mining deformation monitoring

Precise point positioning (PPP)-based deformation monitoring scheme is presented for the use in mining deformation monitoring. Within the solutions of daily observation, outliers are detected and removed to avoid any potential misinterpretation of the results and then the deformation can be extracted by the coordinate differences between the two consecutive solutions. Meanwhile, because of the special location of a rover station in mining areas, the satellite geometry may be insufficient for a reasonable PPP solution, and the multipath impact an also be significant. Therefore, it is necessary to predict the satellite geometry before any daily observation. To evaluate the ability of extracting the deformation using the PPP-based method, various quality measures were introduced. The results of three datasets of the same station show that the precision of deformation monitored by PPP can reach up to cm level and even mm level.     

Application of magnetic Barkhausen noise in non-destructive testing fields of residual stress

Magnetic Barkhausen noise （ MBN） is a phenomenon of electromagnetic energy due to the movement of magnetic domain walls inside ferromagnetic materials when they are locally magnetized by an alternating magnetic fields. According to Faraday＇s law of electromagnetic induction, the noise can be received by the coil attached to the surface of the material being magnetized and the noise carries the message of the characteristics of the material such as stresses, hardness, phase content, etc. Based on the characteristic of the noise, researching about the relationship between the residual stress in the welding assembly and the noise are carried out. Furthermore, data process is performed by RMS （Root Mean Square） equation and Power Spectrum analysis.     

The deformation and cooling of ceramic particles sprayed with a thermal radio-frequency plasma under atmospheric conditions

Common thermal-spray techniques use the strong acceleration of powder particles to produce dense ceramic coatings with high bond strength. The residence time of the powder particles within the plasma jet is correspondingly low, and only relatively small particles can be molten. In this work, on the contrary, an inductively coupled radio-frequency (RF) inductively coupled plasma (ICP) torch was used to spray large oxide-ceramic powder particles under atmospheric conditions. The slow plasma flow of a RF plasma leads to large residence times of the powder particles, so that the powder size of the feedstock can be 100 μm and more. It was observed that these particles will not be strongly accelerated in the plasma and that their velocity at the moment of impact is in the range of 10 to 20 m/s. Ceramic coatings were ICP sprayed with a low porosity and a high bond strength, similar to direct current (DC) or high-velocity-oxygen-fuel (HVOF) sprayed coatings. The morphology of ICP-sprayed particles on smooth steel surfaces, as a function of the surface temperature, is described and compared with DC plasma-sprayed splats. Furthermore, the degree of deformation was measured and determined by different models, and the pronounced contact zones formed between the pancake and the substrate were investigated. The ICP-sprayed ceramic coatings show some special properties, such as the absence of metastable crystalline phases, which are common in other spray technologies.     

A new process of manufacturing “Oxygen-free” Gd

Abstract: “Oxygen-free” Gd was fabricated by Hydrogen plasma arc melting (HPAM). The Oxygen concentration had a tendency of reduction compared with that done by Ar PAM. All these are attributable to the process of melting, especially the hydrogen atoms dissociated and activated in high temperature HPAM. An increased diffusion of oxygen in Gd-O solid solution to the surface is also believed to play an important role in removal of oxygen. The optical emission spectroscopy (OES) measurement is used to confirm the substances which were involved in the plasma like Ar I, Ar II and H I and some possible reactions. The effect of H with thermodynamic estimation is discussed in details.