Search

Carbon inoculation is a well-known method to grain refine Mg-Al-based alloys, but the underlying mechanisms remain unclear. Here we study carbides and their relationship with the surrounding magnesium in inoculated Mg-9Al-0.7Zn-0.2Mn (wt.%, AZ91) by combining controlled solidification experiments with analytical electron microscopy. Up to three carbides formed depending on the solidification conditions: T1-Al 2 MgC 2 , T2-Al 2 MgC 2 and Al 4 C 3. All carbides grew with their basal planes as the largest facet and the trigonal carbides, T2-Al 2 MgC 2 and Al 4 C 3 , often contained basal planar growth faults and growth twins. In many cases there was evidence of eutectic-like Al 4 C 3 growing off T2-Al 2 MgC 2 , indicating that Al 4 C 3 formed later in the solidification sequence after α-Mg had nucleated, consistent with recent phase diagram calculations. A basal-to-basal OR was measured between α-Mg and T2-Al 2 MgC 2 for approximately 10% of particles, indicating that T2-Al 2 MgC 2 is the heterogeneous nucleant for α-Mg. Particles with the OR had diverse locations including near grain boundaries and near the centre of grains, suggesting that the OR can form by pushing and engulfment as well as by heterogeneous nucleation. • Grain refinement of a Mg-Al-Zn-Mn alloy was achieved by carbon inoculation. • Three carbides were found and their crystal growth was studied. • T2-Al 2 MgC 2 was proven to lead to heterogeneous nucleation of the grains. [ABSTRACT FROM AUTHOR]

The high-temperature deformation mechanism and processing maps of cast Al 0.5 CoCrFeMnNi that comprises face centered cubic (FCC) and body centered cubic (BCC) phases (where BCC phase is a minor phase) were studied at temperatures in the range of 1023–1323 K and at strain rates in the range of 10−3 to 101 s−1. During hot compressive deformation, the hard BCC phase provided nucleation sites for dynamically recrystallized (DRXed) grains in the soft FCC matrix through particle stimulated nucleation (PSN). The PSN-induced DRX occurred by continuous dynamic recrystallization (CDRX) and CDRX accelerated as temperature increased. Due to the effect of PSN, the fraction of DRXed grains was notably higher and the size of the DRXed grain size was considerably smaller in Al 0.5 CoCrFeMnNi than those in the equiatomic CoCrFeMnNi with a single FCC phase. The effect of the BCC phase on the fraction of DRXed grains was pronounced even at the high strain rate of 10 s-1 in the temperature range between 1173 and 1323 K, which is advantageous for the practical use of cast Al 0.5 CoCrFeMnNi in the hot-working industry. Solute drag creep appeared at low strain rates and at high temperatures as the rate-controlling deformation mechanism due to the presence of Al solutes in the FCC matrix phase. The activation energy for plastic flow associated with solute drag creep was estimated to be 251 kJ/mol. This value most likely represents the activation energy for the diffusivity of aluminum solutes in Al 0.5 CoCrFeMnNi. The solute drag creep behavior could be predicted by the Weertman model, suggesting that Al 0.5 CoCrFeMnNi behaves similar to a typical class I type solid solution metal alloy. By adding aluminum to CoCrFeMnNi, the hot workability can be greatly improved according to the processing maps. The power dissipation efficiency notably increases, and the flow instability regime decreases in size. • High-temperature deformation mechanism and processing maps of Al 0.5 CoCrFeMnNi were studied. • Solute drag creep appeared as the rate-controlling deformation mechanism due to presence of Al. • Hot workability was greatly improved due to the formation of BCC phase by the addition of Al. • Continuous dynamic recrystallization simultaneously occurred with the PSN-induced DRX. [ABSTRACT FROM AUTHOR]

Abstract A thermodynamic description of the Fe-Te system needs to be developed in order to model internal corrosion by fission products in fuel pins of Generation IV nuclear reactors. In preparation for a thermodynamic assessment of the system, an experimental study has been performed in order to clarify some unknown or conflicting phase diagram data. New phase diagram data have been obtained using Differential Thermal Analysis and isothermal heat treatments followed by electron microscopy with EDS and WDS analysis. The DTA analysis revealed new phase boundary data, and confirmed a very steep Fe-rich liquidus, supporting the possibility of a liquid miscibility gap in the Fe-FeTe region. The analyses also confirmed the probable eutectoid reaction δ → β + δ ' at 523 ° C. The invariant arrests of the unknown γ phase were consistent with information available in literature, but the phase was not identified via XRD of samples at its postulated composition. However, metallography of the samples revealed an unexpected microstructure pertaining to the δ phase, which might be the γ phase, and is discussed in this paper. The monoclinic space group C 2 / m is proposed for the δ phase based on XRD. The collected data will be used together with that available in literature to perform a thermodynamic Calphad assessment in a subsequent paper Part II: Thermodynamic modeling. Highlights • Steep liquidus supports miscibility gap in the Fe-FeTe composition range. • Microstructures of gamma phase suggest structure related to delta phase. • Improved DTA measurement suggest gamma phase non-stoichiometry. • Proposed delta/delta' phase eutectoid transition identified at 523 °C. • C 2/ m proposed as space group of monoclinic delta phase. [ABSTRACT FROM AUTHOR]

In the present work, the microstructure modifications and corrosion behaviors of a Mg-4Sm alloy treated by high current pulsed electron beam (HCPEB) with different number of pulses were investigated. The microstructure, composition and phase component in the treated surface layers were characterized by using optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS) and transmission electron microscope (TEM). The results showed the dissolution of large Mg 41 Sm 5 segregates, the formation of Mg 41 Sm 5 nano-precipitates and twins in the surface layers after treatments. Electrical impedance spectroscopy (EIS) and polarization tests in the 3.5 wt% NaCl solution showed that the 15 pulses treated Mg-4Sm alloy sample exhibited the lowest corrosion current density, highest corrosion potential and polarization resistance among all samples. This is attributed to the homogeneous microstructure and composition with fewer defects in the surface layer after sufficient number of HCPEB pulses. [ABSTRACT FROM AUTHOR]

Ti-Ag alloy is characterized by a flat liquidus line in the binary phase diagram. The microstructure of binary Ti-Ag alloys was investigated in terms of liquid phase separation. In the Ti-rich Ti 66.67 Ag 33.33 alloy, the conventionally cast ingot showed a dendritic structure that included Ti-Ag-based intermetallic compounds; on the other hand, the rapidly solidified melt-spun ribbon showed a particulate microstructure comprising Ag-rich globules and a Ti-rich matrix phase. The formation of emulsion-like structures in the rapidly solidified specimens can be explained in terms of liquid phase separation. In the Ag-rich Ti 33.33 Ag 66.67 alloy, macroscopic phase-separated ingots were obtained via liquid phase separation. The metastable liquid miscibility gap in Ti-Ag alloy system was discussed based on thermodynamics. [ABSTRACT FROM AUTHOR]

Due to the cooperation of the torsion, tension and compression in metal plastic flow process of axial closed die rolling (ACDR), the effect of deformation schedule on grain refinement is still ambiguous. Therefore, the evolutionary mechanism of microstructure with periodic thermal parameters during ACDR process was established through the numerical simulation and metallography experiment. The results show that gradient distribution is ubiquitous in most areas in terms of both the strain and temperature throughout the deformation process, except the strain distribution in the center axis. With regard to the microstructure, the spheroidization efficiency of lamella α phase is enhanced during the especial deformation schedule. Factors influencing the uniformity of the globular α phase size are based on the vibration frequency of periodicity thermal parameters. The efficiency of broken α GB and the occurrence of DRX β have a closely related to the additional torsion. [ABSTRACT FROM AUTHOR]

We report a research describing a new route for the production of Fe-Si-B powders, which is the so-called gas atomisation technology, being one of the challenges to study the conditions under which the glass structure is achieved. There have been produced powders of five different compositions in the Fe-Si-B ternary system. The particles with a diameter below 10 μm of the alloy Fe 70 Si 18 B 12 (at%) were completely amorphous, exhibiting an excellent soft magnetic behaviour (coercivity of around 7 Oe), which is, without any doubt, of significant scientific merit and supports the use of this new route to produce soft amorphous magnetic materials. [ABSTRACT FROM AUTHOR]

The precipitates of α phase cooled from recrystallization annealing temperature were rather inhomogeneous from grain to grain in a metastable β titanium alloy. Electron backscatter diffraction technique (EBSD) had confirmed that inhomogeneous distribution of α precipitates was directly related to nonuniform recrystallization (or recovery). The accelerated precipitation kinetics in the deformed regions may be explained in terms of the increased number of nucleation sites provided by the substructure. Thus, the recrystallized and deformed regions can be easily distinguished by optical metallography. [ABSTRACT FROM AUTHOR]

The sintering behaviour of Ti-2.5 wt% Fe was investigated to help in the development of new, lower cost titanium alloys and powder metallurgy production methods. In contrast to previous studies of blended elemental (BE) Ti-Fe mixtures, the present work focused on introducing the iron (Fe) as a Fe-40 wt% Ti master alloy (MA). Under certain conditions, BE mixtures were previously found to exhibit rapid swelling and an exothermic reaction near the first eutectic temperature of 1085 °C due to intermetallic formation. Under similar conditions, the MA mixtures studied here underwent only melting since the additions were already in intermetallic form. However, as with the BE mixtures, coarse MA mixtures (d 50 = 50–90 μm) resulted in additional large porosity due to liquid formation as well as microstructural inhomogeneity during sintering. Introducing a pre-eutectic hold to the sintering cycle nearly eliminated any liquid formation, but additional coarse porosity was still present due to imbalanced diffusion of Fe into Ti. The use of fine MA particles (d 50 = 20–25 μm) was found to eliminate incipient melting and coarse porosity and resulted in improved homogeneity. Only small differences in final sintered density were observed between unalloyed Ti and the Ti-2.5Fe mixtures with BE or MA additions. However, alloys with higher Fe concentrations may result in more noticeable differences in densification behaviour. [ABSTRACT FROM AUTHOR]

Nickel-free austenitic powder metallurgy stainless steels were prepared and characterized. The main issue was to obtain potential biocompatible materials. Mechanical alloying in a nitrogen atmosphere was used to obtain these powders. The main factor to be controlled was the milling time. Powder metallurgy was the technique to obtain massive samples from alloyed powders. Two sintering processes were applied by controlling the sinter-cooling rate (furnace and water-cooling). The sintering atmosphere applied was nitrogen because of its gammagenic effect. Samples made of powders milled for 48 h, sintered in nitrogen and water-cooled showed a clean austenitic microstructure, which is a suitable microstructure for biological applications. A complete microstructural characterization, including optical metallography, image analysis, Scanning Electron Microscopy with X-ray microanalysis, X-Ray diffraction and Vickers hardness and microhardness, was carried out. The electrochemical behaviour in a simulated body fluid, phosphate buffered saline, was also studied. The biocorrosion behaviour was evaluated in terms of anodic polarization measurements. [ABSTRACT FROM AUTHOR]

Two hypereutectic Fe-Cr-C hardfacing alloys were manufactured, whose Nb contents are 0 and 1.2 wt% respectively. Their phase precipitation curves were calculated by Thermal-calc software and their phase structures were detected by X-ray diffractometer, which indicate that NbC precipitates previously to the nucleation of primary M 7 C 3 carbide. The alloys were observed by metallographic microscope, which finds that the primary M 7 C 3 carbides in the alloy with 1.2 wt% Nb are obviously refined. The chemical compositions of carbides were further measured by energy diffraction spectrum, which finds that NbC particles are distributed in the primary M 7 C 3 carbides. The melting process of M 7 C 3 carbide was simulated by molecular dynamics method and the melting point of M 7 C 3 carbide is identified to be 1625±5 K. The melting behaviors of M 7 C 3 embryos with different radii were simulated, and the solid-liquid interfacial energy of M 7 C 3 carbide was calculated to be 3.312 J/m 2 based on the classical nucleation theory. Two kinds of M 7 C 3 (0001)/NbC(111) interface models with different atomic stacking modes were built. By means of first-principles calculations, M 7 C 3 (0001)/NbC(111) interface I is combined by polar covalent/ionic bonds and metallic bonds, while M 7 C 3 (0001)/NbC(111) interface II is combined by ionic bonds and metallic bonds. The works of adhesion are 1.23 J/m 2 and 2.24 J/m 2 respectively. There exists a region where the interfacial energy of interface II is lower than the solid-liquid interfacial energy of M 7 C 3 carbide. The above experimental and calculation results demonstrate that NbC particle is the heterogeneous nucleus of primary M 7 C 3 carbide and thereby refines it. [ABSTRACT FROM AUTHOR]

This paper investigates the β-phase coarsening behaviour during isothermal heat treatment of free-standing CoNiCrAlY (Co-31.7%Ni-20.8%Cr-8.1%Al-0.5%Y, all in wt%) coatings prepared by high velocity oxy-fuel (HVOF) thermal spraying. The microstructure of the coatings was characterised using scanning electron microscopy with energy dispersive X-ray (EDX) analysis and electron backscatter diffraction (EBSD). It comprises a two phase structure of fcc γ-Ni matrix and bcc β-NiAl precipitates. The volume fraction of the γ-Ni and the β-NiAl phases were measured to be around 70% and 30% respectively, with grain sizes varying largely from 0.5 to 2 μm for both phases. Isothermal heat treatments of the free-standing coatings were carried out at 1100 °C for times up to 250 h. The β-phase coarsening behaviour during isothermal heat treatments was analysed by quantitative metallography. It is shown that the coarsening behaviour of β phase in the CoNiCrAlY alloy followed the classical Lifshitz-Slyozov-Wagner (LSW) theory of Ostwald ripening. By incorporating a dimensionless factor which correlates with volume fraction of the β phase, a modified LSW model coupled with formulaic interfacial energy and effective diffusion coefficient of the CoNiCrAlY alloy was utilised to interpret the coarsening behaviour of the β phase. The coarsening rate coefficient obtained from the modified LSW model shows good agreement with the corresponding experimental result. [ABSTRACT FROM AUTHOR]

The influence of solution treatment time on the microstructure of three cast Al-Cu alloys is investigated in terms of the effect on damage accumulation during tensile deformation at room temperature. The microstructure of the alloys is formed by an age hardenable α-Al matrix and interdendritic aluminides whose volume fraction and interconnectivity depends on the chemical composition and solution treatment time as revealed by 2D and 3D investigations. The damage accumulation process during tensile deformation is investigated in situ by synchrotron microtomography. Aluminides oriented perpendicularly to the load direction play a decisive role in damage formation and accumulation in the form of microcracks for all studied alloys and conditions. However, highly interconnected aluminides promote rapid crack propagation within these networks, indicating that the concentration of Cu should be kept <5 wt% and a solution heat treatment of 4 h at 530 °C should be applied to increase ductility of these cast alloys. [ABSTRACT FROM AUTHOR]

A decorative steel is described that is formed by a process that is unlike that of the fabrication methods utilized in making the original Damascus steels over 2000 years ago. The decorative aspect of the steel arises from a three-dimensional surface pattern that results from cryogenically quenching polished austenitic alloy single crystals into the martensitic phase that is present below 190 K. No forging operations are involved – the mechanism is entirely based on the metallurgical phase properties of the ternary alloy. The symmetry of the decorative pattern is determined and controlled by the crystallographic orientation and symmetry of the 70%Fe,15%Ni,15%Cr alloy single crystals. In addition to using “cuts” made along principal crystallographic surface directions, an effectively infinite number of other random-orientation “cuts” can be utilized to produce decorative patterns where each pattern is unique after the austenitic-to-martensitic phase transformation. [ABSTRACT FROM AUTHOR]

This paper reports on the possibility of applying carbon nanotubes as an additive to metallic materials, where a new phase forms in situ from the powder mixture. Multi-walled carbon nanotubes (MWCNT) amounts of 1 vol% and 3 vol% were applied to synthesize a composite with interpenetrating phases obtained from magnesium microsized powder and nanosized silicon (n)Si by sintering under vacuum. In the experiments, two ordered Mg-(n)Si-MWCNT powder mixtures with a (n)Si: MWCNT ratio of 2: 1 were prepared by sonication. The effects of Mg 2 Si silicide in situ synthesis on the behavior of MWCNTs and the Mg 2 Si and Mgα morphology were studied. Using LM with quantitative metallography, SEM with EDS, XRD, HREM, it was found that the MWCNTs were a component of the skeleton formed by submicron and nanosized Mg 2 Si, MgO, and Mgα mixture. Non-agglomerated MWCNTs were also found in microsized Mg 2 Si particles in the composite. A decrease in the silicide crystallite size was also observed compared with material without a carbon nanocomponent. The transformation of MWCNTs into another phase or their morphology change was not observed. Therefore, the effects described in this paper can be adapted to technologies focused on different types of composites and for designing Mg 2 Si-based thermoelectric materials and intermetallic alloys. [Display omitted] • No secondary agglomeration of MWCNTs in sintered Mg-nSi ordered mixture. • No MWCNTs structural degradation induced by in-situ synthesis of Mg 2 Si phase in composite. • Mg 2 Si and Mgα crystallites refinement induced by MWCNTs addition. [ABSTRACT FROM AUTHOR]

The effects of Ni:Co and Al:Ti ratios on the room temperature microstructure, hardness and lattice parameter of twenty-seven quinary Ni-Co-Al-Ti-Cr alloys have been evaluated. All of the alloys exhibited a uniform γ-γ′ microstructure. Differential scanning calorimetry (DSC) showed that the liquidus and solidus temperatures of the alloys increased with greater Al:Ti ratios, decreased with Cr concentration and remained largely unchanged with respect to the Ni:Co ratio. Neutron diffraction measurements of the γ and γ′ lattice parameters revealed that the lattice misfit in all of the alloys was positive and increased with Ti concentration (i.e. lower Al:Ti ratio) regardless of the concentration of Cr, or the ratio of Ni:Co. Importantly, alloys with a Ni:Co ratio of 1:1, were found to have consistently greater lattice misfits than alloys with Ni:Co ratios of either 1:3 or 3:1. The measured lattice misfits were found to be strongly correlated with the Vickers hardness of the alloys, suggesting that lattice misfit plays a key role in the strengthening of γ-γ′ alloys of this type. [ABSTRACT FROM AUTHOR]

SnSe is a semiconductor compound reported to possess very high thermoelectric ZT values at 600 °C–700 °C. Oxidation and sublimation are of significant concern at such temperatures. The oxidation behavior of SnSe at four temperatures between 600 °C and 700 °C in atmospheric air was investigated by monitoring the weight change as a function of time, as well as by characterizing the oxidized samples using optical microscopy, SEM with EDS, and powder XRD. The results show that SnSe oxidizes very rapidly at 600 °C–700 °C to form SnO 2 and possibly Sn(SeO 3 ) 2 . Sublimation of Se and Se oxides is also observed. At 600 °C the consumption of Sn from SnSe to form SnO 2 drives the composition to be Se rich. A layer of SnSe 2 forms between the oxides and SnSe. At ≥ 650 °C, the consumption of Sn likely leads to the formation of a transient liquid phase, which significantly accelerates both oxidation and sublimation. It is concluded that SnSe needs to be used under vacuum or with a protective coating such as pure Si. [ABSTRACT FROM AUTHOR]

The grain-growth behavior of cryogenically-rolled Cu–30Zn brass during isothermal annealing at 900 °C was examined. The observed microstructure coarsening was interpreted in terms of normal grain growth with a grain-growth exponent of ∼4. The relatively slow grain-growth kinetics was attributed to the formation of precipitates at the grain boundaries and the interaction of texture and grain growth. The development of a moderate-strength {110} α fiber texture (∼4 times random) as well as the presence of a limited number of twin variants within the grains suggested the occurrence of variant selection during annealing. [ABSTRACT FROM AUTHOR]

The addition of a trace amount of Ti (<0.01 wt.%) to AZ31 alloy refined the dendritic structure and grain size, supressed the formation of β phase and promoted the formation of the dense and tight network structure of the divorced eutectic α phase with a high aluminium content ≥ 6.3 wt. % along the grain boundaries and interdendritic interfaces in the as-cast microstructure. This network structure made of Al-rich α phase, which resembles the morphology of continuous β phase structure in the cast AZ91 alloy, significantly enhanced the corrosion resistance of AZ31 alloy by playing a role as an effective barrier to corrosion in NaCl solution. [ABSTRACT FROM AUTHOR]

The interdendritic Mo homogenization and relevant sub-solidus melting are investigated in detail during solution treatment for Mo-strengthening single crystal superalloys. During solidification, NiMo-γ eutectics and Ni 2 Mo phases precipitate from the residual liquid and the Mo super-saturated interdendritic γ channel, respectively. Due to such super-saturation of Mo, Mo diffuses to interdendritic Mo-rich eutectic in first 5 min of solution treatment, and hence the eutectic sharply propagates, opposite to homogenization of Mo. The excess propagated eutectic causes the occurrence of sub-solidus melting. The proposed Mo-homogenization treatment can completely eliminate such sub-solidus melting. [ABSTRACT FROM AUTHOR]

A combined technique denoted as seeding-grain selection (SGS) was designed for fabricating single crystal turbine blades. The microstructural evaluation during SGS process was metallographically analyzed in both starter section and spiral section of this technique. Four zones with distinct dendritic morphologies were identified in seed melt back region. After epitaxial propagating from melted seed and branching through the spiral passage, the lined-up dendritic pattern was observed at the outlet of the passage. The effectiveness of the technique on stray grain and orientation control was also assessed by Electron Back-Scattering Diffraction (EDSD) technique. The results indicated that the technique can control stray grain with no detrimental effect on crystal orientation. [ABSTRACT FROM AUTHOR]

The influence of Cr addition on microstructure and mechanical properties of Zr-based alloys corresponding to Zr–C–Cr system was investigated. In the alloy without Cr, the second-phase ZrC particles show the dispersed distribution in the αZr matrix. The alloys with Cr addition contain αZr, carbide ZrC and intermetallic αZrCr 2 phases. The microstructural observation indicates that ZrC particles present mainly the dispersed distribution in the αZr matrix, and αZrCr 2 phases present the dispersed and network distribution. The Cr-added alloys exhibit the dispersed and network hybrid second-phases distribution, and show significant increase of hardness and strength compared with pure Zr and single ZrC dispersed alloy. The hardness and compressive strength of Zr-based alloys increase with the Cr content increasing. The microstructural formation and strengthening mechanism of Cr-added Zr-based alloys are also discussed in details. [ABSTRACT FROM AUTHOR]

In this study, the effect of ultrasonic irradiation is investigated on the solidification microstructure of hypo- and hyper-eutectic Al–Si alloys. Significant grain refinement accompanying dendrite to equiaxed transition was observed for the primary solid in both the alloys. Analysis of cooling curves suggest that enhanced heterogeneous nucleation under ultrasonication is responsible for the refinement of the microstructure. In the region of the ultrasonic energy transfer, strong fluid flow effect resulted in predominant spheroidisation of the eutectic-Si plates. [ABSTRACT FROM AUTHOR]

ZrB 2 -based composites, containing 15, 20, 25, and 30 vol% SiC, have been prepared by hot pressing at temperatures of 1700, 1850 and 2000 °C for 30 min under a relatively low pressure of 10 MPa. Densification and mechanical properties of ZrB 2 –SiC composites have been investigated. Fully dense ZrB 2 –30 vol% SiC composite with a relative density of 99.8% is obtained at 2000 °C. The highest values of Vickers hardness (21.3 GPa) and fracture toughness (4.7 MPa m 1/2 ) belong to this sample. Vickers hardness increases exponentially as the relative density of composite increases. A simplified equation was developed for the Vickers hardness of the investigated ZrB 2 –SiC composites as a function of relative density and SiC content. Microstructural investigation by means of optical and scanning electron microscopy shows that by addition of SiC particles, some toughening mechanisms such as crack deflection, crack branching, microcracking, crack bridging, break of large SiC grains, and crack arresting by porosity are appeared. [ABSTRACT FROM AUTHOR]

The microstructures, thermal stability and high deformation behavior of ultrafine grained (UFG) AZ61 alloys with trace amounts of Ti (0.01–0.02 wt.%), which were prepared by extrusion followed by high-ratio differential speed rolling (HRDSR), were examined. The addition of trace amounts of Ti significantly altered the morphologies and amounts of β (Mg 17 Al 12 ) phase in the alloys. During extrusion, most of β phase dissolved into the matrix, forming a unique microstructure with a number of the Al-rich strip-like bands elongated to the extrusion direction. During subsequent HRDSR, very fine β phase particles were precipitated from the Al-rich band structures and distributed uniformly on the UFG matrix. The addition of Ti also greatly affected the high temperature deformation behavior and superplasticity of the UFG AZ61 alloy by reducing its thermal stability through rapid dissolution of β-Mg 17 Al 12 particles into the matrix at temperatures ⩾523 K. The strain rate-stress relations for the AZ61 alloys with and without trace amounts of Ti, having a wide range of grain sizes between 3 and 145 μm, could be well described using a single constitutive equation, assuming that Coble creep, grain boundary sliding, solute drag creep and dislocation climb creep compete with one another. [ABSTRACT FROM AUTHOR]

The combined effect of high-intensity ultrasonic treatment (HIUST) and 0.3 wt.%Ca addition on modification of primary Mg 2 Si and wear resistance in the hypereutectic Mg–5 wt.%Si alloy has been investigated. The results show that without treatment, the dendrites of primary Mg 2 Si are coarse and non-uniform in size. With HIUST or 0.3 wt.%Ca addition, nearly fine uniform and polyhedral shape of primary Mg 2 Si are achieved. Interestingly, modification and refinement of primary Mg 2 Si arise from the combined effect of HIUST and 0.3 wt.%Ca addition. The sample due to combined effect of HIUST and 0.3 wt.%Ca addition has the best wear resistance due to the lowest weight loss among all the other samples for various loads (10, 30 and 50 N) at constant sliding speed (0.3 m/s). Modification mechanisms resulting in the development of microstructures are also investigated. [ABSTRACT FROM AUTHOR]

During the development of a processing route for the Selective Laser Melting (SLM) powder-bed fabrication of the nickel superalloy CM247LC it has been observed that the ‘island’ scan-strategy used as standard by the Concept Laser M2 SLM powder-bed system strongly influences the grain structure of the material. Optical and SEM micrographs are presented to show the observed grain structure in the SLM fabricated and Hot Isostatically Pressed (HIPped) material. The repeating pattern shown in the grain structure has been linked to the overlapping of the ‘island’ pattern used as standard in the Concept Laser M2 powder-bed facility. It is suggested that the formation of this bi-modal grain structure can be linked to the heat transfer away from the solidifying melt pool. The concept of a ‘band’ heating effect across each ‘island’ rather than ‘moving point’ heating has been suggested and has been supported by Electron Back Scattered Diffraction (EBSD) evidence. For comparison an EBSD map from a sample formed using a simple ‘back-and-forth’ strategy has also been presented and reveals a dramatically different grain structure and crystallographic orientation. MicroCT evidence, supported by SEM microscopy, shows that in the as-fabricated material the bimodal structure caused by the ‘island’ scan-strategy translates directly into the macroscopic pattern for the regions of extensive weld cracking associated with the SLM fabrication of γ′ hardenable materials. Similar microCT data has shown that HIPping can effectively close the internal cracks to provide a retro-fix solution. [ABSTRACT FROM AUTHOR]

The uniaxial compression test was used to assess the influence of micro-additions of V and Zr on the hot deformation behavior of the Al–7Si–1Cu–0.5 Mg–0.1Ti (wt.%) base cast alloy. The temperature in the range of 200–400 °C and, to a lesser extent, strain rate in the range of 10 −3 –1 s −1 affected the flow stress of both alloys with the peak stress of the V and Zr modified alloy being consistently higher. Constitutive equations were employed to evaluate the material constants and to correlate them with the hot deformation behavior. The presence of V and Zr increased the activation energy of the plastic deformation from 282.6 kJ/mol to 315.2 kJ/mol, supporting improved resistance to hot deformation. As revealed through metallographic examinations, fracturing and re-orientation of the second phase particles occurred during compression. For both alloys, the intermetallic particles experienced substantially more frequent cracking than the eutectic silicon. At the same time, in the modified alloy, both the eutectic silicon and intermetallics experienced less frequent fracturing. The precipitates in the modified alloy were also more resistant to rotation within the alloy matrix as a result of hot deformation. The beneficial role of the transition metals V, Zr and Ti in improving the high temperature performance of cast Al alloys was discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] The Fe–Cr–B alloyed powder is successfully prepared by sintering method. [•] The boron is an effective strengthened element for Fe matrix alloys. [•] The Fe–Cr–B alloys are composed of Fe, FeCr and Fe2B phases. [•] The hardness of FCB7 is 14.86 GPa. [•] The specimen containing 7 wt.% boron shows the best properties. [ABSTRACT FROM AUTHOR]

Highlights: [•] IMC growth in Sn–Bi/Cu joints was effectively suppressed by minor Ga addition. [•] Ga segregated quickly towards Cu and the dense γ 1-Cu9Ga4 phase formed first. [•] The γ 1-Cu9Ga4 phase grew slowly following the diffusion-controlled mechanism. [•] The γ 1-Cu9Ga4 layer acts as a native barrier for Sn diffusion and Cu–Sn reactions. [•] Phase equilibria of the Bi–Cu–Ga–Sn system were calculated using the CALPHAD method. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ni-added Sn-Zn-Bi were characterized metallographically, thermally and mechanically. [•] The volume fraction of α-Zn phase increased with both Bi and Ni in Sn-Zn-Bi alloys. [•] Micron-sized Ni particles reacted with neither Sn nor Zn to form intermetallics. [•] Better combination of thermal and mechanical properties can be achieved with Ni. [Copyright &y& Elsevier]

Highlights: [•] Isothermal section of the Eu–Ag–Ga (0–33.3at.% Eu) system at 500°C. [•] Identification six new ternary intermetallic phases. [•] Crystal structure determination of the Eu2Ag13.6–13Ga3.3–4. [ABSTRACT FROM AUTHOR]

• Al-based metal matrix composites are lightweight solutions. • Nickel and zirconium improve their high-temperature resistance. • Nickel led to a continuous improvement of strength. • Zirconium increase was not beneficial to strength. [Display omitted] The present work investigates different additions of nickel and zirconium to the matrix alloy of Al-SiC metal matrix composites to enhance their high-temperature performance. These composites are promising for the demand for lightweight solutions for automotive components like brake discs. In such components, the compression behaviour at elevated temperatures is crucial. The resulting properties were combined with microstructural analysis. Ni additions led to a continuous improvement of the mechanical response, but the same result did not hold for the Zr additions. The interaction of SiC particles, eutectic silicon, and eutectic Ni-based phases led to a 44 % increment of the activation energy. [ABSTRACT FROM AUTHOR]

• The composition of the ternary V ss -V 3 Si-V 5 SiB 2 eutectic reaction was determined. • The liquidus projection surrounding the ternary eutectic reaction was carefully investigated experimentally. • Competitive solidification behavior between V ss -V 5 SiB 2 and V ss -V 3 Si-V 5 SiB 2 eutectics was observed depending on cooling. • The competitive formation of the two eutectics was discussed employing the Jackson-Hunt theory. The solidification behavior close to the ternary V ss -V 3 Si-V 5 SiB 2 eutectic reaction in the V-Si-B system has been experimentally investigated via arc-melting. According to the microstructure investigation, which is performed by SEM observations, EDS and EBSD measurements and XRD analysis, the composition of the ternary eutectic reaction has been determined at V-9Si-6.5B (at%). Its microstructures in two different sample sections with different cooling rates were further investigated and compared with the calculated result of the developed eutectic growth theory based on the Jackson-Hunt model to reveal the competitive solidification behavior between the two-phase V ss -V 5 SiB 2 and three-phase V ss -V 3 Si-V 5 SiB 2 eutectic growth. As a result, the liquidus projection around the ternary eutectic reaction was modified and the cross section of the ternary V ss -V 3 Si-V 5 SiB 2 eutectic coupled zone along the monovariant V ss -V 5 SiB 2 and V 3 Si-V 5 SiB 2 reaction lines was schematically proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] The high intensity ultrasonic treatment (HIUST) can modify and refine the primary Mg2Si. [•] The optimal pouring temperature of HIUST is 800°C. [•] The optimal vibration time of HIUST is 90s. [•] The mechanisms for HIUST influence on solidification have been discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] 14YWT ferritic ODS nanostructured powders were prepared by mechanical alloying. [•] A comparative study was done on structural evolution by OM, SEM and XRD. [•] A physical model consisted of five stages was proposed for morphology evolution. [•] Particular morphology and structural features were found required to start alloying. [•] Relationship between hardness and crystallite size showed Hall–Petch type behavior. [ABSTRACT FROM AUTHOR]

Abstract: The influences of the Si content on the mechanical and shape memory properties of Fe–17Mn–xSi–0.3C alloys (wt.%) were examined, and a specific focus was placed on the properties of the Fe–17Mn–8Si–0.3C alloy. The 8%Si addition changed the initial microstructure from an austenite to an austenite/ferrite dual phase. A sufficient amount of deformation-induced ε-martensite was observed despite the pre-existing ferrite. Mn and C were preferentially distributed to the austenite, while Si was localized in the ferrite. The formation of ferrite increased the yield strength and the shape recovery stress, and decreased the starting temperature for the shape recovery. [Copyright &y& Elsevier]

Highlights: [•] Quantitative phase analysis of α″ martensite was achieved by the Rietveld method. [•] Martensite forms after a quenching only from above a particular annealing temperature. [•] Only α″ martensite can form from β-phase after a water quenching. [•] α″ and β phases decompose both in a fine α+β needle-like structure. [•] The hardening is proportional to the amount of the fine needle-like α+β structure. [Copyright &y& Elsevier]

Abstract: The effect of Mo on the microstructure and mechanical properties of Nb–Ti–C–B multiphase alloy was investigated. The alloy without Mo contains the primary Nb solid solution (Nbss) dendrites and interdendritic eutectic network containing Nbss, (Nb,Ti)C and (Nb,Ti)B. In Mo-added alloys, the solubility of Mo is found in Nbss and (Nb,Ti)B. Mo addition refines the primary Nbss dendrites and promotes the coarsening of boride phase, but does not obviously change the volume fraction of primary Nbss and total secondary particles. The hardness, compression properties and fracture toughness were evaluated to determine the strengthening and toughening effect of Mo-added alloys at room temperature. The results indicate that the hardness and compressive yield strength increase with increasing Mo content, but Mo addition decreases the room temperature fracture toughness. [Copyright &y& Elsevier]

Abstract: Aluminum alloy A356 filled with silicon carbide hollow spheres (SiCHS) is investigated for quasi-static (10−3 s−1) and high strain rate (up to 1520s−1) compressive properties. Such closed cell composite foams, called syntactic foams, are of interest in weight sensitive structural applications. The present work is focused on understanding the compressive failure mechanism and relating them with the material microstructure. The compressive and plateau strengths of syntactic foams with SiCHS are found to be 163 and 110MPa, respectively. The measured properties are considerably higher than the existing fly ash cenosphere filled aluminum matrix syntactic foams. Compressive failure mechanisms are studied for A356/SiCHS syntactic foams and direct evidence of hollow sphere crushing at the end of the elastic regions is obtained. The predictions of compressive strength obtained from an existing model are validated with the experimental results. Extensive analysis of data on open and closed cell foams containing gas porosity and syntactic foams is presented. A clear advantage in terms of low density and high yield strength is observed in A356/SiCHS syntactic foams compared to other foams. Yield strength of aluminum foams may be different at high strain rate compression compared to quasi-static values but most of the foams do not show strong evidence of strain rate sensitivity within the high strain rate regime. [Copyright &y& Elsevier]

Abstract: This work studies the microstructure and hardness evolution in MAR-M247 Ni-based superalloy processed by controlled cooling and double heat treatment. The solidification experiments with controlled cooling rates in the range of 0.25–10K/s were carried out using GLEEBLE thermo-mechanical simulator. In the as-solidified material, with increasing cooling rate, grain and carbide size decreased, whereas volume fraction of carbides and microhardness increased. The as-solidified samples were subjected to a double heat treatment consisting of solution treatment followed by aging. The double heat treatment did not affect much the microstructure evolved in the sample solidified at 0.25K/s while it led to dissolution of the γ/MC eutectic in the samples solidified with the cooling rates of 5 and 10K/s. No significant effect of the double heat treatment on grain size, size and volume fraction of carbides is seen in all samples. The processing – microstructure–microhardness relationship in the material is discussed. [Copyright &y& Elsevier]

Abstract: The microstructures and tensile properties of a Mg–6Zn–4Si alloy with calcium additions at ambient and elevated temperature were investigated by means of X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and standard high temperature tensile testing. The results indicate that the morphology of the primary Mg2Si in the alloys changes from large dendritic (>100μm) to fine polygon (<20μm). Meanwhile, the eutectic Mg2Si changes gradually from Chinese script shape to a fine fibre morphology with increasing Ca content. The grain size of the primary Mg2Si decreases initially and then slowly increases with increasing Ca content. Experimental analysis shows that the concentration distribution of Ca atoms on the growth front of the Mg2Si cause a “poisoning effect”. The coarse CaMgSi compound is formed due to an excessive Ca addition, which resulted in the over-modification. Therefore, it can be concluded that the appropriate level of Ca addition can both effectively modify and refine the primary Mg2Si, and also decrease the amount of the primary Mg2Si. Tensile testing results show that the addition of Ca improves the ultimate strength, yield strength and elongation of the Mg–6Zn–4Si alloys at both ambient temperature and 150°C. Optimal mechanical properties can be achieved with a Ca addition of 0.4%. [Copyright &y& Elsevier]

Abstract: The aim of the experiments was to study the influence of Si and Fe on size and formation of secondary phases and recrystallization behavior of Al–Mn–Zr alloys prepared by twin-roll casting (TRC) in the industrial conditions. Microstructure (grain structure, phase composition, particle analysis) of these alloys was characterized during downstream processing. Quantitative particle analysis was carried out on FEG–SEM micrographs at both high and low magnifications. The phases were examined by light metallography, energy dispersive X-ray spectroscopy (EDXS) and by means of electron back-scattering diffraction (EBSD) according to their crystallographic structure. The microstructure at the final gauge was also observed by transmission electron microscope (TEM). A relatively high (0.5wt.%) Si content and low (0.2wt.%) Fe content in one of the alloys resulted in balancing of nucleation and dissolution rate for small particles. Hence a higher density of small particles was stable during the downstream processing, and this alloy showed improved recrystallization resistance. [Copyright &y& Elsevier]

Abstract: The cellular pattern evolution during directional solidification of a nickel-base single crystal superalloy has been studied in different crystallographic orientations using re-oriented seed crystals. Under the same thermal gradient and solidification velocity, the microstructures of differently oriented cellular single crystals are schematically investigated. It is concluded that the cellular growth direction is less affected by the seed orientation and depends on the heat flow, and is usually along heat flow direction. Cellular interface stability and microstructure are greatly influenced by the crystallographic orientation. When increasing the misorientation, the cell spacing increases correspondingly and the cellular growth interface becomes more unstable. [Copyright &y& Elsevier]

Abstract: The phase equilibria in the Gd–V–Sn and Er–V–Sn ternary systems were studied at 870K by means of X-ray and metallographic analyses in the whole concentration range. Both Gd–V–Sn and Er–V–Sn systems are characterized by formation of one ternary compound at investigated temperature, with stoichiometry RV6Sn6 (SmMn6Sn6-type, space group P6/mmm, a =0.55322(3)nm, c =0.91949(7)nm for Gd, a =0.55191(2)nm, c =0.91869(8)nm for Er). Solubility of the third component in the binary compounds was not observed. Compounds with the SmMn6Sn6-type were also found with Dy, Ho, Tm, and Lu, while YV6Sn6 compound crystallizes in HfFe6Ge6 structure type. All investigated compounds are the first ternary stannides with rare earth elements and vanadium. [Copyright &y& Elsevier]

Abstract: The phase equilibria in the Y–Mn–Sn and Dy–Mn–Sn ternary systems were studied at 770K by means of X-ray and metallographic analyses in the whole concentration range. Both Y–Mn–Sn and Dy–Mn–Sn systems are characterized by formation of two ternary compounds RMn6Sn6 (MgFe6Ge6-type, space group P6/mmm) and R4Mn4Sn7 (Zr4Co4Ge7-type, space group I4/mmm). The disorder in Dy4Mn4Sn7 compound was found by single crystal method. Compounds with the same type of structure were also found with Gd, Tb, Ho, Er, Tm (confirmed), Yb, and Lu and their lattice parameters were determined. [Copyright &y& Elsevier]

Abstract: A solid state diffusion bonding between two metallic biomaterials, Ti–2.5Al–2.5Mo–2.5Zr alloy and Co–Cr–Mo alloy (F75), has been investigated by using energy-dispersive spectrometer analysis, metallographic observation and bonding strength evaluation. The experiments indicate that bonded at 750°C leads to insufficient atoms diffusion and weak bond. When bonded at 900°C some intermetallics, CoTi2, Co2Ti, and Cr2Ti, form in the diffusion zone, which significantly deteriorate the plasticity and lead to lower bonding strength. A high bonding strength can be achieved when bonding at 850°C for 60min. During the bonding process each element exhibits various diffusion velocity in the opposite alloy. The diffusion coefficients for those elements can be ranked in following sequence: D Co > D Cr > D Mo in the Ti–2.5Al–2.5Mo–2.5Zr alloy and D Ti > D Al > D Zr in the Co–Cr–Mo alloy. [Copyright &y& Elsevier]

Abstract: The isothermal section of the phase diagram of the Gd–Ni–Y ternary system at 773K was investigated by means of X-ray powder diffraction, metallographic analysis and scanning electron microscopy with energy dispersive analysis. The isothermal section consists of 12 single-phase regions, 15 two-phase regions and 4 three-phase regions. Six pairs of corresponding compounds in the Gd–Ni and Y–Ni systems, i.e., Gd2Ni17 and Y2Ni17, GdNi5 and YNi5, Gd2Ni7 and Y2Ni7, GdNi3 and YNi3, GdNi2 and YNi2, Gd3Ni and Y3Ni and metals Gd and Y form a continuous series of solid solutions, respectively. At 773K, the maximum solubilities of Gd in YNi and Y in GdNi were about 20at.% Gd and 8at.% Y, respectively. No solubility of Gd in YNi4 and Y in GdNi4 was observed. [Copyright &y& Elsevier]

Abstract: The high chromium cast iron and medium carbon steel bimetal was fabricated by liquid–solid casting technology. The effect of volume ratios of liquid to solid (6:1, 10:1 and 12:1) on the interfacial microstructure and mechanical properties of bimetal was investigated. The interfacial microstructure was analyzed using scanning electron microscope (SEM) and transmission electron microscope (TEM). The shear strength and microhardness in as-cast condition were studied at room temperature. The results show that the volume ratios of liquid to solid affect significantly the interfacial microstructure. When liquid–solid volume ratio was 6:1, the unbonded region was detected in interface region because the imported heat energy cannot support effectively the diffusion of element, whereas, when liquid–solid volume ratios reach 10:1 and 12:1, a sound interfacial microstructure was achieved by the diffusion of C, Cr, Mo, Cu and Mn, and metallurgical bonding without unbonded region, void and hole, etc. was detected. With the increase of liquid–solid volume ratio, the elemental diffusion activity improves, resulting in the increase of width of interface transition region. At the same distance from interface, with the increase of liquid–solid volume ratio, the microhardness is degraded in HCCI, but increased in MCS. The shear strength is also improved with the increase of liquid–solid volume ratio. [Copyright &y& Elsevier]

Abstract: The phase equilibria in the Lu–Ni–Sn ternary system were studied at 770K (up to 50at.% Sn) and 670K (more than 50at.% Sn) by means of X-ray and metallographic analyses in the whole concentration range. The Lu–Ni–Sn system is characterized by formation of 10 ternary intermetallic compounds at investigated temperatures: LuNi5Sn (CeCu5Au-type), LuNi4Sn (MgCu4Sn-type), Lu6Ni2Sn (Ho6Co2Ga-type), Lu2Ni2Sn (Mo2FeB2-type), LuNi2Sn (MnCu2Al-type), LuNi2−x Sn (YbNi2−x Sn-type), LuNiSn (TiNiSi-type), LuNiSn2 (LuNiSn2-type), Lu2NiSn6 (Lu2NiSn6-type), and LuNiSn4 (LuNiSn4-type). Three new binary compounds, LuNi3 (PuNi3-type), Lu3Ni2 (Er3Ni2-type), and Lu3Ni (Fe3C-type), were found in the Lu–Ni system. [Copyright &y& Elsevier]