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• Tin (Sn) whiskers were observed to grow out of Ti 6 Sn 5 intermetallic particles. • The critical role (as tin atom source) of Ti 6 Sn 5 intermetallic compound in Sn whisker growth is identified. • An atomic diffusion-based whisker growth model is proposed, and a new preparation method of metal nanowires is expected. Spontaneous growth of metal whiskers, represented by tin whiskers, has haunted tin-based platings and solder joints for decades and caused huge losses to the electronics industry. Despite numerous efforts, the underlying growth mechanism has been resisting interpretation, and the whiskering phenomenon even continues to expand its territory. Here, we report the growth of tin whiskers from a Ti 6 Sn 5 intermetallic. These tin whiskers share similar characteristics with those found on the platings or solder joints, but grow more and faster, with finer diameters. After tin whisker growth, Ti 6 Sn 5 retains its crystal structure, implying a dealloying process. Combining experimental and first-principles calculation results, we analyzed the growth mechanism of tin whiskers in detail, and proposed a diffusion-based growth model. The strain energy stored in Ti 6 Sn 5 during deformation provides a driving force for whisker growth, and the short-circuit diffusion paths generated by such deformation accelerate whisker growth. These findings identify the critical role of intermetallic substrate in the whiskering phenomenon, shedding new light for comprehensively understanding the whisker growth mechanisms. Furthermore, the plenty and rapid growth of tin whiskers also means a new method for the preparation of one-dimensional metallic materials. [ABSTRACT FROM AUTHOR] more...

• The oxidation resistance of (γ'+β) two-phase NiAlDy alloy is optimized by LSP. • LSP reduces scale growth rate due to its impact on initial oxidation behavior. • LSP promotes θ-α transition by increasing dislocation density and surface roughness. • LSP leads to distinction in oxide scale morphology on both the γ' and β phase. • LSP facilitates the formation of large Al 2 O 3 particles (2–3 μm) on the β phase. (γ'+β) two-phase Ni-Al is a promising high-temperature protective coating material used on Ni-base superalloys since it has good interfacial compatibility with superalloys due to the low Al content compared to single-phase β-NiAl. In this paper, we aim to improve the oxidation resistance, whereby Ni-34Al-0.1Dy, a (γ'+β) two-phase Ni-Al alloy, was treated by laser shock processing (LSP) and the oxidation behavior at 1150 °C was investigated. The results showed that after oxidation, Al 2 O 3 scale formed on the original β phase of the untreated alloy with a small grain size (200–800 nm), while for the LSP-treated samples, the scale grown on the original β phase was dominantly composed of larger Al 2 O 3 grains with a size of 2–3 μm. The distinction was attributed to the promotion of θ-Al 2 O 3 to α-Al 2 O 3 transformation induced by the LSP, because the dislocation density, as well as surface roughness, were increased during LSP treatment which can provide heterogeneous nucleation sites for α-Al 2 O 3. In addition, the larger-size Al 2 O 3 particles, derived from the direct conversion of needle-like θ-Al 2 O 3 in the initial oxidation stage, could rapidly overspread the whole β phase surface thus reducing the scale growth rate. [ABSTRACT FROM AUTHOR] more...

• Cu-containing phases exhibit much higher volta potential than Mg 17 Al 12 and α-Mg. • The volume fraction of Cu-containing phase determines the corrosion rate of alloys. • Al content and annealing adjust the corrosion performances of Mg-Cu-Al alloys. • The alloy is feasible for making fracturing tools. The effects of Al content and annealing condition on the microstructures and corrosion performances of Mg-3 wt.%Cu- x Al (x = 0, 4 wt.%, 8 wt.%) alloys were investigated. The Mg-3 wt.%Cu alloy contains Mg 2 Cu phase, but Al-bearing alloys contain MgAlCu and Mg 17 Al 12 phases. The Mg 2 Cu and MgAlCu phases exhibit much higher Volta potential compared to Mg 17 Al 12 and α-Mg, and their volume fractions are related to Al content of alloys and annealing condition. The weight loss measurement and electrochemical tests are conducted to explore the corrosion performances of alloys. The close relationship between weight loss rate of alloys and volume fraction of Cu-bearing phases indicates that the corrosion performances of alloys can be controlled by adjusting Al content of alloys and annealing conditions. [Display omitted] [ABSTRACT FROM AUTHOR] more...

• The local breakage of oxide films determine the formation of τ1 and τ2 crystals and their morphologies. • Both τ1 and τ2 crystals have an intrinsic plate morphology, but τ2 crystals were thinner due to their more anisotropic growth. • τ1 lamellar domains generate during growth of τ2 crystals accompanied by decrease in density of SFs. • τ1 crystals coarsen at the expense of τ2 crystals, leading all reaction products to finally convert into large τ1 plates. Due to the similarity in composition and crystal structure of some TiAlSi ternary intermetallics, it is quite difficult to accurately confirm their physic characteristics, and thus, to tailor microstructure to improve mechanical properties of metal materials related to the TiAlSi intermetallics. Therefore, the formation process of TiAlSi intermetallics was investigated during heating Ti-A356 mixed powder compact at a A356 alloy semisolid temperature of 595 °C. The results indicated that two kinds of intermetallics of τ1 (tetragonal, I41/amd) and τ2 (orthorhombic, Cmcm) generated, and both the concentration and supply direction of Ti atoms, which are related to local breakage of oxide films on neighboring Ti and A356 alloy powders, determined the phase and morphology of the intermetallics. τ1 and τ2 crystals all had an intrinsic plate morphology, but τ2 crystals were thinner due to more anisotropic growth resulted from their high density of stacking faults (SFs). τ1 lamellar domains generated during growth of τ2 crystals, which were accompanied by decrease in density of SFs. The combined effect of size difference and internal energy difference between τ1 and τ2 crystals made large τ1 crystals coarsen at the expense of τ2 crystals in Ostwald ripening, leading them to finally evolve into an agglomerate of large τ1 plates. [ABSTRACT FROM AUTHOR] more...

• ppm level Fe/Si deteriorate the corrosion performance of Mg-0.5Zn after heat treatment. • Longer heat treatment induces Fe-Si particle with higher concentration of Fe. • Fast cooling rate and short heat treatment are important in micro-alloying Mg systems. • Corrosion resistance loss induced by Fe-Si particles is not compensated by further extrusion. The corrosion performances of the as-cast and solution-treated Mg-0.5Zn samples were investigated in 0.9% NaCl solution and compared. From the electrochemical measurement results and corrosion morphology observations, it is found that the corrosion resistance of Mg-0.5Zn deteriorated with the extension of solution treatment duration. The main reason was the formation of Fe-Si precipitates with higher Fe concentrations during heat treatment. The Fe-Si precipitates, especially the ones with high Fe contents influenced the corrosion initiation and propagation significantly. In regard of corrosion performance, the solution-treated and then extruded sample was also performing not as good as the cast and then directly extruded sample. [Display omitted] [ABSTRACT FROM AUTHOR] more...

Optimization of the intermetallic layer thickness and the suppression of interfacial defects are key elements to improve the load bearing capacity of dissimilar joints. However, till date we do not have a systematic tool to investigate the dissimilar joints and the intermetallic properties produced by a welding condition. Friction Melt Bonding (FMB) is a recently developed technique for joining dissimilar metals that also does not exempt to these challenges. The FMB of DP980 and Al6061-T6 was investigated using a new physical simulation tool, based on Gleeble thermo-mechanical simulator, to understand the effect of individual parameter on the intermetallic formation. The proposed method demonstrates its capability in reproducing the intermetallic characteristics, including the thickness of intermetallic bonding layer, the morphology and texture of its constituents (Fe 2 Al 5 and Fe 4 Al 13), as well as their nanohardness and reduced modulus. The advantages of physical simulation tool can enable novel developing routes for the development of dissimilar metal joining processes and facilitate to reach the requiring load bearing capacity of the joints. [ABSTRACT FROM AUTHOR] more...

For NiAl intermetallic compound with B2 structure, there is still no calculation combining models of single and multiple layers while using the same basic set. Furthermore, some recently proposed criteria for brittleness and toughness have not been used to analyze its deformation behavior. Thus, first-principles calculation was applied to comprehensively study the elastic properties, ideal strength, generalized stacking fault energy and surface energy of B2-NiAl intermetallic compound. The results suggest that calculations based on the current basic set give more accurate lattice parameters and elastic moduli. The Pugh criterion and Cauchy pressure cannot be used to interpret the intrinsic brittleness of NiAl. In comparison, the ductility parameter based on the strain energy under elastic instability and ZCT and Rice criteria based on generalized stacking fault energy and surface energy successfully identify the intrinsic brittleness of the NiAl intermetallic compound. The reason why [111] slip always occurs in the deformation along [100] direction was clarified by examining the critical value for brittle-ductile transition. The results of density of state indicate shear deformation has less impact on structural stability, and the change of charge density difference implies that <001> shear induces more intensive redistribution of charge density, which is well correlated to the brittleness and deformation behavior of NiAl intermetallic compound. [ABSTRACT FROM AUTHOR] more...

Mo-12Si-8.5B and Mo-12Si-8.5B-1.0wt%ZrB 2 alloys were fabricated using mechanical alloying, followed by hot-pressing. Both alloys exhibited uniform microstructure, with the Mo 3 Si and Mo 5 SiB 2 phases distributing dispersedly in the α-Mo matrix. Mo-12Si-8.5B-1.0wt%ZrB 2 showed a finer-grained microstructure than Mo-12Si-8.5B alloy owing to the addition of ZrB 2 . The results of isothermal oxidation tests at 1300 °C in air revealed that Mo-12Si-8.5B and Mo-12Si-8.5B-1.0wt%ZrB 2 alloys initially suffered a transient stage with high mass loss due to the volatilization of MoO 3 , and then achieved a steady stage owing to the formation of a protective borosilicate scale on the alloy surface. Especially, the transient stage of Mo-12Si-8.5B-1.0wt%ZrB 2 alloy was shortened to be less than 300 s, and the mass loss of this stage was reduced by at least 88% compared with that of Mo-12Si-8.5B alloy, indicating a significant improvement in the oxidation resistance. The addition of ZrB 2 not only resulted in a continuous borosilicate scale quickly covering the entire base alloy during the transient stage, but also improved the protectiveness of the borosilicate scale of the steady stage by bringing out a large number of ZrO 2 /ZrSiO 4 particles embedded discontinuously in the borosilicate scale, which effectively restricted the inward diffusion of oxygen by acting as diffusion barriers and decreased the thickness of inner oxide layers in particular. [ABSTRACT FROM AUTHOR] more...

In this study, cold spraying (CS) was used to deposit a mixture of nickel-coated graphite and 40 vol.% Al powder (Ni-Gr/Al) on a steel substrate aiming to effectively preserve a certain volume fraction of graphite in the deposited Ni-Gr/Al composite coating. The microstructure of the as-sprayed coating and the effect of post-spray heat-treatment (PSHT) temperatures on the in-situ formation of Ni-Al intermetallic phases in coating were studied. The tribological behaviors of the as-sprayed coating and the PSHTed coating under 450 °C were tested at 25 °C, while the as-sprayed coating was tested at 450 °C for comparison. As a result, the Ni-Gr particles showed a homogenous distribution in the coating. The multilayer Ni-Al intermetallics-coated graphite/Al composite coating was achieved in situ after the PSHT of 450 °C, where the graphite did decompose at 550 °C leaving big pores in the coating. The coefficients of friction (COF) of the CSed coating and the PSHTed coating were measured at 450 °C as well as 25 °C, which showed a similar tendency, much higher than that of the CSed coating tested at 25 °C. The lubrication phase (graphite) improved the formation of a graphite film during sliding friction and decreased the COF, while the hard Ni-Al intermetallic phases contributed to the increase of COF. [ABSTRACT FROM AUTHOR] more...

The Fe- and Mn-rich intermetallics are of great effect on the mechanical properties of the AA5083 type alloy (Al–5Mg–0.8Mn). The effect of Fe, Si and cooling rate on the formation of the intermetallics were investigated by analyzing the microstructures of the alloys with different Fe and Si contents. The results indicated that increasing the Fe content resulted in the increase of the Al 6 (Fe,Mn) phase in both amount and size. In the alloys with high Fe content, the platelet-like Al 6 (Fe,Mn) compounds lined up and formed a band. Increasing the content of Si resulted in the increase of the Mg 2 Si phase which formed a network structure. Increasing the cooling rate significantly refined the intermetallics. However, increasing the cooling rate did not change the characteristic of the intermetallic compounds in the alloys with low or medium Si contents. For the alloys with high contents of Fe and Si under the condition of near-rapid cooling, the Fe- and Mn-rich intermetallic compound changed to the quaternary Al 15 (Fe,Mn) 3 Si phase and displayed a fine fish bone or Chinese script structure. The refinement of the intermetallics would allow higher tolerance of Fe and Si contents in the AA5083 alloy produced, for instance, via the continuous strip casting process. [ABSTRACT FROM AUTHOR] more...

The present work aims to compare the amorphous phase forming ability of ternary and quaternary Al based alloys (Al 86 Ni 8 Y 6 , Al 86 Ni 6 Y 6 Co 2 , Al 86 Ni 8 La 6 and Al 86 Ni 8 Y 4.5 La 1.5 ) synthesized via mechanical alloying by varying the composition, i.e. fully or partially replacing rare earth (RE) and transition metal (TM) elements based on similar atomic radii and coordination number. X-ray diffraction and high resolution transmission electron microscopy study revealed that the amorphization process occurred through formation of various intermetallic phases and nanocrystalline FCC Al. Fully amorphous phase was obtained for the alloys not containing lanthanum, whereas the other alloys containing La showed partial amorphization with reappearance of intermetallic phases attributed to mechanical crystallization. Differential scanning calorimetry study confirmed better thermal stability with wider transformation temperature for the alloys without La. [ABSTRACT FROM AUTHOR] more...

Mo–Si–B nanocomposite powders with a composition of Mo–12Si–8.5B (in at.%) were processed using mechanical alloying under milling conditions for different milling time and powder-to-ball ratios. The Mo–12Si–8.5B alloy, which consists of α-Mo and intermetallic Mo 3 Si and T2 phases, was also synthesized by hot-pressed sintering the mechanically alloyed powders under a pressure of 50 MPa at 1600 °C. The results demonstrated that the sizes and morphologies of the powder particles became gradually refined and uniform by both increasing the milling time and decreasing the powder-to-ball ratio. After 15 h of milling, the powders were completely homogenized at the 1:10 and the 1:15 powder-to-ball weight ratios, and the homogenization was accelerated to rapidly stabilize the milling process because of their high milling energy. Annealing the Mo–Si–B milled powders could promote the growth of the intermetallic Mo 3 Si and the T2 phases, which formed even after low-temperature annealing at 900 °C. Increasing the annealing temperature only improved the crystallinity of various phases. When the milled and annealed powders were hot-pressed sintered, the Mo–Si–B alloy exhibited a fine-grained microstructure, where the intermetallics Mo 3 Si and T2 were distributed in a continuous α-Mo matrix. [ABSTRACT FROM AUTHOR] more...

In this study, AA 1050 aluminum alloy and commercially pure copper in annealed and severely plastic deformed conditions were used. The technique used for imposing the severe strain to the sheets was constrained groove pressing (CGP) process. The annealed and severely plastic deformed sheets were subjected to friction stir welding (FSW) at different rotation and traverse speeds. Cu was placed in advancing side. Constant offset of approximately 1 mm was used toward Al side for all welds. A range of welding parameters which can lead to acceptable welds with appropriate mechanical properties was found. For the FSWed CGPed samples, it was observed that the welding heat input caused grain growth and decrease in hardness value at Al side of the stir zone. It was found that, generally the weakest parts of weld joints of annealed and CGPed samples were Al base metal and stir zone, respectively. Further investigations showed that several forms of intermetallic compounds were produced. [ABSTRACT FROM AUTHOR] more...

In general, the modification performance of Al-Sr master alloys is primarily dependent upon the morphologies and sizes of the Al4Sr intermetallic phase. In this paper, the crystal structure, morphologies, sizes, hardness and elastic modulus of Al4Sr in Al-Sr master alloys prepared from variant processes were studied by means of optical metallurgical microscope, X-ray diffraction (XRD), scanning electron microscopy (SEM), and nanoindentation system. The results revealed that the microstructures and modification performance of the Al4Sr phase were related to the preparation processes. That is to say, when a “direct reaction-hot extrusion” process was used, the Al4Sr phase exhibited a homogeneous distribution in the Al matrix with small size and roundish shapes, which ensured the Al-Sr master alloy wire advantages involving high recovery, good reproducibility, no delitescence of modification, no corrosion on equipments, and good workability. However, in the case of the traditional “direct reaction” process, the Al4Sr phase was in large size with shapes of rectangular stripe and plates, which limited the Sr content increasing due to the brittleness of the Al-Sr alloy It was also found that the morphology and size of the Al4Sr phases changed during heat treatment at high temperature up to 600 °C. [Copyright &y& Elsevier] more...

The growth, transformation, and lattice structure of intermetallic compounds formed between Sn-0.3Ag-0.7Cu lead-free solder and copper substrate were investigated. Dip soldering was used to initiate the reaction between the solder and substrate. An η-Cu6Sn5 intermetallic phase possessing a hexagonal lattice structure was found at the as-soldered interface. Thermal aging at a number of conditions resulted in the formation of a Cu3Sn intermetallic phase between the Cu6Sn5 layer and the copper substrate. ɛ-Cu3Sn with an orthorhombic lattice structure was found together with hexagonal Cu3Sn. Subsequently, the activation energies of the intermetallic phases were calculated and compared to results obtained from the literature. The comparison showed that good agreement existed between the findings from this study and literature data within a similar temperature range. [ABSTRACT FROM AUTHOR] more...

Pure copper and its composites reinforced with Ni3Al particles were produced by powder metallurgy (PM). Ni3Al powders were produced by mechanical ball milling from vacuum arc melted compounds. The Ni3Al powders were characterized by X-ray diffraction (XRD). The microscopy examinations revealed that the Ni3Al particles were distributed uniformly in the matrix. The effects of the particle fraction on the density, electrical conductivity, strength and dry sliding wear resistance of composite were investigated. It was found that the density and electrical conductivity of the composites decrease while the compression yield strength and wear resistance of composites increase with an increase in the particle fraction. The dry sliding wear tests were performed with pin-on-disk geometry. After sliding wear tests, the worn surfaces were examined by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). Results have shown that the wear mechanism is oxidative and adhesive. [ABSTRACT FROM AUTHOR] more...

In the present research, mechanically alloyed Ni-AI powder was utilized to develop plasma sprayed coatings, and the effect of the spray distance and heat treatment on the phases, microstructure, and hardness of the coatings were examined. Coatings were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and through microhardness measurements. Although mechanically alloyed Ni-AI powder showed no intermetallic phases, the coatings did. Different spray distances from 5 to 19 cm were employed for plasma spray and the specimens were heat treated at different temperatures, then the amount of oxides, porosity and hardness of the coatings were changed according to the spray condition. The thermal energy of the plasma spray caused the formation of NiAl phases while particles flew to the substrate or after that. Extreme increase in heat treatment temperature and spray distance resulted in oxidation and reduction in the quality of the coating. Furthermore, the best spray distance and heat treatment temperature to gain the NiAl intermetallic coating were established. [Copyright &y& Elsevier] more...

The intermetallic compound (IMC) growth kinetics in pure Sn/Cu and Sn10 wt%Bi/Cu solder joints was studied, respectively, after they were aged at 160–210°C for different time. It was found that the total IMC in SnlO wt%Bi/Cu joint developed faster than it did in pure Sn/Cu solder joint, when they were aged at the same temperature. And the activation energy Q a for total IMC in Sn10 wt%Bi/Cu joint was lower than that for pure Sn/Cu interconnect. The IMC growth process was discussed. The IMC Cu6Sn5 was enhanced in compensation of reduced IMC Cu3Sn growth. The work reveals that Bi element containing in lead free solder alloys with 10 wt% can enhance IMC growth in lead free solder/Cu joint during service. [Copyright &y& Elsevier] more...

The nanostructured CoAl intermetallic compound was produced by mechanical alloying (MA) of the Co50Al50 elemental powder mixture in a planetary high energy ball mill. The ordered B2-CoAl structure with the grain size of about 6 nm was formed via a gradual reaction after 10 h of MA. A thermodynamic analysis of the process was also done. The results showed that the intermetallic compound of CoAl had the minimum Gibbs free energy compared to solid solution and amorphous states indicating the initial MA product was the most stable phase in the Co-Al system which was changed to a partially disordered structure with a steady long-range order of 0.82 at further milling. This amount of disordering caused the enthalpy of final product to show an increase of about 5.1 kJ-mol−1. Calculation of enthalpy related to the triple defect formation revealed that the enthalpy required for Al anti-sites formation was about 3 times greater than that for Co anti-sites formation. [ABSTRACT FROM AUTHOR] more...

Gold wires of different chemistry (denoted as Types A and B) are ballbonded on identical metallization and isothermally aged at 175°C. In both wire types the same intermetallic compounds AuAl and AuAl grow with parabolic time dependence as long as there is a supply of Al from the bondpad. After Al is completely reacted, composition of intermetallics in Type A wire remains unchanged but in Type B wire, the AuAl compound undergoes a phase transformation into a second layer of Au Al. The phase transformation does not affect mechanical reliability of the ballbonds. Intermetallic growth kinetics, growth sequence and the possible origins of the phase transformation are discussed. [ABSTRACT FROM AUTHOR] more...

The fundamental aspects of ab-initio simulations of materials properties and of processes in materials based on density-functional theory, and their implementation at various levels of theory in the Vienna ab-initio simulation package are reviewed. The state-of-the-art is illustrated at selected examples, chosen from nanostructured materials, quasicrystals, surface science and catalysis. Finally a brief outlook is given on current developments attempting to make post-DFT approaches applicable to materials-science problems. [Copyright &y& Elsevier] more...

Plastic deformation in the lamellar microstructure of the L10 tetragonal phase is strongly affected by special rotational lamellar interfaces on the {111} close packed planes and by general grain boundaries separating the lamellar colonies. The activity of possible deformation modes in Ti-rich TiAl alloys is explained considering in addition to generally known asymmetry of deformation twinning the asymmetry of superdislocation motion. The restrictions imposed on the direction of propagating deformation by the lamellar interfaces are analysed in detail. Even in the case when the transfer of plastic deformation across the interfaces does not occur, the presence of interfaces as strong obstacles to moving dislocations and deformation twins can lead to localisation of strain parallel to the lamellae, to so called channelling of deformation. General grain boundaries can also significantly influence plastic deformation by stress redistribution due to the compatibility stresses arising from the crystal elastic anisotropy and from the anisotropy of plastic deformation. [ABSTRACT FROM AUTHOR] more...