Formation of Metallic Glass Coatings by Detonation Spraying of a Fe66Cr10Nb5B19 Powder

The present work was aimed to demonstrate the possibility of forming Fe66Cr10Nb5B19 metallic glass coatings by detonation spraying and analyze the coating formation process. A partially amorphous Fe66Cr10Nb5B19 powder with particles ranging from 45 µm to 74 µm in diameter was used to deposit coatings on stainless steel substrates. The deposition process was studied for different explosive charges (fractions of the barrel volume filled with an explosive mixture (C2H2 + 1.1O2)). As the explosive charge was increased from 35% to 55%, the content of the crystalline phase in the coatings, as determined from the X-ray diffraction patterns, decreased. Coatings formed at explosive charges of 55–70% contained as little as 1 wt.% of the crystalline phase. In these coatings, nanocrystals in a metallic glass matrix were only rarely found; their presence was confined to some inter-splat boundaries. The particle velocities and temperatures at the exit of the barrel were calculated using a previously developed model. The particle temperatures increased as the explosive charge was increased from 35% to 70%; the particle velocities passed through maxima. The coatings acquire an amorphous structure as the molten particles rapidly solidify on the substrate; cooling rates of the splats were estimated. The Fe66Cr10Nb5B19 metallic glass coatings obtained at explosive changes of 55–60% showed low porosity (0.5–2.5%), high hardness (715–1025 HV), and high bonding strength to the substrate (150 MPa).

Formation of Fold Defects in Permanent Mold Cast AE42 Magnesium Alloy

Application of magnesium alloys potentially plays a key role in weight reduction of automotive and aerospace components. Majority of magnesium components are manufactured via the high-pressure die-casting (HPDC) or permanent-mold casting (PMC) processes. In general, castability of magnesium alloys is comparable to aluminum alloys. However, unique defects related to the high susceptibility of magnesium to rapidly solidify, dissolve hydrogen or form oxides potentially contribute to material failure. In this research, AE42 magnesium alloy castings were manufactured via the PMC process. Formation of fold defects in regions of high melt turbulence was observed on the macro-scale as visible surface flow-lines. Microstructural analysis revealed that folds in the AE42 alloy we related to the rapid solidification and short alloy freezing range. Further, segregation of Al2RE intermetallics at the metal front hindered proper fusion of merging metal fronts.

Production of Rapidly Solidified Composite Deposits Based on Iron with Vanadium Carbide Particles by Plasma Spraying

In the thermal spraying process, spray material is heated, melted, and accelerated by a high temperature flame. Thermal spraying can produce thick materials that rapidly solidify, because the alloy droplets accumulate successively on the substrate and solidify at a cooling rate in the range of 105-108Ks-1. Depending on the cooling conditions of the substrate and on the alloy composition, deposits are produced with metastable phases or extremely fine crystalline phases. Thermal spraying is an attractive method for the production of composite deposits with fine particles formed in-situ. In particular, iron based alloy with vanadium carbide, is useful in metal molds and also in pump parts due to its high wear resistance and high corrosion resistance. In the present work, low-pressure plasma spraying of Fe-C-V/Ni-Mg and Fe-C-V-Cr-Ni/Ni-Mg blend powders were iron based composite deposits with finely dispersed vanadium carbide particles. The as-sprayed deposit produced from Fe-C-V/Ni-Mg blend powder is composed of αFe and V8C7. The as-sprayed deposit produced from Fe-C-V-Cr-Ni/Ni-Mg blend powder is made up of γFe, αFe, V8C7 and Cr7C3. The fine precipitates of approximately 0.3μm in the as-sprayed deposit are carbide. With increasing the heat-treatment temperature up to 1273K, the carbide particles coarsen. The hardness of as-sprayed deposit produced from the Fe-C-V-Cr-Ni/Ni-Mg, which has many fine carbide precipitates, is the hardest of the deposits.

Thermocapillary Patterning of Nanoscale Polymer Films

We investigate a method for non-contact patterning of molten polymer nanofilms based on thermocapillary modulation. Imposed thermal distributions along the surface of the film generate spatial gradients in surface tension. The resulting interfacial stresses are used to shape and mold nanofilms into 3D structures, which rapidly solidify when cooled to room temperature. Finite element simulations of the evolution of molten shapes illustrate how this technique can be used to fabricate features of different heights and separation distances in a single process step. These results provide useful guidelines for controlling proximity effects during evolution of adjacent structures.

Thermal Spray: Current Status and Future Trends

Thermal spray is a continuous, directed, melt-spray process in which particles (e.g., 1–50 μm in diameter) of virtually any material are melted and accelerated to high velocities, through either a combustion flame or a dc or rf nontransferred thermal-plasma arc. The molten or semimolten droplets impinge on a substrate and rapidly solidify to form a thin “splat.” The deposit is built up by successive impingement and interbonding among the splats. The splats accumulate into a wellbonded deposit, generally > 10 μm thick.

Nucleation behavior of Al–Mn icosahedral phase

Electrohydrodynamic (EHD) atomization has been used to rapidly solidify micron and submicron size droplets of Al-14 at. % Mn to study nucleation behavior of icosahedral phase. Icosahedral grain size has been found to decrease continuously with decreasing droplet size. Based on this result, formation of the icosahedral phase is explained by homogeneous nucleation. Extremely low resistance to nucleation of icosahedral phase can be understood if possible topological similarities between liquid and icosahedral quasicrystal are considered. Formation of glass as configurationally frozen liquid in Al-Mn and similar alloy systems is questionable, implying that the reported Al-Mn glass probably has a microquasicrystalline structure.