An Experimental and Numerical Simulation Study of Single Particle Impact during Detonation Spraying

A comparison of the numerical simulation and an experimental study of the collision of the particles and the substrate during detonation spraying is presented. The spraying regimes were chosen to provide unmelted, partially melted, and completely molten particles. The numerical simulation was performed using the smoothed particle hydrodynamics (SPH) method with velocity and temperature settings as initial conditions. Good agreement was obtained between the simulation results and the experimental data, making the SPH simulation suitable for analysis of the deformation of particles and the substrate during detonation spraying. Information about the particle’s shape evolution during the collision is presented. An increase in temperature and plastic strain is analyzed at different points of the particle and substrate. Under certain spraying regimes, it is possible to melt a solid particle due to its high-strain-rate deformation, but no melting of the substrate was observed during the simulation

Structure and Oxidation Behavior of NiAl-Based Coatings Produced by Non-Vacuum Electron Beam Cladding on Low-Carbon Steel

NiAl-based intermetallic coatings were obtained using non-vacuum electron beam cladding on low-carbon steel. The structure of the coatings was investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). The coatings mostly consisted of grains elongated perpendicular to the substrates, with a strong <100> texture along the grain growth direction. The coatings contained about 14 at. % Fe, which appeared due to the partial melting of the steel substrate. At the bottom of the coatings, an inhomogeneous mixing zone with an increased concentration of Fe was formed; at the “substrate–coating” interface, a thick layer with a Fe50-Ni25-Al25 at. % composition was observed. The samples exhibited weight gains of 0.1, 0.8, 2.14, and 3.4 mg/cm2 after 100 h of oxidation at 700, 800, 900, and 1000 °C, respectively. The oxide layer contained α-Al2O3 and θ-Al2O3, and the presence of iron atoms contributed to the formation of a small amount of spinel. During the oxidation process, a layer with a high Fe content (~60 at. %) formed along the boundary between the oxide film and the NiAl-based material, which had a positive effect on the formation of a non-porous “oxide–coating” interface

Structure and Properties of Ti-Al-Ta and Ti-Al-Cr Cladding Layers Fabricated on Titanium

Being one of the most high-demand structural materials, titanium has several disadvantages,including low resistance to high-temperature oxidation and wear. The properties of titaniumand its alloys can be improved by applying protective intermetallic coatings. In this study, 2 mm thickTi-Al-Ta and Ti-Al-Cr layers were obtained on titanium workpieces by a non-vacuum electron-beamcladding. The microstructure and phase compositions of the samples were different for variousalloying elements. The Cr-containing layer consisted of 2, , and B2 phases, while the Ta-containinglayer additionally consisted of !0 phase (P3m1). At the same atomic concentrations of aluminum andan alloying element in both layers, the volume fraction of the B2/! phase in the Ti-41Al-7Ta alloywas significantly lower than in the Ti-41Al-7Cr alloy, and the amount of phase was higher. The Ti-41Al-7Cr layer had the highest wear resistance (2.1 times higher than that of titanium). The maximumoxidation resistance (8 times higher compared to titanium) was observed for the Ti-41Al-7Ta layer

Structure and Oxidation Behavior of NiAl-Based Coatings Produced by Non-Vacuum Electron Beam Cladding on Low-Carbon Steel

NiAl-based intermetallic coatings were obtained using non-vacuum electron beam cladding on low-carbon steel. The structure of the coatings was investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). The coatings mostly consisted of grains elongated perpendicular to the substrates, with a strong texture along the grain growth direction. The coatings contained about 14 at. % Fe, which appeared due to the partial melting of the steel substrate. At the bottom of the coatings, an inhomogeneous mixing zone with an increased concentration of Fe was formed; at the “substrate–coating” interface, a thick layer with a Fe50-Ni25-Al25 at. % composition was observed. The samples exhibited weight gains of 0.1, 0.8, 2.14, and 3.4 mg/cm2 after 100 h of oxidation at 700, 800, 900, and 1000 °C, respectively. The oxide layer contained α-Al2O3 and θ-Al2O3, and the presence of iron atoms contributed to the formation of a small amount of spinel. During the oxidation process, a layer with a high Fe content (~60 at. %) formed along the boundary between the oxide film and the NiAl-based material, which had a positive effect on the formation of a non-porous “oxide–coating” interface

Influence of the Ti/Al/Nb ratio on the structure and properties on intermetallic layers obtained on titanium by non-vacuum electron beam cladding

Ti-Al-Nb based intermetallic layers of sufficient quality and thickness were obtained by non-vacuum electron beam cladding on the surfaces of Ti workpieces. Optical microscopy and X-ray tomography did not reveal any dramatical defects in the structure of cladded layers. X-ray diffraction as well as scanning and transmission electron microscopy were applied to thoroughly investigate the structure and phase composition of coatings. It was found that non-equilibrium cooling conditions of coatings provided by fast removal of heat to untreated Ti substrate after the electron beam cladding was terminated induced the proceeding of metastable phase transformations. For example, γ-phase formation was suppressed in these coatings. In coatings with 8 and 20 at.% Nb (46 and 43% Al respectively) along with ordered with α2, formation of disordered solution of the alloying elements in α-Ti took place. In high-Nb alloys β(B2) phase has undergone the diffusionless transformation to ω’, which is the intermediate phase in β → ω and the coating with the maximum Nb content characterized by appearance of γ1 as a main phase. ω-phase had negative influence to hardness and wear resistance of coatings, however, generally this paremeter increased in 1.3–1.75 times compared to cp-Ti. The high temperature creep and oxidation properties decreased proportionally with increasing Nb and decreasing Al content in the cladded layers

On the texture and superstructure formation in Ti–TiAl3_3–Al MIL composites

In recent decades, metal-intermetallic laminated (MIL) composites are of great interest to the scientific community. The intermetallic layers in such composites possess a strong crystallographic texture and can form various superstructures. However, these effects are rarely discussed in the literature. By application of synchrotron X-ray diffraction (SXRD) we show, that an intermetallic layer in explosively welded and annealed Ti-Al-based MIL composite consists of two modifications of titanium trialuminide: TiAl$_3$ with a D0$_{22}$ structure and its superstructure Ti$_8$Al$_{24}$. According to SXRD analysis, the volume fraction of the Ti$_8$Al$_{24}$ modification increases from Al/intermetallic interface towards Ti/intermetallic interface. This may be caused by the lack of Al for the formation of stoichiometric titanium trialuminide near the interface with Ti, which leads to the formation of a long-period structures having Ti$_{1+x}$Al$_{3-x}$ stoichiometry. Two types of fiber texture were formed in the titanium trialuminide layer: [001] near the Ti/intermetallic interface and near the Al/intermetallic interface, which is caused by peculiarities of Ti and Al atoms migration. To explain the features of the forming texture, hypothetical mechanisms of Al and Ti diffusion in the intermetallic layer are discussed in this study: a vacancy diffusion, an interstitial diffusion, and a six jump vacancy cycle (6JVC)

In situ synchrotron X-ray diffraction study of reaction routes in Ti-Al3Ti-based composites: The effect of transition metals on L12 structure stabilization

In the last few decades, Ti-Al$_3$Ti composites have attracted great attention due to their outstanding mechanical characteristics, such as low density, high specific strength and stiffness, and ballistic properties. However, their application is still limited due to the low ductility and fracture toughness of the Al$_3$Ti phase. A promising way to improve the composite’s properties is to transform the Al$_3$Ti crystal structure from the tetragonal D0$_{22}$ type to the cubic L1$_2$ type. In this study, the stabilization of the L1$_2$ structure of titanium trialuminide during the fabrication of the Ti-Al3Ti composite is discussed. For this reason, the method of in situ synchrotron X-ray diffraction analysis was used to observe the reactions in the ternary Ti-Al-M systems (where M is Zn, Au, Ag, Ni, Pd, Pt, Mn, Fe, Co or Cr) during heating from room temperature to 830 °С. Zn and Ag were found to be the most efficient stabilizers of the L1$_2$ structure. In composites alloyed with Fe, Co, and Cr, the L1$_2$ structure of Al$_3$Ti was not stabilized. Formation of L1$_2$-structured titanium trialuminide in the remaining systems was accompanied by the formation of a large number of co-products. To select the elements stabilizing L1$_2$ structure in the composite with an excess amount of Ti, the following principle was formulated: the preferable stabilizers are the elements with FCC and HCP structures and a melting temperature below 1100 °С, and which do not form refractory Al-rich binary compounds with a melting point above 1000 °С