Effect of surface roughness on the development of protective Al2O3 on Fe-10Al (at.%) alloys containing 0-10 at.% Cr

The effect of alloy surface roughness, achieved by different degrees of surface polishing, on the development of protective alumina layer on Fe-10 at.% Al alloys containing 0, 5, and 10 at.% Cr was investigated during oxidation at 1000 °C in 0.1 MPa oxygen. For alloys that are not strong Al₂O₃ formers (Fe-10Al and Fe-5Cr-10Al), the rougher surfaces increased Fe incorporation into the overall surface layer. On the Fe-10Al, more iron oxides were formed in a uniform layer of mixed aluminum- and iron-oxides since the layer was thicker. On the Fe-5Cr-10Al, more iron-rich nodules developed on an otherwise thin Al₂O₃ surface layer. These nodules nucleated preferentially along surface scratch marks but not on alloy grain boundaries. For the strong Al₂O₃-forming Fe-10Cr-10Al alloy, protective alumina surface layers were observed regardless of the surface roughness. These results indicate that the formation of a protective Al₂O₃ layer on Fe-Cr-Al surfaces is not dictated by Al diffusion to the surface. More cold-worked surfaces caused an enhanced Fe diffusion, hence produced more Fe-rich oxides during the early stage of oxidation.     

高压下Al与Fe-Mo-Si-B合金固态反应形成Al-Fe基玻璃合金的研究

 在4 GPa，700~900 K温度范围内研究了Al与非晶(Fe_0.99, Mo_0.01)₇₈Si₉B₁₃合金的固态反应过程。利用透射电镜、X射线衍射仪和扫描电镜研究了Al与非晶(Fe_0.99, Mo_0.01)₇₈Si₉B₁₃合金界面所形成的扩散层的微观结构。在780~840 K温度范围内形成的扩散层中观察到Al-Fe基玻璃合金，其晶化温度为870 K左右。还对Al-Fe基玻璃合金的形成机理进行了研究。     

Growth of Ni-Al alloys on Ni(1 1 1): (I) Formation of epitaxial Ni3Al from ultra-thin Al deposits

In this paper we describe the alloying process of ultra-thin Al layers (below 8 × 10¹⁵ Al/cm²) deposited on Ni(1 1 1). For this purpose Auger electron spectroscopy, low energy electron diffraction, and ion beam analysis-channelling measurements have been performed in situ in an ultra-high vacuum chamber. Al deposits formed at low temperature (about 130 K) are strained defective crystalline layers retaining the substrate orientation. Alloying takes place, with very progressive Ni enrichment, in a very broad temperature range between 250 K and 570 K. This feature shows that diffusion of the alloy species is more and more difficult when the Ni concentration increases. At 570 K a crystallographically and chemically ordered Ni₃Al phase is formed, and its order continuously improves upon annealing, up to 750 K. We have shown by ion beam methods that this alloy is three-dimensional, extending up to 16 (1 1 1) planes for the thickest deposits. The Ni₃Al phase can also be obtained directly by Al deposition at 750 K, but its crystalline quality is lower and the layer is probably formed of grains elongated along 〈1 1 −2〉 directions. The Al content of the thin Ni₃Al layers formed mostly dissolves in the bulk above 800 K. However a small amount of Al remains segregated at the Ni crystal surface.     

Self-diffusion of aluminium in the intermetallic compound Fe-48 at.% Al

The self-diffusion coefficient of Al in the B2-type intermetallic compound Fe-48 at.% Al has been determined using the intrinsic diffusion coefficients of Fe and Al and the self-diffusion coefficient of Fe with the help of the Darken-Manning relation. The self-diffusion coefficient of Al in Fe-48 at.% Al is estimated to be a factor of about 0.6 smaller than that of Fe, and the activation energy for the self-diffusion of Al is obtained to be 280 kJ mol^?1 which is a little larger than the value of 262 kJ mol^?1 for the self-diffusion of Fe, indicating that the diffusion mechanisms for both components are nearly equal.     

Positron annihilation spectroscopy characterization of effect of intermetallic nanoparticles on accumulation and annealing of vacancy defects in electron-irradiated Fe–Ni–Al alloy

The effect of intermetallic nanoparticles like Ni₃Al and nanoparticles of an Fe-rich bcc phase on the evolution of vacancy defects in an fcc Fe–34.2 wt% Ni–5.4 wt% Al model alloy under electron irradiation at elevated temperatures (423 and 573 K) was investigated using positron annihilation spectroscopy. Nanosized (1–8 nm) particles, which are homogeneously distributed in the alloy matrix, cause a several-fold decrease in the accumulation of vacancies as compared to their accumulation in a quenched alloy. This effect depends on the size and the type of nanoparticles. The effect of the nanoparticles increases when the irradiation temperature increases. The irradiation-induced nucleation and the growth of intermetallic nanoparticles were also observed in an alloy pre-aged at 1023 K under irradiation at 573 K. Thus, a quantum-dot-like positron state within ultrafine intermetallic particles, which we revealed earlier, allows control of the evolution of coherent precipitates like Ni₃Al, along with vacancy defects, during irradiation and subsequent annealing. Possible mechanisms of the absorption of point defects by nanoparticles are discussed.     

Microstructure evolution process of Ferro-Aluminum based sandwich composite for electromagnetic shielding

In this paper, sandwich composite (SWC) with Fe–Al soft magnetic alloy sandwiched between pure iron substrates was proposed and fabricated by hot pressing and diffusion treatment. The microstructure evolution process of the composite was investigated. Fe/Fe₂Al₅/Fe diffusion couple was obtained at 700 °C and subsequently kept at 900 °C for further isothermal diffusion. During the diffusion reactive process, we confirmed that major FeAl₂ and minor Fe₄Al₁₃ were produced when Fe₂Al₅ dissolved. After 10 h of diffusion treatment, FeAl and α-Fe(Al) were the only two intermetallic phases left. Except FeAl₂, the thickness of each intermetallic layer held good parabolic relationship with the diffusion annealing time.     

Ion-beam-induced atomic transport and phase formation in the system nickel/antimony

We report on the ion-beam mixing processes of Sb/Ni marker layers and bilayers under the irradiation of ions ranging from He to Pb, at 80 K and at room temperature. The concentration profiles are obtained by Rutherford backscattering spectroscopy with 900 keV -particles. At 80 K, the bilayer mixing rates cannot be reproduced by purely ballistic mixing; the essentially linear scaling of the bilayer mixing rate with the energy F _D deposited at the interface points to local spike formation. A transition to global spike formation seems to be visible for the Pb-irradiations. Additional mixing effects at 300 K are due to radiation enhanced diffusion and scale with F _D. The marker mixing rates at 80 K are reproduced by the ballistic mixing approach, but are equally well described by local spike models. High fluence Xe-irradiations of Sb/Ni bilayers lead to intermetallic phases in the interface region as verified by transmission electron microscopy.     

A CEMS investigation of57Fe+Al implanted in Al foil

⁵⁷Fe implanted and post Al implanted in aluminum foil have been performed at low energy of 27keV and the CEMS shows the formation of intermetallic compounds FeAlσ and Fe₂Alσ during the ion bombardment. The results are discussed with the enhanced diffusion by energetic ion bombardment.     

Investigation of magnetic properties in 57Fe/Al multilayers

Fe/Al multilayer thin films prepared by ion beam sputtering, with an overall atomic concentration ratio of Fe/Al = 1:2 have been studied by x-ray diffraction spectroscopy (XRD), X-ray reflectivity (XRR) and D.C. Magnetization. These studies show the formation of Fe–Al intermetallic layers. Two magnetic regions and transition temperatures of 473 and 533 K are evident from magnetization studies. Conversion Electron Mössbauer Spectroscopy (CEMS) shows formation of off-stoichiometric Fe₃Al like phase and phases consisting of pure Fe and Fe-rich extended Fe–Al solutions.     

Study of the Microstructure,Crystallographic Structure and Thermal Stability of Al–Ti–Nb Alloys Produced by Selective Electron Beam Alloying

This paper aims an investigation of the microstructure and crystallographic structure as well as the thermal stability of Al–Ti–Nb formed by selective electron beam surface alloying. The fabrication of the samples has been carried out using circular sweep mode, as two velocities of the sample movement have been chosen: V₁ = 1 cm/s and V₂ = 0.5 cm/s. The studied microstructure and crystallographic structure have been investigated by X-ray diffraction (XRD) and Scanning electron microscopy (SEM) respectively. The thermal behavior of the obtained surface alloys are evaluated by the coefficient of thermal expansion (CTE) which has been evaluated by neutron diffraction measurements at high temperature. The results show that in the earlier stages of formation, the microstructure of the intermetallic phase is mainly in the form of coarse fractions, but at the following moments they dissolve, forming separated alloyed zone and base Al substrate as the alloyed zone consists of fine (Ti,Nb)Al₃ particles dispersed in the Al matrix with small amount of undissolved intermetallic fractions. Formation of preferred crystallographic orientation as a function of the speed of specimen motion has not been observed. The performed neutron diffraction measurements show that the lattice parameters of the obtained intermetallic (Ti,Nb)Al₃ are less upshifted in comparison to pure Al. It has been found that the aluminium lattice is much more unstable at high temperatures than that of the intermetallic phase. The CTE for the intermetallic phase is 8.70 ppm/K for a axis and 7.75 ppm/K for c axis respectively while considering Al it is 12.95 ppm/K.     

Theoretical study of Ti and Fe surface alloys on Al(0 0 1) substrate

Accurate density-functional calculations are performed to investigate the formation of Ti and Fe ultrathin alloys on Al(0 0 1) surface. It is demonstrated that a deposition of Ti monolayer on Al(0 0 1) substrate leads to the formation of Al₃Ti surface alloy with Ti atoms arranged according to the L1₂ stacking, distinct from the D0₂₂ structure characteristic of a bulk Al₃Ti compound. A quest for the reason of this distinct atomic arrangement led us to the study of the surface structure of Al₃Ti(0 0 1) compound. It is concluded that even the Al₃Ti(0 0 1) surface is terminated with three layers assuming a L1₂ stacking and hence this stacking fault can be classified as a surface-induced stacking fault. Several possibilities of Fe atoms distributed in the surface region of Al(0 0 1) have been examined. The most stable configuration is the one with the compact Fe monolayer on Al(0 0 1) and covered by one Al monolayer. Lastly, our calculations show that there is no barrier for the penetration of Fe adatoms below the Al(0 0 1) surface; however, such a barrier is present for a Ti-alloyed Al(0 0 1) surface.     

Vacancies effect on the mechanical properties in B2 FeAl intermetallic by the first-principles study

ABSTRACT

The geometric structures, electronic and mechanical properties of the high vacancy concentration intermetallic FeAl (experimental value: 3.3 at.% at 1451?K) were investigated by first-principles calculations based on density functional theory. The FeAl structures of different vacancy concentration with minimum energy were addressed, which shows that vacancies of iron (V_Fe) are more favourable and tend to gather together. For mechanical properties, both Young's modulus and elastic constants show an overall downward trend as vacancy concentration increases, but increase abnormally with the vacancy concentration ranging from 3.7 at.% to 5.6 at.%. All can be explained by the strength of Al–Fe bond, in other words, the Al–Fe interaction. Interestingly enough, intermetallic FeAl shows a transfer from the brittle manner to ductile manner, which also behaves as an important feature of FeAl in experiments. All the mechanical properties agree well with experimental data, indicating the reasonable vacancy model of FeAl intermetallic.     

Effect of temperature on solid-state formation of bulk nanograined intermetallic Al3Ni during high-pressure torsion

A bulk form of nanograined intermetallic Al₃Ni was produced by severe plastic deformation using high-pressure torsion (HPT). Powder mixtures of 75?mol% Al and 25?mol% Ni were processed by HPT at a selected temperature in the range of room temperature (RT) to 573?K under a pressure of 6?GPa. X-ray diffraction analysis revealed that the Al₃Ni intermetallic formed after processing for 50 revolutions at RT but, as the processing temperature increased, less revolutions (i.e. lower imposed strain) were required for the formation of Al₃Ni. Observations by transmission electron microscopy showed that the microstructure consists of ultrafine grains having a size of 300–2000?nm after 3 and 10 revolutions. Once the Al₃Ni formed after a higher number of revolutions, equiaxed nanograins with a size of ~30?nm prevailed with a significant increase in hardness. The increase in hardness was more significant when processed at higher temperatures because of increasing the fraction of Al₃Ni. It was shown that the solid-state formation of Al₃Ni occurred due to enhanced diffusion (i.e. decreased activation energy for diffusion) through the presence of high density of lattice defects.     

Magnetic properties of RAuNi4 rare earth compounds

Magnetization studies of new f.c.c. RAuNi₄ intermetallic compounds were performed. The compounds with R = Gd, Tb, Dy, Ho and Er are ferromagnetically ordered at temperatures ranging from 14 to 38K. Two ferromagnetic transitions were observed in the magnetization curves. TmAuNi₄ and YbAuNi₄ exhibit paramagnetic behaviour for temperatures as low as 4.2 K.     

Diffusion in ordered Fe-Si alloys

The measurement of the diffusional Mössbauer line broadening in single crystalline samples at high temperatures provides microscopic information about atomic jumps. We can separate jumps of iron atoms between the various sublattices of Fe-Si intermetallic alloys (D0₃ structure) and measure their frequencies. The diffusion of iron in Fe-Si samples with Fe concentrations between 75 and 82 at% shows a drastic composition dependence: the jump frequency and the proportion between jumps on Fe sublattices and into antistructure (Si) sublattice positions change greatly. Close to Fe₃Si stoichiometry iron diffusion is extremely fast and jumps are performed exclusively between the three Fe sublattices. The change in the diffusion process when changing the alloy composition from stoichiometric Fe₃Si to the iron-rich side is discussed.     

A Mössbauer study on the ion-beam-induced phases in the Fe/Al thin film bilayer

Conversion Electron Mössbauer Spectroscopy, (CEMS), has been used to study ion-beam-induced mass transport and phase formation in the Fe/Al bilayer system. In a previous work it was shown that ion irradiation in the same system with noble gases (Ar⁺, Kr²⁺, and Xe³⁺) leaded to the formation of non intermetallic phases when the samples were kept at 77 and 300 K during the bombardments. On the other hand, intermetallic phases were observed for irradiations at substrate temperature of 500 K. The last experimental condition for phase formation corresponds to a lower temperature than conventional thermal treatment needs to reach the same phase. Here, the irradiation conditions were devised to account intermediate substrate temperatures, namely 200 and 400 K, in order to identify the effect of the implantation dose in the phase formation. The intermetallic phases observed in the samples submitted to irradiations at substrate temperature of 500 K, are now formed by even lower temperature-400 K. The results also show a threshold dose of irradiation above which the intermetallic phases are formed. These observations are discussed in terms of a superposition of collision cascades.     

Diffusion in the aged aluminium film on iron

Metallic coatings of many types can be applied to steel to provide outstanding, long-term corrosion protection. A thin Al film is studied at an Fe substrate by the molecular dynamics method at temperatures ranging from 300 K to 1173 K. Al atoms are found to penetrate the Fe matrix at a temperature of 873 K. The potential energy of the system changes step-like at a temperature of 1173 K. At such temperature mean square atomic displacement significantly changes. The behaviors of the Al and Fe diffusion coefficients are mainly determined by the temperature dependence of the diffusion activation energy.     

Untersuchungen zur Supraleitung des Legierungssystems Zr-Rh

The transition temperatures of Zr-Rh alloys with small amounts of Rh are essentially higher than the transition temperature of pure Zr. Rhodium is not dissolved in the Zr lattice. In the unannealed specimens Rh stabilizes the body centered cubic phase which has aT _c of 6.4°K. After annealing an intermetallic compound is formed with aT _c of about 12°K. This compound is also formed in the unannealed specimens at higher Rh content.     

Microstructure and tribological properties of TiCu2Al intermetallic compound coating

TiCu₂Al ternary intermetallic compound coating has been in situ synthesized successfully on pure Ti substrate by laser cladding. Tribological properties of the prepared TiCu₂Al intermetallic compound coating were systematically evaluated. It was found that the friction coefficient and wear rate was closely related to the normal load and sliding speed, i.e., the friction coefficient of the prepared TiCu₂Al intermetallic compound coating decreased with increasing normal load and sliding speed. The wear rate of the TiCu₂Al intermetallic compound coating decreased rapidly with increasing sliding speed, while the wear rate first increased and then decreased at normal load from 5 to 15 N.     

Mössbauer study of the stability of Fe5Si95 produced by inert gas condensation

Fe₅Si₉₅ specimens with an enhanced solubility of Fe in Si by about twenty-one orders of magnitude relative to crystalline Si at room temperature were prepared by the inert gas condensation technique. The thermal stability of the Fe₅Si₉₅ sample was investigated by Mössbauer spectroscopy. The spectrum of the as-prepared Fe₅Si₉₅ exhibited a broadened many different iron sites in the sample. This material was thermal stable up to temperatures of 673k for one hour. After annealing at 773K for one hour, the intermetallic compound α-FeSi₂ was formed in the annealed sample, probably via the precipitation process. The amount of the α-FeSi₂ phase increased with the annealing temperature. No β-FeSi₂ phase was observes in any of the annealed samples up to an annealing temperature of 1273K For one hour.