Tonica Bončina

Structure of continuously cast Ni-based superalloy Inconel 713C

Abstract In this work, we characterised the structure of continuously cast Ni-based superalloy IN 713C (∅ 10 mm, water cooled Cu–Be mould, argon atmosphere) using several microstructural characterization techniques (LM, SEM, TEM, EDS, XRD). The structure consisted of columnar dendritic γ-grains with apparently fully coherent and rather uniformly distributed γ′ precipitates (size ∼50 nm), primary MC carbide and MC/γ eutectic. The eutectic MC carbide contained a considerable amount of Cr: (Nb0.4Mo0.25Ti0.18Cr0.16)C resulting in a decrease in the MC lattice constant from 0.441 to 0.435 nm. Due to higher cooling rates at continuous casting the microstructural constituents were much finer than in the as-received and DTA samples. In addition, the continuously cast specimens did not contain the γ/γ′ eutectic and some minor phases despite stronger segregation of solute elements. The partition coefficients of solute elements Ti, Mo, Nb, Al, Cr, Fe and Ni in the continuously cast IN 713C were 0.55, 0.82, 0.46, 0.99, 0.96, 1.02 and 1.03, respectively.

Characterization of cast Al86Mn3Be11 alloy.

An Al86Mn3Be11 alloy cast into copper mould was subjected to metallographic investigation. The as‐cast microstructure consisted of a quasicrystalline icosahedral phase (i‐phase), Be4AlMn phase and, occasionally, a hexagonal phase. Al‐rich solid solution represented the dominant phase. The chemical compositions of phases were determined using AES. The composition of the Be4AlMn slightly deviated from the stoichiometric composition, whereas the composition of the i‐phase was approximately Al52Mn18Be30, containing an appreciable amount of Be. The average composition of the hexagonal phase was Al66Mn21Be13. Deep etching and particle extraction provided a deep insight into the three‐dimensional morphology of the i‐phase and the hexagonal phase, whereas Be4AlMn was slightly attacked by the etchant. The i‐phase was present predominantly in the form of dendrites and a rodlike eutectic phase. The hexagonal phase was primarily in the form of hexagonal platelets, whereas Be4AlMn was rather irregular in shape. The morphology of the i‐phase can be explained by predominant growth in 3‐fold directions and the lowest energy of the 5‐fold planes, leading to the faceting and adopting a pentagonal dodecahedron shape. The brightnesses of phases in the backscattered electron images were rationalized by determining their backscattering coefficients. TEM investigation showed considerable phason strain in the i‐phase, and the polycrystalline nature of the Be4AlMn phase.

Development of an Al–Mn–Be–Cu alloy with improved quasicrystalline forming ability

Abstract An Al94Mn2Be2Cu2 cast alloy was developed displaying increased quasicrystalline formation ability at moderate cooling rates. The as-cast microstructure consisted of a mainly icosahedral phase in the Al-matrix. The microstructure remained stable during uniform heating to 580 °C and isothermal annealing at 400 °C. Most of the icosahedral phase was preserved even after 24 h annealing at 500 °C. For that reason, this alloy presents a promising basis for further development of cast Al-alloys containing quasicrystals.

Effect of Ce on morphology of α(Al)–Al2Cu eutectic in Al–Si–Cu alloy

Abstract The effect of Ce addition on the morphology of the α(Al)–Al 2 Cu eutectic in Al–Si–Cu alloy was investigated using thermal analysis, light microscopy, scanning electron microscopy, focused ion beam and energy dispersive analysis. The results show that the eutectic α(Al)–Al 2 Cu forms within small space between dendrites, silicon and AlSiFeMn plates. Eutectic Al 2 Cu is not lamellar but degenerated. However, Al 2 Cu in Ce-modified alloys is more compact. Ce partially dissolves in Al 2 Cu, which is a viable reason for the formation of coarser Al 2 Cu. The addition of Ce also increases the microhardness of the α(Al)–Al 2 Cu eutectic by almost 10% compared with the basic Al–Si–Cu alloy.

Microstructural constituents of the Ni-based superalloy GMR 235 in the as-cast condition

Abstract The Ni-based superalloy GMR 235 was investigated in different as-cast conditions. It consisted of the γ matrix with γ ′ precipitates, and of three minor constituents: M 3 B 2 , MC and Ti(C,N). The cooling rate influenced the size and morphology of microstructural constituents, and the composition and lattice constants of M 3 B 2 and MC.

Phases in the Al-corner of the Al-Mn-Be system.

This work studied the phases in the Al corner of the Al-Mn-Be phase diagram in the as-cast state and heat-treated conditions. Metallographic investigations, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy were used for identifying the phases. The Be contents in the identified phases were precisely determined using Auger electron spectroscopy. The results indicated that Al₆Mn does not dissolve Be, whilst λ-Al₄Mn dissolves up to 7 at.% Be. The average composition of the T phase, which is normally designated as Al₁₅Mn₃Be₂, was 72 at.% Al, 19 at.% Mn, and 9 at.% Be. The phase with the nominal composition Be₄AlMn contained more Al than Mn. The atomic ratio Al:Mn was between 1.3:1 and 2:1. The hexagonal Be-rich phase did not dissolve any Al and Mn. The icosahedral quasicrystalline (IQC) phase contained up to 45 at.% Be. The compositions of T phase, λ-Al₄Mn, IQC, and Be₄AlMn may vary, however, the ratio (Al + Be):Mn remained constant, and was close either to four or six indicating substitution of Al atoms with Be atoms in these phases.

Metallographic techniques for the characterization of quasicrystalline phases in aluminium alloys

Abstract Several Al-alloys strengthened by quasicrystalline phases have been developed over the last few years showing the considerable potential for practical application. Therefore there is a strong need for developing new metallographic methods or adapting the traditional ones in order to identify and characterize quasicrystalline phases in a reliable, quick and economical way. This paper describes different techniques: the classical metallographic method, deep etching, particle extraction technique and cross-sectioning using focused ion beam (FIB), and discusses their advantages and disadvantages when identifying quasicrystalline particles. It was discovered that particle extraction techniques are very powerful methods for the identification of phases according to their morphology, and preparation of quality samples for X-ray diffraction (XRD). Transmission electron microscopy (TEM) analyses are also possible provided the extracted particles are thin enough.

Orientation Relationships of Precipitates with the Matrix in an Aluminum Quasicrystalline Alloy

Aluminum quasicrystalline alloys present a novel class of high-strength alloys. They possess a high potential for practical applications in many fields. In this study, we used a quasicrystalline Al-alloy with a copper addition to achieving strengthening by heat treatment. The alloys were prepared by melt-spinning and by casting into a copper mold. In both cases, quasicrystals formed during solidification either as a primary phase or as a part of a quasicrystal-containing eutectic. Afterward, the samples were subjected to T5 heat treatment. The hardness of the melt-spun ribbons increased considerably while the hardness of the gravitationally cast samples did not change noticeably. A detailed investigation using transmission electron microscopy (TEM) showed that different types of precipitates can form. At lower temperatures, binary Al-Cu precipitates formed, in the intermediate region prevailed the quasicrystalline precipitates, while at higher temperatures formed T-precipitates (Al20Mn3Cu2). Particular attention was given to determination of their orientation relationships with the Al-rich matrix.

Dynamic Deep Etching and Particle Extraction For High‐Strength Aluminum Alloys

Aluminum alloys contain many phases that can form during different processing steps. Their type, size, and morphology have a significant influence on various properties of the alloys. Thus, the determination of all their geometrical features is very important. Knowing the 3D particle shapes is essential not only for choosing the best processing routes for conventional alloys but also for designing new alloys.

Analytical TEM of i-phase in an Al94Mn2Be2Cu2 alloy

Quasicrystals form an additional state of matter to those of crystalline and glassy. The atoms positions are ordered but with non-crystallographic rotational symmetry and without three-dimensional periodicity (Shechtman, Blech et al. 1984). The first icosahedral quasicrystal (i-phase) discovered in the Al-Mn system was metastable. It could be formed by rapid solidification, but not during conventional casting, e.g. by casting into metallic dies. Several ternary and quaternary alloys based on the Al-Mn system were developed during the last decade, forming quasicrystals during conventional casting. Yet, considerable amounts of crystalline intermetallic phases could not be avoided (Kim, Song et al. 2002). Recently, the Al94Mn2Be2Cu2 alloy has been developed exhibiting very high quasicrystalline forming ability. The i-phase formed at moderate cooling rates typical for the conventional die casting (around 1000 K/s) (Zupanic, Boncina et al. 2008). It is of great interest to understand the role of Be and Cu when increasing the tendency for forming the iphase, and their influence on its structure and composition. Analytical TEM was chosen as a convenient method due to small particle sizes, the specifics of the quasicrystalline structure and the content of beryllium in the alloy.