Franc Zupanič

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.

Microstructural evolution in Al–Mn–Cu–(Be) alloys

This study investigates the effects of alloying elements on the microstructural evolution of Al-rich Al–Mn–Cu–(Be) alloys during solidification, and subsequent heating and annealing. The samples were characterised using scanning electron microscopy, energy dispersive X-ray spectroscopy, synchrotron X-ray diffraction, time-of-flight secondary-ion mass spectroscopy, and differential scanning calorimetry. In the ternary Al94Mn3Cu3 (at%) alloy, the phases formed during slower cooling (≈1 K s−1) can be predicted by the known Al–Mn–Cu phase diagram. The addition of Be prevented the formation of Al6Mn, decreased the fraction of τ1-Al29Mn6Cu4, and increased the fraction of Al4Mn. During faster cooling (≈1000 K s−1), Al4Mn predominantly formed in the ternary alloy, whereas, in the quaternary alloys, the icosahedral quasicrystalline phase dominated. Further heating and annealing of the alloys caused an increase in the volume fractions of τ1 in all alloys and Be4Al (Mn,Cu) in quaternary alloys, while fractions of all other intermetallic phases decreased. Solidification with a moderate cooling rate (≈1000 K s−1) caused considerable strengthening, which was reduced by annealing for up to 25% in the quaternary alloys, while hardness remained almost the same in the ternary alloy.

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.

Effect of thermal processing on the characteristics of incineration fly ash

This work investigated the possibilities of immobilizing incineration fly ash by applying different processing methods. Direct sintering of fly ash at 1050 °C produced material with increased resistance to leaching; however, the high content of halides prevented the achievement of appropriate strength. Fly ash melting and casting into metallic moulds resulted in the formation of glass with good chemical resistivity and mechanical properties, which were further improved by devitrification, and the formation of glass-ceramics. The most successful combination of strength and resistance to leaching was obtained by a process consisting of fly ash melting, by pouring the melt into water, then grinding, and sintering without additives at 850–950 °C. In this way, a material was produced that cannot only be landfilled as a stabilised and non-reactive waste in landfills for non-hazardous wastes, but can also be utilized as a valuable material for manufacturing useful products. This article provided valuable results for policy-makers in Slovenia, about the handling fly ash from incineration plants. Implications Fly ash from an incineration plant was thermally treated using several processing routes. Ash-melting, by pouring the melt into water and sintering, produced glass-ceramics having an optimal combination of strength and resistance to leaching that can find applications as useful products. These results provide important data for policy makers in Slovenia regarding the building of incineration plants, and handling the solid-waste products, especially fly ash.

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.

Microstructural evolution on continuous casting of nickel based superalloy Inconel* 713C

Abstract In the present work, the evolution of microstructure in the nickel based superalloy Inconel 713C was investigated for the vertical continuous casting of small cross-section rods (10 mm dia.), using several microstructural characterisation techniques. Microstructural evolution was greatly affected by the mould design, average casting speed, and distance from the rod surface, but the strongest influence was from the alternating drawing mode consisting of the drawing stroke, the resting period, and the reverse stroke, which caused periodic orientation changes of columnar γ crystal grains. Combined with other casting parameters this determined the local solidification conditions, influencing the formation and growth of γ dendritic grains and primary and eutectic MC carbide, as well as the stress distribution in the solidified shell, which caused shell deformation and the appearance of the inverse segregation and, occasionally, hot tears. A physical model is presented to explain the influence of casting parameters on microstructural evolution on the continuous casting of this alloy.