Dispersed Oxide Inclusions Research Articles

Effect of Al and Ti addition on the characteristics of oxide inclusions in Ni-based superalloy

The characteristics of inclusions have a significant influence on the performance and fatigue life of Ni-based alloy and some cracks usually initiate and propagate from inclusions. High-temperature experiments were carried out at 1823 K to study the effect of Al and Ti addition on the characteristics of oxide inclusions in Ni-based alloy. The size, number, distance, distribution of oxide inclusions and degree of homogeneity in inclusion dispersion in Ni-based alloy with [%Al]i = 0.3–0.7 and [%Ti]i = 0.7–1.2 (i represent initial addition of deoxidant) were analyzed systematically. It is found that the oxide inclusions in alloys with [%Al]i = 0.7, [%Ti]i = 0.7/1.2 had smaller average size of 2.4 µm and distributed more homogeneously. The Ostwald ripening theory and collision model were applied to point out the relationships among compositions of Ni-based alloy, behaviors of oxide inclusions and their characteristics under the condition of no external stirring. The calculated results were in good agreement with experimental results. The mechanism on obtaining fine and dispersed oxide inclusions in Ni-based alloy was summarized.

Microstructural characterisation of thick-walled wire arc additively manufactured stainless steel

• Microstructural features of a thick-walled WAAM stainless steel part are investigated. • Microstructure exhibits periodically repeating characteristics across the WAAM part. • Oriented and textured structure with large grains at the overlapping region of adjacent fusion zones. • Significant spatial variations in terms of fusion zone shape, grain structure, texture, and phases. Wire arc additive manufacturing (WAAM) is a class of technologies suitable for producing large parts due to its high material deposition and building rates. Among the many possible materials processed by WAAM, austenitic stainless steels, e.g. 316L, are commonly employed. The structure of WAAM 316L thin parts has been studied extensively before. However, multiwalled or thick WAAM 316L parts remain largely unexplored. Hence, in this study, the microstructure of a thick 316LSi WAAM part is characterised in detail. The microstructure of the part consists of large and highly-oriented columnar grains dominated by epitaxial and competitive growth. The overlapping regions between neighbouring fusion zones contain long grains with a dominant <100> texture, which cross several layers and are aligned with the building direction. The grains' internal microstructure consists of an austenite matrix, ferrite with locally varying dendritic morphologies and dispersed oxide inclusions. The texture spatially varies across the part, and this variation is correlated to the local thermal gradient induced by the building strategy and processing conditions used during the manufacturing of the thick-walled part.

Influence of oxide inclusion compositions on microstructure and toughness of weld metal for high-strength steel

The effect of oxide inclusion compositions on microstructure and notch toughness of weld metal for HT780MPa class high-strength steel was investigated. Three different types of weld metals were prepared by varying deoxidant elements. Intragranular bainite microstructure and dispersed oxide inclusions were observed and quantified by an optical microscope and by electron backscattered diffraction analyses to reveal the affectors of notch toughness. It has been found that fracture appearance transition temperature of the weld metal depends on the size of intragranular bainite (acicular ferrite) nucleated on oxide inclusions and that the upper shelf energy is affected by the density of dispersive oxides inclusions. It has also been clarified that all oxide inclusions, which contribute to intragranular transformations, consisted of titanium-rich crystalline phases and manganese-rich amorphous phases. By detailed finite element (FE)-TEM observation, the crystalline phases were identified as MnTi2O4 having Baker–Nutting orientation relationship with the intragranular bainite. It is considered that the reason for the bainite to have the orientation relationships of both MnTi2O4 and austenite is that the MnTi2O4 is generated at the interface between the amorphous phases and austenite previous to the intragranular transformation.

高強度溶接金属の組織および靭性に及ぼす酸化物系介在物組成の影響

The effect of oxide inclusion compositions on microstructure and notch toughness of weld metal for HT780MPa class high strength steel was investigated. Three different types of weld metals were prepared by varying deoxidant elements. Intragranular bainite microstructure and dispersed oxide inclusions were observed and quantified by an optical microscope and electron backscattered diffraction (EBSD) analyses to reveal affectors of notch toughness.It has been found that FATT of the weld metal depends on size of intragranular bainite (acicular ferrite) nucleated on oxide inclusions and that the upper shelf energy is affected by density of dispersive oxides inclusions. It has also been clarified that all oxide inclusions, which contribute to intragranular transformations, consisted of titanium-rich crystalline phases and manganese-rich amorphous phases. By detailed FE-TEM observation, the crystalline phases was identified as MnTi2O4 having B-N orientation relationship with the intragranular bainite. It is considered that the reason the bainite have the orientation relationships both MnTi2O4 and austenite is that the MnTi2O4 is generated at the interface between the amorphous phases and austenite previous to the intragranular transformation.

Enhanced ionic conduction in NaNO 3 by dispersed oxide inclusions

The composite solid electrolytes, NaNO 3 dispersed with Al 2O 3, CeO 2, ZrO 2 and SiO 2 have been prepared by melt quenching method and investigated through XRD, DSC and electrical conductivity techniques. Typical increase in conductivity is about two orders of magnitude for 10 mol% of Al 2O 3 at 200 °C. The electronic transference number evaluated through dc polarization method was found out to be 1×10 −2 at 200 °C. The dependence of conductivity on concentration of dispersoids and particle size is in accordance with the space charge theory of conduction. The enhanced conductivity of NaNO 3 homogenously doped by Ca(NO 3) 2 was further enhanced by heterogeneous doping of Al 2O 3. By the contribution of these doping processes, the conductivity is enhanced by three orders of magnitude at 200 °C. The experimental and theoretically calculated values of conductivity using Maier's space charge layer model are in reasonable agreement.

Prediction of the kinetics of breakdown of the metastable solid solution of an inert gas in aluminum and changes in the heat conductivity of microporous aluminum

Special heat treatment which causes the breakdown of supersaturated solid solutions of gases in metals [i] is one of the new types of synthesis of porous metals. For example, the authors of [2] developed compositions and synthesis technologyfor metastable solid-phase ternary compositions of the aluminum--argon-oxygen type (0,05-0.1% (wt.%) of argon; 0.016.6 oxygen). Argon and oxygen are added to aluminum by treating the latter in the cold plasma of a gas discharge. Argon forms a supersaturatedsubstitutional so!idsolution with the metal and oxygen combined with aluminum in the form of finely dispersedoxide inclusions. Those inclusions which retain their form and dimensions at elevated temperatures under high external loading increase the plastic deformation ~esistance of the composite.

Enhancement of ionic conductivity by dispersed oxide inclusions: Influence of oxide isoelectric point and cation size

Doping of a halide salt by dispersion of oxide particles rather than subtitutional impurities is a proven method of enhancing the extrinsic ionic conductivity of the host. The conductivity mechanism in any space-charge layer at the oxide/host interface is determined by the chemical reactions at the interface. These interactions are discussed by analogy with the particle hydrates. The enhancement of the F −-ion conductivity in PbF 2 is predicted to be via F −-ion vacancies in the space-charge region and to increase with decreasing oxide isoelectric point and increasing normal anion coordination of the oxide cation. This prediction accounts satisfactorily for the relative enhancement factors measured for PbF 2 containing dispersed CeO 2, SiO 2, ZrO 2 and Al 2O 3.

Some features of the rupture of a sintered nickel-chromium alloy containing dispersed oxide inclusions

1. The addition of dispersed ZrO2 to a sintered 80% Ni-20% Cr alloy reduces its resistance to rupture, mainly by facilitating crack initiation. 2. The crack propagation process, being much more energy-intensive than the crack initiation process, constitutes the critical stage of the rupture of a sintered Ni-Cr alloy containing dispersed zirconia. 3. The presence of fairly evenly distributed ZrO2 particles (up to 4%) does not significantly lower the resistance to crack growth of a sintered Ni-Cr alloy. 4. The tensile mechanical properties of a sintered Ni-Cr alloy (ultimate strength σv and elongation δ) are not uniquely related to its resistance to fracture crack propagation and do not constitute a criterion by which its low-temperature service performance can be judged.

Growth of dispersed oxide inclusions in 80% Ni - 20% Cr alloys during annealing

1. A study was made, using optical and electron microscopy techniques, of grain growth in an 80% Ni-20% Cr alloy matrix and of the behavior of ZrO2 and Al2O3 particles in this matrix during annealing at temperatures of 900 and 1150° C. 2. In dispersion hardening, the final structure of hot-extruded alloys is a result of two opposing processes, collective recrystallization of the original grains and recrystallization through nucleation. During the early stages of annealing, the principal process taking place is the growth of the starting grains, resulting in the formation of large aggregates of dispersed particles following the latter's displacement by the boundaries of growing grains. With increasing duration of annealing, a metallographically visible growth of recrystallization nuclei begins, resulting in a coarsening of fine particles of the dispersed phase. Annealing in air as opposed to hydrogen produces less coarsening of the dispersed phase, which is apparently attributable to a stabilizing effect of oxygen on the dissolution of fine oxide particles.

Strengthening of the 80%Ni - 20%Cr alloy with dispersed oxide inclusions : Ansiferov, V. N. and Polyakov, V. A. Soviet Powder Metallurgy, No 8, pp 654–656 (August 1969)

Strengthening of the 80%Ni - 20%Cr alloy with dispersed oxide inclusions : Ansiferov, V. N. and Polyakov, V. A. Soviet Powder Metallurgy, No 8, pp 654–656 (August 1969)

Nichrome with dispersed oxide inclusions

1. The addition of dispersed oxides Al2O3 or ZrO2 to Nichrome increases its heat resistance and restrains the development of recrystallization. 2. The strength at elevated temperatures is highest for Nichrome with ZrO2. The strength of Nichrome with 3% ZrO2 exceeds that of alloy KhN60V at 950°C.

Strengthening of the 80% Ni-20% Cr alloy with dispersed oxide inclusions

1. Reduction of 80% Ni-20% Cr alloy (VTU TsNIITsM 1277-65 technical specification) powder increases the tensile strength of the sintered alloy obtained from this powder 1.6–1.8 times. 2. Compared with a pure, sintered 80% Ni-20% Cr alloy, the same sintered alloy with dispersed A12O3 or ZrO2 inclusions possesses a higher heat resistance and improved short- and long-time strengths. 3. A technique has been developed for the preparation of virtually nonporous rods from 80% Ni-20% Cr alloy powder with A12O3 or ZhO2 inclusions. The highest heat resistance is exhibited by an alloy with 3% ZrO2; its tensile strength at 900°C is 39.6 kg/mm2, while its ductility properties are similar to those of a pure, sintered 80% Ni-20% Cr alloy.

The effect of dispersed oxide inclusions on certain properties of sintered chromium

1. The mixtures of chromium and dispersed zirconium oxide inclusions had the highest pressability and compaction during sintering. 2. Porosities are formed in the vicinity of MgO particles during sintering of Cr-MgO alloys. These evidently result from the volatility of MgO at the sintering temperatures investigated. 3. Increasing the sintering temperature from 1500 to 1600°C leads to an increase in the particle size of the hardening phase. 4. The mechanical properties (σbend,ak) were highest for the alloys with dispersed inclusions of zirconium dioxide and aluminum oxide.