T. Rojhirunsakool

Point-by-point compositional analysis for atom probe tomography

Graphical abstract

Probing the crystallography of ordered Phases by coupling of orientation microscopy with atom probe tomography

The determination of atomic scale structural and compositional information using atom probe tomography is currently limited to elemental solids and dilute alloys. In the present article, a unique coupling of orientation microscopy and atom probe tomography successfully facilitates the crystallographic study of non-dilute alloy systems, with high evaporation fields. This reproducible methodology affords a new perspective to the conventional atom probe tomography of ordered precipitate strengthened superalloys. The high accuracy in crystallographic site-specific sample preparation results in high spatial resolution in APT, which has been demonstrated in Co-base superalloys. The practical applications of this technique can be extended to accurately characterize the nature of buried order/disorder interfaces at the atomic scale, as well as the site occupancies associated with different solute atoms in multi-component superalloys.

Coarsening behaviour of gamma prime precipitates and concurrent transitions in the interface width in Ni-14 at.% Al-7 at.% Cr

Coupling atom probe tomography and transmission electron microscopy, the temporal evolution of γ′ precipitate morphology and size distribution and compositional width of the γ/γ′ interface, have been tracked in a model Ni-14Al-7Cr (at.%) alloy, during isothermal annealing at 800 °C subsequent to rapid quenching. During the initial annealing period, coalescence-dominated growth and coarsening of γ′ precipitates are accompanied by a gradual decrease in the interface width, eventually leading to classical LSW coarsening with a constant interface width at extended annealing time periods.

Effect of deposition energy on the microstructure and phase purity of pulsed laser deposited iron fluoride thin films

Conversion material electrodes, such as FeF2, possess the potential to deliver transformative improvements in lithium-ion battery performance because they permit a reversible change of more than one Li-ion per 3d metal cation. Nanostructured thin films provide a model platform for obtaining basic insight to the structural and chemical underpinnings of the phase conversion processes, provided that they can be grown with a high degree of phase purity and the required microstructure. The results from X-ray diffraction and scanning and transmission electron microscopies together with electron energy loss spectroscopy indicate that at low supersaturation and growth rate, porous films and secondary phases are obtained. Good phase purity and dense nanostructured films were obtained at high surface supersaturation. The growth mechanism is three dimensional and is governed by direct supersaturation of the growth surface and the number of stable critical nuclei formed at a given substrate temperature.

Probing the Crystallography of Ordered Phases by coupling Orientation Microscopy and Atom Probe Tomography

Superalloys are a class of materials that possess stable microstructures at elevated temperatures due to the presence of coherent L12 ordered γ’ precipitates spatially aligned along elastically soft directions in a face centered cubic (FCC) γ matrix [1]. Nickel-base superalloys are used in a variety of applications such as in turbine blades of aircraft engines and land-based turbine engine [1]. The recent discovery of novel Co-base alloys [2] which also form γ-γ’ microstructures, similar to nickel base superalloys, has led to rapid research in these alloys as potential next generation superalloys.

Multi-Scale Characterization of Different Generations of Gamma Prime Precipitates in Nickel-based Superalloys Using Correlative Microscopy Techniques

Nickel-based superalloys have been widely used for elevated temperature applications such as turbine disc of jet engines due to their excellent mechanical properties. The typical microstructure of these alloys primarily consists of dispersed precipitates of the ordered γ’ phase with L12 structure within a disordered face-centered cubic γ matrix. The γ -γ’ microstructure in these alloys can be controlled via a combination of composition and cooling rate from the high temperature single γ phase field during processing. Typically during continuous cooling from γ’supersolvus temperature, various size scales of γ’ precipitates are formed, primarily due to multiple nucleation events occurring at various temperatures in the γ -γ’ regime [1,2]. The complex interplay between thermodynamic and kinetic factors lead to the formation of a complex microstructure consisting of a multimodal size distribution of γ’ precipitates (often consisting of three different distinct size distributions ranging from microns to nanometers) and γ’ precipitate-free zones, within the γ matrix. The precipitates not only differ in their size and morphology but also in nucleation density and compositions. The resulting morphology, volume fraction, size distribution of these γ’ precipitates determine the mechanical properties of these alloys [3,4].

Effect of Alloying Modification in Arc Melted Hastelloy X on Microstructures and Oxidation Resistance at Elevated Temperatures

The present research work has an aim to modify microstructure and oxidation behavior of Hastelloy X, a solid solution nickel base alloy, by both aluminium and titanium additions by mean of arc melting process. The Hastelloy X was added both Al and Ti (50:50) for 2% 4% and 6% by weight and casted by vacuum arc melting furnace. Then all received specimens were performed heat treatment, which consist of solutioning treatment at 1175°C for 4 hours and aging temperatures for 760°C, 800°C and 845°C for 24 hours. From the obtained results, it was found that the amount of both Al and Ti additions as well as precipitation aging temperature provided significant effect on both final microstructure and oxidation behaviors at 900°C and 1000°C. Widmanstatten type of microstructure was found in many case. Intermetallic phase formation of molybdenum and chromium was also found in all cases by element mapping. This phase should be γ’-phase. Both aluminium and titanium additions could not provide beneficial effect on oxidation resistance tests at temperature of 900°C and 1000°C. However, with 4%wt. of both aluminium and titanium addition, it resulted in slightly increasing of oxidation resistance at temperature of 1000°C

Effect of Pre-Weld Heat Treatment Temperatures on TIG Welded Microstructures on Nickel Base Superalloy, GTD-111

Nickel-base superalloys have been used as high temperature materials in land-base gas turbine application. When subjected to long term, high temperature service, large crack propagation was observed. Typical refurbishment method of these turbines is carried out by using TIG welding followed by post-weld standard heat treatment. However, new crack initiation is found in the heat-affected zone after TIG welding. Pre-weld heat treatment has been discovered to improves final γ + γ’ microstructure. This study focuses on the effect of pre-weld heat treatment temperature on final γ + γ’ microstructure. Seven different conditions of pre-weld heat treatment temperature were investigated. Scanning electron microscopy studies were carried out after pre-weld and post-weld heat treatments to compare the γ + γ’ microstructure and capture microcracks. The best pre-weld heat treatment temperature produces uniform distribution of finely dispersed γ’ precipitates in the γ matrix without post-weld crack.