In-Situ XRD Study of Phase Transformation Kinetics in a Co-Cr-W-Alloy Manufactured by Laser Powder-Bed Fusion

Abstract

The additive manufacturing process of laser powder-bed fusion (L-PBF) is an increasingly popular approach for patient-specific production of dental frameworks made from Co-Cr alloys. Macroscopically, frameworks produced in this way exhibit high anisotropy especially in Young’s modulus, and are missing standardized requirements. Microscopically, pronounced texture and high residual stresses are characteristic. To reduce resulting detrimental effects, the as-built (AB) parts are heat treated. Dependent on the treatment temperature, effects like the transformation of the γ-phase matrix in the AB condition to ϵ-phase, precipitation, stress relief, and grain growth were observed. While the existence of these processes was established in the past, little is known about their kinetics. To fill this gap, these effects were studied with in-situ X-ray diffraction (XRD) methods in isothermal heat treatments (HTs) at four different sample surface temperatures TS reaching from 650∘C to 900∘C. Furthermore, room temperature ex situ XRD and SEM/EDS measurements completed the analysis. An evaluation of the datasets, with single peak fitting and QXRD methods, yielded the following results. In the HTs below a certain threshold, a γ-to-ϵ transformation was observed in the sample bulk and close to the sample surface. In the latter case, evidence for a partially strain-induced transformation related to oxide formation was present. Above this threshold and possibly slightly below, σ- and Laves-phase precipitated. Additionally, peak profile evolutions hinted at a drop of inter- and intragranular stresses within the first 30 to 60 min. Therefore, an HT of about 30 to 60 min slightly above the threshold is proposed as optimal for reducing residual stresses while retaining a predominantly single-phased microstructure, possibly superior in corrosion properties and likewise in bio-compatibility.

Deformation-induced martensitic transformation in Co-28Cr-6Mo alloy produced by laser powder bed fusion: Comparison surface vs. bulk

“…Please note, that the EBSD maps of the bulk specimen were collected from the deformed tensile test specimen (2 mm in thickness) that was electropolished to a distance of 1 mm from the surface. Hegele et al [31] pointed out that the extent of martensitic transformation on the surface may be enhanced in the presence of oxides. However, the X-ray diffraction analysis performed in the current work did not reveal the existence of oxides.…”

Probing the Annealing-Induced Phase Evolution of Nanostructured Manganese Oxide Thin Films by X-Ray Diffraction

“…After deposition in an oxygen atmosphere, samples were taken out of the PLD chamber and moved to the stage for X-ray diffraction measurements. XRD was carried out in grazing-incidence configuration (GIXRD, incidence angle ω = 2°) with a HRD3000 diffractometer (Ital Structures, Riva del Garda, Italy), equipped with an Anton Paar DHS 1100 domed heating stage (Anton Paar, Graz, Austria) with a polyether ether ketone (PEEK) dome. − The diffractometer was operated with monochromated Cu Kα radiation (λ = 0.1541 nm) and was equipped with a curved position-sensitive multichannel gas-filled detector (2θ range 0°–120°, resolution 0.029°, Inel CPS-120). GIXRD, carried out under in situ conditions during postdeposition thermal annealing, allowed us to probe the real-time phase evolution of the films, emphasizing the role of morphology, initial crystal orientation, and annealing atmosphere on the crystallization pathways.…”

Systematic Development of Eutectic High Entropy Alloys by Thermodynamic Modeling and Experimentation: An Example of the CoCrFeNi-Mo System

“…Conventional alloys are currently used for the majority of structural applications. Some of the common examples include the use of aluminum alloys and titanium alloys for applications requiring high strength/weight ratios (aerospace industry) [1], steels as a loadbearing material for applications requiring high strength and ductility at low cost [2][3][4][5][6][7], cobalt-based alloys for biomedical applications [8][9][10], and nickel-based superalloys for applications requiring high resistance to mechanical degradation at elevated temperatures [11,12]. It is believed that the conventional alloy design approach has more or less reached its limits and cannot meet the requirements of demanding structural applications.…”