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

Crystals

卷:11

Jonas von Kobylinski¹  Patrick Hegele¹  Leonhard Hitzler¹  Christian Krempaszky¹  Ewald Werner¹ 

[1] Institute of Material Science and Mechanics of Materials, Technical University of Munich, Boltzmannstr. 15, 85748 Garching, Germany;

关键词: in-situ XRD;    SLM;    L-PBF;    phase transformation kinetics;    Co-Cr(-W)-dental alloys;    residual stresses;   

DOI  :  10.3390/cryst11020176

来源: DOAJ

【 摘 要 】

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 $\gamma$-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 $T_{\mathrm{S}}$ reaching from $650{}^{\circ }\mathrm{C}$ to $900{}^{\circ }\mathrm{C}$. 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 $\gamma$-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, $\sigma$- 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.

【 授权许可】

Unknown