Thermal analysis and microstructure of oxide dispersion strengthened ferritic steels produced by ball milling with different amounts of process control agent

• Published in: Journal of thermal analysis and calorimetry Vol. 138; no. 4; pp. 2515 - 2528
• Main Authors: Mihalache, V., Aldica, G., Pasuk, I., Mercioniu, I.
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01-11-2019; Springer; Springer Nature B.V
• Subjects: Analysis; Analytical Chemistry; Annealing; Ball milling; Carbides; Chemistry; Chemistry and Materials Science; Chromium; Consolidation; Crystallites; Curie temperature; Degassing; Densification; Density; Diamond pyramid hardness; Diffraction; Disintegration; Dispersion hardening steels; Ethanol; Ferritic stainless steels; Heating; Inorganic Chemistry; Iron; Iron compounds; Lattice parameters; Measurement Science and Instrumentation; Mechanical properties; Microstructure; Oxide dispersion strengthening; Oxides; Physical Chemistry; Plasma sintering; Polymer Sciences; Powders; Process controls; Spark plasma sintering; Thermal analysis; X-rays; Vickers hardness; ODS Fe14Cr ferritic steel; Ball milling; Process control agent; Thermal analysis; Microstructure; Density
• ISSN: 1388-6150; 1588-2926
• DOI: 10.1007/s10973-019-08593-y

Fe–14Cr–3 W–0.4Ti–0.25Y
2
O
3
ferritic steels were produced by ball milling of initial mixture of elemental powders with various amounts of process control agent (PCA), ethanol (0.25 mass%, 2.5 mass%, 4 mass% and 20 mass%) under an Ar atmosphere and spark plasma sintering (SPS) consolidation at 1070 °C. The influence of the quantity of PCA on the properties (microstructure, density and Vickers hardness) of the as-milled powders and of the consolidated steels was investigated. X-ray diffraction shows a bcc–α-phase with fine crystallite size, 6.7–11 nm, for all powders. The particle size and the lattice constant of
α
-ferrite of the as-milled powders decrease as the amount of PCA increases. The powder milled with the highest amount of PCA, 20 mass%, contains carbides (M
3
C) and oxides ((Fe,Cr)
2
O
3
). The thermal analysis shows that as the amount of PCA increases, (1) the Curie temperature,
T
c
, increases, (2) the temperature of
α → γ
transition,
T
α→γ
, decreases, (3) the mass loss with CO/CO
2
degassing increases, and (4) the milling with PCA hinders the nitrogen incorporation from milling media and air. The density and Vickers hardness of the SPS-consolidated and post-SPS annealed steels show an increasing trend with the increase in the amount of PCA. Carbides and oxides were detected in the post-SPS annealed steels derived from the powders milled with 2.5 mass% PCA and 4 mass% PCA (M
23
C
6
and (Fe,Cr)
2
O
3
), and 20 mass% PCA (M
3
C and (Fe,Cr)
2
O
3
). The obtained results were discussed in terms of: (1) dissolution into the alloy matrix of carbon and oxygen released after the disintegration of PCA, (2) carbides and oxides precipitation during milling and/or upon heating and (3) promotion of thermally activated processes (such as carbothermal reaction) upon heating which can develop as well at the contact points/particle surfaces during SPS consolidation and can influence the process of densification.