High temperature properties of several chromium-containing Co-based alloys reinforced by different types of MC carbides (M=Ta, Nb, Hf and/or Zr) (original) (raw)
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Effect of alloy preheating on the mechanical properties of as-cast Co-Cr-Mo-C alloys
Metallurgical and Materials Transactions A, 1999
The effect of various alloy preheatings followed by full solid solution treatments on the resultant strength and ductility of as-cast Co-Cr-Mo-C alloys was investigated. Three preheating temperatures were evaluated: 815 ЊC, 950 ЊC, and 1100 ЊC for 4 hours and then solid solution treated at 1225 ЊC for 4 hours. Tensile and compressive tests were carried out on the heat-treated alloys. It was found that the strength and ductility of the heat-treated alloys exhibited significant improvements over the as-cast condition. In particular, optimum ductility of the heat-treated alloys and alloy strength were promoted by preheating at 815 ЊC. A relatively fine grained structure coupled with a uniform distribution of second-phase particles promoted homogeneous plastic deformation in the bulk. Fractographic observations indicated that the exhibited ductility was associated with the development of numerous plastic bands combined with band interlockings. Alloy preheats at 950 ЊC and 1100 ЊC prior to solutionizing lead to inferior strength and ductility. Although preheating at 1100 ЊC led to slight improvements, in both cases, the fracture path was dominated by the presence of continuous carbide films surrounding the dendritic grains. Hence, less than optimum combinations of strength and ductility were achieved by the heat treatments at the higher temperatures.
Morphology and Material Properties of Carbides in High (24%) Chromium Cast Iron
2018
The present paper is a presentation of results of a study on morphology, chemical composition, material properties (HVIT, HIT, EIT), and nanoindentation elastic and plastic work for carbide precipitates in chromium cast iron containing 24% Cr. It has been found that the carbides differ in chemical composition, as well as in morphology and values characterizing their material properties. The carbides containing the most chromium which had the shape of thick and long needles were characterized with highest values of the analyzed material properties.
Protection of cobalt-based refractory alloys by chromium deposition on surface
Surface and Coatings Technology, 2011
The feasibility of surface chromium enrichment by pack-cementation was assessed for different low chromium-containing cobalt alloys, in order to improve their resistance against high temperature. A binary Co-10Cr alloy, two ternary Co-10Cr-0.5C and Co-10Cr-1.0C alloys and two TaC-containing Co-10Cr-based alloys were elaborated by foundry for the study. 7.5h-long and 15h-long cementations at 1050°C, followed or not by a 75h-long heat treatment at 1200°C were performed on these alloys. Microstructure examinations performed using a Scanning Electron Microscope and concentration profiles using Electron Probe Micro Analysis-Wavelength Dispersion Spectrometry were realized in order to analyze the level of Cr-enrichment of the sub-surface region, with as studied criteria: the nature of the external Crenriched zone, the maximal chromium content on surface and the depth of chromium enrichment. The Cr-enrichment of the sub-surface succeeded for the Co-10Cr alloy and for the two tantalum-containing alloys, with the formation of an external metallic zone containing around 30wt.%Cr. In contrast the chromium carbides-containing alloys were effectively enriched in chromium in surface but in the form of a continuous chromium carbide layer which can induce other problems such as spallation and then possible fast oxidation of the denuded alloy. Finally it appeared that only the carbon-free alloys, and the alloys reinforced by carbides more stable than chromium carbides, are potentially able to be successful enriched in chromium in their sub-surface by pack-cementation.
Metallurgical Transactions A, 1976
Microstructures produced in the Co-Cr-Mo-C alloy H.S.21 were observed by transmission electron microscopy in cast specimens following solutionizing at 1230~ and aging at 650~ and in low-carbon wrought specimens following solutionizing and aging at 650~ and 750~ In all cases, aging was found to promote the formation of fcc stacking faults and to cause an initial martensitic transformation from the Icc phase to a heavily faulted hcp structure. Precipitate formation was observed in hcp areas of the cast material after 20 h at 650~ and in hcp areas of wrought material after 20 h at 750~ Prolonged aging at 750~ produced a transformation in the hcp structure of wrought specimens, with a relatively faultfree structure replacing the heavily faulted martensitic form. Interruption of fcc slip by both fcc stacking faults and bands of hcp phase was found to be the principal strengthening mechanism activated by aging. Precipitate formation in the hcp plays an increasingly significant role as aging time is increased. This microstructural information is used to explain the observed tensile properties of these alloys after the heat treatments mentioned.
Effect of carbon content on microstructural characteristics of the hypereutectic Fe–Cr–C claddings
Materials Chemistry and Physics, 2009
The hypereutectic Fe-Cr-C claddings with different C contents were deposited on ASTM A36 steel substrates by flux cored arc welding (FCAW) to investigate that the effect of C content on microstructural characteristics. The results showed that the microstructure of hypereutectic Fe-Cr-C claddings consisted of primary proeutectic (Cr,Fe) 7 C 3 and the austenite plus (Cr,Fe) 7 C 3 eutectic. Proeutectic carbides undergone to several microstructural changes in response to higher carbon content in the cladding. The morphologies of proeutectic (Cr,Fe) 7 C 3 carbides changed from blade-like to rod-like with hexagonal cross section. The amounts of proeutectic (Cr,Fe) 7 C 3 carbides increased with increase of the C contents. The nucleation sites of proeutectic (Cr,Fe) 7 C 3 carbides increased under high undercooling condition. Hence, the latent heat of solidification can be released by formed proeutectic (Cr,Fe) 7 C 3 carbides and then the growth of proeutectic (Cr,Fe) 7 C 3 carbides were suppressed. Consequently, it showed a maximum hardness value (about HRC 62) when the amount of proeutectic (Cr,Fe) 7 C 3 carbides exceeded 86%.
PROCEEDINGS OF THE INTERNATIONAL CONFERENCE “PHYSICAL MESOMECHANICS. MATERIALS WITH MULTILEVEL HIERARCHICAL STRUCTURE AND INTELLIGENT MANUFACTURING TECHNOLOGY”
The effect of carbon content on structure and mechanical properties of Fe 65 (CoNi) 25 Cr 10 and Fe 65 (CoNi) 25 Cr 9.5 C 0.5 high-entropy alloys was studied. In addition, the effect of thermomechanical treatment on structure and properties of the Fe 65 (CoNi) 25 Cr 9.5 C 0.5 alloy was investigated. Microstructure of the alloys in the as-cast conditions had a two-phase structure consisting of a face-centered cubic (fcc) and a body-centered (bcc) phases. An increase in the carbon content from 0 to 0.5 at % led to a decrease in the bcc phase amount from 90 to 35%. Besides the carbon addition resulted in higher plasticity without significant loss in strength. Cold rolling of the Fe 65 (CoNi) 25 Cr 9.5 C 0.5 alloy to 80% thickness reduction leads to an increase in the bcc phase amount up to 40%. Subsequent annealing at 700-900°C for 10 min led to the development of a recrystallized microstructure with an increased volume fraction of the bcc phase, and the precipitation of M 23 C 6-type carbides. Relationships between the chemical composition, processing, structure and mechanical properties of alloys are briefly discussed.
ISIJ International, 2012
The chemical composition and morphology of M7C3 eutectic carbides in 19 mass% Cr-2.8 mass% C white iron with up to 4.7 mass% V additions have been studied. Eutectic colonies are mainly composed of a very fine rod-like carbides at the center and become coarser rod-like or blade-like with increased distance from the center. The volume fraction, size and distribution of rod-like and blade-like carbides in the eutectic colonies are changing with increasing vanadium content in the alloys. The formation of the eutectic colonies of different morphology is the consequence of the segregation of alloying elements in the alloy melt, which was confirmed by EDS analysis of the chemical composition of carbides. Three different compositions of M7C3 carbides were found in all tested alloys. The main difference between them is in the amount of chromium and iron and in the degree of their replacement by vanadium. Due to different melt composition in particular zones, the constitutional undercooling, and subsequently the growth rate, will be different, which will induce the formation of eutectic colonies of different morphologies.
A Ready to Use CR3C2 Doped Cobalt Powder as Binder in Cemented Carbides
Mechanical alloying is a method that allows producing mixtures of compounds in solid state. This paper investigates the possibility to produce by mechanical alloying ready-to-use cobalt powder doped with chromium carbide to be used as binder in cemented carbides. The role of inhibitors in cemented carbides is to prevent the growth of tungsten carbide particles during the sintering process. A review of previous work leads to the conclusion that chromium carbide is a good candidate for an inhibitor: it ensures the best ratio between hardness and toughness for cemented carbides. Various amounts (1%, 5%, 10% and 20% in weight) of chromium carbide (Cr3C2) are mixed and milled together with cobalt in a Fritch planetary ball mil. They are compared to a batch of cobalt only that was milled in the same conditions, as reference. The milling conditions were as follow: vials rotation :600 rpm; Milling sequence: 5 minutes of milling followed by 5 minutes of cooling; 10 mm WC-Co milling balls; WC-Co milling bowls ; maximal milling time 10h. Samples were taken every 2 hours. They were analyzed to study the evolution of particles size and the dispersion of chromium carbide into the cobalt matrix, using the following methods: SEM, laser granulometry and X-ray diffraction. A reduction of particle size was observed for longer milling times and the best particles size distribution was obtained for the materials containing 5% wt and 10% wt of chromium carbide.