Three series of ternary alloys of the {M-30Cr-xC}-type with M = Co, Ni or Fe and x ranging from 2.5 to 5 wt% were elaborated by casting. Their microstructure characterizations by XRD and SEM show that very high volume...Three series of ternary alloys of the {M-30Cr-xC}-type with M = Co, Ni or Fe and x ranging from 2.5 to 5 wt% were elaborated by casting. Their microstructure characterizations by XRD and SEM show that very high volume fractions in chromium carbides (even more than 50%) may be obtained in a metallic matrix by this way. However graphite may also appear in very low quantities in the carbon-richest alloys. The hardness increases with the carbon content (up to 1000 Hv30kg) but it may be a little lowered when graphite is also present. The results show that very hard alloys may be simply obtained by casting of rather cheap elements.展开更多
High temperature applications such as turbine blades for aeronautics or molten glass-shaping tools require the use of refractory metallic materials.Among the later ones,cast superalloys based on some transition metals...High temperature applications such as turbine blades for aeronautics or molten glass-shaping tools require the use of refractory metallic materials.Among the later ones,cast superalloys based on some transition metals and reinforced by MC carbides stay in good place and their metallurgy merits to be well known.This work consists in a general exploration of the as-cast microstructures which can be obtained after solidification and solid state cooling down to ambient temperature for a wide series of alloys for which the base element and the MC-former element both vary.For fixed contents in chromium and carbon contents,the compositions of a total of nineteen alloys were considered.These alloys are based on Ni,Co,Fe or Nb and the M content was each time chosen to favor the appearance of TiC,TaC,NbC,HfC or ZrC,as single carbide in a given alloy.After elaboration,metallographic samples were observed by electron microscopy to investigate the obtained microstructures.The obtained results show first that the MC carbides were in many cases successfully obtained at the expense of other possible carbides(for all Co-based alloys for example)but there are also several exceptions(notably for some Nibased alloys).Second,the obtained monocarbides have a eutectic origin and they are script-liked shaped.However they are here too some exceptions,as the rare HfC obtained in a Nb-base).In general,the results obtained in this work show that the principle of dendritic matrix combined with MC carbides with a script-like morphology is not necessarily obtained:the nature of the{base element,MC-former element}combination governs the microstructure of the alloy in its as-cast state for these particular compositions in chromium and carbon.In some cases other carbides may appear and the microstructures may be even of another type.展开更多
In this work two new alloys were obtained by extrapolation from a well-known high entropy alloy,the equimolar CoNiFeMnCr one.This was done by the addition of carbon and of tantalum,Ta being one of the strongest MC-for...In this work two new alloys were obtained by extrapolation from a well-known high entropy alloy,the equimolar CoNiFeMnCr one.This was done by the addition of carbon and of tantalum,Ta being one of the strongest MC-former elements.They were produced by conventional casting under inert atmosphere.The obtained microstructures were characterized by X-ray diffraction,metallography,electron microscopy,and energy dispersion spectrometry.Their hardness was also measured by hardness indentation.In parallel,the original CoNiFeMnCr alloy was also synthesized and characterized for comparison.The reference HEA alloy is single-phased with an austenitic structure,while the two{Ta,C}-added alloys are double-phased,with an austenitic matrix and interdendritic script-like TaC carbides.The matrixes of these HEA/TaC alloy are equivalent to an equimolar CoNiFeMnCr alloy to which 2 wt.%Ta is present in solid solution.The presence of the TaC carbides caused a significant increase in hardness which suggests that the HEA/TaC alloys may be mechanically stronger than the HEA reference alloy at high temperature.展开更多
文摘Three series of ternary alloys of the {M-30Cr-xC}-type with M = Co, Ni or Fe and x ranging from 2.5 to 5 wt% were elaborated by casting. Their microstructure characterizations by XRD and SEM show that very high volume fractions in chromium carbides (even more than 50%) may be obtained in a metallic matrix by this way. However graphite may also appear in very low quantities in the carbon-richest alloys. The hardness increases with the carbon content (up to 1000 Hv30kg) but it may be a little lowered when graphite is also present. The results show that very hard alloys may be simply obtained by casting of rather cheap elements.
文摘High temperature applications such as turbine blades for aeronautics or molten glass-shaping tools require the use of refractory metallic materials.Among the later ones,cast superalloys based on some transition metals and reinforced by MC carbides stay in good place and their metallurgy merits to be well known.This work consists in a general exploration of the as-cast microstructures which can be obtained after solidification and solid state cooling down to ambient temperature for a wide series of alloys for which the base element and the MC-former element both vary.For fixed contents in chromium and carbon contents,the compositions of a total of nineteen alloys were considered.These alloys are based on Ni,Co,Fe or Nb and the M content was each time chosen to favor the appearance of TiC,TaC,NbC,HfC or ZrC,as single carbide in a given alloy.After elaboration,metallographic samples were observed by electron microscopy to investigate the obtained microstructures.The obtained results show first that the MC carbides were in many cases successfully obtained at the expense of other possible carbides(for all Co-based alloys for example)but there are also several exceptions(notably for some Nibased alloys).Second,the obtained monocarbides have a eutectic origin and they are script-liked shaped.However they are here too some exceptions,as the rare HfC obtained in a Nb-base).In general,the results obtained in this work show that the principle of dendritic matrix combined with MC carbides with a script-like morphology is not necessarily obtained:the nature of the{base element,MC-former element}combination governs the microstructure of the alloy in its as-cast state for these particular compositions in chromium and carbon.In some cases other carbides may appear and the microstructures may be even of another type.
文摘In this work two new alloys were obtained by extrapolation from a well-known high entropy alloy,the equimolar CoNiFeMnCr one.This was done by the addition of carbon and of tantalum,Ta being one of the strongest MC-former elements.They were produced by conventional casting under inert atmosphere.The obtained microstructures were characterized by X-ray diffraction,metallography,electron microscopy,and energy dispersion spectrometry.Their hardness was also measured by hardness indentation.In parallel,the original CoNiFeMnCr alloy was also synthesized and characterized for comparison.The reference HEA alloy is single-phased with an austenitic structure,while the two{Ta,C}-added alloys are double-phased,with an austenitic matrix and interdendritic script-like TaC carbides.The matrixes of these HEA/TaC alloy are equivalent to an equimolar CoNiFeMnCr alloy to which 2 wt.%Ta is present in solid solution.The presence of the TaC carbides caused a significant increase in hardness which suggests that the HEA/TaC alloys may be mechanically stronger than the HEA reference alloy at high temperature.
