Carbon-containing Alloys Research Articles

Influence of Process Parameter and Alloy Composition on Misoriented Eutectics in Single-Crystal Nickel-Based Superalloys.

The nucleation and the growth of misoriented micro-structure components in single crystals depend on various process parameters and alloy compositions. Therefore, in this study, the influence of different cooling rates on carbon-free, as well as carbon-containing, nickel-based superalloys was investigated. Castings were carried out using the Bridgman and Bridgman-Stockbarger techniques under industrial and laboratory conditions, respectively, to analyze the impact of temperature gradients and withdrawing rates on six alloy compositions. Here, it was confirmed that eutectics could assume a random crystallographic orientation due to homogeneous nucleation in the residual melt. In carbon-containing alloys, eutectics also nucleated at low surface-to-volume ratio carbides due to the accumulation of eutectic-forming elements around the carbide. This mechanism occurred in alloys with high carbon contents and at low cooling rates. Furthermore, micro-stray grains were formed by the closure of residual melt in Chinese-script-shaped carbides. If the carbide structure was open in the growth direction, they could expand into the interdendritic region. Eutectics additionally nucleated on these micro-stray grains and consequently had a different crystallographic orientation compared with the single crystal. In conclusion, this study revealed the process parameters that induced the formation of misoriented micro-structures, which prevented the formation of these solidification defects by optimizing the cooling rate and the alloy composition.

Ball Milling Effect on Corrosion and Biocompatibility Behavior of FeMnC Alloys Produced by Powder Metallurgy in Simulated Body Fluids Environment

Carbon-containing Fe-Mn alloys have been developed for the materials for stent application. The alloys fabricated by the powder metallurgy route retain a significant amount of porosity and require a longer sintering time. In this study, the corrosion behavior and cytotoxicity of FeMnC alloy fabricated by powder metallurgy were investigated. The ball-milling process was applied to increase the sample density. Mn content was set to 25 or 35 wt.%, while 1 wt.% carbon was added to all samples. The austenite stability was independent of porosity and the ball-milling process, whereas hardness had a strong dependence on porosity and the ball-milling process. The corrosion resistance of FeMnC alloy depends mainly on the porosity rather than Mn content. The concentration of Fe ions was higher than that of Mn ions in all immersion times in the Ringer’s lactate solution. The released metallic ion concentration rate is also dependent on the porosity of the sample rather than Mn content. However, the ion concentration was lower than the upper intake limit. The extract of FeMnC alloy in Ringer’s lactate solution reduced cell viability. The ball-milled (BM) FeMnC alloys showed higher cell viability than the non-BM sample. However, the FeMnC alloy shows the same level of biocompatibility as SS316L. This result indicates that the FeMnC alloy has a suitable corrosion behavior and proven biocompatibility for biodegradable materials.

Effect of Low-Temperature Treatment on the Structure and Physical Properties of Castable Carbon-Containing Invar Alloys

The effect of low-temperature thermocycling treatment of castable invar alloys on the microstructure and temperature coefficient of linear expansion (CLTE) is studied. The tooling used in the production of precision articles from carbon-filled plastic should possess a maximum CLTE, temperature stability of the structure, and invariability of the coefficient of thermal expansion under the impact of thermal cycles. It is shown that an optimum castable invar alloy with steadily low coefficient of thermal expansion should contain at least 32.7 wt.% nickel and about 0.8 wt.% additional carbon. The effect of the distribution of carbon in the alloy on its structural stability is discussed.

Microstructural evolution and mechanical performance of carbon-containing CoCrFeMnNi-C high entropy alloys

The effect of carbon addition up to 1.84 at.% on the mechanical performance and microstructure of a CoCrFeMnNi high-entropy alloy was studied. Both M23C6- and M7C3-type carbide particles were dispersed in the matrix and at grain boundaries in the cold-rolled and annealed carbon-containing alloy. The decrease of grain size in carbon-containing CoCrFeMnNi was predominantly due to grain boundary pinning by the carbide particles. With the addition of 1.84 at.% carbon, the yield stress of the annealed CoCrFeMnNi alloy increased from 253 to 527 MPa at the expense of its ductility. Carbon atoms strengthened the CoCrFeNiMn with 1.84 at.% carbon by grain size refinement (147 MPa) and enhanced friction stress (127 MPa) associated with interstitial carbon atoms and carbide particles. The strain-hardening rate as well as the yield strength increased at the early stage of deformation with increasing carbon content. Carbon addition had a beneficial effect on the mechanical properties by decreasing the grain size, increasing the friction stress associated with interstitial carbon, and enhancing twin stability.

Changes in the Structure and Properties of Single-Crystal Refractory Alloys Under Long-Term Operation

The structure and properties of carbon-containing single-crystal alloy ZhS32 and carbonless single-crystal alloys ZhS36, VZhM4 and VZhM5U are studied after 500 – 3000-h aging at 850 – 1100°C. The resistance to elastoplastic strain, creep and fatigue and the characteristics of long-term strength of the alloys are determined. It is shown that the expected values of long-term strength and creep resistance of the single-crystal alloys should be corrected with allowance for the changes in their initial structure after long-term operation.

Effect of thermomechanical processing on microstructure and mechanical properties of the carbon-containing CoCrFeNiMn high entropy alloy

Microstructural evolution during cold sheet rolling to 80% thickness strain and annealing at 600–1100 °C for 30 min of the CoCrFeNiMn high entropy alloy doped with 1 at.% of C and resulting mechanical properties of the alloy are reported. It is shown that in the initial homogenized (24 h at 1000 °C) condition the alloy has single fcc phase structure. Cold rolling is accompanied by dislocation slip, deformation twinning and formation of shear bands. Annealing at 600 °C after 80% cold rolling results only in partial recrystallization of cold-deformed structure, while an increase of the annealing temperature produces fully recrystallized microstructure. Comparison with the data on undoped CoCrFeNiMn alloy demonstrates that the addition of carbon pronouncedly increases dislocation activity simultaneously retarding deformation twinning during rolling and decreases the fraction of twin boundaries in the annealed condition. The effect of carbon can be attributed to an increase of stacking fault energy of the carbon-containing alloy. Cold rolling results in a substantial strengthening of the alloy; its ultimate tensile strength approaches 1500 MPa, but at the expense of low ductility. Good combination of strength and ductility can be obtained after annealing. For example, after annealing at 800 °C, the alloy has yield strength of 720 MPa, ultimate tensile strength of 980 MPa, uniform elongation of 21% and elongation to fracture of 37%. It is shown that the high strength of the annealed alloy can be attributed to (i) strong grain boundary strengthening; (ii) solid solution strengthening by carbon.

Effect of carbon content and annealing on structure and hardness of the CoCrFeNiMn-based high entropy alloys

A set of CoCrFeNiMn-based high entropy alloys, containing 0, 2.0, 3.4 and 4.8 at.% of carbon (CoCrFeNiMnCx (x = 0; 0.1; 0.175; 0.25) alloys), was prepared by vacuum arc melting. The structure of the alloys was examined in as-solidified conditions and after annealing at 600 °C, 800 °C, 1000 °C and 1200 °C for 14 h. In the as-solidified condition, the CoCrFeNiMn alloy is composed of single fcc (face-centered cubic) solid solution phase, the CoCrFeNiMnC0.1 alloy contains an insignificant fraction of nanoscale M7C3 carbides, and in the CoCrFeNiMnC0.175 and CoCrFeNiMnC0.25 alloys, coarse M7C3 carbides with the volume fraction of 5% and 9.5% respectively are found. The microhardness increases with the increase of carbon content in the alloys from 160 HV of the CoCrFeNiMn alloy to 275 HV of the CoCrFeNiMnC0.25. After annealing at 800 °C nanoscale M7C3 carbides precipitate in the CoCrFeNiMnC0.1, CoCrFeNiMnC0.175 and CoCrFeNiMnC0.25 alloys. Precipitation of carbides is accompanied by a strong hardening of the alloys. For example, the microhardness of the CoCrFeNiMnC0.1 alloy increases from 205 HV in as-solidified condition to 240 HV. Further increase of annealing temperature results in a decrease of hardness. Carbon concentration in the fcc solid solution is estimated and compared with equilibrium thermodynamic predictions. Thermodynamic modeling also demonstrates that increase of the number of components in fcc equiatomic alloys of the Co-Cr-Fe-Ni-Mn system decreases possible carbon solubility level in the fcc solid solution phase, and in the studied alloys Cr is the main element which determines carbon solubility. Hardening mechanisms of the carbon-containing alloys are analyzed quantitatively, and prospects of development of age-hardenable high entropy alloys of Co-Cr-Fe-Ni-Mn-C system are discussed.

Tensile and fracture behavior of boron and carbon modified Ti-15-3 alloys in aged conditions

This work illustrates the effect of boron and carbon addition on the mechanical behavior of a beta Ti alloy, Ti–15V–3Cr–3Al–3Sn (Ti-15-3), in differently aged conditions. The alloys were prepared by consumable vacuum arc melting followed by forging and hot rolling. These were subsequently solution treated and aged at different temperatures above 500°C for 8h. Standard tensile and plane strain fracture toughness tests were carried out to understand the mechanical behavior of the alloys and its correlation with the microstructural features characterized by scanning and transmission electron microscopy. Both the boron- and the carbon-containing alloys exhibit improved strength with comparable elongation to failure values as compared to the base Ti-15-3 alloy. The presence of TiB and TiC precipitates in a matrix of fine α with β results in lower fracture toughness (KIC) in the boron- and carbon-containing alloys as compared to the base alloy. However, at higher aging temperatures KIC improves due to more tortuous crack path because of the presence of coarse α-phase. An empirical relationship has been proposed correlating KIC with the volume fraction, size and interspacing of α in these alloys.

IMPACT OF COOLING CHARACTER ON STRUCTURE AND CTE OF INVARALLOY WITH 0,6% C

The qualitative and quantitative analysis of distribution of structural components (-phase + graphite) in the carbon-containing invar alloy with 0,6% C was conducted. It is demonstrated that velocity of crystallization produces a strong influence on the dispersion of graphite and on the volume fraction of graphite components in the alloy, i.e. at faster cooling the graphite volume fraction and its dispersion are noticeably higher than at slower cooling. The linear thermal expansion coefficient of both slowly cooled and fast cooled alloys maintains its values constant at heating temperatures lower 200 oC. However, in the alloy received as a result of fast cooling this coefficient values are lower than at slow cooling which can be explained by a lower content of carbon in the -phase, being a carrier of invar properties, of the slowly cooled alloy.

Structure changes in invar Fe–Ni and Fe–Ni–C alloys under the deformation by upsetting

Changes in the dimensional and microstructural characteristics of the samples of two invar fcc alloys, Fe–35.0% Ni–0.49% Mn and Fe–30.9% Ni–1.23% C, have been investigated by X-ray diffraction, metallographic, and electron-microscopic methods after upsetting with the logarithmic deformations e = 0.5 and 1.1. It has been shown that the regularities of changes in the macroscopic dimensions of the samples, as well as in the parameters of structural elements, which are presented by coefficients of the shape change after upsetting, are common for both alloys, although they have some distinctions. These distinctions are caused by the presence of a second phase in the carbon-containing alloy, which is concentrated predominantly along the boundaries of structural elements and affects the changes in the size and microstructural characteristics, as well as by a higher density and greater uniformity of the defect distribution.

Structure–property correlation of a boron and carbon modified as cast β titanium alloy

Beta titanium alloys, Ti-15V-3Cr-3Al-3Sn, with minor additions of boron and carbon were prepared by consumable vacuum arc melting. Detailed microstructural characterizations were carried out using optical, scanning electron microscopes and transmission electron microscopes. Addition of boron resulted in refinement of the as cast beta grain while carbon addition resulted in the precipitation of extremely fine α phase during ageing. Formation of boride and carbide particles due to addition of boron and carbon, respectively, and refinement of the aged microstructure increased the hardness and strength as compared to the base alloy but reduced elongation to failure considerably, especially in the carbon-containing alloy where no measurable plasticity was observed. Fracture toughness values, however, were comparable for the boron- and carbon-containing alloys but these were lower than that of the base alloy.

Metastable Ge1–xCx Alloy Nanowires

Carbon-containing alloy materials such as Ge(1-x)C(x) are attractive candidates for replacing silicon (Si) in the semiconductor industry. The addition of carbon to diamond lattice not only allows control over the lattice dimensions, but also enhances the electrical properties by enabling variations in strain and compositions. However, extremely low carbon solubility in bulk germanium (Ge) and thermodynamically unfavorable Ge-C bond have hampered the production of crystalline Ge(1-x)C(x) alloy materials in an equilibrium growth system. Here we successfully synthesized high-quality Ge(1-x)C(x) alloy nanowires (NWs) by a nonequilibrium vapor-liquid-solid (VLS) method. The carbon incorporation was controlled by NW growth conditions and the position of carbon atoms in the Ge matrix (at substitutional or interstitial sites) was determined by the carbon concentration. Furthermore, the shrinking of lattice spacing caused by substitutional carbon offered the promising possibility of band gap engineering for photovoltaic and optoelectronic applications.

Application of Density Functional Theory to Point Defect Anelasticity of Carbon-Containing Austenitic Alloys

We have used density functional theory (DFT) to determine binding energies (BE’s) of carbon-vacancy (C-v) point-defect complexes of probable importance to C-based anelastic relaxation processes in fcc iron alloys. Calculations are presented for three types of stable point defect clusters: C-v pairs, di-C-v triplets, and tri-C-v quadruplets. We demonstrate semi-quantitative consistency of the calculated BE’s with internal friction results on Fe-36%Ni-C alloys. The BE’s, which are in the range-0.37 eV to-0.64 eV, were determined for a hypothetical non-magnetic (NM) fcc Fe. The effect of the magnetic state of fcc Fe on some of these quantities was investigated by DFT and is shown to be significant; the BE’s appear to be reduced in antiferromagnetic (AFM) fcc Fe.

Alloy liquid metal ion source for carbon focused ion beams

A carbon-cerium alloy liquid metal ion source (LMIS) with unintentional aluminum content is presented for generating focused ion beams of carbon ions, as well as ionized clusters with sizes of 2, 4, and 8 atoms. Emission-current-dependent measurements were carried out for the mass spectra and energy spread of all species, but focused on the carbon monomer ions and clusters. The full width at half maximum of the energy distribution was determined to be 6.5eV for the monomer carbon ion and 14eV for the light clusters at an emission current of 5μA. The source showed good beam performance when used with a mass-separated focused ion beam column. Applications to graphene structures, organic matter, and other carbon-containing materials are promising tasks for the new carbon-containing alloy LMIS.

Effect of minor alloying additions on the solidification of single-crystal Ni-base superalloys

Grain boundary elements, such as carbon and boron, were initially removed from single-crystal alloys, but more recently they have been added back into single-crystal alloys for increased castability and defect tolerance. The mechanism(s) for the increased castability is not completely understood. In this study, carbon was added to the second generation, single crystal, Ni-base superalloy and CMSX-4, to form MC-type carbides. Then either nitrogen or boron was added to the carbon-containing alloy to alter the carbide morphology and the castability of the alloy. The segregation coefficients of the alloying elements in CMSX-4 were measured with varying techniques, but no changes in partitioning were observed. The addition of carbon to CMSX-4 did reduce the number of solidification defects observed in the samples. The addition of carbon and boron to CMSX-4 did not significantly change the number of solidification defects compared to the carbon-only alloy. However, the addition of nitrogen and carbon resulted in an increase in the number of solidification defects in the CMSX-4 samples compared to the baseline CMSX-4 and carbon-containing CMSX-4 samples. The effects of these alloy additions on the carbide morphology and solidification defects are discussed.

Influence of carbon on the giant magnetocaloric effect of LaFe 11.7Si 1.3

The influences of carbon on phase formation, Curie temperature, and magnetic entropy change of the NaZn 13-type LaFe 11.7Si 1.3 were investigated. Seven carbon-containing alloys, LaFe 11.7Si 1.3C x, with x = 0, 0.03, 0.06, 0.10, 0.20, 0.30, and 0.50, respectively, were prepared for this investigation. Experimental results show that addition of a small amount of carbon in LaFe 11.7Si 1.3 is favorable for the formation of the NaZn 13-type structure of LaFe 11.7Si 3C x. The lattice constant increases with C addition and x increases in the alloy because of the introduction of C as interstitial atoms. The Curie temperature of LaFe 11.7Si 1.3C x increases from 194 K to 225 K as x increases from 0 to 0.5. Large magnetic entropy changes were observed in these carbon-containing alloys LaFe 11.7Si 3C x because of their first-order structural/magnetic transition. The maximum magnetic entropy change of 27.5 J·kg −1K −1 at 202 K for the 0–1.56 T magnetic field change was observed in the alloy with x = 0.06. The large magnetic-entropy changes corresponding to low magnetic field change, and the low cost of the material of LaFe 11.7Si 1.3C x makes it a promising candidate to be used as magnetic refrigerants in the corresponding temperature range.

Thermodynamics of Oxygen Solutions in Carbon-Containing Fe-Ni Alloys

Thermodynamics of Oxygen Solutions in Carbon-Containing Fe-Ni Alloys

Effects of alloying elements on martensitic transformation behavior and damping capacity in Fe–17Mn alloy

Abstract Effect of carbon and Ti on ɣ ↔ e martensitic transformation behavior and damping capacity is investigated in an Fe–17Mn alloy. The suppressive force of carbon against ɣ → e transformation increase linearly with an increase in its content, lowering Ms temperature and volume fraction of e martensite. Carbon deteriorates damping capacity by reducing the area of ɣ/e boundaries and mobility of the boundaries contributing to anelastic deformation. The reduction in the mobility of the boundaries is accelerated when carbon-containing alloy is aged at higher temperatures than room temperature. The effect of Ti on damping capacity is found to be beneficial in carbon-containing alloy, which is attributed to the depletion of carbon solute due to the formation of TiC.

Mechanically alloyed Zr–Cu–Al–Ni–C glassy powders

Abstract In this contribution we report on the synthesis of glassy Zr55Cu30Al10Ni5 alloys with a carbon content up to 4 at.% by mechanical alloying which cannot be produced by casting techniques. X-ray analysis and differential scanning calorimetry, both in isochronal and isothermal mode, were carried out to assess the glassy nature of the powders. The viscosity was investigated by parallel plate rheometry and the crystallisation mechanism and kinetics are discussed in the framework of the Johnson–Mehl–Avrami (JMA) model. The comparison between carbon-free and carbon-containing alloys suggests a strong influence of increasing carbon content on the total free volume and viscous flow behaviour of the alloys and on the chemical and topological short-range order, affecting significantly the thermal stability and the crystallisation behaviour of the glassy phase and the supercooled liquid.

Phase instabilities and carbon additions in single-crystal nickel-base superalloys

The phase stability of a number of experimental single-crystal nickel-base superalloys with elevated levels of rhenium, tungsten and tantalum (Ta) has been studied. Carbon additions of 0.1 wt.% were found to enhance the phase stability of the as-cast alloys, with respect to inhibiting the formation of topologically close-packed (TCP) phases. In addition to forming a variety of primary Ta-rich MC carbides upon solidification, intentional carbon additions also affected the segregation behavior of the constituent refractory elements. Comparison of experimentally measured distribution coefficients assessed via application of a Scheil-type analyses revealed reduced segregation of the refractory elements associated with precipitation of TCP phases in the carbon-containing alloys.