Pearlite growth rate in Fe–C and Fe–Mn–C steels

The kinetic theory for the growth of pearlite in binary and ternary steels is implemented to ensure local equilibrium at the transformation front with austenite, while accounting for both boundary and volume diffusion of solutes. Good agreement is on the whole observed with published experimental data, although the reported growth rate at the lowest of temperatures is much smaller than predicted. To investigate this, experiments were conducted to replicate the published data. It is found that the cooperation between cementite and ferrite breaks down at these temperatures, and surface relief experiments are reported to verify that the resulting transformation product is not bainite.     

Pyrolytic-grown B–C–N and BN nanotubes

We report the growth of pyrolytic boron–carbon–nitrogen (B–C–N) nanotubes on iron (Fe) and nickel (Ni) catalysts. It was discovered that different catalysts had effect on the elemental compositions of B–C–N nanotubes, which may allow one to tune the transport properties of B–C–N nanotubes in a wide range. A new synthetic route was also developed to generate H₃N:BH₃ as the precursor and yield boron nitride (BN) nanotubes by pyrolysis. The typical growth scenario of multi-wall BN tubes will be discussed.     

Pyrolytic-grown B–C–N and BN nanotubes

We report the growth of pyrolytic boron–carbon–nitrogen (B–C–N) nanotubes on iron (Fe) and nickel (Ni) catalysts. It was discovered that different catalysts had effect on the elemental compositions of B–C–N nanotubes, which may allow one to tune the transport properties of B–C–N nanotubes in a wide range. A new synthetic route was also developed to generate H₃N:BH₃ as the precursor and yield boron nitride (BN) nanotubes by pyrolysis. The typical growth scenario of multi-wall BN tubes will be discussed.     

Co–C and Pd–C Eutectic Fixed Points for Radiation Thermometry and Thermocouple Thermometry

Two Co–C and Pd–C eutectic fixed point cells for both radiation thermometry and thermocouple thermometry were constructed at NMC. This paper describes details of the cell design, materials used, and fabrication of the cells. The melting curves of the Co–C and Pd–C cells were measured with a reference radiation thermometer realized in both a single-zone furnace and a three-zone furnace in order to investigate furnace effect. The transition temperatures in terms of ITS-90 were determined to be \(1324.18\,{^{\circ }}\hbox {C}\) and \(1491.61\,{^{\circ }}\hbox {C}\) with the corresponding combined standard uncertainty of \(0.44\,{^{\circ }}\hbox {C}\) and \(0.31\,{^{\circ }}\hbox {C}\) for Co–C and Pd–C, respectively, taking into account of the differences of two different types of furnaces used. The determined ITS-90 temperatures are also compared with that of INRIM cells obtained using the same reference radiation thermometer and the same furnaces with the same settings during a previous bilateral comparison exercise (Battuello et al. in Int J Thermophys 35:535–546, 2014). The agreements are within \(k=1\) uncertainty for Co–C cell and \(k = 2\) uncertainty for Pd–C cell. Shapes of the plateaus of NMC cells and INRIM cells are compared too and furnace effects are analyzed as well. The melting curves of the Co–C and Pd–C cells realized in the single-zone furnace are also measured by a Pt/Pd thermocouple, and the preliminary results are presented as well.     

Solid state phase transformations in Ti–Al–C and Ti–Al–Nb–C alloys

Abstract

Results are reported of an investigation of solid state transformations in a series of α₂ based alloys having an aluminium content of 26 at.-% with carbon up to 3 at.-%; two α₂ basedquaternary Ti–Al–Nb–C alloys with 5 and 12 at.-%Nb and 3 at.-%C were also studied. Ordering occurs in the ternary Ti–Al–C alloys and also in the 23Al–5Nb–3C alloy on quenchingfrom 1250°C. Additional carbide precipitation was not observed in the ternary Ti–Al–C alloys on reheating to 750°C. Additions of niobium resulted in the presence of the β phase at 1050°C in the 5%Nb alloy and at 1050 and 750°C in the 12%Nb alloy. In the quaternary Ti–Al–Nb–C alloys, (Ti, Nb)₃AlC was found to be the primary phase and was present in the microstructure over the temperature range studied. In the 21Al–12Nb–3C alloy, the ordered β phase transformed to α″₂ martensite on quenching from 1250;amp;#x00B0;C.

MST/1306     

Effect of Al and C on structure and mechanical properties of Fe–Al–C alloys

Abstract

Effect of aluminium and carbon content on the microstructure and mechanical properties of Fe–Al–C alloys has been investigated. Alloys were prepared by combination of air induction melting with flux cover (AIMFC) and electroslag remelting (ESR). The ESR ingots were hot forged and hot rolled at 1373 K. As rolled alloys were examined using optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to understand the microstructure of these alloys. The ternary Fe–Al–C alloys containing 10·5 and 13 wt-%Al showed the presence of three phases: FeAl with disordered bcc structure, Fe₃Al with ordered DO₃ structure and Fe₃AlC_0·5 precipitates with L′1₂ structure. Addition of high concentration of carbon to these alloys resulted in excellent hot workability and superior tensile at room temperature as well as tensile and creep properties at 873 K. An increase in Al content from 9 to 13 wt-% in Fe–Al–C alloys containing the same levels of carbon has no significant influence on strength and creep properties at 873 K, however resulted in significant improvement in room temperature strength accompanied by a reduction in room temperature ductility.     

Wetting behavior and interfacial microstructure of palladium- and silver-based braze alloys with C–C and SiC–SiC composites

High-temperature sessile-drop wettability tests were conducted on unpolished C–C and SiC–SiC composite substrates using commercial braze alloys Palco (Pd-35Co), Palni (Pd-40Ni), Cusil-ABA (63Ag–35.3Cu–1.75Ti), and Ticusil (68.8Ag–26.7Cu–4.5Ti). Observations revealed non-uniform, anisotropic spreading, copious braze infiltration of the composite substrates, particularly C–C composite, and Ti enrichment at the composite/braze interface together with dissolution of Si (from SiC–SiC composite) in braze and diffusion of Co (from Palco) in the composite. The droplet/composite contact region near the droplet center revealed intimate and microstructurally sound bonding. However, inter-laminar shear cracking within the SiC–SiC composite in contact with Ticusil, Palco, and Palni, and partial substrate/droplet de-cohesion near the edge of the droplet were also observed. In Palco and Palni droplets, fiber tows in the contact region de-laminated from the main body of the composite via inter-laminar shear cracking resulting in fiber flotation, segregation, and surface degradation. The study is one of the first empirical enquiries into the complex wetting and spreading behavior of brazes on commercial C–C and SiC–SiC composites.     

Investigation of TiC–C Eutectic and WC–C Peritectic High-Temperature Fixed Points

TiC–C eutectic (2,761°C) and WC–C peritectic (2,749°C) fixed points were investigated to compare their potential as high-temperature thermometric reference points. Two TiC–C and three WC–C fixed-point cells were constructed, and the melting and freezing plateaux were evaluated by means of radiation thermometry. The repeatability of the TiC–C eutectic within a day was 60 mK with a melting range roughly 200 mK. The repeatability of the melting temperature of the WC–C peritectic within 1 day was 17 mK with a melting range of ∼70 mK. The repeatability of the freezing temperature of the WC–C peritectic was 21 mK with a freezing range less than 20 mK. One of the TiC–C cells was constructed from a TiC and graphite powder mixture. The filling showed the reaction with the graphite crucible was suppressed and the ingot contained less voids, although the lack of high-purity TiC powder poses a problem. The WC–C cells were easily constructed, like metal–carbon eutectic cells, without any evident reaction with the crucible. From these results, it is concluded that the WC–C peritectic has more potential than the TiC–C eutectic as a high-temperature reference point. The investigation of the purification of the TiC–C cell during filling and the plateau observation are also reported.     

Morphology and crystallographic phase of V–C particles formed in Fe–Cr–Ni–V–C alloys

Abstract

The morphology and crystallographic phase of V–C carbide particles formed in cast Fe–Cr–Ni–V–C alloys were investigated by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy (TEM). The combination of results obtained with these techniques revealed that cuboidal, cruciform and spherical carbide particles were formed, depending on the alloy composition, all having the cubic-VC_1?x structure (Fm-3m). Detailed TEM observations suggested that small carbide particles were initially cubic in shape and became spherical with increasing particle size. All cuboidal and spherical carbides were single crystallites with no grain boundary at any particle sizes, even after growing to 6 μm in diameter.     

Co–C and Pd–C Fixed Points for the Evaluation of Facilities and Scales Realization at INRIM and NMC

Two hybrid cells for realizing the Co–C and Pd–C fixed points and constructed at Istituto Nazionale di Ricerca Metrologica (INRIM) were used for an evaluation of facilities and procedures adopted by INRIM and National Metrology Institute of Singapore (NMC) for the realization of the solid–liquid phase transitions of high-temperature fixed points and for determining their transition temperatures. Four different furnaces were used for the investigations, i.e., two single-zone furnaces, one of them of the direct-heating type, and two identical three-zone furnaces. The transition temperatures \(T_{90}\) were measured at both institutes by adopting different procedures for realizing the radiation scales, i.e., at INRIM a scheme based on the extrapolation of fixed-point interpolated scales and an International Temperature Scale of 1990 (ITS-90) approach at NMC. The point of inflection (POI) of the melting curves was determined and assumed as a practical representation of the melting temperature. Different methods for deriving the POI were used, and differences as large as some hundredths of a kelvin were found with the different approaches. The POIs of the different melting curves were analyzed with respect to the different possible operative conditions with the aim of deriving reproducibility figures to improve the estimated uncertainty. As regard to the institutes inter-comparison, differences of 0.13 K and 0.29 K were found between INRIM and NMC determinations at the Co–C and Pd–C points, respectively. Such differences are compatible with the combined standard uncertainties of the comparison, which are estimated to be 0.33 K and 0.36 K at the Co–C and Pd–C points, respectively.     

Properties and microstructure of WC–TiC–Co and WC–TiC–MO2C–Co(Ni) cemented carbides

Abstract

The present study is an attempt to observe the changes in microstructure and properties of modified WC–10Co cemented carbides from the viewpoint of the distinctive role played by modified binder phase. Introduction of TiC into WC–10Co cemented carbide results in microstructural non-uniformity, i.e. a wide range of grain size distribution, which in turn gives rise to a drastic drop in values of transverse rupture strength and toughness. The modification of binder and carbide phases by incorporating, respectively, nickel and M02C improves the microstructural uniformity, which ensures better mechanical properties. The present findings have been interpreted in terms of various quantitative microstructural parameters, with particular attention being given to the wettability factor.

MST/1363     

Mechanical properties and oxidation behaviors of carbon/carbon composites with C–TaC–C multi-interlayer

To improve the mechanical properties and oxidation-resistance properties, a C–TaC–C multi-interlayer structure was introduced in carbon/carbon (C/C) composites by chemical vapor infiltration. Compared with conventional C/C composites, a higher fracture toughness and strength have been achieved by using the C–TaC–C multi-interlayer. In addition, the composites also exhibit a higher preliminary oxidation temperature and a lower mass loss at high temperatures. The oxidation rate of the composites increases with temperature increasing in the range of 700–1300 °C, reaching a maximum value at 1300 °C, then decreases in 1300–1400 °C. A hexagonal structure of Ta₂O₅ phase is obtained when being oxidized at 700–800 °C, and it transforms to an orthorhombic phase at temperatures above 900 °C. The structures of C–TaC–C multi-interlayer are intact without cracks or porosities after being oxidized at 700–800 °C. In 900–1300 °C, the composites are oxidized uniformly with the formation of pores. At temperatures above 1300 °C, there are oxidation and non-oxidation regions with the oxidation process being controlled by diffusion.     

Grain boundary and fracture surface analysis of Fe–C–P steel

Abstract

The present paper investigates the distribution of grain boundary types and fracture surface crystallography in an Fe–C–P alloy. It is shown that electron backscatter diffraction (EBSD) is an effective technique with which to conduct these investigations. The proportions of both Σ1 and particularly Σ3 (in coincidence site lattice notation)present after various heat treatments were higher than would have been expected for random generation. There was limited evidence that both higher annealing temperatures and longer annealing times promoted generation of Σ3 type boundaries. The standard EBSD technique was modified and extended to encompass both the novel ‘matched fracture’ specimen approach and direct mapping from fracture surfaces to provide crystallographic information. A correlation was noted between higher aging temperatures and proportions of cleavage fracture. Furthermore, there was a strong correlation between cleavage fracture surfaces exhibiting river markings and an {001} surface orientation.     

Microindentation creep of secondary hydrated cement phases and C–S–H

Microindentation creep measurements were obtained on compacted specimens of several secondary hydrated cement phases in equilibrium with water vapor at 11%RH. Values of creep modulus, indentation modulus and indentation hardness for calcium hydroxide, ettringite, gypsum and calcium carbonate are reported. The porosity dependence of these parameters was established and the significance of porosity on the time-dependent deformation of these materials was discussed. In addition the microindentation creep behavior of pure C–S–H and C₃S paste hydrated 32 years was determined. The discussion focuses on the relative importance of the contribution of the secondary phases in hydrated cement-based materials to creep with respect to the more ‘active’ C–S–H phase.     

Interface temperature measurement of M2C and M6C eutectic carbides in the Fe–Mo–C system

The High speed cast iron, which is used for hot rolling parts, needs high fracture toughness and wear resistance. To improve these properties, the control of eutectic carbides, M₃C, M₇C₃, M₆C and MC is important by adding elements such as Cr, W, V and Mo.The aim of this study is to estimate which carbide will solidify under certain solidification conditions and compositions. This prediction criterion can be gained by measuring the interface temperature of each carbide in various samples with different solute elements, composition and growth rate.In this report, the solidified temperature of γ+M₂C and γ+M₆C eutectic carbide in the Fe–Mo–C ternary system in the composition range near to the eutectic monovariant line, was measured during the unidirectional solidification process. The relationship between solidified interface temperature and growth rate was obtained. In eutectic solidification along the γ+M₆C monovariant line, a coefficient of undercooling, the k value, was obtained.The authors have already measured the k values of other eutectic carbides, such as γ+M₃C, austenite+M₇C₃, and γ+VC in Fe–Cr–C and Fe–V–C system. The paper also discusses the relationships between these properties of eutectic carbides.     

Interface temperature measurement of M2C and M6C eutectic carbides in the Fe–Mo–C system

The High speed cast iron, which is used for hot rolling parts, needs high fracture toughness and wear resistance. To improve these properties, the control of eutectic carbides, M₃C, M₇C₃,M₆C and MC is important by adding elements such as Cr, W, V and Mo.

The aim of this study is to estimate which carbide will solidify under certain solidification conditions and compositions. This prediction criterion can be gained by measuring the interface temperature of each carbide in various samples with different solute elements, composition and growth rate.

In this report, the solidified temperature of γ + M₂C and γ + M₆C eutectic carbide in the Fe–Mo–C ternary system in the composition range near to the eutectic monovariant line, was measured during the unidirectional solidiication process. The relationship between solidified interface temperature and growth rate was obtained. In eutectic solidification along the γ + M₆C monovariant line, a coefficient of undercooling, the k value, was obtained.

The authors have already measured the k values of other eutectic carbides, such as γ + M₃C, austenite + M₇C₃, and γ + VC in Fe–Cr–C and Fe–V–C system. The paper also discusses the relationships between these properties of eutectic carbides.     

Boron-alloyed Fe–Cr–C–B tool steels — Thermodynamic calculations and experimental validation

This study focuses on the development of boron-alloyed tool steels. The influence of Cr additions from 0 to 10 mass% on microstructural changes were investigated for a constant metalloid content (C + B = 2.4 mass%). In the first step, thermodynamic calculations were performed to map the quaternary Fe–Cr–C–B system. In the second step, thermodynamic calculations were validated with laboratory melts that were investigated with respect to the microstructure and phase composition. The results of thermodynamic calculations correspond to real material behavior of Fe–Cr–C–B alloys. Furthermore, the influence of chromium on hard phase formation was investigated by means of phase analysis methods, X-ray diffraction (XRD), and energy dispersive spectrometry (EDS). Nanoindentation was used to determine hard phase properties (hardness, Young's modulus). It was shown that chromium promotes the formation of M₂B-type borides. An increase in the Cr content within the M₂B phase led to a transformation from the tetragonal structure into an orthorhombic structure. This transformation is accompanied by an increase in hardness and in the Young's modulus. In contrast, Cr also promotes the formation of Cr-rich carboborides of type M₂₃(C,B)₆. However, an increased Cr content within the M₂₃(C,B)₆ phase is not associated with an increase in hardness or elastic modulus.     

Synthesis and characterization of photoconductive C60–N-vinylcarbazole copolymers

Soluble C60–N-vinylcarbazole copolymers with different C60 contents were synthesized in lithium naphthalene-initiated anionic polymerization reactions. 13C nuclear magnetic resonance (NMR) results provided strong evidence for the covalent attachment of poly(N-vinylcarbazole; PVK) units to the C60 cores. The chemical shifts located at 142.16, 143.21, 144.70, 145.61, 146.65, 147.09, 149.08 and 170.28 p.p.m. in the 13C NMR spectrum of the copolymer are assigned to the unsaturated carbon signals of the substituted C60 cage. Its ultraviolet–visible absorption spectrum tends to move to the longer wavelength compared with those of the N-vinylcarbazole (NVC) monomer and PVK, and the peak range also extended from about 350 to 640 nm due to charge-transfer interaction between C60 and N-ethylcarbazole units. X-ray diffraction evidence suggests that the structure of the resultant copolymer might be a layered structure. Like the C60 chemically modified PVK, this material also exhibits good photoconductivity and temperature sensitivity. An unusual temperature dependence of the ESR spectrum is observed. In addition, it is also found that both [60] fullerene polyanion salts [(Cn-60) M+n, M=Li, Na, K] and fullerene itself are unable to initiate the polymerization of such monomers as N-vinylcarbazole, styrene and acrylonitrile, etc. © 1998 Kluwer Academic Publishers     

Synthesis and phases evolution of Si–C–Ti from polycarbosilane (PCS) and metal Ti

Si–C–Ti ceramics were synthesized by reactive pyrolysis of polycarbosilane (PCS) precursor filled with metal Ti powder. Pyrolysis of mixture with atomic ratio of Ti:Si through 3:1–3:2 was carried out in argon atmosphere at given temperature up to 1500 °C. The metal–precursor reactions, and phase evolution were studied using X-ray diffraction and scanning electron microscopy with EDX. The Ti₃SiC₂ phase was obtained firstly from reaction of PCS and Ti. Ti₃SiC₂ formation starts at 1300 °C and its amount increases significantly in a narrow temperature range between 1400 °C and 1500 °C. In addition, addition of CaF₂ can promote the formation of Ti₃SiC₂ phase.