Volume 104, Issue 11

To accurately define important phase boundaries in the iron–nitrogen (temperature–composition) phase diagram as well as the (temperature–potential) Lehrer diagram, the solubility of nitrogen in ferrite was determined as a function of the nitriding potential (which defines the chemical potential of nitrogen) and the temperature. To this end, thin iron foils were homogeneously nitrided in flowing gas mixtures composed of ammonia and hydrogen. Phase identification was performed by means of X-ray diffraction analysis. Further, from the data obtained, the absorption function and the enthalpy for dissolution of nitrogen into ferrite and the enthalpy of the reaction occurring at the α/(α + γ′)-phase boundary were determined. The data obtained were corrected for the occurrence of a stationary state instead of a local equilibrium at the surface of the specimens. It followed that parts of the phase boundaries in the Lehrer diagram do not represent equilibrium states but rather stationary states.

Experimental work using X-ray diffraction and differential scanning calorimetry was conducted on key samples in the Li–C binary system. Reproducible differential scanning calorimetry data with multiple heating cycles were produced only by samples sealed in arc welded Ta-capsules. Only one compound, α/βLi 2 C 2 , is found to be stable. A comprehensive Calphad-type assessment was performed and for the first time a consistent thermodynamic description, covering all thermodynamic and phase equilibrium data, is developed. Phase diagrams calculated from that validated database, including the gas phase, are presented. The phase LiC 6 , was also studied experimentally. It is metastable with respect to α/βLi 2 C 2 + (C), but may be formed from Li + (C). Phase transitions of LiC 6 , claimed in the literature, are discussed.

The partitioning of tin between the slag and metallic phases, and the effect of oxygen partial pressure on the slag liquidus at tridymite saturation in the “SnO”–SiO 2 –“FeO” system at 1473 K have been measured. The experimental methodology includes high temperature equilibration and quenching, followed by the analysis of the compositions of the oxide phases by means of electron probe X-ray microanalysis, and the analysis of the compositions of the metallic phases using inductively coupled plasma mass spectrometry. The activity coefficient of SnO in slag has been calculated to be 1.13 ± 0.06, and Henry's law is shown to be obeyed in the slag at least up to 0.20 mol fraction of SnO.

Oxide dispersion strengthening of steels has become quite popular during the last few years. Especially because of their thermal stability, Y–O clusters can improve high temperature properties such as strength, hardness and creep strength. Oxide dispersion strengthened steel is a promising candidate for applications mainly in fast breeder reactors. In order to establish a better understanding of the strengthening mechanism, this study focuses on an evolution of the Y distribution in mechanically alloyed iron during the process route, employing atom probe tomography. After mechanical alloying, Y seems to be distributed in extremely fine clusters and partly dissolved in the matrix. Enrichment of alloying elements in the Y–O clusters in the mechanically alloyed state is evidence for diffusion processes taking place during mechanical alloying. During hot isostatic pressing at elevated temperatures, dissolved Y atoms accumulate and build distinct clusters. These clusters stay stable even after annealing at 600°C for 8 hours.

The NiAl-γ–γ′-system is numerically modeled using a multi-phase-field approach near its peritectic. The free energies are approximated as second order polynomials of the concentration. The parameters of these functions are fitted using experimentally determined values for the peritectic equilibrium concentrations and the liquidus/solidus slopes at the peritectic temperature. A study on lateral growth of a peritectic phase (γ') layer on a primary (γ) substrate reveals an oscillation of the layer interfaces at very low undercoolings (0.08 K). This morphology has its seeds in an oscillatory rotation of the triple junction. A mechanism for the origin of rotation is described and a reason for its disappearance at higher undercoolings is discussed. While the γ–γ′ surface energy as well as the γ interdiffusion constant are unknown, the influence of these parameters on the oscillation morphology is investigated.

In this paper, the characteristics of the oxide film formed on the surface of 2017A aluminium alloy by sulphuric oxidation are investigated. Morphological features on the oxide film are studied using scanning electron microscopy. Crystallographic details are obtained using X-ray diffraction. The composition of the oxide layer is estimated using wavelength dispersive X-ray spectrometry and Raman spectroscopy. Through systematic structure–property studies, the microstructure of the oxide layer is identified providing the incorporation of the alloying elements in the inner layer with a copper enrichment at the interface.

The synergistic effects of chloride and sulphate ions on friction, wear and pitting corrosion of AISI 310 and AISI 316 have been investigated using electrochemical methods and a tribometer. The results show that increasing the sulphate concentration in synthetic mine water mitigates the detrimental effects of chloride ions on both the general corrosion rate and pitting potentials of both materials. The E corr shifted to more positive values as the sulphate-to-chloride ratio increased in the electrolyte. The AISI 316 is more resistant to wear than the AISI 310 both in dry and wet unidirectional sliding conditions. Whereas the wear mechanism under the dry condition is mainly adhesive, there was transition from abrasive wear to adhesive wear under the wet sliding condition as the sulphate concentration increased in both materials.

The superplastic behavior of Ti-13V-11Cr-3Al alloy with beta single phase structure and average grain size of 220 μm was investigated. It was found that elongation increases with temperature at strain rates of 0.1 and 1 s −1 . The optimum condition for superplastic deformation of the alloy was achieved in the temperature range 1030–1080°C and with a strain rate of 0.1 s −1 . In this condition the amount of elongation reaches 200%. Grain refinement occurred during deformation which can be attributed to the occurrence of dynamic recovery and continuous dynamic recrystallization. In addition, it was seen that in the temperature range 930–1080°C, the strain rate sensitivity parameter ( m ) was higher than 0.3, which is an appropriate value for superplastic deformation. A high value of m , elongation over 100%, and coarse-grained microstructure of the alloy suggested that superplastic behavior of the Ti-13V-11Cr-3Al alloy can be similar to the behavior of coarse-grained superplastic alloys.

The creep fracture mechanism of FGH95 superalloy has been investigated by means of microstructure observation and creep behaviour measurement. Results show that, after solution treatment at 1150°C, the coarser γ′ precipitates distribute in the wider regions of previous particle boundaries. As the solution temperature increases to 1165°C, the grains grow in the alloy and carbide films precipitate along the grain boundaries. When the alloy is solution treated at 1160°C, the coarser γ′ phase in boundary regions is fully dissolved, and granular carbides precipitate along the grain boundaries, which may effectively restrain boundary sliding and hinder dislocation movements to improve the creep resistance of the alloy. During creep, the deformation feature of the alloy is that slipping dislocations with single or double orientations and stacking faults are activated in the alloy. As creep progresses, the amount of slip traces increases to bring about stress concentration and cause microcracks to be initiated and propagated along the grain boundaries up to the rupture of the alloy.

As a sintering aid, diopside was introduced into alumina matrix ceramic materials. Composites were fabricated using transient liquid phase sintering, during which new phases such as mullite, anorthite and CaO · 6Al 2 O 3 were produced by the chemical reactions taking place between alumina and diopside. The densification rate of the composites as a function of diopside volume content is discussed. The hardness, fracture toughness and bending strength of the composites were tested. Meanwhile, the effects of diopside content, grain size and interface on mechanical properties and fracture mechanism of alumina matrix ceramic materials are analyzed and discussed.

This paper presents the preliminary test of tungsten heavy alloy as a filler metal for repair welding of high pressure die casting dies. H13 grade hot work tool steel was used as a base material. Multipass gas tungsten arc welding was used to fill a single-V butt joint with tungsten heavy alloy in the form of a welding rod. The microstructure of the weld was examined using scanning electron microscopy and optical microscopy. It was found that tungsten grains are not dissolved completely during welding and areas of fine eutectic were formed during solidification of the weld. The hardness of the weld was measured in three courses across the weld and increased in the heat affected zone while the weld hardness was below 380 HV 0.3 . Charpy V-notched samples were prepared from the weld. The high content of tungsten grains distributed in the nickel–iron weld matrix resulted in low impact toughness of 5.1 J. Face bend testing of the weld was conducted in order to study weld ductility.

Ag/α-Fe 2 O 3 nanoplates with a size range of 40–60 nm were fabricated by means of a facile gelatin assisted hydrothermal technique. The samples were characterized using X-ray diffraction, transmission electron microscopy, and UV-vis spectroscopy. The results demonstrate that these composites consist of silver and hematite (α-Fe 2 O 3 ) and the band gap of the Ag/α-Fe 2 O 3 composite is much narrower than for the pure α-Fe 2 O 3 . Furthermore, the photocatalysis test shows that the Ag/α-Fe 2 O 3 composite exhibits a higher photocatalytic activity than the pure α-Fe 2 O 3 nanoplates, thereby implying that the Ag/α-Fe 2 O 3 interfaces promote the separation of photogenerated electron–hole pairs and enhance the photocatalytic activity.

Previously, we have shown that the effects of the coating solution concentration of coupling agent on the interlaminar shear strength of fiber/epoxy composites were best investigated with 4 wt.% nano-CaCO 3 content. Here, five different types of composites were prepared: (E–0–4): composites modified by untreated nano-CaCO 3 , (E–1.1–4): composites modified by nano-CaCO 3 with 1.1 wt.% coating solution concentration treatment. Similarly, samples E–2.3–4, E–3.5–4 and E–4.6–4 were also fabricated. The results show that nanocomposites prepared with 2.3 wt.% and 3.5 wt.% coating solution concentration treatment have the best shear properties, including interlaminar shear strength, elongation at break and fracture work. With 2.3 wt.% coating solution concentration treatment, these have values of 142.4 MPa, 1.95 mm and 1.86 J, which can increase 11%, 41% and 39% compared to the composite prepared with untreated nano-CaCO 3 , respectively.