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Compared with traditional stainless steels, high nitrogen stainless steels (HNSS), have been widely used due to their high strength, toughness along with excellent corrosion resistance and low cost, formed by partial replacement of Ni (austenite-forming element) by N. The evolution of the microstructure of a Cr19Mn19Mo2N0.7 stainless steel is investigated after solution treatment at 1010, 1060, 1200 or 1250°C for 30min. A complex multilayer structure has been found under a negative pressure vacuum. A white ferritic layer at the surface is formed, and a subsurface layer with full austenitic structure and a bulk microstructure comprising of austenite and ferrite are detected. With increasing solution temperature, the surface layer thickness increases. The formation of the multilayer structure is attributed to an outward diffusion, a diffusive retardation and an abnormal accumulation of nitrogen during solution treatment.

A commercial unalloyed ductile iron has been developed to produce a multiphase matrix microstructure consisting of lenticular prior martensite, feathery upper bainite and a nano-scaled super bainite of lath bainitic ferrite and carbon-enriched film retained austenite. Multi-step heat treatment composed of austenizing, rapidly quenching and isothermally holding at low temperature have been developed. A tensile strength of more than 1.6 GPa, a hardness higher than HRC 54, and an elongation in excess of 5%, are achieved. This is attributed to a synergistic multi-phase strengthening effect. The developed nano super bainite exhibits a good balance between strength and toughness. The presence of martensite formed during the quenching prior to the isothermal treatment, accelerates the kinetics of subsequent nano super bainitic transformation by bainitic laths nucleating quickly at the martensite-austenite interfaces.

A simple, new method utilizing the hydrolysis of Mg2Ni has been successfully developed for the synthesis of Ni nanoparticles. The possible growth mechanisms of Ni nanoparticles are discussed. Compared with conventional preparation methods for Ni nanoparticles, this method has the potential to inexpensively produce Ni nanoparticles on a large scale. In addition, the principle of the method could be applied to the synthesis of other transition metal nanoparticles such as Co, Cu, Ag, Au, Pt, and Pd.

Full-density nickel/aluminide multilayer composites were successfully fabricated by reaction synthesis using Ni and Al foils. The Al is the dominant diffusing species, and Ni2Al3 is the first phase formed during reaction between the Ni and Al foils at 620 °C. The reaction mechanism is such that only Al atoms can diffuse through the Al2O3 films formed on the Al foils, and the Al atoms then transform into Ni2Al3 by reaction with Ni. The Ni and Ni3Al layers in the composites can therefore cooperatively deform through slipping of dislocations in the Ni and Ni3Al layers through the Ni3Al/Ni interfaces. Thus, Ni/Ni3Al multilayer composites exhibit high ultimate tensile strengths and large elongations (1050 MPa and 18.2 pct).

Long and coarse AlN whiskers comprising more than 80 vol% of the combustion product have been successfully produced through combustion synthesis. Addition of ammonia halides can accelerate the vaporization of Al, and retard the deposition rate of AlN, with the result that the growth of AlN whiskers is markedly promoted. A growth model for a spiral whisker by a helical screw dislocation mechanism, or a combination mechanism of a helical screw dislocation and the VLS process, is proposed. Periodic interactions of vacancies and the tip of a screw dislocation cause the growth of a spiral whisker in the model. Under an atmosphere of supersaturated “AlN vapor,” the growth of whiskers along the axial direction slows down and gradually arrests, due to the limitation of the diffusion distance. A series of deposition sites are then produced at regular, isolated locations along the center line on the prismatic plane, and eventually cause the formation of dendritic whiskers.

The characteristics and mechanisms of the mechano-electrochemical effect were investigated both theoretically and experimentally for two steels (AISI 1020 and 52100) in various heat-treated conditions subjected to sequential erosion and corrosion. A mathematical equation is developed to describe the mechano-electrochemical effect in which the corrosion rate is exponentially related to the change of corrosion potential and increased stored strain energy. The agreement between calculated and measured corrosion rate is good for the annealed AISI 1020 steel and both the annealed and the tempered AISI 52100 steels, in which the microstrain and stored strain energy originate only from erosion.

The mechanisms and characteristics of the mechano-electrochemical effect were investigated for eroded AISI 1020 steel specimens. The effect of erosion on open-circuit potential, corrosion potential, linear polarization resistance, and corrosion rate was determined. The corrosion rate was exponentially related to the decrease in corrosion potential and increase in the strain energy. The corrosion rate was quantitatively calculated using a mechano-electrochemical dynamic equation, which is based on the decrease in corrosion potential and increase in strain energy. The calculated rate agrees well with the experimentally measured corrosion rate.

The definition of the practical upper temperature limit of the bainite reaction in steels is discussed. Because the theoretical upper temperature limit of bainite reaction, B 0, can neither be obtained directly from experimental measurements, nor from calculations, then, different models related to the practical upper temperature limit of bainite reaction, B S, are reviewed and analyzed first in order to define the B 0 temperature. A new physical significance of the B S and B 0 temperatures in steels is proposed and analyzed. It is found that the B 0 temperature of the bainite reaction in steels can be defined by the point of intersection between the thermodynamic equilibrium curve for the austenite→ferrite transformation by coherent growth (curve Z $$\gamma \to \overrightarrow \alpha $$ ) and the extrapolated thermodynamic equilibrium curve for the austenite→cementite transformation (curve ES in the Fe-C phase diagram). The B S temperature for the bainite reaction is about 50–55 °C lower than the B 0 temperature in steels. Using this method, the B 0 and B S temperatures for plain carbon steels were found to be 680 °C and 630 °C, respectively. The bainite reaction can only be observed below 500 °C because it is obscured by the pearlite reaction which occurs prior to the bainite reaction in plain carbon steels. A new formula, B S(°C) =, 630-45Mn-40V-35Si-30Cr-25Mo-20Ni-15W, is proposed to predict the B S temperature of steel. The effect of steel composition on the B S temperature is discussed. It is shown that B S is mainly affected by alloying elements other than carbon, which had been found in previous investigations. The new formula gives a better agreement with experimental results than for 3 other empirical formulae when data from 82 low alloy steels from were examined. For more than 70% of these low alloy steels, the B S temperatures can be predicted by this new formula within ±25°C. It is believed that the new equation will have more extensive applicability than existing equations since it is based on data for a wide range of steel compositions (7 alloying elements).

High-purity monoclinic ZrO2 and monoclinic Nb2O5 powder samples were mixed in varying ratios, and heated at 1300°C for 24 h before furnace cooling. X-ray diffraction analysis showed that two compounds, Nb2O5-6ZrO2 and Nb2O5·8ZrO2 (or (Zr, Nb)8O17 and (Zr, Nb)10O21), were formed. Some of the reflections from the two compounds were overlapped and interfered with those from the zirconium oxide, especially the tetragonal ZrO2. A thermodynamic analysis was used to demonstrate that it is possible to have ZrO2 as well as Nb2O5 formed on Zr-Nb alloys in an oxidizing environment. The relevance of these results (experimental and calculated) to the corrosion of a Zr-Nb alloy in high temperature aqueous environments is discussed. It is suggested that the incorporation of niobium into the oxide during the corrosion of Zr-Nb alloys could be by the formation of compounds such as (Zr, Nb)8O17 and (Zr, Nb)10O21. Also, the tetragonal ZrO2, which has been found to be a barrier layer oxide, could, in fact, be either of the ternary compounds Nb2O5·6ZrO2 and Nb2O5·8ZrO2 both of which are orthorhombic with lattice parameters very close to those of the tetragonal ZrO2.

Recent progress in the understanding of high-temperature creep of alloys is discussed in the context of theoretical modeling and its application to alloy development. Emphasis is placed upon those engineering alloys specifically designed for high-temperature applications, such as precipitation and dispersion-strengthened (DS) alloys and metal-matrix composites (MMCs). Currently, these theoretical models use one of two different approaches, (a) a phenomenological approach, which is used in such models as those based on the internal stress concept, and those based on empirical creep equations; and (b) micromechanical models that are based on dislocation mechanisms and the interactions of dislocations with solute atoms, second-phase particles, and other reinforcements such as fibers. All these theoretical models have a common goal, namely, the understanding of high-temperature strengthening mechanisms and the relationship between high-temperature strength and the micromechanical mechanisms during high-temperature plastic deformation of the alloys. These theoretical studies can provide information that is useful in alloy design and processing, such as the selection of alloy chemistry, and the optimization of phase microstructural features (e.g., reinforcement amount, shape, size, and distribution; matrix grain size; and matrix and reinforcement interfaces) by optimization of processing methods.

Three different low-carbon steels, namely ASTM 516 Gr70 PVQ, CSA G40.21 350 WT and CSA G40.21 350 AT plates, were tensile tested at temperatures from ambient to 623 K over a range of strain rates (1.48×10−5–1.48×10−3 s−1). The lower yield strength generally decreases with increasing temperature, but there is a strength plateau, or a small peak, at temperatures between 423 and 573 K. The results of computer modelling show that concentration of nitrogen in the atmospheres at dislocations decreases with increasing temperature, approaches a minimum value at a temperature around 423 K, then increases with increasing temperature for temperatures above 423 K. This effect of temperature on the concentration of nitrogen in atmospheres at dislocations results in the strength plateau or small peak.

Two construction- grade steels— G40.21 350 WT and G40.21 350 AT— were tensile tested under a range of temperature and strain- rate conditions. Results showed that both the strain- hardening exponent and strength coefficient at first decrease with increasing temperature, then increase with increasing tempera-ture and reach a maximum at a temperature between 523 and 573 K before decreasing. With increasing temperature, the strain- rate dependence of the strain- hardening exponent and the strength coefficient changes from positive to negative. This behavior reflects the effects of strain aging on the strain- harden-ing exponent and the strength coefficient.

Two wrought biomedical cobalt-chromium alloys have been developed, and their mechanical properties and corrosion resistance determined by means of tensile and hardness tests and by electrochemical potential-time curves for isolated specimens in a 6.0 wt% NaCl solution at room temperature. In comparison with a current dental alloy, SC-H, and the basic type 18-8 austenitic stainless steel, it is shown that alloy II (chemical composition in wt%:0.11 C, 22.07 Cr, 15.20 Ni, 3.75 Mo, 9.30 W, balance Co) has superior properties. The alloy has a high strength together with a good ductility which permits adequate workability. Also, both cobalt-chromium alloys show a passive behaviour in 6.0 wt% NaCl solution, whereas the basic type 18-8 austenitic stainless steel shows a fluctuating potential and is thus susceptible to pitting, making it unsuitable for surgical implants.

Two wrought Co-Cr alloys for dental and surgical implant and equipment applications were designed and their microstructures and hot workability determined and compared to a current dental alloy SC-H. The chemical composition of the alloys was selected with regard to the general requirements for biomedical alloys and the general principles of alloying theory. A phase-control law originally developed for nickel-base superalloys, PHACOMP, was utilized in order to avoid the formation of topologically close-packed (tcp) phases and to ensure the ductility and workability of the alloy. The alloys were cast using a vacuum induction melting technique which was found to allow a fairly good chemical composition control of the alloys. Hot forging of the as-cast alloys confirmed their good workability. Optical metailography showed the as-cast alloys to have a dendritic structure with some spherical carbide particles in the interdendrite regions. In contrast, the dental alloy SC-H in the as-cast condition had continuous carbide along the grain boundaries which impaired the ductility and prevented hot forging of this alloy die to cracking of the specimens. X-ray diffraction analysis showed that both alloys I and II have the fcc-Co matrix and Cr23C6 type carbide particles. No tcp phases were observed.

The two treatments, namely rare-earth (RE) additions to the mould and Ca-Si injection into the ladle, were used to control the MnS inclusion shape in a 16 Mn steel. The critical crack opening displacement, δc, method and tensile testing were used to determine the fracture properties of the steel sheets. Scanning electron microscope (SEM) fractography of the fracture surface of tensile specimens tested at room temperature clearly showed the banded structure of the steel sheets in all, even modified, steels. The RE treatment improved the fracture properties both by sulphide inclusion shape control and by reducing microstructural heterogeneity.

Thermoelectric power (TEP) measurements are used to study recovery, recrystallization, and other microstructural changes during annealing of cold worked Zr-1wt.%Nb and Zircaloy-4 tubing at temperatures from 300 to 1100 °C. The measured value of thermoelectric power is very sensitive to microstructural evolution in zirconium alloys, and TEP measurements correlate well with both microstructural changes, as seen using optical microscopy, and microhardness measurements.

The oxide-metal interface formed during the aqueous corrosion of a Zr-2.5 wt% Nb alloy has been studied by SEM, using a specimen preparation method which also has potential application to other materials containing an oxide-metal interface. The oxidation of cold-worked Zr-2.5 wt% Nb pressure tubing in pressurized lithiated water proceeds first along grain boundaries at which there is β-zirconium or its decomposition products, and then continues on the α-zirconium grains. Oxides at the oxide-metal interface formed in an aqueous environment were mainly extended along grain boundaries, and were characterized by long filaments which consisted of many fine zirconia grains. This oxidation behaviour is attributed to short-circuit diffusion at the grain boundaries which is caused by the nature of the crystallite boundaries of the oxide, the flaws arising from the oxidation of the grain boundary phases (β-Zr, its decomposition products as well as impurities), and cracking of the oxide due to phase transformations in ZrO2. When different plane sections of the tubing are corroded, there are different corrosion rates, with the sections containing a higher area fraction of the grain boundaries with β-zirconium exhibiting higher corrosion rates. The formation of long ‘fingers’ of oxide made up of longer filaments of oxide, together with the higher corrosion rates in the post-transition specimens, result in the destruction of the barrier oxide layer and an increase in the oxide rate.

Two treatment methods, namely Ca-Si injection into the ladle and rare earth (RE) additions to the mold, were investigated for their effectiveness in controlling the microstructure, particularly sulfide inclusions, and hence the properties of a 16Mn plain-carbon steel. A combined Ca + RE treatment increased the critical crack opening displacement in the transverse direction of sheet material to that in the rolling direction. The combined treatment also improved the resistance to stress-corrosion cracking (SCC) in a boiling 20 wt.% NH4NO3 solution. Too large a RE addition, ultimately lowers SCC resistance. The RE additions retarded austenite grain growth, whereas the Ca-only addition accelerated grain growth. The changes in fracture behavior, SCC resistance, and austenite grain growth behavior are explained in terms of the segregation of the RE to the grain boundaries and the subsequent changes in the electrochemical and mechanical properties of the grain boundaries relative to the grain interiors. A combined treatment of injecting 3.4 kg Ca-Si per ton of steel into the molten steel and adding 0.03 wt.% RE to the mold yielded optimum properties.

Two treatment methods, namely Ca-Si injection into the ladle and rare earth (RE) additions to the mold, were investigated for their effectiveness in controlling the sulphide inclusions in a 16 Mn steel. Ca desulphurization did not completely remove all of the MnS inclusions and the RE inclusion shape modification treatment increased the amount of inclusions compared to using only a Ca treatment. A combined RE plus Ca treatment gave the best control of inclusion shape, amount, and distribution. The combination treatment also provides a relatively homogeneous distribution of Mn in the banded (ferrite + pearlite) structure of hot rolled sheet. A criterion for effective inclusion control is established whereby [RE/S]effective is equal to (or slightly higher than) 3. [RE/S]effective is given by the formula [RE/S]effective = [RE/S] + 1.875 [Ca/Si] where RE, Ca, and S are the compositions of rare earth, calcium, and sulphur in weight percent in the steel sheet.

Metal hydrides provide an efficient and safe method for storing hydrogen. Hydrogen can be stored indefinitely and released as needed for a number of energy usages. The commercially available alloys for storage are LaNi5-based, FeTi-based, and Mg-based alloys. In this paper we conduct an overall review of these alloys and compare them with other alloys, and in particular with zirconium based binaries and pseudobinaries. Also described in this paper is the apparatus required for hydrogen absorption and desorption experiments.

The influence of various alloying elements on the thermoelectric power (TEP) of zirconium is determined. The data indicate that the thermoelectric power is very sensitive to both the type of alloying element and its solubility in the α-phase of zirconium. For example, where tin strongly reduces the thermoelectric power of zirconium, the magnitude of the reduction increasing as the amount of tin in solution in α-Zr increases, the effect of niobium is much less pronounced and variable with first a decrease and then an increase in TEP with increasing niobium.

Irradiation growth, a shape change in the absence of an applied stress, is one of the factors limiting the performance of pressure tubes in CANDU-PHW (Canadian Deuterium Uranium-Pressurized Heavy Water) nuclear reactors. Irradiation growth has been measured in zirconium, Zircaloy-2, Zr-2.5wt%Nb and ExCel alloy (Zr-Sn-Nb-Mo) specimens using neon ion bombardment to simulate the reactor environment. This growth data is compared to that obtained from neutron irradiation experiments. Recommendations are made as to the microstructure/processing routes required for the pressure tubes in order to reduce the magnitude of irradiation growth.

The effect of various thermomechanical processing schedules on the corrosion/hydriding behavior of Zr-2.5 wt. pct Nb alloy nuclear reactor pressure tubing has been studied using accelerated corrosion tests in a pressurized LiOH solution. Coldwork had a detrimental effect on both the corrosion and hydriding rate. A final heat treatment of five to 10 hours at 560 °C is recommended to give a low level of hydrogen pickup and a relatively low level of general corrosion, and to prevent the formation of throughwall radial hydrides which could provide a ready crack path for failure of the pressure tube.

A number of zirconium pseudobinaries of the type Zr(BxB1-x′)2 demonstrate potential for application as hydrogen storage materials. Pseudobinaries of the above type with B = Fe,Co, B ′ = Mn, Cr, andx =0.4, 0.5, 0.6 have been investigated here and their hydrogen storage characteristics are reported. These alloys exhibit two-phase microstructures, identified as the cubic and hexagonal Laves phases. Hydrogen is absorbed into interstitial sites in the lattice with maximum capacities approaching 1.0 H-atoms per metal atom. Hydrogen capacities and hydride stabilities decrease with ‘x’. Incomplete desorption has been observed in all instances.

Irradiation growth, which is defined as irradiationinduced changes in dimensions in the absence of an applied stress, is of concern both for fuel cladding and nuclear reactor structural components such as pressure tubes and calandria tubes. A critical review is presented of irradiation growth data for zirconium alloys together with a discussion of the various operating and material factors affecting growth. Empirical and mechanistic models used to explain and predict irradiation growth are reviewed and the most applicable are identified. On the basis of the data presented, implications are drawn with respect to the optimum fabrication procedures and material characteristics of zirconium alloys used for structural components in nuclear reactors.

Metal hydrides, as energy storage media, are receiving considerable attention. The amount of literature concerning the properties of these materials has increased markedly over the past few years. In this paper, we conduct a review of the alloy groups which absorb large quantities of hydrogen. These alloy classes are designated as AB5, AB, AB2, AB3 and A2B7 and Mg-based compounds. These materials are discussed with emphasis placed on thermodynamic and kinetic properties, activation and deactivation, poisoning effects and storage capacity.

The corrosion/hydriding behavior of Zr-2.5 wt pct Nb nuclear reactor pressure tubing has been studied in two metallurgical conditions, namely cold worked or heat treated. Two different corrosion tests were used, for total exposure times of up to 2000 hours. The study involved weight gain measurements and hydrogen pickup analyses, x-ray diffraction identification of oxides and hydrides, optical microscopy of oxides and hydrides, and TEM and SEM examination of the thin film oxides. The corrosion of the tubing follows a parabolic rate law in the pretransition period, which then changes to linear kinetics after the breakaway point. The monoclinic oxide was the predominant phase found in the oxide, while the γ-hydride (ZrH) was the predominant hydride phase in the metal. Comparison of the behavior of the coldworked and the heattreated material would suggest that a certain amount of cold work is beneficial in order to strengthen the metal and its oxide, to avoid lateral detachment of the oxide and to avoid the formation of radial (throughwall) hydrides.

Etude experimentale sur l'alliage soumis a des essais de fluage a 650 C dans deux etats microstructuraux differents: β et β+α+TiCr 2 . Determination des courbes de fluage primaire et des vitesses de fluage a l'etat stable. On montre que l'etat β+α+TiCr 2 a une resistance au fluage superieure. Ce phenomene serait du a la presence de precipites et/ou remplacement partielle de la phase β par la phase α