Candidate Alloys Research Articles

Impact of irradiation on the tensile and fatigue properties of two titanium alloys

The attachment of the first wall modules of the ITER FEAT fusion reactor is designed using flexible connectors made from titanium alloys. An assessment of the tensile and fatigue performance of two candidate alloys, a classical two phase Ti6Al4V alloy and a monophase α alloy Ti5Al2.5Sn, has been carried out using 590 MeV protons for the simulation of the fusion neutrons. The dose deposited was up to 0.3 dpa and the irradiation temperature was between 40°C and 350°C. The unirradiated tensile performances of both alloys are roughly identical. The radiation hardening is much stronger in the α+β alloy compared with the α alloy, and the ductility is correspondingly strongly reduced. A very fine precipitation observed by TEM in the primary and secondary α grains of the dual phase alloy seems to be the cause of the intense radiation hardening observed. Two different regimes have been observed in the behaviour of the cyclic stresses. At a high imposed strain, the softening is small in the Ti6Al4V and larger in the Ti5Al2.5Sn. At a low imposed strain, and for both alloys, cyclic softening occurs up to about 800 cycles, but then a transition occurs, after which a regime of cyclic hardening appears. This cyclic hardening disappears after irradiation. In both materials, and for all test conditions, the compressive stress of the hysteresis loop was found to be larger than the tensile stress. The stress asymmetry seems to be triggered by the plastic deformation. The fatigue resistance of the Ti5Al2.5Sn alloy is slightly better than that of the Ti6Al4V alloy. The irradiation did not significantly affect the fatigue performance of both alloys, except for high imposed strains, where a life reduction was observed in the case of the Ti6Al4V alloy. SEM micrographs showed that the fractures were transgranular and pseudo-brittle.

Corrosion investigations of steels in flowing lead at 400°C and 550°C

Experiments were conducted in a liquid lead pumped loop at 400°C and 550°C to examine the corrosion behaviour of ferritic and austenitic steels. The aim of this work is to identify suitable structural containment materials for a lead cooled accelerator driven transmutation reactor (ADS). During exposure to liquid lead containing 3–4×10 −5 wt% oxygen, protective oxide layers grow on the surface of each candidate alloy. The total thickness of the multiphase layers increases parabolically with increasing exposure time. After 3000 h, they reach a maximum of 50 μm on one ferritic steel (Optifer) and of 30–40 μm on electron pulse-treated austenitic steels. Austenites with an untreated surface develop oxide layers of just 1–2 μm thickness. In each case the oxide layers prevent the dissolution attack of liquid lead.

Microstructural origins of radiation-induced changes in mechanical properties of 316 L and 304 L austenitic stainless steels irradiated with mixed spectra of high-energy protons and spallation neutrons

A number of candidate alloys were exposed to a particle flux and spectrum at Los Alamos Neutron Science Center (LANSCE) that closely match the mixed high-energy proton/neutron spectra expected in accelerator production of tritium (APT) window and blanket applications. Austenitic stainless steels 316 L and 304 L are two of these candidate alloys possessing attractive strength and corrosion resistance for APT applications. This paper describes the dose dependence of the irradiation-induced microstructural evolution of SS 316 L and 304 L in the temperature range 30–60°C and consequent changes in mechanical properties. It was observed that the microstructural evolution during irradiation was essentially identical in the two alloys, a behavior mirrored in their changes in mechanical properties. With one expection, it was possible to correlate all changes in mechanical properties with visible microstructural features. A late-term second abrupt decrease in uniform elongation was not associated with visible microstructure, but is postulated to be a consequence of large levels of retained hydrogen measured in the specimens. In spite of large amounts of both helium and hydrogen retained, approaching 1 at.% at the highest exposures, no visible cavities were formed, indicating that the gas atoms were either in solution or in subresolvable clusters.

Advances in lead-free electronics soldering

Lead-free soldering has emerged as one of the key technologies for assembling in environmental-conscious electronics. Among several candidate alloys, the Sn–Ag–Cu alloy family is believed to be the first choice with the combination of other alloys such as Sn–Zn–Bi, Sn–Cu and Sn–Bi–Ag. Phase diagrams of lead-free alloy systems have been intensively examined by using careful thermal and microstructural analysis combined with the thermodynamic calculation such as the CLAPHAD method. The Cu 6Sn 5/Cu 3Sn layers are formed at most lead-free solder alloy/Cu interfaces, while Cu–Zn compound layers are formed in the Sn–Zn/Cu system. Growth kinetics of intermetallic layers both in solid-state and in soldering are also discussed. Creep and fatigue phenomena are also reviewed. In many aspects of lead-free soldering, much more work is required to establish a sound scientific basis to promote their applications.

A surface modified ODS superalloy by thermal oxidation for potential implant applications.

In the present work attention is paid on the composition, structure and protective properties of alumina layer produced by high temperature oxidation on MA 956 superalloy (Fe-20Cr-4.5Al-0.5Ti-0.5Y(2)O(3) (wt %)). The combination of good mechanical properties of this material and the excellent biocompatibility, the good wear and corrosion behavior of an outer alpha-alumina layer, limiting the release of ionic species and wear debris from the bulk material into the body-fluid environment, can make this material a candidate alloy for medical applications. Isothermal oxidation at 1100 degrees C in air of the alloy has led to the formation of a fine-grained, compact and adherent alpha-alumina scale. Oxide nodules rich in Ti, Y, Cr, and Fe were found on the top of the surface. In vitro electrochemical corrosion experiments showed good protective properties of the oxide scale. Moreover, no spallation of the alumina layer was observed. This feature is significant considering that the alumina layer has to withstand very high compressive stresses resulting from both growth and thermal stresses incorporated during cooling.

Erosion of construction materials in a reverse osmosis plant utilizing seawater in Kuwait

The development and production of fresh potable water by reverse osmosis (RO) from the high saline Arabian Gulf sea requires several considerations. Among the number of considerations are minimized energy consumption, improved membrane performance, increased recovery and salt rejection, and improved materials of construction. The state-of-the-art for selection of appropriate corrosion-resistant alloys for a specific environment is not sufficiently advanced to make the obvious choices for a specific environment. Many metallic components in RO units still exhibit corrosion attacks in different forms. Localized corrosion in the form of pitting and crevice and mechanically induced erosion-corrosion are some of the problems behind many of the failures in RO equipment. It still remains necessary to conduct laboratory and plant testing of candidate alloys to establish those alloys that may be suitable for use. Results of laboratory tests conducted on a number of candidate construction materials for the various components and piping systems are described. The materials were exposed to an erosion-corrosion regime.

The effect of temperature on the low cycle fatigue properties of a 15Cr-15Ni, Ti modified austenitic stainless steel

A titanium modified 15Cr-15Ni-2.5 Mo austenitic stainless steel designated as Alloy D9 is currently a favored material in liquid metal cooled fast breeder reactors for fuel clad and sub-assembly wrappers and is also being considered as a primary candidate alloy for fusion reactor first wall applications. The choice of this material in the nuclear industry is primarily based on its excellent resistance to radiation induced void swelling. In nuclear reactor applications the components are often subject to temperature gradient induced thermal stresses which are cyclic in nature as a result of start-ups, shutdowns and transients. Therefore there is a need for comprehensive understanding of both the macroscopic cyclic deformation behavior and the micromechanisms which influence such behavior. Further this understanding must include not only the behavior at maximum operating temperature but also the behavior at lower temperatures encountered during transients. Till date the cyclic stress response and fatigue life of Alloy D9 over a wide temperature range has not been examined and there is no information available on the deformation-induced microstructure during fatigue loadings. The purpose of this paper is to report some recent observations pertaining to the temperature dependence of cyclic stress response and evolving deformation substructure of Alloymore » D9 between 300 and 923 K.« less

Stress corrosion cracking of alloy C-22 and Ti Gr-12 using double-cantilever-beam technique

Susceptibility to stress corrosion cracking (SCC) of two candidate alloys for the inner container of the multi-barrier nuclear waste package was evaluated by using wedge-loaded precracked double-cantilever-beam (DCB) specimens in deaerated acidic brine (pH≈2.70) at 90°C. Materials tested included Alloy C-22 and Ti Grade-12. Duplicate samples of each material were loaded at different initial stress intensity factor ( K I) values ranging between 22 and 43 MPa√m. Both metallography and the compliance methods were used to determine the final crack length. The final stress intensity for SCC ( K f) was computed from the measured final wedge load and the average crack length. The results indicate that, in general, the final crack lengths measured by metallography and compliance agreed well with one another, thus, providing very similar K f values. The alloy C-22 showed higher susceptibility to SCC than Ti Grade-12 in terms of the average crack growth. Fractographic evaluation by scanning electron microscopy (SEM) of broken DCB specimens revealed three distinct regions showing the characteristics of fatigue precrack, SCC, and fast fracture.

Selecting alloys for severely corrosive service

Selecting the most suitable, cost‐efficient alloy for a given application should not be difficult if the methodology described in this paper is followed. The first step is to identify those alloys with the desired corrosion resistance. Factors other than chemical composition have a bearing on an alloy’s corrosion resistance. Service environment and nature of the product application must also be considered. These conditions are discussed in the text. Consideration should be given to other key issues such as mechanical properties required as well as method of fabrication, design, condition and availability of the candidate alloy. To simplify selection, the author discusses severe corrodents and aggressive environments that are commonly encountered in the process industries, and describes the characteristics of alloys that might be considered for each type of corrosive service. Cross referenced charts position these alloys to show their relative resistance to each type of corrosion attack. While the paper is not designed to replace the technical expertise of a corrosion engineer, the author feels it can serve as a good starting point in the alloy selection process.

二輪車冷鍛排気バルブ用Ｆｅ基超合金の開発

Conventional exhaust engine valves of motorcycles made of heat resistant steels of SUH35 or SUH38 have been produced through hot forming, heat treatment and hard-faced weld of Stellite #6 or 12. In order to reduce valve cost, it is necessary to reduce processing cost. One of the promising processes is cold forming and direct aging without solution heat treatment after cold forming and hard-faced weld. However, cold formability of SUH35 and SUH38 are too poor to cold-form valves. To develop new alloys having superior cold-formability, high temperature strength and good wear resistant is a key to realize the process. γ' strengthened iron-based superalloy with good cold formability is a candidate alloy for cold-forming valve material. In this study, to develop a cold formable new γ' strengthened iron-based superalloy for exhaust valves of motorcycle engines, Fe-24Ni-15Cr-Cu-Al-Ti-Nb-C-B alloy system was selected. To enhance cold formability of the alloy, effect of Cu addition was examined. To satisfy high temperature strength and phase stability required for engine valves, optimization of the amount of γ' former elements (Al+Ti+Nb) and the ratio of Ti/Al was carried out in direct aged and over aged conditions after cold-forming. It was found that addition of 2mass%Cu was effective for cold-formability. Moreover, lower amount of Al+Ti+Nb and lower ratio of Ti/Al improved cold-formability. High temperature fatigue strength of the alloys satisfied target strength over 5.4mol% of Al+Ti+Nb and showed the highest at Ti/Al=0.8. Growth of γ' precipitates and η phases were least at Ti/Al=0.8 in over aged condition after cold work. Consequently, NCF2415C (Fe-24Ni-15Cr-1.5Al-2.2Ti-0.5Nb-0.03C-0.003B) showed best combination of cold-formability, high temperature strength and phase stability. NCF2415C was successfully cold-formed to exhaust valves.

98/03134 Distribution of PAH generated in domestic solid fuel boilers

The efficiency of conventional fossil power plants is a strong function of the steam temperature and pressure. Research to increase both has been pursued worldwide, since the energy crisis in the 1970s. The need to reduce CO2 emission has recently provided an additional incentive to increase efficiency. The main enabling technology in achieving the above goals has been the development of stronger high-temperature materials. Extensive R&D programs have resulted in numerous high strength alloys for heavy section piping, and tubing needed to build boilers. The study reported here is aimed at identifying, evaluating and qualifying the materials needed for the construction of the critical components of coal-fired boilers capable of operating with 760 °C (1400 °F)/35 MPa (5000 psi) steam. The economic viability of such a plant has been explored. Candidate alloys applicable to various ranges of temperature have been identified. Stress rupture tests have been completed on the base metal and on welds to a number of alloys. Steamside oxidation tests in an autoclave at 650 (1200 °F) and 800 °C (1475 °F) have been completed. Fireside corrosion tests have been conducted under conditions simulating those of waterwalls and superheater/reheater tubes. Weldability and fabricability of the alloys have been investigated. The capability of various overlay coatings and diffusion coatings have been examined. This paper provides a status report on the progress achieved to date on this project.

Development of very-high-density low-enriched-uranium fuels

Following a hiatus of several years and following its successful development and qualification of 4.8 g U cm −3 U 3Si 2–Al dispersion fuel for application with low-enriched uranium in research and test reactors, the US Reduced Enrichment for Research and Test Reactors program has embarked on the development of even-higher-density fuels. Our goal is to achieve uranium densities of 8–9 g cm −3 in aluminum-based dispersion fuels. Achieving this goal will require the use of high-density, γ-stabilized uranium alloy powders in conjunction with the most-advanced fuel fabrication techniques. Key issues being addressed are the reaction of the fuel alloys with aluminum and the irradiation behavior of the fuel alloys and any reaction products. Test irradiations of candidate fuels in very-small (micro) plates are scheduled to begin in the Advanced Test Reactor during June, 1997. Initial results are expected to be available in early 1998. We are performing out-of-reactor studies on the phase structure of the candidate alloys on diffusion of the matrix material into the aluminum. In addition, we are modifying our current dispersion fuel irradiation behavior model to accommodate the new fuels. Several international partners are participating in various phases of this work.

Appearance of a hypercooled liquid region for completely miscible alloys

Systematic calorimetric measurements on the thermodynamic properties of several completely miscible binary alloys (Co-Pd, Co-Pt, Ni-Pd, Fe-Pd, Au-Cu, Au-Ni) were performed in order to investigate the hypercooling abilities. Differential thermal analysis was used to determine the enthalpy of fusion of the materials and the specific heat capacity of the undercooled liquid state in dependence on temperature and concentration. From the results candidate alloys are identified for experiments on hypercooled liquids. Further on the effect of liquid undercooling on the respective microstructure evolution was investigated. The revealed microstructures of samples solidified from the hypercooled liquid were found quite different from those obtained at low undercooling.

Volatilization from PCA Steel Alloy

The mobilizations of key components from Primary Candidate Alloy (PCA) steel alloy have been measured with laboratory-scale experiments. The experiments indicate most of the mobilization from PCA steel is due to oxide formation and spalling but that the spalled particles are large enough to settle rapidly. Based on the experiments, models for the volatization of iron, manganese, and cobalt from PCA steel in steam and molybdenum from PCA steel in air have been derived.

Development and testing of vanadium alloys for fusion applications

Vanadium-base alloys are promising candidate materials for application in fusion reactor first-wall and blanket structure because of several important advantages, i.e., inherently low irradiation-induced activity, good mechanical properties, good compatibility with lithium, high thermal conductivity, and good resistance to irradiation-induced swelling and damage. To screen candidate alloys and develop an optimized vanadium-base alloy, extensive investigations of physical and mechanical properties of various VTi, VCrTi, and VTiSi alloys have been conducted before and after irradiation in lithium environment in fast fission reactors. From these investigations, a V4Cr4Ti alloy containing 500–1000 wppm Si and < 1000 wppm O + N + C has been identified as the most promising alloy, and more comprehensive testing on the performance of this alloy is being conducted for fusion-relevant conditions. Major results of the comprehensive work to develop the optimal alloy and test the irradiation performance are presented in this paper. The reference alloy V4Cr4Ti exhibited the most attractive combination of the mechanical and physical properties that are prerequisite for first-wall and blanket structures, i.e., good thermal creep behavior, good tensile strength and ductility, high impact energy, excellent resistance to swelling, and very low ductile-brittle transition temperature before and after irradiation. The alloy was highly resistant to irradiation-induced embrittlement in Li at 420–600°C, and the effects of dynamically charged helium on swelling and mechanical properties were insignificant. However, several important issues remain unresolved, e.g., welding, low-temperature irradiation properties, helium effect at high dose and high helium concentration, irradiation creep, and irradiation performance in air or helium environment. Initial results of investigation of some of these issues are also given.

Effects of Grain Morphology and Texture on High Temperature Deformation in Oxide Dispersion Strengthened Ferritic Steels

Oxide Dispersion Strengthened (ODs) ferritic steel is the promising candidate alloy for long-life core materials of fast reactor. A series of experiments, such as tensile tests, creep rupture tests, texture measurements and microstructure observations, are performed for the fabricated sheets of ODs ferritic steel with simulating type of morphology and also for the cladding tube in order to clarify the origin of the peculiar strength anisotropy of the cladding tube: degraded creep rupture strength in hoop direction. From these experiments, effects of grain morphology and texture on deformation of ODs ferritic steels are evaluated. The sheets and the cladding tube have strong texture of {001}⟨110⟩ and {111}⟨110⟩, respectively. In longitudinal and transverse directions of the sheets, strength level is significantly different from each other, but crystallographic orientation is almost equivalent. From that finding, it is considered that strength anisotropy of the cladding tubes is not attributed to the textur...

96/06770 Radioisotope X-ray fluorescence analysis of some elements in fly ash of Afsin-Elbistan power plants

The efficiency of conventional fossil power plants is a strong function of the steam temperature and pressure. Research to increase both has been pursued worldwide, since the energy crisis in the 1970s. The need to reduce CO2 emission has recently provided an additional incentive to increase efficiency. The main enabling technology in achieving the above goals has been the development of stronger high-temperature materials. Extensive R&D programs have resulted in numerous high strength alloys for heavy section piping, and tubing needed to build boilers. The study reported here is aimed at identifying, evaluating and qualifying the materials needed for the construction of the critical components of coal-fired boilers capable of operating with 760 °C (1400 °F)/35 MPa (5000 psi) steam. The economic viability of such a plant has been explored. Candidate alloys applicable to various ranges of temperature have been identified. Stress rupture tests have been completed on the base metal and on welds to a number of alloys. Steamside oxidation tests in an autoclave at 650 (1200 °F) and 800 °C (1475 °F) have been completed. Fireside corrosion tests have been conducted under conditions simulating those of waterwalls and superheater/reheater tubes. Weldability and fabricability of the alloys have been investigated. The capability of various overlay coatings and diffusion coatings have been examined. This paper provides a status report on the progress achieved to date on this project.

Effect of current pulse discharge on specific resistivity of copper and iron compacts: K. Matsugi et al. (Hiroshima University, Hiroshima, Japan). J. Japan Inst. Metals, vol 59, no 7, 1995, 740–745. (In Japanese.)

New theory is presented to describe the occurrence of plasticity-induced transitions in titanium alloys. The approach is able to predict the composition dependence of transformation induced plasticity (TRIP), superelasticity, as well as martensite formation upon quenching. Martensite formation in the absence of stress is considered as the result of a competition between elastic strain energy and chemical driving force. Assuming that the formation of martensite is the result of a thermally activated nucleation process followed by athermal growth, a nucleation parameter is postulated to describe the conditions under which martensite is formed upon quenching; the parameter accounts for the ratio between the available thermal energy and an energy barrier for nucleation, suggesting that ω phase is not the main factor controlling martensite inhibition. This nucleation parameter is able to describe, for the first time, martensite occurrence in 130 alloys from the literature, quantifying the martensite start temperature (Ms) reported for 49 alloys with great precision. An empirical parameter ([Fe]eq) is proposed and, when combined with the Ms prediction, it allows to define regions within which TRIP and superelasticity occur. By defining threshold values for the Ms, the [Fe]eq and the nucleation parameter, candidate alloys likely to display TRIP, superelasticity or martensitic transformation upon quenching can be identified. As a result, this method can be adopted to design alloys with tailored plasticity behaviour.

Modelling of fracture process in annealed sheet of AISI 202 stainless steel

The similarities and differences in the cracking susceptibility between welding and resolidification after plasma disruption were examined experimentally using a number of primary candidate alloy samples with different chemical compositions. The product of the number density and the average depth of the cracks was measured after simulated disruption, employing a hydrogen ion beam as the heat source, and was compared with the Varestraint test result. An adequate correlation was observed between them, which indicates that the cracking susceptibility during plasma disruption can be well estimated from the welding cracking susceptibility.

A New Zr-Based Alloy for Tritium Recovery from Tritiated Water

The dissociation of tritiated water and the recovery of tritium is an important issue for the future thermonuclear fusion device. Various solutions have been proposed including chemical dissociation on active beds. The results of H{sub 2}O sorption tests performed on different possible candidate alloys, by means of vacuum microbalance technique at a pressure of some hundreds Pa and at temperatures ranging from 300 to 400{degree}C, are presented. From these tests a ternary Zr-Mn-Fe alloy appears to have promising features, combining good dissociation characteristics for H{sub 2}O with low hydrogen pick up. The basic properties of this material are discussed, including structural aspects and sorption characteristics vs. other gases. 14 refs., 11 figs., 1 tab.