Minor Alloy Research Articles

Topologically Ordered Corrosion Maps of Nickel Alloys

This study was developed to provide an optimum methodology for designing metal alloys. Information on general and localized (pitting and crevices) corrosion of the most commonly used Nickel alloys were obtained from NIST. A 2-dimentional Kohonen map was designed and trained with the available data. We constructed a 3D figure (2D Kohonen map and a third dimension containing the corrosion rates of each cell in the Kohonen map) for all alloy-environment couples in the data. Once the Kohonen map was trained, we "designed" new Nickel-alloys by choosing two of the alloys (C22 and Incoloy 825 (UNS: N008825, alloy 825)) on the Nickel NIST list (composition, environment and corrosion rates), and by systematically modifying the alloy compositions by adding minor alloy elements (one at a time). For the newly created alloy, we chose the same environment as that of the original alloys (C22 or Incoloy 825). We located-in the Kohonen map-- the cells in which the original alloys (C22 and Incoloy 825) were stored; then, we located in which cells the "new alloys" are clustered. The alloys may migrate towards higher or lower corrosion rate cells. Accordingly, the beneficial or detrimental impact of adding those minor alloy elements in the alloys of origin (C22 or Incoloy 825) can be explored. Thereby, the "evolutionary road" of corrosion properties of metal alloys can be traced in the 3D figure and "If-then" scenarios for the new alloys - can be explored.

Wear Evaluation of High Interstitial Stainless Steels

A new series of high nitrogen-carbon manganese stainless steel alloys are studied for their wear resistance. High nitrogen and carbon concentrations were obtained by melting elemental iron-chromium-manganese (several with minor alloy additions of nickel, silicon, and molybdenum) in a nitrogen atmosphere and adding elemental graphite. The improvement in material properties (hardness and strength) with increasing nitrogen and carbon interstitial concentration was consistent with previously reported improvements in similar material properties alloyed with nitrogen only. Wear tests included: scratch, pin-on-disk, sand-rubber-wheel, impeller, and jet erosion. Additions of interstitial nitrogen and carbon as well as interstitial nitrogen and carbide precipitates were found to greatly improve material properties. In general, with increasing nitrogen and carbon concentrations, strength, hardness, and wear resistance increased.

Mechanical and hardness evaluations of Fe–18Cr–18Mn alloys

A series of Fe–18Cr–18Mn–N–C alloys was produced and evaluated to determine their mechanical and hardness properties. In one group, different levels of nitrogen and carbon were added to a base composition of Fe–18Cr–18Mn. The base Fe–18Cr–18Mn alloy had a fcc–bcc duplex microstructure. The addition of nitrogen and carbon stabilised the fcc phase. These alloys had increasing room temperature hardness, strength, and failure energy with increasing interstitial concentrations. At cryogenic and elevated temperatures, these alloys had increasing hardness (and by implication, increased strength) with increasing interstitial concentrations. In a second group, different levels of nitrogen and carbon were added to the base Fe–18Cr–18Mn composition to which minor solid solution additions of silicon, molybdenum, and nickel had been added. Minor alloy additions made only nominal improvement to mechanical and hardness properties. Nitrogen remained interstitial. However, these minor solid solution additions reduced carbon solubility resulting in the formation of M23C6 precipitates that, while increasing alloy hardness and strength, greatly reduced fracture toughness. The present study suggests that replacing nickel with manganese in stainless steels results not only in more economical alloys but also in alloys with higher strength and hardness.

Effects of minor alloy additions and oxidation temperature on protective alumina scale formation in creep-resistant austenitic stainless steels

Niobium was found to be beneficial for alumina scale formation in newly developed creep-resistant austenitic stainless steels. Additions of both Ti and V degraded alumina scale formation, whereas alloys with individual additions of Ti or V were able to form protective alumina scales. The ability to form external alumina scales was lost in the lower Al- and Nb-containing alloys between 800 and 900 °C. Compositions with the potential to form alumina at 900 °C were identified.

Effects of tungsten on environmental systems

Tungsten is a metal with many industrial and military applications, including manufacturing of commercial and military ammunition. Despite its widespread use, the potential environmental effects of tungsten are essentially unknown. This study addresses environmental effects of particulate and soluble forms of tungsten, and to a minor extent certain tungsten alloy components, present in some munitions formulations. Dissolution of tungsten powder significantly acidifies soils. Tungsten powder mixed with soils at rates higher than 1% on a mass basis, trigger changes in soil microbial communities resulting in the death of a substantial portion of the bacterial component and an increase of the fungal biomass. It also induces the death of red worms and plants. These effects appear to be related with the soil acidification occurring during tungsten dissolution. Dissolved tungsten species significantly decrease microbial yields by as much as 38% for a tungsten media concentration of 89 mg l −1. Soluble tungsten concentrations as low as 10 −5 mg l −1, cause a decrease in biomass production by 8% which is possibly related to production of stress proteins. Plants and worms take up tungsten ions from soil in significant amounts while an enrichment of tungsten in the plant rhizosphere is observed. These results provide an indication that tungsten compounds may be introduced into the food chain and suggest the possibility of development of phytoremediation-based technologies for the cleanup of tungsten contaminated sites.

Sintered Nd–Fe–B magnets with high strength

The effect of boron variation in the minor addition of grain-boundary alloys on the mechanical properties and microstructure of sintered Nd–Fe–B magnets has been studied. It shows that the bending strength of most magnets with minor grain-boundary alloy additions is much higher than that of the magnet prepared by the single alloy. The maximum of the former reached 397 MPa, which was higher than the bending strength of cast/hot-rolled magnets. The latter was only 309 MPa. Minor additions of the grain-boundary alloys made the distribution of grain-boundary phase more uniform so that the phenomena of the direct contacts between main-phase grains nearly disappeared. The irregular grain growth was restrained. This is also one of the reasons that the magnets with minor grain-boundary alloy additions have possessed higher bending strength. In addition, the phase analyses indicated that the reduction of crystal structure anisotropy probably helps to increase bending strength. The study results also show that minor additions of the grain-boundary alloys do not almost affect the magnetic properties of sintered Nd–Fe–B magnets. It suggests that slightly adding grain-boundary alloys and properly adjusting its composition can substantially increase the bending strength of sintered Nd–Fe–B magnets without a sacrifice of magnetic properties.

Processing and properties of high aluminium Fe-Al-C alloys

A method was investigated to minimise or totally prevent the formation of the undesirable Al4C3 phase in high-aluminium cast iron composites (>19% Al). When aluminium carbide is absent in these castings, both mechanical strength and corrosion resistance are significantly improved. Accordingly, Ti additions were introduced to high-aluminium cast iron to develop Fe-Al-Ti-C alloys, which resemble “in-situ” composites where the inter-metallic FeAl phase is the matrix, and TiC acts as the reinforcement. It was found that the minimal amount of Ti that needs to be added has to be equal or above 4.5 wt% in order to totally remove the Al4C3 phase. It was found that Fe-Al-Ti-C alloys exhibit relatively high oxidation resistance, which easily exceeds that of high-chromium cast iron and cast chromium steels. Finally, in order to improve alloy ductility, minor alloy additions of elements such as B and Cr were added to the melt. It was found that additions of 0.03% B and 0.03%B-5% Cr combined with heat treatment lead to significant improvements in the ductility of the alloy with elongations of up to 15%.

Progress in vanadium alloy development for fusion applications

Vanadium alloys have been identified as a leading candidate low-activation structural material for fusion first-wall blanket applications. Candidate vanadium alloys exhibit favorable safety and environmental characteristics, good fabricability, high temperature and heat load capability, good compatibility with liquid metals and resistance to irradiation damage. The focus of the vanadium alloy development program has been on the vanadium-chromium-titanium (0–15%Cr, 1–20%Ti) alloy system. Investigations include effects of minor alloy elements such as Si, Al and Y and substitution of iron for chromium in the ternary alloy. A V-4Cr-4Ti alloy is currently regarded as the reference alloy. Significant progress has been made in the development of vanadium alloys for fusion applications. Two production-scale heats (500 and 1200 kg) of the V-4Cr-4Ti alloys have been produced with controlled levels of impurities. The baseline properties of the 500 kg heat are similar to those of the previous laboratory-scale heats. Additional data have been obtained on baseline tensile and fracture properties. Results obtained on several heats with minor variations in composition indicate high uniform and total elongation of these alloys at temperature from RT to 700°C. Results obtained to date indicate that the V-Cr-Ti alloys are resistant to swelling and embrittlement after exposure to relatively high neutron fluences at temperatures of 400–600°C. The properties are not significantly different when modest amounts of helium are generated during neutron irradiation by the dynamic helium charging experiment method. However, recent results have indicated that these alloys are susceptible to irradiation embrittlement at lower temperatures. Additional irradiation experiments are in progress to investigate these effects at temperatures of 200–400°C. This paper presents an update on the experimental results on candidate low activation vanadium alloys.

Cleaning of copper traces on circuit boards with excimer laser radiation

Cleaning of Cu traces on circuit boards is studied using pulsed excimer laser radiation (pulse width ∼ 20 ns, wavelength 248 nm), with the goal of improving the properties of the Cu surface for soldering and bonding. Traces with well-defined oxide overlayers are cleaned by irradiation in air using ≤ 103 laser pulses at fluences per pulse of ≤ 2 J cm−2. After treatment the surface morphology is analyzed using optical microscopy, optical profilometry, and scanning electron microscopy, while the chemical state of the surface is investigated with X-ray photoelectron (XPS) spectroscopy. Ellipsometry is used to determine the oxide overlayer thickness. Prior to cleaning samples exhibit a contamination overlayer about 15–25 nm in thickness containing Cu2O and C. Cleaning reduces the overlayer thickness to ≤ 10 nm by material removal. The process tends to be self-limiting, since the optical reflectivity of the oxidized Cu surface for laser radiation is smaller than that of the cleaned surface. Additionally, the interaction with the laser radiation results in surface segregation of a minor alloy component out of the bulk (e.g. Zn), which may help to passivate the surface for further chemical reactions.

Void swelling resistance of phosphorus-modified austenitic stainless steels during HFIR irradiation at 300–500°C to 57 dpa

The austenitic stainless steel prime candidate alloy (PCA) is a Ti-modified alloy (14Cr16Ni) developed for void swelling resistance at 400–600°C by the US Fusion Reactor Materials (FMR) program. During irradiation in the High Flux Isotope Reactor (HFIR) to 34 and 57 dpa (70–75 appm He/dpa) at 300–600°C, th e PCA (and the closely related D9 type alloy) has been shown to be highly susceptible to void swelling at 500°C. Generally such alloys show good void swelling resistance to higher doses during irradiation in fast-breeder reactors (FBRs, 0.5–1 appm He/dpa) in the 20–25% cold-worked (CW) condition. New multiply-stabilized, phosphorus-modified PCA alloys have been developed, with specific amounts and combinations of minor alloy elements added for improved MC formation and stability characteristics during irradiation. After HFIR irradiation at 300–500°C to 34–57 dpa, the multiply-stabilized, phosphorus-modified PCA and phosphorus-modified D9 alloy showed better swelling resistance (by density-change measurements) than similar alloys without phosphorus, particularly at 500°C. Microstructural studies after 34 dpa at 500°C showed that void swelling resistance in the multiply-stabilized, phosphorus-modified PCA alloys was directly related to the formation of ultrafine dispersions of MC precipitates during HFIR irradiation.

The development of Fe-Al intermetallics

The intermetallics based on aluminides have long been known for their excellent resistance to high-temperature oxidation. However, for use in structural components the poor ductility at ambient temperatures has always been felt as a stumbling block. Interest in these materials has been revived recently, after achieving some success in improving the ductility at ambient temperatures and creep at elevated temperatures in titanium aluminides. For the iron aluminides, too, similar methodologies have been attempted, namely alloying with elements such as titanium, boron, molybdenum, chromium, silicon and manganese, as well as grain refinement for improving high-temperature creep and room-temperature ductility. Raising the creep resistance close to 600 °C and improving the ambient-temperature ductility to around 6% have been the major immediate aims. Attempts are also being made to improve the high-temperature fatigue and creep properties in these materials, particularly by pushing the stability temperature of ordered D03 upwards. It is now visualized that once the above properties are achieved, the iron aluminides, particularly the types based on Fe3Al, could offer themselves as excellent candidate materials For structural purposes. Their attractiveness also stems to a large extent from their low cost, as they contain only abundantly occurring materials. The present work examines two routes for introducing ductility in the Fe3Al-based materials: one by ternary-Quarternary additions and the other by grain refinement. Structural studies have been made on materials obtained through conventional casting as well as through rapid solidification with minor alloy additions. The results confirm that Fe3Al-based alloys, even when air-melted, are amenable to a high degree of hot working and could be made to display improved ductility at room temperature by a careful control of the chemistry. Rapidly solidified ribbons also show reasonably good bonding during high-temperature compaction. Ordering in these alloys is not suppressed even by rapid solidification.

Microstructure and Elevated Temperature Flow Properties of Rapidly Solidified TiAl-Base Alloys

ABSTRACTRapid solidification processing (RSP) of TiAl-base alloys often results in the formation of metastable crystalline products (e.g., Ti3Al) A key parameter controlling both the solidification pathway and the stability of the metastable structure is alloy chemistry. This study focuses upon the influence of minor alloy additions on the microstructure and properties of Ti52Al48 alloys produced by RSP. While alloys having minor Ta addi ions (<1 at.%) maintain near-equilibrium solidification structures similar to the binary alloy, the addition of Cr at a level of 5 at.% results in a nearly 100 vol.% metastable Ti3Al structure containing a fine dispersion of TiCr2 grain boundary precipitates. These precipitates limit grain growth during elevated temperature exposure, maintaining the fine (TiAl) grain size created during decomposition of the metastable product structure. Mechanical property evaluation of the consolidated RSP material indicates a greatly reduced flow stress for the fine grained Cr modified alloys. A preliminary analysis attributes this to the reduction in grain size and enhanced elevated temperature diffusion rates for the Cr containing TiAl-base alloys.

A new series of advanced 3Cr-Mo-Ni steels for thick section pressure vessels in high temperature and pressure hydrogen service

A new series of 3Cr-Mo-Ni steels has been developed for use in thick section pressure vessels, specifically for coal conversion (high temperature and high pressure hydrogen) service. The new steels rely on minor alloy modifications to commercial 2.25Cr-1Mo (ASTM A387 Grade 22 Class 2) steel. Based on evaluations in relatively small heats (55 kg), the experimental alloys, which employ additions of Cr, Ni, Mo, and V, with Mn at 0.5 wt pct and C at 0.15 wt pct, display improved properties compared to commercial steels. Specifically, they show significantly improved hardenability (i.e., fully bainitic microstructures following normalizing of 400-mm (16-in.) plates), enhanced strength (i.e., yield strengths exceeding 600 MPa), far superior hydrogen attack resistance and better Charpy V-notch impact toughness, with comparable tensile ductility, creep rupture resistance and temper embrittlement resistance. The microstructural features contributing to these improved mechanical properties are briefly discussed.

Experimental Work on Alloy Development for High-Temperature Gas-Cooled Reactor Systems

In the context of developing high-temperature wrought alloys especially designed for advanced high-temperature gas-cooled reactor systems at temperatures up to 1000°C, a program of investigations has been performed during the past few years. The progress of the work can be traced through several stages: the addition of single minor alloying elements to model Fe-Cr-Ni alloysthe study of multiple minor alloy additions in commercial alloysthe additions of preferred minor alloy combinations to modified commercial alloysthe variation of chromium in experimental nickel-base alloys containing titanium and aluminumthe variation of iron, molybdenum, tungsten, and cobalt in nickel-base alloys containing low chromium, titanium, and aluminum. The first three stages were directed toward the study and improvement of the corrosion resistance of existing alloys, but in the last two stages, radical changes in composition have been investigated. The work so far has culminated in a family of alloys that have excellent microstructural stability and corrosion resistance combined with strengths comparable with those of traditional alloys.

Hydrogen attack in a low [formula omitted] steel

Two 2 1 4 Cr-1Mo steels, one with the addition of vanadium and titanium, were exposed to high pressure hydrogen at 600°C. A comparison of the observed cavity number densities in these two steels suggests that minor alloy conditions can improve the resistance to hydrogen attack in 2 1 4 Cr-1Mo steels.

ChemInform Abstract: Oxidation of Dilute Iron‐Silicon Alloys ([Si] ⩽ 1 w/o) in Carbon Dioxide.

AbstractWie Untersuchungen des Einflusses geringer Si‐Gehalte auf das Oxidationsverhalten von Fe in COz/V/n CO bei 500°C zeigen, setzen steigende Si‐Gehalte im Bereich [Si] = 0‐1 Gew.‐"z die Oxidationsgeschwindigkeit immer weiter herab.

The oxidation of dilute iron-silicon alloys ( [formula omitted]) in carbon dioxide

The manner in which silicon, present as a minor alloy constituent, modifies the oxidation of iron in CO 2/1 %CO at 500°C has been studied. Increasing amounts of silicon progressively reduce the oxidation rate within the range [ Si] = 0–1 w o and a variety of physical techniques have been used to examine oxidized specimens in pursuit of the origins of this beneficial influence. The scale forming on the alloys is composed of two layers in each of which iron is present as Fe 3O 4. The inner layer of scale contains silicon at approximately the same level (on a vol. % basis) as the original metal while the outer scale appears to contain no silicon. The boundary between the two layers is also marked by an abrupt change in grain size and in texture of the Fe 3O 4. At the boundary between the alloy and the scale there develops a thin layer of non-ferrous material in which the concentration of silicon is increased by more than an order of magnitude above that in the bulk alloy. This layer also includes a substantial accumulation of carbon which is thought to derive from carbon oxide gases which have penetrated to the base of the scale before taking part in the oxidation reaction. The observation of the layer of non-ferrous material between the alloy and the scale constitutes a qualitative agreement with theoretical studies which indicate that the reduction in oxidation rate conferred by the presence of silicon in the alloy is at least partly due to the impeded passage of Fe 3+ ions from the alloy into the scale.

Concerning the question of recovery before recrystallization

In a recent investigation, Haessner and Hoschek have given some very interesting results on minor alloy additions and the stored energy for rolled copper crystals. They interpreted their results as showing, for example, that 200 ppM Ag reduced the stored energy by 70 percent. The purpose of this paper is to point out an alternate interpretation of their results; an interpretation that appears more probable and which supports certain of our earlier conclusions.

Ni-Cr-W-C系合金の不純Heガス中における高温腐食挙動

Influence of the minor alloy constituents such as Al, Mn and Si on the hot corrosion behavior of Ni-20Cr-20W-0.07C alloy was studied in 99.995% helium gas at 1 000°C, comparing with that behavior of commercial Ni-base superalloys (Hastelloy X and Inconel 617).The low oxidizing potential in the impure helium gas usually causes selective oxidation of these elements and the growth of oxide whiskers on the surface of specimen at elevated temperature.The intergranular attack was caused by selective oxidation of Al, Si and Mn. The spalling of oxide film was restrained by addition of Mn and Si, providing tough spinel type oxide film on the surface and ‘Keyes’ on the oxide-matrix interface respectively.The amount and the morphology of the oxide whiskers depended on Si and Mn content. More than 0.29% of Si content without Mn always caused the growth of rather thinner whiskers with smooth surface, and the whiskers analyzed by electron diffraction patterns and EPMA to be Cr2O3 containing Si. Mn addition changed the whiskers to thicker ones of spinel type oxide (MnCr2O1) with rough surface.On the basis of these results, the optimum content of Al, Mn and Si to minimize the growth of whiskers, the intergranular attack and the spalling of oxide film was discussed.

Effect of Minor Alloy Variations on the Thermal Densification of Austenitic Stainless Steels

Increasing the carbon content of AISI Type-316 stainless steel can produce density changes >0.1% after aging at 1500 deg F for 100 h. Large additions of phosphorus (0.04 wt%), boron (0.006 wt%), and nitrogen (0.13 wt%) produce no significant density change upon aging. It was concluded that the thermal densification phenomenon observed in austenitic stainless steels is due to the formation of carbides and is linear with the carbon content of the alloy. (auth)