Major Alloying Elements Research Articles

Material Characterization of Follower Assembly of G5 155mm Gun Howitzer Breach Mechanism Block

Medium alloy steel is widely used as a material for guns and rocket launchers due to its high strength and excellent machinability characteristics. The purpose of this study is to determine the material properties of the follower assembly used in a breech block gun launcher which is significantly important f or t he future product improvement. The microstructure and the effect of alloying elements in the follower assembly is evaluated in this study. The SPECTRO Optical Emission Spectroscopy (ES) method is used to analyse the chemical composition of the material and the Field Emission Scanning Electron Microscope coupled with Energy Dispersive X-Ray (FESEM-EDX) were used to analyse the inclusions of the sample. Results of the ES chemical composition analysis found that Nickel (Ni) is the major alloying elements beside Molybdenum (Mo), Chromium (Cr), Manganese (Mn), Silicon (Si), Sulphur (S), and Carbon (C) while chemical mapping and line scanning analysis of FESEM-EDX on inclusions distributed in the material microstructure identified as a compound of Manganese Sulphur(MnS). Fine dendritic microstructure arrangement and distribution in the microstructure analysis showed that the sample had been quenching in the heat treatment process, which also played a significant role in the material characterization. From the analysis, it is found that the material can be defined as medium alloy steel that is also typical for high strength material for ballistic application.

Acceleration of 475 °C embrittlement in weld metal of 22 mass% Cr-duplex stainless steel

The present study has demonstrated the differences in the 475 °C embrittlement behavior of the base and weld metals of a 22 mass% Cr-duplex stainless steel. A grade 2205 solution-annealed plate was used as the base metal. The corresponding Ni-rich weld metal, which comprised multiple layers, was fabricated using a grade 2209 filler wire. The base and weld metals were subjected to isothermal aging for various durations (up to 1000 h) at 400 °C. Microstructural characterization, Charpy impact toughness testing, and Vickers microhardness measurements were conducted before and after aging. Furthermore, the microstructure of the ferrite phase, after aging, was evaluated using transmission electron microscopy (TEM). There was a substantial decrease in the impact toughness in both the base and weld metals with increasing aging time, although the decrease in the impact toughness was more pronounced for the weld metal. The hardening of ferrite was more prominent in each layer of the weld metal than in the base metal. The TEM observations indicated that the ferrite phase in both the base and weld metals underwent spinodal decomposition, which was accelerated in the weld metal. Regarding the major alloying elements (i.e., Cr, Mo and Ni) contained in the ferrite phase, the content of each, Cr and Mo, was lower in each layer of the weld metal than in the base meal, while the Ni content was, conversely, higher in each layer of the weld metal than in the base metal. The higher Ni content promoted the decomposition of ferrite in each layer of the weld metal during aging. This resulted in an acceleration of the 475 °C embrittlement in the multilayered weld metal of the 22 mass% Cr duplex stainless steel compared to the base metal.

Spectral Emission Signatures from Cased High-Explosive Charges.

Spectroscopic signatures of cased high-explosive charge denotations are examined using emission spectroscopy with sub nanometer resolution. Eleven distinct case materials are investigated for atomic features of their major alloying elements. Molecular features of case material combustion products are also investigated for five case materials. Emission is monitored within the 275-425 nm range for atomic features and in the 310-755 nm range for molecular features. Major alloying elements with concentrations greater than 5% are generally detected through atomic emission. Al, Cu, Fe, Mg, Cr, Mn, Pb, and Ni are all detected in concentrations less than 5%. Undetected elements include Zn, Nb, Ta, and V. Molecular emission from aluminum monoxide, titanium monoxide, and CN is measured for aluminum alloy, titanium alloy, and carbon fiber cases, respectively.

High-Temperature Oxidation Resistance of Alumina-Forming Austenitic Stainless Steels Optimized by Refractory Metal Alloying

Alumina-forming austenitic stainless steels are known for their superior high-temperature oxidation resistance. Following our previous work that solved the matching of major alloying elements in their specific 16-atom cluster formula, we here focus on the 800 °C air-oxidation resistance of 0.08 wt. % C alloy series satisfying cluster formula [(Al0.89Si0.05NbxTa0.06−x)-(Fe11.7−yNiyMn0.3)]Cr3.0−z(Mo,W)z, x = 0.03 or 0.06, y = 3.0 or 3.2, z = 0.07 or 0.2, to explore the effect of minor alloying elements Mo, Nb, Ta and W. This cluster formula is established particularly based on alloys which were originally developed by Oak Ridge National Laboratory. All samples are graded as complete oxidation resistance level according to Chinese standard HB 5258-2000, as their oxidation rate and oxidation-peeling mass are generally below 0.1 g/m2 × h and 1.0 g/m2, respectively. In alloys without Ta and W, a Cr2O3-type oxide layer is formed on the surface and Al2O3 particles of sizes up to 4 μm are distributed beneath it. In contrast, in Ta/W-containing alloys, a continuous protective Al2O3 layer is formed beneath the outer Cr2O3 layer, which prevents internal oxidation and provides the lowest weight gain. Instead of internal Al2O3 particles, AlN is formed in Ta/W-containing alloys. The W-containing alloy possesses the thinnest internal nitride zone, indicating the good inhibition effect of W on nitrogen diffusion.

Roles of the semisolid heating on the microstructure of a hypereutectic Al\u2013Fe\u2013Cu alloy

A hypereutectic Al–Fe–Cu alloy with a high-volume fraction ferro-aluminum second phase (AlFe phases for short) was reheated in the solid–liquid region and the microstructure evolution was investigated. During semisolid heating, the high-melting AlFe phases in the Al–Fe–Cu alloy were demonstrated to stunt the grain growth and to block the liquid coalescing and the solid moving. Consequently, the grain sizes in the alloy increased rapidly and then slowly with increasing holding time, and the grains increased gradually with increasing temperature. Smaller grain grew into the large grain but it did not continually grow into the larger grain with increasing temperature or holding time. The shape factor (SF) of the alloy increased gradually and then decreased quickly with increasing temperature or holding time. The major alloying elements in addition to magnesium in the hypereutectic Al–Fe–Cu alloy were finally enriched at the grain boundaries or around the AlFe phases. Besides dissolving in the grains or AlFe phases, copper also diffused between the grains or around AlFe phases, resulting in the formation of diverse Cu-enriched zones. Cu constituents in the inter-grains are outnumbered in the intra-grains. The coarsening kinetics of the alloy was controlled by grain boundary diffusion. The coarsening rate constants K in the initial stage of heating (5–20 min) were several times larger than that in the later stage of heating (20–60 min), indicating the blocking effect of AlFe phases on coarsened grain being obvious.

Effect of solution treatment on micropore and mechanical properties of DD6 superalloy

Effect of solution treatment on the micropore and mechanical properties is investigated for the DD6 superalloy. The results show that solution treatment has positive and negative effects on the DD6 superalloy, which can weaken the segregation significantly. After solution treatment, the segregation ratio of the major alloying elements tends to 1. However, the amount of micropores increases with increasing solutionising time and can reach 0.46%, which is one order of magnitude higher than that of the as-cast superalloy. The hardness increases slightly, especially for the superalloy solutionised at 1310°C with a 5% increase in hardness compared to the as-cast superalloy. Hardness, tensile and stress rupture properties of the DD6 superalloy can reach the best after solution treatment at 1310°C and 4 h.

Recent developments and applications on high-performance cast magnesium rare-earth alloys

Abstract During the past decades, with the increasing demands in lightweight structural materials, Mg alloys with low density and high performance have been extensively investigated and partly applied in some industries. Especially when rare earth (RE) elements are added as major alloying elements to Mg alloys, the alloy strength and creep resistance are greatly improved, which have promoted several series of Mg-RE alloys. This paper reviews the progress and developments of high-performance Mg-RE alloys in recent years with emphasis on cast alloys. The main contents include the alloy design, melt purification, grain refinement, castability, novel liquid casting and semisolid forming approaches, and the industrial applications or trials made of Mg-RE alloys. The review will provide insights for future developments of new alloys, techniques and applications of Mg alloys.

Investigation on corrosion behaviour of aluminium 6061-T6 alloy in acidic, alkaline and salt medium

Aluminium 6061 is a precipitation-hardened aluminium alloy, containing magnesium and silicon as its major alloying elements. T6 temper 6061 has an ultimate tensile strength of at least 290 MPa (42,000 psi) and yield strength of at least 240 MPa (35,000 psi). More typical values are 310 MPa (45 ksi) and 270 MPa (39 ksi), respectively. Corrosion acts on a continuous basis and it is a tedious issue to normalize it or to eradicate it. Hardened aluminium alloy containing Magnesium and Silicon as its major alloying elements. This research work deals with investigating the corrosion behaviour of this Aluminium 6061-T6 reaction in the acidic alkaline and in the salt medium. By analyzing the comparative results it will clarify that the Aluminium 6061 T6 alloy has higher corrosion rate in alkaline solution than in the acidic solution. The corrosion resistance of aluminium alloy is higher in solutions of acids and salts containing sulfate and nitrate ions than in chloride ions.

Relationship between amounts of low-melting-point eutectics and hot tearing susceptibility of ternary Al−Cu−Mg alloys during solidification

Abstract A systematical study on the relationship between the amounts of different eutectic phases especially the low-melting-point (LMP) eutectics and the hot tearing susceptibility of ternary Al−Cu−Mg alloys during solidification was performed. By controlling the concentrations of major alloying elements (Cu, Mg), the amounts of LMP eutectics at the final stages of solidification were varied and the corresponding hot tearing susceptibility (HTS) was determined. The results showed that the Al−4.6Cu−0.4Mg (wt.%) alloy, which contained the smallest fraction of LMP eutectics among the investigated alloys, was observed to be the most susceptible to hot tearing. With the amount of total residual liquid being approximately the same in the alloys, the hot tearing resistance is considered to be closely related to the amounts of LMP eutectics. Specifically, the higher the amount of LMP eutectics was, the lower the HTS of the alloy was. Further, the potential mechanism of low HTS for alloys with high amounts of LMP eutectics among ternary Al−Cu−Mg alloys was discussed in terms of feeding ability and permeability as well as total viscosity evolution during solidification.

Influence of aging heat treatment on microstructure and tensile properties of laser oscillating welded TB8 titanium alloy joints

Investigations were conducted on TB8 titanium alloy to assess the influence of aging heat treatment on microstructure and phase transformations induced by laser oscillating welding, and establish a correlation between tensile properties and microstructure. Low-temperature aging joint consists of ω phase and β phase, while high-temperature aging joint is comprised of α phase and β phase. The formation of poor and rich precipitation zone in weld area was due to segregation of major alloying elements like Al, Mo and Nb. Low-temperature aging deteriorates plasticity of joints, but high-temperature aging improved ambient-/elevated-temperature tensile properties. The effect of aging temperature and aging time were discussed in depth. After aging treatment at 450° Celsius for 1 h, intermediate ω phase in gathering place transformed to α phase, but dispersed ω phase still retained. With the increase of aging temperature and aging time, size of α precipitate increased. Note that there is a significant increase (85%) in tensile strength after high-temperature aging treatment and Portevin-Le Chatelier (PLC) effect can be avoided under thermo-mechanical loading conditions. It was found that after 1 h of aging treatment at 550° Celsius followed by air cooling, the welded joints owned the best tensile properties at both ambient and elevated temperature.

Element Transfer Behaviors of Fused CaF2-TiO2 Fluxes in EH36 Shipbuilding Steel During High Heat Input Submerged Arc Welding

Fused CaF2-TiO2 fluxes are developed and applied on EH36 shipbuilding plates under high heat input submerged arc welding. Transfer behaviors of O and major alloying elements are systematically investigated. TiO2 contributes to O gain in the weld pool, but leads to concurrent losses of Si, Mn, and C via deoxidation and decarburization reactions. Transfer of Ti to the weld metal is suppressed due to improved flux O potential and chemical interaction between CaF2 and TiO2.

A solution to the hot cracking problem for aluminium alloys manufactured by laser beam melting

A method to eliminate hot cracking phenomena for aluminium alloys in Laser Beam Melting (LBM) is presented in this paper, focused here on the 6061 alloy. 6061 is a precipitation-hardened aluminium alloy, containing magnesium and silicon as its major alloying elements. This alloy, commonly used in the aeronautic and automotive industries, thanks to its excellent weight to strength ratio and high thermal conductivity, is particularly prone to hot cracking, in particular during LBM processing. The solution to remove cracks proposed in the present paper is to induce grain refinement to avoid the development of large columnar structures. To this end, various quantities of Yttrium Stabilized Zirconia (YSZ) are added to an Al6061 base powder using a dry mixing (TurbulaⓇ) procedure. Experiments highlight a grain refinement effect depending on the added YSZ quantity. From 1 vol% on, SEM and EBSD images reveal an equiaxed-columnar bimodal grain microstructure. Results show that the addition of 2 vol% YSZ allows to fully avoid cracks due to a continuous equiaxed band at melt pool boudaries. Additionally, TEM and DRX investigations provide new insights into the becoming of added particles along the printing process. The experimental results are then discussed on the basis of a number of existing solidification models, with a focus on the necessary conditions for the establishment of an equiaxed solidification regime.

Solute-vacancy clustering in aluminum

We present an extensive first-principles database of solute-vacancy, homoatomic, heteroatomic solute-solute, and solute-solute-vacancy binding energies of relevant alloying elements in aluminum. We particularly focus on the systems with major alloying elements in aluminum, i.e., Cu, Mg, and Si. The computed binding energies of solute-vacancy, solute-solute pairs, and solute-solute-vacancy triplets agree with available experiments and theoretical results in literature. We consider physical factors such as solute size and formation energies of intermetallic compounds to correlate with binding energies. Systematic studies of the homoatomic solute-solute-vacancy and heteroatomic (Cu, Mg, or Si)-solute-vacancy complexes reveal the overarching effect of the vacancy in stabilizing solute-solute pairs. The binding energy database presented here elucidates the interaction between solute cluster and vacancy in aluminum, and it is expected to provide insight into the design of advanced Al alloys with tailored properties.

The effect of water environment on microstructural characteristics, compositional heterogeneity and microhardness distribution of 16Mn/304L dissimilar welded joints

Dissimilar joint between low alloy steel 16Mn and 304L austenitic stainless steel was welded in the air and under water with two different flux-cored wires: commercially obtained ER308 filler and specially developed nickel-based tubular wire. For microstructure comparison, dissimilar welded joints in the air and under water were acquired at the same welding procedures. The effect of water environment on microstructure, alloying elements distribution and microhardness profiles of dissimilar welded joints was discussed. The results show that typeⅡ boundary existed between austenitic weld metal and ferritic base metal in underwater welds similar to that in the air welds. The underwater Ni-based welds had a lower dendritic spacing than air welds. The amount of delta-ferrite present in underwater welds with ER308 filler was more than that in air welds because of the higher cooling rate in water environment. Major alloying elements were non-uniformly distributed along the austenitic weld metal/16Mn interface. Macroscopic composition gradients did not tend to form in air welds because of high heat input. Maximum microhardness value of 470 HV in wet welded joints was found in coarse-grained heat affected zone instead of transition zone. The transition zone at 16Mn side of underwater austenitic stainless steel welded joints exhibited high microhardness of 330 HV, which was strongly diluted by ferritic base metal.

A comparison of experimental time-secondary dendritic spacing and coarsening models for Al-Si-Cu alloys

Most of the secondary dendrite arm spacing (λ2) growth models existing in the literature deal with predictions for binary aluminum (Al) alloys. Only two solutions are available to estimate λ2 for chemistries of major alloying elements in Al alloys, such as copper (Cu) and Silicon (Si). The coarsening models developed by Rappaz-Boettinger and Tiryakioglu were employed in this investigation. The multicomponent models enabled very distinct matches with the experimental data of Al-9 and 11 wt.% Si-3.0 wt.% Cu alloys.

Design biodegradable Zn alloys: Second phases and their significant influences on alloy properties

Alloying combined with plastic deformation processing is widely used to improve mechanical properties of pure Zn. As-cast Zn and its alloys are brittle. Beside plastic deformation processing, no effective method has yet been found to eliminate the brittleness and even endow room temperature super-ductility. Second phase, induced by alloying, not only largely determines the ability of plastic deformation, but also influences strength, corrosion rate and cytotoxicity. Controlling second phase is important for designing biodegradable Zn alloys. In this review, knowledge related to second phases in biodegradable Zn alloys has been analyzed and summarized, including characteristics of binary phase diagrams, volume fraction of second phase in function of atomic percentage of an alloying element, and so on. Controversies about second phases in Zn–Li, Zn–Cu and Zn–Fe systems have been settled down, which benefits future studies. The effects of alloying elements and second phases on microstructure, strength, ductility, corrosion rate and cytotoxicity have been neatly summarized. Mg, Mn, Li, Cu and Ag are recommended as the major alloying elements, owing to their prominent beneficial effects on at least one of the above properties. In future, synergistic effects of these elements should be more thoroughly investigated. For other nutritional elements, such as Fe and Ca, refining second phase is a matter of vital concern.

Solute-Vacancy Clustering in Aluminum

We present an extensive first-principles database of solute-vacancy, homoatomic, heteroatomic solute-solute, and solute-solute-vacancy binding energies of relevant alloying elements in aluminum. We particularly focus on the systems with major alloying elements in aluminum, i.e., Cu, Mg, and Si. We consider physical factors such as solute size and formation energies of intermetallic compounds to correlate with binding energies. Systematic studies of the homoatomic solute-solute-vacancy and heteroatomic (Cu, Mg, Si)-solute-vacancy complexes reveal the overarching effect of the vacancy in stabilizing solute-solute pairs. The computed binding energies of the solute-solute-vacancy triplet successfully explain several experimental observations that remained unexplained by the reported pair binding energies in literature. The binding energy database presented here elucidates the interaction between solute cluster and vacancy in aluminum, and it is expected to provide insight into the design of advanced Al alloys with tailored properties.

Influence of chloride and sulphate anions on the electronic and electrochemical properties of passive films formed on steel reinforcing bars

Reinforced concrete structures are suffering from the application of de-icing salts, particularly due to premature reinforcement corrosion. To understand and, thereby, identify solutions to this problem, a study has been conducted of the chloride- and sulphate-induced instability of the semiconductor passive films formed on carbon and 2304 stainless steel alloys in a simulated concrete pore solution environment. Steels’ vulnerability to corrosion when depassivation occurs, typically in the presence of chloride and/or low pH, makes it essential to understand the nature of their passive films in the effort to mitigate the effect of corrosion. The influence of major alloying elements in five different reinforcing bars and testing on different surface roughness was investigated in the first part of the study. In this second part, linear polarization resistance and potentiodynamic cyclic polarization techniques and Mott-Schottky (M-S) analysis were used to investigate the influence of varying ionic concentrations and, thus, pH of simulated concrete pore solutions on passive films formed on duplex 2304 stainless steel and carbon steel reinforcing bars. It was found that chloride ions increased the defect densities of passive films, most significantly in the lower pH solution, while sulphates decreased the densities. This is attributed to the formation of stable solid sulphides of Fe and Ni (as FeS, FeS2, NiS, Ni3S2) in the outer Fe-rich layer of the passive films as predicted by ThermoCalc© calculations.

Segregation of the major alloying elements to Al3(Sc,Zr) precipitates in an Al–Zn–Mg–Cu–Sc–Zr alloy

Solute segregation of Zn, Mg and Cu in and around Al3(Sc,Zr) precipitates in an Al-Zn-Mg-Cu-Sc-Zr alloy was systematically studied using atom probe microscopy, aberration-corrected scanning transmission electron microscopy and first-principles simulations. Results show that the Al3(Sc,Zr) precipitates occur as a Sc-rich ‘core’ and Zr-rich ‘shell’ structure. Zn segregates to the Zr-rich shell of Al3(Sc,Zr) precipitates and substitute mainly for the Al atoms, and the Zn segregation intensifies with increasing ageing time. Mg and Cu atoms segregate to the Zr-rich shell during the early stages of ageing, while the Mg atoms prefer the Al-matrix with longer ageing time. Density functional theory calculations demonstrate that such segregation is energetically favored and highlight the diverse role of Al3(Sc,Zr) in influencing the distribution of the major alloying elements.

Influence of Sulphate on the Electronic and Electrochemical Properties of Passive Films Formed on Steel Reinforcing Bars

Reinforced concrete structures are suffering from the application of de-icing salts, particularly due to premature reinforcement corrosion. To understand and, thereby, identify solutions to this problem, a study has been conducted of the chloride- and sulphate-induced instability of the semiconductor passive films formed on carbon and 2304 stainless steel alloys in a simulated concrete pore solution environment. Steels' vulnerability to corrosion when depassivation occurs, typically in the presence of chloride and/or low pH, makes it essential to understand the nature of their passive films in the effort to mitigate the effect of corrosion. The influence of major alloying elements in five different reinforcing bars and testing on different surface roughness was investigated in the first part of the study. In this second part, linear polarization resistance and potentiodynamic cyclic polarization techniques and Mott-Schottky (M-S) analysis were used to investigate the influence of varying ionic concentrations and, thus, pH of simulated concrete pore solutions on passive films formed on duplex 2304 stainless steel and carbon steel reinforcing bars. It was found that chloride ions increased the defect densities of passive films, most significantly in the lower pH solution, while sulphates decreased the densities. This is attributed to the formation of stable solid sulphides of Fe and Ni (as FeS, FeS2, NiS, Ni3S2) in the outer Fe-rich layer of the passive films as predicted by ThermoCalc© calculations.