Wide Range Of Metal Alloys Research Articles

Stepwise Multi-Temperature Thermogravimetric Analysis (SMT-TGA) for Rapid Alloy Development

A stepwise multi-temperature thermogravimetric analysis (SMT-TGA) method is a rapid and time- and material-efficient measurement procedure for oxidation kinetics over a wide range of temperatures. It is suitable for alloy design and material selection procedures. It involves subjecting a sample to a series of steps at increasing temperatures, followed by steps at decreasing temperatures to identify possible effects on the evolution of oxide layer microstructures on oxidation kinetics. This method has been tested for a wide range of metallic alloys in the present work, allowing for the mapping of possible ranges of parabolic oxidation kinetics of industrial alloys between 600 and 1300°C. Two examples of effects of thermal history have also been described in this publication.

Understanding grain boundary segregation and solute drag using computational and machine learning studies

Grain boundary (GB) solute segregation has been used as a strategy to tailor the properties and processing pathways of a wide range of metallic alloys. GB solute drag results when segregated alloying elements exert a resistive force on migrating GBs hindering their motion. While GB segregation has been the subject of active research, a detailed understanding of solute drag and the migration kinetics of doped boundaries is still lacking, especially in technologically-relevant alloys. Through theoretical analysis, mesoscale modeling, and machine learning studies, we investigate GB segregation and solute drag and establish design maps relating drag effects to relevant alloy and GB properties, i.e., the complete alloy design space. We find that solute drag is dominant in immiscible alloys with far-from-dilute compositions in agreement with experimental observations of GB segregation in metallic alloys. Our analysis reveals that solute–solute interactions within the GB and the degree of segregation asymmetry greatly influence solute drag values. In broad terms, our work provides future avenues to employ GB segregation to control boundary dynamics during materials processing or under service conditions.

On the use of the plastic component of the CTOD for fatigue analysis in austenitic stainless steel

In this work a new methodology for characterising the fatigue crack propagation of metallic alloys is proposed. The methodology is based on the plastic component of the Crack Tip Opening Displacement (CTODp) as a driving force. This CTODp parameter is evaluated from full-field displacement maps obtained by Digital Image Correlation (DIC). The method is applied on austenitic stainless steel but appears to be very suitable to a wide range of metal alloys. The methodology appears to improve some of the issues related to Linear Elastic Fracture Mechanics predictions for fatigue crack growth.

Effect of single spark micro-EDM on crater size of different alloys

Owing to the fact of continuous discharges in RC circuit based μ-EDM process, it is indeed very difficult to analyse difficult-to-control single discharge pulse. This work is thus aimed to develop an innovative technique for generating single discharge in the process. An electrical circuit, parallel to the existing discharge circuit of μ-EDM, has been integrated in-house for the purpose and verified for its applicability over a wide range of metal alloys. For example, single crater diameters of approximately 7μm, 10μm and 18μm have been achieved for stainless steel, Inconel and brass respectively at minimum energy input. The single discharge generatorhas been developed expecting it would be helpful in gathering information such as volume removal by each discharge which will definitely lead to development of a robust thermal model for material removal in μ-EDM.

Wire + Arc Additive Manufacture of 17-4 PH stainless steel: Effect of different processing conditions on microstructure, hardness, and tensile strength

Wire + Arc Additive Manufacture (WAAM) is receiving increasing attention as it offers a way to fabricate meter scale parts, with relatively low capital cost, lower material wastage and logistical advantages. A wide range of metallic alloys could be manufactured using this process. Martensitic grade precipitation-hardening stainless steel 17-4 PH offers excellent combination of high strength and corrosion resistance. Hence, it is important to investigate the behaviour of this alloy in WAAM. In the present work, the effect of different process variables such as shielding gas, deposition path and post-fabrication heat treatment, on microstructure and mechanical properties were studied. A number of specimens were manufactured by WAAM using the Fronius Cold Metal Transfer (CMT) process under different controlled processing conditions. These specimens were subsequently characterized by optical and electron microscopy and mechanical properties in terms of tensile strength and hardness. It was found that using shielding gases that result in higher heat input reduces the amount of retained austenite in the as-deposited microstructure. It has been demonstrated that the required tensile properties can be achieved by applying post-deposition heat treatment. However, it is suggested that direct aging in as deposited condition resulted in formation of harmful intermetallic phases which embrittles the deposit.

Dispersing small, bimetallic nanoparticles

Catalysis For applications of nanoparticles in sensing and catalysis, smaller nanoparticles are often more effective because they expose more active surface sites. The properties of metallic nanoparticles can also be improved by creating bimetallic alloys, but typical synthetic methods yield larger nanoparticles where the metals are poorly mixed. Wong et al. show that well-mixed bimetallic ∼1-nm-diameter nanoparticles can be made on silica supports. To do this, they exploited strong electrostatic adsorption, in which the metal precursors are strongly adsorbed onto the surface by controlling pH relative to the surface point of zero charge. Their method was successful for a wide range of metal alloys. Science , this issue p. [1427][1] [1]: /lookup/doi/10.1126/science.aao6538

Synthesis of ultrasmall, homogeneously alloyed, bimetallic nanoparticles on silica supports.

Supported nanoparticles containing more than one metal have a variety of applications in sensing, catalysis, and biomedicine. Common synthesis techniques for this type of material often result in large, unalloyed nanoparticles that lack the interactions between the two metals that give the particles their desired characteristics. We demonstrate a relatively simple, effective, generalizable method to produce highly dispersed, well-alloyed bimetallic nanoparticles. Ten permutations of noble and base metals (platinum, palladium, copper, nickel, and cobalt) were synthesized with average particle sizes from 0.9 to 1.4 nanometers, with tight size distributions. High-resolution imaging and x-ray analysis confirmed the homogeneity of alloying in these ultrasmall nanoparticles.

Sub-Zero Temperature Effect on Impact Properties of 17-4PH Stainless Steel Processed by Selective Laser Melting

The Selective Laser Melting (SLM) process has been proved as the most effective method among Additive Manufacturing (AM) technologies to produce hard, dense and strong metallic structures with intricate shapes and profiles from wide range of metallic alloys. The SLM generated structures from 17-4PH stainless steel high strength alloys involve layer by layer building up through laser melting of successively deposited powder layers. Therefore, the mechanical properties of such structures need to be thoroughly checked and investigated before putting these materials to practical applications. This research mainly investigates the cryogenic impact properties of SLM generated 17-4PH specimen. These characteristics are very important in applications requiring high strength customized structures that could maintain their mechanical properties at sub-zero temperatures. The experimental analysis proves that SLM is a very reliable technology to produce high strength metallic structures and these specimens can function efficiently in extreme conditions.

Intrinsic ductility for structural materials as a function of stress and temperature

In recent years, a method has been developed to measure current creep strength at nearly constant structure in a high precision stress relaxation test (SRT), covering at least five decades in creep rate in a one day test. Results have been reported on a wide range of metallic alloys, polymers, composites and ceramics. In the present paper it is shown that these same data can be used to determine a measure of intrinsic ductility over the same range of stress, using results on a low alloy Cr–Mo–V steel. This is based on an experimental and theoretical correlation between elongation at failure and strain rate sensitivity, m. This refined SRT test can now be used to evaluate both the intrinsic creep strength and the intrinsic ductility as a function of stress in a single short-time test. The test can detect embrittling phenomena at very low creep rates as a function of temperature. This measure of ductility may be used directly in engineering design and remaining life assessment.

Microstructural Evolution of Cast Hyper-Eutectic Al-18% Si Alloy during Cyclic Semi-Solid Heat Treatment

The cyclic semi-solid heat treatment represents a promising technique for improving microstructure and mechanical properties of a wide range of metallic alloys. In the current research the influence of cyclic semi-solid heat treatment on microstructure of Al-18% Si alloy containing 0.8% Fe has been studied. All specimens were heated in an electrically heated resistance furnace with heating rate of 10˚C∙min −1 to 585˚C. For a complete one cycle heat treatment (5 min heating time), samples after 5 min holding at 585˚C were cooled to a temperature of 550˚C in still air cooling and the samples were taken out immediately for water quenching. It was found that heat treatment cycles should be limited to 3 cycles or less in order to maintain fine grain size and globular structure without agglomeration and coalescence. Cyclic semi-solid heat treatment changes morphology of iron-rich intermetallics phases to be plate-like and fine plate iron-rich intermetallics phases, in stead of needle-like iron-rich intermetallics phases that are observed in as-cast samples. Cyclic heating shows a relatively higher hardness for all heating cycles compared with as-cast one due to its finer and globular structure. Cyclic semi-solid heat treatment technique results in lower coarsening rate constant compared with isothermal heat treatment one due to coarsening discontinuous effect.

Ceramic based lightweight composites with extreme dynamic strength

On the basis of several years experiments in development of high performance technical ceramics and in investigation of hetero-modulus and hetero-viscous materials and ceramic matrix composites the authors successfully developed a new family of ceramic reinforced lightweight composites with extreme dynamic strength. To obtain these lightweight composites first the matrix materials were developed from different sort of sintered ceramics with high porosity and after the prepared items were re-sintered using reactive sintering methods or were impregnated with nanoparticles of Si3N4, SiAlON ceramics or light metal alloys having excellent mechanical strength and properties. Where it was necessary the pores and material structures of ceramic matrix materials anchored excellent wetting for a wide range of metal alloys, so it was possible to develop several types of ceramic reinforced hetero-modulus light metal composites with extreme dynamic strength of different density. In this work the authors present the c-Si3N4 diamond particles reinforced corundum matrix composite shield plate structures and some of the specially developed low density ceramic foams and high porosity ceramic matrix materials for lightweight metallic composites.

Effect of Slope Plate Variable and Reheating on the Semi-Solid Structure of Ductile Cast Iron

Semi-solid metal casting and forming is a promising production method for a wide range of metal alloys. In spite of many applications for semi-solid processed light alloys, few works have reported on the semi-solid processing of iron and steel. In this research, an inclined plate was used to change the dendritic structure of iron to globular. The effects of the length and slope of the plate on the casting structure were examined. The results show that the process effectively changes the dendritic structure to globular. A sloped plate angle of 7.5° and length of 560 mm with a cooling rate of 67 K·s −1 gave the optimum graphite nodularity and solid particle globularity. The results also show that the sloped plate more easily prevents inoculant fading since the total time processing is rather short. In addition the semi-solid ductile cast iron prepared using the inclined plate method was reheated to examine the effect of reheating conditions on the microstructure and coarsening kinetics of the alloy. The solid fractions at different reheating temperatures and holding times were used to find the optimum reheating temperature range.

Effect of slope plate variable and reheating on the semi-solid structure of ductile cast iron

Abstract Semi-solid metal casting and forming is a promising production method for a wide range of metal alloys. In spite of many applications for semi-solid processed light alloys, few works have reported on the semi-solid processing of iron and steel. In this research, an inclined plate was used to change the dendritic structure of iron to globular. The effects of the length and slope of the plate on the casting structure were examined. The results show that the process effectively changes the dendritic structure to globular. A sloped plate angle of 7.5° and length of 560 mm with a cooling rate of 67 K·s −1 gave the optimum graphite nodularity and solid particle globularity. The results also show that the sloped plate more easily prevents inoculant fading since the total time processing is rather short. In addition the semi-solid ductile cast iron prepared using the inclined plate method was reheated to examine the effect of reheating conditions on the microstructure and coarsening kinetics of the alloy. The solid fractions at different reheating temperatures and holding times were used to find the optimum reheating temperature range.

Development of semi-solid ductile cast iron

Semi-solid metal casting and forming is a promising process for production of a wide range of metal alloys. In spite of the growing application of semi-solid processed light alloys, little research has been reported on semi-solid processing of iron and steel. In this study, inclined plate and stirring processes were used to change the dendritic structure of iron to globular structure. The effect of stirring time and speed, length and slope of plate on the casting structure was examined. The results show that both processes can effectively change the dendritic structure to globular. Optimum graphite nodularity and solid particle globularity were achieved following mechanical stirring at 150 rev min-1 for 9 min with a cooling rate of 0.25 K s-1 (15°C min-1) and with a slope plate angle of 7.5° and length of 560 mm with cooling rate of 67 K s-1. In addition, the results show that inoculant fading can be prevented more easily using a slope plate, since the total process time is short.

Atom Probe Field Ion Microscopy of High Resistivity Materials

Abstract Over the last 30 years, the atom probe has proved to be a powerful tool for studying nanometer-sized compositional fluctuations in a wide range of metallic alloys but has had only limited applications to semiconductors and ceramics. One of the primary reasons for this difference is the higher resistivity of semiconducting and ceramic specimens. Because of this high resistivity, the high voltage field evaporation pulse is attenuated before it reaches the apex of the specimen thereby making the pulse ineffective for field evaporation. Experiments have demonstrated that both variants of the voltagepulsed atom probe (i.e., those instruments in which the field evaporation pulse is applied directly to the specimen and those in which the negative pulse is applied to a counter electrode in front of the specimen) are equally affected. In this overview, the limits of applicability of the voltage-pulsed atom probe to high resistivity materials are examined.

Ultrasonic determination of grain size variations around weldments

Previous work has shown that measurements of ultrasonic attenuation are sensitive to grain size variations in a wide range of metallic alloys. In this report it is shown that the technique can be applied to the determination of grain-size variations in the heat affected zone and weld metal regions of different types of weldment made to PWR specifications. Data are presented in both C-scan and absolute terms to demonstrate that quantitative interpretation is possible. The immediate application is seen to be production of ultrasonic macrographs to supplement time-consuming optical methods. However, there are possible extensions to assessment of in situ weld condition.