High Melting Temperature Alloys Research Articles

Active learning and molecular dynamics simulations to find high melting temperature alloys

Active learning (AL) can drastically accelerate materials discovery; its power has been shown in various classes of materials and target properties. Prior efforts have used machine learning models for the optimal selection of physical experiments or physics-based simulations. However, the latter efforts have been mostly limited to the use of electronic structure calculations and properties that can be obtained at the unit cell level and with negligible noise. We couple AL with molecular dynamics simulations to identify multiple principal component alloys (MPCAs) with high melting temperatures. Building on cloud computing services through nanoHUB, we present a fully autonomous workflow for the efficient exploration of the high dimensional compositional space of MPCAs. We characterize how uncertainties arising from the stochastic nature of the simulations and the acquisition functions used to select simulations affect the convergence of the approach. Interestingly, we find that relatively short simulations with significant uncertainties can be used to efficiently find the desired alloys as the random forest models used for AL average out fluctuations.

Phase Transformations from Nanocrystalline to Amorphous (Zr70Ni25Al5)100-xWx (x; 0, 2, 10, 20, 35 at. %) and Subsequent Consolidation.

Glasses, which date back to about 2500 BC, originated in Mesopotamia and were later brought to Egypt in approximately 1450 BC. In contrast to the long-range order materials (crystalline materials), the atoms and molecules of glasses, which are noncrystalline materials (short-range order) are not organized in a definite lattice pattern. Metallic glassy materials with amorphous structure, which are rather new members of the advanced materials family, were discovered in 1960. Due to their amorphous structure, metallic glassy alloys, particularly in the supercooled liquid region, behave differently when compared with crystalline alloys. They reveal unique and unusual mechanical, physical, and chemical characteristics that make them desirable materials for many advanced applications. Although metallic glasses can be produced using different techniques, many of these methods cannot be utilized to produce amorphous alloys when the system has high-melting temperature alloys (above 1500 °C) and/or is immiscible. As a result, such constraints may limit the ability to fabricate high-thermal stable metallic glassy families. The purpose of this research is to fabricate metallic glassy (Zr70Ni25Al5)100-xWx (x; 0, 2, 10, 20, and 35 at. %) by cold rolling the constituent powders and then mechanically alloying them in a high-energy ball mill. The as-prepared metallic glassy powders demonstrated high-thermal stability and glass forming ability, as evidenced by a broad supercooled liquid region and a high crystallization temperature. The glassy powders were then consolidated into full-dense bulk metallic glasses using a spark plasma sintering technique. This consolidation method did not result in the crystallization of the materials, as the consolidated buttons retained their short-range order fashion. Additionally, the current work demonstrated the capability of fabricating very large bulk metallic glassy buttons with diameters ranging from 20 to 50 mm. The results indicated that the microhardness of the synthesized metallic glassy alloys increased as the W concentration increased. As far as the authors are aware, this is the first time this metallic glassy system has been reported.

Low-Cost Fabrication of Tungsten-Rhenium Alloys for Friction Stir Welding Applications

Friction stir welding (FSW) of high-melting temperature alloys, such as steel and Inconel, requires tooling that can survive under the applied loads at the elevated temperatures. Tungsten-Rhenium (W-Re) alloys are a suitable candidate for this application; however, the costs typically associated with achieving the required densities and grain structure for the tooling are high due to the lengthy traditional processing required. Further costs are incurred in machining the starting bar stock to the final FSW tooling configuration. An alternate processing method is used in this study to shorten the fabrication time using direct current sintering which rapidly consolidates the starting powders at lower temperatures than used in traditional powder metallurgy. Although this process enables retention of the fine grain size, the sintering time is too short to form the desired single, solid phase. Therefore, the specimens were subjected to a post-consolidation heat treatment to fully solutionize the W matrix. Once the desired density and solid solution phase was verified in coupons, the final processing parameters were used to consolidate a net shape tool for FSW.

Advanced numerical modelling of friction stir welded low alloy steel

The development of advanced joining processes such as friction stir welding (FSW) is necessary to maintain manufacturing competitiveness in any industrial nation. Substantial research that has been carried out on FSW of aluminium alloys has demonstrated considerable benefits; this has led to greater interest in FSW of steel and other high melting temperature alloys. In this context, numerical modelling can provide cost-effective development of steel FSW. Due to the limitations associated with the Johnson Cook model when employed in high melting temperature metals, a three-dimensional thermo-mechanical simulation of FSW featuring low alloy steel with previously generated experimental temperature dependant properties has been successfully solved in Abaqus/Explicit. Unlike any previous research in which either the workpiece is assumed as a high viscous body or the tool is modelled as a moving heating source, the Coupled Eulerian Lagrangian approach has been innovatively applied to model the FSW process on steel. All stages of FSW (plunge, dwell and traverse) have been modelled for slow and fast process parameters and their results compared with previous experimental work on the same grade of steel. In each model, the weld shape and weld surface flash were found to be in exceptionally close alignment with previous experimental results.

Effect of the solidification time on the median particle size of powders produced by water atomisation

Present empirical correlations to predict the median particle size of water atomised powders have a validity restricted to a particular atomiser and alloy family. This work proposes a mathematical function that takes into account the influence of the heat transfer coefficient and, therefore, of the solidification time on the median particle size. This equation is applied in combination with previously proposed empirical correlations to extend their validity to a broader range of alloys. Experiments were conducted with alloys of different melting point (Fe base, Cu base and Sn). Quantitative measurements of the median particle size, tap density and several shape factors, and qualitative observations of the particle shape confirmed the importance of the heat transfer rate. It is shown that the inclusion of the solidification time effect results in a better agreement between calculated and experimental data when both low and high melting temperature alloys are taken together.

Fracture toughness of ISO 3183 X80M (API 5L X80) steel friction stir welds

Abstract Friction stir welding (FSW) is a solid-state joining process with numerous advantages such as good dimensional stability and repeatability, which is widely used Al alloys and with a great potential for critical joining applications involving high melting temperature alloys. Twelve millimeter thick plates of ISO 3183 X80M (API 5L X80) steel was friction stir welded using two passes on both sides of the plate using ceramic tools. Different heat inputs were obtained using a fix travel (welding) speed in combination with several spindle speeds. The fracture toughness of the two-pass joints was evaluated at 25 °C using the critical crack tip opening displacement (CTOD m ), revealing that joints produced with lower spindle speeds presented higher toughness at the heat-affected zone (HAZ) and stir zone (SZ), which are comparable with the base metal (BM) toughness. On the other hand, joints produced using higher spindle speeds presented low fracture toughness at the SZ and elevated CTOD m toughness at the HAZ. The joints produced with low spindle speeds showed CTOD m -values above the offshore standard (DNV-OS-F101) requirements.

Isothermal plastic forming of high melting temperature alloys

This paper deals with the problem of an unconventional plastic forming process—deformation of high melting temperature alloys under isothermal conditions. The test were performed for alloyed steel containing 0.5% C. The upsetting process at various temperatures and strain rates was used to determine the optimum parameters of deformation. In order to obtain fine grains prior to deformation and create the superplasticity effect, the samples were subjected to thermomechanical processing. The main experiment included axisymmetrical closed-die forging. Very good filling of the grove and low loads were observed in all tests. Despite the relatively long time of deformation at high temperatures, the material maintained a fine microstructure.

Isothermal plastic forming of high-carbon steel

The work deals with the problem of an unconventional plastic forming process—deformation of high melting temperature alloys in isothermal conditions. The tests were performed for alloyed steel containing 0.5%C. Upsetting the process at various temperatures and strain rates was used to determine the optimum parameters of deformation. In order to obtain fine grains prior to deformation and to create the superplasticity effect, the samples were subjected to thermomechanical processing. The main experiment included axisymmetrical closed die forging. Very good filling of the groove and low loads were observed in all tests. In spite of relatively long time of deformation at high temperatures, the material maintained fine microstructure.

New aspects of the plastometric tests for middle and high carbon steels in the superplastic conditions

Searching for the optimum conditions of plastic deformation of some materials has to guarantee a possibility of obtaining the final shape of the product without applying additional grinding. This leads to the necessity of taking the advantage of the superplasticity effect which allows to obtain the required mechanical properties and shape of the product. The superplasticity phenomenon, investigated widely some time ago, is not completely explained. This effect is well observed in the alloys based on Al, Cu, Sn, V, Ti, Co and Fe. The alloys are divided into two groups. The first group includes average melting temperature alloys which show good workability in the superplastic conditions. The second group includes high melting temperature alloys which are of particular interest for the technologists. These alloys, however due to high temperatures and long deformation times require thermal-resistant tools. The strain rate sensitivity parameter m is the main material parameter which determines the superplasticity. That parameter is a part of the consecutive equation which describes the relationship between the stress and the strain at high temperatures. The materials with the parameter m exceeding the value of 0.3 are considered to be superplastic. An attempt of establishing the optimum conditions of plastic deformation was undertaken using the torsion test. The tests were carried out at various temperatures and at various strains.

Pre- and postirradiation properties of brazed joints of AISI 316L stainless steel

An extensive test campaign has been performed to verify the reliability and the endurance of brazed joints between AISI 316L parts for structural applications in the nuclear field. The tests, conducted for comparison with three different high melting temperature alloys, included tensile tests (normal and shear), fatigue tests (fatigue crack propagation, low cycle fatigue, 4-point bending fatigue) and impact tests; besides, tensile tests have been performed with both unirradiated and irradiated specimens. Generally, the tests demonstrated satisfactory mechanical properties of the joints and revealed occasionally strong differences in the behaviour of the different brazing alloys, thus providing important design indications.

Development of test bed system for high melting temperature alloy fabrication and mass spectroscopy analysis of liquid metal ion beam source

Recent advances in microlithography with focused ion beam (FIB) systems for submicron integrated circuit fabrication, and the important role of liquid metal ion source (LMIS) in FIB systems to produce a stable ion beam current of selected specie, require a test bed system capable of testing, analyzing, and fabricating a variety of alloy sources. Most fabrication of alloy sources require a contaminant-free environment, therefore wetting and fabricating of the alloy for LMIS must be carried out in high vacuum at a pressure of 10−7 Torr or lower. The development of a high-vacuum LMIS test bed system capable of fabricating high melting temperature alloys for FIB system as well as testing the sources are described in detail. The mass spectra of remelted alloys of Cu3P, Pd73B27, and Pt58B42 show no nitrogen or oxygen contamination during alloy fabrication process.

Single-roller rapid quenching of high melting temperature alloys using plasma-arc melting

A single-roller rapid quenching apparatus with a plasma-arc torch and a water-cooled copper hearth has been developed for the rapid quenching of high melting temperature alloys (mp>2000 °C). Details of the apparatus and a mathematical analysis of thermal conditions during the quenching process are described together with the results obtained from high melting temperature alloy experiments. Amorphous ribbons were obtained from Nb80Si20, Nb3Ge, and Ta–(Si,B) alloys. Amorphous Nb3Ge ribbon was successfully converted into an A15 single phase by heat treatment, and showed a superconducting transition temperature as high as 18.3 K. Crystallization of Ta80Si10B10 amorphous ribbon was observed at a very high temperature of 1233 K.