Characterization of the Role of Post-Build Heat Treatment on the Localized Corrosion Susceptibility of Laser Powder Bed Fused Inconel 718 Parts

As more industries look toward additively manufactured (AM) components to combat lead times, re-design, cost of complexity, etc., those industries are faced with re-evaluating the performance of AM-based materials as compared to their well-documented wrought or machined counterparts. A particular alloy of interest to many industries including aerospace and energy/power generation is Inconel 718 due to its resistance to oxidation and high temperature degradation [1]. Additively manufactured Inconel 718 parts typically receive a series of post-build heat treatments prior to deployment. If not properly controlled, these post-build treatments may introduce secondary precipitates and other inhomogeneities that will affect the parts’ mechanical properties and susceptibility to corrosion. This is specifically true of susceptibility to localized corrosion mechanisms that may lead to crack initiation, accelerated crack growth and ultimately premature failure. By utilizing electrochemical parameter testing to analyze for localized breakdown potentials, this work investigates the variation in tolerance to localized corrosion that results from common post-build heat treatment steps and the secondary phase precipitation that can ensue in Inconel 718 AM parts.

Improvement on Mechanical Properties of Submerged Friction Stir Joining of Dissimilar Tailor Welded Aluminum Blanks

Friction stir welding is a solid-state welding method that produces joints with superior mechanical and metallurgical properties. However, the negative effects of the thermal cycle during welding dent the mechanical performance of the weld joint. Hence, in this research study, the joining of aluminum tailor welded blanks by friction stir welding is carried out in underwater conditions by varying the welding parameters. The tensile tests revealed that the underwater welded samples showed better results when compared to the air welded samples. Maximum tensile strength of 229.83 MPa was obtained at 1000 rpm, 36 mm/min. The improved tensile strength of the underwater welded samples was credited to the suppression of the precipitation of the secondary precipitates due to the cooling action provided by the water. The lowest hardness of 72 HV was obtained at the edge of the stir zone which indicated the weakest region in the weld zone.

Design of a Co–Al–W–Ta Alloy Series with Varying γ′ Volume Fraction and Their Thermophysical Properties

The γ′ volume fraction is a key parameter in precipitation-strengthened Co- and Ni-base superalloys and mainly determines the alloys’ properties. However, systematic studies with varying γ′ volume fractions are rare and the influence on thermal expansion has not been studied in detail. Therefore, a series of six Ta-containing Co-based alloys was designed with compositions on a γ–γ′ tie-line, where the γ′ volume fraction changes systematically. During solidification, Laves (C14-type) and µ (D85-type) phases formed in alloys with high levels of W and Ta. Single-phase γ or two-phase γ/γ′ microstructures were obtained in four experimental alloys after heat treatment as designed, whereas secondary precipitates, such as χ (D019-type), Laves, and μ, existed in alloys containing high levels of γ′-forming elements. However, long-term heat treatments for 1000 hours revealed the formation of the χ phase also in the former χ-free alloys. The investigation of the thermal expansion behavior revealed a significant anomaly related to the dissolution of γ′, which can be used to determine the γ′ solvus temperature with high accuracy. Compared to thermodynamic calculations, differential scanning calorimetry (DSC) and thermal expansion analysis revealed a larger increase of the γ′ solvus temperatures and a lesser decline of the solidus temperatures when the alloy composition approached the composition of the pure γ′ phase.

Copper Precipitation Behavior during Continuous Cooling and Subsequent Aging of Powder-Forged Fe-2.5Cu-C Alloy

Microstructure and property evolution of a powder-forged Fe-2.5Cu-C alloy during continuous cooling and subsequent aging were investigated to improve its mechanical properties. During continuous cooling, copper precipitates formed were consistent with the interphase mechanism when the cooling rate was less than 7 °C/s; however, the hardness of the specimen was always higher at faster cooling rates because finer grains and harder phases formed. During subsequent aging, copper precipitates formed and/or coarsened continuously while the hardness of the alloys was greatly influenced by the combined effects of the primary and secondary precipitates, as revealed by the theoretical calculations. In addition, the forming and evolving mechanisms of the copper precipitates at different stages were also discussed based on the experimental results. This study will provide guidance to the industry for achieving high performance in the powder-forged products by treatment manipulation.

Towards image based assessment and characterization of cyclic paleo-wind and flow fields

<p>Cylcostratigraphy is used to investigate quasi-cyclic patterns in sediments. It often provides insight about time and climate. While most studies utilize proxies related to precipitation and temperature, reconstruction of wind and flow directions is more challenging. Due to this, the dynamic change of atmospheric circulations from geophysical data is not well established on orbital timescales. One key method for this purpose is the assessment of the anisotropy of the magnetic susceptibility. Nevertheless, the so derived data are of volume-integrated nature, i.e. a result of the combined mineral composition and structure of the entire investigated sample material. Accordingly, it would be most favorable to link and assess the volume integrated data with spatial sample features. X-ray micro computed imaging enables extensive and non-destructive sample material characterization in three dimensions, with special regards to mineralogical, textural, geometrical and topological material features. By combining volume specific magnetic anisotropy data with state of the art X-ray micro CT imaging data sets, we can derive spatially resolved information about (e.g.) grain sizes, grain shapes, sorting, layering patterns, preferential grain / pore/ layer orientations, secondary precipitates, pore sizes, pore shapes and many other parameters. With this, we greatly increase our understanding about the ancient depositional environment, which is important for investigating and characterizing the dynamic and quasi-cyclic wind and flow fields.</p>

Instant Attraction: Clay Authigenesis in Fossil Fungal Biofilms

Clay authigenesis associated with the activity of microorganisms is an important process for biofilm preservation and may provide clues to the formation of biominerals on the ancient Earth. Fossilization of fungal biofilms attached to vesicles or cracks in igneous rock, is characterized by fungal-induced clay mineralization and can be tracked in deep rock and deep time, from late Paleoproterozoic (2.4 Ga), to the present. Here we briefly review the current data on clay mineralization by fossil fungal biofilms from oceanic and continental subsurface igneous rock. The aim of this study was to compare the nature of subsurface fungal clays from different igneous settings to evaluate the importance of host rock and ambient redox conditions for clay speciation related to fossil microorganisms. Our study suggests that the most common type of authigenic clay associated with pristine fossil fungal biofilms in both oxic (basaltic) and anoxic (granitic) settings are montmorillonite-like smectites and confirms a significant role of fungal biofilms in the cycling of elements between host rock, ocean and secondary precipitates. The presence of life in the deep subsurface may thus prove more significant than host rock geochemistry in directing the precipitation of authigenic clays in the igneous crust, the extent of which remains to be fully understood.

Investigating the Effect of Friction Stir Welding on Microstructure and Corrosion Behaviour of Al-Zn-Mg Alloy

In this work, Friction Stir Welding (FSW) of alloy 7039 was carried out in T4 temper and resulting microstructure and corrosion behaviour of developed weld were studied. FSW transformed the starting microstructure of base metal and formed stirred zone (SZ) and heat affected zone (HAZ) with varying microstructure and precipitate morphology. The observed zones in welded joints exhibited decreased protection to corrosion resistance than base metal. Dissolution of secondary precipitates in SZ and occurrence of precipitate free zones (PFZs) in HAZ enhanced susceptibility to corrosion of HAZ and weld nugget zone (WNZ) than base metal.

Chemical Aspects of Scandium carbonate leaching from Red Muds

Red Muds (R.M.) – waste of bauxite reprocessing by the Bayer's method include many rare elements, such as Gallium, Titanium, Zirconium, Rare Earth Elements and Scandium, concentration of which in its reached 130 g/t. In the problem solving of Scandium extraction from R.M. get a two directions: immediate leaching of Scandium from R.M. and in passing Scandium recovery under complexing processing of R.M. The method of carbonate leaching of Scandium from R.M., which was work out in Institute of Solid State Chemistry Russian Academy of Sciences Urals Branch, include saturation by carbon dioxide of alkaline solutions, obtained after water process of R.M. and allow up to 20 % Scandium recovery in solutions. It is not effective for work out of technological scheme of R.M. processing. In recent paper, the chemical aspects of carbonate leaching of Scandium from R.M. in heterogeneous systems solid – liquid – gas carbon dioxide were investigated to determine of conditions for more Scandium recovery from R.M. It was shown, that Scandium leaching by aqueous sodium solutions without carbon dioxide gives small recovery yield and accompanied by alkaline hydrolysis under high pH in concentrated Na2CO3 solutions. Under saturation by carbon dioxide of carbonate R.M. pulp, the hydrolytic polymerization of hydroxocarbonates of Scandium and Aluminum in presence of carbonic acid proton take place. In the both process secondary precipitates are settle down and reduce of Scandium recovery yield. For increase of Scandium recovery from R.M. it is necessary to exclude the secondary precipitates under carbonate leaching with saturation by carbon dioxide.

Effect of nanosecond unipolar electropulse effects on the properties of the alloy Cu-1% Cr. Part 2. Relation of alloy properties with Cr content in Cu lattice

The effect of treatment of copper melt with chromium additives in the amount of 1% by weight is considered nanosecond unipolar electric pulses with a frequency of 1000 Hz, a single signal duration of one nanosecond and a power of 10 kW on the electrical resistivity and hardness of the resulting alloy. A study was made of the macro and microstructure of alloy samples created using electropulse effects and comparison samples obtained under the same thermal conditions, but without it. The samples were aged for 2 hours at 4500C. It has been found that electropulse treatment of the melt leads to an increase in hardness and decrease in the electrical resistance of the alloy as well as during aging, and the influence of this effect remains noticeable even after the aging process. Hardness and electrical resistance in all alloy samples are described mathematically as a function of chromium content in the copper lattice and in secondary precipitates. The role of nanosecond unipolar electroimpulsive effects on the Cu-1% Cr melt in improving the above characteristics of the resulting alloy compared with the thermo-time treatment without the electropulse effect is revealed. An explanation of the mechanism of the electropulse effect on the melt, leading to the separation of chromium atoms in the liquid state and the subsequent decrease in its solubility in the copper lattice, is proposed. The results of the study are presented in the form of drawings of macro- and microstructure of samples of the alloy Cu-1% Cr, tables, graphs and mathematical formulas. It was concluded that it is advisable to use a nanosecond unipolar electropulse effect with a frequency of 1000 Hz, a single signal duration of one nanosecond and a power of 10 kW per Cu-1% Cr melt to produce the corresponding alloy with improved hardness and electrical resistance.