Alloy UNS Research Articles

Investigating the process parameter window for laser powder bed fusion of copper chrome zirconium

ABSTRACT Copper-based alloy UNS C18150 has become an attractive material for laser powder bed fusion (LPBF) processing. However, the complexity of LPBF mandates that unique process parameters be devised for each alloy as these are highly sensitive to material chemistry. This work aims to clarify the general boundaries of the process window for the most influential parameters alongside an exploration into the effects of scan strategy on the density. A series of statistical design of experiments were utilised to model density as a response and predict process parameters that would result in minimised residual porosity. Using optimised parameters, specimen with up to 99.1% of theoretical density were produced, and a window of process parameters was established that yielded similarly dense products. Post-build aging of the LPBF parts was also explored. Here, direct aging of the as-built product at 390°C for 100 h resulted in a peak hardness of 83.3 ± 0.6 HRB.

Hydrogen embrittlement of the nickel alloy UNS N07718 for two different heat-treating schedules

The role of the nickel alloy 718 microstructure has been widely discussed and it is well established the δ phase detrimental effect on the material’s ductility and toughness when exposed to hydrogen. However, other microstructural features that might influence the embrittlement process are more elusive, which requires more in-depth studies. Having selected heat-treating schedules to mitigate δ phase precipitation, this work aims to assess the hydrogen embrittlement of two alloy 718 variants with nominal yield strengths of 120 and 150 ksi. Fundamentally, the idea is to understand the extent of the hydrogen damage caused by an increase in mechanical strength beyond the limit of 140 ksi specified in the API 6ACRA. Slow strain rate (SSR) and fracture toughness (FT) testing were applied to evaluate the mechanical behavior under cathodic polarization. The microstructure of both variants is comprised of recrystallized austenite grains and a very low content of grain boundary δ phase. Nanosized disk-shaped γ″ particles are also present for both variants, although the 150 ksi material shows a higher volume fraction and a finer distribution of this phase. Despite having the same overall fracture features, nanostructure differences between the variants and the consequent impact on hydrogen apparent solubility and slip planarity produced lower values of plastic elongation and initiation fracture toughness for the stronger material.

Lean manufacturing of dissimilar weld joints using Taguchi method

The lean manufacturing concepts and tools are presented as a good alternative to increase production efficiency, promoting cost reduction and increasing the quality of manufactured products. Tungsten inert gas (TIG) welding is a kind of metal joining processes that has found widespread usage across the industries; it involves the employment of a non-consumable conductive tungsten electrode in a shield of inert gas. A204GRB alloy steel and UNS 317 stainless steel have been used extensively in high pressure vessel fabrication and in similar applications, owing to their great strength and corrosive resistiveness. Further, the quality of the weldments is sturdily depending upon the input process variables, and finding their optimum combination is quite important. In the present investigation, the optimized quantities of the TIG welding variables namely, current, voltage level and the weld speed were identified with the aid of the Taguchi’s method for the dissimilar weld joints created with the aforementioned materials.

Study of Abrasive Water Jet Machining as a Texturing Operation for Thin Aluminium Alloy UNS A92024.

Surface modification of metallic alloys can create hydrophilic or hydrophobic surfaces that enhance the functional performance of the material. For example, hydrophilic surfaces have improved wettability, which improves mechanical anchorage in adhesive bonding operations. This wettability is directly related to the type of texture created on the surface and the roughness obtained after the surface modification process. This paper presents the use of abrasive water jetting as an optimal technology for the surface modification of metal alloys. A correct combination of high traverse speeds at low hydraulic pressures minimises the power of the water jet and allows for the removal of small layers of material. The erosive nature of the material removal mechanism creates a high surface roughness, which increases its surface activation. In this way, the influence of texturing with and without abrasive has been evaluated, reaching combinations where the absence of abrasive particles can produce surfaces of interest. In the results obtained, the influence of the most relevant texturing parameters between hydraulic pressure, traverse speed, abrasive flow and spacing has been determined. This has allowed a relationship to be established between these variables and surface quality in terms of Sa, Sz and Sk, as well as wettability.

Effect of environmental variables and main alloying elements on the repassivation potential of Ni–Cr–Mo–(W) alloys 59 and 686

Abstract Chloride-induced crevice corrosion (E R,CREV) of alloys UNS N06059 and UNS N06686 was studied at different temperatures in 0.1, 1 and 10 M chloride solutions. Crevice corrosion occurred several degrees below the reported critical crevice temperatures obtained through standard immersion tests. The repassivation potential of the tested alloys as a function of temperature and chloride concentration was given by E R,CREV = (A + BT)log[Cl−] + CT + D for a range of environmental conditions. When temperature and chloride concentration increased E R,CREV showed a lesser dependence on the environmental variables. The repassivation potential of Ni–Cr–Mo–(W) alloys was described by a new proposed equation in terms of [Cl−], T, Cr, Mo and W, alloys in wt%. The dependence of E R,CREV with the weight % of main alloying elements was 5–6 mV/%Cr, 17–18 mV/%Mo and ∼9 mV/%W, at 85 °C in chloride solutions. An optimal main alloying elements relationship was noted that maximizes the E R,CREV value. The optimal alloy ratio would be 1:3.3:1.65 for wt%Cr, wt%Mo and wt%W, the same factors as in the PRE equation. The optimal alloying ratio would be independent of the alloy composition since it is not a function of the content of main elements.

A constitutive model for the uniaxial tensile plastic behavior of metals based on the instantaneous strain-hardening exponent

The present work develops a new constitutive equation model for strain-hardening behavior of metallic materials (named herein as the Gonoring model) based on the definition of the instantaneous strain-hardening exponent. This new proposal was applied to experimental uniaxial tensile data of a lean duplex stainless steel alloy UNS s32304 (LDSS 2304) in the as-received (AR) condition and on identical heat-treated specimens at four different temperatures. This choice was justified because this is a steel that presents two phases (ferrite and austenite), which makes it a more universal example from the point of view of applying a new constitutive equation model. These heat treatments induced sigmoidal strain-hardening behavior at uniaxial tensile in this alloy. The Gonoring proposal was able to predict the strain-hardening behavior of both the sigmoidal and parabolic-shaped strain-hardening curve of a lean duplex stainless steel alloy 2304.

Influence of Welding Parameters of Resistance Spot Welding on Joining Aluminum with Copper

The resistance spot welding (RSW) method was used to join aluminum alloy AA 1050 and copper alloy UNS C50100 sheets. Mechanical properties of the joints were examined. The influence of welding process parameters on tensile shear force of the joints was discussed. The design of experiments (DOE) method was used to analyze the influence of welding parameters on the mechanical properties of the joints. Three RSW parameters were used: welding current, squeeze time, and welding time. The results showed that the joint shear stress increased with increasing the welding current until a value of 12000 Amp. Then the shear stress decreased. The tensile shear stress increased with increasing the welding and squeeze time. As a consequence, it can be possible to weld copper with aluminum by RSW.

Tantalum Alloy Welding: Does the Thermal Cycle Influence the Microstructure?

The aim of the present work is to verify the microstructural behavior of a B 521 tantalum alloy UNS Grade R05200 after welding, in relation to the welding thermal cycle. The joint design was a 1.5 mm thickness circumferential butt welding, on a 32 mm outside diameter pipe, welded in 1 G position (horizontal, flat, and rotating). The chosen welding process was gas tungsten arc welding (GTAW). The microstructural analysis showed the presence of coarse, dendritic-columnar structures, as well as a hexagonal cell, with no cracks noted. Hardness tests showed an increase in hardness, from 120 HV to 425 HV, in the heat-affected zone. Through finite element methods, the behavior of the temperature field was estimated and compared.

Analysis of the Influence of Continuous-Drive Friction Welding on the Microstructure and Mechanical Properties of the UNS C64200 Bronze-Aluminum-Silicon Alloy

Friction welding (FRW) is an important commercial solid-state welding process in which coalescence is achieved by frictional heat combined with pressure. The objective of this work is to analyze the microstructure and the mechanical behavior of the copper alloy UNS C64200 – bronze-aluminum-silicon, as well as to raise the ideal welding parameters so that there is adequate weldability after process of continuous-drive friction welding. Regarding the analysis of the microstructure, scanning electron microscopy was used to characterize phases. The mechanical properties were evaluated by means of a hardness test of the center of the welded joint, traversing the entire extent of the thermally affected zone. Results show that the UNS C64200 alloy, when subjected to conventional friction welding, behaves satisfactorily in terms of weldability, without the appearance of cracks or defects arising from the temperature characteristic of this process, as well as good hardness with values above the minimum established in norm and higher than the base material.

The Localized Corrosion of Ni-Cr-Mo-W Alloy UNS N06022 in Aprotic Solvents Containing Chlorides

Syntheses of pharmaceuticals often require a series of intermediate steps involving reactions in aprotic organic solvents. Some of these solutions can be aggressive towards the metallic materials that constitute the reaction vessels used, so often corrosion-resistant alloys (CRA) such as the Ni-Cr-Mo-W UNS N06022 are employed. Ni-Cr-Mo-W alloys are known for their outstanding corrosion resistance in reducing and oxidizing aqueous solutions as a result of their passive oxide film. However, the application of passive alloys in nonaqueous solvents raises additional concerns due to: i) limited availability of passivating species; ii) different behavior of aggressive halides and acids as a result of the solvent’s physicochemical properties.The aim of this work is to investigate the corrosion of Ni-Cr-Mo-W alloys in aprotic organic solvents and to understand the influence of properties of the solvent on the susceptibility to pitting and to uniform corrosion, at room temperature. A series of experiments was carried out in acetonitrile, dimethylacetamide (DMA) and dimethylformamide (DMF) solutions containing HCl or tetrabutylammonium chloride (Bu4NCl), and with the oxidant 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). A combination of electrochemical tests and subsequent microscopy has shown that N06022 corrodes uniformly in acetonitrile-HCl solutions at much lower HCl concentrations than in aqueous solutions. In DMA- or DMF-HCl solutions, however, N06022 is passive, but undergoes pitting upon anodic polarization. Furthermore, N06022 undergoes pitting in chloride concentrations as low as a few mM in neutral solutions of all aprotic solvents tested. Depending on solvent and concentration, residual water can inhibit or promote corrosion, influencing anodic kinetics and changing corrosion morphology.Ultimately, this study aims to understand why Ni-based CRAs are much more susceptible to localized corrosion in aprotic organic solvents than in water, and explain how the properties of the solvent – or mixture of solvents – can impact corrosion behavior. This work will provide fundamental understanding of the passivity of Ni-based alloys in organic solvents, assisting the selection of materials for nonaqueous applications.

Investigation of the Localized Corrosion of Ni-Cr-Mo-W Alloy UNS N06022 in Aprotic Solvents at Room Temperature

Syntheses of pharmaceuticals often require a series of intermediate steps involving reactions in aprotic organic solvents. Some of these solutions can be aggressive towards the metallic materials that constitute the reaction vessels used, so often corrosion-resistant alloys (CRA) such as the Ni-Cr-Mo-W UNS N06022 are employed. Such materials are expensive, but their use is required to prevent contamination of the product by metal ions. Ni-Cr-Mo-W alloys are known to exhibit outstanding corrosion resistance in reducing and oxidizing aqueous solutions as a result of their passive oxide film. However, the application of passive alloys in nonaqueous solvents raises additional concerns due to: i) limited availability of oxygen atoms for passivation; ii) different behavior of aggressive anions and acids as a result of the solvent’s physicochemical properties. Nevertheless, the literature on corrosion of CRA is focused on behavior in aqueous solutions and the literature on corrosion in organic solvents lacks information on the application of commercial alloys. The aim of this work is to investigate the corrosion of Ni-Cr-Mo-W alloys in aprotic organic solvents and to understand the influence of properties of the solvent on the susceptibility to pitting and to uniform corrosion, at room temperature.Preliminary work was carried out with anhydrous acetonitrile solutions containing HCl and the oxidant 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Mass loss and electrochemical tests have shown that alloy N06022 exhibits high-rate dissolution in such conditions. The corrosion rates observed after 24 h of immersion are greater than 10 mm/year, which is remarkably high when compared with the existing literature on corrosion of Ni-Cr-Mo alloys. Moreover, in neutral acetonitrile containing chloride, N06022 undergoes pitting at much lower Cl– concentrations and temperature than in aqueous solutions. In order to understand the enhanced susceptibility to pitting and uniform corrosion in aprotic solvents, potentiodynamic polarizations and electrochemical impedance spectroscopy were performed in various solution compositions, followed by surface characterization with scanning electron microscopy. The correlation of passivation and breakdown phenomena with variables of importance, namely water content, chloride concentration, and acidity will be investigated. Ultimately, this study will provide fundamental understanding of the passivity of Ni-based alloys in organic solvents, assisting the selection of materials for nonaqueous applications.

Study of the Influence of Helical Milling Parameters on the Quality of Holes in the UNS R56400 Alloy

Helical milling has been positioned as an alternative to conventional drilling, where the advantages it offers make it very attractive for use on difficult-to-machine alloys such as the titanium alloy UNS R56400. However, the correlation between the indicator of hole quality and the kinematic parameters has rarely been studied. The kinematics are what bring most advantages and that is why it is necessary to know their influence. In this aspect, there are different focuses of problems associated with the complexity of the process kinematics, which makes it necessary to undertake a deeper analysis of the process and to carry out a preliminary study. To address this problem, a DOE (Design of Experiments) is proposed to identify the sensitivity and the main trends of the properties that define the quality holes with respect to the kinematic parameters. At the same time, a nomenclature is proposed to unify and avoid misinterpretations. This study has allowed us to obtain conclusive results that offer very relevant information for future research

Evaluation of microstructural and mechanical properties of dissimilar Inconel 625 nickel alloy–UNS S32205 duplex stainless steel weldment using MIG welding

Inconel 625 nickel alloy and UNS S32205 duplex stainless steel (DSS) were welded with ER2209 filler metal using MIG (Metal Inert Gas) welding method. The weld metal obtained by DSS filler metal was subjected to mechanical and microstructural evaluation. Toughness and hardness properties had been examined by mechanical and microstructural characterization of weld metal, fusion line, and HAZ (Heat Affected Zone) region, and precipitations were investigated by light microscopy (LM), scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS). Corrosion behavior of base metals and face and root of weld metal were examined by using potentiodynamic polarization test. Additionally, detailed elemental analysis and mapping of weld metal with both optical emission spectrometer (OES) and X-Ray spectrometer were attained. Results demonstrate a significant decrease in toughness of the welding due to the presence of Nb and Mo rich intermetallic precipitations in the Inconel HAZ and root region, although there is no significant increase in hardness. Potentiodynamic polarization test shows that the dilution-induced microstructural transformation in the root of weld has the worst corrosion resistance in the weld metal. Therefore, this dissimilar welding does not have optimum properties for neither toughness nor corrosion.

Feasibility Study of Hole Repair and Maintenance Operations by Dry Drilling of Magnesium Alloy UNS M11917 for Aeronautical Components

Magnesium alloys are increasingly used due to the reduction of weight and pollutants that can be obtained, especially in the aeronautical, aerospace, and automotive sectors. In maintenance and repair tasks, it is common to carry out re-drilling processes, which must comply with the established quality requirements and be performed following the required safety and environmental standards. Currently, there is still a lack of knowledge of the machining of these alloys, especially with regards to drilling operations. The present article studies the influence of different cutting parameters on the surface quality obtained by drilling during repair and/or maintaining operations. For this propose, an experimental design was established that allows for the optimization of resources, using the average roughness (Ra) as the response variable, and it was analyzed through the analysis of variance (ANOVA). The results were within the margins of variation of the factors considered: the combination of factor levels that keep the Ra within the established margin, those that allow for the minimization of roughness, and those that allow for the reduction of machining time. In this sense, these operations were carried out in the most efficient way.

Cutting speed and feed-rate influence on fatigue behavior of dry machined UNS A97075 alloy

Fatigue behavior takes a special relevance in manufacturing aeronautical parts due to safety reasons. Considering friendly environmental techniques, dry machining results in higher severe cutting conditions, which may negatively affect the part surface integrity, depending on cutting parameters values applied. In this sense, surface finish can be related to fatigue behavior. Notwithstanding, there is a lack of research that evaluates how cutting parameters affect fatigue life of aeronautical aluminum alloys, and their relationship with geometrical deviations. This work aims to analyze cutting speed and feed-rate influence on fatigue behavior of aeronautical aluminum alloy UNS A97075-T6 dry turned specimens. In order to do this, several rotating bar bending fatigue test have been carried out. Surface roughness have been also analyzed through the arithmetical mean roughness value (Ra) and the mean roughness depth (Rz). Results obtained seem to indicate that an increase of feed-rate and cutting speed negatively affects the fatigue life of the tested specimens, taking surface conditions a special influence in this behavior.

Technical and Economic Analysis on Bimetallic Clad Pipes for Sour Service

With the development of sour gas fields in China, the problem of corrosion protection about gathering and transporting pipes used in CO2/H2S-containing condition gradually appeared, and the demand for economic and technical anticorrosion measures became more and more urgent. As we known, non-metallic material could not give consideration to performance and price, carbon steel with corrosion inhibitor was sometimes still seriously corroded and corrosion resistant alloy pipes was too expensive to use independently. Moreover, for bimetallic lined pipes it had hard to get rid of some inherent safety risks. Therefore, bimetallic clad pipes might be the best options for sour service. In order to provide theoretical basis and technical support for engineering application, taking typical sour environment as an example, fit for purpose of materials, processes and cost about bimetallic clad pipes were conducted in this paper. By analyzing materials applicable range, comparing processes reliability and sorting out anticorrosion cost, the superiority about bimetallic clad pipes would be fully demonstrated from the perspective of technology and economy. The results showed that UNS N08825 rather than non-metallic pipe, carbon steel and low alloy steel, UNS S31603 and UNS S31803 could withstand corrosion in sour environments. Additionally UNS N08825 bimetallic clad pipes are more cheaper than UNS N08825, and more reliable than bimetallic lined pipes. Meanwhile UNS N08825 bimetallic clad pipes more economic than carbon steel with corrosion inhibitor in the whole life cycle. In summary, UNS N08825 bimetallic clad pipes, which has the greatest economic and technical superiority in the whole life cycle, might be suitable for sour service.

Influence of Abrasive Waterjet Parameters on the Cutting and Drilling of CFRP/UNS A97075 and UNS A97075/CFRP Stacks.

The incorporation of plastic matrix composite materials into structural elements of the aeronautical industry requires contour machining and drilling processes along with metallic materials prior to final assembly operations. These operations are usually performed using conventional techniques, but they present problems derived from the nature of each material that avoid implementing One Shot Drilling strategies that work separately. In this work, the study focuses on the evaluation of the feasibility of Abrasive Waterjet Machining (AWJM) as a substitute for conventional drilling for stacks formed of Carbon Fiber Reinforced Plastic (CFRP) and aluminum alloy UNS A97050 through the study of the influence of abrasive mass flow rate, traverse feed rate and water pressure in straight cuts and drills. For the evaluation of the straight cuts, Stereoscopic Optical Microscopy (SOM) and Scanning Electron Microscopy (SEM) techniques were used. In addition, the kerf taper through the proposal of a new method and the surface quality in different cutting regions were evaluated. For the study of holes, the macrogeometric deviations of roundness, cylindricity and straightness were evaluated. Thus, this experimental procedure reveals the conditions that minimize deviations, defects, and damage in straight cuts and holes obtained by AWJM.

Optimization of deep cryogenic treatment conditions for the wear rate of UNS R56400 (Ti6Al4V) medical titanium alloy using Taguchi’s method

ABSTRACTUsing the Taguchi’s method assisted design of experiments approach, this study presents systematic optimization of deep cryogenic treatment conditions for the wear behaviour of medical titanium alloy UNS R56400 (Ti6Al4V). In addition to different soaking durations and tempering temperatures, three pin-on-disk wear test variables i.e. sliding speed, contact pressure, and sliding time were used to conduct the tests. Pin-on-disk tribo-testing setup, under dry sliding wear conditions, is employed to slide Ti6Al4V against En31 steel in accordance with ASTM G99 standard. Experimentally found results were transformed to signal-to-noise ratios and results pertaining to the influence of controlled variables were statistically analyzed and optimized using ANOVA and F-test. Statistically optimized results are verified experimentally.Microstructural characterizations suggested that cryogenic treatment favours the precipitation of refinement of grain size and homogeneity in size distribution in the microstructure of alloy. The possible mechanism for improvement of wear property underlying microstructural modifications has been discussed.

Localized Corrosion of UNS A95052 Aluminum Alloy for Application in Multi-Effect Desalinator Plants

Aluminum alloy UNS A95052 (AA5052) is very attractive for desalination applications because of its good corrosion resistance in seawater at temperatures up to 125°C, low cost, good thermal conductivity, and non-toxicity of its corrosion products. The pitting corrosion potential, Epit, and the pit repassivation potential, Er,pit, of AA5052 were measured in deaerated 65,000 ppm sodium chloride (NaCl) solutions at 30°C, 60°C, and 85°C. Epit decreased with temperature, in accord with literature results. Er,pit was a function of anodic charge passed during pit growth stage. A complete evaluation of suitability of this alloy from a corrosion perspective requires also studies of crevice corrosion at different temperatures, considering that multi-plate designs of desalinators have metal plates in contact with rubber gaskets and seals. Cyclic potentiodynamic polarization was used to estimate crevice repassivation potentials, Er,crev, at 30°C, 60°C, and 85°C, in specimens with an attached rubber O-ring as a crevice former. This crevice former simulated the partially occluded geometry expected in desalination plants. Stable crevice corrosion potentials, Ecrev, were similar to Epit, and, when polarized to a similar anodic charge density, Er,crev were similar to Er,pit. Based on this result, from a corrosion perspective, the presence of crevices in the desalination plant is not expected to present an additional risk during operation of the plant. Electrochemical tests were also performed in saturated AlCl3 solutions to explain the results using Galvele’s localized acidification model.

Sensitivity analysis of the expansion process for alloy UNS N08028

Due to the good mechanical properties of forged parts, the forging process plays a decisive role in the manufacturing of seamless stainless steel pipes for oil country tubular goods (OCTG) lines. Tough competition between manufacturers gives them plenty of incentive to make their processes in raw material and energy usage more and more efficient. In this context the expansion process is one of the critical production steps in the manufacturing of seamless stainless steel pipes. This work presents a sensitivity analysis of a finite element method (FEM) for the simulation of the expansion of the alloy UNS N08028. The input parameters ram speed, tool angle, initial ID and final ID of the billet as well as temperature were used to describe responses like tool wear and material loss. With the aim to minimize the tool wear and to reduce the material waste, a study of influence of the input parameters on the mentioned responses were performed. This development is supported by experimental work in order to validate the simulation model. The sector demand for new materials with specific properties and the cost-intensive experimental trials justifies the use of such simulation tools and opens great opportunities for the industry.