The presently disclosed subject matter relates primarily to the technology of electropolishing. In some embodiments, the presently disclosed subject matter relates to the use of electrochemical-based surface treatments for achieving uniform surface material removal and surface finish improvements for metal components with complex external geometries.
Surface quality has long been a significant issue for powder bed fusion additive manufacturing (PBF-AM) processes. In addition to the staircase effect which is intrinsic to most additive manufacturing (AM) processes, PBF-AM processes also faces an additional challenge. As the powder in fabrication area is melted, heat transfer occurs inevitably, which causes the powder adjacent to the fabricated area to be partially sintered and attached to the part surface. The surface sintering effect not only reduces the geometrical accuracy of the fabricated geometries, but also creates surface defects which could serve as crack initiation sites. For structures with large surface-to-volume ratios such as cellular structure or honeycomb structures, surface properties can sometimes dominate the overall performance of the structures, which further highlights the significance of the issue. On the other hand, fatigue performance is of importance to many applications in aerospace, automobile and bi-devices, which are widely regarded as the most promising targeting markets of AM technologies. Therefore, surface quality improvement of PBF-AM fabricated structures is of importance for the future adoption of the technologies.
Various efforts have been reported in the attempt to improve the surface qualities of PBF-AM parts. Surface quality of the PBF-AM parts are largely influenced by process parameters (1-3). In some works, active process control such as surface re-melting (2, 4, 5), selection of fine powder (6) and the use of optimized parameters (7, 8) have been utilized to improve the surface quality of the parts. However, due to the intrinsic characteristics of the process, these in-process surface quality control methods only achieve limited effects.
On the other hand, multiple post-process surface treatment methods have also been used to improve the geometrical accuracy of the final parts. Traditional surface treatment methods such as machining (9, 10), mechanical polishing (11), abrasive flow polishing (12), chemical milling (2, 13) and electroplating (11) have been investigated for their efficiency in treating AM fabricated parts, and they achieved mixed results. With most of the surface treatment processes, geometrical complexity of the treated parts is a significant challenge. For example, mechanical polishing and machining can be difficult to apply on undercut features and internal features, and abrasive flow polishing can usually only achieve desired surface finish on selected surfaces due to the directional flow of the abrasive fluid. Chemical milling and electroplating both rely on the mass transportation between a polishing fluid and the workpiece and therefore are both capable of accessing surfaces as long as they are external. Chemical milling is capable of removing surface materials at a wide range of controlled rate, and it also leaves minimum residuals on the treated surface as long as the stirring or mass transportation is sufficient. However, chemical milling often does not completely eliminate surface features due to the isotropic etching effect.
As shown in
Therefore, processes and systems for selective smoothing of surface features and the improvement of surface finish, particularly for complex surfaces, of AM parts represent an unmet and continuing need in the art.
This summary lists several embodiments of the presently disclosed subject matter, and in many cases lists variations and permutations of these embodiments. This summary is merely exemplary of the numerous and varied embodiments. Mention of one or more representative features of a given embodiment is likewise exemplary. Such an embodiment can typically exist with or without the feature(s) mentioned; likewise, those features can be applied to other embodiments of the presently disclosed subject matter, whether listed in this summary or not. To avoid excessive repetition, this Summary does not list or suggest all possible combinations of such features.
In some embodiments, the presently disclosed subject matter relates to processes for treating surfaces of metal workpieces. In some embodiments, the methods comprise providing a metal workpiece having a surface comprising a complex external geometry; and contacting the workpiece in the presence of a predetermined electrical field at a predetermined temperature with a solution comprising electrolytes at a flow rate that varies according to a local shape of the surface to thereby treat the surface of the metal workpiece. In some embodiments, the temperature can be adjusted over a course of treatment or wherein the temperature is maintained substantially constant over a course of treatment. In some embodiments, a voltage of the electrical field is controlled by a DC power supply.
In some embodiments, the methods comprise providing the electrical field through a predetermined placement of a cathode and an anode, wherein the workpiece serves as the anode.
In some embodiments, the methods comprise adjusting a location and/or rotational angle of the cathode and the anode.
In some embodiments, the methods comprise adjusting a location and/or rotational angle of the cathode and/or the anode through a linear and/or rotational motion control mechanism.
In some embodiments, the linear and/or rotational motion control mechanism comprises a stepper motor or a gear motor.
In some embodiments, electrolyte flow circulation is controlled by a liquid pump system.
In some embodiments, the methods comprise comprising initially conducting a fluid flow simulation analysis for the workpiece whereby surface flow rate characteristics of the samples under different levels of overall electrolyte flow rates are estimated.
In some embodiments, the methods comprise comprising varying a location and/or a rotational angle of the workpiece numerous times or continuously during the process.
In some embodiments, the metal workpiece is produced by an advanced manufacturing technique.
In some embodiments, the presently disclosed subject matter also relates to systems for treating surfaces of metal workpieces. In some embodiments, the systems comprise a container for containing a metal workpiece having a surface comprising a complex external geometry and for containing a solution comprising electrolytes at a flow rate that varies according to a local shape of the surface to thereby treat the surface of the metal workpiece; one or more electrodes for creating an electrical field; and a temperature control device configured to provide a predetermined temperature or range of temperatures. In some embodiments, the container comprises a predetermined shape that directs flow of the electrolyte solution to the surface. In some embodiments, the container is configured to adjustably contain the workpiece such that a location and/or a rotational angle of the workpiece in the container can be adjusted.
In some embodiments, the presently disclosed systems comprise a DC power supply, wherein a voltage of the electrical field is controlled by the DC power supply.
In some embodiments, the one or more electrodes comprises a cathode and an anode and the electrical field is provided through a predetermined placement of the cathode and the anode, wherein the workpiece serves as the anode.
In some embodiments, a location and/or a rotational angle of the cathode and/or the anode are configured for linear and/or rotational motion control such that a location and/or a rotational angle of the cathode and the anode can be adjusted.
In some embodiments, the presently disclosed systems comprise a stepper motor or a gear motor, wherein stepper motor or the gear motor provide for linear and/or rotational motion control of the cathode and/or the anode.
In some embodiments, the temperature control device is configured so that the temperature can be adjusted over a course of treatment or wherein the temperature is maintained substantially constant over a course of treatment.
In some embodiments, the presently disclosed systems comprise a liquid pump system, wherein electrolyte flow circulation is controlled by the liquid pump system.
In some embodiments, the presently disclosed systems comprise a processor for initially conducting a fluid flow simulation analysis for the workpiece, whereby surface flow rate characteristics of the workpiece under different levels of overall electrolyte flow rates are estimated.
Accordingly, it is an object of the presently disclosed subject matter to provide processes and systems for electrochemical-based surface treatments of metal components. This and other objects are achieved in whole or in part by the presently disclosed subject matter. Further, an object of the presently disclosed subject matter having been stated above, other objects and advantages of the presently disclosed subject matter will become apparent to those skilled in the art after a study of the following description, Figures, and Examples. Additionally, various aspects and embodiments of the presently disclosed subject matter are described in further detail below.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawings will be provided by the United States Patent and Trademark Office upon request and payment of the necessary fee.
The presently disclosed subject matter relates in some embodiments to the use of electrochemical-based surface treatments for achieving uniform surface material removal and surface finish improvements for metal components with complex external geometries, usually produced by advanced manufacturing technologies such as additive manufacturing.
In representative, non-limiting Examples, the use of electropolishing in the surface treatment of Ti6Al4V metal parts made by powder bed fusion processes including direct metal laser sintering (DMLS) and electron beam melting (EBM) was investigated. A non-aqueous alcohol-based electrolyte was used, and the relationship between the process and surface roughness was evaluated. Based on the results, the feasibility of electropolishing as a post-surface treatment for additive manufactured metal parts was established.
I. General Considerations
Electropolishing is in principle the reverse of electroplating. The treated part is not connected as a cathode but as an anode, and when voltage is applied, the anode is polished by the removal of surface metal particles into electrolyte. Driven by electrical potential, the ionized particles from the treated workpiece will move towards the cathode enabled by the pathway provided by the electrolyte. Since the process is the reverse of electroplating, electropolishing is also driven by Faraday's Law, which means that the extruded features on the surface are selectively polished.
As the ion particles forms from the workpiece, they will need to be carried away sufficiently by the flow of the electrolyte. Thus, in establishing an electropolishing process and configuring an electropolishing system, consideration is given to the possible formation of a compact oxide layer at the newly polished surface. If the compact film could be readily dissolved by the electrolyte chemicals with the assist of electrical field, then the electropolishing process could continue with a characteristic equilibrium oxide layer on the surface of the anode that is sufficiently thin to allow for cations to diffuse. The thin oxide layer also prevents the etching effect when acidic solution is used since no selective chemical reaction at grain boundaries would take place. The higher viscosity and dissolution concentration at the valleys of the anode surface would eventually contribute to the smoothing effect of the electropolishing. There exists a threshold voltage potential for the breakdown of the oxide layer, which would result in significant gas generation and is usually avoided in the electropolishing process due to its tendency to deteriorate the polishing quality. Therefore, through careful adjustment of the process, electropolishing can effectively achieve selective smoothing of surface features and the improvement of surface finish. This feature, combined with the ability to access complex surfaces, enables the electropolishing as a desirable candidate for the surface treatment of AM parts.
In establishing an electropolishing process and configuring an electropolishing system, consideration is given to setting a voltage, such as a mildly high voltage, in order to sustain sufficient anode ionization while avoiding the onset of decomposition reaction of the oxide layer. Beside oxides, reaction products from the electropolishing process could also deposit on the workpiece surface under the effect of diffusion, which is sometimes undesired since it creates a barrier for mass transportation between the workpiece and the electrolyte and thus inhibit the electropolishing rate. Thus, in establishing an electropolishing process and configuring an electropolishing system, consideration is given to avoiding excessive oxide and precipitation layer formation on the workpiece surface through establishing a flow of electrolytes, such as by stirring, agitation or flow guiding of the electrolytes.
Further, in establishing an electropolishing process and configuring an electropolishing system, consideration is given to particular potential-current relationship(s) that contribute(s) towards desired electropolishing parameters. This relationship is impacted by the type of material and electrolyte used in the process. In a representative relationship, the current would increase approximately linearly at low potential levels until it reaches a threshold, after that there exists a plateau stage in which the current keeps more or less constant as the potential increases. At this stage, the electropolishing is dominated by mass transportation phenomenon. The ions diffuse through the surface layer at a stable rate, creating electropolishing current that is little dependent on the voltage level. When the potential is sufficiently high, the current will start to increase again in a more drastic rate, which is often referred to as chemical pitting. At this stage, significant breakdown of either the electrolyte or oxide layer could occur, and the resulting part surface is often affected by pitting effect.
Other factors such as temperature and water content in the electrolyte are also considered. Higher temperature could promote the mass transportation and therefore facilitate the polishing reaction; however, it could also cause unwanted decomposition reactions. On the other hand, water content in the electrolyte should also be controlled carefully according to the process needs, since it could facilitate the formation of the oxidation film of the surface.
Thus, the presently disclosed subject matter involves multiple aspects, including but not limited to: (1) the design of the treatment apparatus or system that can enable accurate control of various process variables such as solution temperature, electrical voltage, electrode spacing, and electrolyte flow rate; (2) the pre-processing analysis of the optimum manner of placement (e.g., orientation, location) of the samples in the electropolishing container in order to ensure uniform polishing rates; and (3) secondary subsystems or components in the treatment apparatus that can achieve accurate manipulation of the electrolyte flow field characteristics.
II. Processes and Systems
Provided in accordance with some embodiments of the presently disclosed subject matter is a process for treating a surface of a metal component or workpiece, such as a surface having a complex external geometry. In some embodiments, the method comprises providing a metal workpiece having a surface, such as a surface comprising a complex external geometry; and contacting the workpiece in the presence of a predetermined electrical field at a predetermined temperature with a solution comprising electrolytes at a flow rate that varies according to a local shape of the surface to thereby treat the surface of the metal component. In some embodiments, the metal component or workpiece is produced by an advanced manufacturing technique, examples of which are described elsewhere herein.
By “predetermined electrical field” it is meant to refer to an electrical field chosen based on the workpiece to be treated, including the material the workpiece comprises and the surface geometry of the workpiece. By way of example and not limitation, consideration is given to setting a voltage, such as a mildly high voltage, in order to sustain sufficient anode ionization while avoiding the onset of decomposition reaction of the oxide layer. Consideration is given to particular potential-current relationship(s) that contribute(s) towards desired electropolishing parameters. This relationship is impacted by the type of material and electrolyte used in the process. In a representative relationship, the current would increase approximately linearly at low potential levels until it reaches a threshold, after that there exists a plateau stage in which the current keeps more or less constant as the potential increases. At this stage, the electropolishing is dominated by mass transportation phenomenon. The ions diffuse through the surface layer at a stable rate, creating electropolishing current that is little dependent on the voltage level. When the potential is sufficiently high, the current will start to increase again in a more drastic rate, which is referred to as chemical pitting. At this stage, significant breakdown of either the electrolyte or oxide layer occurs, and the resulting part surface is often affected by pitting effect. Additional guidance for electric field parameters, such as but not limited to voltages and voltage ranges, can be found in the Examples and Figures discussed elsewhere herein. Typically, the desired electrical voltage should introduce relatively stable electropolishing rate that is less sensitive to the fluctuation of the voltage control, which corresponds to the plateau voltage range in the case that the oxide-film induced process occurs. In some embodiments, a voltage in the range of 50 to 150 volts is employed, including 50, 60, 70, 80, 90 and 100 volts. In some embodiments, a voltage of the electrical field is controlled by a DC power supply. In some embodiments, a voltage of the electrical field is controlled by a DC power supply with a waveform modulation function. In some embodiments, the voltage chosen provides a desired current or current density, such as but not limited to 0 to 5 A current and/or 6-8 kA/m2 current density.
In some embodiments, the electrical field is provided through a predetermined placement of a cathode and an anode. Here as well, the placement of the cathode and anode is based on the workpiece to be treated, including the material the workpiece comprises and the surface geometry of the workpiece. In some embodiments, the workpiece acts as the anode. In some embodiments, the process comprises adjusting a location and/or rotational angle of the cathode and the anode relative to a flow of electrolytes. In some embodiments, adjusting a location and/or rotational angle of the cathode and/or the anode through a linear and/or rotational motion control mechanism. In some embodiments, the linear and/or rotational motion control mechanism comprises a stepper motor or a gear motor. In some embodiments, the rotational angle is varied by rotating the workpiece by a predetermined angle, such as but not limited to 90° during the course of treatment. In some embodiments, the time of treatment ranges for 1 minute to 30 minutes, including 1, 5, 10, 15, 20, 25, and 30 minutes. In some embodiments, the distance between electrodes ranges from 1 to 10 mm, including 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 mm. Adequate polishing time should be allowed for the electropolishing effect to be apparent. For example, apparent electropolishing effect might become apparent after 20 minutes of polishing.
By way of elaboration and not limitation, a sample that after electropolishing at 60V+5 mm+20 minutes setup, and the best surface finish at some area achieves Ra<100 nm, a significant reduction from the original value of such as Ra>20 μm. Robust correlations among the electric field (related to various parameters, such as voltage and distance), the electrolyte flow, and the polishing rate guide the design of process and system embodiments and the achievement of better control of the process and system for the reduction of the polishing rate variability.
Further, in establishing an electropolishing process and configuring an electropolishing system, consideration is given to avoiding excessive oxide and precipitation layer formation on the workpiece surface through establishing a flow of electrolytes, such as by flowing electrolytes over the workpiece. In some embodiments, flowing the electrolytes over the workpiece is controlled by a liquid pump system, such as but not limited to a peristaltic pump. Additional guidance for electrolyte flow parameters, such as but not limited to flow rates, ranges of flow rates, establishing laminar flow or other flow criteria, can be found in the Examples and Figures discussed elsewhere herein. In some embodiments, the flow rate ranges from 800 mL/minute to 1,200 mL/minute. In some embodiments, laminar flow is provided. In some embodiments, the electrolyte flow field can be fine-tuned via introducing variable-rate flow rate functions (e.g. sinusoidal flow rate), the use of specifically-designed electrolyte reaction container, and/or utilizing acoustic arrays and/or utilizing flow filters. For example, the use of electrolyte reaction container could potentially enhance the control of the flow rate of the electrolyte across a specimen with flat surface features. For another example, when non-differentiating electrolyte flow is desired, a flow filter with hole patterns could be implemented inside the inlet of the electrolyte reaction container to introduce turbulent flow across the entire specimen. For yet another example, an array of ultrasonic transducers could be installed on the sides of the electrolyte container walls, which will then introduce periodic vibration waveform of various patterns, such as sinusoidal, checkerboard or even more complex ones across the entire electrolyte fluid. Consequently, specific areas of the specimen surface achieve higher polishing rates, whereas other areas archive lower polishing rates.]
By “predetermined temperature” it is meant a temperature or temperature range chosen based on the workpiece to be treated, including the material the workpiece comprises and the surface geometry of the workpiece. By way of example and not limitation, a higher temperature, e.g. above room temperature, could promote the mass transportation and therefore facilitate the polishing reaction. However, the temperature or temperature range should not be so high as to cause unwanted decomposition reactions. In some embodiments, the temperature can be adjusted over a course of treatment. In some embodiments, the temperature is maintained substantially constant over a course of treatment. In some embodiments, the temperature ranges from 60° F. to 100° F., including 60° F., 70° F., 80° F., 90° F., and 100° F. For example, when the non-aqueous solution (700 mL ethanol, 300 mL isopropyl alcohol, 60 g aluminum chloride, 300 g zinc chloride) is used to electropolish the Ti6Al4V PBF-AM parts, a temperature window of 60° F.-100° F. can be selected. Lower temperature could potentially halt the electropolishing reaction, whereas higher temperature could potentially cause the decomposition of the chloride ingredients through accelerated exothermal electropolishing reaction.
In some embodiments, the process comprises initially conducting a fluid flow simulation analysis for the workpiece. In some embodiments, the fluid flow analysis comprises various fixing locations and/or rotational angles of the workpiece, whereby surface flow rate characteristics of the workpiece under different levels of overall electrolyte flow rates are estimated. In some embodiments, the workpiece fixing locations and/or rotational angles are adjusted to achieve a desired uniform overall surface flow rates across the exterior surface of the workpiece. In some embodiments, the rotational angle is varied by rotating the workpiece by a predetermined angle, such as but not limited to 90°, during the course of treatment. In some embodiments, the time of treatment ranges for 1 minute to 20 minutes, including 1, 5, 10, 15 and 20 minutes.
In some embodiments, during simulation, actual treatment, or both, dynamic workpiece-electrode orientation and/or electrode spacing can be adopted by varying the location and/or rotational angle of the samples numerous times or even continuously during the simulation, the surface treatment process, or both. In some embodiments, during simulation, actual treatment, or both, flow characteristics of the electrolyte can be further controlled and/or adjusted by implementing more advanced liquid flow control methods. Representative such techniques include but are not limited to use of the ultrasonic waveform generating transducer array, combined by continuous reorientating of the specimens during the polishing process, controlled by a motorized fixture. In some embodiments, the rotational angle is varied by rotating the workpiece by a predetermined angle, such as but not limited to 90° during the course of treatment. In some embodiments, the time of treatment ranges for 1 minute to 20 minutes, including 1, 5, 10, 15 and 20 minutes.
In some embodiments of the presently disclosed subject matter, an electropolishing system is provided. In some embodiments, the system configured to control one or process variables, such as solution temperature, electrical voltage, electrode spacing, and/or electrolyte flow rate. In some embodiments, a secondary subsystem in the system that achieves accurate manipulation of the electrolyte flow field characteristics is provided.
The solution temperature of the electrolyte can be adjusted by typical methods with target temperatures such as condenser heat exchanger or methods with to provide a temperature such as ice-water bath. The electrical voltage is typically controlled by a DC power supply with waveform modulation functions (e.g. capable of achieving step functions or sinusoidal functions with the DC voltage). The electrode spacing control is achieved by adjusting the locations and rotational angles of both the cathode and the anode (workpiece) through linear and rotational motion control mechanisms such as stepper motor or gear motor. The electrolyte flow circulation is controlled by typical liquid pump systems (e.g. peristaltic pump).
In some embodiments, for each new incoming sample or workpiece, fluid flow simulation analysis for the samples at various fixing locations and rotational angles are carried out, the surface flow rate characteristics of the samples under different levels of overall electrolyte flow rates are estimated. The sample fixing locations and rotational angles can be adjusted to achieve the most uniform overall surface flow rates across the exterior surfaces of the samples. Alternatively, dynamic sample-electrode orientation or electrode spacing can be adopted by varying the location and rotational angle of the samples/workpieces numerous times or even continuously during the surface treatment process.
Besides the controllability of location and rotational angles of the samples either continuously or intermittently, the flow characteristics of the electrolyte can be further controlled and adjusted by implementing more advanced liquid flow control methods. In addition to the overall flow rate control through the pump, the electrolyte flow field can be fine-tuned via introducing variable-rate flow rate functions (e.g. sinusoidal flow rate) or utilizing acoustic arrays.
Referring now to the Figures, wherein like reference numerals refer to like parts throughout, and referring particularly to
Continuing with reference to
Continuing with reference to
In some embodiments, a non-aqueous electrolyte is employed in the methods and systems of the presently disclosed subject matter. In some embodiments, the electrolyte comprises ethanol, isopropyl alcohol, aluminum chloride and zinc chloride. In some embodiments, a 1 L solution of the electrolyte comprises 700 mL of ethanol, 300 mL of isopropyl alcohol, 60 g AlCl3 and 250 g ZnCl2. Any desired volume of electrode can be used, such as but not limited to about 100 mL of electrolyte, about 200 mL of electrolyte, about 300 mL of electrolyte, about 400 mL of electrolyte, or about roughly 500 mL of electrolyte. Depending on the types of materials, other electropolishing solutions can be considered. For example, when Ti6Al4V or nickel alloy is polished, other solutions such as hydrofluoric acid and perchloric acid.
Representative metals include Ti6Al4V and Inconel 718 (IN718). Metal workpieces can be fabricated via any suitable technique as would be apparent to one of ordinary skill in the art upon a review of the instant disclosure. Representative processes include electron beam melting additive manufacturing process and laser melting powder bed fusion. Typical starting surface finish is around mean roughness (Ra)=20-40 μm. The electropolishing achieved surface finish can be Ra<1 μm. Titanium alloys have been notoriously difficult to process with chemical and electrochemical methods. Due to the existence of the highly stable oxide thin film on the surface, traditionally only a few acids could effectively react with titanium alloys, including hydrofluoric acid and perchloric acid. These chemicals are highly hazardous and could cause serious accidents if not used with extreme care. Ti6Al4V is the most widely used material for EBM processes, which sees many potential applications in aerospace and biomedical industries. The surface finish of typical EBM parts ranges between Ra 20-30 μm. The surface finish of the top surface is usually slightly better, while the sides are usually rougher. Due to the use of relatively coarse powder compared to the laser based PBF-AM process and the larger size of the electron beam, the surface quality issue is more significant with the EBM process.
Metal workpieces to be treated can be any desired sized. By way of example and not limitation, metal workpieces can be plates with a flat surface area of 5 mm×20 mm
The presently disclosed subject matter considers relationships between various process parameters (temperature, electrical voltage, electrode spacing, polishing time). The significance of the flow characteristic to the surface treatment is considered by evaluating the surface finish of samples under various circulation flow rate and container designs.
The process and system setup and guidelines are configured based on additional electrolyte flow simulations. Such simulations establish effective spacing and part orientation strategies that ensure uniform surface material removal rate and surface quality improvement by assessing possible geometry options of the parts and consequently possible flow characteristics.
Headings are included herein for reference and to aid in locating certain sections. These headings are not intended to limit the scope of the concepts described therein under, and these concepts may have applicability in other sections throughout the entire specification.
In describing and claiming the presently disclosed subject matter, the following terminology will be used in accordance with the definitions set forth below.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the presently disclosed subject matter.
In describing the presently disclosed subject matter, it will be understood that a number of techniques and steps are disclosed. Each of these has individual benefit and each can also be used in conjunction with one or more, or in some cases all, of the other disclosed techniques.
Accordingly, for the sake of clarity, this description will refrain from repeating every possible combination of the individual steps in an unnecessary fashion. Nevertheless, the specification and claims should be read with the understanding that such combinations are entirely within the scope of the presently disclosed subject matter and the claims.
All technical and scientific terms used herein, unless otherwise defined below, are intended to have the same meaning as commonly understood by one of ordinary skill in the art. References to techniques employed herein are intended to refer to the techniques as commonly understood in the art, including variations on those techniques or substitutions of equivalent techniques that would be apparent to one of skill in the art. While the following terms are believed to be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter.
While the following terms are believed to be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter.
As used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. For example, a nucleic acid molecule refers to one or more nucleic acid molecules. As such, the terms “a”, “an”, “one or more” and “at least one” can be used interchangeably. Similarly, the terms “comprising”, “including” and “having” can be used interchangeably. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like, in connection with the recitation of claim elements, or use of a “negative” limitation.
Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, some embodiments includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms an embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. It is also understood that when a value is disclosed that “less than or equal to” the value, “greater than or equal to the value” and possible ranges between values are also disclosed, as appropriately understood by the skilled artisan. For example, if the value “10” is disclosed, then “less than or equal to 10” as well as “greater than or equal to 10” are also disclosed. It is also understood that the throughout the application, data are provided in a number of different formats, and that these data represent in some embodiments endpoints and starting points and in some embodiments ranges for any combination of the data points. For example, if a particular data point “10” and a particular data point “15” are disclosed, it is understood that greater than, greater than or equal to, less than, less than or equal to, and equal to 10 and 15 are considered disclosed as well as between 10 and 15. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.
The term “and/or”, when used in the context of a list of entities, refers to the entities being present singly or in combination.
The terms “optional” and “optionally” as used herein indicate that the subsequently described event, circumstance, element, and/or method step may or may not occur and/or be present, and that the description includes instances where said event, circumstance, element, or method step occurs and/or is present as well as instances where it does not.
In a further Example, a process in accordance with the presently disclosed subject matter is illustrated in
Referring to
Continuing with reference to
This Example relates to the use of a non-aqueous alcoholic solution as disclosed herein for the electropolishing of IN718 fabricated via laser melting PBF-AM. Various process parameters including the electrode spacing, voltage, temperature and polishing time all have significant effects on the surface qualities were investigated for IN718.
The electropolishing station configuration is shown in
The workpiece design is shown in
To investigate the effect of each parameter on the surface quality of the IN718 parts, a 52 full factorial experimental design was developed. As shown in Table 1, five input variables, including temperature, electrode spacing, voltage, flow rate and split configuration were investigated, with each variables having 2 levels. For the electrolyte, the following recipe was used: 1 L of electrolyte comprises: 700 mL of ethyl alcohol, 300 mL of isopropyl alcohol, 60 g AlCl3 and 250 g ZnCl2. 1 sample was polished for each parameter combinations. After polishing, the surface roughness of the samples were measured with a Dektak 8 profilometer along the longest direction (i.e. build direction 14c as shown in
In the fluid flow simulations, the viscosity value of the electrolyte was taken as 9.58 cP, which was obtained via the measurement with the fresh electrolyte solution using viscometer. The effect of temperature on viscosity was ignored during the simulation. The measured surface roughness of the as-received sample was used to set up surface roughness in the simulations. The electrode spacing was set to be 7 mm for all the simulations.
The typical surface profile of the as-received IN718 samples is shown in
Further analysis with the results using ANOVA provided additional insights into the significance of each design factors and their interactions.
As shown in
The better-regulated electrolyte flow control with the split configuration also appears to have some effects on the uniformity of the surface roughness, although the effect is not as significant.
The significance of the interaction between the voltage and the factors for flow control (flow rate, split configuration) might be a result of the change of significance of the ion mass transportation through the electrolyte due to the reaction rate change. With higher electropolishing voltage the ion release rate from the sample might be enhanced, which would facilitate the mass transportation limiting electropolishing mechanism that is highly influenced by the electrolyte flow. On the other hand, the relatively low significance levels for various factors might be a result of the fact that relatively low electropolishing rates were observed in the experiments, which might correspond to a more “passive” electropolishing process that is dominated by macromachining. This electropolishing mechanism tends to be less sensitive to the electrolyte flow and would reduce large features more effectively while lacks the efficiency to reduce micro-protrusions on the part surfaces. In addition, the lack of accurate control of temperature (i.e. via the use of ice water that establishes an open-loop control) might also have contributed to the low significance of temperature factor.
In this study, an experimental design was employed to evaluate the significance of various process variables (voltage, temperature, electrode spacing, electrolyte flow rate and flow rate uniformity) on the surface quality of the IN718 parts fabricated via laser melting PBF-AM process. Overall, the use of electropolishing was able to achieve average surface roughness of Ra˜3 μm that is a significant improvement compared to the original surfaces.
The voltage used for the experiment might not have achieved a significant level to introduce mass transportation limiting polishing mechanism.
This Example relates to the corrosion-resistant electrolyte circulation system 10 shown in
In this example, a lack of a plateau stage was observed, as was a reaction rate sensitive to temperature. Voltages selected were 60-80V and 6-8 kA/m2 current density was provided. Treatment temperatures ranged from 38 C to 27 C. See
Mechanical property enhancement was also evaluated. Modified fatigue testing samples fabricated on an Arcam EBM S400. 60V-100F (
Tensile-tensile cyclic loading was tested. Ultimate static strength used as reference R=0.25 and R=0.30 determined based on crack initiation mode. Surface defect induced crack initiation for as received samples. Fatigue life (as-received) ˜450,000. The test was stopped for some samples before failure 80V-80F: Fatigue life >1,675,000 60V-100F: Fatigue life >3,396,000. See
The presently disclosed methods and systems are advantageous compared to the traditional non-solution based surface treatments such as mass finishing methods (e.g. vibratory tumbling), as the use of solution ensures that all exterior surfaces could be accessed for surface treatment. In addition, the combined utilization of chemical reaction and electrical potential allowed for enhanced process control that improves the uniformity of the surface treatment effects.
The presently disclosed methods and systems are also advantageous compared to the other solution-based surface treatment methods. Compared to an abrasive flow polishing method (Microtek Micro Machining Process—MMP), the presently disclosed methods and systems do not impose geometry limitations to the components, and also afford more isotropic surface treatment effects. Compared to the electropolishing method by Extrude Hone (available under the trademark COOLPULSE™), the presently disclosed methods and systems reduce and even eliminate the need of specialized electrodes, which can impose considerable geometrical limitations. In addition, other electropolishing based methods do not involve any control of the electrolyte flow, but instead aim to keep it consistent, whereas in some embodiments of the presently disclosed methods and systems the control of surface polishing effect is largely accomplished via the manipulation of the electrolyte flow.
All references cited in the instant disclosure, including but not limited to all patents, patent applications, and publications thereof, scientific journal articles, and database entries, are incorporated herein by reference in their entireties to the extent that they supplement, explain, provide a background for, or teach methodology, techniques, and/or compositions employed herein.
It will be understood that various details of the presently disclosed subject matter can be changed without departing from the scope of the presently disclosed subject matter. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/716,018, filed Aug. 8, 2018, the disclosure of which is incorporated herein by reference in its entirety.
This presently disclosed subject matter was made with government support under Grant No. #SC-2019-004, OGMB160057 awarded by the National Aeronautics and Space Administration (NASA) and Grant No. RID-3 #7800003125_OGMB160476 awarded by the National Science Foundation (NSF). The government has certain rights in the presently disclosed subject matter.
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Number | Date | Country | |
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62716018 | Aug 2018 | US |