Powder cleaning systems and methods

A powder cleaning system can include a fluidized bed reactor configured to retain powder and fluidize the powder to remove adsorbate and/or other contaminants from the powder, at least one inlet line, and one or more gas sources configured to be in selective fluid communication with the fluidized bed reactor via the at least one inlet line to selectively provide an inlet flow having one or more gases to the fluidized bed reactor to fluidize the powder with the one or more gases within the fluidized bed reactor. The system can include at least one outlet line in fluid communication with the fluidized bed reactor and configured to allow removal of outlet flow which comprises the adsorbate and/or other contaminants from the fluidized bed reactor.

BACKGROUND

The present disclosure relates to powder, e.g., for additive manufacturing.

2. Description of Related Art

For superalloys (e.g. Fe—Ni based, Ni based, and Co based), the relation between surface adsorbed species and mechanical properties (i.e. after densification) has been well documented. Significant effects of oxygen levels on tensile, impact, and creep properties, etc. have been reported. Oxygen at powder surfaces can contribute significantly to the weakening of interparticle boundaries. A prior particle boundary (PPB) issue has been observed during hot isostatic pressing (HIP) and selective laser melting (SLM) of IN718 superalloy.

The presence of highly stable surface oxides has been shown to have detrimental effects on HIP and SLM. The PPB issue was shown to result from surface contamination with pre-alloyed powder and oxide particles formed along the PPB. The precipitates are very brittle, thereby potentially providing a fracture path. Thus, use of traditional powder result in limits placed on consolidated products formed from the powder. Despite significant efforts to reduce the effects of PPB's, and thereby extend the life of related products (e.g., with aerospace applications), there is still no effective and reliable method to do so.

Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved powder cleaning systems and methods. The present disclosure provides a solution for this need.

SUMMARY

A powder cleaning system can include a fluidized bed reactor configured to retain powder and fluidize the powder to remove adsorbate and/or other contaminants from the powder, at least one inlet line, and one or more gas sources configured to be in selective fluid communication with the fluidized bed reactor via the at least one inlet line to selectively provide an inlet flow having one or more gases to the fluidized bed reactor to fluidize the powder with the one or more gases within the fluidized bed reactor. The system can include at least one outlet line in fluid communication with the fluidized bed reactor and configured to allow removal of outlet flow which comprises the adsorbate and/or other contaminants from the fluidized bed reactor.

The system can include a filter for capturing particles, the filter disposed in the at least one outlet line. The system can include a liquid trap disposed downstream of the filter and configured to trap liquid entrained in the outlet flow. The liquid trap can include a vent for venting gas of the outlet flow.

The inlet line can include at least one inlet line valve configured to selectively allow flow from the one or more gas sources to the fluidized bed reactor. The system can include a bypass line configured to fluidly connect the inlet line and the liquid trap to allow at least some gas in the inlet line to flow to the vent, wherein the bypass line includes a bypass valve configured to selectively allow bypass flow.

The system can include a pressure release valve (PRV) disposed in the inlet line to allow bleeding of pressure above a threshold pressure. The system can include a pressure sensor downstream of the PRV.

The at least one inlet line valve can be downstream of the pressure sensor. The one or more gas sources can each include a source valve and/or a mass flow controller (MFC) for controlling an amount and/or proportion of each gas in the inlet flow. The one or more gas sources can include at least one of an argon (Ar) source, an ammonia (NH3) source, a nitrogen (N2) source, a hydrogen (H2) source or a helium (He) source.

The fluidized bed reactor can include an outer housing defining an outer space and a powder container disposed within the outer space and defining an inner space. The fluidized bed reactor can include a gas distributor plate between the outer space and the inner space at the bottom of the powder container. The gas distributor plate can include a plurality of holes smaller than particles of the powder configured to prevent powder from falling through the plate and to allow the inlet gas to pass therethrough into the powder within the powder container to fluidize the powder. The inlet line can be in fluid communication with the outer space and the outlet line is in fluid communication with the inner space such that inlet gas must flow through the gas distributor plate and the powder.

In certain embodiments, a temperature sensor can be disposed in thermal communication with the outer space to sense a temperature of the inlet gas, and a temperature sensor in thermal communication with the outlet line to sense a temperature of the outlet gas. In certain embodiments, the system can include a heater or cooler disposed in thermal communication with the inlet flow to control the temperature of the inlet flow.

A method for cleaning a powder can include fluidizing powder in a fluidized bed reactor with an inlet gas to remove adsorbate and/or other contaminants to produce cleaned powder. Fluidizing powder includes flowing gas through the powder in a direction opposite to gravity. The inlet gas can include at least one of argon (Ar), ammonia (NH3), nitrogen (N2), hydrogen (H2), or helium (He). Fluidizing the powder can be performed after at least one of powder production, powder characterization and/or testing, and/or powder processing. Fluidizing powder can include controlling a temperature and/or pressure of the inlet gas as a function of one or more powder characteristics. The method can include sintering the cleaned powder to form an additively manufactured article.

DETAILED DESCRIPTION

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, an illustrative view of an embodiment of a system in accordance with the disclosure is shown inFIG. 1and is designated generally by reference character100. Other embodiments and/or aspects of this disclosure are shown inFIG. 2. The systems and methods described herein can be used to clean powder (e.g., removing moisture and oxygen adsorbed by the powder) used for additive manufacturing (e.g., alloy powder), for example, Selective Laser Melting (SLM), Direct Metal Laser Sintering (DMLS), Electron Beam Melting (EBM), etc.

Referring toFIG. 1, a powder cleaning system100can include a fluidized bed reactor101configured to retain powder103and fluidize the powder103to remove adsorbate (e.g., moisture, oxygen) and/or other contaminants (e.g., dirt or other impurity) from the powder103. The system100can include one or more gas sources105configured to be in selective fluid communication with the fluidized bed reactor101via at least one inlet line107to selectively provide an inlet flow109having one or more gases to the fluidized bed reactor101to fluidize the powder103with the one or more gases within the fluidized bed reactor101. The system100can include at least one outlet line111in fluid communication with the fluidized bed reactor101which can be configured to allow removal of outlet flow113which comprises the adsorbate and/or other contaminants from the fluidized bed reactor101.

The system100can include a filter115for capturing particles, the filter115disposed in the at least one outlet line111. The system100can include a liquid trap117disposed downstream of the filter115and configured to trap liquid and/or powder entrained in the outlet flow113. The liquid trap117can include a vent119for venting gas of the outlet flow113, for example.

The inlet line107can include at least one inlet line valve121configured to selectively allow flow from the one or more gas sources105to the fluidized bed reactor101. The system100can include a bypass line123configured to fluidly connect the inlet line107and the liquid trap117to allow at least some gas in the inlet line107to flow to the vent119. The bypass line123can include a bypass valve125configured to selectively allow bypass flow. In certain embodiments, the bypass line123and bypass valve125can be utilized to prevent pressure spikes in the fluidized bed reactor101. In certain embodiments, the bypass valve125and the inlet line valve121can be a single three way valve to select between open, closed, or bypass, or to regulate between open and bypass states in any suitable manner.

The system100can include a pressure release valve (PRV)127disposed in the inlet line107(e.g., downstream of the bypass line123) and configured to allow bleeding of pressure above a threshold pressure. The PRV127can be or include a check valve, for example, or any other suitable valve (e.g., to actuate a threshold pressure to avoid overpressure of the reactor101). The system100can include a pressure sensor129downstream of the PRV127, for example, or in any other suitable location in the inlet line127.

The at least one inlet line valve121can be downstream of the pressure sensor129. The one or more gas sources105can each include a source valve131and/or a mass flow controller (MFC)133for controlling an amount and/or proportion of each gas in the inlet flow109. The one or more gas sources105can include at least one of an argon (Ar) source, an ammonia (NH3) source, a nitrogen (N2) source, a hydrogen (H2) source, or a helium (He) source, or any combination thereof, e.g., as shown.

The fluidized bed reactor101can include an outer housing101adefining an outer space101band a powder container101cdisposed within the outer space101band defining an inner space101d. The fluidized bed reactor101can include a gas distributor plate101ebetween the outer space101band the inner space101dat a bottom of the powder container101cas shown. The gas distributor plate101ecan include a plurality of holes smaller than particles of the powder103configured to prevent powder103from falling through the plate101eand to allow the inlet gas109to pass therethrough into the inner space101dto fluidize the powder103within the powder container101c. As shown, the inlet line107can be in fluid communication with the outer space101band the outlet line111can be in fluid communication with the inner space101dsuch that inlet gas109must flow through the gas distributor plate101eand the powder103.

In certain embodiments, a temperature sensor135can be disposed in thermal communication with the outer space101bto sense a temperature of the inlet gas109, and a temperature sensor135can be disposed in thermal communication with the outlet line111to sense a temperature of the outlet gas113. In certain embodiments, the system100can include a heater or cooler disposed in thermal communication with the inlet flow109(e.g., in inlet line107) to control a temperature of the inlet flow109.

In certain embodiments, the system can include a controller (not shown) operatively connected to each of the valves121,125,131and/or sensors129,135to control a state of the system100. The controller can include any suitable software and/or hardware modules to perform any suitable function, e.g., those disclosed herein. For example, at start up, the controller can open the bypass valve125before or while opening one or more of the source valves131and/or inlet line valve121to prevent a pressure spike in the fluidization bed reactor101. The controller can close the bypass valve125after steady state operation is reached either completely and/or partially to regulate pressure to the fluidization bed reactor101. Any valve disclosed herein can be a shut off valve or a pressure regulating valve, or any other suitable valve. For example, inlet line valve121can be configured to regulate pressure.

The controller can be operatively connected to a heater or cooler to control the temperature of the inlet gas. In certain embodiments, the controller can include settings configured to provide a certain pressure, gas mixture or type, and temperature to the inlet flow109based on one or more powder characteristics (e.g., powder type, particle size, powder chemistry, amount of powder).

Referring toFIG. 2, a method200for cleaning a powder can include fluidizing powder in a fluidized bed reactor with an inlet gas to remove adsorbate and/or other contaminants to produce cleaned powder. Fluidizing powder includes flowing gas through the powder in a direction opposite to gravity. The inlet gas can include at least one of argon (Ar), ammonia (NH3), nitrogen (N2), hydrogen (H2), or helium (He).

As shown, fluidizing the powder can be performed after at least one of powder production, powder characterization and/or testing, and/or powder processing. Fluidizing powder can include controlling a temperature and/or pressure and/or a gas composition of the inlet gas as a function of one or more powder characteristics. The method can include sintering the cleaned powder to form an additively manufactured article.

In certain embodiments, argon, nitrogen, and/or helium can be used for removing oxygen and moisture adsorbed by the powder, and ammonia, hydrogen, and/or nitrogen can be used to treat powder after removal of the adsorbed oxygen and moisture. Any single gas and/or any combination (e.g., diluted ammonia) can be used.

Certain embodiments can utilize a fluidized bed reactor to displace undesirable adsorbed species (i.e. oxygen, moisture, etc.) on superalloy powder surfaces, for example. Embodiments of the reactor technique involve suspending solid particles by upward fluid flow. Rapid heat and mass transfer between the gas and solid particles can provide an alternative approach to other powder treatment methods. The treatment conditions (i.e. fluidization velocity, temperature, time, gas compositions, etc.) can be determined on a case-by-case basis according to the superalloy powder properties (e.g. particle diameter, density, etc.), surface oxygen contamination, and desired level of oxygen removal. Embodiments provide a flexible, economically feasible, and scalable method of uniform particle mixing and temperature gradients. Embodiments can remove surface oxygen without affecting bulk structure or morphology.

In certain embodiments, the first step in powder metallurgy (PM) processes can be the fabrication of metal powders. Removal of surface oxygen by fluidized bed gas reaction can be implemented at a several stages during the fabrication process as well as along the pathway of generating a finished part. Example processes used in powder production include solid-state reduction, atomization, electrolysis, and chemical.

In solid-state reduction, an ore material is first crushed (usually mixed with carbon), and passed through a furnace whereby the carbon and oxygen are reduced from the powder leaving behind a compacted sponge metal which crushed, separated from all non-metallic material, and sieved.

In the atomization process, molten metal is separated into small droplets and frozen rapidly before the drops come into contact with each other or with a solid surface. The technique is applicable to all metals that can be melted.

Electrolysis is carried out by selecting conditions, such as electrolyte composition and concentration, temperature, and current density, many metals current density whereby metals are deposited in a spongy or powdery state. Subsequent processing such as washing, drying, reducing, annealing, and crushing is often required to produce high-purity and high-density powders. However, due to high energy costs, this process is typically limited to high-value powders.

The chemical method is the most common whereby chemical powder treatments involve oxide reduction, precipitation from solutions, and thermal decomposition. The powders produced can have a great variation in properties and yet have closely controlled particle size and shape.

Embodiments can be used as post-processing stage associated with any of the processes mentioned above, for example, to generate low oxygen/moisture surfaces. Embodiments can be used at any other suitable point, e.g., before sintering of the powder.

Any suitable combination(s) of any disclosed embodiments and/or any suitable portion(s) thereof are contemplated herein as appreciated by those having ordinary skill in the art.