Patent Grant
10137502
The present invention relates in general to the high-pressure fabrication of materials.
Various advanced high temperature components require varying high temperature properties and durability. Some systems use solid propellants while others use liquids. This includes aluminized (e.g., tantalum carbide suitable material) as well as non-aluminized propellant systems (Mo/Re, W—Re and Re alloys) as well. Material choices are therefore crucial. In either case, the components are subjected to extreme erosive conditions of heat (several thousands of deg F.) and flow velocity. Solutions generally require high performance refractory or refractory based ceramic composite materials with better durability, minimal number of processing steps, and high temperature strength/ductility properties and demand faster and cost-effective production processes.
Vapor deposition techniques are relatively slow and expensive and involve intermediate multi-steps to obtain the near net shape product. Plasma processes have porosity present inherently (e.g., 5 to 15% are typical). Conventional powder metallurgical pressing technology is limited by relatively lower compaction pressures (e.g., <50 tsi) that limits the densification process, with much higher part shrinkages requiring several post-process steps to improve the properties and obtain the final geometry.
The manufacture of the high temperature resistant refractory matrix materials such as Re or Re—W with Hf, Zr or ceramic carbides of Hf-and Ta, in near net shaping with improved properties and surface quality is challenging, time consuming, labor-intensive and costly which demand innovative manufacturing and strategies.
High temperature components have various shapes such as cylindrical disk, rings, plates, or hollow cylinder etc depending on the application. Some high temperature structural parts are made of carbon/carbon (C/C) or carbon/silicon carbide (C/SiC) composites due to their high temperature strength and lightweight properties. However, the oxidation behavior of C/C based composites at temperatures >450-500 deg C. still poses some limitations and demands alternate protective materials against oxidation and erosion.
There have been crucial needs to improve the durability and minimize the manufacturing time and cost in fabricating refractory disks used in the hot section catalyst bed plate components
In a new combustion driven compaction process, a chamber, powder, a piston or ram, and a gas supply are provided. The chamber is filled with a mixture of natural gas and air and the gas supply is closed. The gas is combusted, causing the pressure in the chamber to rise and exert force on the piston or ram. The powder is then compressed into an intended shape. To pre-compress, and remove entrapped air from, the powder, the piston or ram is pressed against the powder as the chamber is being filled with natural gas and air. The pre-combustion load on the powder may be 15 to 20 tsi.
A die may be provided and the powder may be held in the die. The piston or ram is in the chamber and to compress the powder the piston or ram is pushed into the die and against the powder. The die walls may be lubricated. The peak load on the powder may be about 250 tsi or greater. The peak load on the powder may occur within 250 ms of the initiation of combustion. The peak load on the powder may be a direct function of combustion pressure and the area of the piston or ram. The high pressure and temperature exhaust gases produced during combustion may be used for other press operations.
The process of claim 1 may produce only about 5% or less scrap metal. The powder compression can bond refractory tantalum to aluminum substrate. After compression, the shaped powder may be sintered in hydrogen. The powder provided may be metal powder with a fineness determined by the acceptable shrinkage of the compressed powder. The powder provided may include about 1 wt % to 5 wt % hafnium to reduce shrinkage of the compressed powder. The powder provided may be Mo/Re with 2-12.5 wt % HfC and/or a concentration of about 1 wt % to about 5 wt % Hf necessary to produce a desired strength. The powder may be −635 mesh or finer (<20 microns).
The powder may be compressed with a force of about 150 tsi. The intended shape may be a near net shape.
A material made by the new combustion driven compaction process has improved density, strength, and % elongation compared to materials made by traditional powder metallurgy. It may be a Mo/Re alloy with Hf or HfC, exhibiting a strength of about 40,000 psi or more at 2500° F. The material may have surface quality in microns or sub-microns and ductility equivalent or better than wrought metals. The material may contain a material selected from the group consisting of Mo/Re, HfC, TaC, SiC, Molybdenum, Niobium-based alloys, hafnium borides, boron carbides, and other borides and silicides with carbon. The material may contain Mo/Re base alloy with HfC and Hf. The material may have a green density of 75-82% of theoretical and a sintered density of 93-98% of theoretical density.
The material may have less shrinkage during sintering compared to materials made by traditional powder metallurgy. The material after sintering may have good bonding, no cracking, fine surface quality, higher densification and superior mechanical properties compared to traditionally compacted and sintered powder metallurgy materials, and comparable strength and ductility to wrought annealed materials both at room temperature and high temperatures up to 3500° F. The material may have a strength of 135 ksi or more, ductility of 30% or more, hardness of 315 VHN or greater, or a polycrystalline microstructure. The material may have as an average grain size of <64 microns after sintering.
The material may have functional gradient structures of several layers of differing materials and composites. The material may have a high temperature resistant refractory matrix material.
A new combustion driven compaction apparatus has a chamber, a piston or ram, a gas inlet in the chamber, wherein combustion of gas in the chamber pushes the piston or ram. The apparatus may also have an igniter in the chamber for combusting the gas. The apparatus may also have a die, wherein when the piston or ram is pushed outward from the chamber it pushes into the die. One side of the die may be closed by a punch tool. The apparatus may have only one moving part. The apparatus may be less than eight feet long in any dimension and produce a force of 300 tsi with the piston or ram. Such an apparatus may be able to be moved with a standard forklift. The apparatus may be capable of producing a force of 3000 tsi with the piston or ram and still be about 9′ high, 6′ wide, and 4′ deep. Such an apparatus may also be able to be moved with a standard forklift.
These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the drawings.
Innovative approaches allow economically feasible acquisition of new manufacturing process technologies and unique refractory composite materials for advanced high temperature components in ballistic missile defense systems. Cost-effective and rapid fabrication process technology facilitates transition of high performance, near net shape and reliable prototypes from a research and development environment to a manufacturing environment.
One such process technology—the high pressure Combustion Driven Powder Compaction (CDC) technology can be used to manufacture denser, durable near net shape components with improved properties. CDC produces components such as plenum or inlet, pintles, valves, and manifolds with much higher green and sintered densities, much less part shrinkage after sintering and superior surface quality (e.g., microns to sub-microns of average roughness are typical), less post-process machining or materials wastage (Table 1), and near net shapes of simple to complex geometry (
CDC uses a minimal number of steps and has competitively lower manufacturing costs compared to the traditional fabrication methods such as multi-step Conventional Powder Metallurgy (usually limited to <50-55 tsi compaction pressures), Casting/Forging, Chemical Vapor Deposition (CVD), Chemical Vapor Infiltration (CVI) and Vacuum Plasma Processing (VPS) methods for its advanced propulsion systems.
In response to high temperature propulsion materials, innovative near net shape fabrication technology has been developed with tremendous potential for cost-effective manufacturing, minimal or no wastage of expensive and exotic raw materials such as Molybdenum-Rhenium (Mo/Re) based composite alloys and rapid manufacturing (e.g., milliseconds of compaction time) method called high pressure Combustion Driven Powder Compaction (CDC) technology.
Potential Mo/Re-X-Y composite materials (e.g., X=Hf; and Y=HfC) have been fabricated all with CDC method in net shape with higher densification and improved mechanical properties at elevated temperatures (e.g., 3500 F or higher). Testing of CDC processed Mo/Re alloys indicated excellent results up to temperatures at 3500 deg F. (
The CDC high pressure (up to 150 tsi) and faster (few hundred milliseconds) compaction with controlled gentler loading profile are desirable attributes to consolidate variety of micro/nano powders to obtain much higher green and sintered part densities with near net shapes of simple to complex geometry. Other process advantages of CDC processing for refractory Mo/Re alloys with Hf, Ta2C, HfC nozzle components are competitively lower manufacturing costs, minimal wastage (
The high pressure CDC Compaction overcomes several processing challenges with its milliseconds of part pressing time, much higher compaction pressures (up to 150 tsi) and gentler loading profiles (
Issues with fabricating refractory disks used in the hot section catalyst bed plate components are overcome using the high pressure CDC manufacturing. Using fine grained Mo/Rhenium or Re/W alloys with other alloys such as Hf, HfC or Ta2C using commercially available finer powders and careful CDC process optimization, property evaluation and sintering responses, small scale disks and mechanical test samples were fabricated using a 300 Ton Press and representative 2 inch diameter disks were done using a 1000 ton CDC press. Other advanced alloys were fabricated such as Mo/Re with Iridium to further improve the oxidation protection and scale up to fabricate other geometries using the 1000 Ton Press.
Hafnium (which has density of 13.31 g/cc and melting point of 2230 deg C.) was used for CDC refractory composites developed in this innovation to provide high temperature protection up to temperatures (e.g., 2100 deg C. just below its melting point) as well as strengthening for the Mo/Re base matrix alloy. The mechanically blended Mo/Re base alloy (with calculated theoretical density of 13.5 g/cc and melting point of 2450 using simple rule of mixtures), as used in our CDC compaction experiments has a composition of 52.5 Mo-47.5 Re, as provided by the powder vendor (weight %). The powders were then mechanically blended with Hf and HfC in the glove box with Inert gas control at the CDC processing set up.
While
PM processing and CDC in particular can improve the high-temperature properties of Re—W alloys by their ability to disperse other harder and higher-melting carbides such as HfC, TaC. CDC at high pressures at 150 tsi has the ability to generate desired finer and uniform microstructures containing such carbides leading to better high-temperature properties. Some of the carbide based materials are used for protecting carbon-carbon composites in high temperature propulsion systems. It is evident that materials such as HfC, TaC, HfN, and HfB2 have the desired high melting temperatures and potential to serve as ceramic reinforcing materials for refractory based metal matrix composite nozzles such as TZM, Mo/Re and Re—W alloys. The key issues are to match the linear thermal expansion of the composite to prevent thermal cracking/shocking and improve density and interfacial mechanical bonding/thermal shock resistance at higher temperatures.
Near Net-shaping tungsten, molybdenum, Mo/Re alloys (
The use of Mo/Re based composites with strengthening composite reinforcing materials such as Hf and carbides such as HfC, is highly desirable for very high temperature applications. The present invention produces cost-effective, and competitive Mo/Re based composite alloys with and without Hf and HfC with select compositions in the near net shape form with two steps of manufacturing. Innovative high pressure CDC powder compaction at 150 tsi and optimal thermal sintering are used to obtain relatively higher green and sintered part densities, sub-micron surface quality, less part shrinkage characteristics, fine grained microstructures, and excellent strength/ductility attributes with comparable annealed material properties at temperatures up to 3500 deg F.
The potential erosion resistant materials are refractories such as W—Re, Re or Re/Mo and or ceramic composites with carbides, nitrides, and borides such as TaC, HfC, HfN, HfB2, ZrB2, TiB2, SiC, or B4C depending on the type of material properties for high temperature protection (Tables 1 and 2 and
Other additional composite additional material such as Hafnium (which has density of 13.31 g/cc and melting point of 2230 deg C.) used for CDC refractory composites developed in this innovation is desirable to provide high temperature protection up to temperatures (e.g., 2100 deg C. just below its melting point) as well as strengthening for the Mo/Re base matrix alloy.
The CDC Process
Combustion Driven Compaction (CDC) utilizes the controlled release of energy from combustion of natural gas and air to compact powders. In operation the following steps occur: Fill chamber to high pressure with a mixture of natural gas and air; As the chamber is being filled the piston or ram is allowed to move down pre-compressing and removing entrapped air from the powder; The gas supply is closed and an ignition stimulus is applied causing the pressure in the chamber to rise dramatically, further compressing the metal powder to its final net shape.
The basic CDC process is shown in
A CDC press is compact and uncomplicated. For example, a 4137 MPa (300-ton) mechanical or hydraulic press is typically two or more building floors tall and has many moving parts and/or complex hydraulics. A 300-ton rated CDC based press is not much larger than a phone booth and has one moving part. The compact prototype CDC 300-400 ton rated press is shown with traditionally used much larger conventional press in
As a general rule as the compressive load applied to a powder metal is raised the compact density and green and sintered part properties improve. However, if the powder is compressed too rapidly or violently, shock propagation in some materials can cause internal cracks and separations (over-pressing).
CDC Press Scaling
As previously mentioned, since the CDC press directly converts chemical energy into compaction energy it is very energy efficient and capable of producing enormous compaction loads. To date three presses of increasing size have been constructed and operated, 10, 30, 300 and 1000 ton. The CDC compact press has the potential for scaling up further up to 3000 Ton capacity without compromising its compactness, unlike the traditional presses. Scaling from one size to the next is relatively straightforward. Since the process works more or less like a piston in an automobile, although at much higher pressures, the loads that can be produced are a direct function of the combustion pressure and the area of the ram (piston). It is possible then to scale a CDC press to very high tonnages without increasing the size of the press itself dramatically. As an example a 3000 ton CDC press would only be about 2.75 m high, 1.92 m wide, and 1.28 m deep (9 ft×6 ft×4 ft).
There are other engineering issues associated with producing a “high rate” production version of a CDC press. These issues include rapid filling of propellant gases, rapid venting of combustion gases, purging of water produced in the chamber, active cooling of the chamber if necessary, and robust repetitive high-pressure ignition. These issues have largely been resolved and tested. Powder feeders and part conveyers can be readily adapted from off-the-shelf components.
It is interesting to note that the high pressure and temperature exhaust gases produced during combustion in the CDC can be used for other press operations such as part extraction or running other ancillary equipment, further increasing the efficiency of the press. The relatively diminutive size of a CDC press allows powder metal part making to be performed in almost any industrial or commercial building with access to bottled or piped natural gas. Pits and multi-story buildings are not needed, and the presses can be moved with standard forklifts. This relative portability allows, for instance, powder metal presses to be incorporated into “machining centers” as needed and then moved to other centers or sites generally without special equipment.
Properties of CDC Produced Compacts
The CDC process operates at compaction loads of 15 to 150-tsi and above. It is well known that compaction tonnage generally makes a large difference in the final quality of the compacted part, both in the green (unsintered state) and in the sintered state. Another benefit of high part density is lack of dimensional change (shrinkage) when the material is sintered. In many materials pressed by the CDC process at high tonnage there is no measurable change in pre versus post sintering density. The elongation or “toughness” of samples produced with the CDC process is particularly exceptional, often approaching that of comparable non-powdered metals.
The low % of scrap metals in P/M process (
CDC samples have been produced with enhanced material properties such as density, strength and % elongation compared to those made by traditional powder metallurgy method. Single and Multi-component layered compacts have been produced with the CDC process in many combinations including: Al/Al2O3, Ti/Al, Ta/410 SS, Mo/410 SS, Ti/316L, Ta/Steel, Ta/Cu, and Cu/Steel. The representative geometries fabricated include cylinders, rings, and dogbones. Mo/Re alloys with Hf and HfC and optimized in preliminary conditions for obtaining strengths of ˜40,000 psi at 2500F have been successfully fabricated.
The superior surface quality in microns or sub-microns and mechanical/ductility equivalent or better than wrought metals have been obtained on several geometries of materials at higher CDC compaction pressures under optimum process conditions. CDC compacted and sintered various refractories such as tungsten, molybdenum, Re, Mo—Re alloys (Table 3 and
Summary of CDC Benefits
A new press technology based on the direct conversion of chemical energy from natural gas and air combustion is called Combustion Driven Compaction or CDC. The press has three main attributes: First, owning to its high efficiency and unique design, it is very compact relative to other press technologies. A CDC based press is a fraction of the size of a conventional press with the same load capability. Secondly, due to its distinctive loading cycle, the press is capable of delivering “standard” or very high compaction loads without damaging die components or producing cracks in the compacts. Finally, compacts made at high loads in the CDC process with only die wall lubrication display greatly enhanced mechanical properties before and after sintering.
Anticipated Benefits
The potential applications for the proposed CDC technology include Catalyst BedPlates, refractory and ceramic composite inserts, military ammunitions/projectiles/heat shields, gyroscopes, ignitor components, electronic packaging/aerospace components, x-ray targets/tubes (e.g., Tungsten-Rhenium or Moly Alloys), high performance welding and glass melting electrodes, RF damage resistant refractory components for linear collider copper disk structures, boring bars/tools, high temperature dies, brazing fixtures, electrical contacts. Other applications of CDC processing include superconducting accelerator components, couplers, low temperature vacuum seals (e.g. Al—Mg alloys), and nuclear plasma components. Other commercial applications include ball and roller bearings, permanent/superconducting magnets, microelectronic packaging interconnects, sputtering/x-ray targets with conductive copper backing, mould dies with tough steel/copper backing, automotive piston rings, valve seats, gears, high temperature composite bearings, microwave appliances, cutting tools, and other wear/corrosion resistant tribological components.
Significance of the Proposed Research
With greater demands for superior high temperature erosion resistance and protect the C/C or C/SiC composite materials used in components, the needs for cost-effective fabrication in near net shape form and development of suitable high performance, well-bonded refractory based functional gradient composite materials are demanding and crucial. An innovative high pressure CDC powder compaction in near net shape has been used to manufacture small scale parts and select ring and dogbone geometries made of rhenium, molybdenum/rhenium and rhenium/high temperature carbide composites.
Mo/Rhenium and select composite alloys of HfC, TaC and SiC and other advanced alloy composites can be used based on their high temperature properties such as Molybdenum, Niobium-based alloys, hafnium borides, boron carbides, and other borides and silicides with some carbon for absorbing the strains by few % (Table 2 and Table 3) and needs of potential insertion capability with ongoing nozzle and other applications. With the availability of select micro/nano powders in the commercial markets, CDC high pressure compaction is unique to produce high performance, dense, and simple/complex composite parts in both micron and nano structured form by faster (e.g., milliseconds) consolidation.
Such a systematic innovative approach will significantly contribute to improving the efficiency, component design, durability and performance of parts and components. The science of CDC processed powder materials is an emerging research field of critical importance and scientific value.
Experimental Materials, Procedures and Results
Select key results of the physical and geometrical properties of Green (Table 4a-k, Table 6, Table 13) and Hydrogen Sintered CDC samples (Table 5, Table 7, tables 8-12) are provided. The alloys processed include Mo/Re, Re and alloys with Hf and HfC of various compositions. In general the green (75 to 82% of theoretical) and sintered densities (93 to 97% of theoretical densities) were relatively higher due to high pressure compaction at 150 tsi than those obtained normally with traditional powder metallurgical techniques.
The hydrogen sintered samples, in general, were well-bonded, free-from cracking, of smooth surface finish and of near net shape quality. The near net shaping ability is demonstrated (
The Rhenium samples were found to reveal relatively higher shrinkage (˜7-9%, depending on the thickness, width or length dimensions) compared to Mo/Re alloys. (Tables 10-12). The addition of Hafnium (e.g., 5%) was found to decrease the shrinkage characteristics significantly.
The Finer powder sintered samples of Mo/Re (sample#963) revealed relatively lower shrinkage than coarser powder sintered (Sample#969 and 970) samples.
Powder Selection and Morphology
The powder specifications include: Powders of various refractory powdered materials, for example 52.5 Mo-47.5 Re powder with −200 mesh, W-25 Re alloy systems with −635 mesh, Mo-41Re and rhenium with −200 mesh, Hafnium powder with −325 mesh (44 microns or smaller) and 99.6% purity, and Hafnium carbide powder with −325 mesh with 1-4 microns of average size. The powder morphologies were evaluated using microscopy. The distribution, range of sizes within the mesh designation and non-spherical shape of the powders were evident and desirable for compaction. In addition, tensile dogbone samples have been fabricated using powders of fine mesh, for example −635 mesh size powders of Re and Re/Mo. (Tables 6a and 7).
Sintering Responses:
The sintering experiments at 1800, 2100 and 2300 deg C. in hydrogen were carried out on select CDC samples. The sintering responses of samples revealed higher densification, good bonding, no cracking, fine surface quality and comparable mechanical properties of strength and ductility under optimum sintering to those of wrought annealed materials. In fact, the high temperature sintering of CDC samples has improved the densification significantly and mechanical properties as compared to those traditionally compacted and sintered P/M materials.
Samples sintered at 2100-2120 deg C. indicated higher sintered densities up to 97% of theoretical value than those sintered at lower sintering temperature at 1800 deg C.
The evaluation of the densities of cylindrical disk samples sintered in Hydrogen at 2300 deg C. for 4 hours have been completed. The sintered density results are presented as follows:
The ring sample #953 (fabricated with −200 mesh powder) had a sintered density of 13.154 g/cc (93.99% of theoretical density) and sample#954 (fabricated with 50% of −200 mesh powder and 50% of −635 mesh powder) had a sintered density of 12.956 g/cc (92.58% of theoretical density). The shrinkage values of ring samples (Table 12) were relatively lower than those obtained in tensile dogbones (Table 10-11).
As indicated previously, high sintered densities of optimum alloy compositions (e.g., Re, Mo/Re and alloys with low Hf % and HfC) are unique attributes of high pressure CDC compaction. These results also indicate the significance and dire scientific needs for further process optimization in our continuing efforts as of submitting this patent application submission.
Room Temperature and High Temperature Tensile Testing and Results
The room temperature tensile tests of CDC compacted and sintered dogbone samples (Tables 14-16 and
CDC Process Optimized Tensile Dogbones for High Temperature Mechanical Testing
Two identical tensile dogbone samples of the most promising alloy compositions with a total of 22 samples (Tables 6 and 7) for high temperature mechanical strength evaluation. The sintering of these samples was also completed successfully in hydrogen environment at 2300 deg C. for about 4 hours.
Traditionally processed P/M parts with materials such as Rhenium based alloys (Rhenium has HCP crystal structure) using extensive mechanical (extrusion, swaging or rolling) and thermo-mechanical steps are known to have great deal of texturing effects which affect the cracking tendency behavior during fabrication. Hence, it is desirable to minimize such texturing effects by intelligent processing. This CDC high pressure consolidation manufacturing together with the optimal composite material composition leads to a simplified two-step process of high pressure near net shape processing.
Microstructural Results
The microstructural studies (e.g.,
High Pressure Consolidation of Fine Re/Mo—Re Powders:
The unique advantages of high pressure compaction at 150 tsi to fabricate production run tensile dogbone samples of a variety of powder sizes (e.g., −200 mesh, <74 microns and −635 mesh, ˜<20 microns) are apparent. It is important to highlight that the finer grit size (e.g., −635 mesh) powders of Re or Mo/Re are known to be difficult to be pressed by traditional P/M methods at compaction pressures <50-55 tsi. Such composites included the improved strength properties of 50%-50% mix. The technical basis for such approach is beneficial to produce CDC high density metal matrix composites in near net shape with finer carbide distribution to further improve the mechanical properties.
Summary of Conclusions
Rhenium based refractory composites, various Re Mo and W based refractory composites (e.g., 52.5 Mo/47.5 Re Mo-41 Re, W-25 Re, Re by weight %) alloys with and without Hf and HfC have been compacted in various geometrical shapes using high pressure CDC compaction at 150 tsi and sintered successfully for high temperature mechanical property enhancement and optimization.
The geometries fabricated include 0.5 inch dia cylindrical disks (
Crack-free and well-bonded near net shape circular rings of various Re/Mo alloys with Hf and HfC have been fabricated at high pressures as well.
CDC processed materials @150 tsi have showed higher green (e.g., 75 to 82% TD) and sintered densities (e.g., 93 to 97%), improved mechanical strength (up to 135 ksi)/ductility (up to 30%)/hardness (315 VHN) properties, polycrystalline microstructures, fine surface finishes, less shrinkage and near net shaping fabricability.
The sintering response results are better in terms of less shrinkage than traditional P/M parts and comparable to wrought annealed materials.
The sintered microstructures and microchemistry after 2100 deg C.; 4 hrs revealed polycrystallinity, distribution of Hf and other alloying elements, variety of fine grain sizes (<64 microns average size), and relatively finer surface finishes. Such fine grained microstructures developed by suitably and optimally controlling the processing conditions without much grain growth are unique characteristics of high pressure CDC compaction when the refractory composite materials are compacted at 150 tsi which has not been reported previously.
Effects of adding Hafnium and HfC in Mo/Re alloys were found to significantly improve the high temperature strength properties up to at least 3500 deg F., indicating the significance of further Mo—Re—X—Y (X=Hf; Y=HfC) alloy development using CDC high pressure compaction technology. Such improvement using CDC high pressures (e.g., 150 tsi) has not been reported for the developed innovative refractory composite materials using any conventional powder metallurgy technology which is usually limited to <50-55 tsi compaction pressures.
Sintering response at higher temperatures (e.g., 2300 deg C.) increases sintered densities and the mechanical properties as well.
CDC high pressure compacted and sintered Re/Mo composite materials alloys have showed significant necking indicating the desirable ductility behavior before fracture at room temperatures (
Alloys with 1% Hf and 2% HfC have showed reasonable strength and ductility properties at room temperature. (Tables 14-16. Table 18)
Controlled Sintering of CDC samples in Hydrogen plays a key role as well in influencing the mechanical properties of Re and Re—Mo alloys with Hf and HfC.
Near net shape parts have been successfully compacted using both coarse (<70 micron size) and fine (<20 microns) mechanically blended powders (52.5 Mo/47.5 Re) and using 59% Mo-41% Re alloy (<70 micron size powders) obtained again from Rhenium Alloys at varying CDC pressures up to 150 tsi. The highest density of 82.22% is very encouraging simulating the tensile dogbone densities at 150 tsi. (Table 16 and
In summary, the Mo/Re (52.5Mo-47.5Re) composite alloys with and without Hafnium (Hf) and Hafnium Carbides (HfC) in varying compositions and in the optimum composition can be compacted successfully at 150 tsi using a 300 ton CDC press with much higher green and sintered densities, crack-free parts during CDC pressing at high pressures and unique faster CDC loading cycle of milliseconds, comparable room temperature and high temperature (up to 3500 deg F.) mechanical properties equivalent to those of traditional annealed wrought materials, near net shaping ability to fabricate different geometries (disk, ring, dogbones), fine surface finish/quality, process flexibility to fabricate novel powder alloys, controllable grain sizes, microstructures and microchemistry and significant cost effectiveness in both materials wastage minimization and manufacturing. This unique technology can manufacture high temperature components economically.
With high pressure CDC compaction press, many of the challenges with other manufacturing methods can be overcome. The powder handling and compaction with both micron as well as nano-sized refractory Mo/Re composite alloys and ceramic powders can be carried out successfully at high pressures to improve the densification, for example. Also, the CDC process can be done in controlled inert conditions (e.g., using glove box and inert gas supply in the die/punch setup). This manufacturing is also amenable for functional gradient structures of several layers of differing materials and composites for multi-functional use. Such manufacturing strategy using CDC process is anticipated to be a competitive alternative than the existing traditional rapid prototyping fabrication methods, conventional P/M and wrought methods and conventional coating processes.
In light of several other manufacturing methods as discussed above, the high pressure CDC compaction process is expected to have several unique cost-effective manufacturing advantages of high pressure densification, ability to press coarse, fine and even nano powders, rapid development for advanced composite materials of unique compositions tailoring to the material property and functional property needs for high temperature applications, near net shaping ability, lot less or no scrap metal % and improved mechanical and microstructural attributes for developing advanced propulsion thruster system components.
Current Status of CDC Mo—Re Based Composites, Processing and Near Net Shape Components
Referring to
The densification attributes (Table 19) after optimal sintering are in upper 90s indicating the unique advantages of high pressure compacted samples and their response for post-compaction thermal processing.
The CDC processed materials (
Microchemistry results were found to confirm the composite materials (e.g., Re with Ta, Hf and C being retained in the microstructures).
Out of all the alloys, Rhenium has exhibited the maximum and significant strengthening effect (Rc 34 to 55) using composite alloying. Mo-41Re and W-25 Re materials also responded to some improvement in strengthening. (Table 20)
The mechanical strengthening attributes at room temperature (Table 20) of refractory and composite alloying (especially with Hf and HfC) have been provided in the following Table.
The additional high temperature property results of CDC compacted (at 150 tsi) and sintered Mo-41Re, W-25 Re and Rhenium together with previously tested 52.5 Mo-47.5 Re materials and their composites tested at 3500 deg F. are presented. Tensile specimen densities of the CDC compacted and sintered samples were measured using Archimedes technique in alcohol (Table 22).
A comparison plot of all the specimens tested shows the differences in material responses from alloy to alloy.
The pure rhenium specimens were made with various powder sizes (−635 and −325 mesh) and various powder manufacturers.
The tensile samples revealed varying mode of fracture from necking (mostly on Mo—Re based alloys) to less necking modes in Rhenium samples.
While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention.
Table 4a-k. CDC Pressure, Physical and Geometrical Properties of CDC Green Parts [41]
This application claims the benefit of U.S. Provisional Application No. 60/853,360 filed Oct. 20, 2006, which is hereby incorporated by reference in its entirety.
This invention was made with Government support under Contract HG0006-05-C-7224, awarded by the Missile Defense Agency. The government has certain rights in this invention.
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| Number | Date | Country | |
|---|---|---|---|
| 60853360 | Oct 2006 | US |
