Patent Application: US-70381510-A

Abstract:
a process of making useful shapes by joining of tungsten alloys . joining of tungsten heavy alloys which are alloys typically made from w — ni — fe is used . these alloys are typically manufactured by liquid phase sintering . this leads to difficulty in producing large length to diameter ratio parts that have some significant weight . a “ brick and mortar ” approach is employed wherein smaller segments of this alloy are joined to together to produce a larger part with higher length to diameter ratio .

Description:
the first process relies on obtaining targets ( similar to sputtering targets ) of the desired compositions , which can be used on a machine that can do sputtering or thermal evaporation . sputtering is of course a slower process while the process of thermal deposition results in a fast rate of deposition of the desired material . the demonstration has been carried out with the thermal evaporation process . targets can be made from a variety of different compositions containing the following elements : w , ni , fe , cu , b , mo , ta , pt , re , and pd . for demonstration purposes , two targets were used for the coating work with compositions of : for the coating , the lapped face of tungsten heavy alloy cylinders having a composition of 90w - 7ni - 3fe alloy ( 1 . 5 inch diameter and 1 . 5 inch high ) was placed in a special chamber . the alloy faces were cleaned prior to coating . thermal evaporation was used to coat one of the lapped faces of each of the cylinders . before the actual coating , the face of the sample to be coated was first plasma etched for 2 minutes . the actual coating was started after that . the coating was by thermal evaporation of the target material and its subsequent deposition on anything that is placed below the target material . two 1 . 5 - inch diameter tungsten heavy alloy samples were coated for using the ni — cu — fe target . two 1 . 5 - inch diameter tungsten heavy alloy samples were coated using the ni — cu — mo target . a one coated sample 1 . 5 - inch diameter tungsten heavy alloy sample coated with the ni — cu — fe target was placed on the bottom of the furnace floor . the coated face was on top . another sample of 1 . 5 - inch diameter tungsten heavy alloy that was coated using the same ni — cu — fe target was then placed on top of the other sample , with the coated face of this sample at the bottom i . e . butting against the coated face of the other sample . a pre - machined ceramic sleeve , which has an inner diameter slightly greater than 1 . 5 inch is placed around the laid up cylinders . a similar arrangement was used to build the other joint segments using the ni — cu — mo at the interface . fig1 shows the faces 10 of the two ni — cu — fe coated samples 7 that will butt against each other during the run . fig2 shows the faces 11 of the two ni — cu — mo coated samples 8 that will butt against each other during the run . the time - temperature profile used to join all the set of samples is given below : room temperature to 1000 ° c . at 10 ° c ./ min ( in dry hydrogen ): hold at 1000 ° c . for 1 hour ( after half an hour hold change to wet hydrogen by passing the gas through a bubbler ); from 1000 ° c . to 1400 ° c . at 5 ° c ./ min ( in wet hydrogen ); hold at 1400 ° c . for 2 . 5 hours ( in wet hydrogen ); from 1400 ° c . to 1200 ° c . at soc / min ( in wet hydrogen ; changed to dry hydrogen at end ); from 1200 ° c . to 1000 ° c . at 10 ° c ./ min ( in dry hydrogen ; switched to dry nitrogen at end ); hold at 1000 ° c . for 1 hours ( in dry nitrogen ) furnace cool to room temperature in dry nitrogen . the joined samples were subsequently containerless hot isostatically pressed using the following conditions : hip conditions : hip at 2380 ° f . for 1 hour using a pressure of 15 , 000 psi . samples from the joined sections were cored out , machined into tensile bars and tested . the properties proved to be quite good with an excellent combination of strength and tensile elongation . some of the conditions that were varied during the investigation include other compositions of the joint area , different joint layer thickness , different temperature for joining , different hold time for joining , etc . these have been used to process the optimum joining technique for these heavy alloys . thus , the process outlined can be used to form large components using smaller segments of tungsten heavy alloy . another process that can be used is to have special materials of the desired composition cast or made by a powder metallurgy approach as shown in fig3 . these can then be prepared into foils 12 of the desired thickness . as shown in fig3 these foils 12 can then be placed between the two mating surfaces 13 of the tungsten alloy segments 9 that need to be joined . thus , the foil is actually sandwiched between the two segments to be joined . this complete set up is then heated to the desired temperature for joining . another process that can be used is a combination of the foil and coating approach . the heavy alloy segments can be first coated with the desired material . in addition , a separate foil of another material composition can be introduced between the coated heavy alloy segments to obtain a unique layered joint structure . the foil 12 is of a suitable composition that is placed between the two coated segments 13 . these are the faces of the two coated samples that will butt against each other during the run . another processing approach would be use of a foil that can be modified by some other approach such as coating of other elements or compounds on the foil itself . for example , a copper foil may be electrolytically coated with nickel - boron or a nickel foil may be coated with copper , or a nickel - iron foil may be coated with copper and then with sputtered palladium , etc . it can be imagined that different composition of the joint area and the ways of applying the different compositions to the joint area may be varied by people trained in the art . this type of joining can be used to make penetrator structures with large length to diameter ratios . these combination of joint compositions and processing can be used not only to produce joint structures which will have excellent joint strength and ductility , but can also be tailored to intentionally produce a weaker joint ( a joint that has significantly lower strength compared to the parent structure ) where the failure is induced through the joint only for various applications . heretofore , ways to join tungsten alloys have been disclosed , specifically liquid phase sintered tungsten heavy alloys , to form large parts with high length to diameter ratio . these parts have application as penetrators that can penetrate through deep dug bunkers maybe with concrete reinforcements . the main requirement of these alloys is the density but additional minimum requirements of strength and ductility is also important for surviving the launch and staying intact during the flight path . though to the best of the inventors &# 39 ; knowledge , there is no specific numbers for the minimum strength and ductility requirement for the penetrator , a minimum value of these can be assumed which would allow the launch of the penetrator and let it remain intact till it hits the target . one of the major concerns is always the ductility of the joint area , which has been quite low ( less than 50 % of the ductility of the parent alloy or less than 10 %). often , as the joint ductility is improved , the strength of the joint area is drastically reduced . however , with the method and compositions that have been used in this invention , it has been possible to consistently obtain joint strengths greater than 125 , 000 psi and elongations greater than 10 %. these properties can be considered adequate for both launch and the penetrator remaining intact until it hits the target . between the two properties the ductility is one that needs to be carefully controlled . though 10 to 15 % tensile elongation at room temperature may be more than adequate , it is always better if greater ductility is achieved . the room temperature tensile elongation of parts joined so far ( for the optimized processing and composition ) has been on average around 18 %. however , the strength values have been consistently high ( greater than 125 , 000 psi ). one of the best ways of increasing the tensile elongation at the expense of strength is to take the material to a slightly elevated temperature . this was tried with the joined structures . tensile property measurement at a low and high temperature was carried out on joints with optimal composition and processing conditions . table 1 givens the tensile properties of the joints sintered at room temperature , at − 50 ° c ., and at + 150 ° c . it can be noted that the strength of the joint is highest when the material was tested at a temperature of − 50 ° c . but was lowest at a temperature of + 150 ° c . the trend is reversed for elongation with the highest values being obtained when the test temperature was + 150 ° c . the average elongation value when tested at a temperature of + 150 ° c . was 26 % while the strength was around 110 , 000 psi . it is postulated that the strength of 110 , 000 psi and elongation of 26 % is enough to hold the penetrator together after launch . the recommended procedure for the use of these joined penetrators would be to have the penetrators pre - heated to a temperature in the range of 50 ° c . to 80 ° c . before launching . this is an important step which will ensure that the joint ductility , even if slightly low , will be more than compensated by ensuring an elevated temperature before its use . for penetrators with the explosives already loaded it may not be a good idea to heat them to temperatures over 100 ° c ., but certainly going to around 60 to 80 ° c . may be a possibility . it is expected that even these modest temperatures would provide a significant gain in ductility which would be beneficial . it was determined from the phase i investigation that the impact properties of the joined tungsten heavy alloys were significantly lower than the parent tungsten heavy alloy . since tungsten heavy alloys are also very notch sensitive , their properties are typically determined by carrying out unnotched charpy tests . generally , the smooth bar impact properties of tungsten heavy alloys range from 20 to 150 ft - lbs , while the notched impact properties are typically in the range of 2 to 3 ft - lbs . it was decided that the smooth ( unnotched ) bar impact properties would be carried out on the parent tungsten heavy alloy bars and on the joined tungsten heavy alloy rods . phase i investigation results were extremely poor ( typically the joined tungsten heavy alloy properties studied in phase i was around 30 times lower compared to the parent tungsten heavy alloy ). thus , there was not too much hope that the properties would be significantly better . however , in phase ii , since the joint properties have been optimized , it was decided to try and carry out the smooth ( unnotched ) bar charpy impact testing on these parts . for the testing , it was decided that sub - sized unnotched charpy specimens would be ideal . from various joined tungsten heavy alloy parts as well as from the straight tungsten heavy alloy ( no joint ) parts , electro - discharge machined coring was used to extract around 9 mm × 9 mm size parts whose length was around 75 mm ( typically the length of the joined rods ). these electro - discharge machined extracted cores were final machined to produce 8 mm × 8 mm unnotched charpy bars . these bars were tested in impact . the absorbed energy in the best joined samples in phase 1 was around 3 ft - lb while the parent heavy alloy examined in phase i had a value of 94 . 1 ft - lb . thus , the impact results for phase i was indeed very poor . the phase i process was of course not optimized at all but was simply a proof of the concept of producing parts by joining . during phase ii , the parent tungsten heavy alloy showed an absorbed energy value of 90 . 5 ft - lb which was close to the value of the parent tungsten heavy alloy results of phase i . the surprise was the improvement in the impact resistance values of the joined samples . impact testing was also carried out on samples at both low (− 50 ° c .) and elevated (+ 150 ° c .) temperatures . these test results followed the expected trend . the low temperature tested samples showed a mean absorbed energy value of around 10 ft - lb while the high temperature samples had a mean absorbed energy value that was quite good ( around 40 ft - lb ). the best result , however , was surprisingly attained in the joints made by joining 6 inch hollow cylinders . the mean absorbed energy value was around 53 . 7 ft - lb . the variation was around 16 . 7 ft - lb . judging from the results , the phase ii optimization work was indeed a success for the impact properties of the joined wha . the best phase i joined samples had an absorbed energy value of 3 ft - lb which is significantly lower than most of the joints investigated in phase ii . the only joint that exhibited very poor impact properties was the 3 inch solid cylinder joints . this joint had also exhibited poor tensile properties too . the conclusion from this investigation is that the impact properties have been vastly improved during this phase ii investigation . a study of the dynamic properties of the joined tungsten heavy alloys was also very encouraging . to study the dynamic properties of the joined tungsten heavy alloys , the joined samples were ** edm cored for machining the tensile bars . there were two types of tensile bars that were machined . six tensile bars ( 3 from each of the two joints ) were machined to the size of the normal tensile samples for the medium strain rate testing set . the other three bars ( two samples extracted from sr - 1 / sr - 2 and one sample from sr - 3 / sr - 4 ) were machined into smaller tensile bars for the high strain rate testing in the split hopkinson pressure bar set up . the set of six samples were tested at the medium strain rate of 1 s − 1 . this strain rate was much higher than the quasi - static strain rate that was being used for all the earlier experiments ( 0 . 0001 s − 1 ). the other set of three samples were tested in the split hopkinson pressure bar . the strain rate achieved in the case of the high strain rate experiments was 1400 s − 1 . the results of the medium and high strain rate tests are shown in table 2 . this table also contains the results from the quasi static tests . the medium and high strain rate test results are extremely encouraging . generally in tungsten heavy alloys with increasing strain rates the strength of the alloy is increased while the tensile elongation decreases . this trend was followed for the joined samples also . however , in the case of the samples tested at the medium strain rates , the ductility was still greater than 20 %, which can be considered to be extremely good . the strength of the joined material , however , was found to be significantly higher compared to both the joined sample and the parent heavy alloy tested under quasi - static conditions . the average ultimate tensile strength of the samples tested at the medium strain rate was found to be around 158 ksi which is significantly higher than that of the baseline tungsten heavy alloy which was around 136 ksi and the joined ** wha , which was around 133 ksi . thus , it can be concluded that the joint material would not have any problems at medium stain rates . the strain range of & gt ; 10 2 sec − 1 exceeds the capabilities of the standard servo hydraulic test systems and such the performance of tensile and compression test in this regime requires the use of a split hopkinson pressure bar . the split hopkinson pressure bar tests carried out at high strain rates ( 1400 s − 1 ) showed a similar trend of decreasing tensile elongation and increased strength . the average tensile elongation was found to be around 14 %. this was quite surprising as at these strain rates , as it was thought that the elongations would be significantly below 10 %. the failure strength that was recorded was , however , the highest that has been recorded so far . the average ultimate tensile strength was found to be around 180 ksi , which was greater than 30 % compared to that of the parent heavy alloy tested under the quasi - 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