ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Figure 1. Crystal structure of WS 2 Hexagonal P6 3/mmc [5 - 9] （0.3154×0.3154×1.236 nm3） The purpose of this research is to evaluate three fabrication techniques of WS 2 coating films for an  application at high temperature in a vacuum environment: bonded films with an inorganic binder, sputtered  films with titanium intermediate layer, and shot peening films of WS 2 powder. Experimental Procedure  Two types of friction testing equipment were utilized: a pin-on-disk type reciprocating tribometer and a pinon-disk type rotary tribometer, each in a vacuum chamber. After the friction tests, the surfaces of both disk  and ball were observed by an optical microscope and the surface profile at the wear tracks was measured  by a contact profilometer. The structural and chemical properties were analyzed with a scanning electron  microscope (SEM) and energy dispersive X-ray spectrometry (EDS). Crystallographic structures of the wear  and the non-wear regions were examined by imaging plate X-ray diffraction (IPXRD).   Pin-on-disk type reciprocating tribometer  Pin-on-disk type friction tests were carried out using a reciprocating tribometer to investigate the friction  characteristics of various types of lubricant coatings in air and in vacuum. The test conditions are listed in  Table 1. Figure 2 shows a schematic diagram of the reciprocating tribometer, which can evaluate friction  under a constant applied load and sliding speed. The tribometer was installed inside a vacuum chamber to  allow tests to be carried out in air and under vacuum. A pin slides repeatedly against a disk coated with  lubricant, with a load of 10 N applied by a weight located outside the vacuum chamber. The speed of the  sliding is controlled by the reciprocating motion of the disk.   The sliding speed and the stroke were 10 mm/s and 10 mm, respectively. For tests under vacuum  conditions, the chamber was evacuated by a turbo molecular pump to a pressure on the order of   10-4-10-6 Pa. The friction test was interrupted when the friction became high or it was suspected that the wear had reached the substrate of the disk. NASA/CP—2018-219887 114
Figure 2. Overview of reciprocating tribological test Pin-on-disk type rotary tribometer  The friction characteristics of many types of WS 2 and MoS 2 coatings were investigated at elevated  temperatures under vacuum using a pin-on-disk rotary tribometer. The test conditions are listed in Table 2.  Figure 3 shows a schematic drawing of the test apparatus. The vacuum chamber was evacuated by a turbo  molecular pump to a pressure on the order of 10-5 Pa, and the temperature of the specimen was controlled  by a molybdenum heater and a thermocouple welded on the specimen. The temperature relationship  between the test specimen and the outer cover was monitored using thermocouples. Table1. Tested condition of the reciprocating tribometer  Load [N] 10  Contact Pressure [GPa] 0.35  Speed [mm/s] 10  Friction Distance [mm] 10  Atmosphere [Pa] Vacuum（under 10-5） Temperature [°C] 22–24  Vacuum Chamber Load Bellows Load Cell Reciprocation  Stage Counterpart Material Tested Specimen Rotary PumpTurbo Molecule Pump Ball ScrewMotorReciprocating Control Device Top view Side view NASA/CP—2018-219887 115
Figure 3. Diagrams of the rotary tribological test apparatus X-Ray Diffraction Analysis The crystallographic structure of wear and non-wear regions were examined by IPXRD. The wavelength of  the X-ray was 0.1542 nm and it was collimated to a spot size of 0.3 mm, which was small enough to  distinguish between a worn or non-worn area of the coating. A high-magnification CCD camera was used  to align the X-ray spot on the specimen. In order to capture a diffraction image of the surface film layer of  the coating, the X-ray was introduced at a low angle relative to the face of specimen. The incident angle of  the X-ray, and the specimen rotation angle were set to 45 ° as shown in Figure 4. 360° Debye-ring pattern  can be used to quantify the textured crystal structure, because the development of preferred orientation  was expected due to the wear. A beta diffraction peak can be obtained from one rotation of the specimen  (360 degrees). XRD patterns were quantified by measurements of the imaging plate.  Table 2. Test conditions of the rotary tribometer  Load [N] 10，30  Speed [m/s] 0.1, 0.5 (inspection)  Friction Distance [mm]  (rotational speed [rpm]) 40π（47.7） 36π（53.0） 32π（59.7） 28π（68.2） Atmosphere [Pa] Vacuum (<10-5)  Temperature [°C] 20, 100, 200, 300, 400, 500  Thermocouple Test specimen Outer  Wall  Counterpart  Stage Specimen Vacuum Chamber Rotary PumpTurbomolecular PumpMolybdenum Heater Load CellLoad Cell Top view Side view NASA/CP—2018-219887 116
Figure 4. Geometry between incident X-ray beam angle and the sample stage in IPXRD equipment. Materials  Three kinds of coatings on the SUS316L stainless steel disk (Φ40 mm×8 mm), which has relatively good  creep strength at high temperature, were fabricated. Counterpart material was a SUS316 ball (7.93-mm  diameter).   Bonded Film  MoS 2 is known as a high performance solid lubricant in a vacuum environment [10-13] from numerous  research results and applications on spacecraft mechanisms. Two bonded films were fabricated using WS 2 and MoS 2 lubricant powder by one vendor in order to compare tribological characteristics in vacuum at  elevated temperatures under the same conditions. Table 3 lists the fabricating conditions for the lubricant  powder quality, quantity, and binder material, etc. The coating is fabricated by an annealing treatment for  60 minutes at 200°C using a furnace, then drying in an air environment for 20-30 minutes. This coating  method is necessary to form a chemical inorganic binder with better elevated-temperature performance in  vacuum than organic binders [14]. Thickness of all coatings were controlled to 10 μm.  Table 3. Coating condition of the bonded films  MoS 2 WS 2 Grain size(μm) 0.94 0.94  Degree of crystallization (%) 80 -  Powder morphology circularity(%) 0.7～1 0.7 ～1  Inorganic specimen Vol (%) 40 40  Binder material Na2SiO 3 Na2SiO 3 Thickness 10 μm 10 μm  NASA/CP—2018-219887 117
Sputtered Film  A sputtering technique is suitable for applying a high purity coating with only WS 2 on the top surface of the  SUS316L stanless steel disk. As a result of preliminary testing, which showed that the film did not have  good adhesion with the interlayer on the mirror-polished surface, a titanium interlayer was applied between  the base material and the WS 2 coating. Furthermore, the surface roughness of the SUS316L substrate was  varied to improve adhesion. Roughness treatments were carried out using a shot blast method after the  mirror surface treatment. Three levels of surface roughness were evaluated; Ra: 0.013 (this is the mirror  treatment), Ra: 0.4, and Ra: 0.7.   Table 4. Coating condition of the sputtered film  Surface Roughness of Base Materials [μm] Ra:  0.013, 0.4, 0.7  Target Material Ti (Inter layer), WS 2(Top layer) Pre-Sputtered Pressure [Pa] 4×10-3 Ar Injection Pressure [Pa] 3.2×10-1 Output [W] 100  Ar Flow [ccm] 7.5  Ar Etching Time [h] Ti : 0.5, WS 2 : 0.5  Sputtered Time [h] Ti : 1,    WS 2 : 4 - 5  Film Thickness [μm] 1.5～1.8  Shot Peening Film   The WS 2 shot peening coatings on the SUS316L stainless steel disk were applied using WS 2 powder of   2-μm and 0.5-μm particle size with a coating pressure of 8.0 MPa in open air. The average thickness of the WS 2 coating was less than 0.5 μm. This coating method is also available to coat only WS 2 on an outermost surface without an interlayer and/or binder. Furthermore, this coating does not have a part size limit and can be fabricated without special chambers or furnaces. The lack of a size limit for the shot-peening film is an important point, especially for spacecraft with large wearing parts. Quantitative surface condition measurements of the coatings were made by EDS analysis. Figure 5 shows  the EDS detection results of tungsten and sulfur across the surface of the disk. Vertical axis shows the ratio  of the counts of tungsten (W) and sulfur (S) normalized by the peak intensity of the steel (Fe) in the  specimen for each measurement. Horizontal axis is the location of the measurement across the disc from  0 mm to 45 mm. The thickness of coating film has a gradient since the W and S atomic counts were found  to increase across the width of the disk.   Figure 6 shows the measured friction coefficient data versus position. Friction coefficient data was  measured by a rotary tribometer with a load of 10 N in the air of room temperature and sliding speed of 0.5  m/s, data accumulation rate is 1000 points per second. Vertical axis is friction coefficient and horizontal  axis is measurement location. Accordingly, the friction coefficient is inconsistent across the coating. Friction  coefficient was decreased at locations showing high atomic counts via EDS. Thus improvement is  necessary, however this coating method was included in the study since it has useful characteristics such  as ease of application.   NASA/CP—2018-219887 118
Figure 5. Detection result of tungsten and sulfur atomic from top surface by EDS  Figure 6. Measured friction coefficient versus position Results and discussions  Results of the Reciprocating Tribo Tests  The friction test was continued for 100,000 cycles with a load of 10 N under vacuum (10-5 Pa) at ambient  temperature. The test was conducted using two substrates with different bonded films, one with MoS 2 and  the other with WS 2. Both bonded films were fabricated using the same inorganic binder. Results of the  friction test with each bonded film are shown in Figure 7. Both coefficients of friction have similar trends  that increased with number of wear cycles. Maximum friction coefficient and/or when friction test finished  were 0.04 for MoS 2 and 0.06 for WS 2. Figure 8 shows optical microscope photos, measured surface wear  roughness, SEM observation and EDS analysis of each specimen after the friction tests. A transfer film was  observed on the surface of the ball (counterpart material), verified by optical microscope and EDS analysis  from both tests. Furthermore, neither substrate was exposed due to wear after completion of 100,000 cycles.  NASA/CP—2018-219887 119
Figure 7. Friction coefficients as a function of time for WS 2 bonded film and MoS 2 bonded film by  reciprocating tribometer in the vacuum at room temperature [13] Figure 8. Optical microscope observation, SEM micrographs and EDS mappings of the surface of each  bonded film after reciprocating friction test [9] Figure 9. Friction coefficient of WS 2 sputtering and WS 2 shot peening coating by reciprocating tribometer  in vacuum at room temperature NASA/CP—2018-219887 120
Figure 9 shows the results of friction measurements taken using the reciprocating tribometer over 5000  wear cycles under a normal load of 10 N, under vacuum at ambient temperature with a variety of coupons.  Sputtered films with a Titanium interlayer applied over substrates with different surface roughness levels,  and shot-peened films with different WS 2 particle sizes were tested. Both of these coating methods are  capable of creating a pure WS 2 outer surface. With the sputtering films, the friction coefficient of the Ra:  0.01 specimen increased before 5000 cycles and the Ra: 0.4 mm and Ra: 0.7 mm coupons were stable  throughout the test. The Ra: 0.7 mm specimen produced a lower friction coefficient than the Ra: 0.4 mm  specimen. With the shot peening films, 0.5-µm WS 2 shot peening produced the lowest and most stable  friction coefficient.  Results of the rotary tribo tests  Figure 10 shows the temperature dependence of friction coefficient for two types of WS 2 shot peening  measured by rotary tribometer with a load of 10 N and speed of 0.1 m/s in a 10-5 Pa vacuum condition at several temperatures. These friction tests were continued for a nominal 1000 cycles, or the test was  interrupted when the frictional force became high.  Friction coefficients of 0.5-μm WS 2 shot peening and 2-μm WS 2 shot peening increase almost linearly with  increasing test temperatures. Friction coefficient of 0.5-μm WS 2 was lower than that of 2-μm WS 2 at all  temperatures. Testing of the 2- µm WS 2 was terminated before reaching 500°C due to wear-through of the  WS 2 layer. The 0.5-μm WS 2 shot peening coupon did not reach 1000 cycles at 300°C for the same reason.  Although 2-μm WS 2 shot peening did not produce the lowest friction coefficient, it did maintain friction  coefficients below 0.1 at 400°C in the vacuum. We propose that 2-μm WS 2 shot peening has potential for  continued research for high-temperature spacecraft applications.  Since spacecraft generally receive no maintenance after launch, the durability of the coating and wear life  in the intended environment are considered. Figure 11 shows the comparison between WS 2 bonded films  and MoS 2 bonded films by rotary tribometer with a load of 30 N and sliding speed of 0.5 m/s in a 10-5 Pa  vacuum condition at high temperatures. These films were made by the same coating method using the  same inorganic binder. The endurance life of WS 2 was longer than that of MoS 2 at all temperatures tested  under vacuum [14].  Figure 10. Behavior of friction coefficient of 2-μm powder WS 2 and 0.5-μm powder WS 2 with increasing  temperature by Rotary tribometer in vacuum  NASA/CP—2018-219887 121
Figure 11. Comparison of endurance life between WS 2 bonded film and MoS 2 bonded film by Rotary  tribometer in vacuum at elevated temperature (300°C, 400°C, 500°C).  IPXRD observations  For each specimen, a two-dimensional diffraction image was used to capture the diffraction pattern in worn  and non-worn areas, as shown in Figure 12. The (0002) plane is formed and the (0004) plane overlaps a  layer. The (0002) plane consists of the two hexagonally closed-packed sulfur atom layers which form the  slip-plane. All specimens were fixed at an angle of 45 degrees for measurement conditions of the (0002)  plane. Existence of the (0002) plane is established from X-ray Debye ring patterns. An area detector is  used to obtain a 360° Debye-ring pattern and to quantify the textured structure because the development  of preferred orientation was expected during the friction test.   No clear (0002) plane Debye-ring pattern was detected from the bonded films in the non-wear points. This  is likely due to the fact that the WS 2 particles are distributed randomly in a binder so the (0002) planes do  not align. WS 2 sputtering film did not show the (0002) planes on the non-wear point. Consistent (0002)  plane Debye-ring patterns were detected from the wear points on all coupons. Only WS 2 shot peening film  showed (0002) Debye-ring patterns before friction. Since there is no doubt that the existence of the (0002)  plane is the friction mechanism for tungsten disulfide[15], the presence of the (0002) plane before wear is an  important point. The relationship between friction coefficient and X-ray diffraction results is shown in Table  5. All WS 2 coating films showed extraordinary low measured friction coefficients at room temperature. The friction coefficient was lowest in the specimens having only pure WS 2 coatings.0 2000 4000 6000 8000 10000300℃ Number of rotationTested temperatureWS2 MoS2 0 500 1000 1500 2000500℃ 400℃ Number of rotationTested temperature WS2 MoS2 NASA/CP—2018-219887 122
Figure 12. X-ray Debye ring patterns and Intensity profile against β angle of (0002) plane on the wear  point and non-wear point of WS 2 specimen surface.   Table 5. Results of friction test and X-ray diffractions  Coating Method Bonded Sputtered Shot Peening  Lubricant WS 2 Film Thickness [μm] 10 1.5～1.8 0.1 ～0.5  Friction Coefficient at Room temperature 0.01～0.06 0.016 ～0.028 0.01 ～0.02  Endurance life at Room temperature Not less than  100,000 Not less than  10,000 Less than  10,000  Friction Coefficient at 400°C 0.05～0.23 - 0.06～0.1  Friction Coefficient at 500°C 0.05～0.15 - Doesn’t work  (0002) Plane in Non-Wear Region △ × ○  (0002) Plane in Wear Region ○ ○ ○  〇: Exist, ×: Not Exist, △: Partially Exist Figure 14 demonstrates the temperature dependence of the half width of (0002) peaks in Figure 13. The  half width of (0002) peaks decreased with increasing test temperature from room temperature to 200°C,  however, the half width jumps to a high value at 300°C. Data of half width at 300°C are scattered widely,  since different areas were examined. The half width of the X-ray peak is directly related to both grain size  and elastic strain of the WS 2 crystal. As severe deformation occurs during friction, materials can undergo  recovery and recrystallization at elevated temperature. WS 2 could be recrystallized to form finer grains at  temperatures above 300°C. The abrupt increase of the half width can be explained by a recrystallization  process of the WS 2 film.  NASA/CP—2018-219887 123
Figure 13. Measurement half width of (0002) peaks by X-ray Debye ring patterns  Figure 14. Effects of test temperatures on half width of (0002) peaks on 2-μm WS 2 shot peening  00.10.20.30.40.50.60.70.8 0 100 200 300 400 500 600HALF WIDTH /DEGREE TEMPERATURE / ℃WEAR NON WEARDebye ring of wear  point in 400 °C case (0002)half width of Debye ring NASA/CP—2018-219887 124
References  1. Robert L. Fusaro. "Lubricant of Space System." NASA/ TM-1994-106392 , (1994). 2. Peter M. Magie. "A review if the properties and potentials of the new heavy metal derivative solid lubricant." Lub. Eng ., (Jul.1966). 3. William A. Brainard. "NASA Technical note." NASA TN D-5141 , (10. Apr. 1969). 4. S Watanabe, J Noshiro, S Miyake: Friction properties of WS 2/MoS 2 multilayer films under vacuum environment, Surface and Coatings Technology Vol. 188–189, pp 644–648, (2004). 5. Somuri Prasad and Jeffrey Zabinski. " Hollow nanoparticles of WS 2 as potential solid-state lubricants", Nature  387, 761-763, (19 June 1997). 6. L. Rapoport, V. Leshchinsky, M. Lvovsky, I. Lapsketr, Yu. Volovik, Y . Feldman, R. Popovitz-Biro, R. Tenne. " Superior tribological properties of powder materials with solid lubricant nanoparticles", Wear 255, pp.794-800, (2003). 7. Fredrik G., Fredrik S., Ulf B., Staffan J. " Nanoparticle based and sputtered WS 2 low-friction coating – Differences and similarities with respect to friction mechanisms and tribofilm formation", Surface & Coating Technology,  232, pp.616, (2013). 8. Monica Ratoi, Vlad Bogdan Niste, Jhon Walker, Jurgita Zekonyte. "Mechanism of Action of WS 2 Lubricant Nanoadditives in High-Pressure Contacts" ，Tribol. Lett . DOI 10.1007/s11249-013-0195-x, (21 August 2013). 9. V. L Kalikhman: Izv. Akad. Nauk SSSR, Neorg. Mater . 19, 1060, (1983). 10. Farr, J.P.G., "Molybdenum Disulfide as a Lubricant: A Review of the Fundamental Knowledge", Wear ,10, 442-452, (1967). 11. Spalvins, T., "Deposition of MoS 2 Films by Physical Sputtering and Their Lubrication Properties in Vacuum," ASLETrans ., Volume 12, pp.36-43, (1969). 12. Johnson, R. L., "A Review of the Early Use of Molybdenum Disulfide as a Lubricant," NASA TMX 52343, (1967). 13. K. Matsumoto, H. Shiomi, S. Kawamoto, Y. Ohkawa, K. Iki, and A. Takahashi,  "Mechanisms and lubrication of electrodynamic tether system for debris removal", 1 5th European Space Mechanisms & Tribology Symposium,  (25–27 September 2013). 14. K. Matsumoto, M. Suzuki, T. Nogi, Y. Aoki, M. Kawamura, “Tribological characteristics of several bonded MoS 2 films under various conditions." JAXA-RM-07-020 , (31. March.2008). 15. A. Takahashi, and K. Hashimoto, "Evaluation of Frictional Properties of Tungsten Disulfide Bonded Films at High Temperature in Vacuum Environments." J. Japan Inst. Met. Mater. Vol. 80, No. 4, pp. 289-296, (11. March. 2016). NASA/CP—2018-219887 126
Figure 1. Roughness profiles of pinion teeth, measurement along the involute direction.  (a) Prior to sputtering. (b) After sputtering and then exposure to humid air. Gear Test Rig To accomplish gear testing in vacuum, a test rig previously used for testing of rollers [5-7] was adapted  for gear testing. To adapt the rig, the spacing from the input to the output shaft was increased from  36 mm used for roller testing to 112 mm for gear testing. Otherwise, the rig setup was the same as had  been used for roller testing.  The vacuum gear rig is depicted in schematic form in Figure 2. The pinion motion is provided by a  variable speed electric motor. A magnetic-particle brake attached to the output shaft imposes torque on  the gear. A pressurized air cylinder controls the pinion position. The air cylinder acts through a pivot axis  to rotate the drive motor plate that mounts the driving shaft and drive motor. The rotation of the drive  motor plate moves the pinion toward the gear in an arc motion to bring the teeth into mesh. The pressure  to the cylinder, and thereby shaft center distance, is adjusted by a hand-operated valve. A linear variable  displacement transducer (LVDT) measures the position of the drive motor plate, and this sensor output  was used to establish the proper operating center distance. The rig features a turntable that is used to  impose controlled misalignment of shafts for roller experiments. For gear testing, the turntable was  adjusted to provide for an aligned shaft condition. A turbomolecular pump assisted by a scroll pump  provides vacuum in the test chamber. Ferrofluid seals maintain the vacuum at the shaft-chamber  interfaces. The typical condition in the test chamber is a pressure of 3x10-7 Torr. The most prevalent  remaining constituent in the chamber during testing is water vapor as was determined using a residual  gas analyzer [8].  The torque on the output shaft is measured by a strain-gage type torquemeter of 22 N-m (200 in-lb)  torque capacity. Calibration was done in place using deadweights acting on a torque arm of known length  attached at the test gear position and reacting the output shaft to ground.  NASA/CP—2018-219887 129
(a)    (b)  Figure 2. Schematic representation of vacuum gear rig.  (a) Side view.  (b) Overhead view.  The force created by the meshing gear teeth can be described as three orthogonal forces. Each of these  force components influences a sensor as will be described with the aid of Figure 2. The tooth force  component directed tangent to the pitch circle is termed the tangential force. The torque on the gear is a  product of the tangential force and the operating pitch radius. The gear tooth tangential force attempts to  rotate the drive motor plate about a pivot axis, but the table is constrained to the turntable through a load  sensor termed as the “tangential” force sensor. The tooth force component directed along the line joining  the gear centers, the separating force, acts through a pivot axis and thereby attempts to tilt the drive  motor table, but the table motion is constrained by the air cylinder through a sensor termed the  “separating load” force sensor. Because the drive motor plate is not balanced about the pivot point, the  force measured on this “separating force” sensor is a combination of the gear separating force action and  the unbalanced overhung weight of the motor and plate. The third component of gear tooth force acts  along the direction of the gear shaft, the gearing thrust force. Although spur gears create, theoretically,  zero thrust forces, in practice a thrust force is indeed created because of inevitable manufacturing  tolerances and small mounting misalignments. The magnitude of the resulting thrust force depends in part  NASA/CP—2018-219887 130