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[AD AD-E4CO 972 TECHNICAL REPORT ARLCD-TR-82028 ,,",EROSION RESISTANCE EVALUATION OF 'eV POTENTIAL GUN BARREL COA fINGS ARTHUR J. BRACUTI JOSEPH A. LANNON LARGEC ALBE WA ERAPDON YT LABORATORYE PAOIMCR . 91SEEAY - 4 APUSOARM AORMAMENTC FEEASE: ANTDBUIO UNELIMINTE COMN LAGECLIE OTI C.)j The views, opinions, and/or findings contained in this report are those of the author(s) and shoald . not be construed as an official Deps rtment of the Armyv position, policy, or decision, unless so designated by other documentation. The citation in this report of the narr~s of firms or commercially available -comMercial products or services does not constitute official en~dorsement by or approvai of the U.S. Government. -~ .Destroy this report when no longer needed. Do IL- . - - - -- UNCLASEIFIED SECURITY CLASSIFICATION OF TMIS PAGE (Whan Does 5,IreV REPORT DOCUMENTATION PAGE IWMCPLMG m 1. REPORT NlUMUeR GO. T AC988IO1 NO: S. RCIPIENT'S CATALOG NUMBER Technical-Repgrt ARLCD-TR-82 028 ' . -APEOCVRD 4. 1ITLt (and Swbiltle S TYPE OF REPORT&PE00C2Ia EROSION RESISTANCE EVALUATION OF Final POTENTIAL~~~JA ~98GU04 ARLCAIG - Jan 1981 POTETIA CATGIUGNSBSA.R EL PERFORMING ORO. REPORT NUMBER 7. AUTHOR(e) D. CONTRACT Oft GRANT NUMSIE194) Arthur 3. Bracuti. Joseph A. Lannon, Louis A. Bottei, Project Engineers, AREMDCOM :D. Bhat, San Fernando Laboratories ______________ S. PERFORMING ORGANIZATION NAME AND ADDRESS IT -PROGREALME MENT, PROJECT. TASK ARRADCOM, LCWSL AREA St WORK UNIT NUMBERS Applied Sciences Div (DRDAR-LCA-G) TOA 9 Dover, NJ 07801 ______________ ARRADCOM, TSD Feray18 STI.CNTROD L.N FFIC ANMDRE ND CDE IS. RUMEPRTOD ATE Unclassified 16 DISTRIBUTION STATEMENT (of this Report) Approved for public release; distribution unlimited. 17. DISTRIBUTION STATEMENT (of the abstract entered in Block 20. If differet from Report) K It. SUPPLEMENTARY NOTES Dr. Bhat was responsible for applying the various sample coatings to reduce gun barrel erosion. IS. KEY WORDS (continue ani reverse side It necesary mid Identify by bloc$, number) Gun barrel coating Gun barrel erosion 0 Gun barrel wear 20. ABSTRACT (Caftmin a iowairs 014110 f nmemyfl ad Identlif by block numnbor) The erosion resistance of tungsten/carbon and tantalum/tungsten deposited on AISI 4340 steel and molybdenum substrate were investigated. Erosion data ac- * quired with the ARRADCOM test device indicated poor adhesion between each re- S fractory metal coating and 4340 steel. Mechanical failure of the molybdenum substrate complicated the erosion data, but it was concluded that the tungsten/ carbon coating performed better than steel at higher pressures. No apparent ad- vantage was observed with the tantalum/tungsten coating at any pressure. (cont) DID 1473 FA'7 EDITION Of I NOV 69 IS OBSOLETE UCASFE SECURITY CLASSIFICATION OF THIS PAGE (When Does Britered) INCLASSIFTED SECURITY CL.AWPICATION OPP THIS PAIK~ DOS 20. ABSTRACT (cont) Microscopic examination of the coatings shoved extensive gas erosion of the surface of the tantalum/tungsten coating, but very little erosion in the tungsten/ carbon surface. UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGEr'Shon Date Enteed,) CONTENTS Page Introduction 1 Procedure I Tungsten/Carbon Coatings I Tantalum/Tungsten Coating 2 Erosion Testing 2 Results and Comparisons 3 Steel Sleeves (AISI 4340) 3 Tantalum/Tungsten Coatings (Steel Sleeves) 4 Molybdenum Sleeves 5 Tantalum/Tungsten Coatings (Molybdenum Sleeves) 6 Conclusions 6 Distribution List 21 AcOession For NTIS GRA&I DTIC TAB U Justific3ati- ByJ 7... D .. p. p. TABLES 1 Typical conditiond for depositing Q4500L and 90Ta-10W alloy 7 2 M30 composition and phyuico-chemico properties 8 3 Erosion data for CK500L coated steel sleeves 9 4 Erosion data for AISI 4340 steel 9 5 Erosion data for Ta/W coated steel sleeves 10 6 Erosion data for C4500 coated molybdenum sleeves 11 7 Erosion data for Ta/W coated molybdenum sleeves 13 I. - *- * * FIGURES I Erosion apparatus 15 ' 2 4500L coating on steel (600X/3000X) 16 3 Eroded CH500L coating on steel (SSOX/220OX) 16 4 Fractured and eroded Ta/W coating on steel (ISOX) 17 5 Eroded steel substrate adjacent to Ta/W coating 17 (700X/3500X) 6 04500 coating on molybdenum substrate with radial crack 18 7 Eroded CH500 coating on molybdenum substrate (60X/350X) 18 8 Chipped C4500 coating at bore leading edge (220X/IOOX) i9 M INTRODUCTION This report documents an attempt to minimize or reduce gun barrel erosion in large caliber guns. The correction of the gun barrel erosion problem can be addressed from several directions* One approach is to formulate new propellants or modify current propellants to produce less erosive combustion products without significantly sacrificing I-'nvllant energetics; another is to modify gun barrels in some way to better resist the erosive combuation environments ,roduced bv current propellants. Both approaches have been used with varyi, degrees of success, including new low flame-temperature propellants and tradiL 'al plating of gun barrels with chrome, Although refractory metals that are potentially superior to chromium have been available, and more are being discovered every day. limited use has been made of these materials because of the difficulties encountered in coating gun barrels. Recently, however, coating deppsition technology has made such stridea that use of these exotic refractory metals in gun barrels is now feasible. Spe- cifically, Cullinan and D'AndreaI reported encouraging results in using tantalum coated 20-mr steel liners. The main thrust of this program was to develop refractory coatings suitable for use in large caliber gunt . Three candidate refractory metal alloys, tungsten/ (cid:127). cargon alloy; (CH500) low-temperature deposited tungsten/carbon alloy; (CM500L), and 98% Ta/2% W alloy were applied to AISI 4340 steel and molybdenum substrates to test each alloy's erosion behavior under controlled, simulated gun firing S~ conditions. PROCEDURE Tungsten/Carbon Coatings Both AISI 4340 steel and molybdenum inserts were coated with tungsten/carbon alloy by means of the chemical vapor deposition (CVD) process. The steel samples were coated at low temperature (725 K) wIth tungsten carbon alloy (W/C), identified by the contractor as C4500L, while the molybdenum inserts were coated at higher temperatures ranging from 1165 to 1245 K with the W/C alloy identified by the contractor as CM500. To protect the steel substrate from the corrosivity of the reactive gases at the deposition temperature when WF is used as the tungsteu precursor, an initial 6 1R. Cullinan and G. D'Andrea, "Ercrion Studies of Tantulum Gun Barrels," 1980 JANNAF Propulsion Meeting, vol 1, p 201, 1980. thin layer of relatively inert metal, in this case electroless nickel, was deposited onto the steel substrate. In addition to being inert, nickel is also compatible with both steel and tungsten. The deposition parameters, substrate temperature, chamber pressure, gas flow rate, and gas composition are presented in table I. Tantalum/Tungsten Coatings Test inserts of AISI 4340 steel and molybdenum were coated with Ta/W alloy at deposition temperatures ranging from 1300-1450 K. An initial layer of titanium was deposited from the vapor phase onto the steel substrate to form an inter- layer which is compatible with both iron (steel) and tantalum. Titanium waa selected rather than nickel because, in addition to the higher melting point, -titanlum also reacts with the carbon and the steel substrate to form a thin surface layer of titanium carbide (TiC). This stable TiC layer is an effective carbon diffusion barrier which prevents any further interaction of carbon in the steel with the tantalum coating. This eliminates the possibility of the forma- tion of the undesired brittle -TaC. After this titanization process, Ta/W alloy was coated onto the Ti-TiC layer. This was accomplished by passing chlorine over 90 Ta/IOW alloy chips from a mixture of metal chloride gases, Ta C1 (g), WC1I 5 (g), WCI (g) which was reduced onto the substrate surface by hydrogen aa Ta/0 alloy. 1lthough the target composition was 90% tantalum and 10% tungsten, the achieved composition was 982 tantalum and 2% tungsten. The working parameters for this process are presented in table 1. Erosion Testing The erosion data were obtained with a closed bomb modified to accept a gun barrel and i cylindrical metal erosion sleeve. This variation of the elosed bomb is usually referred to as the vented erosion tester and is shown in figure 1. In this investigation, the erosion sleeves consisted of AISI 4340 steel, refractory metal coated AISI 4340 steel, and refractory metal coated molybdenum. Each sleeve was fabricated to have an outer diameter of 2.70 cm, an inner diameter of 0.95 cm, and a length of 2.06 cm. The average masses of the steel and molybdenum erosion sleeves were 80 g and 103 g, respectively. A pressure transducer posi- tioned inside the chamber (closed bomb) was connected to a Nicolet digital oscil- loscope which was scaled to display pressure versus time. To control pressure, a stainless steel rupture disc was inserted between the barrel and the erosion sleeve. In addition, the barrel was filled with water and a rubber stopper inserted into the muzzle to insure proper pressure %uildup. The Bach CM50OL coated steel sleeve and the CM500 coated molybdenum sleeve were cleaned, weighed, fired three times, recleaned, and reweighed. After three -hots, the average weight loss was used as a measure of erosivity. For the Ta/W- coated steel sleeves, an initial single-shot mass loss was measured for each sample. All subsequent measurements made on thebe samples were based on average 2 .- I weight losses for three successive shots. All erosion measurements made on Ta/W- coated molybdenum sleeves were based on single shot weight-loss measurements. The internal ballistics were controlled by arbitrarily adjustLng the pro- pelling charge weights to 30, 40 and 30 g which yielded peak pressure in the ranges of 150, 180 and 260 MPe, respectively. Since the same propellant (K30) was used throughout this study, flowe temperature was a constant while burn times and peak pressu,-es were measured charge-mass dependent parameters. The composition and physleo-chemico properties of M30 propellant are listed in table 2. RESULTS AND COMPARISONS Steel Sleeves (AISI 4340) CH500L Coatings Two steel sleeves identified as nos 398 and 400 were received from the contractor with CK500L coatings of 0.010 ca and 0.015 cm thicknesses, respectively. Cursory visual examination by the Large Caliber Weapon Systems Laboratory indicated that each coating was deposited uniformly along the bore surface with no apparent local areas of defects. However, the contractor reported2 that the coating on sleeve no. 400 did not appear to be as well bonded to the bore surface as did the oth r coatings. The hardness of the coating on sleeve no. 398 varied from 700 kg/mm HV N near the steel substrate to 2400 kg/mm2 HV at the i.d. 50 U free surface. This hardness gradient was caused by the incorporit~on of carbon into the tungsten coating during the process. This results in a carbon rich tungsten carbide and tungsten layer at the i.d. free surface which displays greater hardness. The erosion test data for the 04500L-coated sleeves are presented in table 3. In this work, all bore surface losses are reported as volume losses rather than mass losses. This departure from the usual convention of reporting mass losses was necessary to normalize all erosion data to a common scale to make erosion comparisons among the different coatings and steel meaningful. Erosion data, obtained in the 150 MPa range indicated that sleeve no. 398 with the 0.010 cm CM500L coating retained 89.0% of the coating after three shots and 73.7% after the ninth shot, while the sleeve no. 400 with the 0.015 cm. coating retained only 0.782 of the coating after three shots and 0.00% after the six shots. On an averale per shot basis, the sleeve with the 0.010 cm coating lost 0.0017 + .00041 cm- and the other sleeve lost 0.01045 * .01696 cm3. Steel sleeves on the other hand, displayed an average per shot erosion value of 0.00067 .00014 in the 150 MPa pressure range (table 4). A comparison nf these data suggested that 4340 steel apparently erodes less per shot thu.". does CM500L alloy. The larger standard deviations observed in the erosion data for QC500L 2 chemetal letter from Rcber(cid:127) ilolzl dated October 8, 1(79. 3