Lightweight body armor is important for the protection of US soldiers in the field. Here, fabrication techniques were developed for producing graded porosity B{sub 4}C, and for producing aluminum-B{sub 4}C and epoxy-B{sub 4}C functionally graded materials. The key fabrication aspect was obtaining the graded porosity B{sub 4}C. The feasibility of producing graded porosity B{sub 4}C using a grading of carbon densification aid produced from a gradient of furfuryl alcohol carbon precursor was demonstrated. This approach is quite promising, but it was not optimized in the present investigation. Graded porosity B{sub 4}C materials were produced by a layering approach using different size distributions of B{sub 4}C powders in the green state, and then densifying the layered assembly by hot pressing at 1,900 C. The hardness of uninfiltrated graded B{sub 4}C, aluminum infiltrated B{sub 4}C, and epoxy infiltrated B{sub 4}C was observed to be similar

Hoover, R. C.

Kise, C. D.

McClellan, K. J.

Petrovic, J. J.

Scarborough, W. K.

UNT Digital Library

Em LA- U R- 9 J Approved for public release: distribution is unlimited. Title: Author(s): Submitted to Los Alamos N A T I O N A L  L A B O R A T O R Y  FUNCTIONALLY GRADED BORON CARBIDE J. J. Petrovic K. J. McClellan C. D. Kise R. C. Hoover W. K. Scarborough #A! 2 8 O S T f  22nd Annual Cocoa Beach Conference and Exposition. January 20-24, 1998 b DISTRIBUTION OF W1S DOCUMENT 1s UNUMIlEl3 Los Aiamos National Laboratory, an affirmative action/equal opportunity employer, is operated by the University of California for the U.S. Department of Energy under contract W-740CENG-36. By acc8ptance of this article, the publisher recognizes that the U.S. Government retains a nonexclusive, royally-free license to publish or reproduce the published form of this contribution, or to allow others to do so, for U.S. Government purposes. Los Alamos National Laboratory requests that the publisher identify this article as work performed under the auspices of the U.S. Department of Energy. The Los Alamos National Laboratory strongly supports academic freedom and a researcher‘s right to publish; as an institution. however, the Laboratory does not endorse the viewpoint of a publication or guarantee its technical correctness. Form 836 (1 W96) This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government oor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or use- fulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any spe- cific commercial product, process. or senice by trade name, trademark, manufac- turer, or otherwise dots not necessariiy constitute or imply its endorsement, m m -  mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. FUNCTIONALLY GRADED BORON CARBIDE J.J. Petrovic, K.J. McClellan, C.D. Kise, RC. Hoover, and W.K. Scarborough, Materials Science & Technology Division, Los Alamos National Laboratory, Los Alamos,NM 87545 ABSTRACT and for producing aiuminum-B4C and epoxy-B4C finctionally gaded materials. The key fabrication aspect was obtaining the graded porosity BJC. The feasibility of producing graded porosity B& using a grading of carbon densification aid produced fiom a gradient of fi&ryl alcohol carbon precursor was demonstrated. This approach is quite promising, but it was not optimized in the present investigation. Graded porosity B4C materials were produced by a layering approach using different size distributions of B4C powders in the green state, and then densifying the layered assembly by hot pressing at 1900 "C. The hardness of uninfiltrated graded B4C, aluminum infiltrated B4C, and epoxy infiltrated B4C was observed to be similar. Fabrication techniques were developed for producing graded porosity B4C, INTRODUCTION the field. Advanced body armor must satisfy a number of factors: Lightweight body armor is important for the protection of U.S. soldiers in . Ballistic performance: It must defeat the specified threat in accordance with standards developed by the military and the National Institute of Justice (NIJ). Weight: Additional weight carried by the soldier should be minimized. At least a 40% reduction fiom the present weight at the same or greater threat level. Multi-hit capability: Ability of the armor to defeat multiple hits within an approximately 5 cm spacing of hits. Articulation: Comfort and ability to conform to body shape and movement. Heat load: Removal of body heat during periods of high stress or activity. Multi-threat capability: Provide protection from additional threats such as sharp penetrators. 1 Protection of extremities: The armor should protect as much of the soldier as possible, including neck and extremities. Biunt trauma: A specification that the deflection of the back of the armor not exceed 44 mm. This requirement prevents damage to internal organs and is a major design requirement. Cost: For special military applications, cost is not an important factor compared to the value of the soldier, but in most cases cost is important. The present top-of-the-line body armor vests are the Army PASGT and the Ranger vests. The Ranger vest is capable of defeating an NU Level III threat (high powered rifle, 7.62 NATO metal jacket (<2750 fvs), 5.56 NATO metal jacket, 12 gauge shotgun rifled slug), but only with the use of A 1 2 0 3  ceramic plate inserts and a vest areal density of greater than 6 pounddsquare foot. At the current time, there is no body armor system capable of defeating NTJ Level N threats, namely armor piercing rifle fire (-30 caliber armor piercing, <2850 tvs). The objective of the present work was to develop materials for an FGM- based armor concept, where a hard ceramic front face would transition gradually to an energy absorbing metal or polymer back face. In this concept, the hard ceramic face would blunt the projectile threat, while the tough back face would allow for energy absorption and shrapnel containment. MATIERIALS carbide (B4C) was chosen as the ceramic material since it is very lightweight (density 2.52 gdcm’) and very hard (hardness of 30 GPa) (1). Commercial B4C powders were obtained from the ESK Corporation. Aluminum was chosen as the metal material because of its light weight, and because of previous work on Al- B4C cermets (2). A Ciba Geigy 05 10 epoxy was chosen as the polymer material, due to its low viscosity and good wetting behavior with B4C (3). The materials chosen for the FGM-based armor were the following. Boron GRADED POROSITY B4C The key t o  producing boron carbide-to-aluminum and boron carbide-to- polymer FGM materials is the production of graded porosity BJC microstructures. Two approaches were examined: 1) Densification aid gradients; 2) Green density gradients. These approaches were selected because they were considered to be cost effective and commercially viable, Densification Aid Gradients approximately 6 wt.% is indicated to be optimum for maximizing the sintered Carbon is the major densification aid for B4C. A carbon addition level of 2 density, for sintering temperatures in the range of 21 70-2270 "C (4). Furfuryl alcohol (CsH70$ was chosen asthe source for the addition of carbon to the B4C powders (5). FurfUryI alcohol is a liquid at room temperature and uniformly coats fine B4C powder particles. This material decomposes to nanosize carbon when heated to 850 'C, producing a 40 wt.% carbon yield. It can be diluted with acetone. To produce functionally graded porosity in B&, the approach adopted was to start with a 50% dense cold pressed powder disc (3 1.8 mm diameter x 6.35 mm thick), and then paint fUrfury1 alcohol layers on one side of the disc, using a simple paint brushing technique. The fUfiryl alcohol would then penetrate the cold pressed disc in a graded manner, leading to a gradient in carbon content. B& discs coated in this manner were heat treated to carbonize the furfuryl alcohol (5), then hot pressed in graphite dies at 1900 "C and 20 MPa for one hour in an argon atmosphere, to densify the B4C. The feasibility of this approach was demonstrated, in that a B4C pellet with 25% porosity on the painted face and 37% porosity on the unpainted face was produced. Thus, the fUrfUryl alcohol painting approach was promising. However, for programmatic reasons, it was not possible to optimize this approach to achieve a larger porosity gradient. Optimization of the fiifiryl alcohol approach would require applying the fUrfuryl alcohol in a more controlled manner than hand painting, so that the graded carbon concentrations obtained from its decomposition would be reproducible and better characterized. Green Density Gradients Three different grades of ESK commercial B4C powders were used in the investigation. F400 powder had an average particle size of approximately 30 pm. F1200 powder had an average particle size of approximately 5 pm. 3000F powder had an average particle size of approximately 0.5 pm. These B4C powders were employed to produce layered green density materials. Discs were prepared with five 1 mm thick layers of the following powders: 3000F, 3000F/F1200, F1200, F1200/F400, F400. The mixed-powder layers were a 50-50 wt.% mixture. The above five powder configurations were hand-layered in a graphite hot pressing die, and then hot pressed at 1900 "C and 20 MPa for one hour in argon, to densify the layered assembly. Figure 1. The percent densities of the various layers are: 3000F, 96%; 3000F/F1200,90%; F1200,87%; F1200/F400,66%; F400,49%. Thus, a substantial porosity gradient was achieved by this approach. Ultrasonic vibration of the green density layers for 30 seconds was effective in grading some of the layer boundaries, particularly at the lower density regions. B4C graded porosity microstructures obtained in this manner are shown in TOP - as-layered vibrated (SO SI ___)_ BOTTOM Figure 1 : Graded porosity B4C microstructures derived from the layering of B4C powders. Microstructures for both as-layered and vibrated are shown. INFILTRATION OF GRADED POROSITY B,C Molten aluminum infiltration of the graded porosity 3,C materials shown in Figure 1 was performed by the heating of pieces of aluminum stacked above the graded porosity B4C pellet. The infiltration was performed by rapidly heating to 4 - 1300 "C in vacuum, then immediately coolins. The temperature of 1300 "C was chosen because previous work (2) indicated very low wettins contact angles for aluminum on B4C at this temperature. The short time was chosen to minimize the formation of reaction phases between the aluminum and the BJC (2). Epoxy infiltration into the graded porosity B4C materials of Figure 1 was performed at room temperature under vacuum conditions. In this case, the graded porosity disc was immersed in the epoxy under vacuum, until the epoxy material hardened. PROPERTIES OF FGM B4C MATERIALS The microhardness behavior of the graded porosity B4C and of the B4C- aluminum and B4C-epoxy FGM materials was examined. Figure 2 shows 10 kg Vickers microhardness indentations in the 49% dense layer and the 96% dense layer of the graded porosity B4C. 49 % dense 96% dense F igre  2: 10 kg Vickers indentations in porous and dense layers of graded porosity BJC. -. The 49% dense Iayer exhibits little cracking near the indentation, probably due to densification processes under the indentation. In contrast, the 96% dense B,C layer shows a highly brittle indentation, with extensive lateral cracking. A comparison of uninfiltrated, aluminum infiltrated, and epoxy infiltrated B,C is shown in Figure 3. Plastic deformation of the aluminum in the aiuminum infiltrated FGM is clearly evident in the Iight aluminurn phase at the indentation. The epoxy infiltrated indentation is similar in appearance to the uninfiltrated indentation. 5 Uninfiltrat ed Aluminum infiltrated Epoxy infiltrated Figure 3 : 10 kg Vickers indentations in BJC region containing 5 1 % porosity in the uninfiltrated condition. Hardness versus B& % density is shown in Figure 4, for the uninfiltrated B4C, the B4C-aIuminum FGM, and the B4C-epoxy FGM. 40 35 30 - - h m n 2 25 - ul u) 20- s 15 - I 10 + Uninfiltrated -I)- AT infiltrated + Epoxy infiltrated 51 I 1 1 I I 40 50 60 70 80 90 100 84C %Density Figure 4: Hardness versus B4C density for uninfiltrated, aluminum infiltrated, and epoxy infiltrated condition. 6 The hardness is little affected by infiltration with either the aluminum or the epoxy. This indicates that the B4C is the only phase controlling the hardness, since it is much harder than either the aluminum or the epoxy. The hardness of 49% dense B4C is approximately 10 GPa, while that of 96% dense B4C is approximately 30- 35 GPa. REFERENCES . I. F. Thevenot, ‘Boron Carbide-A Comprehensive Review”, J. European Ceram. SOC., 6,205-225 (1990). 2. D.C. Halverson, AJ. Pyzik, LA. Aksay, and W.E. Snowden, ‘?Processing of Boron Carbide-Aluminum Composites”, J. Am. Ceram. SOC., 72, 775-780 (1989). 3. D. Hemphill, Los Alamos National Laboratory, private communication. 4. S.L. Dole and S. Prochazka, ‘Densification and Microstructure Development in Boron Carbide”, Proceedings, January 1985 American Ceramic Society Cocoa €leach Meeting, Cocoa Beach, Florida. 5. U.S. Patent No. 3,124,625, H. Sheinberg, J.R. Armstrong, and D.H. Schell, Los Alamos National Laboratory, 10 March 1964. ACKNOWLEDGEMENTS National Laboratory for this work. The authors would like to acknowledge the support of the Los Alamos 7 

Functionally graded boron carbide

https://digital.library.unt.edu/ark:/67531/metadc689062/m2/1/high_res_d/304111.pdf

Functionally graded boron carbide

Abstract

Similar works

Full text

Available Versions

UNT Digital Library