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REPORT No: NML/MST/IAF/1.13/69/2005 Restricted Circulation
December, 2005
FAILURE ANALYSIS OF COPPER DRIVING BANDAND DE-COPPERING AGENT OF 30 mm GSH HEI
(INERT) AIRCRAFT AMMUNITION------
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Sponsored by.. 28 ED, Air ForceAmla Depot (PO)
MP -460553
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Materials Science & Technology Division
National Metallurgical Laboratory
(Council of Scientific and Industrial Research)
Janlshedpur - 831007~
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}NATIONAL METALLURGICAI,.. LABORATORY
(Council of Scientific & Industrial Research)JAMSHEDPUR
PROJECT COMPLETION REPORT
Project Title: FAILURE ANALYSIS OF Project No.: If--{ 1>-q lfl)'1COPPER DRIVING BAND AND DE- (Report No.: (NM L/MST/IA F/1.13/69/20(5)COPPERING AGENT OF 30mm GSH HEI
Date of Project Initiation:27.1 0.2005(INERT) AIRCRAFT AMMUNITION.
Date of Completion: 09.] 2.2005
Project Team Members: Class: Public document (Free/Priced)Dr. S. R. Singh (PL) Restricted circulation (X)Dr. M. Ghosh (CoPL) Only to clientMr. S. K. Das Secret
Customer / Client's name and address: Classification:
Wg Cd Sanjay Bose In-houseChief Technical Officer Grant-in-aid
28 ED, Air Force Sponsored (X)Amla Depot(PO) ConsultancyMP - 460553 Collaborative
Date of Report: 12.] 2.2005
Area: Material Characterization. Specify Type:Sub Area: Failure analysis Ongoing Area: (X)
New Area Initiated:
Key Words: Copper-fouling, 300 mm GSH gun, copper-driving band, de-coppering agent, strainhardening, precipitation, intermetallic phases.
Abstract: MIG-29 aircraft is equipped with the 30mm GSH gun firing system, where copper-drivingband (COB) on the projectile provides spin-stabilisation. The de-coppering agent (DCA) is used to cleanthe copper-fouling from the barrel of the gun. The present investigation deals with the root cause ofcopper-fouling in the barrel.COB has high concentration of silicon which is found to be mainly associated with precipitates in thecopper matrix. However. the wet chemical analysis of bulk did not reveal high amount of silicon. Thishappens when the silicon-bearing precipitates in copper matrix are not able to digest in the acid solution.Exceedingly low amount of phosphorous indicates that the COB is not made of specified phosphorousdeoxidized copper (DHP grade). It seems that the copper is deoxidized by silicon. Moreover, the unusedCOB has much higher hardness than the specified limit. This indicates that the COB is made of harddrawn copper which has to be annealed after fabrication. Heat treatment experiments has demonstratedthat the specified hardness is achievable if it is annealed. The strain hardened COB is prone toembrittlement/fragmentation due to high strain rate deformation during the firing and may tends toadhere at the inner wall of barrel. The elemental composition of de-coppering agent (DCA) is as per thespecification limit except Sb content which is little higher than the specified limit. But its effect on the
melting temperature of DC A is insignificant. The differential scanning calorimetry ?f DC A revealed thatthe melting point is 328.I"C while pure lead has melting point of 327.5"C. The observed intergranularcracking at the surt:1ce of the DCA wire seems £l)be originated due to the long-term creep phenomenon.In Pb and Pb-alloys creep is observed to occur at room temperature. Therefore. this do's not seem to because of concern. Moreover. as per the requirements of the specification, the surface of the DCA wire isclean without foreign inclusions and corrosion.
Ih'tails of IPRs (PI tkk): N:\ If no IPR taken, reasons: N:\Patcnt
CopyrightTrade Marks -Rqwrt IssuanCl' Anthlll"ity: Dr. S. R. Singh Signatur': S. R....' s:- <)
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE ANALYSIS OF COPPER DRIVING BAND AND DE-COPPERING AGENT OF GSH 30MM
HEI (INERT) AIRCRAFT AMMUNITIONREPORT NO. NMLlMST/IAF/I.13/69/2005, December 2005
BACKGROUNH
There was a study on the incident of MIG-29 aircraft post 30mm GSH gun firing by an
independent investigation team of IAF, which found thick layer of copper deposit inside the gun
barrel. The copper driving band (CDB) is used to provide spin stabilization to projectile through
rifling action and the de-coppering agent (DCA) is suppose to clear the copper deposits from the
barrel of the gun. These two materials are manufactured indigenously by OF-Khamaria under
transfer of technology from Russia. Residual copper deposits resulted in reduction of diameter of
gun barrel leading to accidents. As the cause of in-efficiency could not be ascertained at 28 ED,
Air Force, Amla Depot, hence there was a request to carry out investigation to find out exact
material composition. In case of non-conformity, the nature of problem it may create inside the
rifling groove/ gun baITeli."~d its effect onlhe performance .0Lpmjectile._at Jh~Jime of firing,
have to be investigated. The work was assigned to NML vide letter No. 28ED/S l7/1/Tech dated
24th Oct'05. Subsequently, foHowing items were brought by Sgt. G. Mishra and received at NML
on 27th Oct'05;
GSH 30mm (I) explosive-free items (unused) consisting oC
i)
ii)
Empty case - six numbers.
Projectile - six numbers.
iii) De-coppering agent - four numbers.
SCOPE OF THE WORK
Based on the information provided and discussions held at N~1L, it is decided to carr)
out following assignments for detailed investigation of the CDB and DCA:
i) Visual observation, dimensional measurements, photographic recordin(1~ and
ii)
determination of sampling locations.
Microstructural analysis of longitudinal and transverse sections of COB and longitudinal
section of DCA by optical and scanning electron microscopy.
iii) Determination of chemical composition of the materials hy \\\:t analysis mcthod and by
energy dispersive spectroscopy.
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE ANALYSIS OF COPPER DRIVING BAND AND DE-COPPERING AGENT OF GSII 301'11'1
HEI (INERT) AIRCRAFT AMMUNITIONREPORT NO. NML/MST/IAFII.13/69/2005, Deccmber 2005
iv) Annealing heat treatment of copper driving band and determination of bulk hardness of
as received as well as annealed copper driving band.
Determination of melting temperature of DCA wire by differential scanning calorimetry.v)
vi) Find out the root cause of failure/ in-effectiveness of COB and/or DCA.
COMPONENT'S MATERIAL AND SERVICE EXPOSURE
The MIG-29 aircraft is equipped with 30mm GSH gun firing system, where copper
driving band (COB) on the projectile provides spin-stabilization through riffling action at the
time of firing to hit the target and the de-coppering agent (DCA) is used to clean the "copper-
fouling" from the wall of barrel of gun. In the present case, the "copper-fouling" are not
removed completely during the firing and causes reduction of inner diameter of the barrel
leading-tonumbe-rOIacCldenfs..-HEl (inert) shells are u~~": for aerial target practice.
The defect investigation at 28ED, Air Force, Amla Depot, MP could not ascertained the
root cause of in-effectiveness of indigenously made (at OF Khamaria) COB and DCA through an
independent investigation. Hence. the components of the system were sent to NML for
identification of material in terms of chemical composition to clarify whether they meet the
specification or not, for finding out actual problem inside the riffling groove/gun barr~1 and its
affect on the perforn1ance of the projectile.
The material specification of COB and DCA are collated in table-I. The COB ring
supposed to be made of99.8% purity phosphorous de-oxidized copper of1S:191 (grade DHP-I
with restricted Bi content) specification. The finished rings should be in annealed condition
haying hardness not more than 55 HV. The DCA wire is made of 99.9% purity lead whose
chemical composition is governed by GOST-3778-77 (Grade C3) and wire diameter and surface
ckanness are goyerned by GOST 5655-67.
2
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE ANALYSIS OF COPPER DRIVING BAND AND DE-COPPERING AGENT OF GSH 30MM
HEI (INERT) AIRCRAFT AMMUNITIONREPORT NO. NML/MST/IAF/I.13/69/2005, Dccember 2005
Table 1: Material Specification of CDB and DCA.
INTRODUCTION
Most guns have a barrel with a ritled internal bore that imparts a stabilizing spin on an
expelled projectile. The internal bore may be coated with a hard .facing material. such as
chromium, to minimize erosive wear, and thus increasing the number of projectiles that may be
fired from the gun. The typical large caliber projectile has a diameter slightly less than the
diameter of the internal bore. One or more rotating driving bands gird the circumference of the
pwjectile. At the driving bands, the diameter of the projectile is slightly larger than the internal
diameter of the gun barn.:!. Whcn thc projectik is cxpclkd, the rotating band is engraved by the
rining, contacting the rifling throughout the kngth of the tubc imparting the projectile with a
J
Component Specification RemarksCopper driving OST 384-365-71 / Cu = 99.80 minband (COB) .ISS4710-1 .Ian 1980 Sn = 0.01 max
/IS:191 Pb = 0.01 maxFe = 0.03 maxNi = 0.15 maxAs = 0.05 maxSb = 0.005 maxBi = 0.0015 maxP = 0.02 to 0.10Se & Te = 0.02 maxTe = 0.01 maxTotal impurities excluding Ag, As, Ni, P = 0.06Hardness not more than 55 BY.- -- - - -- -. -
De-coppering GOST-3778-77 Pb = 99.9 min
agent (DCA) Grade C3 Ag = 0.0015 maxCu = 0.002 maxZn = 0.005 maxBi = 0.06 maxAs = 0.005 maxSn = 0.002 maxSb = 0.005 maxFe = 0.005 max
Mg+Ca+Na = 0.04 maxTotal impurities = 0.1 maxRound lead wire diameter (Governed by GOST5655-67) = 1.25 +/- 0.25 mm. The surface shouldbe free from foreign inclusions and corrosion.
NATIONAL METALLURGICAL LABORATORY, JAMSI-IEDPURFAILURE ANALYSIS OF COPPER DRIVING BAND AND DE-COPPERING AGENT OF GSH 30MM
HEI (INERT) AIRCRAFT AMMUNITIONREPORT NO. NML/MST/IAF/I.13/6912005. Dccember 2005
stabilizing spin. Projectiles for rifles and pistols normally do not have a rotating band, but they
very often have a jacket made out oftombac, which is engraved by the rifling. The gun barrel is
manufactured from a material such as steel and sometimes coated with a hard material such as
chromium facing. The gun barrel is harder than the rotating band of jacket, which is typically
copper or copper alloy. As a result, a portion of the copper from the rotati ng band or the jacket is
deposited on the rifling inside the gun barrel. This copper deposition, referred to as "copper
fouling", can affect the ballistics of the projectile and major fouling can prevent the projectile
from being inserted and seated, positioned in the barrel prior to firing, properly. Copper fouling
is currently a major problem for large artillery weapons, such as 155-millimeter howitzers, and is
also noted in small and medium caliber cannons, such as 20-millimeter canons. The current
solution to copper fouling is including a de-coppering agent into the propellant. The de-
coppering agent removes the copper withOt".-)amaging the gun barreL-A common de-coppering ---
agent is a sheet of lead foil deposited between the propellant and the projectile. On ignition of the
propellant charge, the lead is vaporized and diffuses into the copper adhered to the inner surface
of barrel. The resultant alloy is brittle and easily shattered. The combination of the heat
generated by the burning propellant and the mechanical movement of the propellant gases
separates the brittle lead-copper alloy from the surface of the barrel. The fractured debris is
swept from the muzzle of the gun with the propellant gases. A second viewpoint as to. why lead
foil is effective as a de-coppering agent is that the heat generated by the burning propellant melts
the lead foil. Liquid lead contacts the copper deposition and dissolves the copper. and the copper
bearing lead solution is then expelled as a liquid from the muzzle with the propellant gases.
EXPERIMENTAL RESULTS & DISCUSSIONS
The dis-assembled projectiles and explosive-free casings as well as wires of DCA are
shown in Figs. I (a-c). From the received items. sampling was done for metallographic analysis
by optical and scanning electron microscopy for both COB and DCA. The sampling locations of
con are shown in Fig.l c and indicated in table 2.
4
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE ANALYSIS OF COPPER DRIVING BAND AND DE-COPPERING AGENT OF GSH 30MM
HEI (INERT) AIRCRAFT AMMUNITIONREPORT NO. NMLlMST/IAF/1.13/69/2005. Dccember 2005
Table 2: Samples and its location for metallography.
Sample 1.0Specimen 1Specimen 2Soecimen 3
The transverse and longitudinal sections of COB and the longitudinal section of DCA
were mounted in bakelite moulds. Conventional metallographic technique was employed for
COB for grinding and finally polished using 0.5 ~m diamond paste- The COB samples were
etched with the mixture containing 50 cc NH4OH, 40 cc I-h02 and 10 cc H2O. The DCA was also
ground using emery paper moistened with paraffin. Final polishing was done with 0.25 ~m
alumina. The -sample-was.-etched-with 5% Nital. Both t~~' samples were observed in optical and
scanning electron microscope (SEM) in secondary electron mode. Bulk chemical composition
was determined by energy dispersive spectroscopy (EOS) as well as conventional chemical
analysis. The microanalysis of constituent phases in the material was analyzed by EOS. Melting
and solidification temperatures of DCA wire were evaluated by differential scanning calorimetry
(1'A Instruments: Q 600 SOT). The bulk hardness of the copper driving band in as-received as
well as in annealed conditions were determined in Vickers scale (Ar-FRI. VRSO 270) using 10
Kg load. The details of the investigation are presented in the following subsections.
[bl
-- .-- ._.~-
5
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE ANALYSIS OF COPPER DRIVING BAND AND DE-corPERING AGENT OF GSH 30MM
HEI (INERT) AIRCRAFT AMMUNITIONREPORT NO. NMLlMST/IAF/I.13/69/2005. December 2005
Figs.1 (a, b & c): Photographs of components of 30mm GSH gun firing system (a) emptycasings, projectiles and de-coppering agent, (b) de-coppering agent, (c) projectiles with COB.
1. VISUAL EXAMINATION 0:. - -
As mentioned above three components of 30mm GSH gun firing system were received.
The solid projectile is flat at one end and tapered at the other end having total length of ~ 142 mm
with the maximum base diameter of -27 mm. Two grooves, each of width -4mm are there over
the periphery and -6 mm apart from each other. From the flat bottom end the distance of the first
grove is also -6 mm. The copper band is lixed in a 10 mm wide groove located above the two
grooves mentioned earlier. The thickness of the copper band is -I mm. Beneath the copper band,
two peripheral sets of teeth are present. probably, for friction gripping of copper band. The
copper band is also tapered towards the pointed end of the projectile. The casing length is ~ 163
mm with a ~40 mm diameter. It has a collar of width -6 mm located 4 mm from llat bottom-end.
The casing is also slightly tapered at the other end.
The wire of de-coppering agent is dull in appearance having diameter in the range of 1.28
- 1.30 mm. The measured diameter and its deviation are within the specitied limits as per the
GOST 5655-67 specifications (the specilied diameter should be 1.25 +/- 0.25 mm and the
ditlerence hetween maximum & minimum values of diameter should not L':\cecd 0.14 m111in a
batch).
2. CII EI\IIC\ L Co 1\1POSITION
The concentration of major alloying clements present in the two alloys is analyzed using
EDS and wet chcmical analysis methods. The minor elements present in both the allo\'s could
6
~
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE ANALYSIS OF COPPER DRIVING BAND AND DE-COPPERING AGENT OF GSH 30MM
HEI (INERT) AIRCRAFT AMMUNITIONREPORT NO. NML/MST/IAF/I.13/69/2005, Dcccmber 2005
not be analyzed by EDS because of its limited detectabi'lity. The analyses are collated in Table-3
and compared with specified compositions. As per JSS 4710-1, issued by Raksha Mantralaya,
Ministry of Defense, the COB should conforms the specification of Dc-oxidized Copper as per
IS:191(Grade DHP-l with restricted Bi content) or OST 384-36S-71 of Russian specification.
The wrought copper specification C 12200 (by Copper Development Association) also
designated as DHP and indicates "phosphorus deoxidized copper" with high residual phosphorus.
The phosphorus content in COB is extremely low (S ppm) whereas it contain I.Swt.% Si which is
not specified the specification. This indicates that the copper is not deoxidized by phosphorus but
by silicon. The high Si content in COB might be originated from the deoxidation process.
Therefore the COB may not be of DHP grade.
-t.:CA.-should be as per the. Russian specification of GOST 3778-77 grade C3. It is
observed from the EDS microanalysis that the DCA has 0.98wt.% Cd which is much beyond the
specified limit. This amount of Cd remains in solid solution of Pb. A perusal of Pb-Cd phase
diagram indicates steep slope of liquidus line which give rise to significant reduction in melting
point of the Pb-l%Cd alloy. Pure Pb melts at 327.SoC whereas estimated melting point of the Ph-
I%Cd alloy is ~31S°C. The melting point evaluation by differential scanning calorimetry (see
section 4) did not reveal any significant change, indicating possibility of much lower Cd content
as compared to 0.98wt% Cd. Therefore, the DCA wire is further analyzed by wet chemical
analysis which yielded the Cd content of 0.0 13 wt%. The higher amount Cd indicated by EDS
microanalysis may be erroneous because of interference of Pb Ma line with Cd La line.
However, the limit of cadmium impurity in the DCA is not specified. therefore, its affect may be
insignificant. Moreover. the Sb content in the DCA wire is 0.02 \\'t% which is above the
specified limit ofO.OOS \\1%.
7
...
NATIONAL METALLURGICAL LABORATORY, JAM SHED PURFAILURE ANALYSIS OF COPPER DRIVING BAND AND DE-COrPERING AGENT OF GSII30MM
. HEI (INERT) AIRCRAFT AMMUNITIONREPORT NO. NML/MST/IAF/I.13/69/2005, December 2005
Table 3: Chemical composition of con & DCA (in W((XI).
3. MICROSTRUCTURAL ANALYSIS
The metallographic prepared sections are examined in optical and scanning electron
microscope and are shovm in Figs. 2 (a, b. c. d & e). The COB exhibits single phase Cu alloy
ha\'ing grain sizc range of 50-250pm (Figs. 2 b &d). Twinnigs are clearly observcd within thc
grains. Precipitation of different shape and size occurred within thc matrix (Figs. 2 a & c) and
s
Elements Chemical composition of CDn Chemical composition of DCAAs per EnS Wet As per EDS Wet
specification Analysi Chemical specification Analysis ChemicalIS:191(Grade s Analysis GOST 3778-77 Analysis
DHP-t) (Grade C3)CU (including 99.8 min Balanc Balance -Ag) eSn 0.01 max 0.002 0.005 max Not foundPb 0.01 max 99.90 min Balance BalanceFe 0.03 max 0.022 0.005 maxNi 0.15 max 0.009 - 0.00027As 0.05 max 0.003 0.005 max 0.002Sb 0.005 max 0.00034 0.005 max 0.02Bi 0.0015max Not found 0.06 max 0.01P 0.02-0.10 5 ppm - -n
Se & Te 0.02 max Se: not .-found
Te 0.01 max 0.013 -Zn - 5 ppm 0.005 max 0.007Total 0.06 max 0.060480 -impurities(including Ag,As, Ni and P)in COBAg - 0.0015 maxCu - 0.002 max 5 ppmMg - 0.01 maxCa + Na - 0.03 maxSi - 1.50 0.00013 -Al - 0.004 -Cd - 0.007 - 0.98 0.013Total impurity - 0.10max 0.042275in DCA
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE ANALYSIS OF COPPER DRIVING BAND AND DE-COPPERING AGENT OF GSH 30l\1M
HEI (INERT) AIRCRAFT AMMUNITIONREPORT NO. NML/MST/IAF/J .13/69/2005, Deccmber 2005
their chemical composition (analysed by EDS) is furni'shed in Table-4. EDS microanalysis of
precipitates having different morphology (as indicated in Fig. 2a) arc collated in table 4.
14 mi('ron
34 minon ~"70!ninon
9
...
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURfAILURE ANALYSIS OF COPPER DRIVING BAND AND DE-COPPERING AGENT Of GSH 30MM
HEI (INERT) AIRCRAFT AMMUNITIONREPORT NO. NML/MST/IAF/I. I3/69/2005, Deccmber 2005
Figs.2 (a, b, c, d & e): Micrographs of the copper driving band; [a] precipitation in Cumatrix, longitudina] section, [b] general view of the matrix revealing twins, longitudinal
section, and [c] precipitation in Cu matrix, transverse section, [d] general view of the
matrix, transverse section., and [e] SEM micrographshowing.precipitation iDCJ.t.ql;1tri~~-
Both the transverse and longitudinal sections do not show any significant difference in
microstructure. Homogeneity is maintained through out the section in terms of its distribution of
precipitates and microstructure.
Table 4: Chemical composition of precipitates observed in the matrix of CDB.
Though in the bulk chemical composition analyzed by wet chemical analysis. the
presence of Si. Fe. Se. Cd and Sb are very small in quantity, yet they are present in substantial
amount in the second phase of the COB matrix. PPT-1 is perhaps the combination of Si-Cu,
whereas PPT-2 is rich in Si-Sb. PPT-3 contains Si-Fe-Cu and PPT-4 is the complex second phase
consisting of Si-Cu-Sb. The concentration of elements indicates the presence of complex brittle
intermetallics. In addition. large amount of silicon is always associated \\"ith all the precipitates.
This is consistent with largL' concentralion or Si observed in the microanalysis by FDS.
10
Type of precipitate Concentration of clements in wt. nercentSi Fe Cu Se Cd Sb
PPT-L square shape ]2.] 0 - Bal - - -
PPT-2. Irregular shape 25.96 3.0 Bal 0.60 1.90 38.66
PPT-3, rectangular with rounded edges 14.67 27.68 Bal - - -
PPT-4, rectangular with sharp edges 30.94 2.17 Bal - 2.01 13.60
=.,~--~
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE ANALYSIS OF COPPER DRIVING BAND AND DE-COPPERING AGENT OF GSH 30MM
HEI (INERT) AIRCRAFT AMMUNITIONREPORT NO. NMLlMST/IAF/I.13/69/2005, December 2005
",
Figs.3 (a & b): SEM Micrographs of the de-coppering agent [a] as cleaned wire surface,[b] metallographic polished sample, and [c] polished and etched sample.
The DCA exhibits single phase Pb base alloy. The material is soft; hence dent marks and
scratches are observed on the surface. Presence of second phases was not found. On the etched
surface grain boundary cracks arc observed. The intergranular cracking at the surface of the
DCA wire seems to be originated Il'om the long-term creep phenomenon. In Pb and Ph-alloys
creep is observed to occur at room temperature. Therefore, this does not seem to be cause of
L"onccrn. More()\'cr, the surt~H;e of thc DC:\ wire is dean \\'ithollt foreign inclusions and
L'orrosion.
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NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE ANALYSIS OF COPPER DRIVING BAND AND DE-COPPERING AGENT OF GSH 30MM
HEI (INERT) AIRCRAFT AMMUNITIONREPORT NO. NML/MST/IAF/I.13/69/2005. Deccmber 2005
4. DIFFERENTIAL SCANNING CALORIMETRY OF DCA WIRE
In order to evaluate the effect of alloying elements present above the specified limit, on
the melting point of DCA wire, the melting and solidification temperature of the DCA are
evaluated in a differential scanning calorimeter. The sample is heated upto 400°C at a heating
rate of IOuC/min and subsequently cooled to room temperature at same rate. The resulting
thermogram revealing endothermic melting peak and exothemlic solidification peak is shown in
Fig. 4. The evaluated melting temperature of DCA wire is 32S.1SoC whereas its solidification
temperature is 323. 14°C. The difference in melting point of pure Pb (327.SoC) and DCA wire is
insignificant.
. -*'- Sample: leadSize: 69.8940 mgMethod: RampComment: dsc
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319.18°C
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Fig. 4: Thermogram or DCA wirL'showing heating and cooling Cllr\CS.
12
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NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE ANALVSIS.oF COPPER DRIVING BAND AND DE-COPPERING AGENT OF GSH 30MM
HEI (INERT) AIRCRAFT AMMUNITIONREPORT NO. NML/MST/IAF/I.13/69/2005, Dccember 2005
5. HARDNESS OF CDB
The hardness of COB is measured in as-received condition as well as in annealed
condition. This is essential for identification heat treatment condition of the as received CD13.
The COB is annealed at 850°C for 15 minutes and then air-cooled to room temperature. The
measured and specified Vickers hardness values of the COB are collated in Table-5. With
respect to the specification, the as-received hardness exhibits quiet higher value. The higher
hardness of COB alloy may be an indication that the alloy is either hard drawn or strengthened
by precipitation. But measured hardness of annealed COB is not more than 55 HV, which
conforms to the specification. Therefore as-received COB is in hardened state which is against
the requirement of the speci fication.t. ... .
Table 5: Vickers hardness of the CDB alloy.
DISCUSSIONS
From the above investigation, it has been noticed that, copper-driving band contains
substantial amount of Si. This silicon perhaps forms intermetallic phases; with Cu, with Cu-Sb.
and with Fe-Cu. These brittle and hard second phases are uniformly distributed in the soft copper
matrix causing precipitation hardening. Moreover, the strain hardening of COB alloy may arise if
the bands are made of hard drawn copper. These phenomena are evident from the increased
hardness value of as-received COB. Even if the CDB is made of hard drawn copper. the hardness
can be brought down by post fabrication annealing treatment. This is demonstrated by annealing
experiments and post-annealing hardness evaluation of COB. It is also indicated in the
specification, that, if the CDB is made horn solid drawn seamless tube, it should be annealed
after fabrication. As the COB is already strain-hardened, it may becomc embrittled/fragmented
during the tiring and tends to adhere at the inner wall of b~l!Tel.
- The elements present in the DCA ,,'ire is as per the specitieatit)n limit except Sb content
which is little higher than the specitied limit. The change in mcltil1t'. IL'mpcratun: due to presclKl'13
Sample l.D. Specified hardness Hardness of Hardness ofas-received CDB annealed CDB
Longitudinal section Not more than 55 HV 82.5 + 2 HV 44.1 + 21-IV
NATIONAL METALLURGICAL LABORATORY, JAMSHEDPURFAILURE ANALYSIS OF COPPER DRIVING BAND AND DE-COPPERING AGENT OF GSH 30MM
HEI (INERT) AIRCRAFT AMMUNITIONREPORT NO. NML/MST/IAF/1.13/69/2005, December 2005
of minor alloying clements in DCA is insignificant. However, intergranular cracking at the
surface of the DCA wire seems to be originated from the long-term creep phenomenon. In Pb
and Pb-alloys crcep is observed to occur at room temperature. Therefore, this does not seem to
be cause of concern. Moreover, the surface of the DCA wire is clean without foreign inclusions
and corrosion.
CONCLUSIONS
1. The copper-driving band has high concentration of silicon which is found to be mainly
associated with precipitates in the copper matrix. However the wet chemical analysis of bulk
did not reveal high amount of silicon. This happens when the silicon-bearing precipitates in
copper matrix are not able to digest in the acid solution. Exceedingly low amount of. .. . 0" 0 0 0- ..
phosphorous indicates that the COB is not made of specified phosphorous deoxidized copper
(DHP grade). It seems that the copper is deoxidized by silicon. Moreover, the unused CDB
~
has much higher hardness than the specified limit. This indicates that the CDB is made of
hard drawn copper which has to be annealed after fabrication. Heat treatment experiments
has demonstrated that the specified hardness is achievable if it is annealed. The strain
hardened COB is prone to embrittlement/fragmentation due to high strain rate defofj11ation
during the firing and may tends to adhere at the inner wall of barrel.
2. The elemental composition of DCA wire is as per the specification limit except Sb content
which is little higher than the specified limit. But its effect on the melting temperature of
DCA is insignificant. The differential scanning calorimetry of DCA revealed that the melting
point is 328.1°C while pure lead has melting point of 327.S"C. The observed intergranular
cracking at the surface of the DCA wire seems to be originated due to the long-term creep
phenomenon. In Pb and Pb-alloys creep is observed to occur at room temperature. Therefore.
this does not seem to be cause of concern. Moreover, as per the requirements of the
specification, the surface of the DCA wire is clean without foreign inclusions and corrosion.
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