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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------

i:.- .

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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04

319.18°C

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II

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+<---..328.1S0C22.38J/g

02

323.14°C22.43J/g

""

~'

( -JI

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I I

, II !I I

. II .I If I

1332.67°C I

-0.2

-0.40 50 100 150 200 250

Temperature (oG)

300 350 400

ExoUp Unr.1.'rsal V3.QA TA Instruments-- -- --~

Fig. 4: Thermogram or DCA wirL'showing heating and cooling Cllr\CS.

12

...

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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