EPNM -2014
Cracow, Poland,
May 25-30, 2014
Enhancement of explosive welding
possibilities by the use of emulsion
explosive
Boris Zlobin*, Victor Sil’vestrov**, Alexandr Shtertser*, Аndrey
Plastinin**, Victor Kiselev*
*Design
& Technology Branch of Lavrentyev Institute of
Hydrodynamics SB RAS
**Lavrentyev Institute of Hydrodynamics SB RAS
Novosibirsk, Russia
*asterzer@mail.ru
Subject of research
1) To specify the boundaries of explosive
welding (EW) window for the couple of very
dissimilar materials;
2) To apply the emulsion explosive (EMX)
developed in LIH SB RAS for EW of very
dissimilar materials.
EXPLOSIVE WELDING LAYOUT
5
4
3
2
D

h
1
6
1- base plate, 2- flyer plate, 3- explosive charge, 4- detonation front, 5detonation products, 6- ground (anvil), D - detonation velocity, γ - collision
angle, h - gap.
Acceleration parameter: R = mass of explosive / flyer plate mass.
Search for new explosives for EW
Presently there are many examples of explosive welding (EW) use in
up-to-date technology. EW is mostly employed in production of steel-titanium,
steel-aluminum, steel-copper, and carbon steel-stainless steel bimetal articles.
Sometimes in the industry, especially when new equipment is being
developed, there is the need to join together low-ductile alloys with ductile
ones, or to clad some articles with thin protective or function layers from special
alloys.
Thin coatings are rather frequently needed on un-massive or thinwalled articles which may be destroyed or defected by explosion of too big high
explosive charge. In these cases, the difficulties arise due to the fact that
the utilized industrial HE cannot detonate steadily in thin (below 8 – 10
mm) layers with the low (2 – 3 km/s) detonation velocity needed for the
EW.
It makes researches seek for new explosives. For example, in [1]
they studied the detonation characteristics of fine PETN mixtures with baking
soda. Similar attempts, but on the base of another compositions, are
undertaken in Lavrentyev Institute of Hydrodynamics (LIH SB RAS).
[1] L. A. A n d r e e v s k i k h, Y u. P. D e n d e n k o v, O. B. D r e n n o v, A. L. M i k h a i l
o v, N. N. T i t o v a, A. A. D e r i b a s, Explosive Mixture for Explosive Welding of Thin
Foils, Propell Explos Pyrot 36, 48-50 (2011).
Emulsion Explosive developed in LIH SB RAS
Emulsion explosive (EMX) detonates in low thickness layer with low detonation
velocity suitable for EW. Hollow glass microballoons are included in composition
of this explosive with the aim to increase its detonation sensitivity. Laboratory
experiments have shown that EE can be successfully employed in explosive
cladding with flyer plate thickness less than 1 mm [1, 2].
EMX density is 0.62  0.01 g/cm3. Detonation velocity has weak dependence on
layer thickness and changes from 2.3 to 2.6 km/s when thickness changes from
3.5 to 25 mm. Critical thickness of flat charge in polyethylene casing (t 0.5 mm)
is less than 3.5 mm.
EMX contains water solution of ammonium and sodium nitrate (oxidizer),
paraffin (fuel), special emulsifying agent, and hollow glass microballoons.
EMX oxygen balance is close to zero. Emulsion density is 1.41  0.01 g/cm3,
oxidizer drop size is not greater than 2 µm.
Microballoon average diameter is 58 µm, green density ~ 0.15 g/cm3.
1V.
V. Sil’vestrov and A. V. Plastinin, Investigation of Low Detonation Velocity Emulsion Explosives, Combustion,
Explosion, and Shock Waves, 2009, Vol. 45, No. 5, pp. 618–626
2Silvestrov V.V., Plastinin A.V., and Rafejchik S.I., Application of emulsion explosives for explosion welding, The
Paton Welding Journal, 2009, N11, p. 61-64.
Explosive welding window
γ
no waves
waves
1
2
3
Critical
angle for
jetting
jetting
no jetting
4
Vt
c
Vc
Explosive welding window on the Vc – γ plane: 1- low boundary, 2- upper boundary, 3- the boundary Vc = Vt
between the ranges of smooth and wavy shape of the bonding zone in the welded couple (Vt is detected
experimentally), 4- the boundary between the ranges of occurrence and absence of cumulative jet at the
collision of flyer and base plates (jetting does not occur if Vc exceeds c); Vc – contact point velocity, γ –
collision angle, c – compression wave speed (c2 = K/ρm, K-bulk modulus, K = E/3(1-2μ ), E- Young modulus, μPoisson ratio). Broken curves and the lines 1, 2 circumscribe the typical experimental area where reliable
welding is achieved.
Formulas
 n 1

R
 1 
;
Vp  2DSin( / 2);   
n

1
2
(
R

2
.
71

0
.
184
/
y
)


     0;
Vc  D 
Sin
Sin
Hv
 mVc2
The low boundary of EW window:
 k
The upper boundary of EW window:
sin( / 2)  14.7 Vc5 / 4 
Tm  / a
m
2
11/ 2
1   2
Vp – flyer plate velocity, Vc – contact point velocity, D – detonation velocity, n –
detonation products polytropic index, y = h/e, h – gap, e – explosive charge
thickness, HV - Vickers hardness, Tm is the melting point,  - thermal
conductivity, a - thermal diffusivity, m - density of the metal, 1 - thickness of
the thinner plate, 2 - thickness of the thicker plate.
k = 5.5·ξ 0.18, where ξ = s/ (s is the surface film thickness,  - flyer plate
thickness). In real practice, k normally varies from 0.6 to 1.2, for the materials
with natural oxide films k = 1.14.
EW window for dissimilar materials

+
+
+
+
+
Vc
Intersection of EW theoretical windows built for two different
materials. In theory welding is possible in the intersection area
(crosses). Investigations show that successful welding can be
ensured in the vicinity of low boundary of a lesser strong
material.
Low boundary of EW window
It would seem that EW of materials having very different physical and
strength parameters is either impossible, either the reliability to get high
bonding quality is low (as the needed collision parameters lie in the
narrow zone in the EW window).
However, to our joy, the experiments show that EW low boundary can
be determined on the basis of the strength of lesser strong component
[1-3]. As a rule, the lesser strong material is, at the same time, more
ductile.
[1] I. D. Zakharenko, B. S. Zlobin. Effect of the Hardness of Welded Materials on the Position
of the Lower Limit of Explosive Welding, Combustion, Explosion, and Shock Waves, 1983, vol.
19, no. 5, pp. 689-692.
[2] B. S. Zlobin. Explosive Welding of Steel with Aluminum, Combustion, Explosion, and Shock
Waves, 2002, vol. 38, no. 3, pp. 374-377.
[3] Lysak V. I., Kuz’min S. V. Explosive Welding. – Moscow: Mashinostrenie-1, 2005 (in
Russian).
The necessity of intensive plastic
deformation
It can be explained by the reason that strong bonding takes place
when only one of two welded plates becomes deformed intensively
with high deformation rates and with generation of disperse particles
jet from its surface layer.
High-speed jet flow of the softer plate material results in the removal
of surface films from the harder plate surface and in deformation and
activation of its surface layer.
For example when aluminum is welded to steel, high deformation
level in the aluminum plate causes the high temperature of the
particles in the jet. The jet mainly consists of aluminum particles. As a
result, as the jet interacts with a steel, the steel surface is heated, its
strength decreases and it becomes prepared to the following process
of bond formation behind the collision point.
When collision angle is high the jet gets solid and moves along the
steel surface scrubbing it like a blade. This process is strikingly
illustrated by the picture on the next slide.
Example of jet formation
The bimetal made by explosive welding: 1 – steel plate, 2 – aluminum
plate, 3 - aluminum jet coming out of collision point
Delicate explosive welding (DEW)
So, to provide strong bonding between soft and hard materials
there is no need to accelerate a flyer plate to a very high velocity. It
is only necessary to stimulate intensive flow of soft material in the
welded couple.
When the base plate material has low plasticity and can crack
under collision we must reduce a flyer plate mass (thickness) and
velocity, and, correspondingly, reduce the explosive charge mass
(thicness). EMX enables to do it. It was shown that use of EMX
reesults in significant reduction of the residual deformation in the
produced bimetal [1]. That is why we call “delicate explosion
welding” (DEW) the explosive welding with the use of EMX, when a
flyer plate is thin.
[1] B. S. Z l o b i n, V. V. S i l’ v e s t r o v, A. A. S h t e r t s e r, A. V. P l a s t i n i n, in: A.A. Deribas and Yu. B.
Sheck (ed), New Explosive Welding Technique for Production of Bimetal Plane Bearings, Abstracts of the XI Intern.
Symp. on Explosive Production of New Materials: Science, Technology, Business, and Innovations (Strasbourg,
May 2-5, 2012), Moscow, Torus Press, (2012), pp. 116-118.
Experiments
In order to clarify the DEW potentiality, welding of materials with
highly differing properties was studied experimentally.
The parameters of flyer plate acceleration were chosen in such
a way to make the collision process pass near the low boundary of
the EW window; the position of this boundary was calculated on the
base of the less strong material characteristics.
Experiments: copper/steel couple
In the first series of tests, under study was the effect of the stronger material
hardness on the forming of copper-steel bonding. Before the welding, the steel
samples (23 х 25 х 125 mm) underwent mechanical treatment in order to reduce the
welded surfaces roughness to Ra= 0.32 – 0.16 m. A copper plate of 1.5 mm thick was
driven on 3 steel samples with different hardness: Н1 = 130 – 160 НВ; Н2 = 32 – 34
HRC; Н3 = 44 – 46 HRC.
1
D
2
3
4
А
3
A
Schematic of the experiment on copper plate drive on the steel samples with different
hardness: 1 - explosive charge, 2 – copper plate, 3 – steel samples, 4 – base plate, D –
detonation velocity
Copper/steel couple
The collision conditions can be assumed similar for all
steel samples. EMX was used as an explosive.
The first test was carried out at the drive parameter R = 0.5,
which corresponds to the collision angle γ ≈ 7°, the contact point
velocity was Vc = 2.6 km/sec.
At the given collision parameters, the corresponding
point on the Vc – γ diagram is located near but above the lower
boundary of the EW window which is calculated on the base of
the copper hardness.
The tests showed that copper was welded similarly
well to every sample.
Evident, that the difference in the strength
characteristics of the steel samples does not influence the
bonding process at such collision parameters.
Copper/steel couple
In the next test, due to reduced explosive charge, the drive parameter
was reduced to R = 0.3, the collision angle decreased to γ ≈ 5°. As the contact
point rate is Vc = 2.6 km/sec, the collision parameters coincide, or are located a
bit lower than the lower boundary of the EW window.
Visibly the welding took place on all three samples. The tests with
copper layer peeling (with hammer and chisel) showed that on the samples with
the hardness of Н1 = 130 – 160 НВ; Н2 = 32 – 34 HRC, strong bonding took
place on more than 95% of the samples area. On the sample with the hardness
of Н3 = 44 – 46 HRC, the copper plate separated from about 25% of the area in
the place of welding process ending. On the peeling site, the steel surface
retained a thin copper layer, which proves that the bonding process took place
indeed.
We believe that the described experiments vindicate that, as the
pressure in the collision zone exceeds the copper strength, and the deformation
processes develop extensively in this area, varying hardness of the steel sample
does not influence significantly on the welding process.
Experiments: stainless steel/carbide composite
couple (CC is in a copper matrix)
1
2
3
4
5
Experimental layout for stainless steel welding with copper and carbide
composite МС 221: 1 –stainless-steel plate (0.8 mm thick); 2 – copper matrix; 3
– carbide composite insert; 4 – explosive charge; 5 – detonator
The composite consists of 82% WC; 3% TiC; 7% TaC; 8% Co. Stainless-steel
hardness - 150 HB, copper - 70 НВ. The hardness of the composite МС 221 is
of 89 HRA, which is much higher than the strongest steels have.
The welding parameters
According to evaluations, to start the bonding process on the copper –
stainless steel interface at Vc = 2.6 km/sec, the minimal necessary collision angle is
γ = 8°, whereas for the carbide composite – stainless steel couple this angle must
be γ = 11°. Taking into account almost complete absence of carbide composite
plasticity, the shock action must be minimal to avoid cracking. In these very cases,
EW is not applicable, and positive results can be achieved with the DEW.
In the first experiment, the EMX charge thickness was 7.5 mm, density of
explosive ρe = 0.63 g/cm3, detonation velocity D = Vc = 2.6 km/sec. At such
parameters R = 0.75, the collision angle γ ≈ 10°. These values of γ and Vc
guarantee the presence of the point (Vc, γ) inside the EW window for the couple
stainless steel / copper. As for the area of the stainless steel and carbide composite,
the point under consideration (Vc, γ) falls on the low boundary of the EW window if it
is calculated on the base of the stainless steel hardness.
The view of the welded sample
1
3
2
The composite resulting from the explosion welding: 1 – stainlesssteel plate; 2 – copper matrix; 3- carbide composite
Results
In the obtained composite sample there are the waves typical
for the explosion welding on the copper / steel interface, whereas the
interface of the stainless steel and carbide composite is flat, there are
no waves, which is natural for the welding of the materials with highly
differing strength parameters. The experiment demonstrates that,
aside for naturally predicted welding on the copper / steel interface,
the bonding also took place on the carbide composite / steel interface.
The 2nd experiment was organized in the same way, its
parameters were the following: detonation velocity D = Vc = 2.6
km/sec, R = 0.6, γ = 8.5°. In this case, the point (Vc, γ) lies almost on
the lower boundary of the EW window calculated by the copper
hardness. The welding took place over the stainless steel / copper
interface, whereas, opposite to the 1st experiment, there was no
joining on the carbide composite / stainless steel interface.
Stainless steel/carbide composite couple
(CC is in a steel matrix)
To be sure that the start of the bonding process in the 2nd
experiment depended on the level of deformation processes development
on the copper surface, the following experiment was carried out. The
copper matrix was replaced with a steel plate quenched to the hardness of
46 HRC. The rest test parameters coincided with the test No. 2. As was
expected, there was no welding on the stainless steel / quenched steel
interface. The signs of bonding on the stainless steel / carbide composite
area are missing, too.
So, it can be suggested that the role of the “special” preparation
of the welded surfaces is played by the deformation processes occurring in
the less strong and ductile material. The hardness of the stronger material
is not of essence providing that its surface roughness influence is minimal.
For additional verification of this concept the experiment on
explosive welding of aluminum with a carbide composite were performed.
For this couple, the hardness difference exceeds 20 times, density
difference is 5 times, the aluminum melting point is about two times lower
than the carbide composite’s one, and nevertheless, the bonding was
obtained.
Summary
• To realize the conditions needed for bonding, it is enough to
provide the well-developed deformation process and intensive
material flow in only one of two collided plates.
• The low boundary of EW window for materials with highly
differing properties can be found on the base of less strong
material strength.
• The use of EMX enables to plate without destroying and
cracking strong low ductile alloy with a thin layer of ductile
material. This extends the possibilities of EW.
Thank you for your
attention!
Formulas