mod12lec57


Hello, I welcome you all in this presentation
related with the subject details of surface engineering and you know that we have talked
about the various aspects related with the fundamentals of the wear mechanism and then
methods which are used to modify the surfaces for improving the surface properties and enhance
the tribological life and after the modification of the surfaces of the substrate for enhancing
the travel logical life it is important that those modified surfaces are also characterized
with regard to the various properties. Such as the soundness depth of the modified
layer the mechanical properties and metallurgical properties and their tribological properties.
So, you know that we are now talking about the characterisation of the modified surfaces
and the main purpose of this chapter is to to find out the values of the various properties
of the modified surfaces, so, that we can take suitable and well informed decisions
about the suitability or applicability of the modified surfaces for the target application. So, basically we decide how; based on the
characterised values of the modified surfaces decision is taken whether modified surface
is fit for given application or not. So, under this previous presentation we have
talked about one method of the depth or thickness of the modified zone thickness of the modified
zone. So, under this we can use the variety of the methods and we have one method we have
talked that was about the weight method. And apart from that the other indirect methods
are like hardness testing or the micro structural variation are the compositional variation.
So, these are the indirect methods, these 3 are the indirect methods. And in case of the weight method we have to
take the weight of the sample before and after the development of the modified surfaces.
And any increase in weight is attributed to the modified thickness of the modified layer.
So, in those methods where additional layer is applied additional layer of the material
is applied this weight method is found to be more effective like say on the surface
of the substrate we apply a layer of the material. So, we have to take the weight of the material
before ah before applying the layer of the material and after we have to take also the
weight of the component or the substrate after applying the layer. And difference of these
two is used to see; is a considered or is attributed to the weight of the layer applied
weight of the material applied in form of layer. And now this weight is used for indirect
calculation of the depth of the thickness of the modified zone. And for that purpose basically we calculate
if the if you see this modified zone in the top view and if this modified zone is in this;
over this area then what will see width width of this modified zone is B and the length
of the modified zone is L density of the material which is applied is Rho, Rho into B into L
into B into say average thickness about which we do not know. So, this is a value to be
obtained and product of these 3 will be giving us the volume. And multiplied by Rho, so this will give us
the weight, so that it can be obtained from the delta w/l into b into Rho this will give
us the average thickness of the layer which is applied on the surface of the substrate.
This is one method there are other two methods which are used for measuring the thickness
of the layer which is applied. And these are like a indentation method indentation
method and the second one is the ultrasonic method. So, the principle of the indentation
method is very simple like this is a substrate over which we have applied thin layer of the
coating or layer of the material has been deposited. Then we apply in we develop one
indentation using suitable ball on the surface of the ah on the modified surface. In this case what we do like the ball of the
large diameter like 25 to 30 mm 25 to 30 mm ball and diameter is used to develop the segmentation
and then the dimensional measurement of the indentation are used for calculating the thickness
of this layer which is applied. So, if we see this is the the surface indentation of
the modified zone. And this is the indentation of the substrate like this. And then we determine the values like y from
one and this is the x this is the, another value. So, these two values of the x and y
are used for calculating the thickness along with the diameter of the ball which is being
used for developing the indentations of thickness of the the coating which is the thickness
of the layer which is applied in this indentation method is obtained from the x multiplied by
y/d gives us the approximate value of the modified zones. This is the method which we can see here in
this case this is the substrate and this is the thin layer of the material which is applied
a ball of the large diameter like 25 to 30 mm diameter is applied and suitable load is
applied, so, indentation is made on to be surface. You know since the modified surface
layer of the material which is applied at the surface of the substrate that will have
the different properties than the substrate. So, accordingly the indentation may vary significantly. In these two cases and then then these dimensions
are are measured in terms of the diameter of the indentation at the surface of the modified
layer and this is the diameter of the indentation at the substrate. So, this is the diameter
of the indentation at the surface of the substrate and this is the diameter of the indentation
at the surface of the modified layer. And once we are able to get these two values we
can easily obtain the value of the y and x. And this y and x are used to calculate the
thickness of the modified layer which is obtained from x into y / d this is how it is obtained. Now will see the another method of the measuring
the thickness this is called ultrasonic testing. In the case of ultrasonic testing
ultrasonic vibrations are transmitted into the modified surface and it uses the typical
property of an very unique property of these ultrasonic vibrations that these can penetrate
into the metallic component. But these get reflected from the interfaces of mediums like,
if there is a change in medium here we have air this is the metal this is the substrate. So, as soon as the vibrations move from the
air to metal it comes across one interface and these are reflected. Similarly if the
vibrations are being transmitted and so this and these are translated into the metal as
soon as these come across any defect then these will then there will be one interface
will be formed and this interface will be between a metal to air. In this case the interface
was between between the air and the metal. Whenever one change of the medium takes place
one interface is formed and the vibrations are reflected from that interface. So, this
is a unique characteristic of the ultrasonic vibrations is exploited in the thickness measurement.
So, what we do like we use ultrasonic vibration probe which is applied on to the surface of
the modified layer like this. This is the modifier which is applied of metals B and
this is the metal S in form of substrate. Then when the vibrations are applied these
are applied on to the modified component through the use of the suitable liquid. So, that if
there is a minimum loss of these vibrations and these get easily transferred to the component
this is this; so, the vibrations are transmitted through the liquid which is mostly in form
of oil or water this is called copular. It has to connect prop with the surface of the
component of surface of the substrate of the modified surface. When these vibrations reach to the surface
they will be initially reflected. So, this reflected vibrations we can see on the oscilloscope
in form of very strong peak like this. And then these will be transmitted through the
modified layer and then they will be coming across one interface between these two metals
which is in form of like say B and S. Again these are reflected and then final reflection
will be coming from the another side where there is a change in medium from the substrate
metal to the air. So, will be getting in this case these three
peaks so the last peak is corresponding to the reflection of the vibrations coming from
the bottom side surface of the substrate and air interface the that the that that first
and strong peak is coming from the air to the the modified surface metal interface which
is also a strong peak. Then there will be one weak peak reflection which will be coming
from the; which will be coming from the modified. The material which is applied from the interface
of the coating and the substrate are the layer which is applied interface of the layer of
the material which is applied and the substrate. So, the spacing between the two is used to
characterize the thickness of the layer which is applied and the spacing between these two
peaks is used to characterize the that entire thickness right from the modified zone to
the bottom of the substrate. And the distance is used to characterize the
thickness of the substrate, so in this case basically we are transmitting the ultrasonic
vibrations at the surface. So, from the; when these are applied at the initial it will be
reflected back from the surface itself. And the part of them will be transmitted in the
metal and as soon as they come across to the lower interface again they will be reflected
back. And if there is any defect or the interface then then will be getting the third peak as
well. So, oscilloscope basically if if there is
no interface and there is just the one substrate layer vibrations will be reflected back from
the top and then vibrations will be reflected back from the bottom. And these two will appear
as a strong peak from the top and the bottom these are the two strong peak corresponding
corresponding to the peaks from the top surface and the bottom surface and this distance will
be indicating the thickness of the substrate. But if we apply one coating like this then
again one interface will inform that will be getting additional peak here and that will
be indicating the thickness of the modified layer or the layer of the material which is
applied on to the surface of the substrate. So, this is what we can see here in the next
diagram like when the Ultrasonic vibration probe is applied to the surface of the component
it will be applied to the coupler it will be transmitted vibrations will be transmitted
so initially it will be reflected from the top surface. So, this is this peak is corresponding
to the top surface and then another strong peak will be getting due to the reflection
of these vibrations from the bottom surface. So, this is corresponding to the bottom surface
and if there is a layer of the material which is applied then we will be getting one additional
peak from the in between and that will be suggesting the presence of the interlayer.
So, the surface peak and the interfacial peak between the layer of the material applied
and the substrate. So, that interface will be giving one additional peak in between especially
when there is no other discontinuity. And when there are discontinued we can get
number of other peaks. So, basically ultrasonic vibration method gives us the direct reading
of thickness of the coating are the modified layer which is applied. And now we will see; so after the thickness
measurement and now we have to see that whatever the modification has been carried out at the
surface of the substrate that modification is a is a perfect or a modified zones which
is formed is a sound or not. Sound means whether it is free from defects and discontinuity
discontinuous or not in form of like say there maybe pores, there maybe cracks there may
be inclusions defective modified surface will be leading to the increased tendencies for
crack easy rack nucleation and there growth and premature fracture, higher metal removal
rate, higher wear rate so this will not be leading to a good situation. Because the defective modified layer, if there
are like defects in form of cracks here and there pores in the modified zones or inclusions
of the foreign material or impurities. Then will be acting as stress raisers. Increasing
the stress concentration increasing stress concentration will be simply leading to the
easy nucleation and growth of crack increased wear, increased corrosion tendency of the
material. So, in that case it may be unfit unsuitable for those applications. So, all
the modified surfaces should be assessed. For their soundness, so integrity and soundness
testing of the modified zones is performed using various methods and it includes like
Dye Penetrant Testing. This is primarily used for assessing the surface discontinuities
which may be there in form of surface cracks or open pores or the blowholes which are present
at the surface. Then we have the magnetic particle test. Magnetic particle test is primarily
used for magnetic materials. To assess both surface defects and subsurface
but these are not them very deep. So, we can say near surface defects can also be assessed
by the magnetic particle test. This may be in form of like say poles are cracks or inclusions
etcetera. Then there are other methods like ultrasonic
testing and x-ray testing. In case of; in other two methods are we have seen they are
primarily used for assessing the surface discontinuities. While these two methods are used for primarily
used for assessing the subsurface or internal discontinuities. For example if the modified
layer at the interface has some kind of the defects poor bonding and then all those cannot
be detected very effectively. Using the other two methods like DPT and MPT
but this can be detected easily by the ultrasonic and x-ray testing. So, the defects which are
present below the surface in form of cracks, poor bonding, and inclusions etcetera can
be detected using the X-ray and ultrasonic testing methods. Now will see some basic principles associated
with these processes in case of the Dye penetrant test if the surface surface having the discontinuities
in that case we apply a very low viscosity low surface tension of liquid having the dye
is spread over the surface. So, this is a spread in this form so that dye which is there
within the pin low viscosity liquid being is spread over the surface. So, this minute and find discontinued is present
at the surface will be sucking the liquid by the capillary action. And once this the
liquid with the dye is spread over the surface after sometime it is wiped out, it is removed.
So, this is the case when all the dyes present at the surface has been removed and the day
with the liquid which has been served is left in the components. There after we apply one
developer developer may be in form of likes a chalk powder or talc powder. So, that is spread over the surface so this
will be as these developer developer will be observing the liquid and since the liquid
is having the dye so it will be leaving behind the stains stain in the developer and wherever
there is strains are present whatever is the extent of to which is tensor present that
will be indicating the location of the size and type of the discontinued is present at
the surface. So, since the penitration of the thin liquid
into the discontinuities is mandatory for assessment of the discontinuities in this
method and that is why this method cannot detect a discontinuous which are present in
the subsurface zone The magnetic particle test is the another
method this test simply lies on the principle is based on the principle like all the magnetic
materials having the north pole and south pole and magnetic lines moving from north
to south like this. And if there is any discontinued then again it will be forming two poles and
again we know that these lines of the magnetic flux will you moving more effectively through
the metals. But if there is open if there is a 4 or if
there is crack then again it will be forming the two poles and wherever the defects and
discontinued is are present the leakage of the magnetic flux start from that area. And
this leakage of the magnetic flux will be leading to the will be leading to this leakage
of the magnetic flux will be leading to the formation of the additional the fields here.
And this aspect is exploited to detect the location where were the discontinued is our
present So, are considering this one in mind like
say this is the component having the discontinuetity it is magnetized either using the permanent
magnet or electro magnetics electro magnets. So, obviously the North and South poles will
be formed and in this case whatever whatever the locations are having the discontinuity
is from there the leakage of the magnetic flux will start and Italy forming the two
additional Falls. Now once the component to be checked component
to become like this the component having discontinuity here so it will be magnetized using flow of
current or using the permanent magnet. So, here will be having the two additional post
and there will be leakage of the magnetic flux. So, after the magnetization we sprinkle
the magnetic powder particles. This is spread all over the surface of the substrate are
the modified surface where there is a magnetic flux is magnetic particles that location And they will get after magnetization of thecomponents
having defects when we sprinkle magnetic powder particles these will be getting piled up at
the location where ever there is leakage of the magnetic flux. So, depending upon the
intensity of the pile up location and the extent to which the pile up is taking place
that will be indicating the location of the the discontinue 30 size of the discontinuity
and so this is how will be able to detect the find cracks present at the surface if
the discontinuities are present below the surface in case of the magnetic particle test
very easy pling of of the Powder particles take place. So, very easy and a little bit piling up of
the particle at particular location of suggests that they discontinue are present near the
surface layer is not at the surface players now I will sunrise this presentation here
in this presentation just have talked about the traditional methods of the thickness testing
and two methods of the soundness testing is important to see that how is the soundness
of the modified zones are free from the defect and is correct or not other two methods of
the soundness and integrity testing in the next generation. Thank you for your attention.

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