NDTnet - August 1996, Vol.1 No.08
Ultrasonic testing of composite castings
Authors J. Pohl, D. Wiedemann, K.-O. Prietzel
NDT is not only applied for quality and production control, but also
during design of new products and materials. . This article describes such an ultrasonic application.
The investigation concentrates on special workpieces that are
used in machines for construction material recycling purposes (breakers).
For this application strong wear-resistant workpieces
must be developed through the design of material composites and treatment,
furthermore, the new design must
permit the economical manufacture of these parts.
Conventional materials do not include all necessary properties as there
are high wear resistance (hardness) and high impact resistance
(toughness) .. This ultrasonic project is part of a program for
characterization of micro
and macro structures, involving many other metallurgical disciplines.
The investigation was carried out on composite casting plates, based on a
steel body (C45 rolled plate)
on top casted chromium white cast iron G-X 300 CrMo 15 3,
both applied with a thickness of 15mm.
Fig 1: Principles of Composite Casting
This composite will include the advantages of both materials, fulfilling the
requirements outlined above.
Good bonding between the two materials is an essential factor.
Traditionally, methods such as soldering, adhesive bonding, and
welding have been applied in order to achieve this.
. Composite casting provides an especially
Composite casting is the production of metal workpieces, carried out through
simultaneous or sequential casting of different melted materials
The example given in the article uses the method of casting chromium white cast iron on a pre-warmed steel body
inside an ingot mould. This production was performed at the Institute for
production methods at the Otto-von-Guericke-University Magdeburg. .
Variation of production conditions, e.g. pre- warming, melting
temperature, cooling condition and the application of different kinds
of flux is included in the examinations.
The ultrasonic testing method was applied for determination workpiece
conditions, especially bonding quality.
The pulse echo technique with straight beam probe and a pitch and
catch technique with angle probes for scattering measurements was
applied, both with post processing of C-scan and D-scan
presentations. Fig 1 and Fig 2 display the principles of both
techniques. According to the gate position, echo signals were recorded in the
area of bonding. In the case of angle beam testing, the gates were
other depth zones.
For the pulse echo technique a high damped 10 MHz transducer was used for
achieving best transversal and longitudinal resolution.
|Fig 2: Pulse echo technique
||Fig 3: Pitch and catch technique for scattering measurements
In the scattering method a miniature angle transducer
45°, 4 MHz. was used for both.
To avoid the disadvantages associated with non-straight surfaces, the
transducers were coupled through delay lines and the
evaluation was released by the interface echo (interface echo start).
The test was executed from the side of the steel body,
because high attenuation in chromium cast iron (alpha=450 dB/m for longitudinal waves at 5 MHz) and the
surface conditions of the casting would
would make a sound
transmission from this side impossible.
Use of ultrasonics for measurement of crack
depth, sound velocity and attenuation are further objects of investigation.
With Ultrasonic testing it is possible to locate disbonding with good local resolution and reproducibility.
(Fig 4a) displays a C-scan presentation of a plate and shows the
Further determinations of defect type are possible through evaluation of
Acoustical impedance was
estimated to be
12*10E6kg/m²s by the composition of the flux, thus
providing a reflection factor of about 0.6.
Hence it could be concluded from this that the defects are flux
inclusions with cavities. This statement can be proven by cut workpieces.
(Fig 4b) ilustrates that. The
position of cavities corresponds as expected with positions of highest
amplitude in the C-Scan.
Bild 4a): C-scan reflection
Fig 4b): Picture of a cut at the marked scan result.
Fig 5: D-scan reflection
For an illustration of simultaneously recorded D-scan presentations showing
clearly the sections with disbonding via the scan area, please see Fig 5.
The ultrasonic scattering results should provide more information on bonding interface within areas without lack of fusion.
The amplification was increased,
so that in the area of defects the signals are displayed
in a saturation condition.
Correlations to the interface process are possible through analysis of these
Fig. 6 shows
an example of low scattering at the marked line which corresponds
with an area of melting of the steel body, to be seen in the cross section
at figure Fig.6b.
Fig 6a): C-scan scattering
Fig 6b): Picture of a cut at the marked scan result.
The D-Scan presentation also shows scattering from a deeper area, obviously from
the cast iron.
After cutting the workpiece at this section a correlation proved
the existence of microshrinkage in this area.
Please see Fig.7.
Fig 7a): D-scan scattering
Fig 7b): Picture of microshrinkage at the marked scan result.
Another application of the ultrasonic method involved crack depth measurement.
After cutting the workpieces cracks on the surfaces were visible, and had to
A Rayleigh-wave technique was applied and due to time of flight
measurement the crack depth could be determined.
Multiple measurements with transversal waves showed similar results of a few
millimeters of crack depth.
To achieve specific mechanical properties, it is
important to determine Elastic modulus of the chromium cast iron.
By known equations this figure can be calculated through measurement of
longitudinal and transversal
sound velocity, as well as density.
Through attenuation and coupling changes it is possible that echo
signals are distorted and this could cause changes of trigger points with further
time of flight measurement accuracy. However, a pre - calculation of
possible errors showed a result of just +/- 4 GPa, so it met the necessary
standard of accuracy.
In general, the results show
ultrasonics to be a good tool for materials characterisation.
It should also be mentioned that the workpiece preparation demands high
an improvement is necessary.
In addition to the results for material characterization, we also gain
Correlations of ultrasonic results to production parameters helps to
In general the Ultrasonic method provides advanced information on composite castings in an early stage.
The results lead directly to the material characterization and to the
developments for production process. It is possible to optimize other
investigations and properties of interest can be determined fast and non-destructively.
This task was part of a DFG and LSA program "Material characterization",
included in the SFB 385 "Baustoffrecycling".
The investigation was carried out in the Institut for materials technology
and material testing at the Otto-von-Guericke-University Magdeburg.
This Article was presented at the NDT'
96 conference in Lindau and won the first prize for best presentation. The
on UT-Highlights and displays all 33 abstracts of the UT contributions.
- Kröning, M.
Neue Aufgaben für die ZfP: DGZfP-Jahrestagung 1990, Trier, S. 8-38
- Motz, J. M.; Christianus, D.
Schlagbeanspruchte Werkstoffe für die Aufbereitung von Altautos und von
Bauschutt: VDI-Berichte 773: Werkstoffe für die Umwelttechnik; VDI-Verlag
Düsseldorf 1990 S. 1-31
- Norman, T. E.; Röhrig, K.
Verschleißfeste martensitische Chromgußeisen:
Aufbereitungstechnik (1970),6, S. 356-364
- Ißleib, A.; Friedel, A.; Lubojanski, I.
Verbundgießen für Verschleißteile - Stand und Zukunftsaussichten:
Gießerei-Praxis (1995), 7/8, S. 146-150
- Lubojanski, I.; Friedel, A.; Ißleib, A.; Ambos, E.
Grundlagen zum Verbundgießen plattenförmiger Bauteile
Vorträge zum Kolloquium des Sonderforschungsbereiches 385
"Baustoffrecycling" der Otto-von-Guericke-Universität Magdeburg am
08.02.1996 / Preprint Nr. 3, S.50-55
Delivery service for this and other NDT literature: At the German NDT
Rolf Diederichs 1.July 1996, firstname.lastname@example.org
/DB:Article /AU:Pohl_J /AU:Wiedemann_D_ /AU:Prietzel_K_O /CN:DE /CT:UT /CT:composite /CT:steel /ED:1996-08