Ceramic filters for bulk inoculation of nickel alloy castings

ARCHIVES
of
ISSN (1897-3310)
Volume 11
Special Issue
3/2011
FOUNDRY ENGINEERING
Published quarterly as the organ of the Foundry Commission of the Polish Academy of Sciences
29 – 32
5/3
Ceramic filters for bulk inoculation of nickel
alloy castings
F. Binczyk*, J. Śleziona, P. Gradoń
Chair of Materials Technology
Silesian University of Technology, Krasińskiego Str. 8, 40-019 Katowice, Poland
* Corresponding author. E-mail address: franciszek.binczyk@polsl.pl
Received 22.06.2011; accepted in revised form 27.07.2011
Abstract
The work includes the results of research on production technology of ceramic filters which, besides the traditional filtering function, play
also the role of an inoculant modifying the macrostructure of cast nickel alloys. To play this additional role, filters should demonstrate
sufficient compression strength and ensure proper flow rate of liquid alloy. The role of an inoculant is played by cobalt aluminate
introduced to the composition of external coating in an amount from 5 to 10 wt.% . The required compression strength (over 1MPa) is
provided by the supporting layers, deposited on the preform, which is a polyurethane foam. Based on a two-level fractional experiment
24-1, the significance of an impact of various technological parameters (independent variables) on selected functional parameters of the
ready filters was determined. Important effect of the number of the supporting layers and sintering temperature of filters after evaporation
of polyurethane foam was stated.
Keywords: Nickel superalloys, Ceramic filter, Inoculation, CoAl2O4 inoculant, Compression strength, Density, Porosity
1. Introduction
Currently, precision castings for parts of aircraft engines are
made from modern grades of nickel and cobalt alloys such as IN
100 and IN 713C, RENE 77, MAR-M257 and MAR M 509 [1, 2].
From castings made of these alloys, tight dimensional tolerances,
excellent surface quality in as-cast state and after heat treatment
as well as minimum gas porosity and shrinkage effects are
expected. Efforts are also made to obtain the structure of equiaxial
grains within the entire volume of the casting
World literature gives a lot of information on microstructure
improvement in nickel superalloys by refining and inoculation
with nanoparticle inoculants [3-5].
The main parameters determining the properties and thus the
quality of nickel alloy castings are metallurgical quality and
proper structure of the casting. The alloy purity can be achieved
through the use of appropriate ceramic filters. In this way,
considerable fraction of the oxide impurities are arrested in the
internal space of the filter. In most cases, these inclusions have
their origin in the poor quality of charge materials, in improper
lining of the induction furnace and oxidation during melting in
the case of low vacuum or improper protective atmosphere. The
reference literature, both national and international, gives a lot of
important information on the effectiveness of ceramic filters and
the quality of castings obtained [6-10].
If the surface of the filter contains an inoculating component, its
presence should influence the structure of the casting by bulk
inoculation, which will produce in this casting the structure of
fine equiaxial grains, impossible to obtain by standard surface
inoculation, after which some columnar grains always remain in
the casting interior, deteriorating considerably the mechanical
properties.
To make the filter capable of playing this role, it should
possess sufficient mechanical and thermal resistance. World
literature gives a variety of information on the use of ceramic
ARCHIVES of FOUNDRY ENGINEERING Volume 11, Special Issue 3/2011, 29-32
29
filters. For economic reasons, the cost of using a filter has to be
compensated with the benefits of clean metal and correct
structure, obtained owing to the use of this filter. Therefore it is
important to develop technologies that will enable manufacture of
high-strength filters, capable of performing at the same time the
role of filtering and inoculating-refining units [11]. Studies
towards the development of such filters have been taken under the
key project POIG.0101.02-00-015/08 in the Operational
Programme Innovative Economy (OPIE).
•
blowing the preform with compressed air ( to protect
the filtrating holes from getting stuck),
• drying.
These operations are repeated the number of times corresponding
to the number of supporting layers. According to the prepared
plan of experiments, 10 or 16 supporting layers were prepared.
This step is illustrated in Figure 1.
2. Plan of research
The aim of the study was to evaluate the significance of the
effect of selected technological parameters (independent
variables) on the functional properties of inoculating filters.
The study was based on a fractional experiment 24-1, requiring
eight experiments. The plan is presented in Table 1.
Table 1.
Plan of fractional experiment 24-1
1
2
3
4
5
6
7
8
Fig. 1. Preform before and after the application of supporting
layers
Independent variable
Experiment
A
10
16
10
16
10
16
10
16
B
2
2
4
4
2
2
4
4
C
150
150
150
150
300
300
300
300
D
600
800
800
600
800
600
600
800
The following parameters were adopted as independent variables :
Stage II:
After drying, onto the last supporting layer, a layer of
inoculant is applied. It is composed of a mixture of colloidal
silica, powdered zirconium and cobalt aluminate, all mixed in
appropriate ratios. The method of applying the inoculating layers
is the same as for the supporting layers, namely:
•
pouring the ready ceramic slurry through preform.
•
blowing of preform with compressed air,
•
drying
A filter after the application of inoculating layers is shown in Fig.
2.
A: The number of supporting layers (REMASOL + zirconium
flour),
B: The number of inoculating layers (colloidal silica + zirconium
flour + cobalt aluminate),
C. Foam evaporation temperature,
D. Sintering temperature.
The following parameters were adopted as dependent variables :
• compression strength, MPa ,
• porosity,%
• loose material flow rate through filter, cm3 / s,
3. Making filters
Fig. 2. Filter after the application of inoculating layers
Stage I:
Stage III:
The first step is to prepare an appropriate mixture of binder
("Remasol") and zirconia powder. Then, the successive
supporting layers are applied in the following sequence:
• pouring the ready ceramic slurry through preform
(polyurethane foam) ,
The last step in the manufacture of inoculating ceramic filters is
evaporation of preforms and sintering of the supporting and
inoculating layers. The evaporation of polyurethane foam was
conducted at 150°C and 300°C, while sintering took place at
600°C and 800°C. The processes were carried out in a resistance
30
ARCHIVES of FOUNDRY ENGINEERING Volume 11, Special Issue 3/2011, 29-32
electric oven. In each case, samples were placed in the oven for
30 minutes. Cooling took place together with the oven. Examples
of the ready filters are shown in Figure 3
3
2,83
2,81
2,66
2,58
Flow rate, cm 3/s
2,5
2
1,89
1,84
1,76
1,67
1,5
1
1
2
3
4
5
6
7
8
Filter no
Fig. 6. Comparison of loose material flow rate through filter
5. The results of investigations and
discussion of results
Fig. 3. The ready inoculating ceramic filters
4. Measurement of filter properties
The following properties of filters were examined: Rc
strength, density, porosity and loose material flow rate. The
results of these measurements are shown in Figures 4 to 7.
1,15
1,2
1,05
1,01
0,74
Rc, MPa
0,8
0,55
0,48
0,4
0,31
The effect of dependent variables (variables A, B, C and D)
on selected properties of the filters was evaluated by multiple
regression analysis. The level of significance α = 0.1, i.e. the
probability of committing an error of first kind at a level of 0.1,
was adopted. How strong the impact of the examined
technological parameter will be depends on the value of
probability p, while the direction of influence (decrease or
increase) depends on the sign preceding the coefficient bo (- or
+). Calculations were carried out using a licensed StatSoft V.7.1
Pl. Statistica software. Statistical calculations were performed on
actual values of the independent variables.
A regression summary for the dependent variables:
compression strength Rc,, porosity and flow rate is shown in Table
2.
0,26
Table 2.
Regression summary for the dependent variables
0
1
2
3
4
5
6
7
8
Parameter
Filter no
Fig. 4. Compression strength compared for different filters
90
82,02
Porosity, %
79,31
79,33
78,68
80
71,35
69,97
69,02
68,58
70
60
1
2
3
4
5
6
7
Filter no
Fig. 5. Porosity compared for different filters
8
Absolute
term B
A
B
C
D
R2
Rc, MPa
bo
p
-1,263
0,008
0,098
0,001
0,024
0,341
-0,001
0,062
0,001
0,012
0,9704
Resultant property
Porosity, %
bo
p
97,78
0,001
-1,68
0,002
-0,53
0,335
0,01
0,258
-0,002
0,685
0,9438
Intensity, cm3/s
bo
p
4,225
0,001
-0,16
0,001
0,018
0,626
0,001
0,128
0,000
0,422
0,9675
Based on the evaluated impact of various technological
parameters on compression strength, the following has been
stated.
The number of supporting and inoculating layers and the
sintering temperature increase the compression strength (positive
value of coefficient B), while higher evaporation temperature
reduces this parameter (negative value of coefficient B). As the
probability value p indicates, a statistically significant effect on
Rc exert in descending order the following parameters: the
number o f supporting layers, sintering temperature and
ARCHIVES of FOUNDRY ENGINEERING Volume 11, Special Issue 3/2011, 29-32
31
evaporation temperature. Statistically insignificant is the number
of inoculating layers.
The value of the adjusted coefficient of determination
R 2 = 0.9704 indicates that approximately 97% of the results can
be explained with a model described by the following
relationship:
7.
aluminate , and from 2 to 4% Al powder. A small addition of
hafnium powder is also recommended. As a binder for these
components it is recommended to use colloidal silica.
Thus made filters provide the effect of bulk inoculation,
eliminating to a significant degree the incomplete effect of
surface inoculation.
Rc = -1,263 + 0,098·A – 0,0008·C + 0,0011·C
Based on the evaluated impact of various technological
parameters on porosity, the following has been stated. The
porosity of filters is significantly affected only by the number of
supporting layers in descending order of their occurrence
(negative value of coefficient B). Other parameters have not a
significant influence (p> α).
The value of the adjusted coefficient of determination
R 2 = 0.9438 indicates that about 94% of the results can be
explained with a model described by the following relationship:
porosity = 97,78 – 1,68·A
Based on the evaluated impact of various technological
parameters on the sand flow rate through filter, the following has
been stated.
The sand flow rate through filter is significantly affected only
by the number of supporting layers in descending order of their
occurrence (negative value of coefficient B). Other parameters
have not a significant influence (p> α).
The value of the adjusted coefficient of determination
R 2 = 0.9675 indicates that approximately 97% of the results can
be explained with a model described by the following
relationship:
Sand flow rate through filter = 4,225 – 0,155·A
6. Conclusions
1.
2.
3.
4.
5.
6.
32
Based on the conducted regression analysis, a significant
effect of the number of supporting layers and of the sintering
temperature on the functional properties of filters was stated.
The effect of the number of inoculating layers and
polyurethane foam evaporation temperature is less
significant.
The required compression strength (above 1 MPa) for
ceramic filters with an inoculating coating is obtained after
application of at least 16 supporting layers.
The most advantageous properties are provided by the
supporting layers based on zirconium silicate bonded with
"Remasol" binder.
The gasification temperature of polyurethane foam should
not be higher than 200°C, while the filters baking
temperature should be from 800 to 1000°C.
It is recommended to apply 2 to 3 inoculating layers
containing zirconium silicate, from 7 to 10% cobalt
Acknowledgments
Research done under Project No. POIG.0101.02-00-015/08 in the
Operational Programme Innovative Economy (OPIE). Project cofinanced by the European Union through the European Zonal
Development Fund.
References
[1] F. Zupanic, T. Boncina, A. Krizman, F.D. Tichelaar:
Structure of continuously cast Ni-based superalloy Inconel
713C, Journal of Alloys and Compounds, volume 329, issue
1-2, november 14, 2001, pp.290-297.
[2] M.Tabuchi, K. Kubo, K. Yagi, A.T. Yokobori Jr, A. Fuji:
Results of a Japanese round robin on creep crack growth
evaluation methods for Ni-base superalloys , Engineering
Fracture mechanics, volume 62, issue 1, january 1999, pp.
47-60.
[3] Hartman D., Muerrle U., Reber G.: The effects electron
beam refining on the cast ability of IN 713 C, Metall, 1992,
nr 5, pp.443-447
[4] L. Liu, T. Huang, Y. Xiong: Grain refinement of superalloy
K4169 by addition of refinerwes:cast structure and
refinement mechanisms, Materials Science and Engineering
A, 394, 2005, pp.1-8
[5] Yang, Y., Nomura, H., Takita, M.: Inclusion removal usimg
ceramic foam filters and filter size estimation. Int. J. Cast
Metals Res. t.9, 1996.
[6] Piech K.: Ceramiczne filtry piankowe, charakterystyka I
zastosowanie praktyczne, Przegląd Odlewnictwa, 1/1995.
[7] Adams A; Modification Properties of Ceramic Foam Filters
–A Summary of Recent Work Modern Casting (USA), vol.
91, no. 3, pp. 34-36, Mar. 2001
[8] V.N. Antsiferov, S. E. Porozova, L. V. Nikulin, et al.: Effect
of the material of foam ceramic filter on the microstructure
of duralumin, Ogneup. Tekh. Keram.,No. 7, 11 14/1997.
[9] Klecikowicki K.: Piankowe filtry ceramiczne w formach na
linii Disamatic, Przegląd Odlewnictwa 6/1999
[10] Asłanowicz M., Ościłowski A., Stachańczyk J.: Filtracja
ciekłych metali z użyciem filtrów produkcji FERROTERM,Przegląd Odlewnicta, 9-10/2002
[11] Zgłoszenia patentowe z dnia 28. 10. 2010r, nr P.392782
„Filtr ceramiczny do modyfikacji objętościowej struktury
odlewów z żarowytrzymałych stopów niklu i kobaltu”
ARCHIVES of FOUNDRY ENGINEERING Volume 11, Special Issue 3/2011, 29-32
Download PDF
Similar pages