In-situ synthesis of Fe-TiC nano-composite coating on CK45 steel from ilmenite concentrate by [600971]

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In-situ synthesis of Fe-TiC nano-composite coating on CK45 steel from ilmenite concentrate by
plasma spray method
Alireza Firouzbakht, Mansour Razavi ♣, Mohammad Reza Rahimipour
Department of Ceramic, Materials and Energy Researc h Center (MERC), P.O. Box 14155-4777, Tehran, Iran

Abstract
In-situ synthesis of Fe-TiC nano-composite as a wea r resistance coating by the plasma spray
process is purpose of this study. Ilmenite concentr ate and carbon black were used as raw
materials. Three kinds of powders with different co nditions were prepared and sprayed on CK45
steel substrates in constant conditions. Microstruc ture, phase identification, wear resistance and
hardness of coated samples were determined. The res ults showed that activate sample was
synthesized during the plasma spray but plasma spra y can’t synthesis of inactive sample. Also
wear resistance and hardness tests showed by synthe sis of Fe-TiC composite in coated samples,
wear resistance and hardness were increased.
Keywords: Fe-TiC; Nano-composite; Plasma spray; Wear resistan t coating.

♣ Corresponding author : [anonimizat]
Tel: +98 26 36204131 Fax: +98 26 36201888

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1. Introduction
Nowadays, due to increasing of part's useful life, composite coatings are used widely in
different fields like wear, corrosion and oxidation resistant coatings, thermal barrier coatings and
etc. because of their properties. Wear resistance c oatings are used in different fields like
aerospace, transport, cutting and abrasive tools an d etc. [1-3]. Metal matrix coatings reinforced by
hard carbide particles like TiC, WC and B 4C have different application. Actually, these hard
particles increase wear resistant of ductile metal matrix [3,4]. Carbides are an important group of
materials with high melting point, hardness and wea r resistance and because of these properties
can be used in different fields like abrasive and c utting tools and etc. Ferrotic composite is a
ferrous matrix composite reinforced by titanium car bide particles [1,5-7]. Titanium carbide
particles are one of the best reinforcements for fe rrous matrix composites because of their
hardness and thermal stability. Existence of titani um carbide particles in ferrous matrix lead to
increasing of wear resistance and hardness of the m atrix, so ferrotic composites are one of the
most common engineering composites that can be used widely in industrial applications like
aerospace, tools, dies, fixtures and etc. Conductin g a comparison between ferrotic and WC-Co in
different aspects like melting point, hardness, den sity, and cost reveals ferrotic has superior
properties to WC-Co. Moreover, the wear resistance of ferrotic is 20% higher than WC-Co, and
unlike WC-Co cermet, ferrotic is not poisonous [6-1 0]. Synthesis routs of ferrotic composites
classified in two main groups including molten and solid state. Conventional melting and casting
are an example of molten state used due to their fl exibility and low-cost these days. Powder
metallurgy (PM), self-propagating high-temperature synthesis (SHS), mechanical alloying,
carbothermal reaction, and thermite reduction are solid state ro uts used for synthesis of
composites [10, 11]. These composites can be used a s a bulk or wear resistance coating in
different fields. Plasma spray is one of the common thermal spray methods used in industrial

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coatings. High temperature (about 1000 K) of plasma jet leads to melting of particles and due to
this capability, plasma spray process used as a con venient method to create of coatings. Generally
plasma spray process has three steps including powd er feeding to plasma jet, powder melting and
spraying of molten particles to substrates. Sprayed coatings properties depend on microstructure
and microstructure of coatings depend on plasma spr ay parameters. Different parameters such as
power, spraying distance, voltage, current, gas flo w rate and feeding rate are so effective in
plasma spray process [11-13]. The surface properties improved considerably by co atings that
include titanium carbide particles and lead to ap ply in different fields [14]. Since production of
ferrotic as a wear resistance coating powders is ex pensive, in this paper has been tried to In-situ
synthesis of ferrotic nano-composite coating from i lmenite concentrate and carbon black by
plasma spray method was studied.

2. Experimental
Ilmenite (FeTiO 3) concentrate that had been prepared from Kahnooj mine with parti cle size
under 100 μm as a titanium and iron source and carb on black with particle size under 60 μm as a
reduction agent were used in this study. Morphology of raw materials is shown in Fig. 1, as it can
be seen morphology of raw materials is in irregular polygons shape. Chemical analyze of ilmenite
concentrate is brought in table 1. The raw material s with a stoichiometric ratio were mixed
according to the reaction (1):
FeTiO 3 + 4C = Fe+TiC+3CO (1)
Three kinds of powder with different condition s were used for coating of CK45 steel substrate
including 30 minutes mixed, 50 hours activated and 50 hours activated and then heat treated in
1250 °C samples. Details of processing were reporte d in our previous work [15].Preparation of

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powder for plasma spray process was carries out by using of 5% PVA (Poly vinyl alcohol) and
distilled water. CK45 steel disks with 50 and 10 mm in diameter and thickness, respectively were
used as substrate and in order to increasing of s urface roughness, the substrates were sand
blasted by SiC powder with 25 μm particles size and MCrAlY(M=Ni) was sprayed on substrates
surface as a bond coat. Then these three powders we re sprayed on substrates in constant
conditions brought in table. 2.
In order to phase identification, X-ray diffra ction analysis (Philips model) was carried out with
voltage, current and radiation of 30 kV, 25 mA and Cu Kα (λ= 1.54), respectively. The
microstructure of the samples was observed by an LE O1450 model scanning electron microscope
(SEM) with a voltage of 25 kV and Olympus BX model optic microscope (OM). Wear resistance of
these samples was examined using the pin on disk me thod. This test was carried out with 52100
steel pin with 66 HRD and 250 g applied force. Hard ness of coatings was examined using UV1
universal model in HRA mode with diamond invertor a nd 60 Kg applied force for two seconds.

3. Results and discussions
X-ray diffraction pattern of raw materials, in cluding ilmenite concentrate and carbon black is
shown in Fig 2. As it can be seen, FeTiO 3 peaks were observed with 01-075-0519 code in this
pattern, but carbon black identification was imposs ible because carbon black was selected in
amorphous form and even if it wasn't amorphous, it wouldn’t be identified because of its MAC
that is less than FeTiO 3 (MAC C= 4.3 cm 2/g, MAC FeTiO3 = 179.81 cm 2/g). As it said, three types of
powder with different conditions (S1=30 minutes mil led sample, S2=50 hours milled samples,
S3=50 hours milled and heat treated sample in 1250 °C in atmosphere control tube as mixed,
active and full synthesis samples, respectively) we re used to spray on substrates and their

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properties are compared together. Fig. 3 shows x-ra y diffraction patterns of S1, S2 and S3 , as it
can be seen only FeTiO 3 peaks are observed in pattern a with mentioned cod e, in fact S1 wasn't
reduced by carbon during the mechanical milling and only the raw materials were mixed together.
X-ray diffraction of S2 sample is shown in pattern b. As it can be seen in this pattern, FeTiO 3 is the
only detected phase with mentioned code. Although m illing was done for 50 h, but carbon black as
a reduction agent couldn't reduce FeTiO 3 and sample was only active. In fact, by increasing the
milling time from 30 minutes to 50 hours, peaks bro adening and intensities decreasing were
occurred. As it said, carbon black peaks weren’t id entified in S1 and S2 because of the mentioned
reasons. Pattern c shows x-ray diffraction of S3, a s it can be seen titanium carbide and free iron
phases are observed in this pattern with 00-002-117 9 and 01-087-0722, respectively. In this
sample FeTiO 3 was reduced by carbon during the heat treating in 1250 °C according to below
reaction:
FeTiO 3+ 4C = Fe+ TiC + 3CO
X-ray diffraction patterns of samples coated w ith these three powders are shown in Fig. 4, as it
can be seen in pattern a relating to coating spraye d by S1 powder (C1), FeTiO 3, free iron, titanium
and iron oxides phases are observed and it can be r esulted that a part of FeTiO 3 was reduced by
carbon during the plasma spray process. Pattern b s hows x-ray diffraction of sample coated with
S2 powder (C2), this pattern includes free iron in Ferrite and Austenite form (01-087-0722 and 00-
023-0298 code) and titanium carbide (00-002-1179 co de) with week iron oxides peaks (01-073-
0603 code). The results show that activated FeTiO 3 was reduced by carbon during the plasma
spray process; in fact in-situ synthesis was occurr ing when the powder was deposited on the
substrate surface and a metal matrix composite with hard particles of titanium carbide was
formed on the surface of CK45 steel. As nickel is a Austenitic phase stabilizer [7], existence of free
iron in Austenite form is due to dissolving of nick el from MCrAlY bond coat in ferrous matrix.

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FeTiO 3 reduction includes two steps, at first iron oxides will be reduced with carbon because its
chemical stability is lower than titanium oxides ac cording to Gibbs free energy – temperature
diagram of titanium and iron oxide that is shown in Fig. 5 [15], so free iron forms in this step. Then
titanium oxides reduction begins before completion of iron oxides reduction. By titanium oxides
reduction second titanium oxide phases as Magneli phases will be formed with lower amount of
oxygen and finally titanium carbide particles will be synthesized in this process [16]. Of course, thi s
coating includes iron oxides because of spraying at mosphere, including high amounts of oxygen. X-
ray diffraction of sample coated with S3 powder (C3) is shown in pattern c, as it can be seen
titanium carbide, free iron and iron oxides are obs erved with 00-002-1179, 01-087-0722, 01-076-
0956 and 01-073-0603 code, respectively. As it sai d, S3 sample includes titanium carbide and free
iron after heat treatment, so during the coating pr ocess, free iron reacted with atmospheres
oxygen because of low chemical stability and iron o xides were formed in deposited coating.
Conducting a comparison between C1 and C2 reveals t hat increasing the milling time from 30
minutes to 50 hours lead to activation of raw mater ials mixture, so reactivity of S2 was increased
by mechanical milling and FeTiO 3 reduction and titanium carbide synthesis were occu rred in this
research. Fig. 6, 7 and 8 show SEM cross section im ages and linear EDS analysis of C1, C2 and C3
coatings, respectively. Approximate thickness of C1 , C2 and C3 are 60, 50 and 40 micrometers,
respectively. Linear analyzes shows that these coat ings include iron, titanium and nickel. In fact, in
C1, titanium and iron are in an oxide form and in C 2 and C3 titanium and iron are in titanium
carbide, free iron and iron oxide forms. Existence of nickel in these samples related to MCrAlY
bond coat sprayed under top coat to increase roughn ess of substrate and matching of thermal
expansion coefficient of substrate and coatings. In creasing of surface roughness leads to better
adhesion of coating to substrate; in fact mechanica l bonding is occurred between coating and
substrate. Optical microscope images of these three samples are shown in Fig. 9, as it can be seen

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coatings are in high quality and free from cracks a nd defects. The hardness of these three coated
samples at room temperatures is shown in table. 3, as it can be seen hardness of C2 and C3 is
higher than C1, because of titanium carbide formati on in these samples, in fact hard particles of
titanium carbide increase hardness of coating. Cond ucting a comparison between hardness of C2
and C3 shows that hardness of C3 is higher than C2; it can be due to the existence of iron oxides
that are harder than free iron. Wear resistance res ults of coated samples are shown in Fig. 10 . As
it can be seen, weigh loss of C1 is more than other samples because titanium carbide particles
weren't synthesized in these samples, existence tit anium carbide particles increase wear
resistance of coatings. As it was concluded, sample s including titanium carbide are harder than
other sample, so it can be said that the existence of titanium carbide in coated samples increases
the wear resistance of them, on the other hand, wei ght loss of C2 is more than C3, it can be due to
existence of more iron oxides in C3 than C2, in fac t iron oxides are harder than free iron and for
this reason wear resistance of C3 is higher than C2 [5].

4. Conclusion
1. In- situ synthesis of Fe-TiC nano-composite coating on CK45 steel from ilmenite
concentrate by plasma spray have done.
2. Mechanical activation was useful as a driving force in order to synthesis of Fe-TiC nano-
composite.
3. Titanium carbide as a reinforcement in ferrous matr ix led to increase hardness and wear
resistance of coatings.
4. Optimized sample is the one activated for 50 hours by mechanical milling and then sprayed
on the surface of substrate.

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References
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spraying of ilmenite. Journal of Alloys and Compoun ds, 1999. 121-125.
[2] McPherson, R., A review of microstructure and p roperties of plasma sprayed ceramic
coatings. Surface and Coatings Technology, 1989. 17 3-181.
[3] Lei, T., et al., Microstructure and wear resist ance of laser clad TiC particle reinforced coating.
Materials science and technology, 1995. 520-525.
[4] Doğan, Ö.N., J. Hawk, and J. Tylczak, Wear of c ast chromium steels with TiC reinforcement.
Wear, 2001. 462-469
[5] Dyjak, S., et al., A simple method of synthesis and surface purification of titanium carbide
powder. International Journal of Refractory Metals and Hard Materials, 2013. p. 87-91.
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carbide. Journal of materials science, 1996. 2573-2577.
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reinforced ferrous based composites. Journal of materials science, 2002. 3881-3892.
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4395.
[9] Brown, I. and W. Owers, Fabrication, microstructure and properties of Fe–TiC ceramic–metal
composites. Current Applied Physics, 2004. 171-174.
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International Journal of Mineral Processing, 2010. 97-100.
[11]Licheri, R., et al., Self-propagating combustio n synthesis and plasma spraying deposition
of TiC–Fe powders. Ceramics International, 2003. 51 9-526.

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[12] Cliche, G. and S. Dallaire, Synthesis and depo sition of TiC-Fe coatings by plasma spraying.
Surface and Coatings Technology, 1991. 199-206.
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1996. 399-442
[14] Dallaire, S. and G. Cliche, Tribological prope rties of TiC-Fe coatings obtained by plasma
spraying reactive powders. Journal of Thermal Spray Technology, 1993. 39-44
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Figure 1: Morphologies of the a) FeTiO3, b) Carbon black.

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Figure 2: X-ray diffraction patterns of raw materia ls mixtures (FeTiO 3=3).

Figure 3: X- ray diffraction patterns of a) S1 powder, b

12 ray diffraction patterns of a) S1 powder, b S2 powder and c) S3 powder (FeTiO
Fe=∆ , TiC= ș).

S3 powder (FeTiO 3=3 ,

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Figure 4: X-ray diffraction patterns of a) coated s ample with S1 powder, b) coated sample with S2
powder and c) coated sample with S3 powder(TiC= ș, Fe(α)=∆, Fe(γ)= *, Fe 2O3=○, TiO 2=□,
FeTiO 3=●, FeO= /rhombuscent).

Figure 5: Gibbs free energy
14 Gibbs free energy – temperature diagram of FeTiO 3, FeO and TiO

, FeO and TiO 2 [15 ]

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Figure 6: Cross section morphology and linear EDS a nalysis of coated samples with S1 powder .

Figure 7: Cross section morphology and linear EDS analysis of coated samples with S2 powder

16 Cross section morphology and linear EDS analysis of coated samples with S2 powder

Cross section morphology and linear EDS analysis of coated samples with S2 powder .

Figure 8 : Cross section morphology and linear EDS

17 : Cross section morphology and linear EDS analysis of coated samples with S3 powder.

analysis of coated samples with S3 powder.

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Figure 9: Optical microscope images of coated sampl e with a) S1 powder, b) S2 powder, c) S3
powder.

500 µm 500 µm 500 µm a b c

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Figure 10: Weight loss of C1, C2 and C3 sample in w ear resistance test.

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Table 1: Chemical analysis of used ilmenite concent rate.
compounds TiO 2 FeO Al 2O3 MnO MgO SiO 2 CaO V2O5 Cr 2O3 P2O5 other
Weight
percent 47.40 44.70 1.33 1.77 1.03 2.00 1.11 0.36 0.05 0.16 0.09

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Table 2: Plasma spray parameters.
Gun Type Voltage(V) Current(A) Feeding
rate(g/min) Distance
spray(cm) Gas
flow(lit/min)
METCO-TB3 50 500 10 12 Ar:85 / H 2:15

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Table 3: Hardness of coated samples and substrate.
samples phases HRA HVR equivalent
C1 FeTiO 3- Fe O- TiO 3-Fe 58±2 210
C2 Fe(α)-Fe(γ)-TiC-Fe 2O3 67±1 355
C3 Fe(α)-Fe(γ)- TiC- Fe 2O3- Fe 3O4 70±2 410
C(substrate) Fe(α) 51±2 160